Medical Edition 2016
Welcome to Titanium Today
If you are reading the Medical edition of Titanium Today you are most likely already familiar with how Titanium improves the quality of individual lives when it is used in medical and dental implants.
Almost every day we hear about the wonders of this high performance metal in the ways it is being used for new medical applications. It’s really a very exciting time for titanium in the medical industry.
Titanium implants are used to replace or stabilize broken bones. Tiny titanium implants are even used to improve hearing in people with some types of deafness by drilling a titanium rod into the skull behind the ear and attaching it to an external sound-processing unit. The external unit picks up sounds and transmits the vibration through the titanium implant to the inner ear, bypassing any problems in the middle ear.
There are continued developments in the use of “Tifoam” a structure of polyurethane foam saturated with titanium powder. The porous structure mimics human bone and allows human bone cells to penetrate and meld with the implant as the person heals.
There are countless examples of how Titanium is used in existing and new medical applications.
I hope you will enjoy this edition and contact the International Titanium Association with your thoughts and suggestions for future coverage.
Understanding Implants in
Knee and Hip Replacement
An interview with
Douglas E. Padgett, MD
Chief of the Adult Reconstruction and Joint Replacement Division, Orthopedic Surgeon,
Hospital for Special Surgery
Russell E. Windsor, MD, PC
Orthopaedic Surgeon, Hospital for Special Surgery
Information about knee and hip replacements is more easily available than ever before. But direct-to-consumer advertising, online articles and other reports in the media may make it more difficult for people considering these surgeries to understand their options. Becoming familiar with the key considerations that go into selection of the implant that is used to replace the injured or damaged joint can make the process easier.
Types of Knee Replacement
In the majority of total knee replacements, the surgeon places components of the implant (also called a prosthesis) on the joint surfaces of three bones that make up the knee joint: the femur, the long bone in the thigh, the tibia, the larger of the two bones in the lower leg and a patellar (kneecap) component, which glides on the femur, the bone that you feel at the front of the knee. The patellar component is sometimes not needed.
Although there are now many different models of knee implants available from a number of different manufacturers, there are two primary types - one that substitutes for the posterior cruciate ligament (PCL), a central ligament that stabilizes the knee joint, and one that spares it. [Figure 1]
“The choice between these two implants usually comes down to surgeon preference,” explains Russell E. Windsor, MD, Orthopedic Surgeon at the Hospital for Special Surgery (HSS). “At HSS, the majority of surgeons prefer an implant that replaces the PCL.”
In part, this preference is based on the pioneering work done at HSS by John Insall, MD, Chit Ranawat, MD and Peter Walker in 1973, the orthopedists and bioengineer who developed the total condylar prosthesis, designed to closely replicate the anatomy and functional characteristics of the knee joint. “This really marked the beginning of successful modern knee replacement,” says Dr. Windsor. Since that time thousands of successful surgeries have been completed using more modern, refined versions of this implant. But research also suggests that equally successful outcomes are achieved with implants that spare the PCL.
“Prospective patients may also read or hear about fixed-bearing implants versus rotating platform implants, and wonder which one is preferable,” Dr. Windsor notes. These terms refer to the portion of the replacement that is attached to the tibia.
When fixed-bearing implants are used, a metal component is inserted into the tibia and a polyethylene (plastic) tray is locked into place on top of it. [Figures 2a,b,c]
In rotating platform implants, a similar metal implant is inserted into the tibia, but the polyethylene tray is placed on a circular stem that allows slight rotation of the tray on the metal tibial platform during knee motion. This mobile-bearing design may allow for slightly greater range of motion in the knee. [Figure 3]
Rotating platform implants were originally designed with the younger, more active patient in mind. Some data suggests that there is less wear of the polyethylene component with this type of implant, but a clinical benefit has not been established. (This choice of fixed-bearing versus rotating platform implants is also relevant to people who are candidates for partial knee replacement, in which only one compartment of the knee is replaced.) [Figures 4 and 5]
During knee replacement surgery these implant components are usually connected to the bone with cement, a technique that generally yields excellent results. However, the orthopedic community is studying “cementless” fixation of implants - a technique already in widespread use in hip replacement - in which the components have a trabecular metal surface (one that resembles a honeycomb). This porous design permits the growth of new bone tissue on the surface of the fixed metal components.
Knee Implant Materials, Shapes and Sizes
As described, knee implants generally include components made of metal and plastic. In order to ensure a smooth, gliding motion, and to avoid friction, metal surfaces never come into contact with one another. Metal components are usually made of cobalt chrome (which contains nickel) or titanium (which is known for its strength and lightness). Titanium-only implants are available for patients who are allergic to nickel, but it is more difficult to obtain the highly polished surface that facilitates smooth motion with titanium than it is with cobalt chrome.
Based on the successful use of ceramic components in hip replacement, one manufacturer has developed a ceramic implant for the knee. “However,” Dr. Windsor notes, “we won’t know for quite a while if this will offer any advantage in the knee, which is a very different kind of joint.”
The patient’s size, weight, and gender also have a bearing on implant selection. While once there were only a few sizes available, surgeons now have a wider selection to choose from. This includes a gender-specific “woman’s knee”, which is designed to accommodate a woman’s narrower bone structure, especially on the femur. “This development reflects the trend toward customizing implants to achieve the best results possible, in terms of comfort, function, and longevity,” says Dr. Windsor.
Prospective patients may find that orthopedists in some hospitals use only one or two different implant systems, whereas, orthopedists at HSS have access to the systems of all the major orthopaedic implant manufacturers.
Types of Hip Replacement
Total hip replacement surgery - in which the damaged joint is replaced with an implant - is associated with a high degree of successful and predictable outcomes.
Orthopedic surgeons may approach the surgery in one of three different ways:
• the direct anterior approach in which the incision is made on the front of the hip; this approach may be less disruptive to the muscles and soft tissues surrounding the hip joint, however, surgeons who employ this approach usually use a custom operating table and fluoroscopy (a type of x-ray) to guide placement of the implant during surgery; fluoroscopy is not routinely used with the other two surgical approaches
• the anterolateral approach in which the incision is made on the side of the hip, toward the front of the body
• the posterolateral approach in which the incision is made on the side of the hip toward the back of the body
Each surgical approach calls for slightly different post-operative precautions related to position restrictions to avoid possible early hip joint dislocation. The posterolateral surgical approach is most commonly used in hip replacement surgery. Although a minor improvement in walking speed during the early phase of recovery has been associated with the direct anterior approach, there is no data to suggest a significant advantage of one approach over another explains Douglas E. Padgett, MD, Chief, Adult Reconstruction and Joint Replacement division and Orthopaedic Surgeon at HSS. “The decision to use a particular approach is usually based on the preference of the surgeon,” Dr. Padgett adds.
Much of the important early work in the development of successful hip implants took place in the late 1960s and early 1970s, including that of British surgeon John Charnley, MD and introduced at HSS by Philip D. Wilson, Jr. MD.
Hip Implant Materials and Fixation
The majority of people who undergo hip replacement receive a traditional hip arthroplasty in which the surgeon uses a stemmed device and prosthetic head to replace the upper part of the femur (the head and neck of the bone) and a hemispherical shaped cup to replace the acetabulum, the socket of the pelvis in which the femoral head fits. [Figure 6]
However, some patients may be candidates for hip resurfacing in which the head and neck of the femur are not removed. In this procedure, the surgeon resurfaces or sculpts the femoral head to accept a metal cap with a short stem. Hip resurfacing is usually most successful in male patients under the age of 55, who are larger in stature There is little data to support functional benefit of one type of hip replacement over the other, although if revision surgery is needed, this may be easier after hip resurfacing. [Figure 7]
Hip implants come in two primary types: the traditional single-piece implants and modular models, in which the stem and head of the implant portion that is placed in the femur can be matched independently. Although the single piece implants provide a good fit for many patients, “modular devices were developed to improve the fit of the implant to the patient’s specific anatomy,” explains Dr. Padgett. However, he adds, some modular implants have recently been found to be associated with problems related to the linkage between the various parts.
