Hydroxyapatite reinforced Ti6Al4V composites for load-bearing implants

Cementless Total Knee Arthroplasty: Is it Safe in Demineralized Bone?

There is concern for cementless total knee arthroplasty (TKA) in patients with decreased bone mineral density (BMD) due to the potential increase in complications, namely failed in-growth or future aseptic loosening. Some data suggest that advances in cementless prostheses mitigate these risks; however this is not yet born out in long-term registry data. It is crucial to expand our understanding of the prevalence and etiology of osteoporosis in TKA patients, survivorship of cementless implants in decreased BMD, role of bone-modifying agents, indications and technical considerations for cementless TKA in patients with decreased BMD. The purpose of this study is to review current literature and expert opinion on such topics.

Additively manufactured Ti-Ta-Cu alloys for the next-generation load-bearing implants

Bacterial colonization of orthopedic implants is one of the leading causes of failure and clinical complexities for load-bearing metallic implants. Topical or systemic administration of antibiotics may not offer the most efficient defense against colonization, especially in the case of secondary infection, leading to surgical removal of implants and in some cases even limbs. In this study, laser powder bed fusion was implemented to fabricate Ti3Al2V alloy by a 1:1 weight mixture of CpTi and Ti6Al4V powders. Ti-Tantalum (Ta)-Copper (Cu) alloys were further analyzed by the addition of Ta and Cu into the Ti3Al2V custom alloy. The biological, mechanical, and tribo-biocorrosion properties of Ti3Al2V alloy were evaluated. A 10 wt.% Ta (10Ta) and 3 wt.% Cu (3Cu) were added to the Ti3Al2V alloy to enhance biocompatibility and impart inherent bacterial resistance. Additively manufactured implants were investigated for resistance against Pseudomonas aeruginosa and Staphylococcus aureus strains of bacteria for up to 48 h. A 3 wt.% Cu addition to Ti3Al2V displayed improved antibacterial efficacy, i.e. 78%-86% with respect to CpTi. Mechanical properties for Ti3Al2V-10Ta-3Cu alloy were evaluated, demonstrating excellent fatigue resistance, exceptional shear strength, and improved tribological and tribo-biocorrosion characteristics when compared to Ti6Al4V. In vivo studies using a rat distal femur model revealed improved early-stage osseointegration for alloys with 10 wt.% Ta addition compared to CpTi and Ti6Al4V. The 3 wt.% Cu-added compositions displayed biocompatibility and no adverse inflammatory response in vivo. Our results establish the Ti3Al2V-10Ta-3Cu alloy's synergistic effect on improving both in vivo biocompatibility and microbial resistance for the next generation of load-bearing metallic implants.

3D printed silicon nitride, alumina, and hydroxyapatite ceramic reinforced Ti6Al4V composites - Tailored microstructures to enhance bio-tribo-corrosion and antibacterial properties

This study utilized directed energy deposition (DED) as a metal additive manufacturing (AM) technique to create ceramic-reinforced composites of Ti6Al4V (Ti64) with hydroxyapatite (HA), alumina (Al2O3), and silicon nitride (Si3N4). The resulting composites had tailored microstructures designed to improve bio-tribological and antibacterial properties simultaneously. A total of 5-wt % ceramic reinforcement were used in Ti64 in four different composites - (1) only Si3N4 (5S), (2) only Al2O3 (5A), (3) 3 wt % Si3N4 and 2 wt% HA (32SH) and (4) 3 wt % Al2O3 and 2 wt% HA (32AH). Microstructural observations revealed that martensite transformation between α and β-Ti in composites resulted in compressive residual stress at the matrix. Coherency is observed between the ceramic particles and Ti64 matrix, preventing cracking, debonding, or porosity. Vicker's hardness of the composite samples increases by 50% over the Ti64 matrix. Various strengthening mechanisms are discussed in detail, representing the reason behind the reduction of compound wear in 5S and 5A composites. Si3N4-added composites demonstrated an antibacterial response against gram-positive Staphylococcus aureus. The multifunctional performance of ceramic-reinforced Ti64 composites makes them suitable for articulating biomedical devices such as femoral heads in hip implants.

Effect of 20 μm thin ceramic coatings of hydroxyapatite, bioglass, GB14 and Beta-Tricalciumphosphate with copper on the biomechanical stability of femoral implants

In the present work, we test four thin coatings for titanium implants, namely, bioglass, GB14, Beta-Tricalciumphosphate (β-TCP) and hydroxyapatite (HA) with and without incorporated copper ions for their osteointegrative capacity. A rabbit drill hole model for time intervals up to 24 weeks was used in this study. Implant fixation was evaluated by measuring shear strength of the implant/bone interface. Quantitative histological analysis was performed for the measurements of bone contact area. Implants with and without copper ions were compared after 24 weeks. Thin coatings of GB14, HA or TCP on titanium implants demonstrated high shear strength during the entire test period of up to 24 weeks. Results confirmed osteointegrative properties of the coatings and did not reveal any negative effect of copper ions on osteointegration. The integration of copper in degradable osteoconductive coatings with a thickness of approx. 20 μm represents a promising method of achieving antibacterial shielding during the entire period of bone healing while at the same time improving osteointegration of the implants.

