Reinforced Hydroxyapatite Research Articles

In Vitro Wear of Titanium Reinforced Hydroxyapatite Coatings in Simulated Body Fluid

Abstract Titanium-reinforced hydroxyapatite (Ti-HAP) coatings have been deposited over 254 SMO stainless steel using a low-velocity oxygen fuel technique. FESEM, XRD, Vickers microhardness, and shear strength tests have been performed to characterize the developed coatings. Further, in vitro wear behaviors of the coatings were evaluated using a pin-on-disc wear tester in simulated body fluid. The results reveal that 40Ti-HAP coating possesses superior wear resistance compared to 60Ti-HAP, Ti, and HAP coatings, attributed to higher surface hardness and higher shear strength values. Amongst the tested samples, the friction coefficient was lower for Ti coating, followed by 60Ti-HAP composite coating. The surface roughness was a prominent factor in reducing the friction coefficient of coating samples. Local detachment and brittle fracture were the dominant wear modes in Ti-HAP coating, whereas an additional micro-plowing wear mode was observed in pure hydroxyapatite and titanium coating.

Mechanical, Tribological, and Biological Properties of Short Carbon Fiber/ Nano Hydroxyapatite Reinforced Hybrid Epoxy Composites

This investigation intends to examine the mechanical, tribological, and biological properties of hybrid epoxy composites reinforced with nanohydroxyapatite (nHA) and short carbon fiber (SCF). Due to its advantageous mechanical, tribological, and biocompatibility features, the proposed E/SCFs-nHA hybrid composites are meant to be recommended for composite structures that can be used to develop fixation plates used in orthopedic applications. In this study, single-layer hybrid composites reinforced with SCFs and nHA in varying ratios, as well as pure epoxy (E) and epoxy-carbon fiber composites, were all fabricated by hand lay-up method. Tensile tests, 3-point bending tests, and Izod impact tests were performed to investigate their mechanical characteristics. Moreover, the hybrid composite samples were tested for their biological properties in simulation body fluid (SBF). Mechanical and biological properties were found to be enhanced according to the results. Consequently, the hybrid composite (E-10CF-3nHA) of 10% carbon fiber (CF) and 3% nanohydroxyapatite (nHA) performed the best in all tests.

Tribological behavior of silver-doped eggshell-derived hydroxyapatite reinforcement in PMMA-based composite

Polymethylmethacrylate (PMMA) and hydroxyapatite (HAp) are the two most promising biocompatible materials used in biomedical applications. The current research performs the wettability and tribological characterization of the novel hybrid biocomposite of PMMA reinforced with eggshell-derived, silver-doped hydroxyapatite (HAPAg). Varying wt% of HAPAg in PMMA were analyzed using a ball-on-disk tribometer. The coefficient of friction shows an increasing trend with an increase in normal load for all the compositions while, with reinforcement of HAPAg, it increases till 5 wt% and then shows a sudden decrement at PHA7.5 due to the formation of flattened asperities at the contact surface. However, the progressive increase in hardness with the inclusion of HAPAg in PMMA correlates with the reduction in the wear rate of the composite samples. The highest wear rate was observed for PHA0 (i.e. 862.42 × 10−5 mm3/m) at 60 N. As observed, the hydrophilicity increases (contact angle changed from 96.30° ± 2.11° [PHA0] to 81.70° ± 1.01° [PHA7.5]), and the porosity decreases (≈2.86%) with the reinforcement of HAPAg in PMMA which further improves the cohesion strength and microhardness of the composite material. The X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analysis confirms the uniform reinforcement of HAPAg, and the worn surface behavior was inspected using scanning electron microscopy, Stereo zoom microscope, and three-dimensional surface profilometer. The low-specific wear characteristic at higher loads ensures the application of developed biocomposite material in dental and orthopedic applications.

