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In this study we report the fabrication of compositionally graded hydroxyapatite (HA) coatings on Ti by combining laser engineering net shaping (LENS) and radio frequency induction plasma spraying processes. Initially, HA powder was embedded in the Ti substrates using LENS, forming a Ti-HA composite layer. Later, RF induction plasma spraying was used to deposit HA on these Ti substrates with a Ti-HA composite layer on top. Phase analysis by X-ray diffraction indicated phase transformation of HA to β-tricalcium phosphate in the laser processed coating. Laser processed coatings showed the formation of a metallurgically sound and diffused substrate-coating interface, which significantly increased the coating hardness to 922 ± 183 Hv from that of the base metal hardness of 189 ± 22 Hv. In the laser processed multilayer coating a compositionally graded nature was successfully achieved, however, with severe cracking and a consequent decrease in the flexural strength of the coating. To obtain a structurally stable coating with a composition gradient across the coating thickness a phase pure HA layer was sprayed on top of the laser processed single layer coatings using induction plasma spray. The plasma sprayed HA coatings were strongly adherent to the LENS-TCP coatings, with adhesive bond strength of 21 MPa. In vitro biocompatibility of these coatings, using human fetal osteoblast cells, showed a clear improvement in cellular activity from uncoated Ti compared with LENS-TCP-coated Ti and reached a maximum in the plasma sprayed HA coating.

Nanocrystalline α-Al2O3 ceramic powders have been prepared from an aqueous solution of aluminum nitrate and sucrose. Soluble Al ion-sucrose solution forms the precursor material once it is completely dehydrated. Heat treatment of the dehydrated precursors at low temperature (600°C) results in the formation of porous single-phase α-Al2O3. The precursor and heat-treated powders have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and BET surface area analysis. The phase-pure nanocrystalline α-Al2O3 particles had an average specific surface area of >190 m2/g, with an average pore size between 18 and 25 nm.

Despite the excellent bioactivity of hydroxyapatite (HA) ceramics, poor mechanical strength has limited the applications of these materials primarily to coatings and other non-load-bearing areas as bone grafts. Using synthesized HA nanopowder, dense compacts with grain sizes in the nanometer to micrometer range were processed via microwave sintering between 1000 and 1150 degrees C for 20 min. Here we demonstrate that the mechanical properties, such as compressive strength, hardness and indentation fracture toughness, of HA compacts increased with a decrease in grain size. HA with 168 +/- 86 nm grain size showed the highest compressive strength of 395 +/- 42 MPa, hardness of 8.4+/-0.4 GPa and indentation fracture toughness of 1.9 +/- 0.2 MPa m(1/2). To study the in vitro biological properties, HA compacts with grain size between 168 nm and 1.16 microm were assessed for in vitro bone cell-material interactions with human osteoblast cell line. Vinculin protein expression for cell attachment and bone cell proliferation using MTT assay showed that surfaces with finer grains provided better bone cell-material interactions than coarse-grained samples. Our results indicate simultaneous improvements in mechanical and biological properties in microwave sintered HA compacts with nanoscale grain size.

Polycaprolactone (PCL) was coated on porous tricalcium phosphate (TCP) scaffolds to achieve controlled protein delivery. Porous TCP scaffolds were fabricated using reticulated polyurethane foam as sacrificial scaffold with a porosity of 70-90 vol %. PCL was coated on sintered porous TCP scaffolds by dipping-drying process. The compressive strength of TCP scaffolds increased significantly after PCL coating. The highest strength of 2.41 MPa at a porosity of 70% was obtained for the TCP scaffold coated with 5% PCL solution. Model protein bovine serum albumin (BSA) was encapsulated efficiently within the PCL coating. The amount of BSA encapsulation was controlled by varying proteins' composition in the PCL coating. The FTIR analysis confirmed that BSA retained its structural conformation and did not show significant denaturization during PCL coating. The release kinetics in phosphate buffer solution indicated that the protein release was controlled and sustained, and primarily dependant on protein concentration encapsulated in the PCL coating.