Some degree of corrosion and fretting has been seen with these metal on metal components, a process that can result in the creation of metallic debris that is destructive to the soft tissue surrounding the joint. As a result, some of these implants have been recalled.
Implants may be made of a variety of materials including metal (usually titanium), ceramic or polyethylene (a type of hard plastic). Ongoing research and enabling technology will determine new directions in materials used in hip replacement surgery. At present, bearing surfaces - where the femoral component of the implant meets the acetabulum - may combine in three different ways:
• Metal or ceramic on polyethylene, in which the metal or ceramic head meets a medical-grade polyethylene socket or acetabulum in the pelvis. This combination is now generally regarded to be the “gold standard” for hip replacement. The polyethylene components currently in use are significantly more wear-resistant and resistant to degradation than earlier generations of these plastics.
• Metal-on-metal, in which a large metal ball at the top of the femur articulates with a metal socket or acetabulum in the pelvis. This combination was originally developed to offer the benefits of increased stability - related to the size of the head - and the ability to create a very thin, but durable metal shell. Owing to the creation of metal fragments or metallic debris that is destructive to the soft tissue surrounding the joint, use of some of these total hip replacement implants has been discontinued in the United States. Metal-on-metal bearing surfaces continue to be used for hip resurfacing.
• Ceramic on ceramic, in which both components are made of the same material; this combination has been shown to have good durability, but there is a risk of the ceramic breaking and ceramic on ceramic hips can produce an audible squeak.
Placement of the hip implant components involves an additional consideration: how the implants are bonded to the bones. This can be accomplished either through the use of acrylic cement or with uncemented fixation, in which the surface of the implant is composed of a porous, honeycomb-like surface that allows for the in-growth of new bone tissue to help hold the component in place.
“On the cup portion of the implant, uncemented fixation is clearly superior,” Dr. Padgett says. “However, cemented fixation may be preferable in older patients or others with compromised bone quality.” With regard to fixation of the stem, Dr. Padgett notes, available data shows no advantage of one type of fixation over the other, and the decision to use one over the other is left to the surgeon’s discretion.
Is Newer Better?
Because the essential design of the knee implants introduced in the mid-1970s has resulted in successful outcomes in a significant number of patients, it’s not surprising that newer models introduced over the years have involved modest refinements rather than radically different designs. While marketing campaigns may seek to persuade consumers that “newer is better”, Dr. Windsor cautions that it’s important to bear in mind that it will take time to determine whether modifications to previous implant systems actually fulfill their promise and whether they offer any advantage over existing systems.
One new technology that may enhance the precision of knee implant placement has also received some coverage in the lay media. Many orthopedic surgeons now use custom cutting blocks - models based on the patient’s specific anatomy - to refine precision and accuracy during surgery. The cutting block is created based on information obtained with pre-operative MRI. The goal of this technology is to allow the surgeon to more precisely plan where surgical cuts in the bone will be made and to preserve as much of the patient’s anatomy as possible. Further long term follow up will be necessary to determine if there is benefit in using custom cutting blocks.
Hip and Knee Implants
With a history of excellent surgical technique and outcomes, the focus of new development in this area is on the use of enabling technology to improve preparation and component positioning in hip and knee replacement surgery. These tools include navigation devices that provide three-dimensional spatial orientation and robotics which can also provide tactile feedback during surgery. “The role of these emerging technologies is still evolving,” Dr. Padgett notes.
Choosing a Surgeon
As with any orthopedic surgery, people contemplating knee or hip replacement are advised to seek out a surgeon whom they trust, who does a high volume of these procedures - and an institution with a reputation for excellence in the field. Surgeons who focus on a given surgery or technique are most likely to have predictably successful outcomes. Single specialty centers of excellence, such as HSS, also have outstanding anesthesiologists, nurses and rehabilitation therapists who collaborate to achieve the best possible outcomes of care.
At specialized institutions like HSS, surgeons may also serve as consultants in the development of implants. These surgeons are particularly practiced in the use of implants they have helped to develop. (All orthopedists at the Hospital for Special Surgery disclose such professional affiliations, information which can be found on the physician’s individual profile on hss.edu.)
When to Schedule Surgery
Timing of surgery is another important consideration in predicting successful outcomes. “Generally I advise patients that it’s reasonable to consider surgery when the disability and pain in the knee or hip is affecting your quality of life and you’ve tried all other means available to alleviate your symptoms,” says Dr. Windsor.
Prospective patients should also take into account the importance of having surgery while they are otherwise in good health. In the past, some middle-aged patients have elected to wait for a joint replacement, because of their concern about the longevity of the new joint; that is, that a second joint replacement surgery might eventually be required. However, not only does the data indicate that knee and hip replacements are lasting as long as twenty-five or even thirty years, but delaying surgery may result in the surrounding muscles becoming de-conditioned owing to reduced function. In turn, this may make recovery from surgery more difficult.
Older individuals, including those in their 80s and 90s may also want to consider the benefits of scheduling surgery sooner versus “living with” disability. While the ability to tolerate surgery and recovery, as well as the existence of co-existing medical conditions must be taken into account, recent data shows that joint replacement that helps to preserve function can have an overall positive effect on the health of older patients. Those who are able to be more active have a reduced risk - when compared to their more sedentary counterparts - of various medical conditions including pulmonary embolism, deep vein thrombosis and pneumonia.
“Knee and hip replacement surgery improves the quality of life of thousands of patients each year,” Dr. Windsor notes. “However, both advertising claims and misinformation on the Internet can lead to confusion about which implant works best or even an exaggerated sense of risk associated with the surgery. In many cases, a discussion with your surgeon can clarify implant options and establish realistic expectations about hip and knee replacement surgery.”
“As with any surgery there is always some risk involved. There have been a few knee and hip implant systems that have not worked well,” Dr. Windsor says, “and isolated recalls of specific models have occurred. But people should be aware of the shared commitment on the part of industry, hospitals, and surgeons to the welfare of the patient and to addressing any problems with implants that do occur.”
One method to monitor performance of hip and knee implants is through a patient registry. The orthopedic surgeons at HSS are dedicated to following the long-term patient centered outcomes of joint replacement surgery in our Total Joint Prospective Clinical Outcomes Research Registry. Using this registry, long term implant performance may be followed and hopefully surgeons can identify as early as possible any poor performing implants.
If you would like more information about knee and hip replacement at HSS, please visit the Physician Referral Service or call 1.877.606.1555.
Influence of Surface Processing
on the Biocompatibility of Titanium
This article was published online by Open Access Materials. As indicated in the online posting, this is the publisher’s final edited version of this article. The text, as it appears here in Titanium Today, is a further condensed and edited version of the article.
Surface conditioning of titanium middle ear implants results in an improved biocompatibility, which can be characterized by the properties of fibroblasts cultured on conditioned surfaces. Titanium has been established as a favorable biomaterial in ossicular chain reconstruction. The epithelization of the surface of the implants is important for their integration and stable positioning in the middle ear. Mouse fibroblast cells were cultured on platelets made from pure Grade 2 titanium. Platelets that had been etched along their production process were compared to unetched platelets. The DNA in the cell nuclei was stained with DAPI and the actin filaments of the cytoskeleton were stained with FITC-conjugated phalloidin in order to analyze the cells grown on etched and unetched platelets by fluorescence microscopy. SEM (scanning electron microscopic) images were used to compare the surface structure of etched and unetched titanium platelets. There was a statistically significant increase of the area covered by the cytoplasm and increased actin expression by fibroblasts grown on the etched titanium platelets. In addition, the area of the platelets covered by nuclei on the etched platelets exceeded on average the one on unetched platelets, although this difference was not significant. The SEM pictures comparing unetched and etched titanium platelets showed a clear difference in surface structure. Surface conditioning of titanium implants improved the epithelization by fibroblasts and consequently etched titanium should be the preferred biomaterial for reconstructive middle ear surgery.