On biodegradability of 3D printed polyvinylidene fluoride composites

Polyvinylidene fluoride (PVDF) is one of the established biocompatible thermoplastics for scaffolding applications. But due to its partial biodegradability, its use as a bio-absorbable implant is limited. Some studies have outlined that reinforcement of hydroxyapatite (HAp), and chitosan (CS) helps in improving the biodegradability of the PVDF composite matrix. But hitherto little has been reported on the biodegradability comparison for virgin PVDF, and PVDF composite matrix (with different proportions of HAp and CS as reinforcement). This study reports the biodegradability of virgin PVDF, 90% PVDF–10% HAp, 90% PVDF–8% HAp–2% CS, and 90% PVDF–9% HAp–1% CS based on a corrosion testing (open circuit potential, polarization resistance, corrosion current, corrosion rate [CR], surface roughness (Ra), and porosity %) in simulated bodily fluid (SBF) for possible bio-absorbable implant applications. The study suggests that the biodegradability of 90% PVDF–9% HAp–1% CS is maximum having CR 26.389mm2/year, mainly due to the presence of more hydroxyl group (-OH). The corresponding porosity % and Ra (after corrosion testing) were noticed as 12.45% and 19.12 µm. The results are supported by scanning electron microscopy (SEM) images.

Stir casting technology for fabrication of biodegradable magnesium metal matrix composites containing different percentages of hydroxyapatite reinforcement material for biomedical purposes

Due to the superior biocompatibility and strength of magnesium and its alloys compared to other metallic alloys, such as those used in orthopaedics as a bone-implant material, they have recently been considered a breakthrough material for biomedical applications. However, before tissues have fully adjusted to the high chloride environment and physiological pH range of the physiological system, pure magnesium might lose its mechanical integrity. Therefore, it is believed that the development of magnesium matrix composites is an approach to decrease corrosion rates and improve their mechanical properties that are similar to those of natural bone. They are not required to be taken out once the wound has entirely healed because they are biodegradable as well, which might reduce the need for additional surgeries in the future. The stir casting technique has been employed in this workto produce samples of magnesium-based biodegradable metal matrix composites, referred to as M2H (Magnesium & 2.0 wt% Hydroxyapatite powder) and M4H (Magnesium & 4.0 wt% Hydroxyapatite powder), with varying amounts of hydroxyapatite powder as a reinforcement material. In this worktensile test samples (M2H-T1,T2 & M4H-T1,T2) andcompression test samples (M2H-C1,C2,C3& M4H-C1,C2,C3,C4)along with microstructural and SEM test samples (M2H-MS & M4H-MS)were prepared and cut to a suitable shape and size in accordance with ASTM standards. This paper mainly focuses on the samples preparation for mechanical testing and SEM characterisation.

Fabrication, Thermo-Mechanical, and Morphological Characterization of Hydroxyapatite-Reinforced Polyurethane Biocomposites as Dye Adsorbent for Effluent.

Petrochemical costs, limited fossil fuel reserves, and concerns about greenhouse gas emissions have raised interest in developing renewable approaches for synthesizing biobased polyurethanes. This study aims to solve these problems by making nanocrystalline hydroxyapatite (HA) reinforcement from waste chicken eggshells and adding it to polyurethane synthesis through in situ polymerization. The novelty of the research lies in the utilization of HA as a reinforcement material and renewable resources for polyurethane production. The results confirm that HA was successfully added to the polyurethane backbone. Fourier transform infrared (FTIR) analysis confirmed that the NCO groups were changed to urethane linkages. TGA examination demonstrated that the samples exhibited thermal stability up to 457 °C with a mass loss of 61%, indicating enhanced thermal stability. DMA measurements showed improved mechanical properties of the synthesized polyurethanes, with storage modulus (E'), complex modulus (E*), and compliance complex (D*) values of 0.177, 22.522, and 0.660 MPa-1, respectively. SEM analysis confirmed the homogeneous surface and well-dispersed HA reinforcement. Swelling characteristics revealed an optimum absorption of 30% H2O, 35% CH3OH, and 45% CCl4. Polyurethane composites exhibited significant chemical resistance and hydrolytic stability in acidic and basic media. Additionally, the composites demonstrated efficient adsorption of methyl orange from wastewater, with the PUHCI series achieving a maximum adsorption capacity of 85.50 mg/g under optimal conditions of 0.030 g/mL dose, 45 °C temperature, 2.5 h contact time, and pH 6.0..

