C. Brad Bennett

Monte Carlo Simulation of Protioglican-Collagen Fibrils

Proteoglycans play a key role in fibril organization. Proteoglycans bind to the surfaces of collagen fibrils affecting their arrangement. A statistical model was constructed to determine the thermodynamics of proteoglycan-connected collagen fibrils that can be used to understand the formation of collagenous tissues. This model was found to be similar to a clock model. A Metropolis Monte-Carlo algorithm generated sample states of the collagen fibrils for different densities of proteoglycan, at different temperatures. Heat capacities, energies, displacements, and other properties were calculated from these states. The data show areas of interest and a possible phase transition at different temperatures depending on the density.

Mechanical Properties of a Short Tropocollagen Molecule from a Molecular-Dynamics Simulation

Molecular-dynamics simulations are performed on a model collagen molecule in SPC/E water, with and without 100 mM NaCl. To calculate the persistence length, we find the center of mass of each amino acid. We then group the amino acids into triplets, representing each by the (unweighted) average of the three centers of mass. These center-of-mass positions are used as end points for directors. The time-averaged and spatially averaged cosines between directors are found (by determining the scalar product of the directors) as a function of contour length between them.Additionally, two-dimensional projections of the three-dimensional images are constructed, in analogy to the experimental deposition of collagen onto a surface. Techniques for measuring and calculating persistence length from AFM images are used on the two-dimensional projection images, and results are compared to the 2D and 3D Flory-model predictions and to actual experimental results. Values for the Youngs modulus are also presented and compared to experimental values.

Examining the Mechanical Dependency of Molecular Type I Collagen on ion Species and Concentration

In the work to be presented, the polyampholyte behavior of molecular type I collagen was explored. The success of tissue engineering is dependant upon the development of suitable scaffolds for proper cell differentiation. Differentiation is guided, in part, by the mechanical properties of the scaffold housing the cells. Thus, characterization of the mechanics of the native scaffold is of looming importance to this field. The fibrillar collagens, in particular type I collagen, form the native scaffold. The mechanics of these fibrils are determined by the properties of the collagen molecules from which they are formed, and these properties are sensitive to the surrounding ionic environment.The persistence length of molecular collagen was measured as a function of both ionic strength and species in the solvent. It was found that the persistence length increases with ionic strength, for all ion species tested, as might be predicted for a polyampholyte such as collagen. However, the functional form of this increase was not constant for all ionic species, preventing the behavior from being ascribed simply to ionic strength and the effects of electrostatic screening. Using the curves resulting from this work, one can predictably tune the stiffness of molecular collagen by controlling ion type and concentration in the solvent. The research outcomes inform those interested in the physics of biopolymers and those seeking to design biomimetic scaffolds for tissue engineering applications.