A model for biodegradation of polymer fibers made of poly-3-hydroxybutyrate poly(3HB)

Biodegradation of medical devices is a complex process that depends on many factors, ranging from the methods of polymer synthesis to the concentration of active enzymes in the medium. Mathematical modeling of the biodegradation of polyhydroxyalkanoates (PHAs) is of great practical importance as it allows the degradation of the material to be analyzed with different parameters and different product forms to be considered without the need for many lengthy experiments. Considering the kinetics and mechanisms of enzymatic degradation of PHA, two main processes can be distinguished: adsorption and hydrolysis. The first step is the adsorption of the enzyme onto the polymer surface, and the second step is the hydrolysis of the polymer chain. In finite element modeling, adsorption can be described by surface homogeneous diffusion and hydrolysis by a reaction equation, similar to models for polylactides. To find the unknown model parameters, a nonlinear optimization problem is solved using Sparse Nonlinear OPTimizer (SNOPT) and experimental data on the biodegradation of poly(3HB) and poly(3HB-co-3HV) polymer fibers in three biological environments (human blood, blood serum, and in vivo). Based on the simulation results, numerical and experimental results were compared, and the influence of model parameters on the biodegradation profile was analyzed. The model was also applied to assess the biodegradation of other polymeric medical devices such as a vascular stent and a bone implant. The proposed finite element model allows for assessing the biodegradation of polymeric medical devices made from PHA in various biological environments. The biodegradation simulation results are in good agreement with experimental data. This model is the first step towards modeling the biodegradation of PHA and does not include the change in crystallinity, the characteristics of the enzyme during degradation, which may be a further aim of the work.

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