EFFECT OF MULTI-WALLED CARBON NANOTUBES IN REINFORCED HYDROXYAPATITE COMPOSITE COATINGS FOR ORTHOPEDIC APPLICATIONS

Hydroxyapatite (HA)-coated metallic substrates are commonly used for load-bearing orthopedic implants. In this work, Titanium grade 2 and Titanium grade 5 substrates were coated with hydroxyapatite and hydroxyapatite reinforced with 5% (by wt.) multiwalled carbon nanotubes (MCNT) separately using plasma spray coating. The wear behavior of these coated substrates was studied with the simulated body fluid (SBF) having a pH between 7.20 and 7.40. Fracture toughness and wear resistance of HA reinforced with 5% (by wt.) MCNT composite coating was found to be higher as compared to pure HA coating. This improvement is by virtue of inherent mechanical properties and the crack bridging effect offered by MCNT. The addition of MCNT also helped in restricting crack propagation in the coatings. As evident from SEM images, abrasive and adhesive wear mechanisms were observed which reduce greatly with the reinforcement of MCNT.

Multi-length scale strengthening and cytocompatibility of ultra high molecular weight polyethylene bio-composites by functionalized carbon nanotube and hydroxyapatite reinforcement

The mechanical properties, such as hardness and elastic modulus, of ultra-high molecular weight polyethylene (UHMWPE) composites for acetabular cup liner are improved by adding hydroxyapatite (HAp) and carbon nanotubes (CNT). However, the weak adhesion of HAp (H) and CNT (C) with UHMWPE (U) limits the enhancement of mechanical properties. Thus, the surface of these reinforcements is silane-treated to improve the adhesion with polymer via Si–O and C=O bonds, as evidenced from spectroscopy techniques. An increased dispersion and interfacial adhesion of functionalized HAp (fH) and CNT (fC) with the polymer matrix is confirmed by nearly two-fold increased reinforcement fraction (Rf: 0.55) of U-10 wt% fHAp-2 wt.% fCNT (U10fH2fC) in comparison to U-10 wt% HAp-2 wt.% CNT (U10H2C). Additionally, Voronoi Tessellation (VT) on SEM micrographs of U10H2C and U10fH2fC revealed the dispersion of functionalized CNTs in U10fH2fC with a center-to-center distance of 0.076 μm, which is 74% higher for unfunctionalized CNT in U10H2C. The multilength scale strengthening of the UHMWPE matrix is confirmed from atomic level modification via functionalization of fillers which effectively adhered to the polymer chain on a micro-scale level. A uniform distribution of CNTs rendered increased crystallinity (+28%) of U10fH2fC, which in turn resulted in significant improvement in bulk mechanical properties (18%, 49%, and 12% increased hardness (148.1 MPa), elastic modulus (3.51 GPa) and tensile elastic modulus (219.8 MPa), respectively) in comparison to that of U10H2C. Functionalized-HAp/CNT reinforced UHMWPE composites maintained its cytocompatibility in the MTT test and fluorescence microscopy, affirming their potential employment as acetabular cup liners for hip joint arthroplasty.

Current trends, applications, and challenges of coatings on additive manufacturing based biopolymers: A state of art review

