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PurposeThe purpose of this paper is to evaluate the feasibility of direct fabrication of lunar/Martian regolith simulant parts, in a freeform environment, using Laser Engineering Net Shaping (LENS™) – an additive manufacturing technology.Design/methodology/approachBulk lunar regolith simulant structures were fabricated using a LENS™‐750. Dense parts without any macroscopic defects were produced at a laser power of 50W, a scan speed of 20 mm/s, and a powder feed rate of 12.36 g/min. The laser processed parts were characterized using X‐ray diffraction, differential scanning calorimetry, scanning electron microscope and X‐ray photoelectron spectroscopy to evaluate the influence of laser processing on the microstructure, constituent phases and chemistry of lunar regolith simulant.FindingsA combination of laser parameters resulting in a 2.12 J/mm2 laser energy appeared to be ideal for generating a melt pool necessary for lunar regolith powder deposition without excessive liquid pool spreading and cracking of solidified parts. The results show that LENS™ based laser processing transformed crystalline regolith into nanocrystalline and/or amorphous regolith structures as a result of complete melting followed by resolidification. Laser processing also resulted in marginal changes in the composition of the regolith.Originality/valueEstablishment of a lunar/Martian outpost necessitates the development of methods to utilize in situ mineral resources for various construction and resource extraction applications. Fabrication technologies are critical for habitat structure development, as well as repair and replacement of tools and parts at the outpost. Current experimental results presented in the paper clearly demonstrate that net shape regolith simulant parts can be fabricated using LENS™ by exploiting its capabilities.

Porous metals are being widely used in load bearing implant applications with an aim to increase osseointegration and also to reduce stress shielding. However, fatigue performance of porous metals is extremely important to ensure long-term implant stability, because porous metals are sensitive to crack propagation even at low stresses especially under cyclic loading conditions. Herein we report high-cycle compression-compression fatigue behavior of laser processed NiTi alloy with varying porosities between ∼1% and 20%. The results show that compression fatigue of porous NiTi alloy samples is in part similar to metal foams. The applied stress amplitude is found to have strong influence on the accumulated strain and cyclic stability. The critical stress amplitudes associated with rapid strain accumulation in porous NiTi alloy samples, with varying relative densities, were found to correspond to 140% of respective 0.2% proof strength indicating that these samples can sustain cyclic compression fatigue stresses up to 1.4 times their yield strength without failure.

Tricalcium Phosphate (TCP) was doped with 0.5, 2.0, and 5.0 mol% Strontium Oxide (SrO) through the wet precipitation process to investigate the influence of SrO on the biological and mechanical properties of TCP. XRD results showed that SrO doping did not change the phase stability of the β-phase of TCP during sintering at 1120°C. The apparent density of TCP increased from 95.1 ± 2.5% to 99.4 ± 0.5% with the addition of 5.0 mol% SrO doping. SrO doping also increased the compressive strength of pure β-TCP from 121.1 ± 21.4 MPa to 185.9 ± 16.7 MPa with 5 mol% SrO addition. Initially, the addition of 0.5 and 2.0 mol% SrO had a statistically insignificant impact on the as-processed samples' compressive strength. When the samples were immersed in a simulated body fluid for 12 weeks, the addition of SrO improved the compressive strength from 109.4 ± 22.9 MPa for pure TCP to 208.8 ± 34.6 MPa with 5.0 mol% SrO addition. An improvement in hFOB cell attachment and proliferation was observed for all dopant concentrations using field emission scanning electron microscope (FE-SEM) imaging and MTT assay studies, indicating excellent biocompatibility of all the samples. 2.0 mol% SrO doping showed the best cell differentiation and proliferation results. It was shown that SrO simultaneously improved mechanical properties of TCP such as compressive strength as well as biological properties via enhanced cell attachment and proliferation.

This study investigates the use of hydroxyapatite (HAp) doped with hexavalent tungsten to improve its interaction with bone cells and to influence the polarizing capacity of HAp. Increases in dopant concentration increased the β-TCP phases and decreased the HAp phases in sintered samples. Results of thermally stimulated depolarization current measurements suggested that doped HAp had stored fewer charge compared with pure HAp. However, the decrease in stored charge was related to fraction of HAp or β-TCP phases present in sintered samples. Activation energy of dipole relaxation and stored charge was used to examine the mechanism of polarization. The charge stored in doped samples due to polarization was attributed to the migration of H+ ions in HAp phases and O2− or Ca2+ ions in β-TCP phases. Hindrance of ion migration due to the presence of different phases appeared to lower charge storage ability in doped samples. In vitro study revealed an increase in bioactivity of doped HAp when compared with pure HAp. Polarization further improved the bioactivity of doped HAp. Results of our study provide evidence for the use of higher valent cations to improve biological performance of HAp ceramics. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2012.

Calcium phosphates (CaPs) are the most widely used bone substitutes in bone tissue engineering due to their compositional similarities to bone mineral and excellent biocompatibility. In recent years, CaPs, especially hydroxyapatite and tricalcium phosphate, have attracted significant interest in simultaneous use as bone substitute and drug delivery vehicle, adding a new dimension to their application. CaPs are more biocompatible than many other ceramic and inorganic nanoparticles. Their biocompatibility and variable stoichiometry, thus surface charge density, functionality, and dissolution properties, make them suitable for both drug and growth factor delivery. CaP matrices and scaffolds have been reported to act as delivery vehicles for growth factors and drugs in bone tissue engineering. Local drug delivery in musculoskeletal disorder treatments can address some of the critical issues more effectively and efficiently than the systemic delivery. CaPs are used as coatings on metallic implants, CaP cements, and custom designed scaffolds to treat musculoskeletal disorders. This review highlights some of the current drug and growth factor delivery approaches and critical issues using CaP particles, coatings, cements, and scaffolds towards orthopedic and dental applications.

