Silk is a versatile material that has been used for centuries to solve a variety of biomedical and environmental problems.Silk fibers are composed of many proteins, including silk fibroins and sericins, which contribute to the fiber structure and function.
1 Traditionally, engineers have relied on silk fibers and silk fibroin solutions derived from the domesticated silkworm,
Bombyx mori (B. mori), to develop new technologies.
1 Existing strategies for functionalizing and tuning mechanical properties of
B. mori silk fibroin-based biomaterials have limitations. The large presence of highly crystalline domains makes applications in bioprinting and hydrogel systems difficult, especially under biologically relevant osmolarities and pHs.
2 However, there are a wide array of silk producing organisms that produce silk fibers with unique protein structure and functions that may overcome these challenges. These organisms include other moths in the Lepidopteran order and spiders. Currently, the utilization of alternative silk producing species has been limited due to low scale-up potential. However, laboratory rearing of
Plodia interpunctella (P. Interpunctella), a non-mulberry silk fiber producing insect, has shown promise as an alternative to
B. mori.
P. interpunctella is a Lepidopteran insect that produces silk fibers throughout its lifecycle to aid in survival and reproduction (
Figure 1A).
3 To further explore the potential of
P. interpunctella as a source of silk fibers for biomaterial production, we conducted laboratory rearing experiments to assess the influence of insect culture parameters on silk fiber production and insect growth. We manipulated temperature, population size, and food-to-caterpillar ratio to optimize silk fiber production while reducing energy inputs. Our results showed that higher temperatures accelerated insect growth and reduced life cycle length (
Figure 1B). To maximize silk production relative to energy inputs, we varied the total number of larvae and the amount of food provided along with the temperature changes. We found that the number of larvae did not have a synergistic effect on silk fiber production, but variations in the ratio of larvae to grams of food, along with temperature, altered total fiber production (
Figure 1C). We determined that culture of
P. interpunctella in a 250 mL vessel at 24 ËšC, with 10 larvae per g of food, yielded the greatest advantage in terms of total silk fiber production. Additionally, we compared silk fiber yields to common
B. mori silk fiber regeneration protocols and found that only 9 standard insect rearing boxes were needed to generate 5 grams of dry silk fibers in approximately 20 days, which amounts to ¾ of a standard insect incubator shelf. From these findings, we will continue to pursue
P. interpunctella as an alternative to
B. mori for silk fiber production due to its ease of laboratory rearing and control over fiber reproducibility, allowing for tighter control over environmental conditions.
Furthermore, we aim to establish a reference cytocompatibility response from raw P. interpunctella silk as we work to develop a silk solution regeneration protocol. Initial cytocompatibility was assessed using primary lung fibroblasts cells seeded onto raw P. interpunctella silk, raw B. mori silk, and regenerated silk films using B. mori silk fibroin as comparisons. Cytocompatibility was assessed by initial cell viability (24 hours) and total initial cell attachment. Cell-materials interactions were evaluated over 1 week in culture by monitoring cell proliferation rates, mitochondrial activity, and cell spreading on P. interpunctella materials vs. B. mori materials, demonstrating the utility of P. interpunctella silk fibers and regenerated silk biopolymer solutions for applications in tissue engineering and regenerative medicine.
Citations:
1. Rockwood DN, Preda RC, Yücel T, Wang X, Lovett ML, Kaplan DL. Materials fabrication from Bombyx mori silk fibroin. Nature Protocols. 2011;6(10):1612-31. doi: 10.1038/nprot.2011.379.
2. Wang Q, Han G, Yan S, Zhang Q. 3D Printing of Silk Fibroin for Biomedical Applications. Materials. 2019;12(3):504. PubMed PMID: doi:10.3390/ma12030504.
3. Silhacek DL, Miller GL. Growth and Development of the Indian Meal Moth, Plodia interpunctella (Lepidoptera: Phycitidae), Under Laboratory Mass-Rearing Conditions. Annals of the Entomological Society of America. 1972;65(5):1084-7. doi: 10.1093/aesa/65.5.1084.
