Surface Grafting Modification of Silk Fibroin by Atom Transfer Radical Polymerization

Controlled radical polymerization of hydrophilic and zwitterionic brush-like polymers from silk fibroin surfaces

Bombyx mori silk fibroin is a fibrous protein whose tunable properties and biocompatibility have resulted in its utility in a wide-variety of applications, including as drug delivery vehicles, wound dressings, and tissue engineering scaffolds. Control of protein and cell attachment is vital to the performance of biomaterials, but silk fibroin is mostly hydrophobic and interacts nonspecifically with cells and proteins. Silk functionalised with hydrophilic polymers reduces attachment, but the low number of reactive sites makes achieving a uniform conjugation a persistent challenge. This work presents a new approach to grow brush-like polymers from the surface of degradable silk films, where the films were enriched with hydroxyl groups, functionalised with an initiator, and finally reacted with acrylate monomers using atom transfer radical polymerisation. Two different routes to hydroxyl enrichment were investigated, one involving reaction with ethylene oxide (EO) and the other using a two-step photo-catalysed oxidation reaction. Both routes increased surface hydrophilicity, and hydrophilic monomers containing either uncharged (poly(ethylene glycol), PEG) pendant groups or zwitterionic pendant groups were polymerised from the surfaces. The initial processing of the films to induce beta sheet structures was found to impact the success of the polymerizations. Compared to the EO modified or unmodified silk surfaces, the oxidation reaction resulted in more polymer conjugation and the surfaces appear more uniform. Mesenchymal stem cell and protein attachment were the lowest on polymers grown from oxidised surfaces. PEG-containing brush-like polymers displayed lower protein attachment than surfaces conjugated with PEG using a previously reported "grafting to" method, but polymers containing zwitterionic side chains displayed both the lowest contact angles and the lowest cell and protein attachment. This finding may arise from the interactions of the zwitterionic pendant groups through their permanent dipoles and is an important finding because PEG is susceptible to oxidative damage that can reduce efficacy over time. These modified silk materials with lower cell and protein attachments are envisioned to find utility when enhanced diffusion around surfaces is required, such as in drug delivery implants.

Surface Grafting Modification of Silk Fibroin via ARGET ATRP Method

In this work, silk was grafted using dimethylaminoethyl methacrylate(DMAEMA) via activators regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP) method to produce well controlled grafted silk in water aqueous. CuBr2 was used as catalyst, N, N, N’, N", N" -pentamethyldiethylenetriamine (PMDETA) was used as ligand, vitamin C was used as reducing agent. The effects of monomer concentration, the proportion of catalyst and ligand, the variety and the dosage of catalyst and reducing agent, grafting temperature and time on the silk grafting were discussed, and the optimal grafting technology was obtained. FT-IR characterization of the grafted silk indicated that DMAEMA was grafted onto the surface of silk. The whiteness and permeability to gas of grafted silk slightly decreased. And the moisture permeability of grafted silk nearly had no change. The wrinkle recovery angle of grafted silk dramatically increased.

Grafting of 2-Diethylaminoethyl Methacrylate onto Silk by ATRP

In order to develop silk underwear fabric with good anti-bacterial property, silk was grafted using 2-diethylaminoethyl methacrylate (DEAEMA) by atom transfer radical polymerization (ATRP) method. The amino groups and hydroxyl groups on the side chains of the silk fibroin was reacted with 2-bromoisobutyryl bromide (BriB-Br) to obtain efficient macroinitiator for ATRP. And the macroinitiator was grafted with DEAEMA in water/ethanol media using CuBr/N,N,N',N",N" -pentamethyldiethylenetriamine (PMDETA) as catalyst system. The effects of monomer concentration, the proportion of CuBr and PMDETA, grafting temperature and time on the silk grafting were discussed, and the optimal grafting technology was obtained. FT-IR characterization of the grafted silk showed a peak corresponding to DEAEMA, which indicated that DEAEMA was grafted onto the surface of silk. The quaternized grafted silk had good anti-bacterial property to S. aureus and E. coli. . And the bacteria repellency of the grafted silk had good washing durability.