We report here the fabrication of three dimensional (3D) interconnected macro porous tricalcium phosphate (TCP) scaffolds with controlled internal architecture by direct 3D printing (3DP), and high mechanical strength by microwave sintering. TCP scaffolds with 27%, 35% and 41% designed macro porosity having pore sizes of 500 μm, 750 μm, and 1000 μm, respectively, have been fabricated via direct 3DP. These scaffolds are then sintered at 1150 °C and 1250 °C in conventional electric muffle furnace as well as microwave furnace. Total open porosity between 42% and 63% is obtained in the sintered scaffolds due to the presence of intrinsic micro pores along with the designed pores. A significant increase in compressive strength, between 46% and 69%, is achieved by microwave sintering as compared to conventional sintering as a result of efficient densification. A maximum compressive strength of 10.95 ± 1.28 MPa and 6.62 ± 0.67 MPa is achieved for scaffolds with 500 μm designed pores (~400 μm after sintering) sintered in microwave and conventional furnaces, respectively. An increase in cell density with a decrease in macro pore size is observed during in vitro cell-material interactions using human osteoblast cells. Histomorphological analysis reveals that the presence of both micro and macro pores facilitated osteoid like new bone formation when tested in the femoral defect on Sprague-Dawley rats. Our results show that bioresorbable 3D printed TCP scaffolds have great potential in tissue engineering applications for bone tissue repair and regeneration.

Implant related infection is one of the key concerns in total joint hip arthroplasties. In order to reduce bacterial adhesion, silver (Ag) / silver oxide (Ag2O) doping was used in plasma sprayed hydroxyapatite (HA) coating on titanium substrate. HA powder was doped with 2.0, 4.0 and 6.0 wt% Ag, heat treated at 800 °C and used for plasma spray coating using a 30 kW plasma spray system, equipped with supersonic nozzle. Application of supersonic plasma nozzle significantly reduced phase decomposition and amorphous phase formation in the HA coatings as evident by X-ray diffraction (XRD) study and Fourier transformed infrared spectroscopic (FTIR) analysis. Adhesive bond strength of more than 15 MPa ensured the mechanical integrity of the coatings. Resistance against bacterial adhesion of the coatings was determined by challenging them against Pseudomonas Aeruginosa (PAO1). Live/Dead staining of the adherent bacteria on the coating surfaces indicated a significant reduction in bacterial adhesion due to the presence of Ag. In vitro cell-material interactions and alkaline phosphatase (ALP) protein expressions were evaluated by culturing human fetal osteoblast cells (hFOB). Present results suggest that the plasma sprayed HA coatings doped with an optimum amount of Ag can have excellent antimicrobial property without altering mechanical property of the Ag doped HA coatings.

Objectives To evaluate the effects of silica (SiO 2 ) (0.5 wt%) and zinc oxide (ZnO) (0.25 wt%) dopants on the mechanical and biological properties of tricalcium phosphate (TCP) scaffolds with three dimensionally (3D) interconnected pores. Methods Scaffolds were created with a commercial 3D printer. Post sintering phase analysis was determined by X-ray diffraction. Surface morphology of the scaffolds was examined by field emission scanning electron microscopy (FESEM). Mechanical strength was evaluated with a screw driven universal testing machine. MTT assay was used for cellular proliferation characteristics and cellular morphology was examined by FESEM. Results Addition of dopants into TCP increased the average density of pure TCP from 90.8 ± 0.8% to 94.1 ± 1.6% and retarded the β to α phase transformation at high sintering temperatures, which resulted in up to 2.5 fold increase in compressive strength. In vitro cell–materials interaction studies, carried out using hFOB cells, confirmed that the addition of SiO 2 and ZnO to the scaffolds facilitated faster cell proliferation when compared to pure TCP scaffolds. Significance Addition of SiO 2 and ZnO dopants to the TCP scaffolds showed increased mechanical strength as well as increased cellular proliferation.

SummaryObjectives: To design, manufacture and analyze custom implants with functional gradation in macrostructure for attachment of amputation prostheses.Methods: The external shape of the implant was designed by extracting geometrical data of canine cadavers from computed tomography (CT) scans to suit the bone cavity. Three generations of implant designs were developed and were optimized with the help of fit/fill and mechanical performance of implant-cadaver bone assembly using CT analysis and compression testing, respectively. A final optimized, custom Ti6Al4V alloy amputation implant, with approximately 25% porosity in the proximal region and approximaltely zero percent porosity in the distal region, was fabricated using Laser Engineered Net Shaping (LENS™) – a laser based additive manufacturing technology.Results: The proposed design changes in the second generation designs, in terms of refining thresholds, increased the average fill of the bone cavity from 58% to 83%. Addition of a flange between the stem and the head in the second generation designs resulted in more than a seven-fold increase in the compressive load carrying capacity of the assembly. Application of LENS™ in the fabrication of present custom fit Ti6Al4V alloy implants enabled incorporation of 20 to 30% porosity in the proximal region and one to two percent residual porosity in the distal portion of the implant.Clinical significance: Patient specific prostheses having direct connection to the skeletal structure can potentially aid in problems related to load transfer and proprioception in amputees. Furthermore, application of LENS™ in the fabrication of custom implants can be faster to incorporate site specific porosity and gradients for improving long-term stability.

Multiwall carbon nanotube (CNT) reinforced Cu–10Sn alloy composites were fabricated using high power lasers. Microstructural observations showed that CNTs were retained in the composite matrix after laser processing. The addition of CNTs showed improvement in strain hardening, mechanical and thermal properties of Cu–10Sn alloy. Composites with 12 vol.% CNTs showed more than 80% increase in the Young's modulus and 40% increase in the thermal conductivity of Cu–10Sn alloy. Yield strength estimates using a model based on strengthening mechanisms in metal matrix nanocomposites and thermal conductivities derived from the Maxwell–Garnett effective medium theory were found to be in good agreement with our experimental data.

The photoluminescence (PL) of dense nanocrystalline (anatase) TiO(2) thin films is reported as a function of calcination temperature, thickness, and tungsten and nickel doping. The dependence of the optical absorption, Raman spectra, and PL spectra on heat treatment and dopants reveals the role of oxygen vacancies, crystallinity, and phase transformation in the performance of TiO(2) films used as gas sensors. The broad visible PL from defect states of compact and undoped TiO(2) films is found to be much brighter and less sensitive to the presence of oxygen than that of mesoporous films. The dense nanocrystalline grains and the nanoparticles comprising the mesoporous film are comparable in size, demonstrating the importance of film morphology and carrier transport in determining the intensity of defect photoluminescence. At higher calcination temperatures, the transformation to rutile results in the appearance of a dominant near-infrared peak. This characteristic change in the shape of the PL spectra demonstrates efficient capture of conduction band electrons by the emerging rutile phase. The W-doped samples show diminished PL with quenching on the red side of the emission spectrum occurring at lower concentration and eventual disappearance of the PL at higher W concentration. The results are discussed within the context of the performance of the TiO(2) thin films as CO gas sensors and the chemical nature of luminescent defects.

