Nanomechanical and tribological behavior of hydroxyapatite reinforced ultrahigh molecular weight polyethylene nanocomposites for biomedical applications

Calcium Orthophosphate (CaPO4) Containing Composites for Biomedical Applications: Formulations, Properties, and Applications

The goal of this review is to present a wide range of hybrid formulations and composites containing calcium orthophosphates (abbreviated as CaPO4) that are suitable for use in biomedical applications and currently on the market. The bioactive, biocompatible, and osteoconductive properties of various CaPO4-based formulations make them valuable in the rapidly developing field of biomedical research, both in vitro and in vivo. Due to the brittleness of CaPO4, it is essential to combine the desired osteologic properties of ceramic CaPO4 with those of other compounds to create novel, multifunctional bone graft biomaterials. Consequently, this analysis offers a thorough overview of the hybrid formulations and CaPO4-based composites that are currently known. To do this, a comprehensive search of the literature on the subject was carried out in all significant databases to extract pertinent papers. There have been many formulations found with different material compositions, production methods, structural and bioactive features, and in vitro and in vivo properties. When these formulations contain additional biofunctional ingredients, such as drugs, proteins, enzymes, or antibacterial agents, they offer improved biomedical applications. Moreover, a lot of these formulations allow cell loading and promote the development of smart formulations based on CaPO4. This evaluation also discusses basic problems and scientific difficulties that call for more investigation and advancements. It also indicates perspectives for the future.

Biomimetic Robust All-Polymer Porous Coatings for Passive Daytime Radiative Cooling

Passive daytime radiation cooling (PDRC) has gained considerable attention as an emerging and promising cooling technology. Polymer-based porous materials are one of the important candidates for PDRC application due to their easy processing, free of inorganic particle doping, and multifunctionality. However, the mechanical properties of these porous materials, which are critical in outdoor services, have been overlooked in previous studies. Herein, a nonsolvent-induced phase separation (NIPS) method combined with ambient pressure drying to prepare polyethylene-polysilicate all-polymer porous coatings is developed. The coatings possess a Cyphochilus beetle-like skeleton structure with optimal skeleton size, laminated anisotropy, and high volume fraction (64 ± 1%). These structure features ensure a maximum skeleton density without optical crowding, thus enhancing light scattering and stress dispersion, and balancing optical and mechanical properties. The coatings exhibit significant mechanical robustness (only ≈70 µm thickness reduction after 1000 Taber abrasion cycles at a 750 g load without influencing optical performance), durability, optical properties (a solar reflectance of ≈95% and an average near-normal thermal emittance of ≈96%), and PDRC performance (realizing sub-ambient cooling of ≈3-6 °C at midday with different weather conditions). The work provides a new solution to improve the practicability of polymer-based porous coatings in PDRC outdoor services and other fields.

Synthetic Polymeric Materials for Bone Replacement

Some treatment options available to repair bone defects are the use of autogenous and allogeneic bone grafts. The drawback of the first one is the donor site’s limitation and the need for a second operation on the same patient. In the allograft method, the problems are associated with transmitted diseases and high susceptibility to rejection. As an alternative to biological grafts, polymers can be used in bone repair. Some polymers used in the orthopedic field are poly(methyl methacrylate), poly(ether-ether-ketone), and ultra-high molecular weight polyethylene (UHMWPE). UHMWPE has drawn much attention since it combines low friction coefficient and high wear and impact resistance. However, UHMWPE is a bioinert material, which means that it does not interact with the bone tissue. UHMWPE composites and nanocomposites with hydroxyapatite (HA) are widely studied in the literature to mitigate these issues. HA is the main component of the inorganic phase in the natural bone, and the addition of this bioactive filler to the polymeric matrix aims to mimic bone composition. This brief review discusses some polymers used in orthopedic applications, focusing on the UHMWPE/HA composites as a potential bone substitute.

Ultra-high molecular weight polyethylene bioactive composites with carbonated hydroxyapatite

To develop an orthopedic material for bone substitution, the substitute material must mimic living tissue from an anatomical and physiological point of view. The high wear and impact resistance besides the low friction coefficient, make ultra-high molecular weight polyethylene (UHMWPE) a suitable material to be used in orthopedic applications. However, UHMWPE is a bioinert material, not providing a proper interaction with the bone tissue surrounding to the implant. One way to mitigate this issue is improving UHMWPE bioactivity. This can be done by adding bioactive fillers in the polymeric matrix. In this work, UHMWPE composites were prepared by twin-screw extrusion. The fillers used were carbonated hydroxyapatite (CHA) and hybrids formed by precipitating CHA in collagens (hydrolyzed and type II). The results show that the fillers used caused a slight reduction in UHMWPE crystallinity degree, while both crystallization and melting temperatures remained almost unchanged. Dynamic-mechanical thermal analysis indicated a weak adhesion between filler and polymeric matrix, which is good from the biological point of view since the bioactive filler surface will be available to apatite deposition. The obtained materials exhibited good mechanical properties and in vitro bioactivity assay showed that all of the prepared materials are bioactive.

