Fabrication and evaluation of a collagen-based fiber-gel three-dimensional construct for peripheral nerve repair

Nerve regeneration following a peripheral nerve injury often relies on growth cone- mediated guidance and the presence of Schwann cells to support the regenerating axons and remyelinate portions of denervated nerve pathways. The emphasis of this work is to develop a synthetic nervous tissue construct that contains similar basal lamina or extracellular matrix to peripheral nerve in order to achieve a level of effectiveness in nerve repair and future peripheral nerve regeneration applications. To this end, three- dimensional nervous tissue constructs consisting of type I collagen are fabricated into a composite biomaterial scaffold to promote contact-guided growth of neuronal and glial cultures in vitro. The growth of adult tissue on these collagen-based materials is further evaluated. These constructs are assembled by wet spinning synthetic collagen fibers and loading them onto a soft collagen gel matrix composed of type I collagen. Wet-spun collagen fibers serve as a rigid substrate to reinforce the gel while facilitating axon growth cone advancement along a polarized direction. In this study, the emphasis is to characterize the mechanical stability, thermal properties, and swelling response of the collagen fiber component of the construct. To improve these properties in the fiber component, chemical cross-linking with genipin and glutaraldehyde are evaluated. The result is a construct exhibiting mechanical integrity for facilitating adult Schwann cell orientation and the guidance and survival of adult dorsal root ganglion neurons in a co-culture 3-D system

The extraction of type 1 collagen and the fabrication of multi-filament embedded hydrogels for guided nerve regeneration

Each year, there are approximately 11,000 new cases of spinal cord injury (SCI) in the United States [2]. There have been some success in pre-clinical studies to induce axonal generation, but the reconnection of axons over large distances remains the greatest challenge. Since the development of nerve conduit to facilitate general axonal regeneration, the primary focus has changed to directing the regeneration of axons while also promoting their outgrowth over very extensive lesions to ensure functional recovery of transected nerves during in vitro experiments by using natural materials such as type I collagen, which is the largest constituent of the extra- cellular matrix of living tissue. In this project, fabrication of novel constructs for nerve tissue guidance was carried out using homogenous hydrogels and multi-filament arrays of wet-spun fibers/hydrogel composites derived from extracted type I collagen. A comparison of axonal outgrowth on 2D and 3D environments revealed that dorsal root ganglia (DRGs) slightly favored 3D collagen gels compared to 2D collagen substrates after 9 days of culture. DRG neurites grown on 3D collagen gels exhibited optimal growth on a 0.8 mg/ml collagen gel concentration. Extracted type I bovine collagen was wet spun at 2% and 5% wt bovine collagen in ethanol to yield fibers as small as 1.389 μm in diameter. BCA total protein assay and SDS-PAGE were used to validate the quantity and purity of extracted rat tail collagen. Doublet bands present at 235 kDa and 215 kDa and another pair of doublets at 130 kDa and 115 kDa characteristic of rat tail type I collagen were seen for both extracted and commercial rat tail collagen using SDS-PAGE. Low absorbance values from BCA total protein revealed that this technique is not suitable for quantifying rat tail type I collagen

The effect of low-frequency electromagnetic field on human bone marrow stem/progenitor cell differentiation

Human bone marrow stromal cells (hBMSCs, also known as bone marrow-derived mesenchymal stem cells) are a population of progenitor cells that contain a subset of skeletal stem cells (hSSCs), able to recreate cartilage, bone, stroma that supports hematopoiesis and marrow adipocytes. As such, they have become an important resource in developing strategies for regenerative medicine and tissue engineering due to their self-renewal and differentiation capabilities. The differentiation of SSCs/BMSCs is dependent on exposure to biophysical and biochemical stimuli that favor early and rapid activation of the in vivo tissue repair process. Exposure to exogenous stimuli such as an electromagnetic field (EMF) can promote differentiation of SSCs/BMSCs via ion dynamics and small signaling molecules. The plasma membrane is often considered to be the main target for EMF signals and most results point to an effect on the rate of ion or ligand binding due to a receptor site acting as a modulator of signaling cascades. Ion fluxes are closely involved in differentiation control as stem cells move and grow in specific directions to form tissues and organs. EMF affects numerous biological functions such as gene expression, cell fate, and cell differentiation, but will only induce these effects within a certain range of low frequencies as well as low amplitudes. EMF has been reported to be effective in the enhancement of osteogenesis and chondrogenesis of hSSCs/BMSCs with no documented negative effects. Studies show specific EMF frequencies enhance hSSC/BMSC adherence, proliferation, differentiation, and viability, all of which play a key role in the use of hSSCs/BMSCs for tissue engineering. While many EMF studies report significant enhancement of the differentiation process, results differ depending on the experimental and environmental conditions. Here we review how specific EMF parameters (frequency, intensity, and time of exposure) significantly regulate hSSC/BMSC differentiation in vitro. We discuss optimal conditions and parameters for effective hSSC/BMSC differentiation using EMF treatment in an in vivo setting, and how these can be translated to clinical trials