Calcium phosphate (CaP) nanoparticles with a calcium to phosphorus (Ca:P) molar ratio of 1.5:1 were synthesized using reverse microemulsion. Ca(NO(3))(2).4H(2)O and H(3)PO(4) were used as the aqueous phase, cyclohexane as the organic phase and poly(oxyethylene)(12) nonylphenol ether (NP-12) as the surfactant. Depending on the calcination temperature between 600 and 800 degrees C, CaP nanoparticle showed different phases of calcium-deficient hydroxyapatite (CDHA) and beta-tricalcium phosphate (beta-TCP), particle size between 48 and 69 nm, and a BET specific average surface area between 73 and 57 m(2)g(-1). Bovine serum albumin (BSA) was used as a model protein to study loading and release behavior. The adsorptive property of BSA was investigated by the change in BET surface area of these nanoparticles and the pH of the suspension. At pH 7.5, the maximum amount of BSA was adsorbed onto CaP nanoparticle. The release kinetics of BSA showed a gradual time-dependent increase in pH 4.0 and 6.0 buffer solutions. However, the amount of protein released was significantly smaller at pH 7.2. The BSA release rate also varied depending on the presence of different phases of CaPs in the system, beta-TCP or CDHA. These results suggest that the BSA protein release rate can be controlled by changing the particle size, surface area and phase composition of the CaP nanocarriers.

Electrically polarized bulk sintered hydroxyapatite (HAp) compacts have been shown to accelerate mineralization and bone tissue ingrowth in vivo. In this work, a comprehensive study has been carried out to investigate the influence of surface charge and polarity on in vitro bone cell adhesion, proliferation and differentiation on electrically polarized HAp-coated Ti. Uniform and crack free sol–gel derived HAp coatings of 20 ± 1.38 μm thickness were polarized by application of an external d.c. field of 2.0 kV cm−1 at 400 °C for 1h. In vitro bioactivity of polarized HAp coatings was evaluated by soaking in simulated body fluid, and bone cell–material interactions were studied by culturing with human fetal osteoblast cells (hFOB) for a maximum period of 11 days. Scanning electron microscopic observation showed that accelerated mineralization on negatively charged surfaces favored rapid cell attachment and faster tissue ingrowth over non-polarized HAp coating surfaces, while positive charge on HAp coating surfaces restricted apatite nucleation with limited cellular response. Immunochemistry and confocal microscopy confirmed that the cell adhesion and early stage differentiation were more pronounced on negatively charged coating surfaces as hFOB cells expressed higher vinculin and alkaline phosphatase proteins on negatively charged surface compared to cells grown on all other surfaces. Our results in this study are process independent and potentially applicable to any other commercially available coating techniques.

Oxidized Zr alloys have been shown to exhibit lower friction and superior wear properties, suggesting that they could be used in hip and knee implants. However, conventional oxidation of Zr alloys above 500 degrees C, in dry air, for several hours has been shown to have detrimental effects on the substrate's properties. In this work, we deposited pure Zr on Ti, then oxidized the coating using a continuous-wave Nd:YAG laser, which facilitated localized heating to elevated temperatures without affecting the substrate. Laser-assisted oxidation resulted in a 7microm thick fully dense ZrO(2) layer on Zr in which an increase in oxidation kinetics was evident due to an increase in the laser power and/or the oxygen partial pressure. Due to its high surface energy and wettability, the wear rate of laser-oxidized Zr was two orders of magnitude less compared to that of as-deposited Zr. The oxidized coatings showed comparable in vitro biocompatibility to that of pure Ti and excellent in vitro cell-material interactions. This article reports the processing of Zr/ZrO(2) coatings on Ti using lasers, and the influence of laser parameters and oxygen partial pressure on the coating's mechanical, microstructural, wear and in vitro biological properties using human osteoblast cells.

