Experiment and modelling of the strain-rate-dependent response during in vitro degradation of PLA fibres

Abstract

Polylactic acid (PLA) fibres present, in their pristine state, a strain-rate-dependent behaviour. Their mechanical properties evolve during in vitro biodegradation. Tensile tests of PLA fibres are performed at five different strain rates 0.0001, 0.001, 0.01, 0.05 and 0.1/s and at seven degradation stages, 0, 20, 40, 60, 90, 120 and 150 days in a phosphate buffer solution at constant temperature at 37 °C. The mechanical response is modelled using a modified three-element standard solid model proposed for polymers under finite deformations range. Observations on experimental data lead to the conclusion that the viscous parameters η 1 and η 2 are strain rate dependent, and they vary from 10,762/3202 (N/m s) at the lowest strain rate of 0.0001/s, and 12.2/9.1 (N/m s) at the highest strain rate of 0.1/s for η 1 and η 2 , respectively, thus, depicting the shear-thinning phenomena with the increase in strain rate. Whereas stiffness parameters C 1 and C 2 are degradation dependent, they vary from 21.6/13.7 (N/m) for undegraded PLA fibres and 9.7/5.4 (N/m) for 150 days degraded PLA fibres for C 1 and C 2 , respectively. Decay of stiffness parameters during biodegradation follows an exponential law. The model will be useful to design and develop new fibrous structures for ligament augmentation devices. It could contribute to develop better devices with improved mechanical performance helping those patients in need to repair the ligament tissue.

Biodegradation evaluation of poly (lactic acid) for stent application: Role of mechanical tension and temperature

“…Moreover, the higher the displacement rate, the more stress was generated followed by specimen failure. Similar result was reported in prior research, which illustrated that PLA is a strain‐rate dependent material 43 . According to the risk of fracture, the outputs proved that for the practical applications like stent deployment, it would be better to apply the strain rate as low as possible.…”

Durability of Biodegradable Polymer Nanocomposites

“…Parameters involved in traditional models need to be related to “inherent” degradation of the structure that could also be accelerated by an external mechanical load. In several studies for different biopolymers [ 148 , 152 , 153 , 154 , 155 , 156 ], degradation of mechanical properties (e.g., tensile strength) is directly related to molecular weight reduction.…”

“…Singh and coauthors have studied the effect of hydrolytic degradation and strain rate on the tensile properties of PLA fibres [ 156 ]. The authors applied the modified three-element standard solid model (according to Khan [ 157 ]) introducing degradation-dependent stiffness parameters, while viscous (strain-dependent) parameters are assumed to be unaffected by degradation.…”

“…The stress relaxation was modelled by a linear viscoelastic model introducing a stiffness-related degradation variable. Similarly to [ 156 ], the viscous component was considered independent of degradation time, at least at the early stages. Then, following Viera et al’s definition [ 152 ] and Equation (21), the degradation variable is defined as where is the maximum stress reached at the end of load for a given degradation state and corresponds to the time zero of relaxation, while is the initial value of the relaxation stress for degraded and undegraded material.…”

Influence of viscous-elastic properties of a cylindrical sealing element on its sealing ability

“…In some studies, the focus was given to the study of creep and stress relaxation behavior of biodegradable polymers (Guedes et al, 2017;Martins et al, 2015;Singh et al, 2020).…”