Designing PEG-peptide copolymer hydrogel for biomedical applications Andong Liu 1 , Alberto Saiani 1 , Lu-shin Wong 2 , Aline Miller 3 ,
1 Department of Materials, The University of Manchester, UK, 2 Department of Chemistry, The University of Manchester, UK, 3 Department of Chemical Engineering, The University of Manchester, UK Introduction Hydrogels are widely used in biomedical applications. Polyethene glycol (PEG) and short self-assembling peptides are commonly used to design hydrogels due to their biocompatibility. As a result, the use of peptidePEG conjugates has recently attracted significant interest in designing a novel hydrogel system combining the properties of both building blocks. Fibre formation is a key aspect of the gelation process of self-assembling peptide systems. Unwanted fiber lateral aggregation and assembly often result in the formation of large fiber bindles leading to very stiff non-transparent hydrogels and, in some extreme cases, phase separation1. These effects can limit the usage of peptide hydrogels in many areas2 3. In this work, we decided to conjugate PEG to a family of self-assembling peptides developed in our group to control fiber formation and lateral aggregation to control the hydrogel's physical properties. Materials CF9C(CFEFKFEFKKC, Purity: 95.64,BIOMATIIK); CF9(CFEFKFEFKK, Purity: 97.37%, BIOMATIIK); F9(FEFKFEFKK,Purity97.58%,BIOMATIIK); mPEG-MAL (Molecular Weight: 2k, Creative PEGWorks ); TCEP (tris(2-carboxyethyl)phosphine) (Sigma-Aldrich) MethodCFEFKFEFKK(CF9) (C: cysteine, F: phenylalanine, K: lysine, E: glutamic acid) peptide was conjugated with MALmPEG (Mw: 2, 5 and 10k). RP-HPLC purified PEG-F9 conjugates. The hydrogel where characterised using a range of techniques, including TEM, SAXS and FTIR. Results F9 hydrogels are typically cloudy at pH7 due to significant fiber lateral aggregation and bundling (Figure 1). The conjugation of PEG to F9 was shown to reduce fiber-fiber hydrophobic interactions and, therefore, bundling in the system. Increasing the fraction of di-block conjugate through physical mixing resulted in hydrogels becoming more and more transparent at pH7. TEM confirmed the reduction in fiber budling. It reduces in bundling, and an increase in transparency was accompanied by a reduction in G' (shear modulus) of the hydrogels. This result points to PEG's role in reducing fiber-fiber interactions and, therefore, network crosslinking. As a result, the mechanical properties of the hydrogel decrease and when more than 10% (mol) of the conjugate is added the system stop gelling. However, the samples' secondary structure and betasheet content as determined by FTIR show no significant change upon addition on the conjugate, confirming that the addition of PEG does not affect fiber formation but on fiber crosslinking by preventing fiber - fiber interactions. The conjugate was found to slow down gel formation, suggesting that the PEG chains of the surface of the fiber result in steric hindrance and prevent crosslinking formation, but over time, relaxation processes occur and crosslinks form. Conclusion The attachment of PEG on the peptide can change the peptide fiber arrangement and therefore allows the design of mechanically tuneable and transparent hydrogels. It provides the potential to build novel hydrogel for biomedical applications. References 1. Gao, J. et al. Biomacromolecules 18, 826–834, 2017 2. Takayama. et al. Carbohydrate Polymers 234, 115880, 2020. 3. Jacek K. W Biomacromelecules19-2731-2741, 2018
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