Design And Synthesis Of Shape Memory Polyurethane Based On DMBA

Shape memory polyurethane(SMP)has promising applications in non-/micro-invasive implants because of its shape memroy effects.Its recovery strain or stress may exert mechanical stimuli to cells or tissues so as to promote the growth and differentiation of mechano-sensitive tissues e.g.bone tissues.However,desirable biomaterials require specific bioactivity to promote adhesion and induce tissue growth,by which rapid tissue repair or regeneration can be realized.Unfortunately,few attentions have been paid to the design and prepartion of bioactive SMP.It should be noted that covalent incorporation of bioactive molecules requires reactive groups in SMP.Therefore,the design and prepartion of reactive SMP becomes the most important for the preparation of bioactive SMP.This study is intended to systhesize a SMP with reactive carboxyl groups(SMP-COOH)by using PEG400 co-initiated poly(D,L-lactide)diol(PDLLA-PEG-PDLLA)as soft segment,hexamethylene diisocyanate(HDI)as coupling agent and 2,2-dimethylolbutanoic acid(DMBA)as chain extender.DMBA has better solubility when compared with commonly employed 2,2-dimethylol propionic acid(DMPA),and has moderate reactivity when compared with diamines,which may help to form linear SMP by avoiding cross-linking from highly reactve diamine as chain extender.Subsequently,RGDS adhesive peptide was covalently introduced into SMP-COOH through the reaction sites of carboxyl,forming bioactive SMP(SMP-RGDS)with both shape memory effect and adhesive activity.The main contents and conclusions are as follows:(1)SMP-COOH was synthesized from PDLLA-PEG-PDLLA,HDI and DMBA with anhydrous toluene as the solvent and stannous octoate(Sn(Oct)2)as the catalyst.1)FTIR,1H-NMR results showed the successful synthesis of SMP-COOH by using by using a two-step process.2)The amount of carboxyl group in SMP-COOH was quantitatively detected according to the method of "Determination of partial acid value and total acid number in polyester resin".The results showed that,with the increase molar ratio of HDI/PDLLA-PEG-PDLLLA from 1.4 to 1.6,the content of COOH increased from 47.41 mmol/kg to 86.98 mmol/kg.3)The results of GPC showed that the molar ratio of HDI / PDLLA-PEG-PDLLAD had a significant effect on the molecular weight of SMP-COOH.The molecular weight of SMP-COOH decreased with the increase molar ratio of HDI / PDLLA-PEG-PDLLA.(2)The properties of SMP-COOH with the highest molecular weight of was investigated,which the molar ratio of PDLLA-PEG-PDLLA / HDI / DMBA is 1.0/1.4/0.4.1)Hydrophilic/hydrophobic: The static water contact angle of the film of SMP-COOH is 69.1°,consistent with the forecast,SMP-COOH is a kind of hydrophilic material.2)Thermal performance.Low temperature DSC analysis showed that the glass transition temperature(Tg)of SMP-COOH was 41.96oC.TGA analysis showed that SMP-COOH began to undergo thermal degradation at the temperature of 227oC,and the weight loss rate was 5% at the temperature of 256oC.This result provides guidance for the choice of shape memory temperature and thermal processing temperature.3)Tensile mechanical properties.The tensile strength of the "dumbbell" plate is 40.37 MPa,the modulus is 1669.42 MPa,and the elongation at break is 12.09%,which indicated the good mechanical properties.4)The shape memory performance was detected by SMP-COOH film stretching.The results show that when the deformation rate is fixed at 200%,the fixation rate(Rf)is 93% and the recovery rate(Rr)is 78.6%,the SMP-COOH film possess a good shape memory performance.(3)Using N-hydroxysuccinimide(NHS)as the activator,1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride(EDC)was used as the condensing agent,DMSO as solvent,The amino group of the RGDS adhesion polypeptide is condensed with the carboxyl group of SMP-COOH to form a new material SMP-RGDS having cell adhesion activity.The structure of SMP-RGDS was characterized by elemental analysis(EA)and amino acid analysis(AAA).1)The content of N in SMP-RGDS was 0.66 wt%,which was higher than 0.58 wt% in SMP-COOH.The content of RGDS in SMP-RGDS was calculated to be about 8.16 ?mol/g.2)The results of AAA show that the average content of RGDS in SMP-RGDS is about 11.58 ?mol/g.(4)The cell compatibility of SMP-COOH and SMP-RGDS was preliminarily evaluated by osteoblasts as model cells.Laser confocal observation of cytoskeletons showed that cytoskeleton morphology and spreading of osteoblasts were superior to SMP-COOH films on SMP-RGDS filmsCell proliferation experiments showed that compared with SMP-COOH,osteoblasts on SMP-RGDS thin films could adapt to the membrane environment more quickly and enter the cell proliferation stage.In this study,SMP-COOH prepared with DMBA as a chain extender has good mechanical properties and shape memory properties.After further introduction of cell adhesion polypeptide RGDS,the prepared SMP-RGDS has better cytocompatibility The SMP-RGDS,which is designed according to the overall modification idea,is expected to be a new type of bone repair material with both shape memory properties and biological activity.The related modification ideas and the preparation method of SMP-RGDS are also Can be used to prepare other "SMP-biologically active molecules" materials.