Other than multiple heat waves, this summer has been all about sports and the excitement of different tournaments. The Europe 2016 soccer league, the 2016 Olympics in Brazil and last but not least on my list is my sons’ soccer endeavors. I am a fan of soccer and as the mother of two young soccer rookies, I’ve become more aware of all the potential injuries that happen on the field. Thus, as a biomaterials blog contributor for Signals, I thought I’d explore the types of biomaterials used to treat sports injuries.
A professional athlete can suffer serious injuries with sometimes devastating consequences for her/his career. Many people witnessed the unfortunate bone injury example of Samir Ait Said, the French gymnast who broke his leg during the Olympics this year. Athletes’ knees, ankles and shoulder joints are the most vulnerable to injury. During the 2010 Winter Olympics, the most common injury location reported was the knee. In the 2012 London Olympics, the shoulder joint took home the gold, and the jury is still out on this year’s event.
The most prevalent points of injuries are those to the connective tissues surrounding bones and muscles in the joints such as tendons, ligaments and cartilage. Tendons and ligaments are dense collagenous tissues and cartilage is a rigid, but less dense, elastic tissue. When any one of these gets injured, the first line of treatment is the body’s own regenerative mechanisms.
For the intrinsic regenerative mechanisms to work, the body’s regenerative cells travel through blood vessels to the site of injury. However, tendons and ligaments have low numbers of cells and blood vessels and adult cartilage are void of blood vessels. Even when the regenerative cells pass to the site of injury, they form a haphazard “scar tissue” since the needed underlying structure is damaged.
Thus, it becomes impossible to rely on intrinsic mechanisms when there is a rupture or complete destruction of the injured body part. Additionally, the invasive nature and increased failure rate of standard surgical procedures such as autografts (for tendon and ligament repair) and microfracture (for cartilage repair) warrants alternative strategies. Therefore, biomaterial scientists focus on designing scaffolds that could provide the needed structural support and at the same time serve as both a carrier and stimulator of local regenerative cells.
In the case of connective tissue repair, natural biomaterials such as collagen, silk, and fibrins and synthetic biomaterials such as polyester and poly-propylene are being investigated. A scaffold needs to be bioresorbable, meaning that it should eventually be dissolved into the body without triggering any immune resistance. At the same time, it needs to have structural properties similar to the normal tissue so that it provides correct mechanical and microenvironmental cues to the regenerating cells.
For instance, collagen fibres have been able to direct alignment of regenerating cells into tendon fibres in vitro and in small animal models. When combined with hydrogels, these structures have shown better mechanical properties and improved functionality for the tendon structure in preclinical settings (i.e. small animal models). There is a high variability in production and sterilization methods for natural biomaterials. For these reasons, synthetic biomaterials were initially considered a safe alternative. Some poly-lactic-co-glycolic acid (PLGA) based scaffolds have shown improved mechanical properties and generation of new tissue when combined with growth factors and stem cells (bone marrow derived stem cells, again in pre-clinical studies). However, there are some reports of poor cellular infiltration and immunogenic and allergic responses, which indicates the need for further investigation before actual use.
With recent advancements in biology, chemistry and engineering, scientists are getting a better understanding of the structural and environmental cues and the extent of the complexity of the biological milieu in each case of injured, diseased or degenerated tissue. They are also getting closer to creating structures with much more refined chemical and mechanical properties to best fit the different requirements in each tissue.
Nevertheless, the unfortunate reality is that we are not at the stage of producing the perfect scaffold yet. Some scaffolds that pass through the different levels of testing – in-vitro, small animals, case studies or even clinical studies in humans – have shown initial promising results in the case of new tissue formation. But, the required functional recovery of the injured tissue for an athlete to be able to return to normal activities without increased risk of re-injury is still missing. The “perfect biomaterial” that results in normal functionality of the injured tissue does not appear in the literature.
This does not mean that we should despair. The good news in the case of athletes is that usually their underlying repair system is not degraded due to age or a compromised immune system and therefore can be guided to hasten its activity. These days, the field of biomaterials is focusing on stimulating the body’s own biological and physiological systems to guide and enhance the repair process instead of just replacing the damaged tissue. (Called cell sheet tissue engineering, this technique will need its own separate post.)
Additionally, scientific studies are innovative and don’t just focus on one approach to solve a problem. In the case of sports injuries, back to normal functionality of the repaired tissue is of high importance. From my understanding, the solution will probably lie in the use of a combination of materials, cells and drugs. And the quest to find the perfect combination will continue among academic, clinical and industrial researchers for years to come. Meanwhile, I’ll be teaching my budding soccer stars to practice caution and get proper training and exercise to prevent injuries.
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