Synthetic Polymeric Materials for Bone Replacement

Ultra high molecular weight polyethylene has been commonly used as a biomaterial for total joint replacements. This article concerns with the characterization of nano composites of ultra high molecular weight polyethylene (UHMWPE) with Mg0.15Ni0.15Zn0.70Fe2O3 using analytic techniques such as differential scanning calorimetry (DSC), and thermo gravimetric analysis (TGA). UHMWPE purchased from Sigma Aldrich was used for studies and preparation of nano composites with 1wt% and 2wt% Mg0.15Ni0.15Zn0.70Fe2O3 using the ball milling method. The thermal stability of composites with 1 % of Mg0.15Ni0.15Zn0.70Fe2O3 contents were less stable compared to pure UHMWPE and UHMWPE composites with 2wt% of nano scale Mg0.15Ni0.15Zn0.70Fe2O3. The degree of crystallinity obtained from DSC data was 41%, 40%, and 43% for UHMWPE, UHMWPE+1% of Mg0.15Ni0.15Zn0.70Fe2O3, and UHMWPE+2% of Mg0.15Ni0.15Zn0.70Fe2O3, respectively. The results of current study are useful while considering the nano composites of UHMWPE with Mg0.15Ni0.15Zn0.70Fe2O3 in order to enhance the mechanical strength of UHWMPE for industrial as well as medical applications such as orthopedic implants and bullet proof jackets etc.

The selection of biomaterials as biomedical implants is a significant challenge. Ultra-high molecular weight polyethylene (UHMWPE) and composites of such kind have been extensively used in medical implants, notably in the bearings of the hip, knee, and other joint prostheses, owing to its biocompatibility and high wear resistance. For the Anterior Cruciate Ligament (ACL) graft, synthetic UHMWPE is an ideal candidate due to its biocompatibility and extremely high tensile strength. However, significant problems are observed in UHMWPE based implants, such as wear debris and oxidative degradation. To resolve the issue of wear and to enhance the life of UHMWPE as an implant, in recent years, this field has witnessed numerous innovative methodologies such as biofunctionalization or high temperature melting of UHMWPE to enhance its toughness and strength. The surface functionalization/modification/treatment of UHMWPE is very challenging as it requires optimizing many variables, such as surface tension and wettability, active functional groups on the surface, irradiation, and protein immobilization to successfully improve the mechanical properties of UHMWPE and reduce or eliminate the wear or osteolysis of the UHMWPE implant. Despite these difficulties, several surface roughening, functionalization, and irradiation processing technologies have been developed and applied in the recent past. The basic research and direct industrial applications of such material improvement technology are very significant, as evidenced by the significant number of published papers and patents. However, the available literature on research methodology and techniques related to material property enhancement and protection from wear of UHMWPE is disseminated, and there is a lack of a comprehensive source for the research community to access information on the subject matter. Here we provide an overview of recent developments and core challenges in the surface modification/functionalization/irradiation of UHMWPE and apply these findings to the case study of UHMWPE for ACL repair.

Fabrication of composite using microwave energy is a rapid and emerging manufacturing route. This paper deals to address fabrication challenges during fabrication of nano-hydroxyapatite (HA) reinforced ultra-high molecular weight polyethylene (UHMWPE) composite by utilization of microwave energy. In the proposed fabrication technique, composite constituents were taken as UHMWPE and nano-HA powders with average particle size of 100 μm and 100 nm, respectively. In this work, the weight fraction of nano-HA was 10%, 15% and 20%. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) was done to confirm the dispersion of nano-HA (reinforcement) in UHMWPE (matrix). Mechanical behaviour of the fabricated composite was studied in terms of uniaxial tensile loading, flexural loading and Shore D hardness test. The thermal degradation of UHMWPE/nano-HA composite was studied using differential scanning calorimeter (DSC) and thermal gravimetric analysis (TGA). With addition of 20% wt% of nano-HA fillers, the comparative percentage increase in Young’s modulus, ultimate tensile strength, flexural strength and hardness of UHMWPE/nano-HA composite were 70.65%, 35.52%, 42.84% and 39.24%, respectively

