The covalent grafting of poly (sodium 4-styrene sulfonate) on poly (ɛ-caprolactone) was proved to enhance the bioactivity of this polymer. The aim of this article was to perform kinetic studies of the activation and grafting processes and illustrate the influence of several parameters on the grafting rate and on the degradation of the polymer substrate. Results showed that the active groups created on poly (ɛ-caprolactone) surface by ozonation reach a maximum concentration after a short exposure time. Moreover, a kinetic study of poly (sodium 4-styrene sulfonate) grafting on poly (ɛ-caprolactone) substrate showed that the activation energy of this process was low and the influence of conditions such as pH, monomer concentration, time reaction and grafting temperature was deeply significant for the outcome of the treatment. Besides, ozone oxidation and thermal grafting lead to surface degradation, under certain conditions, for example in the presence of Mohr's salt used as a catalyst to enhance grafting rate. The whole study illustrates that ozone-induced grafting is a strong instrument for surface functionalization, although its parameters should be wisely studied and carefully selected. Poly (sodium 4-styrene sulfonate) functionalization improves bioactivity of poly (ɛ-caprolactone) while decreasing the slowness of its biodegradation.

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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.