Novel structures with functional gradation in composition and structure were successfully made in Ti-TiO(2) combination using laser engineered net shaping. The addition of fully dense, compositionally graded TiO(2) ceramic on porous Ti significantly increased the surface wettability and hardness. The graded structures with varying concentrations of TiO(2) on the top surface were found to be non-toxic and biocompatible. In addition, the higher wettability of surfaces with TiO(2) can enhance their ability to form chemisorbed lubricating films, which can potentially lower the friction coefficient against ultrahigh molecular weight polyethylene liner, thus reducing its wear rate. These unitized structures with open porosity on one side and hard, low friction surface on the other side can eliminate the need for multiple parts with different compositions for load-bearing implants such as total hip prostheses.

The purpose of this study is to synthesize mesoporous calcium silicate (CS or wollastonite, CaSiO(3)) and evaluate its possible application in protein/drug delivery. First, calcium silicate was synthesized by wet chemical method and then mesoporosity was created by acid modification of the synthesized CS particle using hydrochloric acid at pH 7, 4.5, and 0.5. The results showed that a hydrated silica gel with abundant Si-OH functional group formed on the surface of calcium silicate due to acid modification. This surface layer had mesoporous structure, with pore diameter between 4 and 5 nm. BET specific average surface area increased to 221, 333, and 356 m(2) g(-1) due to acid modification at pH 7, 4.5, and 0.5, respectively, whereas the surface area for unmodified CS particles was 65 m(2) g(-1). Protein adsorption studies indicated that mesoporous CS has higher ability to adsorb bovine serum albumin and lysozyme compared to unmodified particles. The release kinetics showed that proteins on mesoporous CS released sequentially over one week, whereas the proteins on unmodified particle followed burst release kinetics within a few hours. Human osteoblast cell-material interaction study showed that these materials were biocompatible and promoted excellent bone cell proliferation. In summary, this work has demonstrated the potential to produce mesoporous CS as a carrier for protein/drug delivery for bone regeneration and other biomedical applications.

Ti surface was modified to simultaneously improve bone cell materials and antimicrobial activities. Titanium surface was first anodized in sodium fluoride and sulfuric acid electrolytic solution to form titania nanotube on the surface to improve the biocompatibility of the surface. Silver was electrodeposited on the titania nanotube surface at 5 V. Silver added titania nanotube surface was tested for compatibility with bone-cell materials interactions using human osteoblast bone cells. The antibacterial effect was studied using Pseudomonas aeruginosa. Our results show that silver-treated titania nanotube surface may provide antibacterial properties to prevent implants against postoperative infections without interference to the attachment and proliferation of bone tissue on titanium, which is commonly used in dental and orthopedic surgical procedures.

Thin film structures have found a wide variety of applications in electromechanical technologies. As the design flexibility for these structures increases, so does the demand for design software that can provide some good insights into the behavior of the structure before it is fabricated. In this study, a finite element code based on a combination of equivalent single-plate theory and classical laminated plate theory was used to predict the dynamic response of thin film structures in micro length scale. As a benchmark for the code development, thin film structures were also fabricated using MEMS technology, and their fundamental frequencies were characterized. It was demonstrated that the model predictions matched fairly well with the experimental data for the small membranes with widths less than 200 microm, but underestimated them for large ones with widths greater than 500 microm. The model also demonstrated that the fundamental frequencies increased with the thickness of the layers. The areas that need to be investigated further in order to improve the predicative capability of the calculations include effects of residual stress, dc bias voltage, parasitic capacitance, interaction of membrane vibration with the supports of the structure, and accurate measurement of the dimensions and material properties of the thin films.

