Biomaterial selection is big in my line of work. This can play a big role into what fabrication method is  used for creation of our various models and mechanical characterization of these samples are a very big issue, especially in high throughput models, stiffness, elasticity etc can play big roles in how cells can react in in-vitro models and if you're trying to develop a model for  bone growth vs neuronal growth you're gonna need very different biomaterials. Aside from mechanical stimulus, chemical composition plays just as an important role, because if I am making a cellular model of the brain I'm not gonna use a hydrogel that doesn't have similar ECM components to its native tissue

At first glance, biomaterial selection may seem like a simple process, you pick the material that fits your use case perfectly(lasts longer then you need it too, has no adverse effects in the body, low risk of breaking/failing, long history of use in the body). However, in many cases, probably the majority, you cannot use this ideal material and may have to settle for something lesser but still workable. The material you want me be far to expensive for your budget, but a cheaper, less ideal material exists. There may not be a supplier for the material you want to use that you can easily and reliably source the material from, especially in the quantities you will need. Even if there is a supplier, if there is only one or two, you may not want to pin all the hopes for your device on one supplier staying afloat for the entire life of your device. There may also be a lesser but still good enough material that has previously been used as a biomaterial, which may allow you to piggyback on compatibility testing that has previously been done, saving valuable time and money.

When it comes to biomedical engineering projects (or any type of project really) material choice can make or break your schedule. If I were a project manager, here's how I would think about choosing material for a project. One of the good things about this is that most of the information that I am looking for to determine the right material has already been documented and put into databases (unless you're trying to make a completely new biomaterial, then you're on your own :)). 

Key factors I would look at:

• Regulatory history:
  If a material has been used clinically before, regulators and reviewers are more comfortable — fewer unknowns, shorter safety packages.
• Source & supply-chain reliability:
  Off-the-shelf, multiple-vendor materials reduce procurement risk and speed iterations.
• Natural vs synthetic:
  Natural materials can vary between lots and require extra acceptance criteria. On the other hand, synthetic materials are usually more reproducible and therefore faster to validate.
• Sterilization compatibility:
  Can it be autoclaved, gamma-irradiated, or EO-sterilized without changing properties?
• Mechanical and functional fit for purpose:
  Can the material handle the load it will be subjected to without the need for modifications which can push the timeline.  
• Degradation profile and byproducts:
  Materials that produce problematic byproducts require additional in-vivo testing and monitoring plans.

When I was working on my senior capstone project, one of the major downfalls of the previous designs was the materials that were used in the device, which posed issues when it was autoclaved. Trying to decide on a material that was autoclavable, biocompatible, and can be machined into a specific shape took some time for my team and I to determine. However, once the right material was chosen, most of the manufacturing process was simple to do, especially since the material was easily procurable from Home Depot.