Long-term hydrolytic degradation study of polycaprolactone films and fibers grafted with poly(sodium styrene sulfonate): Mechanism study and cell response

Abstract

Polycaprolactone (PCL) is a widely used biodegradable polyester for tissue engineering applications when long-term degradation is preferred. In this article, we focused on the analysis of the hydrolytic degradation of virgin and bioactive poly(sodium styrene sulfonate) (pNaSS) functionalized PCL surfaces under simulated physiological conditions (phosphate buffer saline at 25°C and 37°C) for up to 120 weeks with the aim of applying bioactive PCL for ligament tissue engineering. Techniques used to characterize the bulk and surface degradation indicated that PCL was hydrolyzed by a bulk degradation mode with an accelerated degradationthree times increased rate constant -for pNaSS grafted PCL at 37°C when compared to virgin PCL at 25°C.The observed degradation mechanism is due to the pNaSS grafting process (oxidation, radical polymerization) which accelerated the degradation until 48 weeks, when a steady state is reached. The PCL surface was altered by the pNaSS grafting, introducing hydrophilic sulfonate groups that increase the swelling and smoothing of the surface, which facilitated the degradation. After 48 weeks, pNaSS was largely removed from surface and the degradation of virgin and pNaSS grafted surfaces were similar. The cell response of primary fibroblast cells from sheep ligament were consistent with the surface analysis results: a better initial spreading of cells on pNaSS surfaces when compared to virgin surfaces and a tendency to become similar with degradation time.It is worthy to note that during the extended degradation process the surfaces were able to continue inducing better cell spreading plus preserve their cell phenotype as shown by collagen genes expressions.

Melt-Spun, Cross-Section Modified Polycaprolactone Fibers for Use in Tendon and Ligament Tissue Engineering

“…Leroux et al monitored the pH value of PCL fiber bundles for 120 weeks, detecting no release of acidic species. [55] Besides the degradation products, Fuoco et al report a tendency of PLA to embrittlement and drastic strength loss already after 7 weeks of in vitro degradation in PBS at 37 • C. [16] In contrast to that, we did not observe a mentionable reduction of the elongation at break during PBS exposure at 37 • C for 24 weeks for PCL in the present study. Embrittlement is disadvantageous, in particular, since matching the stiffness of the scaffold with the native ACL is of huge importance for the mechanical performance.…”

“…The presented results on mechanical stability are generally in alignment with previously conducted long-term in vitro hydrolytic studies. Lam et al even report a slight increase in tensile strength during the degradation in PBS at 37 C indicates a reduction from ~320 MPa to ~245 MPa after 12 weeks of degradation, followed by another increase to ~310 MPa after 24 weeks [55].…”

“…Taking into account this limitation shortens the list of appropriate materials considerably, leaving mostly PLA and PCL as synthetic homopolymer alternatives. For PLA as well as PCL, studies report a sufficient long-term stability during degradation [51,54,55]. The potential issue of acidic degradation products of PLA, however, can be particularly problematic in bradytrophic tissue through inflammation, on the one hand, and the risk of autocatalytic degradation and a consecutive strength loss, on the other hand.…”

“…Compared with nanofibrous constructs, however, melt-spun PCL was scarcely investigated as a scaffold material for the human ACL. Leroux et al have achieved promising biological and mechanical results using knotted melt-spun PCL fiber bundles consisting only of 20 fibers [55,61]. However, mechanical and processual feasibility is still due for a human ACL-sized scaffold.…”

“…Lam et al studied the material degradation of PCL extensively and report that PCL can maintain its mechanical properties in vivo for more than 6 months [54]. Leroux et al have performed a long-term in vitro degradation study of PCL fibers for 120 weeks, detecting only minor changes in the pH value and molecular weight during the initial 6 months [55]. In many cases, PCL is characterized by insufficient tensile strength and excessive elongation (such as 23 MPa and >700%, respectively) [24,[56][57][58].…”