No abstract

Polyvinyl alcohol (PVA) hydrogels have been widely studied for cartilage replacement due to their biocompatibility, chemical stability, and ability to be modified such that they approximate natural tissue behavior. Additionally, they may also be used with advantages as local drug delivery systems. However, their properties are not yet the most adequate for such applications. This work aimed to develop new PVA-based hydrogels for this purpose, displaying improved tribomechanical properties with the ability to control the release of diclofenac (DFN). Four types of PVA-based hydrogels were prepared via freeze-thawing: PVA, PVA/PAA (by polyacrylic acid (PAA) addition), PVA/PAA+PEG (by polyethylene glycol (PEG) immersion), and PVA/PAA+PEG+A (by annealing). Their morphology, water uptake, mechanical and rheological properties, wettability, friction coefficient, and drug release behavior were accessed. The irritability of the best-performing material was investigated. The results showed that the PAA addition increased the swelling and drug release amount. PEG immersion led to a more compact structure and significantly improved the material’s tribomechanical performance. The annealing treatment led to the material with the most suitable properties: besides presenting a low friction coefficient, it further enhanced the mechanical properties and ensured a controlled DFN release for at least 3 days. Moreover, it did not reveal irritability potential for biological tissues.

Introduction: Polyvinyl alcohol (PVA) hydrogels have been considered very promising materials for the replacement of cartilage tissues due to their biocompatibility, chemical resistance, swelling capacity, and tribological behaviour [1,2]. However, their mechanical properties are still far from those of articular cartilage. In the present work, some PVA hydrogels are prepared with different compositions and under different conditions, to obtain materials with superior physical and mechanical properties. Materials and methods: A 13.5% w/w PVA solution, prepared by dissolving the polymer (Mw 145,000 Da) in pure water for 20 h at 95 C, was poured into Petri dishes and cooled to room temperature (8 h). Cast-drying (CD) (60 C, 80% RH, 7 days) method was used to produce CD PVA gels. Some of these were subsequently annealed for 30 min at 100 C, giving rise to CD PVAþA100 samples. The freeze-thawing (FT) procedure (6 cycles of 16 h of freezing at À20 C and 8 h of thawing at room temperature) was chosen to prepare FT PVA and FT PVAþPAA samples. For the latter case, polyacrylic acid (PAA, MW 100,000 Da) was added to the PVA solution in the ratio of 3:10 (w/w) in relation to the PVA. The materials were characterised in terms of water content, wettability (captive bubble method), microstructure (SEM) and mechanical performance (compression tests). Results: The CD gels presented lower water content and contact angles, a non-porous microstructure (see Figure 1), and higher rigidity than the FT samples. The annealing procedure slightly affected the studied properties of CD PVA , while the addition of PAA improved the water absorption of FT gels. Discussion and conclusions: The characteristics of PVA-based hydrogels can be easily tailored by adjusting the production method or combining PVA with other compounds in order to produce materials that best resemble human cartilage, and that can be used as substitutes for joint cartilage tissue.