Technical Papers and Presentations

Introduction: Keratin protein biomaterials (KTN) are used in various tissue engineering applications including liquid infusions and gel implants. Random movement of molecular species is characterized by Fick’s laws of diffusion (and velocity-dependent convection) with the characteristic diffusivity coefficient (D) of solute in a given solvent. Determining D is vital towards a better understanding of the kinetics and transport of KTN.

Materials and Methods: KTN (as solute) was dissolved in 10 mM NaOH solvent at 2, 4, and 8 mg/mL (or 0.02, 0.04, and 0.08 mol/m3 using Mr = 98 kg/mol) and separately tested for diffusion across a narrow 1D-like channel (Fig. 1). 10 mL of solvent was first loaded, then 1 mL of KTN solution at one corner. Solutions were collected at time points 5, 10, and 20 min, and at the bottom at positions 5, 20, 50, 75, and 95 mm of the 105-mm span. Protein concentrations were quantified spectrophotometrically using standards. Concentrations (c) were nondimensionalized by dividing using the equilibrium concentrations (ceq), and positions (x) with the total channel length (L). A MATLAB^® script was developed using method of lines to solve Fick’s 2nd law partial differential equation for c and iterating the diffusivity to match the experimental values. COMSOL Multiphysics^® simulation software was employed to model the geometry and simulate diffusion using the Transport of Diluted Species interface. Parametric estimation study for inverse modeling was also employed for determination of D.

Results and Discussion: Concentrations close to the region of KTN delivery produced high variability (Fig. 2) but the general trend followed the expected diffusion kinetics, towards c/ceq = 1 (at t = ∞). It was found that the diffusivity coefficient of KTN in 10 mM NaOH is 1×10-6 m2/s based on MATLAB^® and verified using COMSOL Multiphysics^®. This relatively high D may also be driven by KTN acid to NaOH electrodynamic interactions and possibly unintended advection.

Conclusions: KTN diffusivity was obtained using a simple experimental approach and is now utilized to model different KTN-based systems, but requires further verification using more accurate instrumentations.