In this study, we report fabrication of strontium (Sr) and magnesium (Mg) doped hydroxyapatite (HA) coating on commercially pure titanium (Cp-Ti) substrates using inductively coupled radio frequency (RF) plasma spray. HA powder was doped with 1 wt % Sr (Sr-HA) and 1 wt % Mg (Mg-HA), heat treated at 800°C for 6 h and then used for plasma spray coating. X-ray diffraction (XRD) and Fourier transformed infrared spectroscopic (FTIR) analysis indicated that the coatings were primarily composed of phase pure crystalline HA. When compared to undoped HA coating, physical properties such as microstructure, grain size, and adhesive bond strength of the doped HA coatings did not change significantly. Microstructure of the coatings showed coherency in the structure with an average grain size of 200-280 μm HA particles, where each of the HA grains consisted of 20-30 nm sized particles. An average adhesive bond strength of 17 MPa ensured sufficient mechanical strength of the coatings. A chemistry dependent improvement in bone cell-coating interaction was noticed for doped coatings although it had minimal effect on physical properties of the coatings. In vitro cell-materials interactions using human fetal osteoblasts (hFOB) showed better cell attachment and proliferation on Sr-HA coatings compared to HA or Mg-HA coatings. Presence of Sr in the coating also stimulated hFOB cell differentiation and alkaline phosphatase (ALP) expression. Improvement in bioactivity of Sr doped HA coatings on Ti without compromising its mechanical properties makes it an excellent material of choice for coated implant.

Laser processing of Ti-SiC composite coating on titanium was carried out to improve wear resistance using Laser Engineered Net Shaping (LENS�) - a commercial rapid prototyping technology. During the coating process a Nd:YAG laser was used to create small liquid metal pool on the surface of Ti substrate in to which SiC powder was injected to create Ti-SiC metal matrix composite layer. The composite layers were characterized using X-ray diffraction, scanning and transmission electron microscopy equipped with fine probe chemical analysis. Laser parameters were found to have strong influence on the dissolution of SiC, leading to the formation of TiSi2, Ti5Si3 and TiC with a large amount of SiC on the surface. Detailed matrix microstructural analysis showed the formation of non-stoichiometric compounds and TiSi2 in the matrix due to non-equilibrium rapid solidification during laser processing. The average Young's modulus of the composite coatings was found to be in the range of 602 and 757GPa. Under dry sliding conditions, a considerable increase in wear resistance was observed, i.e., 5.91�10-4mm3/Nm for the SiC reinforced coatings and 1.3�10-3mm3/Nm for the Ti substrate at identical test conditions. � 2011 Elsevier B.V.

The aim of this work is to evaluate the influence of MgO, SrO and SiO 2 doping on mechanical and biological properties of β-tricalcium phosphate (β-TCP) to achieve controlled resorption kinetics of β-TCP system for maxillofacial and spinal fusion application. We prepared dense TCP compacts of four different compositions, i) pure β-TCP, ii) β-TCP with 1.0 wt.% MgO + 1.0 wt.% SrO, iii) β-TCP with 1.0 wt.% SrO + 0.5 wt.% SiO 2 , and iv) β-TCP with 1.0 wt.% MgO + 1.0 wt.% SrO + 0.5 wt.% SiO 2 , by uniaxial pressing and sintering at 1250 °C. β phase stability is observed at 1250 °C sintering temperature due to MgO doping in β-TCP. In vitro mineralization in simulated body fluid (SBF) for 16 weeks shows excellent apatite growth on undoped and doped samples. Strength degradation of TCP samples in SBF is significantly influenced by both dopant chemistry and amount of dopant. Compressive strengths for all samples show degradation in SBF over the 16 week time period with varying degradation kinetics. MgO/SrO/SiO 2 doped sample shows no strength loss, while undoped TCP shows the maximum strength loss from 419 ± 28 MPa to 158 ± 28 MPa over the 16 week study. In case of MgO/SrO doped TCP, strength loss is slow and gradual. TCP doped with 1.0 wt.% MgO and 1.0 wt.% SrO shows excellent in vivo biocompatibility when tested in male Sprague–Dawley rats for 16 weeks. Histomorphology analysis reveals that MgO/SrO doped TCP promoted osteogenesis by excellent early stage bone remodeling as compared to undoped TCP.

Load-bearing metal implants often fail prematurely due to inadequate biocompatibility, mechanical/tribological properties, and poor osseointegration. It is well known that biomaterials’ surface plays a vital role in the response to these metal implants in the biological environment. The biological effectiveness of artificial implants is determined mainly by their surface characteristics such as surface morphology, microstructure, composition, mechanical properties, wettabilility, and surface free energy. Hence, there is significant interest toward surface modification and effective design of load-bearing metal implants so as to improve their surface properties and thereby elicit a specific, desired, and timely response from the surrounding cells and tissues. In this article, we provide an insight into laser surface modification of Ti/Ti6Al4V alloy with or without functional gradation in composition and their microstructural, in vitro wear and biological properties for various loadbearing orthopedic applications.

Porous implants are known to promote cell adhesion and have low elastic modulus, a combination that can significantly increase the life of an implant. However, porosity can significantly reduce the fatigue life of porous implants. Very little work has been reported on the fatigue behavior of bulk porous metals, specifically on porous nitinol (NiTi) alloy. In this article, we report high-cycle rotating bending fatigue response of porous NiTi alloys fabricated using Laser Engineered Net Shaping (LENS™). Samples were characterized in terms of monotonic mechanical properties and microstructural features. Rotating bending fatigue results showed that the presence of 10% porosity in NiTi alloys can decrease the actual fatigue failure stress, at 10 6 cycles, up to 54% and single reversal failure stress by ~ 30%. From fractographic analysis, it is clear that the effect of surface porosity dominates the rotating bending fatigue failure of porous NiTi samples.

