Caddisfly Silk-Polycaprolactone Foams: Physicochemical and Biological Properties of Nature-Inspired Biomaterials

Abstract

The unique properties of insect silk have attracted attention for years to develop scaffolds for tissue engineering. Combining natural silks with synthetic polymers may benefit biocompatibility, mechanical strength, and elasticity. Silk-modified biomaterials are a promising choice for tissue engineering due to their versatility, biocompatibility, and many processing methods. This study investigated the physicochemical and biological properties of biocomposites formed by combining caddisfly silk (Hydropsyche angustipennis) and polycaprolactone (PCL). The PCL foams modified with caddisfly silk demonstrated full cytocompatibility and enhanced fibroblast adhesion and proliferation compared to unmodified PCL. These silk-modified PCL foams also induced NF-κB signaling, which is crucial for initiating tissue regeneration. Notably, the antimicrobial properties of the silk-modified PCL foams remained consistent with those of unmodified PCL, suggesting that the addition of silk did not alter this aspect of performance. The findings suggest that caddisfly silk-modified PCL foams present a promising solution for future medical and dental applications, emphasizing the potential of alternative silk sources in tissue engineering.

Keywords: caddisfly; nature-inspired biomaterials; polycaprolactone; silk; tissue regeneration.

Figure 1

Physicochemical characteristics of PCL foams and PCL foams/modified silk scaffolds: (A). First heating/cooling DSC curves, (B) thermogravimetric curves with their first derivatives (DTG), (C) normalized FTIR spectra; dashed lines indicating distinct bands originating from the silk fraction, and (D) comparison of water contact angle values.

Figure 2

The microstructure of PCL foams and PCL foams/modified silk. Silk fibers are marked with yellow arrows.

Figure 3

(A) The viability of L929 fibroblasts after 24 h of incubation in the milieu of obtained foam scaffolds. Data are presented as mean ± SEM (standard error of the mean) of three separate experiments (six replicates for each assay). The dashed line indicates the minimum level (70%) of the cells’ metabolic activity required to recognize the biomaterial as noncytotoxic at the in vitro level. TC—treated control (red bar) and NTC—non-treated control (green bar), in terms of cell metabolic activity, according to ISO 10993-5:2009 and our previous research [43]; (A) demonstrates that both PCL foams and PCL foams/modified silk supported high fibroblast viability after 24 h, meeting ISO 10993-5 cytocompatibility criteria. (B) The proliferation of L929 fibroblasts in the PCL and PCL foams/modified silk was monitored for up to 96 h of culture. The results are shown as mean ± SEM (standard error of the mean) from three separate experiments. (B) shows that PCL foams/modified silk significantly enhanced L929 fibroblast proliferation over 96 h compared to unmodified PCL foams, indicating their potential to support cell growth in tissue regeneration.

Figure 4

The morphology (A) and average size (B) of L929 (mouse skin fibroblast cells) after 96 h of incubation with tested PCL foams and PCL foams/modified silk, as compared to control cells grown directly on microscope slides. Confocal microscopy visualized cellular structures using DAPI (nuclei; blue) and Texas Red™ Phalloidin (F-actin filaments; red) staining. Scale bars indicate 10 µm (2D images) and 25 µm (3D reconstructions). The results represent the mean values ± SEM of three separate experiments. # p < 0.05 between the PCL and PCL foams/modified silk, based on the results of a one-way ANOVA (Kruskal–Wallis test) evaluation. The figure shows that PCL foams/modified silk enhanced fibroblast adhesion and altered cell morphology, promoting more elongated and spread cells compared to PCL foams and control surfaces.

Figure 5

The antimicrobial properties after 24 h incubation with tested compounds (PCL foams and PCL foams/modified silk) against S. aureus or E. coli. The results represent the mean values ± SEM of three separate experiments. * p < 0.05 of the PCL and PCL-modified composites in relation to non-treated samples (100% viability of bacterial cells), based on the results of a one-way ANOVA (Kruskal–Wallis test) evaluation. The figure shows that both PCL foams and PCL foams/modified silk reduced E. coli metabolic activity, while no significant effect was observed against S. aureus after 24 h.

Figure 6

The activation of the NF-κB transcription factor in THP1-Blue NF-κB monocytes incubated for 24 h with tested PCL foams and PCL foams/modified silk in comparison with monocytes stimulated with lipopolysaccharide (LPS) of E. coli (TC) or cell culture medium (NTC). In parallel, samples were preincubated with polymyxin B (PMB). Data are presented as mean ± SEM (standard error of the mean) of three separate experiments (six replicates of each assay). Data were compared using a regular one-way ANOVA followed by Tukey’s multiple comparisons. * p < 0.05 of the PCL foams/modified silk in relation to PCL foams. The figure shows that PCL foams/modified silk significantly activated the NF-κB pathway in THP1-NF-κB reported monocytes, suggesting their potential to modulate inflammatory responses.