AbstractHealing of bone fractures highly depends on the biocompatibility, stability in biological conditions, biodegradability, technical functionality, and shelf‐life of biomaterials. Metallic biomaterials offer excellent mechanical properties and biocompatibility. However, metallic bone implants result in stress shielding, release of toxic ions, excessive wear, and corrosion. Polymer materials are being explored for bone implants due to their light‐weight, biocompatibility, biodegradability, and absence of stress shielding. In the new era, additive manufacturing (AM) is being preferred due to its capability of fabricating customer specific implants with minimum material wastage. However, AM based polymer implants lack in mechanical strength and biological properties. Surface modification of polymeric substrates using coatings and incorporation of bioadditives have been regarded as alternatives for improvement of mechanical and biological properties. This review discusses about various coating techniques and gives an overview about coatings and bioadditives that can be used for enhancement of properties. From the review, it is evident that reinforcement of hydroxyapatite to polylactic acid resulted in prevention of crack growth during shape recovery cycles which can be used for self‐fitting implants. Coatings have been successful in enhancing hydrophilicity, mechanical properties, anti‐biofouling, antibacterial and anti‐coagulative properties, adhesion, proliferation, and differentiation of cells on the coated surface. This review also discusses the challenges that need to be overcome for progression in this field.

Mechanical, wear and thermal conductivity characteristics of snail shell-derived hydroxyapatite reinforced epoxy bio-composites for adhesive biomaterials applications

ABSTRACT This research investigates the effects of snail shell-based hydroxyapatite (HAp) reinforcements on the mechanical, wear, and selected physical properties of epoxy-based composites. The exploitation of these properties was aimed at assessing the suitability and efficiency of the developed bio-composites for adhesive biomedical applications. Snail shell wastes were sourced and processed to obtain (HAp) particles of ˂20 μm. The bio-derived hydroxyapatite-based epoxy composites were produced using the stir-cast method by mixing the hydroxyapatite with the epoxy resin and hardener before pouring into the moulds where they are allowed to cure. Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD) of the snail shell hydroxyapatite particles were carried out while mechanical, wear, and physical properties of the developed composites were evaluated. SEM images of the fracture surfaces were also examined. The results showed that enhancements occurred from the addition of snail shell-derived HAp to epoxy resin in the developed composites. The results revealed that most of the properties gave their optimum values when 15 wt.% reinforcement was used. At this weight fraction, optimum values were obtained which include 43 MPa for maximum flexural strength, 40HS for hardness, 40 J for impact, 0.35 W/mK for thermal conductivity, and 0.07 for wear index.

Assessment of protein adhesion behaviour and biocompatibility of magnesium/Co-substituted HA-based composites for orthopaedic application

Protein adsorption has a great influence on Mg-based metallic implants, which affects cell attachment and cell growth. Adsorption of the proteins (via electrostatic interaction, hydrophobic/hydrophilic, and hydrogen-bonding) on the implant surface is greatly influenced by the surface chemistry of the implant. Hydroxyapatite (HA) is a class of CaP ceramic, beneficial for protein adsorption as it possesses Ca2+ and PO43− in it, which are believed to be the protein binding sites on the HA surface. Moreover, HA is the popular choice for reinforcement in the magnesium matrix owing to its similarity with bone mineral composition. However, negligible interaction between HA and Mg particles during sintering is the major limitation for frequent usage of Mg-HA implants. Doping of HA with Mg2+ and Zn2+ (CoHA) ions leads to its chemistry similar to natural apatite in human bone and facilitates comparatively better bonding with the MgZn matrix. This study mainly aims to delve into the protein adsorption behaviour of Magnesium/Co-substituted HA-based Composites (M3Z-CoHA) along with their biocompatibility. Qualitative and quantitative protein adsorption analysis shows that the addition of 15 wt% CoHA to Mg matrix enhanced protein adsorption by ~60% and renders cell viability >90% after day 1, supporting cellular growth and proliferation. The implants also initiated osteogenic differentiation of the cells after day 7. The leached-out products from all the composites showed no toxicity. The morphology of the cells in all the composites was found as healthy as the control cells. Overall, the composite with 15 wt% HA reinforcement (M3Z-15CoHA) has shown favourable protein adsorption behaviour and cytocompatibility.

