Stitches can be required following contact in various sporting events. This occurs at every level from the professional to the  recreational. In a 2016 basketball contest for the Miami Heat of the NBA, Goran Dragic left the game bloody, as seen in figure 1, after taking an elbow to the face. He returned to the floor in the second half with 8 stitches in his lip. An example that shows this occurring in a more “casual” setting is illustrated in figure 2 which depicts that in 2010 Barack Obama also caught an elbow and required 12 stitches to the lip. A desirable material to perform these stitches would be strong enough to hold tissue together and last long enough to allow the body to heal itself. For the examples provided it would also be beneficial if the patient didn’t have to go to the doctors again to get the stitches removed. Therefore natural polymers are a good choice for this application because they can be disposed of by normal metabolic processes.

Figure 1. “Heat guard Goran Dragic leaves the floor for treatment of a cut lip after being called for a foul against Toronto Raptors in Game 2” of 2016 Eastern Conference semifinal. (Dan Hamilton/USA Today Sports)

Figure 2. President Barack Obama walks to his car after a game of basketball in 2010 where he suffered a busted lip. (Tim Sloan/AFP/Getty Images)

In a 2011 paper, Catechol-Functionalized Chitosan/Pluronic Hydrogels for Tissue Adhesives and Hemostatic Materials, Ryu et al. showed that the natural material chitosan could be used to create a hydrogel that could be used as a tissue adhesive. Figure 3 shows a diagram of how this hydrogel would work and figure 4 demonstrates its adhesion properties and how they were tested.

Figure 3. Schematic representation of tissue adhesive, thermosensitive, and in situ cross-linkable CHI-C/Plu-SH hydrogels. (Ryu et al. Biomacromolecules. 2011)

Figure 4. In vitro quantitative adhesion analysis of hydrogels. (A) Illustration of tissue adhesion test using a universal testing machine. (B) Detachment stress of various compositions (Ryu et al. Biomacromolecules. 2011)

Al-Mubarak et al. state in their 2013 paper, Cutaneous Wound Closure Materials: An Overview and Update, that”there are many advantages of tissue adhesives over suturing and other methods of wound closure, such as a lower infection rate, less operating room time, good cosmetic results, lower costs, ease of use, immediate wound sealing, faster return to athletic and work activities, elimination of needle-stick injuries and eliminating the need for post-operative suture removal.” With these benefits in mind, tissue adhesives  made of natural materials may become the new and preferred way to treat lacerations that occur from sports.

The integration of carbon fiber reinforced polymer (CFRP) composites into the structure of prosthetics has changed the way that amputees are able to participate in sports.Figure 1shows the first below-knee prosthesis made purely from CFRP, the Flex Foot, which was  developed by Phillips in 1985. The mechanical properties of the composite including its lightweight, flexibility and high strength are what make it a good material to use for this application. Those properties allow for energy to be stored when the compressive load of a person’s weight is put on the prosthetic. Lifting body weight off as in a step results in decompression and the material returns to its original shape releasing the stored energy. So the carbon fiber composite stores elastic energy while in the stance phase and releases it during the step which aids in the swinging of the leg. This energy store and release system is what enhances a prosthetic’s performance.  When describing  how the amputee/prosthetic system behaves one could assume that it behaves like a perfect spring meaning Hooke’s law would apply and there’d be a linear relationship between stress and strain and no energy would be lost. However, a more realistic model would account for sources of energy loss such as friction, heat and sound. 

Figure 1. Schematic representation of the Flex Foot design (Scholz M.S. et al. Composites Science and Technology. 2011)

In terms of the make up of the material, the carbon fibers imbue strength and the polymer contributes its flexibility.  The concept of property averaging explains that the properties of a composite represent some average of the constituent properties. Because fibers respond in a different mechanical manner  when load is applied parallel  to their orientation vs transversely, the average material property is sensitive to geometry. Therefore, not only is the design of the prosthetic important for its function, but in order to tune performance for individuals the materials composition can be changed. Adjustments that can be made for possible customizations include differing laminate thickness and or fiber orientation.

In conclusion, the mechanical properties of CFRP make it a good material to design prosthetics with that can closely match human limb performance. An  example of what this means in terms of sports and competition is that in 2012 Summer Olympics Oscar Pistorius, shown in figure 2, became the first amputee runner to compete at an Olympic game.

Figure 2. Oscar Pistorius in the Men’s 4×400-Meter Relay, Track and Field finals at the 2012 Summer Olympics in London (Chang W. Lee/The New York Times)

Source: M.S. Scholz et al., The use of composite materials in modern orthopedic medicine and prosthetic devices: A review, Composites Science and Technology 2011