Written by Rosa Comas (Chair) and Laura McKiel (Clerk)
Our first Science Club session, Biomaterials and Biocompatibility, was held last Thursday. Have a look at the summary and come out this week to learn about Nanobiomaterials!
Over the years, the materials used in biomedical applications has grown considerably, which has also forced the definition of biocompatibility to evolve.
The classical biomaterials include metals, ceramics, and polymers. Metals provide excellent strength and are most often used for bone applications, but low quality metals can leach ions into the surrounding tissues and can corrode. Ceramics also provide great strength and can be machined to have extremely smooth surfaces, which is beneficial in joints and other articulating surfaces as they provide a low-friction surface. The disadvantage to using ceramics is that they are very brittle; hence a high force applied could cause it to shatter. There is a wide range of polymers that can be used as biomaterials, which allows for a large selection of mechanical properties and the ability to choose polymers that will degrade in vivo for applications such as drug delivery. Unfortunately, some polymers can create toxic by-products from degradation, and wear particles are easily created if polymers are put in a high-friction area.
Some additional components have been added to these materials over the years, including drugs, cells, and proteins. A general definition for biomaterials in the biomedical field requires that the material “has to have an interface with tissues or tissue components” (Williams, 2009). Due to this requirement, drugs that are incorporated into polymers for drug delivery would not be considered a biomaterial. When considering cells or tissues that are being used for biomedical purposes, they are considered a biomaterial if they are engineered in any way, such as stimulating stem cells to differentiate into another specific cell type. This means that any unaltered tissues, such as with whole organ transplants, are generally not considered biomaterials, but are instead referred to as biological material.
When biomaterials first started being used, they were meant to remain in the body and act essentially as support, for example with a total hip replacement. At that time, biomaterials had to be biologically inert, nontoxic, and they could not cause cancer or irritation to the surrounding tissues. These requirements are what defined biocompatibility. As biomedical applications and biomaterials became more complex, these requirements were not enough. Every biomaterial used still needs to be nontoxic, non-irritating, and can’t cause cancer, but in many applications they are expected to incorporate in the host; either by having tissue grow through them, or by containing proteins or other components that will stimulate the environment around the device. The generally accepted definition of biocompatibility now is:
“Biocompatibility refers to the ability of a biomaterial to perform its desired function with respect to a medical therapy, without eliciting any undesirable local or systemic effects in the recipient or beneficiary of that therapy, but generating the most appropriate beneficial cellular or tissue response in that specific situation, and optimising the clinically relevant performance of that therapy” (Williams, 2008).
Science club participants were divided into 2 groups and discussed two different biomaterial implants and the material properties required for the specific application.
|Vascular Stents||Total Hip Replacement|
|· Material needs to be flexible but also strong
· Anti-thrombogenic/reduced protein adsorption
· Best material: metal coated in polymer – gives strength/shape memory and flexible properties
· Could have heparin bound to the surface to reduce clotting
· Metal could have a magnetic force applied to induce heating to break up the clot
|· Doesn’t interact with blood
· Traditionally metal into femur, head inside acetabular component coated in polymer
· Older patients – could be cheaper by using Metal: stainless steel and Polymer: polyethylene
· Younger patients – need to last a long time so would want a stronger metal like a cobalt alloy
· Want to avoid ceramic due to brittleness
· Usually rough/porous surface on acetabular head to induce cell integration and securing the implant