Titanium and its alloys are extensively used in load-bearing metallic devices. They are bioinert material and, therefore, get encapsulated after implantation into the living body by a fibrous tissue that isolates them from the surrounding tissues. Here we report modification of titanium surface using bioactive tricalcium phosphates (TCP) and nanoscale TiO2 to enhance cell-materials interaction. We have introduced bioactivity in Ti using laser-assisted coating of TCP and by anodization to grow surface TiO2 at room temperature using a mixed aqueous solution of sodium fluoride, citric acid and sulfuric acid as electrolyte. TCP coating showed a columnar Ti grains at the substrate side of the coating and transitioned to an equiaxed grains at the outside. Coating hardness increased from 882 +/- 67 to 1029 +/- 112 Hv as the volume fraction of TCP increased in the coating. For TiO2 nanotubes, microscopic analysis showed tubes of 50 nm in diameter with wall thickness of 15 nm and typical length between 200 nm and 1 micron based on anodization times. Effects of TCP and nanoscale TiO2 coating on bone cell-material interaction were examined by culturing osteoprecursor cells (OPC1) on coated surfaces. Antibacterial activity analysis using metallic Ag via electrodeposition showed over 99% antibacterial activity against the growth of colonies of Pseudomonas aeruginosa.

Functionally graded, hard and wear-resistant Co-Cr-Mo alloy was coated on Ti-6Al-4V alloy with a metallurgically sound interface using Laser Engineering Net Shaping (LENS). The addition of the Co-Cr-Mo alloy onto the surface of Ti-6Al-4V alloy significantly increased the surface hardness without any intermetallic phases in the transition region. A 100% Co-Cr-Mo transition from Ti-6Al-4V was difficult to produce due to cracking. However, using optimized LENS processing parameters, crack-free coatings containing up to 86% Co-Cr-Mo were deposited on Ti-6Al-4V alloy with excellent reproducibility. Human osteoblast cells were cultured to test in vitro biocompatibility of the coatings. Based on in vitro biocompatibility, increasing the Co-Cr-Mo concentration in the coating reduced the live cell numbers after 14 days of culture on the coating compared with base Ti-6Al-4V alloy. However, coated samples always showed better bone cell proliferation than 100% Co-Cr-Mo alloy. Producing near net shape components with graded compositions using LENS could potentially be a viable route for manufacturing unitized structures for metal-on-metal prosthetic devices to minimize the wear-induced osteolysis and aseptic loosening that are significant problems in current implant design.

The need for unique mechanical and functional properties coupled with manufacturing flexibility for a wide range of metallic implant materials necessitates the use of novel design and fabrication approaches. In this work, we have demonstrated that application of proposed design concepts in combination with laser-engineered net shaping (LENStrade mark) can significantly increase the processing flexibility of complex-shaped metallic implants with three-dimensionally interconnected, designed and functionally graded porosities down to 70vol.%, to reduce effective stiffness for load-bearing implants. Young's modulus and 0.2% proof strength of these porous Ti samples having 35-42vol.% porosity are found to be similar to those of human cortical bone.

The objective of the current study is to investigate the size effect on the performance of piezoelectric micromachined ultrasonic transducers (pMUTs). pMUTs with twenty different dimensions were designed and fabricated. The length/width aspect ratios of the membranes range from 5 to 22. For each design, multiple samples were fabricated in order to collect statistically meaningful data. The performance of pMUTs was characterized by the impedance and phase angle measurements combined with equivalent circuit analysis. The circuit has four electrical components, L1 (motional inductance), C1 (motional capacitance), R1 (motional resistance), and C0 (parallel capacitance), and their values were determined by fitting the circuit equation to the experimental data. The experimental results showed that effective coupling coefficient ( keff 2) increase, and resonance frequency ( fs) and quality factor (Q ) decrease with increasing the width of the membrane.

