Biomedical subjects

Adam L Collette

Publications and source records attributed to Adam L Collette.

3 recordsLinked to original sources

PubMed2006

Mechanisms of silk fibroin sol-gel transitions.

Silk fibroin sol-gel transitions were studied by monitoring the process under various physicochemical conditions with optical spectroscopy at 550 nm. The secondary structural change of the fibroin from a disordered state in solution to a beta-sheet-rich conformation in the gel state was assessed by FTIR and CD over a range of fibroin concentrations, temperatures, and pH values. The structural changes were correlated to the degree of gelation based on changes in optical density at 550 nm. No detectable changes in the protein secondary structure (FTIR, CD) were found up to about 15% gelation (at 550 nm), indicating that these early stages of gelation are not accompanied by the formation of beta-sheets. Above 15%, the fraction of beta-sheet linearly increased with the degree of gelation. A pH dependency of gelation time was found with correlation to the predominant acidic side chains in the silk. Electrostatic interactions were related to the rate of gelation above neutral pH. The overall independencies of processing parameters including concentration, temperature, and pH on gel formation and protein structure can be related to primary sequence-specific features in the molecular organization of the fibroin protein. These findings clarify aspects of the self-assembly of this unique family of proteins as a route to gain control of material properties, as well as for new insight into the design of synthetic silk-biomimetic polymers with predictable solution and assembly properties.

Fibroins↗

PubMed2005

Yarn design for functional tissue engineering.

Tissue engineering requires the ability to design scaffolds with mechanical properties similar to those of the native tissue. Here, B. mori silk yarns are used as a model system to demonstrate the potential benefits and drawbacks of several textile methods used to fabricate tissue engineering scaffolds. Fibers are plied, twisted, cabled, braided, and/or textured to form several geometries with a wide range of mechanical outcomes. Predictable changes in ultimate tensile strength and stiffness are demonstrated following processing and as a function of test environment. The mechanical effects of increasing turns per inch and combining groups of fibers into higher-order yarn structures are demonstrated. Braids, one of the most commonly used textile structures, are shown to be limited by a change in stiffness following the locking-angle and therefore, potentially not the ideal structure for tissue engineering. Cabled yarns appear to allow the most flexibility in mechanical outcomes with a highly organized geometry. Twisted yarns, while more economical than cabled yarns, result in a higher stiffness and lower percent elongation at break than cabled yarns.

Animals↗

PubMed2005

In vitro degradation of silk fibroin.

A significant need exists for long-term degradable biomaterials which can slowly and predictably transfer a load-bearing burden to developing biological tissue. In this study Bombyx mori silk fibroin yarns were incubated in 1mg/ml Protease XIV at 37 degrees C to create an in vitro model system of proteolytic degradation. Samples were harvested at designated time points up to 12 weeks and (1) prepared for scanning electron microscopy (SEM), (2) lyophilized and weighed, (3) mechanical properties determined using a servohydraulic Instron 8511, (4) dissolved and run on a SDS-PAGE gel, and (5) characterized with Fourier transform infrared spectroscopy. Control samples were incubated in phosphate-buffered saline. Fibroin was shown to proteolytically degrade with predictable rates of change in fibroin diameter, failure strength, cycles to failure, and mass. SEM indicated increasing fragmentation of individual fibroin filaments from protease-digested samples with time of exposure to the enzyme; particulate debris was present within 7 days of incubation. Gel electrophoresis indicated a decreasing amount of the silk 25 kDa light chain and a shift in the molecular weight of the heavy chain with increasing incubation time in protease. Results support that silk is a mechanically robust biomaterial with predictable long-term degradation characteristics.

Absorbable Implants↗