The objective of this work is to study the influence of Mg2+ and Sr2+ dopants on in vitro bone cell–material interactions of electrically polarized hydroxyapatite [HAp, Ca10(PO4)6(OH)2] ceramics with an aim to achieve additional advantage of matching bone chemistry along with the original benefits of electrical polarization treatment relevant to biomedical applications. To achieve our research objective, commercial phase pure HAp has been doped with MgO, and SrO in single, and binary compositions. All samples have been sintered at 1200 °C for 2 h and subsequently polarized using an external d.c. field (2.0 kV/cm) at 400 °C for 1 h. Combined addition of 1 wt.% MgO/1 wt.% SrO in HAp has been most beneficial in enhancing the polarizability in which stored charge was 4.19 μC/cm2 compared to pure HAp of 2.23 μC/cm2. Bone cell–material interaction has been studied by culturing with human fetal osteoblast cells (hFOB) for a maximum of 7 days. Scanning electron microscope (SEM) images of cell morphology reveal that favorable surface properties and dopant chemistry lead to good cellular adherence and spreading on negatively charged surfaces of both Sr2+ and Mg2+ doped HAp samples over undoped HAp. MTT assay results at 7 days show the highest viable cell densities on the negatively charged surfaces of binary doped HAp samples, while positive charged doped HAp surfaces exhibit limited cellular growth in comparison to neutral surfaces.

Novel, unitized structures with porous Ti6Al4V alloy on one side and compositionally graded, hard CoCrMo alloy surface on the other side have been fabricated using laser engineered net shaping (LENS™) process. Gradient structures with 50%, 70% and 86% CoCrMo alloy on the top surface showed a high hardness in the range of 615 and 957 HV. The gradient structures were evaluated for their in vitro wear rate and Co release up to 3000 m of sliding distance. The wear rate of ultrahigh molecular weight polyethylene and 100% CoCrMo alloy substrates was found to depend on the hardness and microstructural features of the counter surface rubbing against them. In general, the wear rate of both the substrates increased with a decrease in the CoCrMo alloy concentration on the top surface of gradient pins. However, the wear rate of gradient pins was lower than 100% CoCrMo alloy pins due to their high hardness. Lowest wear rate in the range of 5.07 to 7.99 × 10−8 mm3/Nm was observed for gradient pins having 86% CoCrMo alloy on the top surface. The amount of Co released, in the range of 0.38 and 0.91 ppm, during in vitro wear testing of gradient structures was comparable to that of 100% CoCrMo alloy (0.25 and 0.77 ppm). Present unitized structures with open porosity on one side and hard, wear resistant surface on the other side can minimize the wear-induced osteolysis and aseptic loosening, and eliminate the need for multiple parts with different compositions for load-bearing implants such as total hip prostheses.

Calcium phosphate (CaP) particulates, cements and scaffolds have attracted significant interest as drug delivery vehicles. CaP systems, including both hydroxyapaptite and tricalcium phosphates, possess variable stoichiometry, functionality and dissolution properties which make them suitable for cellular delivery. Their chemical similarity to bone and thus biocompatibility, as well as variable surface charge density contribute to their controlled release properties. Among specific research areas, nanoparticle size, morphology, surface area due to porosity, and chemistry controlled release kinetics are the most active. This article discusses CaP systems in their particulate, cements, and scaffold forms for drug, protein, and growth factor delivery toward orthopedic and dental applications.

Porites Cylindrica was used to understand their compressive deformation behaviour along the growth direction. Powder X-Ray diffraction (XRD), scanning electron microscope (SEM) and uniaxial compression testing were employed to study microstructure, phase analysis and mechanical properties, respectively. An average strength of 8.85±1 MPa and modulus of 12.22±2.4 GPa were measured. Failure analysis showed the influence of nanoscale microstructural features on fracture surface with steps and striations on flat fracture of struts.

The objective of this work was to investigate the influence of trace element (Mg2+, Zn2+, and Sr2+) doping on polarization behavior of sintered hydroxyapatite [HAp, Ca10(PO4)6(OH)2] pertinent to biomedical applications. For this purpose, commercially procured phase pure HAp powder was doped with MgO, SrO, and ZnO dopants in different single, binary, and ternary compositions. All samples were sintered at 1200°C for 2 h and subsequently electro-thermally polarized via application of an external dc field (2.0 kV/cm) at 400°C. Combined addition of 1 wt% MgO/1 wt% SrO in HAp was found to be the most beneficial in enhancing the polarizability (stored charge ∼4.19 μC/cm2) of pure HAp (stored charge ∼2.23 μC/cm2) by inhibiting high-temperature HAp phase decomposition. Furthermore, in vitro bone cell–material interaction has been studied for polarized binary doped (1 wt% MgO+1 wt% SrO in HAp) HAp samples by culturing with human fetal osteoblast cells for a maximum of 7 days to establish the significance of dopants on polarized HAp for bone graft applications. Scanning electron microscope images of cell morphology revealed that favorable surface properties and dopants chemistry led to good cellular adherence and extracellular matrix formation on negatively charged surfaces of binary doped HAp samples in comparison with undoped HAp surfaces. MTT assay results at 7 days showed the highest cell proliferation on negatively charged surfaces of binary doped HAp samples.

Over the years hydroxyapatite (HA) coatings have been used to improve biologic properties of Ti-based load bearing metal implants. However, applicability of HA coated implants is subjected to physical stability of the HA phase and mechanical integrity of the coating-substrate interface. In this study, we have compared the microstructure and in vitro cell-materials interactions of newly developed laser deposited Ta coatings and radio frequency (RF) induction plasma sprayed HA coatings on Ti substrate. In vitro biocompatibility study, using human osteoblast cell line hFOB, showed equally excellent cellular adherence and growth on Ta and HA coatings. Quantitative assay of cell survivability on these coatings showed that the Ta coatings provide comparable initial cell attachment to that of HA coatings. Microstructural analysis of the coatings showed strong metallurgical bonding without sharp interface between the Ta coating and the Ti substrate, while the interface between HA coating and the Ti substrate was sharp. The interface microstructural features and in vitro cell-materials interactions of Ta coatings on Ti clearly demonstrate their potential to replace HA based coatings for enhanced/early biologic fixation. Other significant benefits of these dense Ta coatings include high toughness, strong bonding with the substrate, and long-term stability of the interface.

In this study, we applied electrical polarization technique to increase adsorption and control protein release from biphasic calcium phosphate (BCP). Three different biphasic calcium phosphate (BCP) composites, with hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP), were processed and electrically polarized. Our study showed that stored charge was increased in the composites with the increase in HAp percentage. Adsorption of bovine serum albumin (BSA), as a model protein, on the poled as well as unpoled surfaces of the composites was studied. The highest amount of BSA adsorption was obtained on positively poled surfaces of each composite. Adsorption isotherm study suggested a multilayer adsorption of BSA on the BCP composites. The effect of electrical polarization on BSA release kinetics from positively charged BCP surfaces was studied. A gradual increase in percent BSA release from positively charged BCP surfaces with decreasing stored charge was observed. Our study showed that the BCP based composites have the potential to be used as a drug or growth factor delivery vehicle.