Processing and mechanical properties of HA/UHMWPE nanocomposites

An analytical model for the ballistic performance of ultra-high molecular weight polyethylene composites

Ultra high molecular weight polyethylene (UHMWPE) is widely used in many orthopedic applications because of its good mechanical properties and excellent biocompatability. Mechanical properties are related to its ultra-high molecular weight, but the presence of defects in morphology will cause a decrease in these properties. The aim of this study was to characterize the microstructure and microchemistry of so-called “fusion defects”, observed by optical transmission microscopy, using SEM along with EDXS analysis. The fractured surface of UHMWPE was also studied.Defects similar to those found in commercially prepared UHMWPE were detected in the hot-pressed and extruded samples prepared at U-Mass Lowell using GUR 412. They consist of holes or cavities and sometimes appear to be circular in shape and are composed of variously sized small holes. The size of the defects is around 100 μm in diameter which is similar to the particle size of the raw powders.

Energy transition towards cleaner fuels and renewable energy brings the attention to liquefied natural gas (LNG) and liquid hydrogen (LH2) applications. Cryogenic storage temperatures make the suitable material selection for the construction of such applications difficult. Ultra-high molecular weight polyethylene (UHMWPE) thermoplastics are selected for this research to investigate their shear behavior performances with nanoadditives. Composites made of UHMWPE and carbon nano tubes (CNTs) are subjected to shear loading at room and liquid nitrogen (LN2) temperatures. Considering that UHMWPE films do not bond to other materials easily, significant attention is paid to selecting the correct manufacturing conditions to achieve good bonding between the CNT and the composite plies. Herein, paper formed of CNT, also known as CNT buckypaper (CNT BP), and melt mixed CNT/high density polyethylene (HDPE) are integrated to the structure. The results show that the interlaminar shear strength (ILSS) of UHMWPE composites improved 5% by interleaving the CNT BP with the lowest percentage which is 0.05 with respect to the reference and 8% by adding the melt mixed CNT/HDPE film at room temperature. Under the cryogenic condition, ILSS showed 3% increase with the CNT/HDPE film addition, but no improvement with the CNT BP addition. ? 2019 by German Aerospace Center (DLR). Published by the American Institute of Aeronautics and Astronautics, Inc.

Nanofiber-epoxy with reactive graphitic nanofibers (r-GNFs) showed an improvement in adhesion properties in ultra-high molecular weight polyethylene (UHMWPE) fibers/epoxy resin composite (bundle/tow form) in our previous experiments. In this study, moisture absorption characteristics of pure-epoxy, nanofiber-epoxy materials and their UHMWPE bundle composites were investigated under hygrothermal aging and UV conditions. For the matrix specimens the weight gain deviated from Fick's law, and thus, a two-stage model, which includes both diffusion and structural relaxation, was applied to analyze the moisture absorption behaviors. For the bundle composites the results indicated that the weight gain showed compatibility with Fick's law. The UHMWPE fiber composite with nanofiber-epoxy containing 0.3 wt% r-GNF loading resulted in the lowest rate of water absorption. Bundle composites were also exposed to accelerated UV aging conditions. The UV test results showed that the plateau stress and ultimate tensile strength of the bundle composites have been reduced. However, the ductility of the UHMWPE composites was increased due to the plasticization in hygrothermal aging tests.