Finding the perfect material for ossicular chain reconstruction has been a challenging issue for the last 40 years. In 1999 Stupp et al. were the first to publish their three years experience with titanium ossicular chain reconstruction . Since then titanium has become the most popular biomaterial in middle ear surgery. High biocompatibility, biostability and excellent sound conduction favor the use of titanium for the reconstruction of the ossicular chain [2-5]. In ossicular procedures partial or total ossicular replacement prostheses (PORP/TORP) are interposed between the malleus handle or tympanic membrane and the stapes capitulum or footplate. The fenestrated headplate of the prostheses provides sufficient view for a precise positioning of the shaft on the stapes footplate. Important for integration and stabilization in the middle ear, is the covering of the surface of the biomaterial with fibrous tissue and mucosal cells. Titanium possesses properties that support epithelization without foreign-body reaction. In the presence of oxygen, titanium is coated with a thin layer of titanium dioxide which prevents tissue modifications, cell mediated hypersensitivity, as well as corrosion of the implant . However, the production process can leave behind chemical and physical particles on the surface of the implant, potentially causing tissue reactions and disintegration of the prosthesis. For the removal of these residuals, all KURZ Medicals (Heinz Kurz GmbH, Dusslingen, Germany) ossicular prostheses are subjected to a complex cleaning process that accounts for 30% of the whole manufacturing time. A major part of this process is the surface conditioning by the use of a special etching technique. This is followed by an examination using Scanning Electron Microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) of each batch for residual wear particles.
The aim of the present study was to find out if the surface conditioning process of titanium ossicular implants results in an improved biocompatibility measured by the analysis of fibroblasts grown on conditioned surfaces.
Materials and Methods
KURZ Medicals provided 24 commercially pure titanium platelets (grade 2/ASTM F 67: Standard for unalloyed Titanium, for Surgical Implant Applications DIN ISO 5832-2) with a diameter of 7.92 mm and a thickness of 250 µm. The platelets were submitted to the KURZ standard cleaning process but etching was omitted from the cleaning process in 12 of the 24 platelets. 16 thereof were used for cell culturing; the remaining 8 platelets were examined under a Scanning Electron Microscope. To allow a more even dissemination of cells as well as an easier analysis of the cell growth under the fluoresescence microscope, the provided platelets had no engravings and only a single notch instead of the typical fenestrations of the headplates (see Figure1).
Figure 1. Low power composite images of DAPI stained nuclei (A) and FITC-labeled actin (D) of one etched titanium platelet (see also Figure 2 F). The boxed 1350 µm* 675 µm regions in the low power overviews are shown at higher magnification for nuclei (B) and actin (E). In the binary images (C,F) corresponding to B and E, pixels with gray levels above the respective gray level threshold (see methods) are shown in black. Using adequate threshold settings DAPI stained nuclei (C) and FITC-labeled actin (F) were well discriminated from the surface of the platelet not covered by nuclei or cytoplasm (shown in white).
Frozen mouse fibroblasts (cell line L929 American Type Culture Collection CCL I fibroblast, NCTC clone 929, Manassas, VA, USA) were thawed and cultured in T25 flasks (Easy Flask T25: Nunc Cat. # 156367) in Dulbecco’s Modified Eagle’s Medium (DMEM: PAN Cat. # P04-01550) supplemented with 10% v/v fetal bovine serum (FKS: Sigma Cat. # F7524) and 1% v/v Pen Strep (PAA Cat. No. P11-010). After 3–6 days the cells were dissociated with 0.5% Trypsin-EDTA (Sigma Cat. # T4174) in PBS and seeded in DMEM with 10% FKS and Pen Strep at a density of 100,000 cells per well in 6 well plates (multidish 6 well: Nunc Cat. # 140675).
After 2–7 days these cultures were again dissociated with Trypsin-EDTA and seeded in a EC-Medium (Endothel cell growth medium, Promocell Cat. No C-22010, supplemented with 2.44% v/v Supplement pack Promocell Cat. # C-39215, 0.24 mg/mL L-Glutamin Sigma Cat. # G8415, 50 mg/mL Gentamycin Sigma Cat. # G1397, 0.5 mg/mL Amphotericin B Lonza Cat. # Lonz 17-836E and 10% human serum of own production) at a concentration of 50,000 cells per mL. The titanium probes were sterilized with 70% ethanol and after drying they were placed in the wells of cell culture plates (48 well plates/ Nunc Cat. # 150687) and combined with 500 mL of the cell suspension. The cells were cultivated in the incubator at 37 °C with 5% CO2 for one week and the medium was changed every two to three days. Pairs of etched and unetched titanium platelets were incubated and processed in parallel. Thus corresponding pairs of etched and unetched platelets were regarded as matched pairs (dependent groups) and a non-parametric paired Wilcoxon test was used for the statistical comparison.
The culture medium was gently removed from the wells and replaced by 4% paraformaldehyde solution in 0.1 M posphate buffer (pH 7.4). After 15 min of fixation under low frequency agitation on a shaker, the fixative was exchanged with fresh fixative and the probes were incubated for another 15 min. To permeate cells for the phalloidin staining of actin, the fixative was replaced twice for 30 min by 0.3% Triton in 0.1 M phosphate buffer (pH 7.4) and the specimens were agitated. Then the Triton buffer was replaced by 500 mL FITC-conjugated phalloidin solution (Invitrogen, Cat. # F432, 40 mL stock solution diluted in 2 mL 0.1 M phosphate buffer with 0.3% Triton). The wells were placed on the shaker for the actin staining process. After one hour the FITC solution was aspirated and the specimens washed twice for 10 min with phosphate buffer. Finally, each platelet was placed on a hollow-ground slide and covered with a cover slip using Vectashield with DAPI (Linaris, Cat. # H-1200) in order to stain nuclei. Consequently, the cell nuclei of the fibroblasts on the titanium platelets were stained by DAPI and the actin filaments of the cytoskeleton were labeled by FITC.
The specimens were examined under a Leica DM RBE microscope (Leica Mikrosysteme, Bensheim, Germany) with epifluorescence. Images were digitized with a Spot RT3 Slider camera (Diagnostic instruments, Stirling Heights, Mich., USA) and the software VisiView (Visitron Systems GmbH Puchheim, Germany). In order to get an overview of the whole titanium platelet at sufficient resolution for the subsequent analysis, a grid of overlapping pictures of the whole titanium platelet was taken with a Leica PL Fluotar 5×/0.12 lens resulting in a nominal resolution of 1.50 µm/Pixel. All pictures were digitized as 14 bit gray level images using standardized microscope settings and an exposure time of 1000 ms for the DAPI fluorescence filter and 2000 ms for the FITC fluorescence filter. To cover the whole titanium platelet between 18 and 29 overlapping pictures were digitized and a composite of these overlapping pictures was generated using the software package ImageJ 2.44c with the 2D/3D stitching macro from Stephan Preibisch (“http://fly.mpi-cbg.de/~preibisch/stitching.html”). Composite images of FITC stained actin were assembled without further processing of the individual pictures. To improve contrast, each picture of DAPI stained nuclei was subjected to background subtraction using a “rolling ball radius” of 50 pixels before assembling the composite image. Figure 1 shows examples of DAPI stained nuclei (A) and FITC-labeled actin (D) for one etched titanium platelet as an overview at low magnification and selected regions at higher magnification (B, E).