Titanium dioxide (TiO2) thin film gas sensors were fabricated via the sol–gel method from a starting solution of titanium isopropoxide dissolved in methoxyethanol. Spin coating was used to deposit the sol on electroded aluminum oxide (Al2O3) substrates forming a film 1 μm thick. The influence of crystallization temperature and operating temperature on crystalline phase, grain size, electronic conduction activation energy, and gas sensing response toward carbon monoxide (CO) and methane (CH4) was studied. Pure anatase phase was found with crystallization temperatures up to 800 °C, however, rutile began to form by 900 °C. Grain size increased with increasing calcination temperature. Activation energy was dependent on crystallite size and phase. Sensing response toward CO and CH4 was dependent on both calcination and operating temperatures. Films crystallized at 650 °C and operated at 450 °C showed the best selectivity toward CO.

Spherical hydroxyapatite (HA) nanopowder was synthesized at a rate of 20 g/h from HA sol using a 30 kW inductively coupled radio frequency plasma spray system. The HA sol was axially fed with a water-cooled steel probe in the lower temperature region of the supersonic plasma nozzle, which helped in HA phase stabilization. The HA powder was synthesized at plate power between 19 and 28 kW. Particle size, surface area, particle morphology, and phase composition of the synthesized powder were evaluated using transmission electron microscopy, BET specific average surface area, X-ray diffraction (XRD), and Fourier-transformed infrared spectroscopy. The synthesized nanopowder was spherical in nature, with the particle size ranging from 30 to 70 nm. The increase in plate power resulted in a decrease in particle size. XRD results indicated HA to be the primary phase along with phase decomposition products, such as tricalcium phosphate and calcium oxide. Cytotoxicity behavior was studied using human osteoblast cells to ensure biocompatibility.

Laser engineered net shaping (LENS™) has been used to create dense WC–12%Co composite coatings on stainless steel substrates. Low heat input and controlled atmosphere with oxygen content less than 10 ppm resulted in minimum interface dilution, carbide dissolution and uniform carbide distribution. Under present experimental conditions, coatings produced at laser energy input of 365 and 465 J/mm 3 showed similar phase constituents, hardness and wear rate. The coating hardness varied between 1171 and 1181 HV with an average dry sliding specific wear rate in the range of 3 × 10 −6 mm 3 /Nm and 6.5 × 10 −6 mm 3 /Nm against Si 3 N 4 ball. Deformation and extrusion of cobalt phase followed by fracture and removal of carbide particles was found to be a predominant material removal mechanism in the present laser deposited WC–Co coatings. The influence of laser energy input on the microstructural and wear properties of WC–12%Co composites coatings are reported in this article.

Laser engineered net shaping has been used to create a Ti–SiC composite layer on Ti to improve its wear resistance. The influences of laser power and scanning speed on the microstructure and wear resistance of the coatings were examined. Laser parameters were found to have a strong influence on the dissolution of SiC, leading to the formation of Ti5Si3 and TiC with a high amount of SiC on the surface. The composite coatings with hardness between 976 and 1167 HV exhibited average wear rate between 5.91 and 6.60 × 10−4 mm3 (N m)−1.

Laser Engineered Net Shaping (LENS™) has been used to fabricate dense, net shape melt-cast structures of lead zirconate titanate (PZT), in a single step, directly on a metallic substrate by complete melting and resolidification of PZT powders. From our results, it appears that reasonable dielectric properties can be obtained in LENS™ processed PZT structures without post-fabrication heat treatments. Our results also demonstrate potential application of LENS™ towards direct fabrication of PZT based embedded sensors and transducers on structural components.

The relatively high cost of manufacturing and the inability to produce modular implants have limited the acceptance of tantalum, in spite of its excellent in vitro and in vivo biocompatibility. In this article, we report how to process Ta to create net-shape porous structures with varying porosity using Laser Engineered Net Shaping (LENS) for the first time. Porous Ta samples with relative densities between 45% and 73% have been successfully fabricated and characterized for their mechanical properties. In vitro cell materials interactions, using a human fetal osteoblast cell line, have been assessed on these porous Ta structures and compared with porous Ti control samples. The results show that the Young's modulus of porous Ta can be tailored between 1.5 and 20 GPa by changing the pore volume fraction between 27% and 55%. In vitro biocompatibility in terms of MTT assay and immunochemistry study showed excellent cellular adherence, growth and differentiation with abundant extracellular matrix formation on porous Ta structures compared to porous Ti control. These results indicate that porous Ta structures can promote enhanced/early biological fixation. The enhanced in vitro cell-material interactions on the porous Ta surface are attributed to its chemistry, its high wettability and its greater surface energy relative to porous Ti. Our results show that these laser-processed porous Ta structures can find numerous applications, particularly among older patients, for metallic implants because of their excellent bioactivity.

The aim of this study was to understand and compare the compression deformation behavior of porous metals with random and designed porosity. Direct observation, analysis and quantification of porosity parameters using microcomputed tomography (µCT) enabled the determination of relationship between porosity characteristics and compressive deformation of porous titanium. Porosity and pore size variations before and after deformation showed relatively uniform deformation in the sample with random porosity compared to designed porosity. Strong, continuous and regular arrangement of load-bearing sections in the designed porosity sample imparted higher Young's modulus and 0.2% proof strength than for the random porosity sample. The experimental results clearly showed the dependence of deformation behavior and mechanical properties on pore distribution and continuity of load-bearing cross-section.

Metallic biomaterials currently in use for load-bearing orthopedic applications are mostly bioinert and therefore lack sufficient osseointegration. Although bioactive ceramics such as hydroxyapatite (HA) can spontaneously bond to living bone tissue, low fracture toughness of HA limits their use as a bone substitute for load-bearing applications. Surface modification techniques such as HA coating on metals are current options to improve osseointegration in load-bearing metal implants. Over the last few decades researchers have attempted to find a bioactive metal with high mechanical strength and excellent fatigue resistance that can bond chemically with surrounding bone for orthopedic applications. Recent in vitro, in vivo, and clinical studies demonstrated that tantalum is a promising metal that is bioactive. However, tantalum applications in biomedical devices have been limited by processing challenges rather than biological performances. In this article, we provide an overview of processing aspects and biological properties of tantalum for load-bearing orthopedic applications.