Fiber metal laminates (FMLs) are a sandwich combination of alternate layer of metal and fiber-reinforced polymer (FRP) which has excellent specific strength, fatigue, stiffness and has potential application in defence, aerospace, marine, and automotive due to its high impact resistance. Sandwich combination of ultra-high molecular weight polyethylene (UHMWPE) fiber and an infusible thermoplastic Elium<sup>®</sup> matrix forms a complete thermoplastic FRP composite. Combining UHMWPE/Elium<sup>®</sup> composites with titanium metal alloy forms a hybrid UHMWPE-Ti FML which can be a promising material system for impact damage problems. In achieving optimal performance of this hybrid composite system, interfaces in the composite system play a critical role, which includes a fiber-matrix interface, interlaminar interface, and metal thermoplastic composite interface (MTCI). Therefore, proper tuning of these interfaces determines the overall performance of the hybrid composite system. Two different strategies have been adopted to improve the interfacial properties of the UHMWPE-Ti composites: i) modification of the interfaces in UHMWPE fiber-reinforced system, and ii) tuning of the MTCI via the surface treatment of titanium alloy. Multiwalled carbon nanotubes (MWCNTs) are incorporated into dopamine coating solution and applied onto UHMWPE fiber surface to enhance the interfacial bonding in UHMWPE fiber-reinforced system. The results from the transverse tensile fiber bundle test (TFBT) shows the interfacial strength of the prepared multi-scale phase reinforced composite (MPRC) can be significantly increased in comparison with that of the common composite. It is observed that densification of CNTs forest within the interphase between UHMWPE fiber and thermoplastic matrix during the formation of the nano-composite coating can lead to a high-volume fraction of CNTs within the interphase and augment effects of interface-interlocking, which makes the coating-modification method a more efficient way than a traditional matrix-tuning method for improving interfacial bonding. Results from double cantilever beam (DCB) test at 1 mm/min shows improvement in Mode I interlaminar fracture toughness (G<sub>IC</sub>) for PDA (polydopamine) surface-treated sample and PDA with embedded MWCNT when compared with that of a common composite (UHMWPE/Elium<sup>®</sup>) The surface of titanium alloy is treated by traditional anodization with post-processing of etching and annealing, which is multiple processing steps to improve the MTCI. The generated oxide layer on the metal alloy has the potential to react with recyclable thermoplastic Elium<sup>®</sup> resin matrix by the organo-metallic complex, facilitating the wettability of resin on the Ti metal surface. The double cantilever beam test was utilised to evaluate the G<sub>IC</sub> (Mode I interlaminar fracture toughness at MTCI) for the FML sample with surface treated fiber (PDA and PDA+CNT) and metal. The result shows, after the fiber and metal surface treatment, the average G<sub>1C</sub> can be increased and improving the delamination resistance at MTCI. Thus, surface treatment of fiber and metal can enhance the fiber-matrix interface, interlaminar interface and MTCI. After showing improved performance in the quasi-static test of FML composites, low-velocity dynamic impact test was performed at different impact energy for the fabricated FML. The results show less absorbed energy and low structural damage after the fiber and metal surface treatment. The delamination resistance offered at the composite interface due to surface treatment plays a pivotal role in enhancing the structural performance of UHMWPE-Ti FML composite.

From our previous study, 3 wt% of ultra-high-molecular-weight polyethylene (UHMWPE) powder surface-modified by various ratios of methyl methacrylate (MMA) and poly(methyl methacrylate) (PMMA) solution was impregnated to improve the poor mechanical and thermal properties of conventional PMMA bone cement. In this study, various amounts of benzoyl peroxide (BPO) and hydroquinone were used for the adhesion reinforcement of UHMWPE powder with PMMA polymerized from MMA monomer (polyMMA) by the mixture of BPO and hydroquinone and ultimately to strengthen the poor mechanical and thermal properties of conventional PMMA bone cement. The tensile strengths of 3 wt% of UHMWPE powders surface-precoated with polyMMA prepared by various amounts of BPO- and hydroquinone-impregnated composite PMMA bone cements were similar to that of conventional PMMA bone cement. In particular, 3 wt% of UHMWPE powder surface precoated with polyMMA prepared with 0.75 wt% of BPO and 300 ppm of hydroquinone impregnated composite PMMA bone cement revealed the maximum tensile strength. However, no obvious significant difference was revealed, although the curing temperatures of the composite PMMA bone cements decreased from 103°C to 91–97°C. From these results, it was determined that the mixture of BPO and hydroquinone plays an important role in improving the poor mechanical properties of conventional PMMA bone cement. However, the thermal properties of the composite PMMA bone cements were not remarkably improved. The mechanical, chemical and thermal properties were individually confirmed using a scanning electron microscope (SEM), universal transverse mercator (UTM), Fourier transform infrared-attenuated total reflectance (FT-IR–ATR) and digital thermometer, respectively.

