Tuning assembly and enzymatic degradation of silk/poly(N-vinylcaprolactam) multilayers via molecular weight and hydrophobicity

Abstract

We report on enzymatically degradable nanothin coatings obtained by layer-by-layer (LbL) assembly of silk fibroin with poly(N-vinylcaprolactam) (PVCL) via hydrogen bonding and hydrophobic interactions. We found that both silk β-sheet content, controlled through dipping and spin-assisted LbL, and PVCL molecular weight regulate film thickness, microstructure, pH-stability, and biodegradability with a nanoscale precision. Thickness of (silk/PVCL) films increased with increase in PVCL molecular weight and decrease in deposition pH. The impact of assembly pH on film growth was more dramatic for dipped films. These systems show a significant rise in thickness with increase in PVCL molecular weight at pH < 5 but become independent on polymer chain length at pH ≥ 5. We also found that spin-assisted films exhibited a greater stability at elevated pH and against enzymatic degradation as compared to their dipped counterparts. For both film types, the pH and enzymatic stability was improved with increasing PVCL length and β-sheet content, indicating enhanced hydrophobic and hydrogen-bonded interactions between PVCL and silk. Finally, we fabricated spherical and cubical (silk/PVCL) LbL capsules of regulated permeability and enzymatic degradation. Our approach gives a unique opportunity to tune thickness, morphology, structure, and biodegradability rate of silk films and capsules by varying silk secondary structure and PVCL length. Accounting for all-aqueous fabrication and the biocompatibility of both polymers these biodegradable materials provide novel platforms for delivery systems and medical devices.

Self-Assemblies of Thermoresponsive Poly(N-vinylcaprolactam) Polymers for Applications in Biomedical Field

“…The enzymatically degradable multilayers obtained by all-aqueous assembly of PVCL with silk protein have been developed in our laboratory. 51 Silk fibroin amide and hydroxyl groups can participate in hydrogen bonding with carbonyl groups of PVCL lactam ring with hydrophobic stabilization at high pH values. Hydrogen bonding between carbonyls of PVCL and carboxylic groups of silk at acidic pH provided thicker PVCL/silk coatings, while interaction between phenolic groups in silk fibroin and PVCL carbonyls provided much lower thickness at neutral pH due to the ionization of silk acidic groups.…”

Polyelectrolyte Multilayers on Soft Colloidal Nanosurfaces: A New Life for the Layer-By-Layer Method

“…Another alternative for fastening the deposition is to include a constant stirring of the solutions during the deposition, which allows limiting the deposition times to 10-20 s [177]. Furthermore, the spray-assisted and spin-assisted deposition methods have gained importance as alternatives to the dipping deposition because they allow a significant reduction on the fabrication time, increasing the homogeneity of the deposited films [178][179][180][181][182].…”

Nanostructure Evolution of Biomimetic Hydrogel from Silk Fibroin and Poly(N-Vinylcaprolactam): A Small Angle Neutron Scattering Study

“…Developing hydrogels that exhibit combined properties of stimuli responsiveness and mechanical properties is of significant interest in the biomedical field. It has been reported that RSF and PVCL form stable hydrogen bonding interactions, which have been applied to fabricate capsules and coatings (16,17). Recently, we reported a facile fabrication of RSF-PVCL hybrid hydrogels by a photochemical crosslinking method (18).…”