2023 AIChE Annual Meeting

3D Modeling of Plodia Interpunctella silk Gland: Unraveling Silk Gland Dynamics for Advanced Manufacturing

Silk fibers are produced by silkworms, such as the domesticated silkworm (Bombyx mori) and the pantry moth (Plodia interpunctella). Silk fibers are formed in an insect-specific organ, called the silk gland. Silk glands are complex structures, where the proteins that make up the silk fiber are produced. These proteins self-assemble within the gland, which utilizes pH shifts, enzymes, and shifts in dimensions to aid in silk spinning.1-4 Aside from studies on the domesticated silkworm (Bombyx mori), very little is known about the structure and function of silk glands in other insects. Our laboratory utilizes silk fibers and purified silk fibroin proteins from Plodia interpunctella to form materials for applications in advanced manufacturing and healthcare. To investigate the way Plodia interpunctella silk fibers form, we utilize both experimental and computational tools to develop 3D models of the Plodia interpunctella silk gland.

First, we determined the size, structure, and architecture of the silk gland in a 5th instar Plodia interpunctella larva using nano-computed tomography (Nano-CT). Then, we used image segmentation and reconstruction to model the 3D architecture. Next, we performed post-processing of the surface meshes to ensure a solid object. Once we had this 3D model, we used it in two applications: 1) COMSOL™ modeling and 2) 3D printing.

We are using COMSOL™ modeling to gain insight into changes in fluid shear stress as a function of gland architecture (gland diameter changes) to understand the impact of shear forces on beta sheet formation, a necessary secondary structure to form insoluble silk fibers from liquid silk solutions. First, the 3D model was moved to AutoDesk Inventor to convert the surface mesh into a solid object. Then, we explored shear stresses at the walls based on viscosity and flowrate of the solution flowing through the gland. Results provide wall shear stress and pressure at predetermined intervals. To further visualize the silk gland and build a 3D microfluidic model, we printed the gland at 5X the original size in polydimethylsiloxane (PDMS). Preliminary results evaluate the impact of silk fibroin solution viscosity on flow through the gland.

Overall, this work represents the first steps in understanding the fundamental fluid dynamics of Plodia interpunctella silk fiber self-assembly. Moreover, this work sets the stage for designing artificial silk glands or silk spinning devices, which will aid future manufacturing of silk fibers for a wide range of applications.

References
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2. Dicko C, Vollrath F, Kenney JM. Spider silk protein refolding is controlled by changing pH. Biomacromolecules. 2004;5(3):704-10. doi: 10.1021/bm034307c. PubMed PMID: 15132650.
3. Domigan LJ, Andersson M, Alber􀆟 KA, Chesler M, Xu Q, Johansson J, Rising A, Kaplan DL. Carbonic anhydrase generates a pH gradient in Bombyx mori silk glands. Insect Biochemistry and Molecular Biology. 2015;65:100-6. Epub 2015/09/15. doi: 10.1016/j.ibmb.2015.09.001. PubMed PMID: WOS:000364618800012; PMCID: PMC4628561.
4. Wu X, Wu X, Shao M, Yang B. Structural changes of Bombyx mori fibroin from silk gland to fiber as evidenced by Terahertz spectroscopy and other methods. Interna􀆟onal Journal of Biological Macromolecules. 2017;102:1202-10.