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1. Dual-Crystallizable Silk Fibroin/Poly(L-lactic Acid) Biocomposite Films: Effect of Polymer Phases on Protein Structures in Protein-Polymer Blends

   https://doi.org/10.3390/ijms22041871  

   Wang, Fang; Li, Yingying; Gough, Christopher R.; Liu, Qichun; Hu, Xiao (February 2021, International Journal of Molecular Sciences)

   null (Ed.)

   Biopolymer composites based on silk fibroin have shown widespread potential due to their brilliant applications in tissue engineering, medicine and bioelectronics. In our present work, biocomposite nanofilms with different special topologies were obtained through blending silk fibroin with crystallizable poly(L-lactic acid) (PLLA) at various mixture rates using a stirring-reflux condensation blending method. The microstructure, phase components, and miscibility of the blended films were studied through thermal analysis in combination with Fourier-transform infrared spectroscopy and Raman analysis. X-ray diffraction and scanning electron microscope were also used for advanced structural analysis. Furthermore, their conformation transition, interaction mechanism, and thermal stability were also discussed. The results showed that the hydrogen bonds and hydrophobic interactions existed between silk fibroin (SF) and PLLA polymer chains in the blended films. The secondary structures of silk fibroin and phase components of PLLA in composites vary at different ratios of silk to PLLA. The β-sheet content increased with the increase of the silk fibroin content, while the glass transition temperature was raised mainly due to the rigid amorphous phase presence in the blended system. This results in an increase in thermal stability in blended films compared to the pure silk fibroin films. This study provided detailed insights into the influence of synthetic polymer phases (crystalline, rigid amorphous, and mobile amorphous) on protein secondary structures through blending, which has direct applications on the design and fabrication of novel protein–synthetic polymer composites for the biomedical and green chemistry fields. 

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2. Native Silk Fibers: Protein Sequence and Structure Influences on Thermal and Mechanical Properties

   https://doi.org/10.1021/acs.biomac.4c01781  

   Aikman, Elizabeth L; Eccles, Lauren E; Stoppel, Whitney L (April 2025, Biomacromolecules)

   Silk fibers produced by arthropods have inspired an array of materials with applications in healthcare, medical devices, textiles, and sustainability. Silks exhibit biodiversity with distinct variations in primary protein constituent sequences (fibroins, spidroins) and structures across taxonomic classifications, specifically the Lepidopteran and Araneae orders. Leveraging the biodiversity in arthropod silks offers advantages due to the diverse mechanical properties and thermal stabilities achievable, primarily attributed to variations in fiber crystallinity and repeating amino acid motifs. In this review, we aim to delineate known properties of silk fibers and correlate them with predicted protein sequences and secondary structures, informed by newly annotated genomes. We will discuss established patterns in repeat motifs governing specific properties and underscore the biological diversity within silk fibroin and spidroin sequences. Elucidating the relationship between protein sequences and properties of natural silk fibers will identify strategies for designing new materials through rational silk-based fiber design. 

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3. Comparative Investigation of Thermal and Structural Behavior in Renewably Sourced Composite Films of Even-Even Nylons (610 and 1010) with Silk Fibroin

   https://doi.org/10.3390/polym10091029  

   Callaway, Kayla; Xue, Ye; Altimari, Vincent; Jiang, Guoxiang; Hu, Xiao (September 2018, Polymers)

   As the average life expectancy continues to increase, so does the need for resorbable materials designed to treat, augment, or replace components and functions of the body. Naturally occurring biopolymers such as silks are already attractive candidates due to natural abundance and high biocompatibility accompanied by physical properties which are easily modulated through blending with another polymer. In this paper, the authors report on the fabrication of biocomposite materials made from binary blends of Bombyx mori silk fibroin (SF) protein and renewably sourced low molecular weight nylon 610 and high molecular weight nylon 1010. Films were characterized using scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Results of this study demonstrated that enhanced structural and thermal properties were achievable in composite films SF-N610/N1010 due to their chemical similarity and the possible formation of hydrogen bonds between nylon and silk molecular chains. This study provides useful insight into the sustainable design of functional composite materials for biomedical and green technologies. 

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4. Harvesting Silk Fibers from Plodia interpunctella: Role of Environmental Rearing Conditions in Fiber Production and Properties

   https://doi.org/10.1021/acsbiomaterials.3c01372  

   Shirk, Bryce D; Torres_Pereira_Meriade_Duarte, Isabela; McTyer, Jasmine B; Eccles, Lauren E; Lateef, Ali H; Shirk, Paul D; Stoppel, Whitney L (April 2024, ACS Biomaterials Science & Engineering)

   Silk fibers are produced by a wide variety of insects. The silkworm Bombyx mori (Bombyx) was domesticated because the physical properties of its silk fibers were amenable to the production of fine textiles. Subsequently, engineers have regenerated silk fibroin to form biomaterials. The monocular focus on Bombyx silk has underutilized the expanse of diverse silk proteins produced by more than 100,000 other arthropods. This vast array of silk fibers could be utilized for biomedical engineering challenges if sufficient rearing and purification processes are developed. Herein, we show that the moth, Plodia interpunctella (Plodia), represents an alternative silk source that is easily reared in highly regulated culture environments allowing for greater consistency in the silk produced. We controlled the temperature, resource availability (larvae/gram diet), and population density (larvae/mL) with the goal of increasing silk fiber production and improving homogeneity in Plodia silk proteins. We determined that higher temperatures accelerated insect growth and reduced life cycle length. Furthermore, we established initial protocols for the production of Plodia silk with optimal silk production occurring at 24 °C, with a resource availability of 10 larvae/gram and a population density of 0.72 larvae/mL. Population density was shown to be the most prominent driving force of Plodia silk mat formation among the three parameters assessed. Future work will need to link gene expression, protein production and purification, and resulting mechanical properties as a function of environmental cues to further transition Plodia silk into regenerated silk fibroin biomaterials. 

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5. Microwave Assisted Sol-Gel Synthesis of Silica-Spider Silk Composites

   https://doi.org/10.3390/molecules24142521  

   Giasuddin, Abul Bashar; Britt, David W. (July 2019, Molecules)

   This study introduces a simple and environmentally friendly method to synthesize silica-protein nanocomposite materials using microwave energy to solubilize hydrophobic protein in an aqueous solution of pre-hydrolyzed organo- or fluoro-silane. Sol-gel functionality can be enhanced through biomacromolecule incorporation to tune mechanical properties, surface energy, and biocompatibility. Here, synthetic spider silk protein and organo- and fluoro-silane precursors were dissolved and mixed in weakly acidic aqueous solution using microwave technology. Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) images revealed the formation of spherical nanoparticles with sizes ranging from 100 to 500 nm depending, in part, on silane fluoro- or organo-side chain chemistry. The silane-protein interaction in the nanocomposite was assessed through infrared spectroscopy. Deconvoluted ATR-FTIR (Attenuated total reflectance Fourier-transform infrared spectroscopy) spectra revealed silane chemistry-specific conformational changes in the protein-silane nanocomposites. Relative to microwave-solubilized spider silk protein, the β structure content increased by 14% in the spider silk-organo-silica nanocomposites, but decreased by a net 20% in the spider silk-fluoro-silica nanocomposites. Methods of tuning the secondary structures, and in particular β-sheets that are the cross-linking moieties in spider silks and other self-assembling fibrillar proteins, may provide a unique means to promote protein interactions, favor subsequent epitaxial growth process, and enhance the properties of the protein-silane nanocomposites. 

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