Synthesis and characterization of carbon nanotube reinforced hydroxyapatite ceramics proposed for biomedical applications

The present work reveals a convenient method for synthesis of Carbon Nanotube Reinforced Hydroxyapatite (CNT-HAp) based biomaterial. HAp was synthesized through co-precipitation method from Calcium Hydroxide (Ca(OH)2)and Phosphoric acid (H3 PO4) as the precursor materials. CNTs were incorporated into HAp ceramics with the help of ball milling technique. The structural and functional properties of CNT-HAp composites were thoroughly studied with the help of different characterizations such as FT-IR, Raman spectroscopy, XRD, XPS, SEM and EDX. Crystallite size of CNT-HAp composites was calculated to be 25.22 nm. Morphology of CNT-HAp composites consists of hair-like CNT molecules adjoined on HAP grains. Presence of CNTs leads to augmentation in the crystallinity of HAp ceramics. All the studies indicated towards the improvement in functional behavior of HAp on mixing with CNTs which makes CNT-HAp ceramics an important material that can be used in bio-medical applications.

Mechanical testing of cephalomedullary nail lag screws after the addition of hydroxyapatite substitutes.

Objective:To compare the effects of 3 implant designs, with and without hydroxyapatite reinforcement, on push/pull-out strength and rotational torque.Methods:Three implant designs (Gamma 3, INTERTAN, and PFNA-II) were selected for comparison. A hydroxyapatite cylinder (NEOBRACE) was used to reinforce the interface between the femoral head and the lag screw. Maximum push-out strength, maximum pull-out strength, and peak rotational torque were measured in cellular blocks mimicking osteoporotic cancellous bone, with and without NEOBRACE.Results:In the push-out test, INTERTAN produced a significantly higher push-out strength in osteoporotic bone density cellular blocks than the other lag screws and blades (P < .05). With the addition of NEOBRACE, push-out strength was significantly higher for INTERTAN and PFNA-II (P < .05) than for the non-NEOBRACE group. In the pull-out test, INTERTAN produced a significantly higher pull-out strength in the osteoporotic bone density cellular blocks than did the other lag screws and blades (P < .05). With the addition of NEOBRACE, the pull-out strengths of INTERTAN and Gamma 3 versus those of the non-NEOBRACE group significantly increased (P < .05). In the rotational torque test, INTERTAN produced significantly greater rotational torque in the osteoporotic cellular blocks than the other lag screws and blades (P < .05). The addition of NEOBRACE resulted in a significant increase in rotational torque only for INTERTAN (P < .05).Conclusion:The use of NEOBRACE supported an increase in push/pull-out strength and rotational torque, especially in systems with a relatively increased bone or implant interface area.Level of Evidence: Level V

Micro-scale analysis of HA-PLLA bio-composites: Effect of the interpenetration of voids on mechanical properties

Reinforcement of hydroxyapatite (HA) particles into poly-l-lactic acid (PLLA) enhances the mechanical properties of PLLA and further makes it favorable to use in biomedical applications. A micro-scale computational model for predicting the effective elastic properties of HA-PLLA composites through 3D representative volume element was studied in the presented work. The influence of volume fraction of HA particles, the orientation of HA and voids, and interpenetration of voids were discussed in detail. With perfect bonding conditions, the fracture strength increased with an increase in the volume fraction of the HA particles. The computed longitudinal modulus was in good agreement with the experimental results. This work might help in determining the optimal configuration of the HA-PLLA composites for biomedical applications.

Surface metal matrix nano-composite of magnesium/hydroxyapatite produced by stir-centrifugal casting

