Nanolayer biomaterial coatings of silk fibroin for controlled release

Abstract

An all-aqueous, stepwise deposition process with silk fibroin protein for the assembly of nanoscale layered controlled release coatings was exploited. Model compounds, Rhodamine B, Even Blue and Azoalbumin, representing small molecule drugs and therapeutically relevant proteins were incorporated in the nanocoating process and their loading and release behavior was quantified. In addition, the structure and morphology of the coatings were characterized. Release studies in vitro showed that control of beta-sheet crystal content and the multilayer structure of the silk coatings correlated with the release properties of the incorporated compounds. In particular, higher crystallinity and a thicker silk capping layer suppressed the initial burst of release and prolonged the duration of release. These novel coatings and deposition approach provide a unique option to regulate structure and morphology, and thus release kinetics. The results also suggest these systems as a promising framework for surface engineering of biomaterials and medical devices to regulate the release of drugs, when considered with the all-aqueous process involved, the conformal nature of the coatings, the robust material properties of silk fibroin, and the degradability and biocompatibility of this family of protein.

Figure 1

Structures of small molecule drug model compounds: (A) Rhodamine B; (B) Even Blue.

Figure 2

UV-Vis absorption spectra of (A) (silk/RH)_n and (B) (silk/AA)_n multilayered thin films on quartz slides as a function of the number of bilayers. The arrows indicate the increase of the number of bilayers. The insets show linear increases of the characteristic absorption peaks of Rhodamine B and Azoalbumin in A and B, respectively. Note: RH=Rhodamine B; AA=Azoalubmin.

Figure 3

UV-Vis absorbance at 562 nm of (silk/RH)_n on quartz slides as a function of the bilayer number and rinse stabilization method. Absorbance values were recorded at 3 different locations on the substrate.

Figure 4

Real-time monitoring of the deposition of model compounds on silk pre-coated gold electrode using a research quartz crystal microbalance (RQCM).

Figure 5

X-ray diffraction profiles (λ = 0.154 nm) of multilayer thin films with various compositions and treatment methods: (A) Rhodamine B incorporated silk films; (B) Azoalbumin-incorporated silk films. The description of the samples is shown in Table 1. The cast film was used as a non-crystalline control.

Figure 6

AFM height mode and phase mode images in air obtained for (silk/RH)₆-silk and (silk/AA)₆-silk on mica wafer before and after immersion of the samples in PBS for 24 h. Each image is 1 μm × 1 μm. RH=Rhodamine B; AA=Azoalbumin.

Figure 7

AFM cross-section analysis at the film edge area to obtain film thickness of (silk/Rh)₆-silk.

Figure 8

Cumulative release profiles of Rhodamine B-incorporated silk films (A) and Azoalbumin-incorporated silk films (B) with various multilayer structures and treatment methods.

Figure 9

The experimental data based on the power law model for Rhodamine B (left) and Azoalbumin (right) released from different silk multilayered structures. A linear relationship was observed for each sample.