For the quantitative analysis of the cell coverage of the titanium platelets the images were opened with ImageJ. By choosing an adequate threshold value cytoskeletal elements stained by the FITC conjugated phalloidin and DAPI stained cell nuclei were discriminated from the surface of the titanium platelets not covered by nuclei or cytoplasm of the fibroblasts (Figure 1C, F). Thresholds were determined empirically and set to a gray level value of 200 for DAPI stained nuclei and 1000 for FITC labeled actin and these settings were used for the analysis of all composite images. For each titanium platelet the number of pixels with a gray level above threshold was determined. Using an adequate calibration the area of the platelet covered by supra-threshold pixels was calculated. This area was then expressed as percentage of the total platelet surface area that was used for subsequent comparisons. In addition, the mean gray level of the pixels with gray levels above threshold was determined as a measure of staining intensity. The software SPSS for Windows PASW Statistics 17.0.2 was used for the statistical analysis.
Scanning Electron Microscopy (SEM)
8 titanium platelets (4 etched vs. 4 unetched) were examined by Scanning Electron Microscopy (Cambridge Stereoscan 420; Co. Carl Zeiss NTS GmbH, Oberkochen, Germany) without previous cell cultivation. The platelets were mounted on SEM-stubs using adhesive Conductive-Tabs (Fa. BALTIC Präparation, Koppelheck 34b, 24359 Niesgrau, Germany) and then examined under vacuum with an acceleration voltage of 10 kV. Digital pictures of every probe were taken with a magnification of up to 1000´, displayed and stored with SCAN, Digital Image Processing System 2.1 (Co. point electronic GmbH, Ackerweg 104, 06103 Halle, Germany).
Qualitative Analysis of Fibroblasts Growth
First, we compared the fluorescence microscopic images of the fibroblasts grown on etched and unetched titanium platelets qualitatively by visual inspection. Growth of fibroblasts was present on all etched and unetched titanium platelets although the proportion of the platelet surface covered by fibroblasts varied substantially between experiments (Figure 2).
The pattern for the distribution of FITC-labeled actin and DAPI stained nuclei of the fibroblasts grown on the platelets was similar when viewed at low magnification (compare Figure1A and D). Differences due to the fact that the nucleus is a cell organelle within the cytoplasm became obvious at higher magnifications (compare Figure 1B and E).
The examples illustrated in Figure 2 demonstrate that a qualitative visual comparison was not sufficient to clearly identify an obvious difference of fibroblast growth on the unetched and etched platelets. Thus a quantitative image analysis approach was used in our search for a potential effect of platelet conditioning on cultured fibroblasts.
Quantitative Analysis of Platelet Surface Covered by Cytoplasm
One measure to compare fibroblasts grown on unetched and etched titanium platelets is the proportion of the platelet surface covered by cytoplasm and nuclei that is listed in Table 1 for the different experiments and experimental conditions.
The quantitative analysis presented in Table 1 confirms a considerable degree of variation between the different experiments. Consistent with the fact that the nucleus is only an organelle while the cytoplasm represents the whole cell, the proportion of the platelets covered by nuclei is consistently lower than that covered by the cytoplasm (see also Figure 1C, F).
The data show that in 7 of the 8 experiments a higher proportion of the surface of etched platelets was covered by fibroblast cytoplasm as compared to unetched platelets. On average 42.91% of the area was covered by the cytoplasm of fibroblasts on unetched compared to 50.22% on etched platelets.
This corresponds to a 17% increase on etched as compared to unetched platelets. The statistical comparison of the data from the pairs of unetched and etched platelets using a Wilcoxon test revealed that this difference was significant (p = 0.036).
The quantitative analysis also showed that on average nuclei of fibroblasts grown on etched platelets covered a larger proportion of the surface (29.25%) as compared to unetched platelets (26.24%). This represents an increase by 11%, but the difference was not significant (p = 0.123).
Quantitative Analysis of Staining Intensity
The gray level is a measure of fluorescence or staining intensity respectively. The analysis of gray level or staining intensity is a way to compare the amount of FITC labeled actin or DAPI labeled DNA of fibroblasts grown on differently treated titanium platelets. The mean gray level of the supra-threshold pixels from the FITC and DAPI composite images of fibroblasts grown on unetched and etched platelets are listed in Table 2.
The comparison of the mean FITC gray level of the cytoplasm from fibroblasts grown on unetched and etched titanium platelets demonstrates in 7 out of the 8 experiments higher values for etched (mean 2408) as compared to unetched (mean 2192) platelets. The statistical comparison (Wilcoxon test) confirmed that this difference in gray level was significant (p = 0.017). The higher gray levels in the cytoplasm of fibroblasts grown on etched platelets indicate that they contain more actin as compared to fibroblasts grown on unetched titanium platelets.
Comparing the gray levels of DAPI stained nuclei of fibroblasts grown on the two types of titanium platelets showed no systematic difference. In 4 experiments mean gray level was higher for the etched as compared to the unetched, in one experiment gray level was the same and in 3 experiments the gray level was higher for the unetched as compared to the etched condition. The statistical comparison by a Wilcoxon test revealed no significant difference (p = 0.499). The similarity of the DAPI gray levels indicates that the DNA content of fibroblast nuclei grown on etched and those grown on unetched titanium platelets did not differ.
All 4 examined unetched platelets showed a rough and grainy surface with scratches and parallel grooves (e.g., Figure 3B) as a result of the manufacturing process. Compared to the unetched condition, etching clearly affected the surface of all 4 analyzed titanium platelets in a similar way (e.g., Figure 3A). In etched platelets, the surface appeared smoother and less rough or grainy resembling a relief map with indentations and elevations. The grooves and scratches due to the mechanical surface processing disappeared on the surface of etched platelets (A).
Figure 3. Examples of high power SEM images from the surface of titanium platelets that were either etched (A), or not etched (B). The white bar represents a length of 50 µm.
Titanium has been examined as a material for ossicular replacement with favorable results in human middle ear surgery [2-5,9]. It is characterized as an excellently well tolerated biomaterial with very low disintegration rates and good sound conduction. Grade 2 pure titanium, which is the raw material for KURZ middle ear protheses, has a Ferrite content of 0.3% ensuring high stability (KURZ Medicals). Remarkable is the low weight of the material (specific weight titanium 4.5 g/cm3 vs. gold
19.3 g/cm3). In general, titanium is a material with a high biocompatibility which facilitates cellular overgrowth . The application in an open implant area like the middle ear with potential germ colonization requires excellent biocompatibility. An important histological criterion for judging the biocompatibility of alloplastic material is the amount of surrounding fibrous tissue after implantation . The mucosal injury during insertion of the prosthesis is a strong growth stimulus. Activated local growth factors support the outgrowth of fibroblasts and epithelial cells. Furthermore extracellular proteins like albumin are well adsorbed by the titanium surface and strongly bound. This is the essential condition for the long term integration of the biomaterial in living tissue . Furthermore, the affinity of titanium towards bone, known as osseointegration , leads to a stable fixation between the titanium prosthesis and the stapes footplate. Recent studies have tried to induce this process with osteoinductive substances covering the titanium stapes footplate .
Interestingly, by using titanium middle ear implants, revision procedures are necessary in 4.8%  (second look procedures excluded) up to 8% . Main reason for revision surgery is the dysfunction of the Eustachian tube causing recurring chronic inflammation and scarring. Stupp et al stated a conductive hearing loss due to a too short implant or implant dislocation as another frequent reason for revision surgery.
