Investigation On Biodegradable Shape Memory Polymeric Nanocomposites Based On Poly(ε-caprolactone)

Most of biodegradable polymers don't have so excellent shape memory effect, only to limit their application in biomedicine.And for clinical request,if existing thermal-responsive shape memory polymers is used to prepare medical instrument, it would bring some inconvenience on operation.Thus,a novel shape memory polymer is needed to solve those problems.The research in this dissertation has modified an existing biodegradable polymer and thus prepared an excellent shape memory polymer by a new process.Moreover,an attempt has been made to realize self-recovery of shape by a new stimulating approach.Firstly,the shape memory effect has been increased by the way of modifying biodegradable polymer.The crosslinking modification of polyε-caprolactone(PCL) has been carded out using benzoyl peroxide(BPO) as initiator with high activity and low toxicity.A mixed solution including PCL and BPO was first prepared.Then a series of the dried mixture were press-molded at 130℃for 10 minutes in a mould to prepare required slices of c-PCL when the BPO decomposes to initiators and then change the PCL molecules chains to chains initiators.The characterization of shape memory effect of c-PCL shows that the modified method could increase shape recovery of PCL to 40%～50%,in evidence only if a small amount of BPO(1%) is added.When the BPO concentration comes to 3%,the shape recovery nearly comes to 100%.Secondly,a new stimulating approach had been tried to be applied to stimulate the shape recovery in consideration of the limitation of thermal-responsive shape memory polymer in medicine.The PCL was used again as the matrix to prepare a c-PCL/Fe₃O₄ nanocomposite.In this process,BPO and Fe₃O₄ nanoparticles were first introduced to,the PCL,and the same method was employed to accomplish crosslinking reaction in PCL.The results of shape memory effect showed that this composite posses excellent shape memory effect(shape recocery ratio＞90%) not only in 55℃hot water but in an alternate magnetic field with f=20kH and H=6.8kA/m.However,the more Fe₃O₄ were used,the slower the shape recovery of the c-PCL/Fe₃O₄ nanocomposite.Especially,when the concentration of Fe₃O₄ come to 25%,shape recovery of composite has decreased to the level of PCL before modified.Finally,the effect of in vitro degradation of c-PCL/Fe₃O₄ nanocomposite on the shape memory effect was also investigated.The result showed that the shape memory effect decreased when this nanocomposite experienced in vitro degradation. The reason from the morphologic feature and gel fraction analysis may be that the breakage of physical compactness and chemical network are two key factors resulting in a decreasing shape memory effect for c-PCL/Fe₃O₄ nanocomposite.