Biodegradable performance of PLA stents affected by geometrical parameters: The risk of fracture and fragment separation

Tremendous advances, multifaceted challenges and feasible future prospects of biodegradable medical polymer materials

In recent years, biodegradable medical polymer materials (BMPMs) have stood out among many biomedical materials due to their unique advantages, such as high mechanical strength, good biocompatibility, strong corrosion resistance and excellent processability. In this review, we first provide a brief introduction of biodegradable medical materials from both natural and synthetic perspectives, and then systematically categorize BMPMs based on their applications in clinical medicine and highlight the great progress they have made in recent years. Additionally, we also point out several overlooked areas in the research of BMPMs, offering guidance for comprehensive future exploration of these materials. Finally, in view of the complex challenges faced by BMPMs today, their future directions are scientifically proposed. This work contributes to the ongoing efforts of BMPMs in the biomedical field and provides a steppingstone for developing more effective BMPM-based products for clinical applications.

In Silico Evaluation of In Vivo Degradation Kinetics of Poly(Lactic Acid) Vascular Stent Devices

Biodegradable vascular stents (BVS) are deemed as great potential alternatives for overcoming the inherent limitations of permanent metallic stents in the treatment of coronary artery diseases. The current study aimed to comprehensively compare the mechanical behaviors of four poly(lactic acid) (PLA) BVS designs with varying geometries via numerical methods and to clarify the optimal BVS selection. Four PLA BVS (i.e., Absorb, DESolve, Igaki-Tamai, and Fantom) were first constructed. A degradation model was refined by simply including the fatigue effect induced by pulsatile blood pressures, and an explicit solver was employed to simulate the crimping and degradation behaviors of the four PLA BVS. The degradation dynamics here were characterized by four indices. The results indicated that the stent designs affected crimping and degradation behaviors. Compared to the other three stents, the DESolve stent had the greatest radial stiffness in the crimping simulation and the best diameter maintenance ability despite its faster degradation; moreover, the stent was considered to perform better according to a pilot scoring system. The current work provides a theoretical method for studying and understanding the degradation dynamics of the PLA BVS, and it could be helpful for the design of next-generation BVS.

A phenomenological model of pulsatile blood pressure-affected degradation of polylactic acid (PLA) vascular stent

The stent implantation may alter the post-operative patient's blood pressure, and bioresorbable vascular stents (BVS) as a candidate to treat vascular diseases, its degradation is affected by mechanical stress, thus, the altered pressure representing varying stress level will result in different degradation behaviors of the BVS. This paper first proposed a novel stress-regulated PLA degradation model that included swelling factor, and then the degradation evolutions of a PLA BVS within 180 days under normal and high blood pressures were simulated by finite element method, and more four degradation indexes were defined to study the effects of the two blood pressures on the degradation of the PLA BVS. The results showed that the high pressure weakly accelerated the degradation of the PLA BVS with respect to the normal pressure by examining the four indexes, e.g., the residual stent volumev r ( t ) decreased to 0.72 and 0.69, respectively for the normal and high pressures at day 180. The current finding provided a theoretical understanding of the PLA BVS degradation, and hinted that the PLA BVS may not need to be elaborately selected in clinical practices for treating hypertensive patients.

An integrated mechanical degradation model to explore the mechanical response of a bioresorbable polymeric scaffold

Simulation of bioresorbable medical devices is hindered by the limitations of current material models. Useful simulations require that both the short- and long-term response must be considered; existing models are not physically-based and provide limited insight to guide performance improvements. This study presents an integrated degradation framework which couples a physically-based degradation model, which predicts changes in both crystallinity (Xc) and molecular weight (Mn), with the results of a micromechanical model, which predicts the effective properties of the semicrystalline polymer. This degradation framework is used to simulate the deployment of a bioresorbable PLLA (Poly (L-lactide) stent into a mock vessel and the subsequent mechanical response during degradation under different diffusion boundary conditions representing neointimal growth. A workflow is established in a commercial finite element code that couples both the immediate and long-term responses. Clinically relevant lumen loss is reported and used to compare different responses and the effect of neo-intimal tissue regrowth post-implantation on degradation and on the mechanical response is assessed. In addition, the effects of possible changes in Xc, which could occur during processing and stent deployment, are explored.

Biocompatibility of 3D-printed PLA, PEEK and PETG: Adhesion of Bone Marrow and Peritoneal Lavage Cells

Samples in the form of cylindrical plates, additively manufactured using the fused deposition modelling (or filament freeform fabrication, FDM/FFF) technology from polylactide (PLA), polyethylene terephthalate glycol (PETG) and polyetheretherketone (PEEK), were studied in series of in-vitro experiments on the adhesion of rat bone-marrow cells and rat peritoneal cells. Methods of estimation of the absolute number of cells and polymer samples’ mass change were used for the evaluation of cells adhesion, followed by the evaluation of cell-culture supernatants. The results of experiments for both types of cells demonstrated a statistically significant change in the absolute number of cells (variation from 44 to 119%) and the weight of the polymer samples (variation from 0.61 to 2.18%), depending on roughness of sample surface, controlled by a nozzle diameter of a 3D printer as well as printing layer height. It was found that more cells adhere to PLA samples with a larger nozzle diameter and layer height. For PETG samples, the results did not show a clear relationship between cell adhesion and printing parameters. For PEEK samples, on the contrary, adhesion to samples printed with a lower nozzle diameter (higher resolution) is better than to samples printed with a larger nozzle diameter (lower resolution). The difference in results for various polymers can be explained by their chemical structure.