Structural Design And Injectability Of Temperature Sensitive Injectable Hydrogels

Temperature-sensitive injectable hydrogel can be gelatinized in situ through in body temperature changes after injected into the body.As a new type of biomedical material,it avoids the highly traumatic surgery,simplies the treatment process,reduces patient pain and saves medical costs.Therefore,it has wide applications in drug controlled releasing,cell embedding and tissue scaffolds.Traditional PNIPAm-based injectable hydrogels with the high proportion of hydrophobic groups tend to bind cell adhesion and proliferation due to phase transitions induced by temperature-sensitive properties.At the same time,PNIPAm does not possess bioactive sites and has poor biodegradability.To overcome these shortcomings,we mainly design from the following two aspects.On the one hand,grafting RGD active peptide to polymer molecular chains to increase bioadhesive,introduce cell bioactive sites and hydrophilic groups and reduce its temperature sensitivity.On the other hand,core-shell microgel based on the calcium carbonate/carboxymethyl chitosan microspheres(CaCO3/CMC)as core and PNIPAm as shell grafted onto CMC was designed.The hydrogel structure was support by CaCO3/CMC hard-ball and the damage to cells and tissues reduced due to good biocompatibility and degradability of CMC.A series of Poly(NIPAm-co-IAc)copolymers were designed and prepared.Double-bond functionalized polymer PNI10-ene was successfully prepared by grafting hydroxyethyl acrylate(HEA)through catalyzed esterification and short peptide functionalized polymer PNI10-ene-c(RDGfC)was.successfully prepared by grafting c(RDGfC)short peptides through thiol-ene click reaction.The chemical structure,temperature-sensitive properties,injectability and biocompatibility were characterized.The results showed that the low critical solution temperature(LCST)of PNI10-ene-c(RDGfC)polymer solution with the concentration of 3.0 wt%was 34.9-35.8 0C and the complex viscosity was 0.441 Pa·s.The solution rapidly gelation when injected into 37 0C phosphate buffer solution(PBS).Three-dimensional culture of HepG2 cells showed that the proliferation of PNI10-ene-c(RGDfC)hydrogels had a significant effect on cell proliferation compared with pure PNIPAm and Poly(NIPAm-co-IAc)hydrogels,second only to the two-dimensional culture of HepG2 cells by polystyrene tissue culture plate.At the same time RGD sequences grafted onto PNI10-ene-c(RGDfC)polymers promoted the adhesion and proliferation of cells to some extent.Different particle sizes of CaCO3/CMC microspheres were designed and prepared.The microspheres prepared by 50 mg/20 mL CMC and 0.1 mol/L CaCO3 with 876±27 nm particle size and 0.208 dispersion coefficient were the most suitable by filtrating.The content of CMC in CaCO3/CMC microspheres accounts for about 10 wt%,and vaterite formed in the microspheres induced by CMC.CaCO3/CMC-PNIAm microgels were successfully prepared by grafting PNIPAm to CMC through free radical graft polymerization.The VPTT of PNIPAm and CaCO3/CMC-PNIPAm microgels were 30.4 ℃ and 34.1 ℃,respectively.The temperature sensitivity of CaCO3/CMC-PNIPAm microgel reduced compared with PNIPAm microgel and the CaCO3/CMC-PNIPAm microgel rapidly gelation when injected into 37 ℃ PBS.Compared with PNIPAm microgel,CaCO3/CMC hard-balls in CaC03/CMC-PNIPAm microgel play the role of supporting hydrogel structure,which promote cell proliferation better.