Strain-induced multiscale structural evolutions of crystallized polymers: From fundamental studies to recent progresses

https://doi.org/10.1016/j.bioactmat.2022.01.017

A review on biodegradable biliary stents: materials and future trends

Coronary artery disease (CAD) is the leading killer of humans worldwide. Bioresorbable polymeric stents have attracted a great deal of interest because they can treat CAD without producing long-term complications. Bioresorbable polymeric stents (BMSs) have undergone a sustainable revolution in terms of material processing, mechanical performance, biodegradability and manufacture techniques. Biodegradable polymers and copolymers have been widely studied as potential material candidates for bioresorbable stents. It is a great challenge to find a reasonable balance between the mechanical properties and degradation behavior of bioresorbable polymeric stents. Surface modification and drug-coating methods are generally used to improve biocompatibility and drug loading performance, which are decisive factors for the safety and efficacy of bioresorbable stents. Traditional stent manufacture techniques include etching, micro-electro discharge machining, electroforming, die-casting and laser cutting. The rapid development of 3D printing has brought continuous innovation and the wide application of biodegradable materials, which provides a novel technique for the additive manufacture of bioresorbable stents. This review aims to describe the problems regarding and the achievements of biodegradable stents from their birth to the present and discuss potential difficulties and challenges in the future.

The Development of Design and Manufacture Techniques for Bioresorbable Coronary Artery Stents.

For its unique flexibility, self-expandable braided stent has been wildly used in the treatment of peripheral vascular diseases, such as the superficial femoral artery stenosis. With the application of bioabsorbable polymer materials, stent braided by polymer filaments is explored, and expected to minimize the complications caused by long-term retention of commercial metallic stents in the human body. Poly (L-lactic acid) (PLLA) is the representative of degradable polymer materials, and has been broadly applied in stent for its good mechanical properties and biocompatibility. This study aimed to propose a new preparation method for PLLA self-expandable braided stent by mixed-braided technology, and evaluate its mechanical properties especially in radial supporting performance and flexibility. For this purpose, a series of stent samples were prepared by mixed braiding PLLA monofilament with different diameters. In addition, the pitch angle and monofilament diameter are also considered as two critical design parameters affecting stent mechanical performance. Then, the radial strength and flexibility of different samples were evaluated respectively. The results show that the mixed-braided stent keep the excellent flexibility of thin monofilament braided stent, meanwhile it possesses the good radial supporting performance of the thick monofilament braided stent. This paper provides an idea to improve the comprehensive mechanical properties of PLLA self-expandable braided stent. 

Mixed-braided stent: An effective way to improve comprehensive mechanical properties of poly (L-lactic acid) self-expandable braided stent.

Cardiovascular disease is a major threat to human health worldwide, and vascular transplantation surgery is a treatment method for this disease. Often, autologous blood vessels cannot meet the needs of surgery. However, allogeneic blood vessels have limited availability or may cause rejection reactions. Therefore, the development of biocompatible artificial blood vessels is needed to solve the problem of donor shortage. Tubular fabrics prepared by textile structures have flexible compliance, which cannot be matched by other structural blood vessels. Therefore, biomedical artificial blood vessels have been widely studied in recent decades up to the present. This article focuses on reviewing four textile methods used, at present, in the manufacture of artificial blood vessels: knitting, weaving, braiding, and electrospinning. The article mainly introduces the particular effects of different structural characteristics possessed by various textile methods on the production of artificial blood vessels, such as compliance, mechanical properties, and pore size. It was concluded that woven blood vessels possess superior mechanical properties and dimensional stability, while the knitted fabrication method facilitates excellent compliance, elasticity, and porosity of blood vessels. Additionally, the study prominently showcases the ease of rebound and compression of braided tubes, as well as the significant biological benefits of electrospinning. Moreover, moderate porosity and good mechanical strength can be achieved by changing the original structural parameters; increasing the floating warp, enlarging the braiding angle, and reducing the fiber fineness and diameter can achieve greater compliance. Furthermore, physical, chemical, or biological methods can be used to further improve the biocompatibility, antibacterial, anti-inflammatory, and endothelialization of blood vessels, thereby improving their functionality. The aim is to provide some guidance for the further development of artificial blood vessels.

The Influence of Textile Structure Characteristics on the Performance of Artificial Blood Vessels

Although poly(l-lactic acid) (PLLA) is the widely used material for bioresorbable stents, publications on PLLA braided stents are still lacking. In this paper, the PLLA monofilaments were prepared via melt spinning and solid-state drawing. The total draw ratios are from 2.8 to 30.8. The properties of the monofilaments, such as crystallinity, elastic modulus, elongation at break, were characterized. Due to the relatively good mechanical properties, PLLA monofilaments with draw ratio of 16.8 were used to braid carotid stents. The curve of the radial force of the braided PLLA stent almost overlaps with that of a Carotid Wallstent with similar parameters, which indicates that the braided PLLA stent can provide adequate support to the carotid lesion.

Poly( l -lactic acid) monofilaments for biodegradable braided self-expanding stent

The effect of intrinsic characteristics on mechanical properties of poly(l-lactic acid) bioresorbable vascular stents.

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Poly( l -lactic acid) monofilaments for biodegradable braided self-expanding stent

The effect of intrinsic characteristics on mechanical properties of poly(l-lactic acid) bioresorbable vascular stents.