The present study aims to investigate a liquid state method of stir and centrifugal casting as an in-situ and cost-attractive processing technology for the production of magnesium/hydroxyapatite surface metal matrix nano-composites (Mg/HA surface metal matrix nano-composite). The main contribution of this study is to design the best condition for achieving a uniform Mg/HA surface nano-composite as a potential bone implant. It was shown how casting parameters and the distribution of hydroxyapatite affect mechanical properties of nano-composites measured using nano-indentation, nano-scratch, and compression tests. Response surface method in Design Expert software was used to predict the best model and the optimum condition of casting based on the experimentally measured data. The surface metal matrix nano-composites, consisting of a magnesium matrix with different amounts of nano-sized hydroxyapatite and silicon-doped hydroxyapatite (0.75-3 wt%) particles, were prepared. Hot isostatic pressing was used to homogenize the nano-composites in terms of particle distribution and to reduce porosity. It was shown that the weight percent of hydroxyapatite reinforcement is the parameter which is best suited to tailor targeted strength values. The target values of maximum compression strength (187 MPa) and elastic modulus (33 GPa) were achieved with a combination of the following parameters: 1.83 wt% hydroxyapatite, 800 rpm mold rotational speed, and a propeller rotational time of 6.3 min. A specimen prepared under these conditions had a homogeneous distribution of nano-hydroxyapatite in magnesium metal matrix after hot isostatic pressing at 450 °C and 100 MPa for a holding time of 120 min. It indicated the best mechanical resistance in terms of hardness and material loss during the nano-scratch testing. Moreover, the XRD results show that there is no considerable chemical reaction between the reinforcement particles of n-HA and Mg metallic matrix during casting at 700 °C and thermo-mechanical treatment of HIP at 450 °C.

Sol-Gel Derived Hydroxyapatite Coatings for Titanium Implants: A Review.

With the growing demands for bone implant therapy, titanium (Ti) and its alloys are considered as appropriate choices for the load-bearing bone implant substitutes. However, the interaction of bare Ti-based implants with the tissues is critical to the success of the implants for long-term stability. Thus, surface modifications of Ti implants with biocompatible hydroxyapatite (HAp) coatings before implantation is important and gained interest. Sol-gel is a potential technique for deposition the biocompatible HAp and has many advantages over other methods. Therefore, this review strives to provide widespread overview on the recent development of sol-gel HAp deposition on Ti. This study shows that sol-gel technique was able to produce uniform and homogenous HAp coatings and identified the role of surface pretreatment of Ti substrate, optimizing the sol-gel parameters, substitution, and reinforcement of HAp on improving the coating properties. Critical factors that influence on the characteristics of the deposited sol-gel HAp films as corrosion resistance, adhesion to substrate, bioactivity, morphological, and structural properties are discussed. The review also highlights the critical issues, the most significant challenges, and the areas requiring further research.

Mechanical and thermal properties of vitamin E-doped UHMWPE reinforced with hydroxyapatite

ABSTRACT The unique biocompatible and wear resistant nature of ultrahigh molecular weight polyethylene (UHMWPE) makes it a suitable material for load bearing applications in total joint replacements (TJR). However, oxidation induced wear is a common cause limiting the life span of implants. Hence, Vitamin-E, a common antioxidant, is added to prevent the wear loss due to oxidation of UHMWPE. In addition, Hydroxyapatite does improve the toughening mechanisms occurring in the polymer matrices. Hence, in this study, a novel hydroxyapatite (HA) nanoparticles reinforced Vitamin-E doped UHMWPE nanocomposites (UHMWPE-E/HA) were developed here in this work. The HA concentration was varied between 0.5 - 3 wt.% and optimum wt% is reported. The mechanical and thermal properties were investigated thoroughly using an array of characterizations. Particularly, a considerable improvement in fracture toughness (KIC) was obtained. Detailed examination of fractured surfaces was performed to understand the effect of HA reinforcement on fracture toughness of UHMWPE-E/HA nanocomposites.

Assessment of biomechanical stability and formulation of a statistical model on magnesium based composite in two different milieus

