| The synthetic hydrogels have excellent mechanical properties and quick response to environmental stimulus,but the bad biocompatibility and biodegradability of most of these polymers limit their applications in the biomedical field.Recently the biopolymers(like polysaccharides and proteins),which are biocompatible with tissue and have a lot of sensitive groups in chemical structures,attract much attention on production of smart hydrogels,however,these kind of hydogels are always weak in tensile.To solve this problem,blend with synthetic polymer is a very popular modification way.Soy protein and gelatin are two kinds of natural protein,which are from plant and tissue respectively.They are different in physical and chemical structures,but both of them have a lot of ionic groups which made them environmental sensitive. The main purpose of the dissertation is to prepare the soy protein and gelatin-based smart hydrogel fibers by blend modification with synthetic polymer and novel spinning method,and systematically study their response behaviors.For the first time,soy protein(SP) and gelatin(Ge) are blended with hydrolyzed-polyacrylonitrile(H-PAN) respectively to prepare biocompatible,high pH-electrical response H-PAN/SP and H-PAN/Ge hydrogel fibers by wet spinning method.The Glutaraldehyde(GA) is used as the crosslinker for these proteins.The chemical structures,phase morphology and mechanism of formation of hydrogels were studied.The effects of structural and environmental parameters on pH-electrical response of hydrogel fibers were characterized.A novel spinning method(immiscible polymer solution blend spinning) was set up to produce non-continuous Ge ultra-fine fibers from blend of Ge aqueous solution and cellulose acetate butyrate(CAB) ethyl acetate solution.We characterized the rheological properties of the above two solutions and studied the effects of spinning conditions on formation of ultra-free fibers.The dynamical swelling and electrical response of Ge ultra-fine fibers in electrolyte were also studied.The main results are as follows:1.H-PAN/SP hydrogel fiberThe chemical crosslinking from SP and GA,and physical crosslinking from amidines and 5%nitrile groups made the hydrogel into an IPN structure.Due to the self aggregation of SP and hydrophobic effect from H-PAN,a phase separation was induced,and a multi-porous morphology was formed.With an increase of SP,the porosity increased.H-PAN/SP hydrogel fibers showed very good dynamical pH response.With an increase of SP,the response was improved.In the study of their static pH sensitive behaviors,a hysteresis loop was discovered.Equilibrium swelling elongation and contraction speed of hydrogel fibers were decreased with an increase of crosslinking density,while the increase of chemical crosslinking density showed weak effect on elongation speed.The elongation speed became quick with an increase in temperature, while contraction speed displayed a discontinuous change;and high content of SP can stabilize the response under the change of temperature.The exterior load showed an obvious positive effect on elongation,while for contraction,they played a negative role;and it was considered that in the range of 70-100mg,the physical effort in SP would be destroyed.H-PAN/SP hydrogel fibers showed good dynamical electrical response in an un-contacted electric field.High degree of hydrolysis of H-PAN is good to equilibrium bending.Increase the content of H-PAN and crosslinking density can both help increasing the fixed charge density in the network,and improve the bending response.The thinner the fibers were,and the higher the electric potential was,the faster they tended to bend under the electric field.With an increase of medium ionic concentration,the bending behavior showed a discontinuous change.In the pH range 14 to 3,the fibers bended to cathode,while in 2 to 1,they bended to anode;they exhibited polyampholytic properties.2.H-PAN/Ge hydrogel fibers The chemical crosslinking from Ge and GA,and physical crosslinking from amidines and 5%nitrile groups made the hydrogel into an IPN structure.Due to the strong self aggregation of Ge in low temperature,an obvious phase separation was observed,and a multi-porous morphology was formed.In the shrunken state,with an increase of Ge,the porosity increased,while in the swollen state,most of the pores were closed.Urea can denature Ge and destroy the self-aggregation,and reduce the formation of pores.H-PAN/Ge hydrogel fibers showed very good dynamical pH response.With an increase of Ge,the response was improved.In the study of their static pH sensitive behaviors,a hysteresis loop was discovered and the phase transition was weakened due to its strong polyampholytic properties.Equilibrium swelling elongation and response speed of hydrogel fibers were decreased with an increase of crosslinking density.With an increase in temperature,the elongation speed became quick,while contraction was complicated,which at low content of Ge,the speed displayed a discontinuous change and at high content of Ge,the speed became slow.The exterior load showed an obvious positive effect on elongation,while for contraction,they played a negative role.3.Ge ultra-fine fibersGe ultra-fine fibers was produced by extruding the blend of two immiscible solutions,i.e.Ge aqueous solution and CAB(EA) solution,into a warm air flow,and then washed the blend fibers with special solvent to get rid of the matrix.The diameter range of the ultra-fine fibers is around 300nm to 3μm.The shearing and drawing flows of the blend solution are the key effect on formation of the ultra-fine fibers.High L/D and drawing ratio at the nozzle in the blend solution spinning was good for disperse phase to elongation and coalescence of the short microfibril.The microfibrillar structure was easy to happen when the viscosity of Ge aqueous solution is a little bit lower than that of CAB(EA) solution.With the volume ratio of disperse phase to continuous phase,the diameters of both disperse phase and ultra-fine fibers were small and the distribution of diameter was narrow.During the formation of microfibrillar structure,Ge structural transformation occurred from helical(a-helix and triple-helix) to random coil conformation in some extents.Ge ultra-fine fibers showed excellent swelling and electrical response.The three protein-based smart hydrogel fibers exhibit excellent environmental sensitivity.Comparing with the PAN hydrogel fiber,Umemoto reported,the response of H-PAN/SP and H-PAN/Ge hydrogel fibers improved a lot,where the contraction and elongation response times were around 1 and 2 seconds,respectively.The novel method used in preparation of Ge ultra-fine fibers can also be applied to other non-melt polymer systems.The diameter of these fibers is around 300nm to 3μm,and close to the size of natural muscle. |
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