Possible negative influences on the biocompatibility of titanium middle ear implants are manufacturing residues or an unsuitable surface structure of the prosthesis. One hypothesis is that wear particles or debris can lead to cell mediated hypersensitivity and inflammation. This limits the cell overgrowth with fibrous tissue. In the present study we show, that after surface conditioning of titanium platelets the amount of surface covered with fibroblasts increased by 17%. In addition, the actin content, as determined by FITC gray levels, was significantly increased in fibroblasts grown on etched as compared to those grown on unetched titanium platelets. On average, the area covered by nuclei of fibroblasts grown on etched platelets was also higher compared to unetched platelets, but this difference was not significant in the present sample. The difference of fibroblasts grown on etched and unetched titanium platelets correlates with changes of the surface structure induced by the etching procedure (Figure 3).
In conclusion, our present investigation demonstrates that special processing of titanium middle ear implants leads to increased actin expression and increased coverage by fibroblasts. The cell growth on the prosthesis is a main indicator of its biocompatibility. Furthermore, cell growth supports the stable integration of the implant within the reconstructed ossicular chain. The effects observed in the present study suggest that this type of surface modification may be beneficial for integration in titanium middle ear prostheses. For reconstructive middle ear surgery accordingly processed titanium implants should be preferred.
We are grateful to KURZ Medicals for providing the titanium platelets and thank Sara Bergmann for performing the cell cultures. This publication was funded by the German Research Foundation (DFG) in the funding programme Open Acess Publishing.
Information on the authors:
Kornelia Wirsching, Ear, Nose, and Throat Department, University of Regensburg, Regensburg 93042, Germany
Karla Lehle, Cardiothoracic Surgery Department, University of Regensburg, Regensburg 93042, Germany
Peter Jacob, Ear, Nose, and Throat Department, Sørlandet Sykehus, Kristiansand N-4600, Norway
Otto Gleich, Ear, Nose, and Throat Department, University of Regensburg, Regensburg 93042, Germany
Jürgen Strutz, Ear, Nose, and Throat Department, University of Regensburg, Regensburg 93042, Germany
Pingling Kwok, Ear, Nose, and Throat Department, University of Regensburg, Regensburg 93042, Germany
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‘STEM in 30’ Smithsonian
Air & Space Museum Webcast
Featuring Expert Commentary from Stanley Seagle
Stanley Seagle, a lifelong executive in the titanium industry, was a featured guest on the “STEM in 30” webcast, produced by the Smithsonian Air and Space Museum, Washington D.C., which aired on March 16th. The Education Committee of the International Titanium Association (ITA), sponsored the webcast, which was seen on the Smithsonian museum’s website (http://airandspace.si.edu/explore-and-learn/stem-in-30) and the NASA website (http://www.nasa.gov/multimedia/nasatv).
ITA, headquartered in Denver, Colorado, is a strong advocate of STEM (science, technology, engineering and mathematics) education and workforce development. The STEM education movement has gained traction in the United States in recent years—a curriculum designed to cultivate students, female and male, in the skills needed for 21st century advanced manufacturing and engineering fields.
Marty Kelsey and Beth Wilson, education specialists of the Smithsonian Institution’s National Air and Space Museum, served as program hosts—fielding questions from students and online viewers and interviewing program guests. Wilson said the idea for the webcast was hatched by Smithsonian about 18 months ago as a way to reach students “and make science fun.” Wilson, who has worked at Smithsonian for 11 years, said the STEM in 30 webinar grew out of her “point to point” interactive video conferencing outreach efforts with individual schools and classrooms throughout the United States. “The goal (for STEM in 30) was to take that concept and reach a wider audience,” Wilson said.
Given the advances in online communication technology in recent years, Smithsonian determined that a webcast was the best way to connect with its target audience: middle school and high school students. Wilson added that, early on, the decision was made to do the webcast as a real-time broadcast, taped in front of a live audience, from the floor of the Steven F. Udvar-Hazy Center in Chantilly, VA, a companion museum facility to the Smithsonian Air and Space Museum located in downtown Washington D.C.
“The show was challenging and unique,” Wilson said. “People are always interested to see things in a museum.” Besides one SR-71, the Chantilly center, with its enormous hangar space, displays the Concorde passenger jet, the Space Shuttle Discovery, and the Boeing B-29 Enola Gay.
Wilson singled out Seagle as “a real benefit to the webcast. He was very knowledgeable and very helpful.” In particular, Wilson said she enjoyed Stan’s “show and tell” objects he brought with him: metal rods of different lengths that visually demonstrated the differences between steel, aluminum and titanium. The bar donations were provided by ITA Member, Service Steel Aerospace.
The March 16 webcast was the first of several episodes planned by the Smithsonian Institution’s National Air and Space Museum, and featured a profile of the legendary Lockheed Blackbird SR-71 Mach 3+ reconnaissance aircraft. Built of titanium, the futuristic SR-71 Blackbird is the world’s fastest jet-propelled aircraft. It was operated by the U.S. Air Force and designed as a long-range reconnaissance aircraft with a top speed in excess of 2,000 miles per hour and a range of more than 3,000 miles and was made of a titanium alloy.
The SR-71 Blackbird’s performance and operational achievements placed it at the pinnacle of aviation technology developments during the height of the Cold War. The plane was unveiled in 1966 and was in service until 1999, when it was retired for budgetary reasons. During the program, Kelsey and Wilson said that 32 SR-71s were built; 12 were lost over the years due to accidents, but the plane never was hit by enemy fire on its many high-altitude reconnaissance missions to photograph military installations around the world. Kelly Johnson was identified as the lead engineer for the Lockheed “Skunk Works” program, which designed and built the plane.
During the webcast Stan Seagle explained why a titanium alloy was the strategic metal of choice used in the construction of the iconic SR-71. In addition to being light, strong and corrosion resistant, a titanium alloy was chosen due to its ability to survive the extreme temperatures on the outer skin of the aircraft while it was in flight. He said that, due to its high speed, air friction would generate heat of 450-1200F on the SR-71’s exterior. Seagle also pointed out the design considerations of the plane in terms of titanium’s known coefficient of thermal expansion, and spoke briefly about this history of the “wonder metal”—an element first discovered in 1791 in England by the Reverend William Gregor.
Another unique on-air visual shown by Seagle was a titanium straw used by the popular singer and dancer Beyonce. Various social media websites indicated that the titanium straw, is one of the stated demands of Beyonce and her entourage for the consumption of specially prepared beverages while they are on tour.
In addition to Stanley Seagle, another guest on the webcast was Buzz Carpenter, a docent at the Steven F. Udvar-Hazy Center and one of the pilots that flew the SR-71. Student scholars from Farmwell Station Middle School, Ashburn, VA, also were featured on the program.
Mr. Seagle, who retired last year, has been involved in titanium industry since the industrialization of the metal in the 1950’s. In 2001 he was honored with ITA’s prestigious “Lifetime Achievement Award.” He served for many years as an executive with Reactive Metals Inc. (RTI International) and spent the early portion of his career in technical research, formulating titanium alloys. A number of titanium alloys developed by Seagle are utilized in aerospace and corrosion-resistant industry applications. He eventually transitioned into marketing and focused on developing titanium applications for various industries. After 38 years, he retired from the business and pursued consulting work, which included 14 years as an instructor for the ITA’s “Fundamentals of Titanium” workshop series.
Dr. Markus Holz, the co-chair of the ITA’s Education Committee, explained that the innovative STEM in 30 education program “enables the ITA to reach out to young professionals at an international level and enhance their careers in a flexible, state-of-the-art manner and support the development of future leaders in the titanium industry worldwide.” Holz serves as the president of AMG’s Engineering Systems Division and is the chief executive officer of ALD Vacuum Technologies GmbH, Hanau, Germany. He also is a member of the ITA’s executive board.