Recently tantalum is gaining more attention as a new metallic biomaterial as it has been shown to be bioactive and biologically bonds to bone. However, the relatively high cost of manufacture and an inability to produce a modular all Ta implant has limited its widespread acceptance. In this study we have successfully deposited a Ta coating on Ti using laser engineered net shaping (LENS) to enhance the osseointegration properties. In vitro biocompatibility study, using human osteoblast cell line hFOB, showed excellent cellular adherence and growth with abundant extracellular matrix formation on the Ta coating surface compared with the Ti surface. A six times higher living cell density was observed on the Ta coating than on the Ti control surface by MMT assay. A high surface energy and wettability of the Ta surface were observed to contribute to its significantly better cell-material interactions. Also, these dense Ta coatings do not suffer from low fatigue resistance due to the absence of porosity and a sharp interface between the coating and the substrate, which is a major concern for porous coatings used for enhanced/early biological fixation.

A novel biphasic calcium phosphate ceramic composed of tricalcium phosphate (TCP) and calcium pyrophosphate (CP) is synthesized in order to tailor the biodegradation behavior of the ceramic. The results show that biphasic TCP/CP ceramic has a strength of 62.2 ± 2.1 MPa, which is superior to single-phase TCP and CP ceramics, which show strengths of 44.3 ± 3.0 and 53.0 ± 4.8 MPa, respectively. In addition, biphasic TCP/CP ceramic displays a controlled strength degradation from 62.2 ± 2.1 to 40.5 ± 1.0 MPa in stimulated body fluid over a period of 28 d. An in vitro cell materials interaction study using human fetal osteoblast cells indicates that TCP/CP ceramic is cytocompatible. TCP/CP ceramic also show a good loading capacity for alendronate. Adsorption of alendronate (AD) on the TCP/CP surface is found to proceed via ligand exchange mechanism and the in vitro release profile of AD from TCP/CP surface is characterized by an initial fast release followed by a slow and sustained release. Strong electrostatic interactions between AD groups and surface Ca2+ ions enable the slow and sustained release of AD. These results demonstrate that the newly developed biphasic ceramic, with its controlled strength degradation and drug release, shows promise for use in orthopedic and tissue engineering applications.

Metallic biomaterials are widely used to restore the lost structure and functions of human bone. Due to the large number of joint replacements, there is a growing demand for new and improved orthopedic implants. More specifically, there is a need for novel load bearing metallic implants with low effective modulus matching to that of bone in order to reduce stress shielding and consequent increase in the in vivo life-span of the implant. In this study, we have fabricated porous Ti6Al4V alloy structures, using Laser Engineered Net Shaping (LENS™) to demonstrate that advanced manufacturing techniques such as LENS™ can be used to fabricate low-modulus, tailored porosity implants with a wide variety of metals/alloys, where the porosity can be designed in areas based on the patient's need to enhance biological fixation and achieve long-term in vivo stability. The effective modulus of Ti6Al4V alloy structures has been tailored between 7 and 60 GPa and porous Ti alloy structures containing 23 to 32 vol. % porosity showed modulus equivalent to human cortical bone. In vivo behavior of porous Ti6Al4V alloy samples in male Sprague-Dawley rats for 16 weeks demonstrated significant increase in calcium within the implants indicating excellent biological tissue ingrowth through interconnected porosity. In vivo results also showed that total amount of porosity plays an important role in tissue ingrowth.

In this study, influence of coating chemistry, channel width and tortuosity of various two-dimensional micro-channels were explored on micromachined Si using osteoblast precursor cells line 1 (OPC1). The rationale for our study is to delineate the influence of different porosity parameters on bone cell attachment and proliferation in vitro . Channel widths of 100, 200, 300, 400, and 600 μm; channel bends of 0, 1, and 2 right angles; and gold and silicon dioxide coatings on single-crystal Si were studied. Experiments were conducted with channel tops under glass covered and uncovered conditions keeping the channel depth at 220 μm. Independent samples were evaluated using SEM imaging and MTT assay to measure bone cell morphology and quantity. Images were taken of micro-channels and exterior chambers at 50×, 500×, 1000×, and 5000× magnifications. Channel and chamber cell densities were scored as follows: bare (score = 0), scattered (1), limited (2), abundant (3), and overflowing (4). Samples were then scored and statistically analyzed for major differences. In general, OPC1 cells proliferated at least 5% or better based on cell numbers under uncovered conditions than glass covered. Channel widths of 100 μm largely prohibited cell proliferation and diffusion by narrow path inhibition with the lowest average score of 1.17. Among channel bends of 0, 1, and 2 right angles, an increase in micro-channel tortuosity from 0–2 bends amplified OPC1 cell growth upwards of ~ 6.6%. A one-way ANOVA showed significant differences in cell quantity for alternating channel tortuosity at a significance level of p

Designing load bearing implants with the desired mechanical and biological performance and to fabricate net shape, functional implants with complex anatomical shapes is still a challenge. In addition, patient specific load bearing implants with the possibilities of guided tissue regeneration are gaining significant interest in orthopedics. Novel design approaches and fabrication technologies that can achieve balanced mechanical and functional performance in mono-block implants are necessary to accomplish these objectives. In this article we give an overview of our novel design concepts for load bearing metal implants and demonstrate the manufacturing of unitized implant structures with and/or without porosity using laser engineered net shaping (LENS™) — a solid freeform fabrication technique. We have fabricated porous metal implants with designed porosities up to 70 vol.% in various biomedical metals/alloys, such as Ti, Ti6Al4V, NiTi and CoCrMo, and tailored their effective modulus to suit the modulus of human cortical bone, thus eliminating stress-shielding. Unitized structures with functionally graded CoCrMo alloy coating on porous Ti6Al4V alloy have been fabricated using LENS™ to minimize wear induced osteolysis. Finally, this technology can also be used to fabricate porous, net shape implants with functional gradation in structure and/or composition to mimic natural bone. Since the LENS™ fabrication does not change the chemistry of the biocompatible alloys the inherent in vitro and in vivo biocompatibility will remain the same and therefore, we have not provided any biocompatibility results in this article. This article provide an insight into the important aspects of LENS™ fabrication and properties of CoCrMo alloy structures, which can potentially eliminate long standing challenges in load bearing implants such as total hip prosthesis to increase their in vivo life time.

