Construction And Properties Of Biomimetic Cartilage Hydrogels With Lubricity

Osteoarthritis(OA)is a common degenerative disease of the articular cartilage that causes severe joint pain and even disability to hundreds of millions of people worldwide,and imposes a heavy economic burden on patients and society.Articular cartilage has a complex composition and a unique structure which give it excellent lubrication and mechanical properties that enable cartilage to maintain the daily movements of joints over a lifetime.The ultra-low friction coefficient of articular cartilage is due to the boundary layer composed of hyaluronic acid,phospholipids and lubricants.The lubrication dysfunction of cartilage is the key factor in the initiation and development of OA.Currently,there is no effective therapy available to treat OA,and artificial joint materials have problems of serious wear,so the development of lower friction and wear cartilage replacement materials has been a hot topic and key difficulty.Hydrogels are widely considered as ideal replacement materials for cartilage,but still suffer from several problems,such as unsatisfactory friction and wear properties and difficulty in firmly binding subchondral bone.To address the above problems,we have conducted comprehensive studies and the contents are outlined below:Firstly,HPX/PVA biomimetic cartilage lubricating hydrogels were prepared by blending HA/PA and HA/PM(HPX)with PVA by the freeze-thaw cycle method.Because the friction coefficient of polyvinyl alcohol(PVA)hydrogels incorporated highly hydrophilic polymers have been reduced by hydration lubrication,and biomimetic lubricants HA/PA and HA/PM had excellent lubrication properties.Elemental analysis,UV-vis absorption spectroscopy,Xray diffraction and infrared spectroscopy showed that the HA/PA or HA/PM polymers were retained in the HPX/PVA hydrogels by hydrogen bonding or molecular chain entanglement with PVA.The water content and swelling rate of HPX/PVA hydrogels endowed them with excellent water absorption and retention.Compression and creep tests showed that the HPX/PVA hydrogels has a compression modulus similar to that of natural cartilage and has good elastic recovery.Cytotoxicity tests showed that HPX/PVA hydrogels have good cytocompatibility with chondrocytes.Secondly,the effects of moulds,numbers of freeze-thaws,HPX contents,lubricants,loads,sliding speeds,HPX and PVA bonding method and rehydration on the friction coefficient of hydrogels were systematically investigated.The results showed that the A5M1 hydrogels prepared by freeze-thawing seven times and with with the acrylic mould had the lowest friction coefficient(0.025)when hydrogel slided at loads of 5 N,sliding speeds of 0.5 mm/sec and in PBS buffer.The friction coefficient of the A5M1 hydrogels increased with increasing loads,and tends to decrease and then increase with increasing sliding speed,which indicated that the lubrication mechanism of the HPX/PVA hydrogels was mixed lubrication.The lubrication using externally applied HA/PA and HA/PM was far less effective than the internally incorporated HA/PA and HA/PM.The friction coefficient of rehydrated hydrogels retained its original low value.After 12 h of friction between the PVA hydrogels and A5M1 hydrogels,wear of the HPX/PVA hydrogels reduced by 74%.Many scratches observed on the surface of the PVA hydrogels but no visible wear on the A5M1 hydrogels.Finally,in order to solve the problem of poor integration with subchondral bone,the osteochondral integrated bilayer hydrogels were constructed by HPX/PVA lubricating hydrogels combining with β-TCP/PVA porous hydrogel.The results showed that the upper and lower layers of the osteochondral bilayer hydrogels were tightly bound and had strong interlayer bonding properties.The upper layer exhibited a dense structure with good lubricating properties.The lower layer was porous,which facilitated cell migration and proliferation,then formed a biological anchor with the bone tissue.The osteochondral bilayer hydrogels also had high water content,good load-bearing capacity and cytocompatibility.This provides an idea for solving the problem of poor integration with bone tissue.