Graham P. Walker, the co-chair of the ITA’s Education Committee and another member of the ITA’s executive board, said the STEM in 30 webcasts “are archived on museum’s website for anyone to visit and watch. In this way, the ITA is extending its reach to include future generations of material scientists and engineers.” Walker also underlined the fact that the Education Committee “supports the overall vision of the ITA towards promoting the applications of titanium in new and existing global markets. We do this through a number of initiatives such as furthering titanium education at the university level and expanding the Fundamentals of Titanium workshop series.”
STEM in 30 is an interactive classroom program consisting of 30-minute live webcasts produced to engage students in STEM topics. Students watching the webcast can chat with experts, submit their questions to be answered live, take a poll, discover related content, and participate in follow-up activities. Future STEM webcasts sponsored by the ITA Education Committee include NASA’s ongoing Mars Exploration Rover Mission. Two robotic rovers—Spirit and Opportunity—with many parts made from titanium, are traversing the surface of the Red Planet. The 3rd webinar of STEM in 30 sponsored by ITA will explore Moon rocks and what they can tell us not only about the Moon but also about our own planet.
For additional information on STEM in 30, visit the Smithsonian Institution’s National Air and Space Museum website (https://airandspace.si.edu) or the ITA website (www.titanium.org), which has a special posting on the program.
ITA Prepares to Feature Poster Session Scholars at TITANIUM EUROPE 2016
The International Titanium Association (ITA) will host its annual “Poster Session” for students at TITANIUM EUROPE 2016, which will be held April 18-20 at the Paris Marriott Rive Gauche Hotel and Conference Center.
This program is made available to any graduate student(s) (single or teams) involved in titanium metal research for several years. Specific times during the conference will provide maximum exposure for the Poster Session.
The ITA’s Education Committee organizes and sponsors the Poster Session. Committee members represent a variety of ITA organizations, all which have an interest in furthering ITA education initiatives. The mission of the ITA’s Education Committee to help facilitate the expanded use of titanium based products in existing and new market sectors and applications by enlarging the knowledge about titanium through education, training and exchange of information with universities and other academic networks.
The committee’s objective, through programs like the annual Poster Session, is to contribute to the growth of the overall titanium industry and to promote the selection of titanium as a competitive material providing fundamental knowledge about titanium and its applications.
Members of the ITA’s Education Committee include Dr. Markus Holz (chair), president of AMG’s Engineering Systems Division and chief executive officer of ALD Vacuum Technologies GmbH; Frauke Hogue (member), metallographer, Hogue Metallography; and Graham P. Walker (co-chair), vice president, sales and marketing, AMETEK—Reading Alloys.
The following students represent a sample of what will be presented at the upcoming TITANIUM EUROPE academic poster session, hosted in Paris, France the 18th – 20th April.
Eric Vavra, Oregon State University, Corvallis, Oregon USA
Eric is a second-year graduate student at Oregon State University where he is earning his Master of Science in civil engineering degree under the advisement of Dr. Chris Higgins. Eric has a long-standing passion for bridges and is looking forward to a career in assessment and repair of bridge structures.
Application of Titanium Alloy Bars for Strengthening Reinforced Concrete Bridge Girders in Flexure
Structurally efficient and cost-effective solutions are needed to extend the service-life of deficient and aging highway infrastructure around the world. One critical need is to increase the flexural strength of older concrete structures to carry heavier and more frequent loads. Titanium alloy bars offer a new opportunity to strengthen such existing structures that has not previously been explored.
Titanium’s combination of strength, ductility, durability, and ability to form mechanical anchorages are essential characteristics for effective repair and retrofit applications and are advantageous over competing materials such as steel and fiber-reinforced polymer (FRP) products. Recent research using titanium alloy bars to strengthen existing civil infrastructure has been undertaken in the laboratory through tests of full-scale bridge girders using two alternative strengthening applications for bending. The first technique is called near-surface mounting (NSM) and the second is called external unbonded reinforcement.
The NSM retrofit technique involves cutting grooves into the concrete substrate and bonding specially made titanium alloy bars inside the grooves using structural epoxy. The titanium alloy bars serve as supplemental reinforcement to the girder to allow it to carry larger loads and to increase the deformation capacity. This experimental program tested seven full-scale concrete girders retrofitted with NSM titanium alloy bars. Advantages of using titanium with NSM included less labor cost for cutting grooves, lower epoxy costs, and use of higher stresses when compared to stainless steel. The ability to fabricate hooks at the ends of the bars for mechanical anchorage, increased warning of potential failure, and less field labor costs make it competitive compared with FRP. While research on the fatigue effects and environmental durability of the NSM retrofit is ongoing, this technique has already been put into service on an existing bridge in the USA over a major interstate highway at a significant cost savings compared to the FRP alternative.
The external unbonded reinforcement technique requires only drilling holes through the girder. Smooth as-rolled titanium alloy bars are not bonded along the length and 90o hooks are fabricated on the ends. The hooks are placed through the holes and prestressing chucks anchor the bars only. The elimination of grooves and epoxy required for NSM significantly reduced labor and material costs while also allowing application in all exposure conditions. To investigate the effectiveness of the technique, two full-scale concrete girders were strengthened in the laboratory. Only requiring a one-day installation time, this repair can be completed using standard contracting tools, equipment, and labor. The speed of the repair also reduces costs beyond labor by decreasing costs associated with the economic impact of long-term lane closures and bridge ratings.
This poster will discuss the advantages and disadvantages of the NSM and external unbonded reinforcement techniques for flexural strengthening; describe the titanium alloy bars, bridge girders, and construction practices; and detail the laboratory findings on the structural performance of the specimens. It will further demonstrate that titanium alloy bars offer a structurally effective and cost competitive alternative to current materials for maintaining and preserving aging and deteriorated highway infrastructure assets world-wide.
MacKenzie Lostra, Oregon State University, Corvallis, Oregon USA
Lostra received her bachelor’s degree in civil engineering from the University of Arizona in 2014 and is now pursuing a master’s degree in Structural Engineering at Oregon State University. Her background in research has been focused on seismic resiliency of reinforced concrete structures and innovative retrofitting methods. Her advisors include Christopher Higgins and Andre Barbosa.
Titanium retrofitting of seismically vulnerable columns is an opportunity to expand the amount of viable structural materials and methods for improving stability and safety in older concrete structures that do not meet modern seismic code requirements. The enhancement of reinforced concrete (RC) columns with unsatisfactory ductility properties using external titanium bars and spirals poses room for increased understanding of the behavior of rectangular retrofitted RC columns under seismic demands, simulated by monotonic-cyclic loading sequences.
The research utilizes four physical models at full scale, which are modeled after the McKenzie River Bridge in Oregon, to measure changes in ductility and strength. These columns, similar to many others on RC bridges constructed during the 1950-60’s, have poor internal detailing, with insufficient bending and shear reinforcement, making them susceptible to seismic forces. Specifically, poor detailing of the internal foundation bar lap splice creates a bond-slip failure mode, in which the longitudinal reinforcement between the foundation and column no longer acts as a continuous development when high stress level is reached; this reduces the stiffness of the joint between the foundation and the column.
The bending stresses imposed on a free-standing column are concentrated in this zone, therefore strengthening of the base of the column is necessary to resist seismic loads. Titanium is both economic and efficient for this purpose and possesses many desirable qualities such as its resistance to corrosion, low stiffness, and high strength. Four cases will be tested in this research: a control specimen (conventionally reinforced) and three retrofitted specimens with the retrofit extended above the lap splice, below the lap splice, and the lap splice removed entirely.