Improving Biocompatibility for Next Generation of Metallic Implants

The increasing need for joint replacement surgeries, musculoskeletal repairs, and orthodontics worldwide prompts emerging technologies to evolve with healthcare's changing landscape. Metallic orthopaedic materials have a shared application history with the aerospace industry, making them only partly efficient in the biomedical domain. However, suitability of metallic materials in bone tissue replacements and regenerative therapies remains unchallenged due to their superior mechanical properties, eventhough they are not perfectly biocompatible. Therefore, exploring ways to improve biocompatibility is the most critical step toward designing the next generation of metallic biomaterials. This review discusses methods of improving biocompatibility of metals used in biomedical devices using surface modification, bulk modification, and incorporation of biologics. Our investigation spans multiple length scales, from bulk metals to the effect of microporosities, surface nanoarchitecture, and biomolecules such as DNA incorporation for enhanced biological response in metallic materials. We examine recent technologies such as 3D printing in alloy design and storing surface charge on nanoarchitecture surfaces, metal-on-metal, and ceramic-on-metal coatings to present a coherent and comprehensive understanding of the subject. Finally, we consider the advantages and challenges of metallic biomaterials and identify future directions.

Characteristics of Hydroxyapatite-Modified Coatings Based on TiO2 Obtained by Plasma Electrolytic Oxidation and Electrophoretic Deposition

In order to modify the surface of light metals and alloys, plasma electrolytic oxidation (PEO) is a useful electrochemical technique. During the oxidation process, by applying a positive high voltage greater than the dielectric breakdown value of the oxide layer, the formation of a ceramic film onto the substrate material is enabled. The resulting surface presents hardness, chemical stability, biocompatibility, and increased corrosion wear resistance. The current study aims to investigate the corrosion resistance and tribological properties of PEO-modified coatings on titanium substrates produced by applying either direct or pulsed current in a silicate-alkaline electrolyte. In this way, a uniform TiO₂ layer is formed, and subsequently, electrophoretic deposition of hydroxyapatite particles (HAP) is performed. The morpho-structural characteristics and chemical composition of the resulting coatings are investigated using scanning electron microscopy combined with energy dispersive spectroscopy analysis and X-ray diffraction. Dry sliding wear testing of the TiO₂ and HAP-modified TiO₂ coatings were carried out using a ball-on-disc configuration, while the corrosion resistance was electrochemically evaluated at 37 °C in a Ringer's solution. The corrosion rates of the investigated samples decreased significantly, up to two orders of magnitude, when the PEO treatment was applied, while the wear rate was 50% lower compared to the untreated titanium substrate.

The application of biomaterials in osteogenesis: A bibliometric and visualized analysis

Osteogenesis serves an important role in bone tissue repairing. Novel biomaterials are widely prevalent as materials for orthopedic implants due to their biocompatibility and osteogenetic ability. The purpose of this study was to comprehensively analyze hotspots and future trend of biomaterials research in osteogenesis based on bibliometric and visualized analysis. A total of 1,523 papers about biomaterials research in osteogenesis between 2000 and 2021 were included in this study. During the above 20 years, China’s leading position in the global biomaterials research in osteogenesis was obvious, and it was also the country that most frequently participates in international cooperation. Chinese Academy of Sciences was the most productive institution and the leader of research cooperation. Acta Biomaterialia and Biomaterials have published the largest number of articles in the field of biomaterials research in osteogenesis. Meanwhile, Acta Biomaterialia and Biomaterials were also the two journals with the highest total citation frequency. Wu CT, Chang J, Kaplan DL, and Xiao Y all made important contributions in the field of biomaterials research in osteogenesis. At present, there are five research hotspots in the field of biomaterials research in osteogenesis: 1) the immunomodulatory role of biomaterial-related inflammatory; 2) mechanisms of osteogenesis in biomaterials; 3) 3D printing and clinical application of biomaterials; 4) bone tissue engineering for biomaterial osteogenesis; and 5) regenerative medicine for biomaterial osteogenesis. The results of this study showed that mechanisms of osteogenesis in biomaterials, bone tissue engineering for biomaterial osteogenesis, and regenerative medicine for biomaterial osteogenesis will remain research hotspots in the future. International cooperation was also expected to expand and deepen the field of biomaterials research in osteogenesis.

