Engineering Fiber-Based Nervous Tissue Constructs for Axon Regeneration.

Biomaterial-based scaffolds used in nerve conduits including channels for confining regenerating axons and 3-dimensional (3D) gels as substrates for growth have made improvements in models of nerve repair. Many biomaterial strategies, however, continue to fall short of autologous nerve grafts, which remain the current gold standard in repairing severe nerve lesions (<20 mm). Intraluminal nerve conduit fibers have also shown considerable promise in directing regenerating axons in vitro and in vivo and have gained increasing interest for nerve repair. It is unknown, however, how growing axons respond to a fiber when encountered in a 3D environment. In this study, we considered a construct consisting of a compliant collagen hydrogel matrix and a fiber component to assess contact-guided axon growth. We investigated preferential axon outgrowth on synthetic and natural polymer fibers by utilizing small-diameter microfibers of poly-L-lactic acid and type I collagen representing 2 different fiber stiffnesses. We found that axons growing freely in a 3D hydrogel culture preferentially attach, turn and follow fibers with outgrowth rates and distances that far exceed outgrowth in a hydrogel alone. Wet-spun type I collagen from rat tail tendon performed the best, associated with highly aligned and accelerated outgrowth. This study also evaluated the response of dorsal root ganglion neurons from adult rats to provide data more relevant to axon regenerative potential in nerve repair. We found that ECM treatments on fibers enhanced the regeneration of adult axons indicating that both the physical and biochemical presentation of the fibers are essential for enhancing axon guidance and growth.

Engineering muscle tissue for the fetus: getting ready for a strong life.

Congenital malformations frequently involve either skeletal, smooth or cardiac tissues. When large parts of those tissues are damaged, the repair of the malformations is challenged by the fact that so much autologous tissue is missing. Current treatments require the use of prostheses or other therapies and are associated with a significant morbidity and mortality. Nonetheless, affected children have generally good survival rates and mostly normal schooling. As such, new therapeutic modalities need to represent significant improvements with clear safety profiles. Regenerative medicine and tissue engineering technologies have the potential to dramatically improve the treatment of any disease or disorder involving a lack of viable tissue. With respect to congenital soft tissue anomalies, the development of, for example, implantable muscle constructs would provide not only the usual desired elasticity and contractile proprieties, but should also be able to grow with the fetus and/or in the postnatal life. Such an approach would eliminate the need for multiple surgeries. However, the more widespread clinical applications of regenerative medicine and tissue engineering technologies require identification of the optimal indications, as well as further elucidation of the precise mechanisms and best methods (cells, scaffolds/biomaterials) for achieving large functional tissue regeneration in those clinical indications. In short, despite some amazing scientific progress, significant safety and efficacy hurdles remain. However, the rapid preclinical advances in the field bode well for future applications. As such, translational researchers and clinicians alike need be informed and prepared to utilize these new techniques for the benefit of their patients, as soon as they are available. To this end, we review herein, the clinical need(s), potential applications, and the relevant preclinical studies that are currently guiding the field toward novel therapeutics.

Controlled formation of cross-linked collagen fibers for neural tissue engineering applications.

Fibrous scaffolds engineered to direct the growth of tissues can be important in forming architecturally functional tissue such as aligning regenerating nerves with their target. Collagen is a commonly used substrate used for neuronal growth applications in the form of surface coatings and hydrogels. The wet spinning technique can create collagen fibers without the use of organic solvents and is typically accomplished by extruding a collagen dispersion into a coagulation bath. To create well-controlled and uniform collagen fibers, we developed an automatic wet spinning device with precise control over the spinning and fiber collection parameters. A fiber collection belt allowed the continuous formation of very soft and delicate fibers up to half a meter in length. Wet-spun collagen fibers were characterized by tensile and thermal behavior, diameter uniformity, the swelling response in phosphate buffered saline and their biocompatibility with dorsal root ganglion (DRG) neurons and Schwann cells. Fibers formed from 0.75% weight by volume (w/v) collagen dispersions formed the best fibers in terms of tensile behavior and fiber uniformity. Fibers post-treated with the cross-linkers glutaraldehyde and genipin exhibited increased mechanical stability and reduced swelling. Importantly, genipin-treated fibers were conducive to DRG neurons and Schwann cell survival and growth, which validated the use of this cross-linker for neural tissue engineering applications.