Magnesium (Mg) based temporary implants are an appealing new solution to counter the problems associated with the currently available temporary orthopaedic implants, used in fracture fixing. To make the extensive use of Mg-based implants in-vivo, mechanical integrity in the physiological environment is a prerequisite. This study presents an insight into the biomechanical stability of Mg-3Zn/HA (0, 5, and 15 wt % of HA) composites in two different milieus (simulated body fluid (SBF) and serum contained SBF (m-SBF)). After 14 days of static immersion in SBF, ~65% mechanical strength was compromised in the case of 15 wt % HA reinforcement. However, the degradation rate was slowed down by ~35% with the addition of 15 wt % HA in Mg-3Zn. Mg-3Zn/HA composite, when soaked in both fluids, was found to induce apatite layer formation on the surfaces for several days. However, in the case of m-SBF immersion, 15 wt % HA facilitated less precipitation of apatite growth when compared to SBF immersion. Nevertheless, m-SBF immersed 15 wt % HA composite facilitated better corrosion resistance and excellent mechanical stability after 14 days of immersion. The approach thereby assists in establishing an effective mechanism between the degradation and mechanical stability in in-vitro immersion. In addition, this study has also developed a semi-empirical model for prediction of the compressive strength of these composites as a function of the number of days of immersion and the content of hydroxyapatite (HA). This semi-empirical model will help in predicting the biomechanical stability for long-term in-vitro exposures, which might be of use in evaluating the effect of the in-vivo environment.

The influence of bioactive hydroxyapatite shape and size on the mechanical and biodegradation behaviour of magnesium based composite

Reinforcement of hydroxyapatite in magnesium-based composites stands out due to their inherent properties, like, corrosion resistance, osteoconduction, and osteoinduction, apart from the compositional similarity with human bones. This study highlights the shape and size effect of bioactive HA ceramics on microstructural, mechanical, and biodegradation properties of the biocompatible Mg–3Zn based composites, fabricated via spark plasma sintering. Reinforcement of smaller size cylindrical HA (15 wt%) in Mg–3Zn matrix reduced the interparticle spacing. It generated comparatively higher constraint to the matrix deformation, which enhanced the hardness and elastic modulus by 23 and 16%, respectively, as compared to round HA. Qualitative behaviour of the plastically deformed indents was analysed via SPM imaging. Ultimate compressive strength of cylindrical HA reinforced composite enhanced by ~22 and 40%, when compared to round HA and Mg–3Zn composites, respectively, due to Hall-Petch strengthening. Reduction in the grain size of cylindrical HA reinforced composites increased the grain boundary area per unit volume, which facilitated the apatite precipitation sites in the physiological environment. Consequently, the corrosion resistance was enhanced by 63 and 27%, as compared to Mg–3Zn and round HA reinforced composite. The fabricated composite possesses superior biomechanical and biodegradation behaviour, rendering them potentially useful for temporary orthopaedic implants.

Effects of porogen morphology on the architecture, permeability, and mechanical properties of hydroxyapatite whisker reinforced polyetheretherketone scaffolds

Porous polyetheretherketone (PEEK) and bioactive hydroxyapatite (HA) reinforced PEEK scaffolds have attracted recent interest for enabling biologic fixation of orthopaedic and spinal implants, such as interbody spinal fusion cages. Porous PEEK and HA-PEEK scaffolds have been prepared by compression molding and leaching a fugitive porogen, most commonly NaCl salt crystals which exhibit a cubic morphology. Ellipsoidal or spherical porogen particles have been suggested to improve pore interconnectivity and permeability in scaffolds through improved porogen particle contact compared with a cubic porogen, but a direct comparison without concomitant effects from other factors is lacking. Therefore, the objective of this study was to investigate the effects of the porogen morphology on the architecture, permeability, and mechanical properties of bioactive HA whisker reinforced PEEK scaffolds. HA whisker reinforced PEEK scaffolds were prepared using a cubic or ellipsoidal NaCl porogen of equivalent size at multiple, equivalent levels of porosity and a constant level of HA reinforcement. Scaffolds prepared with an ellipsoidal porogen exhibited greater pore interconnectivity, indicated by a lower specific surface area measured by micro-computed tomography, and greater permeability than scaffolds prepared with a cubic porogen at 75–85% porosity. Compressive mechanical properties were not affected by the porogen morphology. Thus, an ellipsoidal porogen facilitated improved pore interconnectivity and permeability without compromising mechanical properties, and offers a means to circumvent an otherwise inherent design tradeoff between the benefit of increased porosity on permeability and the detriment of increased porosity on mechanical properties.