3 results
Using Peptide Hetero-assembly to Trigger Physical Gelation and Cell Encapsulation
- Andreina Parisi-Amon, Cheryl Wong Po Foo, Ji Seok Lee, Widya Mulyasasmita, Sarah Heilshorn
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- Journal:
- MRS Online Proceedings Library Archive / Volume 1272 / 2010
- Published online by Cambridge University Press:
- 01 February 2011, 1272-NN05-08
- Print publication:
- 2010
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Stem cell transplantation holds tremendous potential for the treatment of various trauma and diseases. However, the therapeutic efficacy is often limited by poor and unpredictable post-transplantation cell survival. While hydrogels are thought to be ideal scaffolds, the sol-gel phase transitions required for cell encapsulation within commercially available biomatrices such as collagen and Matrigel often rely on non-physiological environmental triggers (e.g., pH and temperature shifts), which are detrimental to cells. To address this limitation, we have designed a novel class of protein biomaterials: Mixing-Induced Two-Component Hydrogels (MITCH) that are recombinantly engineered to undergo gelation by hetero-assembly upon mixing at constant physiological conditions, thereby enabling simple, biocompatible cell encapsulation and transplantation protocols. Building upon bio-mimicry and precise molecular-level design principles, the resulting hydrogels have tunable viscoelasticity consistent with simple polymer physics considerations. MITCH are reproducible across cell-culture systems, supporting growth of human endothelial cells, rat mesenchymal stem cells, rat neural stem cells, and human adipose-derived stem cells. Additionally, MITCH promote the differentiation of neural progenitors into neuronal phenotypes, which adopt a 3D-branched morphology within the hydrogels.
Cell-Adaptable Protein Scaffolds for Spinal Cord Nerve Regeneration
- Karin Straley, Cheryl Wong Po Foo, Sarah Heilshorn
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- Journal:
- MRS Online Proceedings Library Archive / Volume 1062 / 2007
- Published online by Cambridge University Press:
- 01 February 2011, 1062-NN03-05
- Print publication:
- 2007
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A key attribute missing from current state-of-the-art biomaterials is the ability to be remodeled by the host after implantation. In contrast, the natural extracellular matrix (ECM) is constantly being remodeled by proteases secreted from cells in response to local environmental changes. Mimicking this strategy, we have designed a new protein-based scaffold that can be degraded and remodeled on demand by the growth cones of regenerating neurites. Using recombinant protein techniques, we synthesized a family of biodegradable and biologically active scaffold materials. The scaffolds include peptide sequences derived from natural ECM proteins. Interspersed with these ECM domains are proteolytic sequences readily degraded by tissue plasminogen activator (tPA) and urokinase plasminogen activator (uPA), two proteases secreted by the growth cones of extending neurites. By altering the primary amino acid sequences of the protease cleavage domains, we can tune the degradation rates of otherwise identical engineered proteins in a controlled and predictable manner over approximately two orders of magnitude. These recombinant proteins are crosslinked to form bulk, protein-based scaffolds with mechanical properties that can be tuned to match that of the spinal cord. Initial cell experiments have shown that the proteins support growth and differentiation of the model PC-12 neuronal-like cell line. By tailoring the scaffold degradation rate to the tPA and uPA secretion levels of specific neuronal populations, we aim to fabricate a scaffold that will promote neurite extension through the matrix by allowing local degradation to occur specifically around the neuronal growth cone while maintaining the bulk integrity of the overall scaffold.
Protein-Based Hydrogels for Cell Transplantation under Constant Physiological Conditions
- Cheryl T Wong Po Foo, Sarah Heilshorn
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- Journal:
- MRS Online Proceedings Library Archive / Volume 1060 / 2007
- Published online by Cambridge University Press:
- 01 February 2011, 1060-LL09-04
- Print publication:
- 2007
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A promising treatment for multiple neurological disorders including stroke, Huntington's, and Parkinson's is the transplantation of stem cells into the diseased site to promote regeneration of the neural tissue. However, viability of transplanted cells is often low (15-35%) and unpredictable. Cell viability has been directly correlated with functional outcome of the treatment, motivating the development of more reliable cell transplantation procedures. To protect transplanted cells from shear stress during injection and from the hostile, inflammatory environment of the diseased brain tissue, many research groups are exploring physical hydrogels as a protective, growth-permissive matrix to enhance cell viability. However, physical hydrogels require an environmental trigger to induce gelation. These environmental triggers include sudden changes in temperature, pH, or salt concentration - all of which are detrimental to encapsulated cells and proteins and complicate their use in a clinical environment. To address this need, we have designed a two-component, protein-based hydrogel system that can self-assemble under constant physiological conditions.
Both components of the hydrogel system are created using recombinant protein technology, which allows synthesis of exact monomer sequences within monodisperse polymers. The first hydrogel component is a block copolymer made of several repeats of a peptide sequence encoding the WW domain-fold, a short triple-stranded, anti-parallel, beta-sheet. The WW domains are interspersed with a random-coil, hydrophilic spacer to enhance polymer flexibility and solubility. The second hydrogel component is made of several repeats of a polyproline rich peptide sequence interspersed with a random-coil, hydrophilic spacer. Upon mixing the two hydrogel components together, the WW-domains in component 1 and the polyproline rich peptides in component 2 bind together with 1:1 stoichiometry. This binding has an apparent association constant of 2.2×105 M, as measured by isothermal titration calorimetry. This peptide-binding event serves as the physical crosslinks to form a polymeric network composed of the two components. Because gelation is initiated by simply mixing the two components together at physiological pH, temperature, and ionic strength, this system is highly biocompatible and easy to use. Furthermore, the precision of protein engineering allows both components to be easily modified. For example, increasing the length of the hydrophilic spacers will increase the resulting network pore size. Additionally, bioactive peptide sequences, such as the RGD cell-binding domain, have been introduced into the hydrophilic spacers to modify cell-scaffold interactions. Our long-term objective is to design a self-assembling hydrogel system for cell delivery that will both improve cell viability and mimic many of the essential cues in the developmental niche to encourage cell differentiation and outgrowth.