A.V. Maksimkin

Structure and properties of ultra-high molecular weight polyethylene filled with disperse hydroxyapatite

The possibility of preparing composite materials filled with hydroxyapatite on the basis of ultra-high molecular weight polyethylene for use in replacement arthroplasty was studied. The composites were prepared by the combined mechanoactivation of the starting components followed by compaction via thermal pressing. The structures of the resulting composite powder and monolithic composite were investigated by means of differential scanning calorimetry and X-ray diffraction analysis, and the effect of introduced hydroxyapatite on the degree of polymer crystallinity was elucidated. The composites were tested to determine the concentration dependences of their physicomechanical and tribological properties. On the basis of the experimental data, it was concluded that the mechanoactivation processing affords the high-quality polymeric composites, thereby providing the disperse distribution of the filler over the matrix. By a combination of physicomechanical and tribological characteristics, the materials developed can be suggested for the production of articulated joint liners of hip and knee endoprostheses.

Application of Microstructured Intermetallides in Turbine Manufacture. Part 1: Present State and Prospects (A Review)

The objective of the present work is the analysis of the present state and prospects of the development of competitive technologies for creating microstructured materials of the class of intermetallides and their application in turbine and engine manufacture. The present review examines the general strategy of the development of the industry of heat-resistant materials of the class of intermetallides. A comparative analysis of the specific properties, advantages, and disadvantages of titanium, nickel, and iron aluminides and transition metals (Nb, Mo, and Ti) silicides in view of their application in construction of aircraft engines and gas-burning power-generating turbines is performed. The state and prospects of the development of competitive pilot technologies of manufacture and application of the above materials are analyzed.

Preparation of porous ultrahigh-molecular-weight polyethylene using subcritical water

We developed a method of subcritical water extraction of NaCl from ultrahigh-molecular-weight polyethylene (UHMWPE) samples as a step in the preparation of a porous polymeric product, a promising material for implant production. Optimum process conditions were determined to be as follows: pressure 250 bar, temperature 120°C, and water flow rate 3 g/min. This method allows decreasing ten-fold (from 10 to 1 h) the time of salt extraction from the samples. The UHMWPE obtained was shown by scanning electron microscopy to have a porous structure with a main pore diameter from 80 to 700 μm.

Application of microstructured intermetallides in turbine manufacture. Part 2: Problems in development of heat-resistant alloys based on TiAl (a review)

The problems of formation of the necessary microstructure of intermetallic materials providing the required mechanical properties under extreme operating conditions are considered by the example of doped TiAl intermetallides. The problem of corrosion stability of intermetallides under extreme operating conditions is examined.

Polyhydroxybutyrate/Hydroxyapatite Highly Porous Scaffold for Small Bone Defects Replacement in the Nonload-bearing Parts

In the present work, Polyhydroxybutyrate (PHB)/Hydroxyapatite (HA) porous composites (10%, 20%, 30 %, 40%, 50% weight HA) were obtained by sintering. PHB/20% HA optimally combines satisfactory mechanical properties with a high content of the bioactive component (HA). Porous PHB/20% HA scaffolds have shown high mechanical properties (compressive strength of 106 MPa and Young’s modulus of 901 MPa). A high volume fraction of interconnected pores (> 50 vol.%) was achieved with pore size of 50 μm - 500 μm. Biocompatibility of porous pure PHB and PHB/20%HA, as its osseointegration were assessed in vitro and after implantation in laboratory animals. PHB/20% HA (−5% ± 0.9%) and pure PHB (−3% ± 1.4%) samples after 24 hours of incubation with human leucocytes showed no significant level of cytotoxicity when p = 0.648 (p-value). In vitro massive adhesion of mouse Multipotent Mesenchymal Stromal Cells (MMSC) to the surface of both porous samples was shown. PHB/20% HA induced more intensive MMSC proliferation compared to pure PHB, which are 31% ± 6.1% and 20% ± 5.7 % respectively when p = 0.039. We observed the resorption (implant surface area was reduced by 49 %) and integration of the porous PHB/20% HA samples into surrounding tissues after 30 days of implantation. The signs of osteoclasts accumulation, neo-angigenesis and new bone formation were observed, which make PHB/20% HA promising for bone tissue engineering.

