Modern regenerative medicine is on the lookout for implantable materials that can change as the surrounding tissue does, and two Stanford University researchers have made some new gel materials that do just that. Karin Straley and Professor Sarah Heilshorn have developed a method for preparing protein-based implant materials that can evolve with the changing needs of the host biological system. Not only can their new materials change in different ways at different times, they can do so at different places within the implant materials.
The materials, of a type known as hydrogels, are prepared from connected blocks of assorted designer proteins. Certain parts of some blocks degrade on exposure to specific enzymes, creating a three-dimensional pattern throughout the gel. If the gels are in a biological system and the triggering enzymes are selected to be ones produced by the system at a certain place and rate, the pattern evolves in response to the biochemistry of the system.
And, as a bonus for medical treatment, "we also demonstrated that the material released during this pattern formation can be modified to serve as a drug-delivery vehicle, enabling the release of multiple small molecules with distinct spatial and temporal delivery profiles," states Prof. Heilshorn.
It seems the designer proteins were the key to the technological breakthrough. The proteins were prepared as block copolymers, which could then be crosslinked to form a hydrogel. Genetic templates were used to synthesize the protein-polymers, allowing precise, molecular level control over their content. This control enabled the Stanford researchers to develop hydrogels that were initially stable and subject to the usual gel mechanisms, and also to finely tune the degradation rates of selected components on exposure to the relevant proteases.
The new structures could contain completely internal voids or be open, connected geometries. Adding and removing material was no problem as both the protease enzymes that cause the degradation and the degraded material fragments diffuse readily through the hydrogel structure.