As the body’s natural scaffolding is largely comprised of collagen, a significant amount of research is being conducted focused on how to engineer collagen scaffolds with properties identical to natively derived collagen. A major benefit of utilizing collagen as the source material for tissue engineering scaffolds is its bioactive chemistry and ability to support cell attachment and growth. Currently, the only commercially successful tissue engineered product, Apligraf®, utilized a collagen scaffolds to form temporary skin. Despite the benefits of collagen-based tissue engineering scaffolds, many challenges are associated with the use of these materials including low strength, low stiffness and long processing times.
This study utilized two materials design approaches to control tissue engineering scaffold mechanics while maintaining the advantageous biological properties of the scaffold. Crosslinking and coaxial electrospinning were utilized to increase collagen scaffold strength, control protein scaffold stiffness, and to control engineered tissue strength. Physical crosslinking of electrospun collagen using dehydrothermal (DHT) treatment was investigated to decrease processing times while increasing the scaffold strength. The efficacy of in situ crosslinking of collagen was also investigated to ascertain whether post-spinning crosslinking could be avoided. Finally coaxial electrospinning was utilized to control the mechanical properties of a gelatin scaffold and the ability of this scaffold type to increase the mechanical properties of engineered tissue was investigated.
All methods employed in these studies, in situ crosslinking, DHT treatment, and coaxial electrospinning, significantly increased the strength of tissue engineering scaffolds. Similarly, every scaffold in this study was able to support human cells within the respective 3D structure. The additional advantage of the scaffolds produced using the coaxial electrospinning process was the ability to control the observed mechanical properties including ultimate tensile strength (UTS) and stiffness. Comparatively the in situ crosslinking method had a low strength which was not significantly different than the DHT treated scaffold and was significantly lower than post-spinning crosslinking with EDC. Based on these results it was determined that in situ crosslinking was not suitable for use in skin tissue engineering scaffolds. While DHT had similar strength as in situ crosslinking, this method did not require chemical treatments and therefore had a significant advantage over chemical crosslinking. The addition of a PCL core to a gelatin fiber had the most significant impact on strength in this study. While the pure gelatin scaffold had a UTS of 223.06±43.58 kPa the coaxial scaffolds ranged in strength from 361.91±114.76 to 623.17±87.26 kPa. Similarly the stiffness of the gelatin was increased from 338.82±67.01 kPa in the gelatin to 1,613.82±670.29 kPa in the coaxial scaffold with the largest core diameter. Engineered skin grown on the coaxial scaffolds was also shown to have significantly greater UTS than the skin grown on the gelatin scaffolds. While in situ crosslinking did not perform as expected, DHT crosslinking and coaxial electrospinning showed promise for use in tissue engineering scaffold stabilization.