Powder metallurgical Ti-Mg metal-metal composites facilitate osteoconduction and osseointegration for orthopedic application

Silk-Fabric Reinforced Silk for Artificial Bones

Bone implants for different body parts require varying mechanical properties, dimensions, and biodegradability rates. Currently, it is still challenging to produce artificial bones with perfect compatibility with human bones. In this study, a silk-fabric reinforced silk material (SFS) composed of pure silk with exceptional biocompatibility, osteogenesis, and biodegradability is reported, and demonstrates its outstanding performance as a bone implant material. The SFS is fabricated using a simple hot-pressing technique, with degummed silk fabric as the reinforcement and silk fibroin as the matrix. The SFS as a self-reinforced composite, has exceptional mechanical properties due to the almost perfect interface between the matrix and reinforcement. More importantly, its mechanical properties, biodegradability rates, and density can be tailored by adjusting the reinforcement structure and the ratio of the reinforcement to the matrix to align with the requirements for bone implantation in different parts of the human body. Besides, the SFS can improve osteoblastic proliferation and increase osteogenic activity, which is not the case with clinically used titanium alloy artificial bone. Therefore, the SFS holds significant potential to replace conventional metal or ceramic implants in the field of medical fracture repair.

Sequentially activating macrophages M1 and M2 phenotypes by lipopolysaccharide-containing Mg-Fe layered double hydroxides coating on the Ti substrate

As cells of innate immunity, macrophages are a class of innate immune cells existing in almost all tissues and play a crucial role in bone repair. However, it remains a challenge to modulate the sequential activation of the deferent phenotypes in macrophage when designing the titanium (Ti) implants. In this study, the Mg-Fe layered double hydroxides (LDHs) was coated on Ti substrate through hydrothermal treatment. Further on lipopolysaccharide (LPS) was introduced onto the LDHs through adsorption and ions exchange. The adsorption efficiency of the coating on LPS reached 72.8% in 24 h due to the anion exchange and electrostatic interactions between the LPS and the LDH layers in deionized water. The LDHs-LPS coating released a large amount of LPS in the early stage, which induced macrophages into M1 phenotype via activating TLR-4 → MyD88 and TLR-4 → Ticam-1/2 signal pathways. Subsequently, the M1 macrophages were transformed into M2 phenotype by regulating the integrin α5β1 of cells by the nanostructures, wetting angle and Mg²⁺ of the coating. The LDHs-LPS coating endows Ti with the ability of stage immunomodulation, indicating the positive osteoimmunomodulatory property.

Biodegradability and Cytocompatibility of 3D-Printed Mg-Ti Interpenetrating Phase Composites

Orthopedic hybrid implants combining both titanium (Ti) and magnesium (Mg) have gained wide attraction nowadays. However, it still remains a huge challenge in the fabrication of Mg-Ti composites because of the different temperatures of Ti melting point and pure Mg volatilization point. In this study, we successfully fabricated a new Mg-Ti composite with bi-continuous interpenetrating phase architecture by infiltrating Mg melt into Ti scaffolds, which were prepared by 3D printing and subsequent acid treatment. We attempted to understand the 7-day degradation process of the Mg-Ti composite and examine the different Mg2+ concentration composite impacts on the MC3T3-E1 cells, including toxicity, morphology, apoptosis, and osteogenic activity. CCK-8 results indicated cytotoxicity and absence of the Mg-Ti composite during 7-day degradation. Moreover, the composite significantly improved the morphology, reduced the apoptosis rate, and enhanced the osteogenic activity of MC3T3-E1 cells. The favorable impacts might be attributed to the appropriate Mg2+ concentration of the extracts. The results on varying Mg2+ concentration tests indicated that Mg2+ showed no cell adverse effect under 10-mM concentration. The 8-mM group exhibited the best cell morphology, minimum apoptosis rate, and maximum osteogenic activity. This work may open a new perspective on the development and biomedical applications for Mg-Ti composites.

Combining Mg–Zn–Ca Bulk Metallic Glass with a Mesoporous Silica Nanocomposite for Bone Tissue Engineering

