Robert Wieduwild

Minimal peptide motif for non-covalent peptide-heparin hydrogels.

Reduction of complexity of the extracellular matrix (ECM) to a non-covalent structure with minimal chemically defined components represents an attractive avenue for understanding the biology of the ECM. The resulting system could lead to the design of tailor-made biomaterials that incorporate varying functionalities. Negatively charged glycosaminoglycans are the major components of the ECM. Their interaction with positively charged proteins is important for dynamic three-dimensional scaffold formation and function. We designed and screened minimal peptide motifs whose conjugates with polyethylene glycol interact with heparin to form non-covalent hydrogels. Here we show the structure/function relationship of the (RA)(n) and (KA)(n) motifs and determined that both basic residues and the heparin-induced α-helix formation are important for the assembly process. Simple rules allowed us to tune various aspects of the matrix system such as the gelation rates, biodegradability, rheological properties, and biofunctionality. The hydrogels can encapsulate cells and support cell survival.

Noncovalent Hydrogel Beads as Microcarriers for Cell Culture

Hydrogel beads as microcarriers could have many applications in biotechnology. However, bead formation by noncovalent cross-linking to achieve high cell compatibility by avoiding chemical reactions remains challenging because of rapid gelation rates and/or low stability. Here we report the preparation of homogeneous, tunable, and robust hydrogel beads from peptide-polyethylene glycol conjugates and oligosaccharides under mild, cell-compatible conditions using a noncovalent crosslinking mechanism. Large proteins can be released from beads easily. Further noncovalent modification allows for bead labeling and functionalization with various compounds. High survival rates of embedded cells were achieved under standard cell culture conditions and after freezing the beads, demonstrating its suitability for encapsulating and conserving cells. Hydrogel beads as functional system have been realized by generating protein-producing microcarriers with embedded eGFP-secreting insect cells.

A Repertoire of Peptide Tags for Controlled Drug Release from Injectable Noncovalent Hydrogel

A repertoire of conjugable tags for controlling the release of drugs from biomaterials is highly interesting for the development of combinatorial drug administration techniques. This paper describes such a system of 11 peptide tags derived from our previous work on a physical hydrogel system cross-linked through peptide-heparin interactions. The release kinetics of the tags correlate well with their affinity to heparin and obey Ficks second law of diffusion, with the exception of the ATIII peptide, which displays a stable release profile close to a zero-order reaction. A system for release experiments over seven months was built, using the hydrogel matrix as a barrier between the reservoirs of tagged compounds and supernatant. The gel matrix can be injected without affecting the releasing properties. A tagged cyclosporin A derivative was also tested, and its release was monitored by measuring its biological activity. This work represents a design of biomaterials with an integral system of drug delivery, where both the assembly process of the matrix and affinity capture/release of tagged compounds are based on the noncovalent interaction of heparin with one class of peptides.

Coacervation‐Mediated Combinatorial Synthesis of Biomatrices for Stem Cell Culture and Directed Differentiation

Combinatorial screening represents a promising strategy to discover biomaterials for tailored cell culture applications. Although libraries incorporating different biochemical cues have been investigated, few simultaneously recapitulate relevant biochemical, physical, and dynamic features of the extracellular matrix (ECM). Here, a noncovalent system based on liquid-liquid phase separation (coacervation) and gelation mediated by glycosaminoglycan (GAG)-peptide interactions is reported. Multiple biomaterial libraries are generated using combinations of sulfated glycosaminoglycans and poly(ethylene glycol)-conjugated peptides. Screening these biomaterials reveals preferred biomatrices for the attachment of six cell types, including primary mesenchymal stromal cells (MSCs) and primary neural precursor cells (NPCs). Incorporation of GAGs sustains the expansion of all tested cell types comparable to standard cell culture surfaces, while osteogenic differentiation of MSC and neuronal differentiation of NPC are promoted on chondroitin and heparan biomatrices, respectively. The presented noncovalent system provides a powerful tool for developing tissue-specific ECM mimics.

Layer-by-Layer Assembly of Heparin and Peptide-Polyethylene Glycol Conjugates to Form Hybrid Nanothin Films of Biomatrices

We investigated the utility of a heparin/peptide-polyethylene glycol conjugate system to build layer-by-layer (LbL) structures, to assemble tailored multilayer-biomatrices for cell culture. The LbL assembly balances the advantages of polyelectrolyte systems and protein-based systems. Human umbilical vein endothelial cells showed distinct responses to the film thickness and structure; the presence, density, and spatial arrangement of a cell adhesion ligand within the nanothin film; and the pretreatment of the film with morphogens. The LbL technique presents a versatile tool for modifying cell culture substrates with defined and diverse biochemical and structural features, for investigating cell-material interactions.