B. Holmes, H. Asfour, P. Koti, N. Muselimyan, N. Sarvazyan
Nanochon LLC, George Washington University,
Keywords: 3D bioprinting, cardiac tissue engineering, venous valves
Summary:3D printing has been gaining popularity as a method of creating heart valves. However, to the best of our knowledge, no one was yet able to 3D print venous valves, particularly using cells or biocompatible materials. Venous valves are much smaller and more delicate structures as compared to heart valves, therefore they are particularly challenging to produce. Our studies represent the first steps toward creating biocompatible and implantable venous valves using 3D printing and tissue engineering tools. Toward this long-term goal, we pursued the following specific tasks. TASK 1 included exploration of several different valve designs, including a single flap valve, a two-flap valve, a floating ball valve and a tri-leaflet valve. Main dimensions included 5 mm diameter valve and a 1-mm wall thickness. Valves were printed from both silicone and polyurethane material, and demonstrated movable flaps in the presence of fluid. TASK 2 was to compare the viability of primary cardiac fibroblasts and their survival in multiple passages after seeding on to the surface of the optimized silicone cardiac valves. Analysis of cell viability was conducted with microscopy, immunocytochemistry, and bioluminescence imaging with Luciferin and CytoscanTM LDH assays. A BioBot 3D bioprinter was used to print optimized valves from task 1, which were then incubated in 0.1% fibronectin solution for 24 hours at 37 deg C. Cells could be observed forming dense fibers on the outer walls of the valves, which beat spontaneously. Finally, for TASK 3 we designed 3D circular structures to support formation of a ring of tissue-engineered cardiac muscle suitable for implantation around the outer circumference of a the valves. When placed around valve-containing vessel segments such self-beating rings can be potentially used to aid venous return. Scaffolds were designed as 2-mm high rings, with a 6-mm outer diameter and a 5-mm inner diameter. The wall of the ring were printed around the cardiac valves, and then cast with cardiomyocyte laden fibronectin. Primary cardiac myocytes were cultured. Cardiac cells with and without fibrin were observed forming beating structures within the fibrin, forming coherent beating cell structures. Our findings bring creation of implantable venous valves one step closer to reality. Ability to replace and repair these vascular structures will be a major development for a broad spectrum of ailments associated with chronic venous disease.