The results are expected to demonstrate improved ductility in the retrofitted columns by increasing passive confinement in the columns and providing additional, more flexible reinforcement. The confinement provided by the titanium coil and the leverage from the vertical ligaments should allow for proactive strengthening and resiliency of the columns, extending the displacement and load capacity. In turn, this can lead to more resilient bridges that are able to withstand larger deformations without losing axial strength. If the testing results in notably improved performance of the retrofitted columns to that of the un-retrofitted column, titanium can continue to be researched as a structural material in civil engineering and become more widely available and practical for use in retrofitting structures that require it.
The research will provide preliminary data for an ongoing study of rectangular RC columns and seismic retrofitting at Oregon State University. Testing for this project is expected to conclude over the course of the next two months and future testing under an additional graduate student over the next several years.
Alfonso Garcia, Rolls Royce UTC Nottingham, Faculty of Engineering The University of Nottingham University Park, United Kingdom.
Garcia started a career in design several years ago in Mexico, working for companies in fields such as near net-shape manufacturing, sheet metal forming, advanced manufacturing processes, product and tooling design. He is currently working in a Ph.D. project funded by Rolls Royce at the University of Nottingham.
The joining of massive titanium sections cut from plate is an attractive alternative to manufacturing large components by forging, as it offers a simple route to near net shaping, reducing the overall cost of components made in this way. A novel approach to this problem, using a process based on diffusion bonding (DB) and hot isostatic pressing (HIP), has been developed as a research PhD project at the Rolls Royce University Technology Centre (RR-UTC) in the University of Nottingham and is currently patented in the United Kingdom.
In this method, gaps between adjoining Titanium plates from dissimilar alloys (Ti-6Al-4V and Ti-6Al-2Sn-4Zr-6Mo) are “sealed” by a shallow laser weld around the majority of the join line. The final part of this interface is sealed in a vacuum by electron beam (EB) welding, thus creating a leak-tight gap containing a vacuum. These structures can then be “HIPed” without needing to be encapsulated, offering considerable cost advantages.
The tensile and high cycle fatigue properties of the resulting bonded parts were only slightly reduced when compared to that the bulk material and are equivalent to or better than those obtained by the traditional canned route. Adopting a can-less route offers significant time and cost savings with what appears to be no detriment to the bond strength and integrity.
Beatriz Eugenia Sanabria Arenas, Politecnico di Milano - Dipartimento di Chimica, Materiali e Ingegneria Chimica “Giulio Natta,” Italy
Sanabria Arenas obtained her M.Sc. degree in Chemical Engineering from university of Sao Paulo, Brazil, in 2014 and currently is a Ph.D. student in Materials Engineering from Politecnico di Milano, Italy. Her current research interests include functional nanomaterial synthesis by electrochemical processes for environmental applications. Her advisors include Davide Prando, Alberto Strini, Luca Schiavi, Andrea Brenna, Maria Vittoria Diamanti, and MariaPia Pedeferri.
In the environmental field, the efficiency of nanostructured titanium dioxide for degrading inorganic and organic substances is demonstrated. However, one of the major concerns about the use of nanostructured materials for water remediation and air purification by photocatalysis is their potential dispersion in the gas or liquid phase, where they are used, and the hazard related to their dispersion in the environment. In this context, the use of anodic oxidation represents a powerful technique for generating photoactive oxides strongly adherent to a metallic substrate—i.e. titanium, and modify their chemical composition by doping. In this work, we present a robust method to obtain immobilized TiO2 by anodic oxidation, in the form of either nanotubes or nanoporous anodic spark deposition (ASD) coatings. The photocatalytic efficiency of these nanostructures was tested and compared in gaseous and liquid phases.
Commercial purity titanium sheets were anodized in three different electrolytes: aqueous solution, fluoride containing aqueous solution and fluoride containing organic solution. The voltage applied and the duration of the essays were changed in order to obtain the best nanostructures in each electrolyte. After anodizing in solutions containing fluorides, samples were annealed at 400°C for two hours to promote the formation of anatase phase TiO2.
Photocatalytic activity was evaluated in the degradation of dyes (rhodamine B, RhB) or VOCs (toluene). Degradation was performed by immersing a sample in 25 ml of 105 m/L RhB solution, irradiating for six hours with a solar spectrum lamp (UV-A intensity 3 mW/cm2) and monitoring color variations. Toluene degradation was assessed in air (25°C and 50-percent RH) in a continuous-flow stirred photo reactor operating at constant toluene concentration (0.75 µmol/m3), under UV-A irradiation of 0.6 mW/cm2.
In aqueous and organic solutions containing fluorides, self-aligned vertical nanotubes stem from the substrate; in organic solution the detachment of single nanotubes is less pronounced, creating a sort of porous template rather than a nanotubular array, but with higher thickness. Conversely, in absence of fluorides a large voltage is applied, generating an oxide with glassy appearance and larger pores. The photocatalytic degradation of dyes with these oxides increases with increasing voltage up to 150V; for higher voltages, too much rutile formation and lower anatase content reduce photo activity. When a nanotubular oxide is obtained, a larger reactivity is ensured.
Although nanotubes obtained in organic solution show the highest efficiency, preliminary results in toluene degradation show a larger dispersion of results compared to other the nanostructures. Conversely, nanotubes produced in aqueous solution exhibit excellent repeatability and good efficiency. Oxides without nanotubular morphology exhibit a very low reactivity in gas phase, while showing good degradation of RhB. This is interesting, because it points out the increased differentiation among the oxides photocatalytic activities in gas phase, in spite of the lower differences observed in liquid phase reactions.
In conclusion, the processes here described open the way to the production of photocatalytically efficient nanostructured TiO2 films immobilized onto a metallic substrate at low cost, avoiding environmental issues related to the use and recycle of conventional photocatalysis.
Davide Prando, Politecnico di Milano, Milano, Italy.
Prando, a Ph. D. student at the faculty of Materials Engineering of the University Politecnico di Milano, graduated in 2015 with a thesis about photocatalysis on titanium dioxide. He is currently working on the corrosion phenomena of commercially pure titanium. His advisors include Maria Vittoria Diamanti, Andrea Brenna, Silvia Beretta, MariaPia Pedeferri, and Marco Ormellese.
Titanium is well known to have an excellent corrosion resistance in natural environment. However much more severe conditions are found in industrial applications and alloys with better behavior were developed; these alloys are often prepared with elements more expensive than titanium (such as palladium in ASTM Grade 7 titanium). This work aims to find a surface treatment capable of improving the performances of the cheaper titanium ASTM Grade 2 on the electrochemical point of view, enable it to be used in critical conditions (such as reducing atmosphere or acid deaerated environments) instead of more expensive alloys.
Anodic oxidation of titanium produces a compact, protective and almost insulating oxide (mainly TiO2) on titanium surface; this technique is fast, easy and satisfactorily applied to other metals so it represents the first natural choice for this investigation.
In order to find the best anodizing treatment three main parameters were identified: anodizing electrolyte, applied potential and anodizing current density. The anodic oxidations were carried out in H2SO4 (because of the wide knowledge available on this electrolyte), and then in Na2SO4, (NH4)2SO4 and NH4BF4, trying to find a neutral electrolyte with good oxide growth times. The applied potential is directly linked to the final thickness of the oxide obtained. A higher potential produces thicker film that is expected to behave better from the corrosion point of view, but leads to oxide crystallization that is known to be detrimental. Thus, in order to investigate a proper range and to avoid conditions of difficult industrial implementation, the potentials were kept from 10V to 80V. Anodizing current density was also expected to have effects on crystallization of the oxide, a current density of 20 mA/cm2 was taken as a reference but also 5 mA/cm2 and 50 mA/cm2 were analyzed.
All the surfaces finishing obtained were tested with potentio-dynamics analyses carried out in different electrolytes. NaCl35 g/L was initially chosen for the common use of titanium in marine environment; then, in order to simulate more severe industrial environment, after a screening on different concentration from 1 g/L to 35 g/L, the electrolyte was substituted with NaF3.5 g/L.