Mg–Zn–Ca bulk metallic glass (BMG) is a promising orthopedic fixation implant because of its biodegradable and biocompatible properties. Structural supporting bone implants with osteoinduction properties for effective bone regeneration have been highly desired in recent years. Osteogenic growth peptide (OGP) can increase the proliferation and differentiation of mesenchymal stem cells and enhance the mineralization of osteoblast cells. However, the short half-life and non-specificity to target areas limit applications of OGP. Mesoporous silica nanoparticles (MSNs) as nanocarriers possess excellent properties, such as easy surface modification, superior targeting efficiency, and high loading capacity of drugs or proteins. Accordingly, we propose a system of combining the OGP-containing MSNs with Mg–Zn–Ca BMG materials to promote bone regeneration. In this work, we conjugated cysteine-containing OGP (cgOGP, 16 a.a.) to interior walls of channels in MSNs and maintained the dispersity of MSNs via PEGylation. An in vitro study showed that metal ions released from Mg–Zn–Ca BMG promoted cell proliferation and migration and elevated alkaline phosphatase (ALP) activity and mineralization. On treating cells with both BMG ion-containing Minimum Essential Medium Eagle-alpha modification (α-MEM) and OGP-conjugated MSNs, enhanced focal adhesion turnover and promoted differentiation were observed. Hematological analyses showed the biocompatible nature of this BMG/nanocomposite system. In addition, in vivo micro-computed tomographic and histological observations revealed that our system stimulated osteogenesis and new bone formation around the implant site.

Design of patient specific bone stiffness mimicking scaffold

The difference in stiffness of a patient's bone and bone implant causes stress shielding. Thus, implants which match the stiffness of bone of the patient result in better bone growth and osseointegration. Variation in porosity is one of the methods to obtain implants with different stiffness values. This study proposes a novel method to design biomimetic bone graft implant based on computed tomography (CT) scan data, that creates similar pre- and post-implant mechanical environment on peri-implant bone. The design methodology is demonstrated by taking three different sections of human femur bone, greater trochanter, diaphysis and epicondyle, with two different implant materials, Ti-6Al-4V and Ti-Mg. Bones from these three sections were replaced with porous implants of effective stiffness of replaced bone, as would have been required after a resection surgery. Models were simulated with physiological loading condition using finite element (FE) method. Variation of maximum von Mises stress and average strain on peri-prosthetic bone were found to be in the range of -6% to 10.7% and -7% to -17.9% for porous implants and 26% to 50% and -36% to -59% for solid implant respectively compared to natural bone. The results revealed that the porous implants, which have been designed based on CT scan data, can effectively produce mechanical response at peri-implant bone, which is very close to pre-implanted condition. Following this methodology, more osseointegration friendly mechanical environment can be achieved at peri-implant bone for any anatomical location independent of implant materials.

An alternative ex vivo method to evaluate the osseointegration of Ti-6Al-4V alloy also combined with collagen

Due to the increasing number of orthopedic implantation surgery and advancements in biomaterial manufacturing, chemistry and topography, there is an increasing need of reliable and rapid methods for the preclinical investigation of osseointegration and bone ingrowth. Implant surface composition and topography increase osteogenicity, osteoinductivity, osteoconductivity and osseointegration of a prosthesis. Among the biomaterials used to manufacture an orthopedic prosthesis, titanium alloy (Ti-6Al-4V) is the most used. Type I collagen (COLL I) induces cell function, adhesion, differentiation and bone extracellular matrix component secretion and it is reported to improve osseointegration if immobilized on the alloy surface. The aim of the present study was to evaluate the feasibility of an alternative ex vivo model, developed by culturing rabbit cortical bone segments with Ti-6Al-4V alloy cylinders (Ti-POR), fabricated through the process of electron beam melting (EBM), to evaluate osseointegration. In addition, a comparison was made with Ti-POR coated with COLL I (Ti-POR-COLL) to evaluate osseointegration in terms of bone-to-implant contact (BIC) and new bone formation (nBAr/TAr) at 30, 60 and 90 d of culture. After 30 and 60 d of culture, BIC and nBAr/TAr resulted significantly higher in Ti-POR-COLL implants than in Ti-POR. No differences have been found at 90 d of culture. With the developed model it was possible to distinguish the biomaterial properties and behavior. This study defined and confirmed for the first time the validity of the alternative ex vivo method to evaluate osseointegration and that COLL I improves osseointegration and bone growth of Ti-6Al-4V fabricated through EBM.

Are Titania Photocatalysts and Titanium Implants Safe? Review on the Toxicity of Titanium Compounds

Titanium and its compounds are broadly used in both industrial and domestic products, including jet engines, missiles, prostheses, implants, pigments, cosmetics, food, and photocatalysts for environmental purification and solar energy conversion. Although titanium/titania-containing materials are usually safe for human, animals and environment, increasing concerns on their negative impacts have been postulated. Accordingly, this review covers current knowledge on the toxicity of titania and titanium, in which the behaviour, bioavailability, mechanisms of action, and environmental impacts have been discussed in detail, considering both light and dark conditions. Consequently, the following conclusions have been drawn: (i) titania photocatalysts rarely cause health and environmental problems; (ii) despite the lack of proof, the possible carcinogenicity of titania powders to humans is considered by some authorities; (iii) titanium alloys, commonly applied as implant materials, possess a relatively low health risk; (iv) titania microparticles are less toxic than nanoparticles, independent of the means of exposure; (v) excessive accumulation of titanium in the environment cannot be ignored; (vi) titanium/titania-containing products should be clearly marked with health warning labels, especially for pregnant women and young children; (vi) a key knowledge gap is the lack of comprehensive data about the environmental content and the influence of titania/titanium on biodiversity and the ecological functioning of terrestrial and aquatic ecosystems.

