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. 

When choosing one biomaterial over another, the project can be extremely difficult or run very smooth depending on if it is biocompatible, its durability, how much it costs along with how simple it is to produce, and how accessible the material is. If for example the biomaterial chosen is rare and is limited, the project, the even begin will be difficult.  By doing research before beginning a project, it can allow the tasks within the project to proceed with little to no disruptions.  These factors would help the project by finding more accessible products which are safe and biocompatible, otherwise, the team will be faced with possible delays and end up needing to change their basis for the project anyway. 

When choosing biomaterials I believe that cost of the resource, availability, vendor, consistency, and time will be my major concerns. The material must be cost-efficient so that we can stay within project budget. The resource should be able to be sourced locally and often so that we know that there is a reliable source in case more is required later on. The vendor should be trustworthy, and there should be backup vendors for the biomaterial in case the original can't provide the required shipment in time or runs into other issues. Consistency of the material is another key factor if the biomaterial tends to behave differently in batches over small uncontrollable factors it is likely not scalable and will determine if the project fails. Finally, time is a huge factor, a project is defined within a time frame and if the biomaterial takes too long to produce, ship or is only in stock at specific seasons, etc. the project is prone to fail. That said, if you work with a specific biomaterial more often than others, what is it and why?