Musculoskeletal disorders are recognized as among the most significant human health problems that exist today, costing society an estimated $254 billion every year, and afflicting one out of seven Americans. It is expected that the number of individuals with musculoskeletal disorders will increase over the coming years, as our population ages. Among the various options to treat musculoskeletal disorders, use of orthopedic devices is becoming a routine, where the number of annual procedures approaching five million in the United States alone. This article reviews materials and design issues of orthopedic devices. It describes how technological advancements in computer aided design and flexible manufacturing like rapid prototyping are reshaping current and future needs in orthopedic devices. Keywords: biomaterials; musculoskeletal disorders; orthopedic devices; biocompatibility; design issues; rapid prototyping; computer aided design; hip implants; coatings

In this study, a finite element code based on a combination of equivalent single-plate theory and classical laminated plate theory was used to study the dynamic behavior of the thin film membrane structures. The structure studied was piezoelectric micromachined ultrasonic transducer (pMUT) fabricated with MEMS technology. The membrane has two different shapes, square and rectangular. Two different types of boundary conditions were considered for modeling, namely, simply supported vs. clamped. It is demonstrated that the model generates correct qualitative trend for the mechanical responses of pMUT structure. Quantitatively, for relatively larger (greater than 1 mm) thin membrane structures, the measured fundamental frequencies fall between the predictions based on clamped and simply supported boundary conditions. However, for smaller structures, both predictions overestimate them. The possible reasons for this discrepancy include the interaction of membrane vibration with the supports of the structure, residual stress, DC bias voltage, parasitic capacitance, and uncertainty of the dimensions and material properties of the constituent thin films

The objective of this study was to compare adhesion, replication, and differentiation of human osteoblasts (OPC1 cell line) on two different ceramic substrates: a bioinert alumina (A12O3), and a bioactive hydroxyapatite (HAp). Scanning electron microscopy (SEM) and confocal scanning microscopy were used to assess production and distribution of specific osteoblast proteins. Cells grew readily on HAp and alumina. On alumina and HAp, OPC1 cells produced distinctive cell-to-cell and cell-to-scaffold filopodia and microextensions. OPC1 cells proliferated faster on HAp than on alumina substrates. Adhesion was further assessed by observing production of the protein vinculin. On alumina, vinculin was detected throughout the cytoplasm, with some peripheral punctate regions. On HAp, OPC1 cells developed few punctate peripheral regions of vinculin; rather, the protein was strongly localized within the cytoplasm. Finally, we measured accumulation of the marker osteopontin (OPN). OPN was first detectable on day 5 and increased through day 11 of culture on alumina. OPC1 cells on HAp produced substantial amounts of OPN beginning at day 5, with apparent secretion from the cells by culture day 11. These results suggest that the function of osteoblasts is strongly affected by the properties of ceramic surfaces, and rapid attachment of osteoblasts may result in earlier differentiation on HAp than on alumina. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2005

Piezoelectric micromachined ultrasonic transducers (pMUTs), a potential alternative for conventional one-dimensional phased array ultrasonic transducers, were investigated. We used a modeling approach to study the performance of lead zirconate titanate (PZT)-driven pMUTs for the frequency range of 2-10 MHz, optimized for maximum coupling coefficient, as a function of device design. Using original tools designed for the purpose, a comprehensive build-test finite element model was developed to predict and measure the device performance. In particular, the model estimates the device coupling coefficient and the acoustic impedance, besides the readily extractable resonance frequency and bandwidth. To validate the model, a prototype device was built and tested, showing good agreement between the model predictions and experimental results. Modeling results indicate that the coupling coefficient is significantly affected by silicon membrane, PZT, and top electrode thickness as well as the top electrode design. Results also indicate considerable flexibility in maximizing the coupling coefficient while maintaining the device acoustic impedance at a level matching that of the human body. The bandwidth proved to be superior to that of conventional transducers, reaching 102% in some cases.

Nanostructured TiO2 based ceramics were synthesized using citrate-nitrate auto combustion method with different concentrations of aluminum oxide as dopant. The powder x-ray diffraction data showed that synthesized TiO2 powders, pure as well as alumina doped TiO2 had anatase phase. Dopant concentration was varied between 0 and 15 wt%. Particle size analysis showed that the particle size was in the range of 50 to 80nm for nanosized TiO2 calcined between 600 and 800°C. Average particle size of doped powders was generally less than pure TiO2. BET specific average surface area was between 10 and 25 m2/g. Doping upto 10wt% alumina is not effective in retarding anatase crystallite growth. The resistance of Al doped TiO2 sample is found to be lower than that of pure TiO2. Al2O3 doped TiO2 sensor was found to be selective to CO sensing at an operating temperature of 600 °C.