Structure and mechanical properties of self-reinforced ultra-high molecular weight polyethylene:

Ultra-high molecular weight polyethylene-based self-reinforced composite materials were studied. Surface of the ultra-high molecular weight polyethylene fibers was modified by direct fluorination and nitric acid treatment. Structure and mechanical properties of self-reinforced ultra-high molecular weight polyethylene depending on the content and type of modified fibers were studied. It was shown that self-reinforcing of ultra-high molecular weight polyethylene allows to obtain materials with improved strength–elastic properties. Tensile strength and Young’s modulus of the self-reinforced composite materials are more than three times higher than that of the unfilled ultra-high molecular weight polyethylene.

Impregnation of Ultrahigh-Molecular-Weight Polyethylene with Amoxicillin in Subcritical Freon R22 Media

The method of impregnation of ultrahigh-molecular-weight polyethylene (UHMWPE) with amoxicillin in subcritical Freon R22 media is developed. For the first time, the possibility of polymer impregnation with a polar substance (a standard antibiotic amoxicillin) in the absence of cosolvents is shown. Cosolvents increase the polarity of the medium and removal of them from the polymer matrix is usually a serious problem. Amoxicillin desorption curves from the impregnated UHMWPE samples are obtained by high-performance liquid chromatography (HPLC). Polymeric samples impregnated with amoxicillin are active against gram-positive and gram-negative microorganisms S. aureus, S. epidermidis, E. faecalis, B. subtilis, and E. coli, allowing them to be considered as real implant models for replacement of bone tissue.

Impregnation of Ultra-High-Density Polyethylene with Unsymmetrical Disulfides in Subcritical Freon Media

For the first time, ultra-high-density polyethylene (UHDPE) samples impregnated with antibacterial unsymmetrical disulfides (allyl benzothiazol-2-yl disulfide and allyl 8-quinolyl disulfide) were obtained in subcritical freon R22 in the absence of organic solvents as modifiers. Freon R22 was completely removed from the impregnated samples that provided a high purity of the final material. Potential implants based on the UHDPE impregnated with unsymmetrical disulfides were shown to manifest antibacterial and antifungal activity.

Bulk Oriented UHMWPE/FMWCNT Films for Tribological Applications

Bulk oriented films based on ultrahigh molecular weight polyethylene (UHMWPE) with a drawing ratio of 35 were prepared by using a low solvent concentration. Bulk oriented films were filled with fluorinated multi-walled carbon nanotubes (FMWCNTs). The structure of bulk oriented films on UHMWPE, which were manufactured at different stages of orientation, was investigated by scanning electron microscope (SEM) and differential scanning calorimetry (DSC). The addition of FMWCNTs at a concentration of 0.05 wt % in bulk oriented UHMWPE films led to an increase in the tensile strength by 10% (up to 1020 ± 23 MPa) compared to unfilled oriented films. However, the addition of FMWCNTs at a concentration of more than 0.5 wt % led to a decrease in tensile strength due to excessive accumulation of nanotubes and hindering of self-diffusion of UHMWPE macromolecules. The multiple increase in tensile strength, doubling the hardness, the formation of fibrillar structure, and the presence of carbon nanotubes led to a significant increase in tribological properties in bulk oriented films. Bulk oriented UHMWPE/1% FMWCNT films can be operated at a maximum contact pressure that is 18 times higher and exhibit a specific wear rate more than an order of magnitude and less than the traditional UHMWPE of isotropic structure. Bulk oriented UHMWPE/1% FMWCNT films have an extremely low dry coefficient of friction (COF) of 0.075 at a contact pressure of 31 MPa. The developed bulk oriented films can be used for manufacturing frictional surfaces for sliding bearings, or for acetabular cups for knee and hip endoprostheses.

Sterilization of a porous ultrahigh-molecular-weight polyethylene in supercritical Freons

The possibility of sterilization of porous ultrahigh-molecular-weight polyethylene in subcritical Freons R22 and R410a in the absence of modifiers is for the first time demonstrated. The maximum sterilization effect is achieved when sterilization with Freon R410a is performed in static conditions for 30 min at 50°С and 250 bar or with Freon R22 for 60 min at 70°С and cyclically varied pressure within 100–290 bar (press–depress mode).