Implantable PEKK/tantalum microparticles composite with improved surface performances for regulating cell behaviors, promoting bone formation and osseointegration

Polyetherketoneketone (PEKK) exhibits admirable biocompatibility and mechanical performances but bioinert while tantalum (Ta) possesses excellent osteogenesis and osseointegration but high elastic modulus and density, and processing is too difficult and expensive. In the present study, combining of the advantages of both PEKK and Ta, implantable composites of PEKK/Ta were fabricated by blending PEKK with Ta microparticles of 20 v% (PT20) and 40 v% (PT40) content. In comparison with PT20 and PEKK, the surface hydrophilicity, surface energy, roughness and proteins adsorption as well as mechanical performances of PT40 significantly increased because of the higher Ta particles content in PEKK. Furthermore, PT40 exhibited the mechanical performances (e.g., compressive strength and modulus of elasticity) close to the cortical bone of human. Compared with PT20 and PEKK, PT40 with higher Ta content remarkably enhanced the responses (including adhesion, proliferation and osteogenic differentiation) of MC3T3-E1 cells in vitro. Moreover, PT40 markedly improved bone formation as well as osseointegration in vivo. In short, incorporation of Ta microparticles into PEKK created implantable composites with improved surface performances, which played key roles in stimulating cell responses/bone formation as well as promoting osseointegration. PT40 might have great potential for bear-loading bone substitute.

Fabrication of Ti + Mg composites by three-dimensional printing of porous Ti and subsequent pressureless infiltration of biodegradable Mg

A semi-degradable Ti + Mg composite with superior compression and cytotoxicity properties have been successfully fabricated using ink jet 3D printing followed by capillary mediated pressureless infiltration technique targeting orthopaedic implant applications. The composite exhibited low modulus (~5.2 GPa) and high ultimate compressive strength (~418 MPa) properties matching that of the human cortical bone. Ti + Mg composites with stronger 3D interconnected open-porous Ti networks are possible to be fabricated via 3D printing. Corrosion rate of samples measured through immersion testing using 0.9%NaCl solution at 37 °C indicate almost negligible corrosion rate for porous Ti (~1.14 μm/year) and <1 mm/year for Ti + Mg composites for 5 days of immersion, respectively. The composite significantly increased the SAOS-2 osteoblastic bone cell proliferation rate when compared to the 3D printed porous Ti samples and the increase is attributed to the exogenous Mg²⁺ ions originating from the Ti + Mg samples. The cell viability results indicated absent to mild cytotoxicity. An attempt is made to discuss the key considerations for net-shape fabrication of Ti + Mg implants using ink jet 3D printing followed by infiltration approach.

Dual delivery of encapsulated BM-MSCs and BMP-2 improves osteogenic differentiation and new bone formation

Stem cell-based therapies provide a promising approach for bone repair. In the present work, we developed a novel 3D vehicle system for dual-delivery of encapsulated bone marrow mesenchymal stem cells (BM-MSCs) and bone morphogenetic protein-2 (BMP-2) for treatment of large bone defects. The vehicle system consists of sodium alginate microcapsules and polylactic acid (PLLA) microspheres. BM-MSCs are encapsulated in the microcapsules, and BMP-2 proteins are encapsulated in the PLLA microspheres. This vehicle system acted as a multicore structure for sustained release of BMP-2, which enabled pulsed dosing induction of osteogenic differentiation of the co-embedded BM-MSCs. in vitro experiments showed that the loaded BMP-2 was constitutively released up to 30 days. Bioactivity of the incorporated BMP-2 in the microspheres was preserved and osteogenic differentiation of the BM-MSCs in the microcapsules was improved. In vivo, osteogenesis studies demonstrated that satisfactory degree of repair of a rat calvarial defect was achieved with the delivery of either encapsulated BM-MSCs alone or encapsulated BMP-2 alone. Transplantation of encapsulated both BM-MSCs and BMP-2 exhibited the greatest repair potential following 4- or 8-weeks treatment. In conclusion, microencapsulation of BM-MSCs and BMP-2 promoted the maturity of newly generated bone and improved new bone formation. Transplantation of BM-MSCs and BMP-2 in our novel 3-D vehicle system is a promising strategy for regenerative therapies of large bone defects.