In this research, we improved densification, hardness, and compression strength of synthetic hydroxyapatite (HAp) ceramics by introducing small quantities of MgO-CaO-P2O5-Na2O-based sintering additives. Biological properties of HAp were not altered by this procedure. Phase analyses were performed by using a Philips Xpert fully automated diffractometer with Co K-alpha radiation to understand the influence of additives on phase purity in the final products. All compositions were characterized at green and sintered densities to understand the influence of additives on densification. Some of the compositions showed >40% increase in Vickers microhardness compared with pure HAp processed under the same conditions. Improvement in compression strength was also detected in some compositions. In vitro biological testing used a modified human osteoblast cell line to test biocompatibility, cell attachment, and cell proliferation. All these compositions were nontoxic and biocompatible. Our results indicate that MgO-CaO-P2O5-Na2O-based sintering additives can be used to improve both mechanical and biological properties of HAp ceramics. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 71A: 35–44, 2004

Bioceramic materials are used for the reconstruction or replacement of the damaged parts of the human body. In this study an improved procedure is described for producing ceramic scaffolds with controlled porosity. Bioinert alumina ceramic was used to make porous scaffolds by using indirect fused deposition modeling (FDM), a commercially available rapid prototyping (RP) technique. Porous alumina samples were coated with hydroxyapatite (HAp) to increase the biocompatibility of the scaffolds. Initial biological responses of the porous alumina scaffolds were assessed in vitro using rat pituitary tumor cells (PR1). Both porous alumina and HAp coated alumina ceramics provided favorable sites for cell attachments in a physiological solution at 37 degrees C, which suggests that these materials would promote good bonding while used as bone implants in vivo. Based on these preliminary studies, similar tests were performed with human osteosarcoma cells. Cell proliferation studies show that both the ceramic materials can potentially provide a non-toxic surface for bone bonding when implanted in vivo.

We have assessed the effect of CaO–P 2 O 5 –Na 2 O-based sintering additives on mechanical and biological properties of hydroxyapatite (HAp) ceramics. Five different compositions of sintering additives were selected and prepared by mixing of CaO, P 2 O 5 , and Na 2 CO 3 powders. 2.5 wt% of each additive was combined with commercial HAp powder, separately, followed by ball milling, and sintering at 1250°C and 1300°C in a muffle furnace. Green and sintered densities of the compacts were analyzed for the influence of additives on densification of HAp. Phase analyses were carried out using an X-ray diffractometer. Vickers microhardness testing was used to evaluate hardness of sintered compacts of different compositions. A maximum microhardness of 4.6 (±0.28) GPa was attained for a composition with 2.5 wt% addition of CaO:P 2 O 5 :Na 2 O in the ratio of 3:3:4. Results from mechanical property evaluation showed that some of these sintering additives improved failure strength of HAp under compressive loading. Maximum compressive strength was observed for samples with 2.5 wt% addition of CaO. Average failure strength for this set of samples was calculated to be 220 (±50) MPa. Cytotoxicity, and cell attachment studies were carried out using a modified human osteoblast cell line called OPC-1. In vitro results showed that these compositions were non-toxic. Some sintering aids enhanced cell attachment and proliferation, which was revealed from SEM examination of the scaffolds seeded with OPC-1 cells.

In our research, PZT film actuated micro-machined Si substrates are being developed for numerous applications in which membranes are actuated primarily in flexural mode. Silicon wafers, 3-inches in diameter, underwent boron doping in order to act as an etch stop. Approximately 200-nm of SiO2 was grown on the boron-doped side of the wafers. Photolithography and backside etching using EDP resulted in 2-μm thick membranes. Using reactive ion etching (RIE), beam structures resulted from the membranes. Nano-mechanical testing of the beams indicated that there were substantial residual tensile stresses in these structures. Initial calculations reveal a tensile stress of 57.7 MPa in the Si/SiO2 beams. The residual tensile stress subsequently caused the overall beam stiffness to be two orders of magnitude higher than it would be without stress. After stripping the oxide with a buffered oxide etchant (BOE), a residual stress of 26.5 MPa was measured, which is presumably caused from the remaining boron concentration. The aim of this paper is to understand influences of boron doping and processing variables on residual stresses.

