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TECHNICAL PAPERS: Cell

# Cellular Cross-linking of Peptide Modified Hydrogels

[+] Author and Article Information
Jeanie L. Drury

Departments of Biologic and Materials Science, Biomedical Engineering, and Chemical Engineering, University of Michigan, Ann Arbor, MI

Tanyarut Boontheekul

Department of Chemical Engineering, University of Michigan, Ann Arbor, MI

David J. Mooney1

Departments of Biologic and Materials Science, Biomedical Engineering, and Chemical Engineering, University of Michigan, Ann Arbor, MImooneyd@deas.harvard.edu

1

Please address correspondence to: David J. Mooney, Harvard University, 29 Oxford Street, Pierce Hall, Room 325, Cambridge, MA 02138

J Biomech Eng 127(2), 220-228 (Nov 18, 2004) (9 pages) doi:10.1115/1.1865194 History: Received November 14, 2003; Revised October 17, 2004; Accepted November 18, 2004

## Abstract

Peptide modification of hydrogel-forming materials is being widely explored as a means to regulate the phenotype of cells immobilized within the gels. Alternatively, we hypothesized that the adhesive interactions between cells and peptides coupled to the gel-forming materials would also enhance the overall mechanical properties of the gels. To test this hypothesis, alginate polymers were modified with RGDSP-containing peptides and the resultant polymer was used to encapsulate C2C12 myoblasts. The mechanical properties of these gels were then assessed as a function of both peptide and cell density using compression and tensile tests. Overall, it was found that above a critical peptide and cell density, encapsulated myoblasts were able to provide additional mechanical integrity to hydrogels composed of peptide-modified alginate. This occurred presumably by means of cell-peptide cross-linking of the alginate polymers, in addition to the usual $Ca++$ cross-linking. These results are potentially applicable to other polymer systems and important for a range of tissue engineering applications.

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## Figures

Figure 1

Alginate polysaccharide schematic (a) without peptide modification and (b) with GGGGRGDSP peptide modification. Any carboxyl group can be modified, although only one G monomer is shown as modified here.

Figure 2

Two syringes (one containing calcium sulfate and one containing alginate) are shown connected by a syringe connector.

Figure 3

Compression modulus as a function of days in incubation for (a) unmodified (–∎–), peptide-modified (1X) (–∎–), and peptide-modified (5X) (–▴–) MVG alginate, (b) unmodified MVG with 0 (–∎–) and 40×106 (–엯–) C2C12cells∕ml alginate, (c) peptide-modified (1X) MVG with 0 (–∎–) and 40×106 (–◻–) C2C12cells∕ml alginate, and (d) peptide-modified (5X) MVG with 0 (–▴–) and 40×106 (–▵–) C2C12cells∕ml alginate. Statistical significance of p<0.005 (**).

Figure 4

Compression modulus as a function of seeded cell number for (a) unmodified, (b) peptide-modified (1X), and (c) peptide-modified (5X) alginate. Here, * denotes one day in incubation, O denotes seven days in incubation, and X denotes 21 days in incubation.

Figure 5

Normalized compression modulus for unmodified (∎) and peptide-modified (5X) (–◻–) MVG with 40×106C2C12cells∕ml alginate as a function of storage time. The modulus and standard deviation were normalized first by the value of the modulus for the given material with 0 C2C12cells∕ml alginate for the given day and then by the modulus of unmodified MVG for the given day and cell number. Statistical significance of p<0.05 (*).

Figure 6

Ultimate tensile stress as a function of days in incubation for (a) unmodified MVG with 0 (–∎–) and 40×106 (–엯–) C2C12cells∕ml alginate, (b) peptide-modified (1X) MVG with 0 (–∎–) and 40×106 (–◻–) C2C12cells∕ml alginate, and (c) peptide-modified (5X) MVG with 0 (–▴–) and 40×106 (–▵–) C2C12cells∕ml alginate. Statistical significance of p<0.05 (*) and p<0.005 (**).

Figure 7

Ultimate tensile modulus as a function of days in incubation for (a) unmodified MVG with 0 (–∎–) and 40×106 (–엯–) C2C12cells∕ml alginate, (b) peptide-modified (1X) MVG with 0 (–∎–) and 40×106 (–◻–) C2C12cells∕ml alginate, and (c) peptide-modified (5X) MVG with 0 (–▴–) and 40×106 (–▵–) C2C12cells∕ml alginate. Statistical significance of p<0.05 (*) and p<0.005 (**).

Figure 8

Normalized tensile modulus for unmodified (∎) and peptide-modified (5X) (–◻–) MVG with 40×106C2C12cells∕ml alginate as a function of storage time. The modulus and standard deviation were normalized first by the value of the modulus for the given material with 0 C2C12cells∕ml alginate for the given day and then by the modulus of MVG for the given day and cell number. Statistical significance of p<0.05 (*) and p<0.005 (**).

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