Design And Appliciation Research Of Responsive Polycaprolactone-based Shape Memory Materials

Shape memory polymers（SMPs）are a class of smart polymers that can recover from a temporary shape to a permanent shape under external stimuli.Among them,polycaprolactone（PCL）is a synthetic biodegradable polyester polymer with good biocompatibility.However,its shape memory performance needs to be further improved,mainly including:the transition temperature exceeds the human body tolerance temperature,the inherent hydrophobicity reduces its bioactivity,and PCL-based SMPs have single responsiveness.To this end,this paper designed and prepared a series of novel PCL-based SMPs and explored their application potential in the biomedical field.The related work is as follows:1.To address the issue of high shape memory transition temperature in traditional PCL-based SMPs,which makes it difficult to achieve shape memory in vivo,a novel near-infrared（NIR）light-responsive shape memory polyurethane（PCL-PDA）reinforced with polydopamine nanoparticles（PDANPs）was prepared.The results showed that the hydrogen bonds in the polyurethane affected the crystallization of PCL and reduced the transition temperature of the material（46°C）.PDANPs endowed the material with NIR light-responsive shape memory properties and enhanced the mechanical properties of the polyurethane.In vitro and in vivo studies demonstrated that PCL-PDA had good biocompatibility and exhibited excellent NIR light-responsive shape memory behavior under low-power(0.33 W cm^-2)near-infrared light irradiation.2.Using the more affordable lignin as a photothermal agent,PCL-based NIR light-responsive SMPs were prepared.To address the poor photothermal performance of natural lignin,an innovative approach was proposed by first modifying lignin through demethylation and then complexing it with Fe³⁺to enhance its photothermal properties.The modified lignin was then combined with PCL to prepare polyurethane(PU-DDL+Fe³⁺).The results showed that demethylation significantly increased the phenolic hydroxyl content of DL,and the DDL-Fe³⁺complex structure exhibited strong absorption of NIR light.Consequently,the PU-DDL+Fe³⁺material demonstrated excellent NIR light-responsive shape memory properties.Moreover,this polyurethane exhibited good biocompatibility.3.Based on the characteristics of chronic wounds,including long-term inflammation,susceptibility to infection,and low skin contractility,the PU-DDL+Fe³⁺obtained from the previous work was prepared into a porous foam（DDLPU-foam）and loaded with a hydrogel based on cystamine and catechol-modified sodium alginate（Alg-Cat）to prepare a novel heterogeneous dressing（DDLPU/Alg-Cat）.This dressing possesses low-temperature photothermal antibacterial properties and can provide mechanical contraction force to the wound site through pre-stretching and NIR light irradiation.Additionally,the catechol groups in the Alg-Cat component of the dressing endow it with antioxidant activity and tissue adhesion properties.The synergistic effect of these functions accelerated the healing of chronic wounds in diabetic mice.This dressing provides an effective strategy for the treatment of diabetic chronic wounds.4.The above-mentioned strategies for preparing heterogeneous materials provide a foundation for the preparation of dual-responsive shape memory materials.To this end,we filled polyacrylamide/sodium alginate/polydopamine（PAM/Alg/PDA）hydrogel into PCL-based polyurethane foam to obtain a heterogeneous hydrogel（PU-PAM/Alg/PDA）.This material can achieve thermal responsiveness through the melting-crystallization transition of PCL.Simultaneously,it exhibits ionic responsiveness through the reversible complexation between Alg and Fe³⁺.These dual-responsive characteristics endow the material with the potential to realize complex shape memory behavior and enable the reconfiguration of permanent shapes.Finally,the strong hydrogen bonding between PDA and polyurethane chains,as well as hydrogel molecular chains,enhances the interfacial adhesion,providing the material with good structural integrity and excellent mechanical properties.This material has potential applications in esophageal drug delivery stents.In summary,this thesis addresses the deficiencies of traditional PCL-based SMPs in biomedical applications.A series of multifunctional novel PCL-based SMPs were designed and prepared to meet practical application requirements.The aforementioned materials provide new ideas for the application of shape memory polymers in biomedical fields such as medical implants,chronic wound treatment,and esophageal drug-eluting stents.