Long-term Hydrolytic Degradation Research Articles

Amphiphilic Chitosan Porous Membranes as Potential Therapeutic Systems with Analgesic Effect for Burn Care.

Eliminating or at least lessening the pain is a crucial aspect of burns management, as pain can negatively affect mental health and quality of life, and it can also induce a delay on wound healing. In this context, new amphiphilic chitosan 3D porous membranes were developed and investigated as burns therapeutic systems with analgesic effect for delivery of lidocaine as local anesthetic. The highly porous morphology of the membranes and the structural modifications were evidenced by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and infrared spectroscopy (FTIR). Improved compression mechanical properties, long-term hydrolytic degradation (28 days) evaluation and high swelling capacities (ranging from 8 to 22.6 g/g) indicate an increased capacity of the prepared membranes to absorb physiological fluids (burns exudate). Lidocaine in vitro release efficiency was favored by the decreased content of cross-linking agent (reaching maximum value of 95.24%) and the kinetic data modeling, indicating that lidocaine release occurs by quasi-Fickian diffusion. In addition to the in vitro evaluation of analgesic effect, lidocaine-loaded chitosan membranes were successfully investigated and proved antibacterial activity against most common pathogens in burns infections: Staphylococcus aureus and Methicillin-resistant Staphylococcus aureus.

Hydrolytic degradation of porous poly(hydroxybutyrate-co-hydroxyvalerate) scaffolds manufactured using selective laser sintering

The long-term hydrolytic degradation of porous poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) bone scaffolds manufactured using Selective Laser Sintering (SLS) process have yet to be explored. In this study, SLS PHBV scaffolds were incubated in phosphate-buffered saline (PBS) solution for up to 20 weeks. The result showed that degradation of the PHBV scaffolds occurred predominantly by bulk degradation. With increasing incubation time, the molecular weight and compressive stiffness of the scaffolds reduced while their crystallinity increased. In the first 8 weeks, the weight loss of the scaffolds was insignificant, indicating very limited amount of soluble product was produced by the hydrolysis process. Weight loss started to occur from Week 8; the average weight loss per fortnight was minimal and in the range of 0.33-0.51 %. The pristine PHBV scaffolds had a highly crystalline surface layer with low concentration of the hydrophilic carboxylic acid (COOH) end-groups. The concentration of COOH groups on the scaffold surface increased initially upon immersion in PBS due to the preferential chain rearrangement to expose hydrophilic segments. During immersion surface hydrolysis proceeded and the quantity of COOH groups declined from Week 2 to 6 due to erosion of the surface layer.

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

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 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 degradation-three 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 and radical polymerization), which accelerated the degradation until 48 weeks, when a steady state is reached. The PCL surface was altered by 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 the surface, and the degradation of virgin and pNaSS grafted surfaces was similar. The cell response of primary fibroblast cells from sheep ligament was 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 and preserve their cell phenotype as shown by collagen gene expressions.

Long-Term Hydrolytic Degradation of the Sizing-Rich Composite Interphase

Glass fiber-reinforced composites are exposed to hydrolytic degradation in subsea and offshore applications. Fiber-matrix interphase degradation was observed after the matrix was fully saturated with water and typical water absorption tests according to ASTM D5229 were stopped. Due to water-induced dissolution, fiber-matrix interphase flaws were formed, which then lead to increased water uptake. Cutting sample plates from a larger laminate, where the fibers were running parallel to the 1.5 mm long short edge, allowed the hydrolytic degradation process to be studied. The analysis is based on a full mechanistic mass balance approach considering all the composite’s constituents: water uptake and leaching of the matrix, dissolution of the glass fibers, and dissolution of the composite interphase. These processes were modeled using a combination of Fickian diffusion and zero-order kinetics. For the composite laminate studied here with a saturated epoxy matrix, the fiber matrix interphase is predicted to be fully degraded after 22 to 30 years.