Osteogenesis Performance of Boronized Ti6Al4V/HA Composites Prepared by Microwave Sintering: In Vitro and In Vivo Studies

The boronized Ti6Al4V/HA composite is deemed to be an important biomaterial because of its potential remarkable mechanical and biological properties. This paper reports the osteogenesis performance of the boronized Ti6Al4V/HA composite, which was prepared by microwave sintering of powders of Ti6Al4V, hydroxyapatite (HA), and TiB₂ in high-purity Ar gas at 1050 °C for 30 min, as dental implant based on both cell experiments in vitro and animal experiments in vivo. The comparison between the boronized Ti6Al4V/HA composite and Ti, Ti6Al4V, and boronized Ti6Al4V in the terms of adhesion, proliferation, alkaline phosphate (ALP) activity, and mineralization of MG-63 cells on their surfaces confirmed that the composite exhibited the best inductive osteogenesis potential. It exerted a more significant effect on promoting the early osteogenic differentiation of osteoblasts and exhibited the maximum optical density (OD) value in the MTT assay and the highest levels of ALP activity and mineralization ability, primarily ascribed to its bioactive HA component, porous structure, and relatively rough micro-morphology. The in vivo study in rabbits based on the micro-computed tomography (micro-CT) analysis, histological and histomorphometric evaluation, and biomechanical testing further confirmed that the boronized Ti6Al4V/HA composite had the highest new bone formation potential and the best osseointegration property after implantation for up to 12 weeks, mainly revealed by the measured values of bone volume fraction, bone implant contact, and maximum push-out force which, for example, reached 48.64%, 61%, and 150.3 ± 6.07 N at the 12th week. Owing to these inspiring features, it can serve as a highly promising dental implant.

Effects of Diatomite Contents on Microstructure, Microhardness, Bioactivity and Biocompatibility of Gradient Bioceramic Coating Prepared by Laser Cladding

Biometallic materials are widely used in medicine because of excellent mechanical properties. However, biometallic materials are limited in the application of biomaterials due to their lack of bioactivity. To solve this problem, a gradient bioceramic coating doped with diatomite (DE) was successfully fabricated on the surface of Ti6Al4V alloy by using the broadband-laser cladding process to improve the bioactivity of metal materials. As well as the DE contents on the microstructure, microhardness, bioactivity and biocompatibility were investigated. The experimental results demonstrate that the addition of moderate amounts of DE is effective in reducing the number of cracks. The X-ray diffraction (XRD) results reveal that the bioceramic coating doped with DE mainly consists of CaTiO3, hydroxyapatite (HA), tricalcium phosphate (TCP) and silicate, and that the amount of HA and TCP in the coating reached maximum when the bioceramic coating was doped with 10wt% DE. The bioceramic coating doped with 10wt% DE has favorable ability to deposit bone-like apatite. These results indicate that the addition of DE can improve cracking sensibility, bioactivity and biocompatibility of the coating.

Bioactive Surface Modifications through Thermally Sprayed Hydroxyapatite Composite Coatings: A Review over Selective Reinforcements

Hydroxyapatite (HA) has been an excellent replacement for the natural bone in orthopedic applications, owing to its close resemblance; however, it is brittle and has low strength. Surface modification techniques...

Mechanical properties and biomedical application characteristics of degradable polylactic acid-Mg-Ca3(PO4)2 three-phase composite

Polylactic acid (PLA), pure magnesium powder, and calcium phosphate powder were used to form a three-phase degradable biomedical composite. The effects of various powder proportions in polylactic acid-Mg-Ca₃(PO₄)₂ composites were analyzed through mechanical and biological tests, which revealed that both the tensile and impact strength of the composite increased. Additionally, ductility presented only after a small proportion of powder was added. Hardness slightly increased because of dispersion strengthening. Furthermore, the addition of pure magnesium and calcium phosphate accelerated the degradation rate, and biocompatible salts were generated after degradation, which can improve healing and renewal in bone tissue. None of the composites exhibited cytotoxicity, meeting biological safety requirements. Overall, PLA10M10C (10 wt.% Mg, 10 wt.% Ca₃(PO₄)₂) exhibited superior performance. Accordingly, PLA10M10C can serve as a reference for degradable biomedical material applications in orthopedic implants.

Engineering functional skin constructs: A quantitative comparison of three-dimensional bioprinting with traditional methods

Tissue engineering has been successful in reproducing human skin equivalents while incorporating new approaches such as three-dimensional (3D) bioprinting. The latter method offers a plethora of advantages including increased production scale, ability to incorporate multiple cell types and printing on demand. However, the quality of printed skin equivalents compared to those developed manually has never been assessed. To leverage the benefits of this method, it is imperative that 3D-printed skin should be structurally and functionally similar to real human skin. Here, we developed four bilayered human skin epidermal-dermal equivalents: non-printed dermis and epidermis (NN), printed dermis and epidermis (PP), printed epidermis and non-printed dermis (PN), and non-printed epidermis and printed dermis (NP). The effects of printing induced shear stress [0.025 kPa (epidermis); 0.049 kPa (dermis)] were characterized both at the cellular and at the tissue level. At cellular level, no statistically significant differences in keratinocyte colony-forming efficiency (CFE) (p = 0.1641) were observed. In the case of fibroblasts, no significant differences in the cell alignment index (p < 0.1717) and their ability to contract collagen gel (p = 0.851) were detected. At the tissue levels, all the four skin equivalents were characterized using histological and immunohistochemical analysis with no significant differences found in either epidermal basal cell count, thickness of viable epidermis, and relative intensity of filaggrin and claudin-1. Our results demonstrated that 3D printing can achieve the same high-quality skin constructs as have been developed traditionally, thus opening new avenues for numerous high-throughput industrial and clinical applications.