Impact of processing parameters on the haemocompatibility of Bombyx mori silk films

Abstract

Silk has traditionally been used for surgical sutures due to its lasting strength and durability; however, the use of purified silk proteins as a scaffold material for vascular tissue engineering goes beyond traditional use and requires application-orientated biocompatibility testing. For this study, a library of Bombyx mori silk films was generated and exposed to various solvents and treatment conditions to reflect current silk processing techniques. The films, along with clinically relevant reference materials, were exposed to human whole blood to determine silk blood compatibility. All substrates showed an initial inflammatory response comparable to polylactide-co-glycolide (PLGA), and a low to moderate haemostasis response similar to polytetrafluoroethylene (PTFE) substrates. In particular, samples that were water annealed at 25 °C for 6 h demonstrated the best blood compatibility based on haemostasis parameters (e.g. platelet decay, thrombin-antithrombin complex, platelet factor 4, granulocytes-platelet conjugates) and inflammatory parameters (e.g. C3b, C5a, CD11b, surface-associated leukocytes). Multiple factors such as treatment temperature and solvent influenced the biological response, though no single physical parameter such as β-sheet content, isoelectric point or contact angle accurately predicted blood compatibility. These findings, when combined with prior in vivo data on silk, support a viable future for silk-based vascular grafts.

Silk proteins for biomedical applications: Bioengineering perspectives

“…For instance, the chemotherapeutic impact of doxorubicin (DOX)-loaded silk films on primary tumor growth and metastasis were examined in mice using a humanized adenocarcinoma model. DOX-loaded silk films not only had a significantly greater primary tumor response than the equivalent dose administered intravenously, but were also not associated with any local or systemic toxicity [109]. Studies with the L929 fibroblast cell line demonstrate that silk fibroin, sericin and collagen films are equivalent in their ability to support cell attachment, physiological morphology and growth [68,110].…”

Silk for Drug Delivery Applications: Opportunities and Challenges

“…[41] This drug-silk interaction is more likely to occur above the isoelectric point of silk, [41] which typically ranges from 3.5 to 4.4 and is partially dependent on the method used to induce bsheets. [42] The lower affinity of doxorubicin for silk at low pH was subsequently exploited for the lysosomal drug delivery of this weakly basic drug. [40] In a separate study, the b-sheet content of the silk was used to control doxorubicin release (Figure 2).…”

“…For example, we have recently demonstrated in hematocompatibility studies that silk has a low thrombogenic response and minimal hemolytic activity, but the inflammatory response was higher when compared to the clinical reference material polytetrafluoroethylene (PTFE). [42] This raises concerns when developing unmodified silk for systemic applications until such studies are systematically performed. Because silk has only recently been proposed for systemic administration, few data are available that support safe transfer of these products to the clinic.…”

Silk Hydrogels for Drug and Cell Delivery

“…For example, silk has been proposed for various vascular tissue engineering applications, but without first undergoing rigorous haematocompatibility assessment. We have assessed the blood compatibility of silk and were able to demonstrate a low haemostasis activity but an inflammatory response that was in part dependent on the processing history of the silk (Seib, Maitz et al 2012, Seib, Herklotz et al 2014). …”