The effects of tensile stress on degradation of biodegradable PLGA membranes: A quantitative study

The inhomogeneous stress distribution of biodegradable stents after implantation affects the local degradation rate of the stents, leading to stress concentration and hence stent fracture. The quantitative relationship between the tensile stress and degradation rate of stent polymer is first investigated in this work. To implement the study, an in vitro degradation of poly(l-lactide-co-glycolide) (PLGA) membranes was incubated in deionized water under different applied tensile stress levels from 0.1 MPa to 0.5 MPa. By a special designed device, the tensile stress level can be maintained constant during degradation. The mass loss and mechanical properties of the membranes during the degradation were sampled each week until the membranes broke. The experimental results showed that over a range of tensile stress, higher tensile stress might lead to quicker loss of mechanical properties. Specifically, remarkable decreases of elastic modulus and tensile strength in 0.5 MPa group were observed. As the magnitude of tensile stress increased, more mass loss was observed in the loaded groups. In conclusion, the mass loss rate and mechanical properties of PLGA was sensitive to the tensile stress level during the in vitro degradation. The load dependency of our data demonstrates the importance of quantifying the effects of tensile stress on the degradation of biodegradable polymers. Moreover, this quantification model could be used as a prediction tool for the optimization of biodegradable polymer stents.