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.