Materials and conversion processing techniques are advancing, resulting in more sophisticated vascular implantable solutions. Textile-covered endovascular grafts, tissue valves for aortic valve replacement and polytetrafluoroethylene (PTFE)-covered stents are just a few examples of the biomaterials that are widely used in minimally invasive vascular intervention. Next-generation devices are aiming to create more effective solutions in terms of treatment, biocompatibility, durability and delivery, thanks to new material grades, functional coatings and innovative processing techniques.
The advantages of resorbable biomaterial solutions
The vascular market, like many other medical indications, is moving toward greater adoption of resorbable implantable solutions for coatings, components, and finished devices. This has been made possible with the introduction of more advanced biomaterial processing techniques, which deliver performance improvements that make resorbable materials a more viable solution. Digitally controlled dispersion technology is facilitating the use of resorbable polymeric coverings on current-generation drug-eluting stents, resulting in a bare-metal stent remaining after release of the drug. A considerable number of companies are also developing next-generation bioresorbable vascular scaffolds. This is enabling thinner struts, more comparable to metal stent dimensions, such as the Meril MeRes100, featuring 100µm strut thickness, made from poly-L-lactide (PLLA) material.
Other biological components, such as porcine and bovine valves, are widely used in structural heart devices. However, material supply, along with extensive post-processing for human implantation, add significantly to manufacturing cost. New materials, including reinforced biomaterials, along with novel processing techniques, are being explored to determine if a synthetic alternative can be developed with sufficient biocompatibility, mechanical performance and durability for long-term implantation.
Introducing implants into the vascular system that disappear once their therapy is delivered is an ideal outcome. That’s why resorbable materials are being considered more than ever for a diverse range of next-generation vascular devices. Trauma or perforation injuries can benefit from resorbable coverings and implantable solutions; devices designed for short-term embolic protection and occlusion could resorb into the body without requiring subsequent removal.
Supporting innovation via biomaterial coverings and fabrics
Biomaterial coverings support a broad range of functions such as occlusion, embolic protection, flow diversion, inhibiting restenosis, containing tumor growth, maintaining vessel integrity or supporting heart function. The application of these devices has evolved far beyond traditional coronary and peripheral indications to include endovascular, structural heart, neurovascular, carotid, below-the-ankle and even venous indications. However, despite the wide range of device applications, biomaterial coverings typically function as porous or non-porous barriers.
Textiles are one of the most well-established implant coverings and have been used for many years in grafts and valves. The versatility of fabric enables it to be formed around diverse implant designs, while being thin and flexible enough to deliver through a catheter. Polyethylene terephthalate (PET) fiber is the most common material used in textile vascular applications, due to its proven biocompatibility and established clinical history. Although the fabric can be knitted, it is typically woven to ensure shape stability and durability, while minimizing blood permeability. Advances in high-density, fine-woven grafts have helped reduce Type IV endoleaks resulting from low-level porosity. In addition, higher-strength braided sutures, using material such as UHMWPE, allow for lower-profile suturing, while supporting the introduction of increasingly lower-profile and durable graft systems. Although mechanical fixation and bonding offers support, suturing remains the primary mode for affixing fabric to vascular implants. It requires highly skilled technicians and is extremely time-consuming. As a result, many companies have sought to overcome this challenge with the use of other biomaterials, such as polytetrafluoroethylene. The completely hydrophobic nature of PTFE helps to reduce porosity, and subsequent risk of endoleaks, while the material is applied to a metal frame without the need for suturing.
PTFE is a well-established biomaterial stent covering for indications such as arteriovenous access treatment and renal stenting. New advances in material and processing technology are leading to greater adoption of this material in vascular indications, as exemplified by the Gore Viabahn stent to treat stenosis of the superior femoral artery or the Microport Willis stent for intracranial aneurysms. PTFE also offers a versatile covering option for balloon and self-expanding stent systems, and it’s likely that we will see greater proliferation of its use, not only in the peripheral vascular market, but potentially in structural heart applications.
Synthetic biomaterial coverings
Synthetic biomaterials, such as polyurethane and silicone, have been used to cover implants for decades, primarily in non-vascular indications. But there are limitations to mechanical performance, including strength, durability and deliverability, and problems with protein adherence and biofilm formation post-implantation.
Theroplastic polymeric coatings and membrane coverings have advanced significantly in recent years. Robust polymeric coverings can be applied at several-micron wall thickness, with additional coatings applied to enhance biocompatibility and functional performance. Synthetic biomaterials, including grades of polycarbonate, polyurethane and silicone, are being reconsidered as implant coverings or membranes in the vascular market, offering low-profile solutions in areas including thrombus retrieval, occlusion and embolic protection.
Next-generation devices will increasingly be modified to lower their profile and cost of manufacture or improve in-vivo performance and durability. New biomaterials, including resorbables and functional coatings, play an important role in enabling the next generation of vascular implants and are being introduced to offer more effective solutions for an increasing range of potential applications.