S. I. Tverdokhlebov

Application of High-Frequency Magnetron Sputtering to Deposit Thin Calcium-Phosphate Biocompatible Coatings on a Titanium Surface

Thin calcium-phosphate coatings were deposited on titanium substrates by high-frequency magnetron sputtering. The elemental composition of coatings and types of chemical bonds were studied by Rutherford backscattering (RBS) and Fourier transform infrared spectroscopy (FTIR), respectively. An analysis of the IR spectra detected absorption bands caused by vibrations of phosphate PO43− groups and pyrophosphate H2PO4− anions, which are typical of apatites. The RBS results showed that the coating contains elements typical of calcium phosphates, i.e., Ca, P, and O; 45.4 ± 1.1, 3.6 ± 0.5, and 41.1 ± 0.7 at %, respectively. The Ca/P atomic ratio depends on sputtering conditions and varies in the range 1.7–4.0. The physicomechanical characteristics of the coatings and their solubility in a biological liquid were studied. The grown coatings can significantly reduce dissolution of substrates and extraction of dopants into the surrounding solution.

Ferroelectric polymer scaffolds based on a copolymer of tetrafluoroethylene with vinylidene fluoride: Fabrication and properties

A solution blow spinning technique is a method developed recently for making nonwoven webs of micro- and nanofibres. The principal advantage of this method compared to a more traditional electrospinning process is its significantly higher production rate. In this work, the solution blow spinning method was further developed to produce nonwoven polymeric scaffolds based on a copolymer of tetrafluoroethylene with vinylidene fluoride solution in acetone. A crucial feature of the proposed method is that high-voltage equipment is not required, which further improves the methods economics. Scanning electron microscopy analysis of the samples demonstrated that the surface morphology of the nonwoven materials is dependent on the polymer concentration in the spinning solution. It was concluded that an optimum morphology of the nonwoven scaffolds for medical applications is achieved by using a 5% solution of the copolymer. It was established that the scaffolds produced from the 5% solution have a fractal structure and anisotropic mechanical properties. X-ray diffraction, infrared spectroscopy, Raman spectroscopy and differential scanning calorimetry demonstrated that the fabricated nonwoven materials have crystal structures that exhibit ferroelectric properties. Gas chromatography has shown that the amount of acetone in the nonwoven material does not exceed the maximum allowable concentration of 0.5%. In vitro analysis, using the culture of motile cells, confirmed that the nonwoven material is non-toxic and does not alter the morpho-functional status of stem cells for short-term cultivation, and therefore can potentially be used in medical applications.

A fiber distribution model for predicting drug release rates

ABSTRACT Sustained drug release can be achieved by loading a drug into polymer material. The drug release can then be controlled for potential use in various biomedical applications. A model for drug release from a polymeric fibrous scaffold, which takes into account the distribution of fiber diameters within its structure, is developed here. It is demonstrated that the fiber diameter distribution significantly affects the drug release profile from electrospun scaffolds. The developed model indicates that altering the fiber distribution can be used as an additional tool to achieve an appropriate drug release profile. Using published data, it was demonstrated that an application of the model allows a more precise calculation of the drug diffusion coefficient within the polymer, which is important for predicting drug release rates from fabricated materials.

Nonwoven Polylactide Scaffolds Obtained by Solution Blow Spinning and the In Vitro Degradation Dynamics

The solution blow spinning is presented as a method of obtaining tissue engineering scaffolds. The different forming modes were used and the optimum experimental conditions were found. It is shown that nonwoven polylactide scaffolds with required surface morphology can be obtained. These samples were studied in case of biodegradation in simulation body fluid. It was found that during scaffold dissolution the pH of the solution changes insignificantly (6.85) despite the exponential increase of the monomers of lactic acid. The calcium and phosphorus ion exchange between the scaffold and solution was observed in the surface and bulk of the material what makes possible to use scaffolds for regenerative medicine.

Osteoinductive composite coatings for flexible intramedullary nails

This work presents composite coatings based on a copolymer of vinylidene fluoride with tetrafluoroethylene (VDF-TeFE) and hydroxyapatite (HA) for flexible intramedullary nails (FIN). The effect of the proportion of VDF-TeFE (100-25% wt.) on physicochemical and biological properties of the composite coatings was investigated. It was shown that a decrease of VDF-TeFE in the coating hinders its crystallization in β and γ forms which have piezoelectric properties. The decrease also reduces an adhesive strength to 9.9±2.4MPa and a relative elongation to 5.9±1.2%, but results in increased osteogenesis. It was demonstrated that the composite coatings with 35% VDF-TeFE has the required combination of physicochemical properties and osteogenic activity. Comparative studies of composite coatings (35% VDF-TeFE) and calcium phosphate coatings produced using micro-arc oxidation, demonstrated comparable results for strength of bonding of these FINs with trabecular bones (~530MPa). It was hypothesized that the high osteoinductive properties of the composite coatings are due to their piezoelectric properties.

