Biomedical polymers: synthesis, properties, and applications

Biomedical polymers have been extensively developed for promising applications in a lot of biomedical fields, such as therapeutic medicine delivery, disease detection and diagnosis, biosensing, regenerative medicine, and disease treatment. In this review, we summarize the most recent advances in the synthesis and application of biomedical polymers, and discuss the comprehensive understanding of their property-function relationship for corresponding biomedical applications. In particular, a few burgeoning bioactive polymers, such as peptide/biomembrane/microorganism/cell-based biomedical polymers, are also introduced and highlighted as the emerging biomaterials for cancer precision therapy. Furthermore, the foreseeable challenges and outlook of the development of more efficient, healthier and safer biomedical polymers are discussed. We wish this systemic and comprehensive review on highlighting frontier progress of biomedical polymers could inspire and promote new breakthrough in fundamental research and clinical translation.

SYNTHESIS AND CHARACTERIZATION OF HYDROPHOBIC-HYDROPHILIC MULTIBLOCK COPOLYMERS FOR BIOMEDICAL APPLICATIONS

The synthesis and characterization of amphiphilic copolymers of poly（dimethyl siloxane）(PDMS),poly（ethylene oxide）(PEO), and heparin（Hep） were investigated. These multiblock copolymers wereidentified using;H-NMR, FTIR, end group analysis, and sulfur elemental analysis. The multiblockcopolymers were characterized by using DSC and X-ray diffractometry. The glass transition temperature,crystalline melting characteristics, annealing effect, and cold crystallization of the block copolymers weredetermined by DSC. The crystallinity of the block copolymers was also determined by X-ray diffractionmethod.

Biomedical applications of shape-memory polymers:how practically useful are they?

Shape-memory effect(SME) is the ability of a material to change its dimension in a predefined way in response to an external stimulus. Polymers that exhibit SME are an important class of materials in medicine, especially for minimally invasive deployment of devices. However, the rate of translation of the concept to approved products is extremely low, with mostly nitinolbased devices being approved. In this review, the general aspects of the different types of stimuli that can be used to activate SME are reviewed and sterilization issues of shape-memory polymer(SMP)-based medical devices are addressed. In addition, the general usefulness as well as the limitations of the shape-memory effect for biomedical applications are described.

Biaxial stretching of polytetrafluoroethylene in industrial scale to fabricate medical ePTFE membrane with node-fibril microstructure

Expanded polytetrafluoroethylene(ePTFE)is promising in biomedical fields such as covered stents and plastic surgery owing to its excellent biocompatibility and mechanical properties.However,ePTFE material prepared by the traditional biaxial stretching process is with thicker middle and thinner sides due to the bowing effect,which poses a major problem in industrial-scale fabrication.To solve this problem,we design an olive-shaped winding roller to provide the middle part of the ePTFE tape with a greater longitudinal stretching amplitude than the two sides,so as to make up for the excessive longitudinal retraction tendency of the middle part when it is transversely stretched.The as-fabricated ePTFE membrane has,as designed,uniform thickness and node-fibril microstructure.In addition,we examine the effects of mass ratio of lubricant to PTFE powder,biaxial stretching ratio and sintering temperature on the performance of the resultant ePTFE membranes.Particularly,the relation between the internal microstructure of the ePTFE membrane and its mechanical properties is revealed.Besides stable mechanical properties,the sintered ePTFE membrane exhibits satisfactory biological properties.We make a series of biological assessments including in vitro hemolysis,coagulation,bacterial reverse mutation and in vivo thrombosis,intracutaneous reactivity test,pyrogen test and subchronic systemic toxicity test;all of the results meet the relevant international standards.The muscle implantation of the sintered ePTFE membrane into rabbits indicates acceptable inflammatory reactions of our sintered ePTFE membrane fabricated on industrial scale.Such a medical-grade raw material with the unique physical form and condensed-state microstructure is expected to afford an inert biomaterial potentially for stent-graft membrane.

Recent advances in organic and polymeric carriers for local tumor chemo-immunotherapy

Combination therapy involves the simultaneous administration of compounds with varying mechanisms of action that can improve the efficacy of antitumor therapy and reduce toxicity.The most widely used combination regimen is chemotherapy combined with focused immunotherapy.This is implemented to induce the apoptosis of tumor cells and can activate immune responses,improving the clearance rate of primary lesions and maintaining the resistance to postoperative tumor recurrence and metastasis.Advances in micro/nanotechnology,nanomedicine and biomaterials have contributed to the development of enhanced local drug co-delivery systems for cancer treatment,improving tumor targeting and ameliorating severe systemic complications.Carrier materials can achieve the local long-term controllable release of multiple drugs,which not only avoids rapid drug diffusion from the pathological site,but can achieve synergistic effects at lower drug concentrations.Polymeric carriers display excellent biocompatibility and biodegradability;especially,some of them also have anti-tumor effects.The aim of this article was to review recent progress in the use of organic and polymeric materials for local tumor chemo-immunotherapy,which can be used as carriers for chemotherapeutic drugs,immune adjuvants and genes,including amphiphilic nanoparticles,nanocapsules,nano-disks,nano-polyplex particles,hydrogels and implantable materials.