During the last few years, hydrogels have raised great interest as potential materials to replace/repair cartilage. Polyvinyl alcohol (PVA) hydrogels have revealed particularly interesting due to their biocompatibility and permeability, ease of processing and manipulation and chemical stability. In addition, PVA hydrogels exhibit a high degree of swelling in water (or in biological fluids) and have a rubbery and elastic nature, making them capable of simulating the natural tissues.
The goal of this study was to investigate the influence of the preparation conditions on the microstructure, mechanical properties and tribological behaviour of hydrogels made of PVA.
Three types of hydrogels were prepared using PVA aqueous solutions (15% wt/v) through different processing methods: cast drying (CD) at 30ºC, freeze-thawing (FT) (5 cycles of 10h of freezing and 2h of thawing) and FT with previous addition of sodium bicarbonate (FT+SB) in the ratio of 5:1 (SB:PVA).
The hydrogels were characterized relatively to their swelling behaviour. Their morphology was analysed by scanning electron microscopy (SEM). The mechanical properties were evaluated through uniaxial tensile and compressive tests, using a texturometer. The friction coefficients (CoF) of the hydrogels (plates) against high density polyethylene and stainless steel (balls) were measured in reciprocal oscillating mode experiments, carried out in a tribometer with loads of 10 and 20N, using PBS as lubricant.
The results showed that the porosity of the hydrogels increased in the order CD<FT<FT+BS. CD samples presented the lowest swelling ratio, but the highest mechanical resistance when compared with the other samples. Concerning the tribological behaviour, low values of CoF (<0.1) were obtained, except for the hydrogels FT+SB.
In conclusion, PVA hydrogels properties are strongly determined by the preparation conditions. CD revealed to be the most suitable method to obtain materials with promising characteristics for cartilage replacement.