Structural, Mechanical, and Tribological Properties of Oriented Ultra-High Molecular Weight Polyethylene/Graphene Nanoplates/Polyaniline Films.

Preparing high-strength polymeric materials using an orientation drawing process is considered one of the most urgent topics in the modern world. Graphene nanoplates/polyaniline (GNP/PANI) were added to the commercial grade UHMWPE (GUR 4120) matrix as a filler with antifriction properties. The effect of GNP/PANI addition on the structure, the orientation process, the void formation (cavitation), the mechanical, and tribological properties was studied using differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA), and scanning electron microscopy (SEM). The paper's findings indicated an increase in the cavitation effect of 120-320% after the addition of GNP/PANI to the UHMWPE polymer matrix. This increase, during the process of the oriented films' thermal orientation hardening, led, in turn, to a decrease in the tensile strength during the process of the oriented films' thermal orientation hardening. Furthermore, the decrease in the coefficient of friction in the best samples of oriented UHMWPE films was two times greater, and the increase in wear resistance was more than an order of magnitude. This process was part of the orientation hardening process for the UHMWPE films containing PE-wax as an intermolecular lubricant, as well as the presence of GNP/PANI in the material, which have a high resistance to abrasive wear.

Hybrid Implants Based on Calcium-Magnesium Silicate Ceramics Diopside as a Carrier of Recombinant BMP-2 and Demineralized Bone Matrix as a Scaffold: Dynamics of Reparative Osteogenesis in a Mouse Craniotomy Model.

Calcium-magnesium silicate ceramics, diopside, is a promising material for use in bone plastics, but until now the possibility of its use as a carrier of recombinant bone morphogenetic protein-2 (BMP-2) has not been studied, as well as the features of reparative osteogenesis mediated by the materials based on diopside with BMP-2. Powder of calcium-magnesium silicate ceramics was obtained by solid-state synthesis using biowaste - rice husks and egg shells - as source components. Main phase of the obtained ceramics was diopside. The obtained particles were irregularly shaped with an average size of about 2.3 µm and ~20% porosity; average pore size was about 24 nm, which allowed the material to be classified as mesoporous. Diopside powder adsorbs more than 150 µg of recombinant BMP-2 per milligram, which exceeds binding capacity of hydroxyapatite, a calcium-phosphate ceramic often used in hybrid implants, by more than 3 times. In vitro release kinetics of BMP-2 was characterized by a burst release in the first 2 days and a sustained release of approximately 0.4 to 0.5% of the loaded protein over the following 7 days. In vivo experiments were performed with a mouse model of cranial defects of critical size with implantation of a suspension of diopside powder with/without BMP-2 in hyaluronic acid incorporated into the disks of demineralized bone matrix with 73-90% volume porosity and macropore size from 50 to 650 µm. Dynamics of neoosteogenesis and bone tissue remodeling was investigated histologically at the time points of 12, 21, 48, and 63 days. Diopside particles were evenly spread in the matrix and caused minimal foreign body reaction. In the presence of BMP-2 by the day 63 significant foci of newly formed bone tissue were formed in the implant pores with bone marrow areas, moreover, large areas of demineralized bone matrix in the implant center and maternal bone at the edges were involved in the remodeling. Diopside could be considered as a promising material for introduction into hybrid implants as an effective carrier of BMP-2.

Effect of recombinant BMP-2 and erythropoietin on osteogenic properties of biomimetic PLA/PCL/HA and PHB/HA scaffolds in critical-size cranial defects model.

Osteoplastic materials PLA/PCL/HA and PHB/HA and scaffolds with a highly porous structure based on them with potential applications in regenerative medicine have been obtained by solvent casting with thermopressing and salt leaching for PLA-based samples and solid-state mixing with subsequent thermopressing and salt leaching for PHB-based samples. The scaffolds were characterized by SEM-EDX, DSC, FTIR spectroscopy, mechanical tests in compression, measurement of the contact angle, in vitro studies, including loading by recombinant BMP-2 and EPO and their release kinetics, and in vivo studies on a model of regeneration of critical-sized cranial defects in mice. Biomimetic scaffolds with micropores sizes ranged from 300 to 500 µm and volume porosity of 70% imitate trabecular bone's structure and have increased hydrophilicity to achieve osteoconductive properties. Mechanical characteristics correspond to native trabecular bone. Elastic modulus - key mechanical characteristics of bone implants - showed the values of 0.15 ± 0.04 and 0.18 ± 0.08 GPa for PLA/PCL/HA and PHB/HA scaffolds, respectively. Both materials have high biocompatibility and can be used together with recombinant proteins BMP-2 and EPO. Introduction of BMP-2 leads to induction of new bone formation, introduction of EPO results in increased angiogenesis in the implantation area. The obtained scaffolds with recombinant proteins can be used as bone implants for reconstruction of defects of lightly or non-loaded bones.

