| Hydrogels are a kind of polymers which have hydrophilic properties, physical and chemical cross-linking structures. Hydrogels can absorb a lot of water but not dissolved in water. Hydrogels can have excellent swelling behaviors, mechanical properties and biocompatibilities by designing different molecular structures. Hydrogels have been applied in tissue engineering and biomedicine fields for their excellent properties. For example, hydrogels can swell or release water and meet the major property requirements of the artificial nucleus. Hydrogels can maintain or imitate the biomechanical function of substances within the disc and have a broad prospect in the application of artificial nucleus pulposus (NP). However, most hydrogels have shortcomings such as low intensity, poor swelling properties and poor stabilities. Therefore, developing hydrogel materials with excellent swelling properties, biocompatibility and biomechanical properties is still full of enormous challenges.Polyurethane (PU) is a kind of polymer materials which is composed of soft segments and hard segments. PU has excellent mechanical strengths, thermal stabilities and workabilities because of the hydrogen bondings between internal micro-phase separation structures and urethane bonds. PU has high design freedom, so the application of PU can be adjusted by designing different structures. Silk fibroin (SF) is a kind of natural protein which is composed of 18 kinds of amino acids. SF has unique secondary structure of macromolecules, excellent mechanical properties, biocompatibilities and thermal stabilities. This study combined the excellent physical and chemical properties of natural and synthetic macromolecules, and prepared a new type of polyurethane/silk fibroin (PU/SF) composite hydrogel. The relationships between compositions, structures and properties of the hydrogels were discussed. The purpose was to prepare a kind of hydrogel material with excellent swelling properties, mechanical properties and explore its potential applications.First, an orthogonal experiment with four factors and four levels was designed. Polyurethane prepolymer (PUP) was synthesized with PEG and polyoxypropylene glycols (PPG) as the main soft segments, IPDI as the hard segment, DMPA and DEG as the chain extender and TEA as the neutralizer. Then PUP was mixed with SF solution in mass ratios. The PU/SF composite hydrogels were synthesized by the reaction between -NH2 and -OH in SF and PUP terminated by -NCO. The swelling behavior and unconfined compression were tested at a constant temperature. The experimental results were analyzed by variance analysis. The results showed that the molecular weight of PEG influenced the properties of hydrogels and the swelling rate most. Swelling kinetics of hydrogels were analyzed, the results showed Fickian diffusion index n was less than 0.5. Fickian diffusion could describle the initial stage of swelling and Schott second-order kinetic model could describle the whole process of swelling. The water absorption of PU/SF composite hydrogels could be as highly as 560% of its own weight. The unconfined compression test showed the stress-strain curves of swollen hydrogels had typical non-linear relationship. The compressive stress of hydrogels were between 0.35-1.20 MPa and the compression modulus of hydrogels increased with the increasing of strains, which indicated PU/SF composite hydrogels had viscoelastic.Two series of different molecular weight PEG hydrogels with different hard segment contents were prepared according to the results of orthogonal experiment. The molecular weight of PEG influenced the properties of PU/SF composite hydrogels was verified by the morphology, swelling properties and compression performance tests. The influences of different hard segments, temperature-sensitive, pH-sensitive and ionic strength-sensitive on the hydrogels were also studied. The results showed that the water absorption was inversely with the temperature, ionic strength, and was proportional to pH, and also influenced by the molecular weight of PEG, which illustrated hydrogels had temperature, ionic strength, pH sensitive. The volume growth rate of swollen hydrogels was proportional to the equilibrium swelling water absorption (ESR). Both of the properties of hydrogels and the change of the volume were taken into account in practical applications, and provide more theoretical and experimental foundations for PU/SF composite hydrogels as artificial nucleus replacement prosthesis materials. |
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