Challenges in tissue engineering have always-motivated scientists and engineers to develop new biomaterials that can restore the structural features and physiological functions of natural tissues. A novel ceramic-polymer composite was processed with bio-active ceramics dispersed in a natural bio-active polymer for bone graft applications. A commercially available caster bean extract polymer (CBP) was used. It is a natural polymer extracted from the oily caster beans of the dicotyledonous class. During processing of these composites, in situ random interconnected porosity was generated similar to natural bone. Hg-porosimetry results of these composites show that most of the pores are between 50 to 150 microns. Compression tests were performed on cylindrical samples to determine the mechanical properties. Average compression modulus was calculated as 173 MPa, while the average failure strength was 6.7 MPa. Cytotoxicity and cell proliferation studies were conducted with modified human osteoblast cell-line (OPC-1) to show that these composites are biocompatible. Composites showed good cell attachment with a continuous increase in cell growth for at least up to two weeks.

Significant research has already been done for the development of bioceramic materials with controlled microstructures using inert, bioactive and bioresorbable ceramics. Microporous implants with controlled pore size in the range of 100-600 μm have proven to be osteoconductive. A minimum pore size of 100 μm is necessary for tissue in-growth and to provide blood supply to the connective tissues to keep them viable and healthy. Bone in-growth takes place within the inter-connected pore channels near the surface and maintains its vascularity and long term viability, and the implant serves as a structural bridge or scaffold for bone formation. Controlled porosity ceramic scaffolds were fabricated using indirect fused deposition modeling (FDM), a commercially available rapid prototyping process, with alumina and tricalcium phosphate (TCP) ceramics. Pore size and pore volumes were varied by changing road width, road gap and slice thickness of the polymeric molds. Mechanical tests were conducted to understand the influence of porosity parameters on strength degradation. In vitro tests were carried out with human osteoblast (HOB) cells to understand the effects of porosity parameters on cell growth. The paper describes the effects of porosity on the biocompatibility and bio-mechanical properties of controlled porosity alumina and TCP scaffolds.

Department of Chemistry, Indian Institute of Technology, Kanpur-208 016, India Manuscript received 12 October 1999 β-Phenylisoserine derivatives can be treated with DEAD (diethyl azodicarboxylate)/PPh3 to afford aziridines which can be regiosp.ecifically opened with oxygen nucleophiles in the presence of catalytic amount of para-toluenesulfonic acid to give the corresponding β-substituled phenylalanine derivatives in good yields. The generality of this transformation is illustrated by converting β-phenylisoserine derived dipeptides to the corresponding β-hydroxyphenylalanine containing dipeptides.

The objective of the current study was to characterize and model the performance of piezoelectric micromachined ultrasonic transducers (pMUTs) with large length/width aspect ratios. Single-element pMUTs with 20 different dimensions corresponding to aspect ratios ranging from 5:1 to 23:1 were designed. Multiple samples were fabricated for each design so that statistically meaningful data could be obtained. The pMUTs were characterized by the impedance measurement combined with an equivalent circuit analysis. A one-dimensional composite beam model was also used to correlate the equivalent circuit components with the structural parameters, and gain insight into the performance characteristics of pMUTs. The resonant frequencies were observed to decrease with the width of the membrane, but have no appreciable length dependence. With the correction of parasitic capacitance, the effective coupling coefficients were observed to increase with the width up to around 150 µm and then decrease. However, they did not show clear and consistent length dependence. The variation of the coupling coefficient as a function of width of the membrane was shown to be mainly due to the relative ratios between the electrode and membrane widths rather than membrane width itself. Although the model presented in this study was a simple one-dimensional electro-mechanical model, it did seem to offer both good qualitative and quantitative insights into the performance of pMUTs and provide a convenient tool for designing thin membrane transducers with a large aspect ratio. The model can also take into consideration the residual stress effect and offer an even more realistic prediction.