The results obtained so far don’t highlight any preferable treatment. Each anodizing sample provided insulation and the consequent lower current density circulating during the potentio-dynamic tests. The results concentrate in the region corresponding to a current density one order of magnitude lower than the one circulating in non-treated samples, and didn’t show any better or more reliable behavior with respect neither of used electrolyte nor of applied potential or current density.
For economical reason and a better applicability, the suggestion is to apply a treatment at low potential (10-20V) and to perform it in Na2SO4, which is the cheapest and easier to handle tested electrolyte. Further investigation is required: alloyed titanium is often used to control localized corrosion and this form of attack will be the next method to distinguish the best of the available treatment.
Jonathan Knudtsen, Oregon State University Civil and Construction Engineering, Corvallis, OR
Knudtsen received his bachelor of science degree in Civil Engineering from the Colorado School of Mines in Golden, CO. He is currently working towards his master of science degree in Structural Engineering at Oregon State University. His research is focused on the use of titanium for strengthening concrete bridge girders deficient in shear. His advisor is Dr. Chris Higgins.
Aging and obsolete infrastructure has become a major problem throughout the world. This is particularly evident in the case of concrete bridges. The cost of completely replacing these bridges is often prohibitive, meaning engineers must find ways to strengthen them. Many older bridges predate our modern understanding of shear in bridge girders, and were thus built with insufficient internal stirrups. These bridge girders often display diagonal tension cracks in the high-shear zones near the columns. One method commonly used to strengthen these bridge girders is called near-surface mounting (NSM), which involves epoxying bars into vertical grooves cut on the surface of the girder.
Although this method was first developed for use with steel bars, it is now most commonly implemented using carbon fiber rods, due to steel’s corrosive properties. The goal of this research is to establish titanium as a viable alternative to steel and carbon fiber for NSM shear strengthening applications.
Titanium has several advantages over the other materials. It’s noncorrosive, so it does not need to be protected like steel. Titanium bars can easily be bent at the ends to provide anchorage. This is titanium’s main advantage over carbon fiber, since carbon fiber rods cannot be bent, and thus rely solely on epoxy for shear transfer. This means that the ultimate strength of carbon fiber is rarely reached, making it an inefficient repair material. Titanium’s low modulus of elasticity allows for large deflections, giving advance warning of impending failure. Due to titanium’s high yield strength, small diameter bars can be used. This significantly reduces the costs associated with time, labor, and materials, resulting in an overall cost savings when compared to other retrofit materials.
For this research program, seven realistically proportioned T-shaped concrete girders were constructed. These girders were intentionally under-designed to force diagonal tension failure, even after being strengthened with NSM titanium bars. The girders were tested in four-point bending. Failure occurred when the titanium bars ruptured at the main diagonal tension crack, meaning their full strength was achieved. This indicates that the method used is highly efficient. To date, four of the seven girders have been tested. Research is ongoing on the effects of fatigue loading and harsh environmental conditions.
Our research has conclusively demonstrated the effectiveness of NSM titanium bars in shear strengthening applications. Titanium has many advantages, including cost, over the methods and materials currently used, and we expect to see it established as a viable repair option for bridges.
Maxim Khatsayuk, Siberian Federal University, Krasnoyarsk Krai, Russia.
In 2013 Khatsayuk defended a thesis of candidate of sciences: “Induction Unit with a Magneto-Hydrodynamic Effects During Preparing and Casting Alloys.” Khatsayuk has 59 published works, three patents, and four software certificates. Khatsayuk currently is engaged in the research and development of a new method for producing the liquid phase of titanium in an electromagnetic field, which will form the basis for his doctoral dissertation. His advisor is Professor V. Demidovich.
The unique opportunity of the obtaining of the liquid phase of titanium alloy inside the cylindrical ingots during the induction heating gives the prospects to develop fundamentally new titanium alloys non-vacuum casting technology.
Such a technology is very competitive and energy efficient in comparison to the existing induction melting technology in a cold crucible. It is because of the fact that, during the process of melting, no additional equipment for vacuum is required. Furthermore, the process of the obtaining of the liquid titanium inside the ingot by the induction method requires a lot less time and energy consumption.
Piotr Wieci´nski, Ph.D. Eng. has scientific experience in characterization of the microstructure, mechanical and tribological properties of the surface layers and coatings obtained by surface engineering methods. He is mostly focused on advanced characterization techniques like focus ion beam, scanning electron microscopy, scanning transmission electron microscopy, nanoindentation.
Piotr Kwaśniak, M.Sc. Eng. conducts research on mechanical properties prediction through ab initio modelling. He is especially focused on titanium and its hexagonal alloys containing substitutional and/or interstitial elements. He develops the knowledge about the structure and properties of planar and linear crystal defects in the above systems.
Jerzy Smolik, Ph.D., D.Sc. Eng. is a manager of the Surface Engineering Department at Institute for Sustainable Technologies - National Research Institute in Radom. He has experience in applying wide range of surface engineering techniques to improve properties of construction parts and tools.
Progress in Properties Improvement of Titanium and its Alloys
One of the goals of our works is improvement of the strength of titanium using severe plastic deformation (SPD) method. Refinement of grain size below 90 nm in titanium grade 2 increases its strength above 1000 MPa, which is close to Ti6Al4V alloy. Nanostructure has a positive influence also on the corrosion properties of titanium in physiological saline (0,9% NaCl). A large number of grain boundaries in nanotitanium promote a rapid formation of homogenous protective passive layer which was evidenced in our work. A combination of good mechanical properties and corrosion resistance in the body fluid indicate that nanocrystalline titanium has a large potential in biomedical applications. Nowadays, our work is focused on methods for improvement of titanium biocompatibility. For example, the most promising method of surface modification of bone implants is mimicking the bone hierarchical surface structure after remodelling process. In order to modify titanium, hybrid method consisting of shot peening, acid etching treatment and laser interference lithography was proposed. Our results evidenced that the appropriate choice of the parameters of such treatment allows to form hierarchical roughness (in a wide range of length scale from nano- to micrometers). Furthermore, laser treatment forms texture favourable for osteogenic passes of the stem cells, which can have a positive impact on the osseointegration process.
Another area of our work is improving the tribological properties of Ti6Al4V alloy, which are insufficient for many industrial applications, by deposition of multilayered coatings using PVD method. Depending on the mechanism of wear, different kinds of multilayer coatings ensure the highest improvement of tribological properties. For example, Cr/CrN multilayer coatings exhibit excellent anti-erosion properties on Ti6Al4V alloy. Moreover, STEM observations evidenced that Cr layers accommodate plastic strain induced by erosion particles while interfaces between layers effectively block crack propagation. These phenomena decrease the number of cracks and ensure structure integrity of the coating during erosion. On the other hand the measurement of wear resistance during pin on disc test reveals the highest improvement of the tribilogical properties for the TiN/CrN coatings. Our results evidenced that not only the phase composition, but also the number and thickness of layers can influence the properties or even change the mechanism of failure.
Titanium and its alloys with outstanding strength-to-density ratio are potentially prime elements for new constructional alloys to reduce the weight and energy consumption in all transport sectors. In our group mechanical properties of Ti and its hexagonal alloys are successfully predicted utilizing ab initio modeling methods. The calculations methodology includes electronic and atomic structure characterizations of binary (α-Ti+O) and selected ternary systems comprised of substitutional and interstitial alloying elements. Mechanical properties evaluation covers single and polycrystalline elastic constant, plasticity criteria as well as generalized stacking fault energy calculations. The achieved results provide insight into the physics of solute-solute element interactions, dislocation nucleation or dissociation mechanisms and atomic configuration of compact (point defects, dislocation cores) or extended (stacking fault, twins) defects.