Every year, 500,000 patients receive treatment for burn injuries, with 40,000 cases requiring hospitalization and 4,000 resulting in fatalities. Swift closure of these wounds is the most important step in burn treatment. However, in patients with massive burn injuries, the area of healthy skin available for grafting is often quite small. In an attempt to solve this problem, skin replacements such as engineered skin are being developed as an alternative method for closing wounds. One of the biggest obstacles for the use of engineered skin is the large disparity in mechanical properties between engineered skin and normal human skin. In order for engineered skin to be a routine alternative for wound closure, significant increases in mechanical properties must be made. It has been found that a biological approach, such as mechanical stimulation, is the most appropriate to achieve the necessary increases in mechanical properties.
The effect of mechanical stimulation on two different scaffold architectures was studied. Non-woven, electrospun fibrous mats along with reticulated sponge scaffolds, both made of collagen, were exposed to mechanical strain profiles to study the effects of mechanical stimulation. The scaffolds were exposed to static strain profiles (0, 5, 10, or 20% additional strain), accumulated strain profiles (20% final strain in 5, 10, or 20% increments), and cyclic strain profiles (0.1 Hz and 5, 10, or 20% strain) then studied using scanning electron microscopy to determine any changes in structure. After undergoing strain, the electrospun scaffolds exhibited significant increases in fiber alignment about the axis of strain and increasing alignment with increasing strain percentages. Although the reticulated sponge scaffolds exhibited pore elongation following mechanical stimulation, the changes in architecture were far less than those of the electrospun scaffolds. It was hypothesized that a scaffold exhibiting less rearrangement would allow more mechanical stimulation to be transferred to the cells and result in a greater increase in mechanical properties.
Following the same static and gradual strain profiles as the acellular scaffolds, engineered skin exposed to mechanical stimulation was found to have a 1.5-2 fold increase in linear stiffness in strained samples, compared to unstrained controls. No change in ultimate tensile strength was measured and no statistical difference was found between stimulation profiles. As this increase in mechanical properties is still far less than for normal human skin, it was thought that increasing the number and frequency of stimulation events would be more effective in increasing the strength of engineered skin. Preliminary data shows that ultimate tensile strength is increased in engineered skin undergoing cyclic strain, however complete conclusions are not possible due to the lack of sufficient data. As expected from acellular experimentation, engineered skin fabricated using reticulated collagen sponges showed greater increases in mechanical properties than engineered skin fabricated using electrospun collagen scaffolds, presumably due to the decreased amount of rearrangement in the collagen sponges following mechanical stimulation.