Nanocrystalline β-tricalcium phosphate (β-TCP) powder was synthesized using reverse micelle as a template system. Cyclohexane was used as the oil phase, aqueous solutions of calcium nitrate and phosphoric acid as the aqueous phase, and poly(oxyethylene)5 nonylphenol ether (NP-5) and/or poly(oxyethylene)12 nonylphenol ether (NP-12) as the surfactants. The powder were synthesized at a fixed Ca/P molar ratio of 1.5 at a pH of 10. The synthesized powder were calcined at 800°C to obtain monophasic β-TCP. Particle size, morphology, and surface area of the synthesized powder were dependent on the chemistry of the surfactant and composition of the microemulsion. The powder were characterized using a BET surface area analyzer, powder X-ray diffraction, dynamic light scattering technique, and transmission electron microscopy. TCP nanoparticles had a particle size between 32 and 135 nm, and a BET-specific average surface area between 57 and 103 m2/g with controlled morphology. The powder were consolidated and sintered at 1250°C in a 3 kW microwave furnace in the form of a compact disk. Human osteoprecursor cells (osteoblastic precursor cell line 1 [OPC1]) were used to assess the biocompatibility of TCP disks after 1, 5, and 11 days in culture using scanning electron microscopy, MTT assay, and alkaline phosphatase expressions. Disk samples were biocompatible and showed excellent OPC1 cell adhesion, growth, and proliferation. Biocompatible β-TCP nanopowder were synthesized with controlled particle size, morphology, and surface area using a reverse micelle-mediated template system.

We introduce a novel approach for synthesizing mesoporous hydroxyapatite (HAp, (Ca)10, (PO4)6(OH)2) using double emulsion droplets as microreactors. By using capillary microfluidic techniques, the size and the geometry of the droplet microreactors can be tuned easily. Double emulsion droplets offer the combined advantages of both shielding the reactants and on-demand addition of reactants; this makes them highly versatile microreactors. Such droplet microreactors also enable simple visualization of the HAp formation process as well as control over the porosity in the HAp that is synthesized. Powder formed with our technique demonstrates a remarkable microstructure, as well as significantly enhanced BET specific average surface area and nanoscale porosity. Our results present a novel synthesis approach for controlling the nanoscale porosity and the morphology of inorganic particles using double emulsion droplets.

In the present research, carbon monoxide (CO) gas sensing response was studied for TiO 2 thick films calcined and sintered between 700 and 900 °C. Crystalline phase, crystallite size, surface area, particle size, and amorphous content were measured for the calcined powder. Crystallinity of the powder was found to affect sensing response significantly towards CO. Anatase phase of TiO 2 thick film was stable up to 900 °C however, as calcination temperature increased from 700 to 900 °C, surface area and amorphous phase content decreased. Films calcined and sintered at 700 °C showed a lower response towards CO than those calcined at 800 °C. Upon increasing the calcination temperature further, particle growth and reduced surface area hindered the sensing response. A calcination temperature of 800 °C was necessary to achieve sufficient order in the crystal structure leading to more efficient adsorption and desorption of oxygen ions on the surface of TiO 2 .

Hydroxyapatite (HA) nanopowder was synthesized by reverse microemulsion technique using calcium nitrate and phosphoric acid as starting materials in aqueous phase. Cyclohexane, hexane, and isooctane were used as organic solvents, and Dioctyl sulfosuccinate sodium salt (AOT), dodecyl phosphate (DP), NP5 (poly(oxyethylene)5 nonylphenol ether), and NP12 (poly(oxyethylene)12 nonylphenol ether) as surfactants to make the emulsion. Effect of synthesis parameters, such as type of surfactant, aqueous to organic ratio (A/O), pH and temperature on powder characteristics were studied. It was found that the surfactant templates played a significant role in regulating the morphology of the nanoparticle. Hydroxyapatite nanoparticle of different morphologies such as spherical, needle shape or rod-like were obtained by adjusting the conditions of the emulsion system. Synthesized powder was characterized using X-ray diffraction (XRD), BET surface area and transmission electron microscopy (TEM). Phase pure HA nanopowder with highest surface area of 121 m2/g were prepared by this technique using NP5 as a surfactant. Densification studies showed that this nanoparticle can give about 98% of their theoretical density. In vitro bioactivity of the dense HA compacts was confirmed by excellent apatite layer formation after 21 days in SBF solution. Cell material interaction study showed good cell attachment and after 5 days cells were proliferated on HA compacts in OPC1 cell culture medium. The results imply this to be a versatile approach for making hydroxyapatite nanocrystals with controlled morphology and excellent biocompatibility.

Implant related infections are of great concern in modern surgery. In order to improve the implant performance and to reduce implant related infections, titanium (Ti) surface was modified to simultaneously improve cell- materials interactions and antimicrobial activity. Ti surface was first coated with tricalcium phosphate (TCP) using Laser Engineered Net Shaping (LENS™) to improve biocompatibility. Silver (Ag) was then electrodeposited from different concentrations of silver nitrate (AgNO(3)) solutions to improve the antimicrobial activity. The Ag-TCP coatings were tested for cytotoxicy with human osteoblast cells. The antimicrobial activities of the Ag-TCP coatings were evaluated using Pseudomonas aeruginosa and Staphylococcus aureus bacteria. In vitro bacterial adhesion study indicated a significant reduction in bacterial colony on Ag-TCP coated surfaces when compared to TCP coated surface.

Our objective was to determine the role of surface charge and wettability on early stage mineralization as well as bone cell adhesion and proliferation on polarized HAp surface. To estimate the surface wettability, contact angles were measured in water, simulated body fluid (SBF) and Dulbecco's modified Eagle's medium/nutrient mixture F-12 Ham (DMEM). Experimental results show that HAp surface wettability and surface energy can be tailored by inducing surface charge without introducing any volumetric effects in the material. Increasing the surface charge increased the wettability and also the energy of HAp surfaces in all tested media. A maximum surface energy of 49.47+/-3.76mJ/m(2) was estimated for positively charged HAp surfaces polarized at 400(o)C. The in vitro bioactivity of polarized HAp samples was evaluated by soaking in SBF and DMEM (cell media). Cell-materials interaction was studied by culturing with human fetal osteoblast cells (hFOB). In vitro results show that tailoring the combined effect of wettability and charge polarity on the HAp surface enable differential binding of inorganic ions (e.g., Ca(2+), Cl(-), Na(+), HCO(3)(-) etc) and organic cell adhesive proteins (e.g., fibronectin, vitronectin etc) with different surface properties, which results in accelerated or decelerated mineralization as well as cell adhesion and proliferation on polarized HAp surface.

