Research Laboratory for the Mechanics of Bio-compatible Materials and Devices

Scientific results:

• Our researchers have developed a universal method of creating models of scaffolds and their prototypes on the basis of open-type cellular mesh structures with the capability of controlling their target physical and mechanical properties by virtue of changing the geometry of periodicity cells. Two-level models have been developed that describe the mechanical elastic and viscoelastic behavior of polymer scaffolds and their prototypes. We have developed an original software algorithm for the numerical discretization of  two-dimensional surfaces and three-dimensional volume of mesh structures. We determined the impact of the porousness and stricture of the inner topology on the mechanical behavior and properties of scaffolds on the basis of open-cellular structures. For latticed structures with various geometries we compared deformations that had been numerically computed on the basis of the created models and models obtained experimentally with the use of a contactless deformation measurement system relying on  correlation  of digital images.
• We have developed the structure and ratios of a viscoelastic two-level model of a endovascular stent, in which we explicitly included the physical mechanisms and processes at the macro- and meso-level. A two-level mathematical model of the viscoelastic deformation of the material of an endovascular stent that explicitly accounts for the grain stricture. We researched the influence of grain sizes on the nature of deformation of a material, built a dependence of a conditional limit of fluidity on the parameters of the lognormal distribution law. Our researchers plotted a polar diagram of the dependence of the conditional limit of fluidity on the direction of deformation in the most dangerous strain state in the stricture of the stent, determined the most hazardous directions of deformation in the space of principal deformations. We compiled a microscopic description of the behavior of the stricture of a stent with balloon expansion  using the COMSOL Multiphysics computation package.
• Polyurethanes have been synthesized for medical uses and samples were prepared for forming a biocompatible carbon nanolayer on the suraces of those polyurethanes with the use of ion-plasma treatment. We have performed ion-plasma treatment of the surfaces of medical polyurethane samples at various doses of nitrogen ion to create a carbon nanolayer on their surface. Our researchers have refined an approach to determining the Young's modulus of a biocompatible nanolayer formed as a result of the ion-plasma treatment of polymerfs. We have found the dependence of the elastic modulus of carbon layer on polyurethanes on the fluence of ion-plasma treatment. An experimental methodology has been proposed  for determining the dependence of the coefficient of thermal expansion (CTE) of polymer biomaterials on the temperature and the rate of its change with the use of film samples. For the first time, we have obtained analytical dependencies describing the dependence of the CTE on temperature for some polymer materials.
• We have created test samples of the porous strcture of scaffolds made of the materials polyether ether ketone (PEEK), polylactide (PLA), polyethylene terephthalate glycol (PETG Biocide), acrylonitrile butadiene styrene (ABS), polystyrol (HIPS). We studied the influence of the parameters of printing, the diameter of the nozzle of the extruder as well as the direction of the stacking of layers while printing on the resulting  mechanical properties and the strength of standard continuous samples in the form of  blades. We have produced experimental samples imitating medical stents using SLM methods (selective laser melting). On the basis of experimental data we verified the developed  numerical models.
• Our researchers have refined a methodology for cultivating cells in the presence of samples of a polymer material. Recomendations have been compiled for modifying surfaces, that help cells to adapt better. From the results of the experiments we determined samples to which the best adhesion of researched cell lines is observed. We arrived to conclusions on the capability of polymer materials to induce hemolysis erythrocyte hemolysis and their impact on the destruction of the membranes of erythrocytes. A methodology for determining the mechanical characteristics of collagen samples.
• We have created and numerically implemented an algorithm that allows to efficiently reconstruct the the three-dimensional structure of biomaterials at various scale levels from computer tomography data. We have built volume finite-element counterparts of  organs and structures from tomography imaging data, which will be used used to model processes of the destruction and collective deformation of prosthetic systems and bone tissue.
• An approach has been proposed to creating biomaterials and  biomedical products on the basis of FFF additive printing technologies with contactless indirect (eddy current) control of the temperature in the process of extrusion. A mathematical model has been created that binds the electromagnetic and thermal processes of the induction heating of the nozzle, which allows to determine the parameters of the inductor  and the nozzle as the control object, allowing to assess the influence of the rate of extrusion on  the temperature of the nozzle and the polymer. We refined the FFF technological approach  to printing with the induction heating of the lightweight nozzle that increases the uniformity of heating, the precision and speed of control of the extrusion temperature of the polymer of the polymer during building-up, and therefore the mechanical properties of the built-up samples. A mathematical model has been created that describes the thermomechanical behavior of structures made of biologically compatible thermoplastics in the process of fused deposition modeling (FDM). We have developed an algorithm for computing nonstationary temperature fields and the stress-strain state of a structure in the process of FDM. The algorithm has been implemented in a program  using APDL of the ANSYS package.
• The laboratory has refined the use of electrolytic-plasma polishing  on the basis of potassium fluoride electrolyte as the finishing operation of surface treatment. We reached conclusions on the feasibility of the use of the electrolyric-plasma polishing technology as a finishing treatment operation for the surfaces of stents and the necessity of further research.
• We have developed a variant of measuring the indicators of temperature fields by sensors embedded into a material. Our researchers have demonstrated the feasibility of obtaining information on the technological temperatures and deformations in the material of the sample.

Implementation of research results:

1. The software program «A  computational module for creating geometrical models for three-dimensional gradient interpenetrating structures on the basis of triply periodic minimal surfaces of the «gyroid» type».
2. The software program «A computation module for creating geometric models for three-dimensional interpenetrating structures on the basis of triply periodic minimal surfaces of the «I-WP» type».
3. The invention «A method of indirect eddy-current resonance control and measurement of temperature of products made of ferromagnetic materials».

Education and retraining of personnel:

We have developed and are now implementing a new education program for master’s degree students  majoring in «Dynamics and strength of machines, structures and mechanisms».

Collaboration:

Institute of Continuous Media Mechanics of the Ural Branch of the Russian Academy of Sciences (Russia): joint research in the domain of creating prototypes of devices with the use of additive technologies, researching models of materials on the basis of computer tomography, functionalizing the surfaces of polymer materials, adapting technologies of the embedded nondestructive testing of temperature and deformations.