Nano-Indentation Response of Ultrahigh Molecular Weight Polyethylene (UHMWPE): A Detailed Analysis

Nano-indentation, a depth sensing technique, is a useful and exciting tool to investigate the surface mechanical properties of a wide range of materials, particularly polymers. Knowledge of the influence of experimental conditions employed during nano-indentation on the resultant nano-mechanical response is very important for the successful design of engineering components with appropriate surface properties. In this work, nano-indentation experiments were carried out by selecting various values of frequency, amplitude, contact depth, strain rate, holding time, and peak load. The results showed a significant effect of amplitude, frequency, and strain rate on the hardness and modulus of the considered polymer, ultrahigh molecular weight polyethylene (UHMWPE). Load-displacement curves showed a shift towards the lower indentation depths along with an increase in peak load by increasing the indentation amplitude or strain rate. The results also revealed the strong dependence of hardness and modulus on the holding time. The experimental data of creep depth as a function of holding time was successfully fitted with a logarithmic creep model (R² ≥ 0.98). In order to remove the creeping effect and the nose problem, recommended holding times were proposed for the investigated polymer as a function of different applied loads.

Biomimetic UHMWPE/HA scaffolds with rhBMP-2 and erythropoietin for reconstructive surgery

A promising direction for the replacement of expanded bone defects is the development of bioimplants based on synthetic biocompatible materials impregnated with growth factors that stimulate bone remodeling. Novel biomimetic highly porous ultra-high molecular weight polyethylene (UHMWPE)/40% hydroxyapatite (HA) scaffold for reconstructive surgery with the porosity of 85 ± 1% vol. and a diameter of pores in the range of 50-800 μm was developed. The manufacturing process allowed the formation of trabecular-like architecture without additional solvents and thermo-oxidative degradation. Biomimetic UHMWPE/HA scaffold was biocompatible and provided effective tissue ingrowth on a model of critical-sized cranial defects in mice. The combined use of UHMWPE/HA with Bone Morphogenetic Protein-2 (BMP-2) demonstrated intensive mineralized bone formation as early as 3 weeks after surgery. The addition of erythropoietin (EPO) significantly enhanced angiogenesis in newly formed tissues. The effect of EPO of bacterial origin on bone tissue defect healing was demonstrated for the first time. The developed biomimetic highly porous UHMWPE/HA scaffold can be used separately or in combination with rhBMP-2 and EPO for reconstructive surgery to solve the problems associated with difference between implant architecture and trabecular bone, low osteointegration and bioinertness.

Influence of purified multiwalled carbon nanotubes on the mechanical and morphological behavior in poly (L-lactic acid) matrix

Poly (L-latic acid) (PLLA) is a bioresorbable polymer widely used as a biomaterial, but its fragility can limit its use. An alternative is to produce polymer nanocomposites, which can enhance the mechanical properties of polymeric matrix, resulting in a material with differentiated properties. In this work, PLLA based nanocomposites containing 0.25, 0.5 and 1.0wt% of purified multiwalled carbon nanotubes (p-MWCNTs) were prepared by the solvent casting method. The morphology and mechanical properties results show an improvement in strain at break for 0.25 and 0.5wt% p-MWCNTs and an increase in stiffness and elastic modulus for all compositions. Nanocomposites presented a p-MWCNTs agglomeration; however, there was a good stress transfer between PLLA and p-MWCNTs, which was confirmed by the increase in the hardness and elastic modulus. Atomic force microscopy analysis indicated an increase in roughness after nanotube addition. The in vitro biological study showed that PLLA/p-MWCNTs nanocomposites are cytocompatible with osteoblasts cells. The capacity of PLLA nanocomposites to stimulate osteogenesis was investigated by alkaline phosphatase (ALP) activity assay. Higher ALP activity was found on osteoblasts cultured on nanocomposites with 0.25 and 0.5wt% p-MWCNT compared to neat PLLA, confirming that PLLA cytocompatibility was improved on these compositions. Finally, our results showed that by a simple and inexpensive solvent casting method, it is possible to manufacture biofunctional nanocomposites devices with potential for orthopedic applications.

