Degradation of 3D-Printed Porous Polylactic Acid Scaffolds Under Mechanical Stimulus.

Polylactic acid (PLA) is a biodegradable polymer commonly used as a scaffold material to repair tissue defects, and its degradation is associated with mechanical stimulus. In this study, the effect of mechanical stimulus on the degradation of 3D-printed PLA scaffolds was investigated by in vitro experiments and an author-developed numerical model. Forty-five samples with porosity 64.8% were printed to carry out the degradation experiment within 90 days. Statistical analyses of the mass, volume fraction, Young's modulus, and number average molecular weight were made, and the in vitro experiments were further used to verify the proposed numerical model of the scaffold degradation. The results indicated that the mechanical stimulus accelerated the degradation of the PLA scaffold, and the higher mechanical stimulus led to a faster degradation of the scaffolds at the late stage of the degradation process. In addition, the Young's modulus and the normalized number average molecular weight of the PLA scaffolds between the experiments and the numerical simulations were comparable, especially for the number average molecular weight. The present study could be helpful in the design of the biodegradable PLA scaffolds.

How does mechanical stimulus affect the coupling process of the scaffold degradation and bone formation: An in silico approach.

BACKGROUND: Implantation of biodegradable bone scaffold is regarded as a promising way to repair bone defects, and the coupling process of scaffold degradation and bone formation is influenced by the physical-exercise-induced mechanical stimulus. METHODS: The scaffold degradation was modeled by a mechanical-stress-regulated degradation algorithm, and the bone formation was modeled by a strain-energy-density-based formation algorithm. Then, the two models were coupled together by considering the transformation of three material states. Employing the finite element method, the effect of the mechanical stimulus represented by exercise duration (ED) and exercise intensity (EI) on the coupling scaffold degradation and bone formation was numerically studied. RESULTS: Both the final and minimum bone volume fraction and Young's modulus of the coupling scaffold-bone system were generally increased with improved EDs and EIs. The bone volume fractions of the formed bone in all cases were comparable to selected natural cancellous bones, but the Young's moduli were greater than the natural cancellous bones. CONCLUSIONS: This work sheds light on the regulation of mechanical stimulus on the coupling process of the scaffold degradation and bone formation, and provides a potential in silico way to pre-evaluate the performance of degradable scaffold for bone repair.

Effect of mechanical stimulation on the degradation of poly(lactic acid) scaffolds with different designed structures.

Biodegradability is one of the required scaffold functions for bone tissue engineering, and it is influenced by the mechanical micro-environment after scaffold implantation into body. This paper aimed to develop a mathematical model to numerically study the mechanical impact on the degradation of poly (lactic acid) (PLA) scaffolds with different designed structures. In addition, the diffusion-governed autocatalysis on the scaffold degradation was also included, and the scaffold collapse time by an author-developed algorithm was determined. The results showed that an increase in mechanical stimulation led to an increase in the scaffold degradation rate. Moreover, different structures with a similar porosity shared a degradation tendency but had different collapse times, which was very sensitive to the diffusion coefficient of the scaffold. The present study could be helpful to understand the dynamic degradation process of PLA scaffolds, and guide the design of PLA material and scaffold structure. It may be also used as a tool for the evaluation of the in vitro and in vivo degradation performance of scaffolds.