| In recent years,shape memory materials have received more and more attention in biomedical research,such as self-expanding cardiovascular and cerebrovascular stents,bone tissue and drug delivery in various minimally invasive surgeries.Polylactic acid(PLLA)and polyvinyl alcohol(PVA)have good biocompatibility and are two typical biomaterials.The constructed shape memory composite system will have great application prospects in the field of biomedical engineering.In the past,the PLLA shape memory system faced the problems of high recovery temperature and poor hydrophilicity,which could not fully meet biomedical applications;although self-healing PVA gel research has been carried out in the past,there are few reports involving shape memory-assisted self-healing and self-healing PVA at the same time.The mechanical strength of the gel is low.In response to the above problems,this paper focuses on polytetrahydrofuran(PTMG)to design and synthesize polymer soft switches with different molecular structures,compositions and properties,which are compounded with PLLA and PVA.The obtained system not only has shape recovery conditions close to the environment adapted to biological tissues,but also The mechanical properties were improved,and the related properties such as hydrophilicity,controlled drug release and self-healing were further studied.The main contents are as follows:(1)A PCL-(PMVS-s-PAA)-PCL-PTMG-PCL-(PMVS-s-PAA)-PCL copolymer was designed as a soft switch,and a water-responsive shape memory system was prepared by compounding PLLA.Since the water absorption of the PAA component of the soft-switching copolymer breaks the hydrogen bonds between the PAA side chains,the mobility of the macromolecules in the switching phase is enhanced,and chain relaxation occurs,and then the switching phase drives the PLLA(stationary phase)for shape switching.At the same time,PTMG is a low melting point elastomer.When the temperature reaches the switching phase transition temperature(Tm),the crystalline region melts into an amorphous segment,and the auxiliary ambient temperature promotes the movement of the switching phase molecules,so the auxiliary ambient temperature helps shape recovery.At 92.0%shape fixation rate,the recovery rate gradually increased from 75%to 94.2%with the increase of water temperature.At the same time,due to the hydrophilicity of the soft-switching polymer,the water contact angle of the composite membrane dropped to 12.0°at 20 min,and the hydrophilicity of PLLA was greatly improved.Due to the uniform dispersion and good interaction of the polymers in the PLLA matrix,the composite films showed excellent toughness and the elongation at break soared to 233.7%.Due to the excellent mechanical properties,hydrophilicity,and water-responsive shape recovery conditions of the composite system,the PLLA composites are expected to be used in the fields of medicine and bionics.(2)On the basis of the previous work,this part used polytetrahydrofuran(PTMG),vinyl acetate(VAc),acrylic acid(AA),tetramethyltetravinylcyclo-tetrasiloxane(D4vi)as raw materials to synthesize amphiphilic soft Switching polymer(PVAD),PVAD is complexed with PLLA,PVAD can encapsulate hydrophilic drugs to form a reservoir-matrix,and controllable drug release system with water-induced shape memory.Since PVAD contains a hydrophilic AA segment,the polymer molecular chain relaxes under water stimulation and drives the movement of the PLLA molecular chain,which leads to an increase in the recovery rate of the composite membrane from 79%at 60°C to 99%at 60°C water.At the same time,due to the influence of soft-segment PTMG in PVAD,when the ambient temperature increases from 25°C to 37°C and continues to increase,PVAD is first activated under the dual stimulation of heat and water(25°C,102 h release 33.3%),and then to the PVAD shell The layer loosened and formed holes(48.7%release at 37°C,18 h),and finally the PVAD molecules were completely loosened,and the PVAD shell opened(60°C,720 min release 84.0%),resulting in accelerated drug release percentage of drug-containing PVAD/PLLA and a burst release.The drug-containing PVAD/PLLA hybrid membrane exhibits symmetric mechanical properties of 29.8 MPa and 44.6%,which can be used as tissue engineering materials.The general strategy easily connects SM with controlled drug release,enabling the encapsulation of hydrophilic drugs by PLLA.A smart biomaterial programming platform.(3)The shape recovery of shape memory can well assist the re-contact of the separated sections of healable materials.In this section,soft-switching polymers(PAA-PTMG-PAA,di PAA-PTMG)containing polyacrylic acid(PAA)and polytetrahydrofuran(PTMG)were synthesized.The PAA block in the molecule not only improves the dispersibility of di PAA-PTMG in water,but also the strong hydrogen bond interaction between its carboxyl group and the matrix PVA,which effectively improves the poor mechanical properties of the previous PVA self-healing materials.The yield stress and elongation at breaking of the PVA composite film were25.97 MPa and 141.2%.The method of shape memory assisting the self-healing process increases the mobility of macromolecular chains and releases the strain energy stored in the molecules,which can then bring detached surfaces closer together to facilitate the healing of damaged materials.The healing effect improved as the healing temperature increased and the healing time increased.After healing,the tensile strength remained at 20.29MPa,and the elongation at break increased to279.8%.And through membrane surface cell proliferation and growth,indicating that the composite membrane has no cytotoxicity.The prepared shape memory and self-healing PVA composites with excellent mechanical properties have broad application prospects in coatings,wearable electronic devices,and medical self-healing synthetic materials. |
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