Preparation And Mechanism Study Of Macroporous And Mechanically Strong Poly(vinyl Alcohol)hydrogels

Articular cartilage plays an important role in absorbing impact,facilitating the even distribution of loads,reducing the friction and wear between the paired joint surfaces and allowing the joints to move smoothly.In case of damage,however,it is hard for the cartilage to self-repair as it is an avascular tissue and lacks sufficient number of chondrocytes.Various interventions have been taken to relieve pain and rebuild the cartilage function.Among them,the replacement of damaged cartilage with artificial materials is a promising treatment method.Poly(vinyl alcohol)(PVA)hydrogel is proposed as the promising candidate for the replacement of articular cartilage due to its high water content,biocompatibility and good mechanical properties.In order to intergate PVA hydrogel with surrounding cartilage tissue firmly,it is necessary to form appropriate pore size and pore structure in the hydrogel to provide a microenvironment for chondrocyte proliferation.Cryogelation is a common method for preparing PVA hydrogels.However,the pore size of the hydrogel prepared by this method is small,which can not meet the need of chondrocyte proliferation and growth.Based on this,PVA hydrogels with macroporous structure and good mechanical properties were prepared by introducing a biocompatible substance(agarose and tannic acid)to promote the formation of ice crystals in cryogelation process.PVA hydrogel with macroporous structure,high porosity and good mechanical properties is prepared by introducing a certain amount of agarose(AG)as ice crystal inducer.Meanwhile,the biocompatibility experiments showed that this PVA hydrogel can maintain cell proliferation and growth well.The formation mechanism of the macroporous and mechanically strong PVA hydrogel is further studied and we find the function of AG is twofold.The addition of AG results in a large number of water molecules being aggregated around AG molecules,which promotes the formation and growth of ice particles and ultimately forms macropore in hydrogel.On the other hand,this water molecules aggregation phenomenon also increases the local PVA concentration thereby the crystallinity,enhancing the mechanical properties of hydrogels.Poly(vinyl alcohol)-tannic acid(PVA-TA)composite hydrogels with macroporous structure and good mechanical properties were further prepared.The biocompatibility experiments show that the PVA-TA hydrogel could promote the proliferation and growth of chondrocytes effectively.The strong hydrogen bond between PVA molecular chain and TA molecule is the key factor for the formation of macropores and the improvement of mechanical properties in the PVA-TA hydrogel.This hydrogen bond improves the mechanical properties of the hydrogel directally.It also causes a large number of PVA molecular chains in precursor to cluster together simultaneously,which results in the non-uniform distribution of PVA in the precursor.The regions with low PVA content have stronger ability to form ice particles.Ultimately,large ice particles formed during freezing induce the formation of macropores in hydrogel.