To overcome the high friction and wear limitations of pure polyether ether ketone (PEEK) under elevated-temperature sliding, this study develops novel PEEK composites by incorporating ultra high molecular weight polyethylene (UHMWPE).Composites with UHMWPE contents ranging from 1.0% to 10.0% were fabricated via hot pressing and tested at an elevated temperature of 100C using a ball-on-disk tribometer.Results show that a low-content addition of 2.0% UHMWPE to PEEK results in optimal tribological performance, achieving reductions of 87%, 98%, and 71% in friction coefficient, wear rate, and surface roughness, respectively, compared to pure PEEK.This study presents an effective approach to enhancing the tribological performance of PEEK composites, with significant implications for elevated-temperature engineering applications, particularly in PEEK-based sliding bearings.

Three ultrahigh molecular weight polyethylene (UHMWPE) composites of differing composition, reinforced with multiwalled carbon nanotubes (MWCNT) were prepared. The homogeneous distribution of MWCNT has been attempted by two dry blending methods and one melt-mixing process. The efficiency of the various methods was characterized by their effects on the quasi-static and dynamic physical properties of the composites. In the case of composites manufactured by ball milling the effects of various adhesion promoter additives (compatibilizers) has also been studied by analyzing the tensile, flexural, Charpy impact and wear properties of the composites.

Sandwich construction has proven to be an excellent low-density multifunctional design for a wide range of applications in ballistic protection, energy absorption, and thermal insulation. Based on the bulletproof effect of each layer of the sandwich structure, this paper expounds and summarizes the material properties that can be used as each layer. The mechanical and ballistic properties of ultra-high strength aramid (Kevlar) and ultra-high molecular weight polyethylene (UHMEPE) composites and the ballistic properties of mixed fibers of these two materials versus the mechanical properties of single fiber materials, the mechanical properties, chemical stability and other properties of aluminum and magnesium alloys, the effects of heat treatment and coating treatment on the ballistic properties of aluminum alloys, and finally the energy absorption properties of several common core materials structures are compared.

A new uncemented acetabular component, the Cambridge cup, has been designed to mimic the anatomy and physiology of subchondral bone in order to minimise stress shielding and enhance long-term component stability. Cambridge cups were implanted in a cohort of 50 women who presented with displaced sub-capital fracture of the femoral neck. The cups were manufactured with an hydroxyapatite (HA) coating. Twenty six cups were implanted after removal of the HA. Twelve Cambridge cups were retrieved post-mortem between two and 84 months after implantation. Histological and histomorphometric testing was undertaken to analyse the residual HA coating thickness, bone apposition to the implant surface and particulate wear debris in the surrounding tissues. The HA-coated implants showed significantly greater bone apposition to the implant surface with significantly less fibrous tissue formation than the uncoated implants. Where HA resorption occurred, bone and bone marrow was seen adjacent to the implant. Excessive wear of the ultra high molecular weight polyethylene liner was not seen. The HA-coated components demonstrated good initial bone implant bonding and the flexible carbon polymer appeared to maintain stability following HA resorption. The uncoated implants showed little or no bony apposition but had a fibrous membrane apposed to the implant surface. This may be explained by a combination of micro-motion at the bone implant interface and having a component surface finish that was poorly suited to osseous attachment. Hydroxyapatite coated acetabular components can provide reliable osseous attachment. Subsequent HA resorption need not compromise medium-term osseous fixation to an appropriate implant surface.

5 - Polymer composites