Polymeric nanobiocomposites for biomedical applications

Polymeric nanobiocomposites have recently become one of the most essential sought after materials for biomedical applications ranging from implants to the creation of gels. Their unique mechanical and biological properties provide them the ability to pass through the highly guarded defense mechanism without undergoing noticeable degradation and initiation of immune responses, which in turn makes them advantageous over the other alternatives. Aligned with the advances in tissue engineering, it is also possible to design three-dimensional extracellular matrix using these polymeric nanobiocomposites that could closely mimic the human tissues. In fact, unique polymer chemistry coupled with nanoparticles could create unique microenvironment that promotes cell growth and differentiation. In addition, the nanobiocomposites can also be devised to carry drugs efficiently to the target site without exhibiting any cytotoxicity as well as to eradicate surgical infections. In this article, an effort has been made to thoroughly review a number of different types/classes of polymeric nanocomposites currently used in biomedical fields. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1241-1259, 2017.

Structure, apatite inducing ability, and corrosion behavior of chitosan/halloysite nanotube coatings prepared by electrophoretic deposition on titanium substrate

In this study chitosan/halloysite nanotube composite (CS/HNT) coatings were deposited by electrophoretic deposition (EPD) on titanium substrate. Using HNT particles were investigated as new substituents for carbon nanotubes (CNTs) in chitosan matrix coatings. The ability of chitosan as a stabilizing, charging, and blending agent for HNT particles was exploited. Furthermore, the effects of pH, electrophoretic bath, and sonicating duration were studied on the deposition of suspensions containing HNT particles. Microstructure properties of coatings showed uniform distribution of HNT particles in chitosan matrix to form smooth nanocomposite coatings. The zeta potential results revealed that at pH around 3 there is an isoelectric point for HNT and it would have cathodic and anionic states at pH values less and more than 3, respectively. Therefore, CS/HNT composite deposits were produced in the pH range of 2.5 to 3. The apatite inducing ability of chitosan-HNT composite coating assigned that HNT particles were biocompatible because they formed carbonated hydroxyapatite particles on CS/HNT coating in corrected simulated body fluid (C-SBF). Finally, electrochemical corrosion characterizations determined that corrosion resistance in CS/HNT coating has been improved compared to bare titanium substrate.

Calcium Orthophosphate-Containing Biocomposites and Hybrid Biomaterials for Biomedical Applications

The state-of-the-art on calcium orthophosphate (CaPO4)-containing biocomposites and hybrid biomaterials suitable for biomedical applications is presented. Since these types of biomaterials offer many significant and exciting possibilities for hard tissue regeneration, this subject belongs to a rapidly expanding area of biomedical research. Through the successful combinations of the desired properties of matrix materials with those of fillers (in such systems, CaPO4 might play either role), innovative bone graft biomaterials can be designed. Various types of CaPO4-based biocomposites and hybrid biomaterials those are either already in use or being investigated for biomedical applications are extensively discussed. Many different formulations in terms of the material constituents, fabrication technologies, structural and bioactive properties, as well as both in vitro and in vivo characteristics have been already proposed. Among the others, the nano-structurally controlled biocomposites, those containing nanodimensional compounds, biomimetically fabricated formulations with collagen, chitin and/or gelatin, as well as various functionally graded structures seem to be the most promising candidates for clinical applications. The specific advantages of using CaPO4-based biocomposites and hybrid biomaterials in the selected applications are highlighted. As the way from a laboratory to a hospital is a long one and the prospective biomedical candidates have to meet many different necessities, the critical issues and scientific challenges that require further research and development are also examined.

Biocompatibility and compressive properties of Ti-6Al-4V scaffolds having Mg element

Porous scaffolds of Ti-6Al-4V were produced by mixing of this alloy with different amount of magnesium (Mg) powders. The mixtures were compacted in steel die by applying uniaxial pressure of 500 MPa before sintering the compacts in sealed quartz tubes at 900 °C for 2 h. Employing Archimedes׳ principle and Image Tool software, the total and open volume percentages of porosities within the scaffolds were found to be in the range of 47-64% and 41-47%, respectively. XRD results of titanium before and after sintering showed that no contamination, neither oxides nor nitrides formed during processes. Compressive properties of the scaffolds were studied using an Instron machine. The observed compressive strength and Young׳s module of the scaffolds were in the range of 72-132 MPa, and 37-47 GPa, respectively. Cell attachment and proliferation rate of MG-63 on porous samples were investigated. The results showed that proliferation rate increased with increasing Mg content. However no clear differences were observed between samples regarding cell attachment, so that bridges were observed in all cell gaps within the scaffolds.