Study On Molecular Structure And Friction Of Doublenetwork Hydrogels

The complicated environment of human body put forward high requirement on biomaterials’ peformances for their biomedical applications, especially on the biocompatibility, mechanical strenghth and lubrication. With the development of biomaterials, a variety of specifically designed products of artificial tissues have been explored for several decades, some of which are already available in the marketplace and routinely used in clinical treatments. Hydrogel is an desired candidate for natural human soft tissue for the polymer networks swollen with large amounts of water, which the same as bio-tissue. The lacking of mechanical strength has long been an limit for hydrogels’ application until the double network (DN) hydrogel which has excellent mechanical performance was proposed. Our research based on the concept of double network, synthesized three hydrogels: sodium alginate/polyacrylamide (SA/PAAm), Polyvinyl alcohol/polyacrylamide (PVA/PAAm), and sodium poly (2-acrylamido-2-methyl-1-propanesulfonic acid)/sodium polyacrylamide-co-acrylic acid to explore the effect of crosslink manners of the first network and the charge of both the two networks to hydrogels’ properties.The SA/PAAm hydrogel exhibits an outstanding elongation and effective energy dissipation. The unnotched sample of SA/PAAm can be stretched to112times its original length while the notched SA/PAAm shows almost no notch-sensitive. Before ruptured, SA/PAAm samples with notches can be stretched to48times its original length as well. As the ionic cross links can rebuilt, SA/PAAm shows good mechanical recovery, the mechanical strength can immediately recovers to30%of the initial value after structure breakdown and the mechanical strength decreased to4%of the initial value. The mechanical and frictional performances of SA/PAAm hydrogel are deeply influenced by ionic solution. In CaCl2solution, the increase of crosslink density of SA network leading the obviously increase of modulus and decrease of swelling degree, but the Debye length of CaCl2solution is too short to screen the repulsive effect between SA and glass substrate. In NaCl solution Na+ionic could exchange the Ca2+which was already associated with SA chains, lead to the decrease of crosslink density of SA network, at the same time, Debye length of NaCl solution enough to screen the repulsive effect between SA and glass substrate and causes the increase of friction.PVA/PAAm hydrogel with a hydrogen bond crosslinked first network shows more excellent mechanical strength and energy dissipation than single PVA hydrogel. Apply an freezing(-20℃,20hour)-thawing(25℃,4hour) cycle to damaged PVA/PAAm, the compress modulus improves69%, as the hydrogen bond rebuilt among freezing-thawing. PVA/PAAm hydrogel has an strong attractive effect with glass substrate because of the attractive effect of both PVA and PAAm with galss.The two networks of PNaAMPS/PNa(AAm-co-AA) hydrogel are both electronegative, strong repulsive force exist between them, couse the increase of hydrogel’s internal stress.-COO-group on AA molecule has stronger polarity than-CONH2group on AAm, leads to the bigger swelling degree of PNaAMPS/PNa(AAm-co-AA). Friction of PNaAMPS/PNa(AAm-co-AA) hydrogel is much more smalle than PNaAMPS/PAAm,as both the two networks have strong repulsive effect with glass substrate, the frictional coefficient of PNaAMPS/PNa(AAm-co-AA) reach0.001, close to the frictional coefficient of animal joint cartilage.