Tunable Degradation of Copolymers Prepared by Nitroxide-Mediated Radical Ring-Opening Polymerization and Point-by-Point Comparison with Traditional Polyesters

Two libraries of well-defined, degradable vinyl copolymers of opposite solubility, based either on methyl methacrylate (MMA) or on oligo(ethylene glycol) methyl ether methacrylate (OEGMA), and containing various amount of 2-methylene-4-phenyl-1,3-dioxolane (MPDL), were synthesized by nitroxide-mediated radical ring-opening polymerization. A comprehensive degradation study (long-term hydrolytic degradation, degradation of thick and thin films, water uptake, enzymatic degradation) was then performed, and results were compared with those from traditional aliphatic polyesters (PLGA, PLA, and PCL). It appeared that P(MMA-co-MPDL) copolymers slowly degraded in PBS with degradation kinetics slower than that of PCL whereas P(OEGMA-co-MPDL) copolymers led to significant degradation, in between that of PLA and PCL, depending on the amount of MPDL, but without leading to a dramatic drop of pH as for PLGA and PLA. Whereas P(MMA-co-MPDL) copolymers might be well-suited for biomaterials intended for long-term use (e.g....

Long-term hydrolytic degradation study on polymer-based embroidered scaffolds for ligament tissue engineering

Following anterior cruciate ligament injury, a mechanically stable tissue replacement is required for knee stability and to avoid subsequent damages. Tissue engineering of the anterior cruciate ligament demands a biocompatible scaffold with a controllable degradation profile to provide mechanical support for 3 to 6 months. It has been argued that embroidered textile scaffolds made of polylactic acid and poly(lactic-co-ɛ-caprolactone) fibres are a promising approach for the ligament tissue engineering with an adapted functionalization and cell seeding strategy. Therefore, the hydrolytic degradation behaviour of embroidered scaffolds made of polylactic acid and a combination of polylactic acid and poly(lactic-co-ɛ-caprolactone) fibres was investigated under physiological conditions for 168 days. The changes in the mechanical behaviour, the molecular weights as well as the surface structures were analysed. Sufficient mechanical properties comparable to native anterior cruciate ligament tissue could be demonstrated for scaffolds made of polylactic acid fibres after 6 months under hydrolysis. These results clarify the potential of using embroidered scaffolds for ligament tissue engineering.

Conformational Footprint in Hydrolysis-Induced Nanofibrillation and Crystallization of Poly(lactic acid).

The origin of hydrolysis-induced nanofibrillation and crystallization, at the molecular level, was revealed by mapping the conformational ordering during long-term hydrolytic degradation of initially amorphous poly(lactic acid) (PLA), a representative model for degradable aliphatic polyesters generally displaying strong interplay between crystallization and hydrolytic erosion. The conformational regularization of chain segments was essentially the main driving force for the morphological evolution of PLA during hydrolytic degradation. For hydrolysis at 37 °C, no significant structural variations were observed due to the immobilization of "frozen" PLA chains. In contrast, conformational ordering in PLA was immediately triggered during hydrolysis at 60 °C and was responsible for the transition from random coils to disordered trans and, further, to quasi-crystalline nanospheres. On the surfaces, the head-by-head absorption and joining of neighboring nanospheres led to nanofibrillar assemblies following a "gluttonous snake"-like manner. The length and density of nanofibers formed were in close relation to the hydrolytic evolution, both of which showed a direct rise in the initial 60 days and then a gradual decline. In the interior, presumably the high surface energy of the nanospheres allowed for the preferential anchoring and packing of conformationally ordered chains into lamellae. In accordance with the well-established hypothesis, the amorphous regions were attacked prior to the erosion of crystalline entities, causing a rapid increase of crystallinity during the initial 30 days, followed by a gradual fall until 90 days. In addition to adequate illustration of hydrolysis-induced variations of crystallinity, our proposed model elucidates the formation of spherulitic nuclei featuring an extremely wide distribution of diameters ranging from several nanometers to over 5 μm, as well as the inferior resistance to hydrolysis observed for the primary nuclei. Our work fuels the interest in controlling nanofibrillation mechanism during hydrolysis of PLA, opening up possibilities for straightforward nanofiber formation.

