Study Of A Poly(Urethane-urea) With Enhanced Mechanical Properties

Polyurethanes(PUs)with segmental molecular chain structure,adjustable mechanical properties and good biocompatibility and biodegradability,play an important role in biomedical fields.However,the main types of PUs are elastomeric PUs,which are featured with low modulus and thus widely employed for soft tissues repairation such as artificial skin and heart valves.To extend the applications of PUs to bone tissues,development of polyurethanes with high modulus and strength is essentially important.Our previously work prepared a linear segmented poly(urethane-urea)(PEG400-PUU-PPZ)from poly(ethylene glycol)(PEG400)co-initiated poly(D,L-lactic acid)macrodiol(PDLLA-PEG400-PDLLA),hexamethylene diisocyanate(HDI)as a coupling agent,and piperazine(PPZ)as a chain extender.PEG400-PUU-PPZ was proved to have enhanced modulus and strength due to the flexible PEG400 and rigid PPZ,demonstrating promising applications in hard tissue reparation fields.Unfortunately,the optimization of process parameters such as the effects of temperature and time has not been investigated.The main purpose of this study is to optimize the synthesis process so as to further improve the mechanical properties of PEG400-PUU-PPZ.Meanwhile,according to the requirements of the clinical application,the mechanical properties,shape memory effects and biocompatibility of PEG400-PUU-PPZ were evaluated.The main contents and conclusions are as follows:?The linear segmental PEG400-PUU-PPZ was synthesized by two-step method using D,L-Lactide,PEG400,HDI,PPZ as raw materials and stannous octoate(Sn(Oct)2)as catalyst.FTIR and 1H NMR results suggested that PEG400-PUU-PPZ with PDLLAPEG400-PDLLA as soft segment,PPZ and HDI as hard segment has been successfully synthesized.?The effects of temperatures and time during chain extending process were investigated by using intrinsic viscosity([?])as the indicator of molecular weight,and a new process based on gradient heating,i.e.30 oC for 1 h,40 oC for 1 h,and 50 oC for 2 h,was developed.Gel permeation chromatography(GPC)results showed that,the number average molecular weight(Mn)of the obtained PEG400-PUU-PPZTD reached 9.14×104,and the polydisperty indice(PDI)decreased significantly.?The differential scanning calorimetry(DSC)results showed that the glass transition temperature(Tg)of PEG400-PUU-PPZTD reached 46.63 oC.Since water as a plasticizer has been proved to decrease the Tg of PEG400-PUU-PPZ,PEG400-PUUPPZTD might have a near-body-temperaure Tg,thus demonstrating shape memory effect in vivo environment.?The mechanical properties of PEG400-PUU-PPZTD were investigated by using tensile test,compression test,bending test and shear test.The results demonstrated that,the tensile modulus(Et)of PEG400-PUU-PPZTD is about 1.02 GPa,the tensile yield strength(?y)is about 35.51 MPa,the elongation at break(?f)is about 60%;the compressive modulus(Ec)is about 1.17 GPa,the compressive yield strength(?c)is 96.83 MPa;the flexural modulus(Ef)is about 1.23 GPa,the maximum flexural strength(?fM)is 27.13 MPa;and the shear modulus(Es)is 0.31 GPa,shear yield strength(?s)is 33.62 MPa.Compared with the control group Poly(D,L-lactide)(PDLLA,Mn=10×104),PEG400-PUU-PPZTD exhibits good toughness.Compared with the mechanical properties of PEG400-PUU-PPZ which was be constant-temperature heating(Et=0.85 MPa;?y=30.11 MPa),the elastic modulus is improved by about 20% and the strength is improved by about 18%.The optimization of synthesis process is beinificial to improve the mechanical properties of PEG400-PUU-PPZ.?The shape memory properties of the PEG400-PUU-PPZTD were characterized by shape fixation ratio(Rf),the shape recovery ratio(Rr)and the recovery stress(?r).When PEG400-PUU-PPZTD plate was stretched,its Rf was > 95%,Rr was about 75%,?r is about 1.25 MPa;When PEG400-PUU-PPZTD cylinder was compressed,its Rf and Rr were > 95% and ? 65% and ?r is about 0.42 MPa,respectively.These results indicate that PEG400-PUU-PPZTD still has good shape memory effects.?The biocompatibility of PEG400-PUU-PPZTD was investigated according to cell spread and proliferation and cytotoxicity.The results indicate that the biocompatibility of PEG400-PUU-PPZTD meet the requirements of medical biomaterials.All together,the process of gradient heating can improve the molecular weight and mechanical properties of PEG400-PUU-PPZ,moreover the PEG400-PUU-PPZ has good shape memory effects near body temperature and good biocompatibility.All of the results demonstrated that PEG400-PUU-PPZ is a promising bone repair material,process optimization to promote its medical applications.