Nonrandom porous mullite ceramic preforms were fabricated by the indirect fused deposition process. MgO was added to commercial mullite powders as a sintering aid. The influence of porosity and the amount of MgO on the densification and mechanical properties was studied. The shrinkage and compressive strength of the porous samples were found to increase with increasing MgO content. At constant MgO concentration, shrinkage was found to decrease linearly as the volume fraction of porosity increased. The compressive strength of porous samples decreased with an increase in the volume fraction of porosity at constant MgO content.

Due to their excellent piezoelectric properties, PZT ceramics are attractive materials for many MEMS applications. By depositing a PZT film on a micro-machined platinized silicon substrate, membranes can be actuated in the flexural mode. In this work, 2D arrays of PZT actuated membranes, which can be used as ultrasonic transducers, have been designed, fabricated, and tested for their ferroelectric response. The device behavior was also modeled using FEA. Data from FEA runs were used to evaluate the device performance based on its effective coupling coefficient (efficiency), acoustic impedance, and resonance frequency. Results show that the device-coupling factor is significantly affected by the PZT and silicon layers' thickness and the top electrode configuration. Results also indicate a considerable flexibility in optimizing the device performance under a wide range of operational requirements, which makes such devices attractive for different applications.

Biomaterials have made significant contributions to the advancement of modern health care and drug delivery industries. The present research is based on development of porous polymerceramic composite scaffolds using polypropylene (PP) polymer and tricalcium phosphate (TCP) ceramic for bone-graft applications. Three dimensionally interconnected controlled porosity scaffolds were fabricated using a fused deposition modeling (FDM) system. First, ceramic and polymeric materials were compounded under high shear using a torque rheometer. Compounded materials were then extruded to a 1.78mm diameter continuous filament using a single screw extruder. These filaments were used as a feedstock material for an FDM 1650 machine for direct fabrication of controlled porosity parts. Hg-porosimetry was done to determine pore size and their distribution in these structures. Tensile properties of neat composites and as received polymer were measured and compared using standard dog bone samples. Uniaxial compression tests were performed on cylindrical porous samples having average pore size of 160 μm and 36 vol% porosity. These samples showed an average ultimate compressive strength of 12.7 MPa. Average compressive modulus was calculated as 263 MPa. Cytotoxicity and cell proliferation studies were conducted with OPC1 modified human osteoblast cell-line. It was found that composite matrices were non-toxic and they showed excellent cell growth with OPC1 cells.

Interconnected-phase mullite-aluminum metal-ceramic composites were processed using the indirect fused-deposition process. In this process, controlled-porosity ceramic preforms were fabricated via the lost-mold process. The molds were designed with computer aided design (CAD) software and fabricated using a fused-deposition modeling (FDM) technique. Porous ceramic preforms were infiltrated with aluminum metal, via pressureless reactive metal infiltration, to form the mullite-aluminum composites. Both the macrostructures and the microstructures of the composites were controlled via CAD and FDM. During metal infiltration, the mullite phase transformed to α-alumina, and an alumina-aluminum composite formed. This paper describes the mullite-to-alumina phase transformation during reactive metal infiltration of the porous preforms, as a function of processing variables.

An indirect fused deposition process was used to fabricate controlled-porosity alumina bone grafts using a computer-aided-design file created from computed tomography (CT) scans of a horse's short pastern bone. Structures with both uniform and gradient porosity were fabricated to show the effectiveness of this process for the fabrication of custom orthopedic implants. Cytotoxicity and cell proliferation studies were conducted with different cell lines to show that these bone grafts are biocompatible. Uniaxial compression tests were also conducted to understand the influence of porosity on the mechanical properties of these structures.