Study On The Preparation And Properties Of Novel Polyurethane/Silk Fabroin Hydrogels

Hydrogels are water-swellable crosslinked polymers that have a hydrophilic groupand can be connected to the water molecules inside networks. Hydrogels can absorblarge amounts of water and swollen to equilibrium, and keep the originalthree-dimensional structure without changing structural integrity. Hydrogels can beused as the nucleus pulposus replacement material because of their good waterabsorption, water retention, and great mechanical properties. Hydrogels can satisfy thenucleus of the human physical and mechanical performance demands, they can freelycontrol the water content when simulating lumbar force, therefore, hydrogels havebeen extensively applicated in the field of artificial nucleus replacement. Polyurethanehydrogel is a crosslinked structure polymer which can absorb large amounts of waterbut insoluble in water, and it is prospected as new functional materials. Silk fibroin is anatural protein polymer which has excellent thermal stability and mechanicalproperties. Here comes a concept which combining advantages of polyurethane andsilk together and designing novel composite polyurethane/silk fibroin hydrogelmaterial, then design orthogonal experimental program table to compare the effects ofdifferent factors on the structure and properties of hydrogels.So the comprehensiveperformance of the hydrogel material can be improved and provide more theoreticalbasis in areas such as artificial disc nucleus replacement.PU was synthesized using isophorone diisocyanate (IPDI) as the hard segmentand poly (ethylene glycol), poly (polyethylene glycol) as the soft segment. PU/SFhydrogels were ultimately prepared by crosslinking interactions. There are manyfactors that affect the properties of PU/SF hydrogels, among which molecular weightof PEG, the ratio of isocyanate and hydroxy, the weight ratio of PEG and PPG and thecontent of SF were the main factors. Orthogonal test carried out based on the four mainfactors with four levels. Orthogonal analysis was applied in swelling properties wastaken as the object, then the optimized parameters were got.The micro structure and morphology of PU/SF hydrogels were investigated usingATR, SEM and DSC. Swelling behaviors including swelling kinetics, the sensitivitiesto temperature, ionic strength and pH were discussed by the traditional gravimetricmethod. The compressive properties of the hydrogels were investigated by mechanicaltests. The relationship between structure and performance of the hydrogels were discussed by swelling and mechanical properties of hydrogels.ATR showed that cross-linked network of hydrogels were formed. SEM imagesshowed irregular porous structure. Changing the molecular weight of the PEG caninfluence the structure of hydrogels, and the greater molecular weight was, the largerthe aperture was. The glass transition temperature was at about-50℃, and the meltingtemperature was in the range of34℃to42℃. Increase the content of PEG or decreasethe content of SF can increase the crystallinity of the hydrogels.Swelling ratio of hydrogels decreased with the increase of the salinity, whileincreased with the increase of molecular weight of PEG and pH, and with increasingtemperature the swelling ratio of hydrogels increased first and then decreased, and37℃was the best temperature. Hydrogels demonstrated impressive swelling behaviors,good sensitivities to temperature, pH and ionic strength. Due to that the Fickianparameters of molecular weight of PEG which was4000were greater than0.5, theinitial swelling stages were thought to be controlled by the non-Fickian diffusion. Thewhole swelling process was well fitted into the Schott second-order kinetic equation.The compressive stress-strain curves of hydrogels showed typical non-linear behaviour.While the molecular weights of PEG were2000,1000,4000and600, the elasticmoduli of hydrogel were in the range of0.29-0.59MPa,0.42-1.14MPa,0.01-0.05MPaand0.50-1.16MPa, and the irreversible compressive failures were above66%.Compressive properties of hydrogels decreased with the increase of the molecularweight of PEG, while increased with the increase of the content of PEG and SF.When molecular weight of PEG was4000, the ratio of isocyanate and hydroxywas3, the weight ratio of PEG and PPG was40%and the content of SF was2%theswelling properties had the best properties.