Application of atomic force microscopy methods for testing the surface parameters of coatings of medical implants

Atomic force microscopy methods are used to study calcium phosphate coatings that are formed on surfaces of various materials, which are used in medicine, by radio-frequency magnetron sputtering of a hydroxyapatite target. The roughness parameters and values of the surface potentials of metal, polymer, and hybrid substrates are determined in a semicontact regime. Calcium phosphate coatings increase the roughness of surfaces of polymer and metal materials, thus presenting a stimulating factor for the attachment and proliferation of osteogenic cells. Using the Kelvin method, it is shown that calcium phosphate coatings change the surface potential of substrates.

Surface modification of electrospun poly-(L-lactic) acid scaffolds by reactive magnetron sputtering

In this study, we modified the surface of bioresorbable electrospun poly-(l-lactic) acid (PLLA) scaffolds by reactive magnetron sputtering of a titanium target under a nitrogen atmosphere. We examined the influence of the plasma treatment time on the structure and properties of electrospun PLLA scaffolds using SEM, XRF, FTIR, XRD, optical goniometry, and mechanical testing. It was observed that the coating formed did not change physicomechanical properties of electrospun PLLA scaffolds and simultaneously, increased their hydrophilicity. No adverse tissue reaction up to 3 months after subcutaneous implantation of the modified scaffolds was detected in in-vivo rat model. The rate of scaffold replacement by the recipient tissue in-vivo was observed to depend on the plasma treatment time.

Plasma treatment as an efficient tool for controlled drug release from polymeric materials: A review

ABSTRACT One of the most actively developing fields in modern medicine is controlled drug delivery, an ability to keep optimal concentration of a drug at the desired body location. In particular, the most attention for potential use as drug delivery vehicles is drawn towards biodegradable polymeric materials. This is due to the versatility of tools for their fabrication, as well as due to the need to extract them after implantation being eliminated. In order to enhance polymer characteristics in terms of biocompatibility their surface can be functionalized. Plasma treatment is a method for the modification of material surface properties, which spans a wide range of applications in tissue engineering and regenerative medicine. The main advantage of this method is its ability to modify a polymeric surface without altering the bulk properties of materials, thus preserving original mechanical characteristics. Moreover, plasma modification is well‐known for its speed, excluded need for solvents, and scalability. Recently, this approach has been gaining popularity for drug delivery applications. The applications of plasma treatment during the fabrication of drug delivery vehicles include surface activation, enhanced wettability, the fabrication of hydrophobic barrier layer, induced cross‐linking and improved drug loading. This review covers the variety of approaches, applied to different polymeric biomaterials, including non‐woven meshes, films, microparticles, microneedles and tablets, in order to achieve a controlled drug release. The applications of drug delivery devices with an implemented plasma treatment modification are also described. Graphical abstract Figure. No caption available.

Structure and properties of nonwoven materials based on copolymer of tetrafluoroethylene and vinyldenefluoride produced by aerodynamic formation

Properties of nonwoven materials based on copolymer of tetrafluoroethylene and vinyldenefluoride produced by aerodynamic formation in a turbulent gas flow are investigated in the paper. By means of scanning microscopy, it is shown that synthesized nonwoven materials are characterized by high porosity and complicated spatial organization. By means of X-ray diffraction, infrared spectroscopy, combination scattering spectroscopy, thermogravimetric analysis, and differential scanning calorimetry, it is shown that fibers that form the nonwoven material are characterized by a crystal structure typical of ferrielectric phases. The quantitative content of residual solvents in the formed materials is determined. By using a mobile cell culture, it is shown that the produced nonwoven materials are not toxic and can be used for medical purposes.

Modification of the Ceramic Implant Surfaces from Zirconia by the Magnetron Sputtering of Different Calcium Phosphate Targets: A Comparative Study

In this study, thin calcium phosphate (Ca-P) coatings were deposited on zirconia substrates by radiofrequency (RF) magnetron sputtering using different calcium phosphate targets (calcium phosphate tribasic (CPT), hydroxyapatite (HA), calcium phosphate monobasic, calcium phosphate dibasic dehydrate (DCPD) and calcium pyrophosphate (CPP) powders). The sputtering of calcium phosphate monobasic and DCPD powders was carried out without an inert gas in the self-sustaining plasma mode. The physico-chemical, mechanical and biological properties of the coatings were investigated. Cell adhesion on the coatings was examined using mesenchymal stem cells (MSCs). The CPT coating exhibited the best cell adherence among all the samples, including the uncoated zirconia substrate. The cells were spread uniformly over the surfaces of all samples.