Ti being bioinert shows poor bone cell adhesion with an intervening fibrous capsule. Ti could be made bioactive by several methods including growing in situ TiO2 layer on Ti-surface. TiO2 nanotubes were grown on Ti surface via anodization process and the bone cell-material interactions were evaluated. Human osteoblast cell attachment and growth behavior were studied using an osteoprecursor cell line for 3, 7, and 11 days. An abundant amount of extracellular matrix (ECM) between the neighboring cells was noticed on anodized nanotube surface with filopodia extensions coming out from cells to grasp the nanoporous surface of the nanotube for anchorage. To better understand and compare cell-materials interactions, anodized nanoporous sample surfaces were etched with different patterns. Preferential cell attachment was noticed on nanotube surface compare to almost no cells in etched Ti surface. Cell adhesion with vinculin adhesive protein showed higher intensity, positive contacts on nanoporous surface and thin focal contacts on the Ti-control. Immunochemistry study with alkaline phosphatase showed enhanced osteoblastic phenotype expressions in nanoporous surface. Osteoblast proliferation was significantly higher on anodized nanotube surface. Surface properties changed with the emergence of nanoscale morphology. Higher nanometer scale roughness, low contact angle and high surface energy in nanoporous surface enhanced the osteoblast-material interactions. Mineralization study was done under simulated body fluid (SBF) with ion concentration nearly equal to human blood plasma to understand biomimetic apatite deposition behavior. Although apatite layer formation was noticed on nanotube surface, but it was nonuniform even after 21 days in SBF.

Nano-structured TiO 2 -based ceramics were synthesized using a citrate–nitrate auto combustion method. Phase purity, particle size, and surface area of TiO 2 nano-powder were studied as a function of citrate-to-nitrate ratio (C/N = 0.1–0.5), water addition during synthesis (0 and 10 vol%), and yttrium as a metal ion dopant (0 and 10 wt.%). The powder X-ray diffraction data showed that all synthesized TiO 2 -based powder was primarily anatase phase. BET surface area analysis showed an increase in specific average surface area up to 48 m 2 /g with increasing C/N ratio and the addition of water during synthesis. Powder XRD, BET, and TEM measurements confirmed particle size ranged from 10 to 50 nm depending on synthesis parameters. C/N ratio of 0.5 and addition of water during synthesis resulted in the smallest particle size. Sintered compacts made from this nano-powder showed an increase in bulk conductivity with increasing temperature inside a tube furnace open to the air. Addition of yttrium increased conductivity by 3 times over that of pure TiO 2 . Higher conductivity was attributed to higher energy of electrons to overcome conduction barriers and higher carrier concentrations caused by both temperature effects and yttrium addition. Thick film sensors made from the synthesized TiO 2 nano-powder with higher surface area showed an improved response to carbon monoxide at 600 °C. Yttrium doping in TiO 2 also increased response to CO compared with pure TiO 2 .

The feasibility of enhancing thermal conductivity of Al–4Cu–1Mg alloy by depositing 80Cu–20Mo coating using high-power lasers has been examined. Coatings of 667±2.5 μm thickness were formed with metallurgically sound interface. Results showed an 86% increase in the thermal conductivity of Al–4Cu–1Mg alloy due to laser-deposited 80Cu–20Mo alloy coating. This coating approach can potentially be used on low coefficient of thermal expansion metal matrix composites to enhance their thermal conductivity in electronic devices.

The objective of this work was to study adhesion, proliferation and differentiation of osteoblast cells (OPC1) on alumina ceramic, a bio-inert material. Alumina ceramic with different average grain sizes, 1 μm and 12 μm, respectively, were used in as-prepared condition without any grinding and polishing to understand the influence of grain size on cell–material interactions. Scanning electron microscopy and confocal imaging were used to study attachment, adhesion and differentiation of OPC1 cells. Cells attached, proliferated and differentiated well on both the substrates. Adhesion of cells, as assessed by observing the production of vinculin, was found to be a consistent phenomenon on both the substrates. On day 5 of cell culture, significant cell-attachment was observed and vinculin was detected throughout cytoplasm. MTT assay showed that proliferation of OPC1 cells was consistently higher in the case of 12 μm-alumina. Cells of different morphology, nodular, plate-like as well as elongated, were found to get anchored at grains, grain boundaries as well as pores. On day 16, there were clear signs of mineralization as well. Over all, alumina with average grain size of 12 μm showed better cell-attachment, growth and differentiation compared to 1 μm grain size samples.

Microwave sintering of hydroxyapatite (HAP) and tri-calcium phosphate (TCP) ceramics were studied using a commercial 2.45 GHz, 3 KW fully automated microwave system. Four different powder compositions, apart from pure HAP and TCP, were prepared with small amount of different oxide additives e.g., magnesium oxide, zinc oxide and titanium oxide. All samples were densified at 1250 °C for 30 min. Sintered samples had high density and homogeneous microstructure for all compositions. Phase analysis using XRD showed no major variations from starting materials. Presence of additives increased compressive strength between 100 and 200%. Fractured surfaces showed clear signs of intergranular fracture in undoped HAP and TCP while in doped samples, fracture modes were either transgranular or mixed mode. In comparison to conventional sintering, microwave sintering of calcium phosphate ceramics was found to be economically exciting due to substantial reduction in processing time and energy expenditure due to volumetric heating of samples.

Effects of hydroxyapatite (HA) whiskers addition on densification, mechanical, and biological properties of HA compacts were studied for their use as an implant material for orthopedic and dental applications. HA nanopowder was synthesized using reverse micelle as template system, and urea hydrolysis synthesis route was used to prepare micrometer-sized HA whiskers. Poly (oxyethylene)12 nonylphenol ether (NP12) and cyclohexane were used as surfactant and organic solvent, respectively, for the reverse micelle microemulsion system. Desired microstructure in sintered HA composite was obtained by mixing Mg2+ as a dopant in HA nanopowders, and Al3+ as a dopant in HA whiskers. Compacts were processed using pressureless sintering. With an increase in whisker content from 0 to 10 wt%, the average compressive strength of HA compacts decreased from 120 to 90 MPa. HA composite processed with 10 wt% HA whisker showed a microhardness of 3.6 GPa and an average indentation fracture toughness of 1.5 MPa·m1/2. Mineralization study in simulated body fluid showed deposition of octacalcium phosphate on sintered HA compacts. In vitro cytotoxicity tests with human osteoprecursor cell line confirmed excellent osteoblast cell attachment and growth on the sintered HA compacts with 0, 10, and 20 wt% HA whiskers.