Design and Production of Customizable and Highly Aligned Fibrillar Collagen Scaffolds

Abstract

The ability to fabricate anisotropic collagenous materials rapidly and reproducibly has remained elusive despite decades of research. Balancing the natural propensity of monomeric collagen (COL) to spontaneously polymerize in vitro with the mild processing conditions needed to maintain its native substructure upon polymerization introduces challenges that are not easily amenable with off-the-shelf instrumentation. To overcome these challenges, we have designed a platform that simultaneously aligns type I COL fibrils under mild shear flow and builds up the material through layer-by-layer assembly. We explored the mechanisms propagating fibril alignment, targeting experimental variables such as shear rate, viscosity, and time. Coarse-grained molecular dynamics simulations were also employed to help understand how initial reaction conditions including chain length, indicative of initial polymerization, and chain density, indicative of concentration, in the reaction environment impact fibril growth and alignment. When taken together, the mechanistic insights gleaned from these studies inspired the design, iteration, fabrication, and then customization of the fibrous collagenous materials, illustrating a platform material that can be readily adapted to future tissue engineering applications.

Probing the alignment-dependent mechanical behaviors and time-evolutional aligning process of collagen scaffolds

“…in our previous paper. 12 More importantly, we find that longer COL chain lengths can enable similar alignment with much fewer total chains and less tethering if a force equal to or above the previously-determined threshold force (0.05 kcal mol À1 Å À1 ) 12 is applied, comparing Fig. 6(a) against Fig.…”

“…17 To study the effects of the alignment on the mechanical properties of COL networks, we perform uniaxial tensile tests for several COL networks, ranging from fully isotropic to fully anisotropic (i.e., with P 2 values of 0.19, 0.49, 0.71, 0.83, and 0.94). P 2 is an effective parameter to track the conformation of a series of connected particles that is used extensively 12,[22][23][24] for measuring the alignment of polymer chains. It is a validated qualitative measure fluctuating between value of 1 (perfectly aligned) and value of 0 (perfectly disordered).…”

“…To test this, we study how multiple COL structural property parameters, such as COL fibril chain length (e.g., polymerization time), chain numbers (e.g., concentration), tethering (e.g., interfacial bonding during polymerization), and initial conformation, influence the alignment. When we create COL scaffolds under Couette flow, 12 we use a rotating spindle that is coated with a uniform layer of gelatin to provide a surface to adhere/tether COL during fibrillogenesis. The spinning process itself involves multiple steps, wherein the COL monomer units first tether to the gelatin, then simultaneously polymerize and align under flow.…”

“…This paper builds off our preliminary studies, where we showed that the Couette flow generated by the device aligns the COL fibrils during the natural polymerization process to form anisotropic COL scaffolds. 12 We expand on this to provide further insight in the dynamic nature of the alignment process. Specifically, we investigate how the alignment of the fibrils quantitatively affects the mechanical performance of the resulting COL scaffolds, and how efficient, high-quality alignment can be achieved theoretically.…”

“…We recently designed and developed an alternative method to simultaneously polymerize and grow aligned COL fibers as scaffolds at the centimeter scale. 12 This device consists of one rotating inner cylinder and another concentric, stationary outer cylinder.…”