Effects of hydroxyapatite filler on long-term hydrolytic degradation of PLLA/PCL porous scaffolds

Poly(L-lactic acid)(PLLA)/poly(ε-caprolactone)(PCL)/hydroxyapatite(HAp) composites appear as promising materials for healing large bone defects. Highly porous PLLA/PCL scaffolds, 80/20, 20/80 weight ratios, porosity >85%, were prepared by a dual technique of freeze extraction and porogen leaching, with and without HAp. A double pore structure was obtained, with interconnected macroporosity together with interconnected microporosity. Subsequent long-term (78 weeks = 1.5 years) hydrolytic degradation behavior was investigated in terms of the samples' mechanical properties, molecular weight (Mw), mass changes, thermal characteristics, X-ray Diffraction and Thermogravimetric Analysis. Elastic modulus and yield strength of as-synthesized scaffolds were higher for PLLA rich blends and including the inorganic phase does not lead to a mechanical strengthening in these materials. Nevertheless, after 30 weeks of degradation, PLLA rich scaffolds lost more than half of their strength and rigidity. On the contrary, the densification modulus of the PLLA based blends increased with degradation time, whereas PCL-based blends had a relatively constant densification modulus. PCL-based samples showed lower hydrolysis coefficients k than PLLA-based samples, as expected from the higher density of ester bonds in the latter. Interestingly, although including HAp leads to a lower hydrolysis coefficient k in PCL rich samples, it increases k in the PLLA-based sample, which is consistent with the other results obtained.

Effect of TiO2 nanoparticles on the long-term hydrolytic degradation behavior of PLA

The longer-than-one-year hydrolytic degradation of poly (lactic acid) (PLA)/TiO2 nanocomposites was investigated in phosphate buffer solution of pH 7.4 at 37 °C so as to elucidate the effect of nanofillers on the degradation characteristics of PLA. The temporal changes in appearance, water absorption, number-average molecular weight (Mn), glass transition temperature, melting temperature, and crystallinity of the samples were traced. The results showed that the heterogeneous degradation and bulk-erosion were general mechanisms for PLA and its TiO2 nanocomposites. The change in surface morphology and molecular weight after hydrolysis revealed that the hydrolysis of nanocomposites occurred at the interface of PLA matrix and nanofillers, and the degradation rate was accelerated by the addition of the TiO2 nanofillers. The dispersion of nanofillers in polymer matrix affected the water absorption and degradation rate. The rapid increase of crystallinity also affected the degradation rate of nanocomposites. The present study suggested that the hydrolyzability of PLA could be controlled by adding TiO2 nanoparticles.

Hydrolytic degradation and cracks in resin-modified glass-ionomer cements.

Water-absorption affects the basic properties of resin-modified glass-ionomer cements (RMGICs). Fick's law is usually invoked to explain the absorption process. The purpose of this study is to show that the absorption in accordance with the Fickian model cannot be extended to the whole of the specimen, and that microcrack formation is the main degradation mechanism for specimens cured in a closed environment. For this purpose, flat disk-shaped paste specimens 1.5 mm thick (aspect ratio 4), irradiated in closed conditions between two glass slides and stored in water for approximately 20 months, were analyzed periodically gravimetrically and under confocal fluorescence microscopy, with absorbed eosin used as the fluorescent probe. At pH 7.0, the specimen surface (10-20 micrometers in depth) absorbed water rapidly, swelled, and disintegrated in 20-40 days. Long-term storage produced isolated cracks and grains, no progress in the swelling, and a slow weight decrease. A lower pH (pH 3.5) produced a significant increase of the number of microcracks. The decrease in the irradiation time (30 s or less) enhanced the erosion process, producing very broad cracks. It was concluded that the prevalent mechanism of long-term hydrolytic degradation was based on the slow formation of cracks, whereas only in the early stage of storage did absorption occur quickly in accordance with the Fickian diffusion.