Biomaterials Popular polymers The main class of polymers used in resorbable
implants belongs to a family called poly α-hydroxy esters. And for good reason: as well as being biodegradable and biocompatible, they’re widely accessible and have a history of safe use. Polyglycolide (PGA) and polylactide (PLA) are two of the most prominent examples. PGA is a high-strength polymer that’s typically completely resorbed within a few months, whereas PLA degrades comparatively slowly. They can also be combined to create the copolymer PLGA, says Paul Hatton, professor of biomaterials science at the University of Sheffield’s School of Clinical Dentistry. “By making PLGA, you can kind of tune the resorption rate.”
These polymers are also known for their mechanical properties, adds Reece Oosterbeek, associate professor of engineering science at the University of Oxford. “PLA and PGA, and copolymers of those, relative to other polymers, are reasonably strong. So, they’re attractive for the types of applications we’re interested in.” For instance, in orthopaedic devices where an implant needs to support the load while the tissue around it is healing. However, they have a notable drawback: as they absorb water, they erode in bulk. That is, rather than degrading layer by layer – called surface- eroding behaviour – the entire implant is affected by degradation throughout its bulk, leading to a progressive loss of mechanical properties over time. While this behaviour can be predicted to an extent, it makes it more difficult to forecast and control the implant’s mechanical properties over time. “What we would really like is surface eroding behaviour,” Oosterbeek says, which is much more predictable. To some extent, the degradation rate of a polymer can be managed. Reducing its crystallinity can accelerate breakdown, while other strategies – such as limiting water absorption, increasing hydrophobicity, or altering the material’s underlying chemical structure – can influence how quickly chemical bonds are broken, thereby slowing the degradation process.
Plus, when the implants do degrade, they can have undesirable knock-on effects. Oosterbeek gives an example: PLA breaks down into lactic acid, which creates an acidic environment around the tissue. “If that builds up too much, that can trigger an unfavourable response in the tissue around it.” All these factors must be considered when designing an implant. As well as ensuring it’s the right shape and stiffness, and will degrade in an acceptable way, you need to be sure it won’t cause harm, says Hatton. “You’ve got to get the right polymer in the right form, in the right situation.”
www.medicaldevice-developments.com
Resorbable polymer vs resorbable membrane
While both are designed to disappear inside the body, resorbable polymers and resorbable membranes serve distinct roles in medical implants. Resorbable polymers – like PLA, PGA and PLGA – are the foundational materials used to build scaffolds and implants. These tend to be denser, offering structural support where needed, and are engineered to degrade safely over time, aligning with the mechanical properties of native tissue. In contrast, resorbable membranes are thin, fl exible sheets made from these polymers, designed primarily as barriers; for example, to guide tissue regeneration or separate healing zones. Their lower density makes them ideal for non-load- bearing applications.
Both play a crucial role in advancing next-generation, surgery-free implant solutions. Dental membranes
The purpose of a dental membrane is to prevent gum from growing into the bone cavity. Dental membrane is placed over the bone but under the gum. Resorbable membranes, also known as dissolvable membranes are made from materials such as collagen (porcine or bovine derived), laminar bone, connective tissue transplants as well as resorbable synthetic membranes. They have excellent protective capabilities and great handling properties,
and will dissolves on its own. Source: United Kingdom Dental Membranes Market Outlook to 2033 – Non-Resorbable Membranes and Resorbable Membranes, GlobalData
Fixing in place
When it comes to load-bearing implants like orthopaedic fixation devices, the strength of the polymer is key. “Polymers like PLA and PGA tend to be favoured, where it’s really about being able to support that mechanical load,” says Oosterbeek. For instance, noted in a 2018 paper in the
journal HAND, resorbable implants can have comparable biomechanical properties to metal ones when it comes to fixation of the metacarpal shaft. Resorbable implants might also reduce stress shielding, because the implant transfers weight slowly to the healing bone over time. Yet, notes Hatton, who works across orthopaedics and dentistry, these polymers aren’t as strong as titanium, so you need to use more material. They are also less reliable and carry the risk of inflammation, he adds.
PLLA, a version of PLA that’s hydrophobic and crystalline, has been used in interference screws and plates to fixate tissue and bone. In fact, when it comes to fractures, PLLA is a popular material choice due to how slowly it resorbs, notes a 2012 paper in the Journal of Healthcare Engineering. However, the authors note that while suitable for many applications, PLLA may not be strong enough
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