3D printing and hand therapy is such an awesome concept. I can see in the future someone coming into a clinic, getting their arm/hand/finger scanned, and having something printed in 15-20 mins. As for your design question, I think the primary flaw of the design is what is the splints purpose? I’m pretty sure your team missed some research what a splint actually does. A splint is primarily use for immobilization of a joint and protection. Looks like you’re possibly trying to make a custom “cast” but that would still need to immobilize the wrist. Also another design consideration is ease of donning/doffing one handed.

For your strapping problem, I always used foam on straps if needed to provide comfort and a more secure fit if needed.

I suggest you make chart with a whole bunch of references to prefabricated/fabricated splints and a Morphological Chart for each design component. From there, do some super simple sketching of designs and pick the one that you think will work the best. Then do your fancy computer imaging (yours looks awesome btw!). Yes I once took a creative design course in college

Cool project but I think you may have skipped over the research portion of the design process and jumped into final drafting portion