Bulk metallic glasses (BMGs) are amorphous metallic alloys with high strength and a low elastic modulus. BMGs have high wear resistance, are resistant to corrosion, and are biocompatible which makes them good potential materials for medical device implants. BMGs with micropatterning also exhibit a reduced foreign body response compared to flat BMGs or some other traditional materials1.
BMGs also exhibit improved endothelial cell adhesion as compared to a nickel-titanium metal1, which may make them good candidates for vascular stents. Additionally, the biocompatibility and relative bio-inertness of many BMGs may allow BMG stents to be implanted with a reduced foreign body response and reduced immunogenicity.
Image 1: Improved endothelial cell adhesion in BMGs as compared to Nitinol, a common material for stents.
Stents can be inserted within the body to open clogged or restricted blood vessels such as arteries or the aorta. Stents are typically made of metal. Stents are typically deployed in two ways: either inflated with a balloon catheter through a procedure known as balloon angioplasty or through the use of a self-expanding stent where no balloon is required. Self-expanding stents are advantageous as they can be easier deployed around bends in arteries or the aorta. However, some current problems with stents are the need for patients to take antiplatelet agents to prevent clotting around the vessel and blockage/occlusion5. Due to the reduced foreign body response seen with BMGs, it is possible that BMGs may mitigate some of the current problems with stent immunogenicity and vessel blockage/occlusion.
Image 2: Left – Balloon expandable stent. Right – self-expandable stent. These are two common methods of deploying stents in humans, using either a shape memory alloy like nitinol that can be self-expanding, or a metal stent that can be inflated using a balloon.
Thus, BMGs may make good biomaterial candidates for fetal stents. Fetal stenting has been performed with some success in clinical trials. Fetal atrial septal stenting with traditional metal-based stent materials resulted in an improved outcome over no treatment2. Fetuses were treated for hypoplastic left heart syndrome. The treatment was only successful in only two of four treated fetuses, which, although an improvement over the current lack of treatments, is not ideal. The two fetuses with unsuccessful treatments developed stenosis of their stents in utero and died after birth. The four untreated fetuses all died after birth.
Image 3: Left – illustration of a healthy aorta. Right – illustration of a restricted aorta that might benefit from the use of a stent.
BMGs may reduce the rate of stent stenosis due to their reduced foreign body response. Therefore, they may represent an important improvement for fetal stent technology.
Future work should be done in the study of BMGs for stenting. First, work should be done in model organisms, such as sheep or pigs. Work in a large-animal model may be easier than a small animal rodent model due to the technical difficulties of delivering a stent in utero. Stenosis of stents composed of nitinol and BMG in treated animals should be compared. The efficacy of stent treatment in reducing infant mortality and/or in utero demise should also be evaluated. Eventually, a clinical trial evaluating these factors should be performed. Hopefully, stents composed of BMG could be used in utero to reduce fetal and neonatal demise.
References:
Ayomiposi Loye. Bulk metallic glasses for biomedical applications. In class lecture.
Charturvedi, R.R., et. al. Fetal stenting of the atrial septum: technique and initial results in cardiac lesions with left atrial hypertension. Int J Cardiol. (2013). 168(3):2029-36.
Kumar, G.P., et. al. Deployment of a bulk metallic glass-based self-expandable stent in a patient-specific descending aorta. ACS Biomater. Sci. Eng. (2016). 2(11): 1951-1958.
Meagher, P., et. al. Bulk metallic glasses for implantable medical devices and surgical tools. Advanced Materials. (2016) 28:27.
“What is a stent?”. American Heart Association.