Biocompatibility and Physico-Chemical Properties of Highly Porous PLA/HA Scaffolds for Bone Reconstruction.

The major problem in bone tissue engineering is the development of scaffolds which can simultaneously meet the requirements of porous structure, as well as have the ability to guide the regeneration of damaged tissue by biological fixation. Composites containing biodegradable matrix and bioactive filler are the new hope in this research field. Herein we employed a simple and facile solvent casting particulate-leaching method for producing polylactide acid/hydroxyapatite (PLA/HA) composites at room temperature. FT-IR analysis confirmed the existence of necessary functional groups associated with the PLA/HA composite, whereas energy-dispersive X-ray (EDX) spectra indicated the uniform distribution of hydroxyapatite particles in the polymer matrix. The beehive-like surface morphology of the composites revealed the presence of macropores, ranged from 300 to 400 µm, whereas the thickness of the pores was noticed to be 1-2 µm. The total porosity of the scaffolds, calculated by hydrostatic weighing, was found to be 79%. The water contact angle of pure PLA was decreased from 83.6 ± 1.91° to 62.4 ± 4.17° due to the addition of hydroxyapatite in the polymer matrix. Thus, the wettability of the polymeric biomaterial could be increased by preparing their composites with hydroxyapatite. The adhesion of multipotent mesenchymal stromal cells over the surface of PLA/HA scaffolds was 3.2 times (p = 0.03) higher than the pure PLA sample. Subcutaneous implantation in mice demonstrated a good tolerance of all tested porous scaffolds and widespread ingrowth of tissue into the implant pores. HA-containing scaffolds showed a less pronounced inflammatory response after two weeks of implantation compared to pure PLA. These observations suggest that PLA/HA composites have enormous potential for hard tissue engineering and restoring maxillofacial defects.

The Structural and Mechanical Properties of the UHMWPE Films Mixed with the PE-Wax.

Since obtaining a highly oriented structure based on a large-scale commercial ultra-high molecular weight polyethylene (UHMWPE) is considered very difficult due to its high molecular weight and melting index, modifying the structure of these cheap commercial UHMWPE brands into a supra-molecular structure with fiber-forming properties by adding a small amount of polyethylene wax (PE-wax) will provide the possibility to obtain highly oriented UHMWPE products with enhanced mechanical and tribological properties. In this work, highly oriented UHMWPE/PE-wax films were prepared. The PE-wax affected the UHMWPE as an intermolecular lubricant. The obtained lamellar structure of the UHMWPE/PE-wax composites had a better processability. The UHMWPE and UHMWPE/PE-wax structures for the xerogels and the films were studied by using differential scanning calorimetry and scanning electron microscopy. The PE-wax presence enhanced the mechanical properties of the UHMWPE/PE-wax films to a high degree. The highest average value of the tensile strength was 1320 MPa (an increase of 78%) obtained by adding a PE-wax content of 1.0 wt.%, and the highest average value of the Young's modulus was 56.8 GPa (an increase of 71%) obtained by adding a PE-wax content of 2.0 wt.%. The addition of the PE-wax increased the work of fracture values of the UHMWPE/PE-wax films up to 233%. The formation of the cavities was observed in the virgin UHMWPE films more than in the UHMWPE/PE-wax films, and the whitening of the oriented films was related to the crystallization process more than to the cavitation phenomenon. The coefficient of friction of the oriented UHMWPE/PE-wax films improved by 33% in comparison with the isotropic UHMWPE, and by 7% in comparison with the oriented virgin UHMWPE films.

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.

The Structure and Mechanical Properties of the UHMWPE Films Modified by the Mixture of Graphene Nanoplates with Polyaniline.

Highly oriented UHMWPE films were reinforced with functionalized graphene nanoplates (GNP). GNP was functionalized by deposition of polyaniline (PANI) on the GNP surface. The structure of GNP/PANI was studied by Raman spectroscopy, and the structure of xerogels and films based on UHMWPE was studied by DSC and SEM. PANI promotes the reduction of the GNP aggregation in the UHMWPE matrix and increases the degree of crystallinity due to heterogeneous crystallization. The new lamellar crystal structure has a high drawability. The highest value of the tensile strength 1330 MPa (an increase of 45%) was obtained with a filler content of 2 wt % GNP/PANI, and the highest value of Young's modulus 41 GPa (an increase of 32%) was obtained with a filler content of 1 wt % GNP/PANI. The effect of GNP with PANI fillers on the dynamic mechanical properties of the UHMWPE films was discussed.