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Early insights into the unique structure and properties of native silk suggested that β-sheet nanocrystallites in silk would degrade prior to melting when subjected to thermal processing. Since then, canonical approaches for fabricating silk-based materials typically involve solutionderived processing methods, which have inherent limitations with respect to silk protein solubility, stability in solution, and time and cost efficiency. Here we report a thermal processing method for the direct solid-state molding of regenerated silk into bulk 'parts' or devices with tunable mechanical properties. At elevated temperature and pressure, regenerated amorphous silk nanomaterials with ultralow β-sheet content undergo thermal fusion via molecular rearrangement and self-assembly assisted by bound water to form a robust bulk material that retains biocompatibility, degradability and machinability. This technique reverses presumptions about the limitations of direct thermal processing of silk into a wide range of new material formats and composite materials with tailored properties and functionalities. Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

Silkworm silk has attracted considerable attention in recent years due to its excellent mechanical properties, biocompatibility, and promising applications in biomedical sector. However, a clear understanding of the molecular structure and the relationship between the excellent mechanical properties and the silk protein sequences are still lacking. This study carries out a thorough comparative structural analysis of silk fibers of four silkworm species ( Bombyx mori, Antheraea pernyi, Samia cynthia ricini, and Antheraea assamensis). A combination of characterization techniques including scanning electron microscopy, mechanical test, synchrotron X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), and NMR spectroscopy was applied to investigate the morphologies, mechanical properties, amino acid compositions, nanoscale organizations, and molecular structures of various silkworm silks. Furthermore, the structure-property relationship is discussed by correlating the molecular structural features of silks with their mechanical properties. The results show that a high content of β-sheet structures and a high crystallinity would result in a high Young's modulus for silkworm silk fibers. Additionally, a low content of β-sheet structures would result in a high extensibility.

As a biomaterial, silk presents unique features with a combination of excellent mechanical properties, biocompatibility, and biodegradability. The biodegradability aspects of silk biomaterials, especially with options to control the rate from short (days) to long (years) time frames in vivo, make this protein-based biopolymer a good candidate for developing biodegradable devices used for tissue repairs and tissue engineering, as well as medical device implants. Silk materials, including native silk fibers and a broad spectrum of regenerated silk materials, have been investigated in vitro and in vivo to demonstrate degradation by proteolytic enzymes. In this Review, we summarize the findings on these studies on the enzymatic degradation of Bombyx mori (B. mori) silk materials. We also present a discussion on the factors that dictate the degradation properties of silk materials. Finally, in future perspectives, we highlight some key challenges and potential directions toward the future study of the degradation of silk materials.

Hierarchical molecular assembly is a fundamental strategy for manufacturing protein structures in nature. However, to translate this natural strategy into advanced digital manufacturing like three‐dimensional (3D) printing remains a technical challenge. This work presents a 3D printing technique with silk fibroin to address this challenge, by rationally designing an aqueous salt bath capable of directing the hierarchical assembly of the protein molecules. This technique, conducted under aqueous and ambient conditions, results in 3D proteinaceous architectures characterized by intrinsic biocompatibility/biodegradability and robust mechanical features. The versatility of this method is shown in a diversity of 3D shapes and a range of functional components integrated into the 3D prints. The manufacturing capability is exemplified by the single‐step construction of perfusable microfluidic chips which eliminates the use of supporting or sacrificial materials. The 3D shaping capability of the protein material can benefit a multitude of biomedical devices, from drug delivery to surgical implants to tissue scaffolds. This work also provides insights into the recapitulation of solvent‐directed hierarchical molecular assembly for artificial manufacturing.

Investigating the interface between biomolecules and nanoparticles has attracted considerable attention in recent years since it has great significance in numerous fields including nanotechnology, biomineralization, cancer therapy, and origin of life. In this paper, we present a thorough solid-state NMR study on alanine adsorption and thermal condensation on fumed silica nanoparticles. The structure and dynamics at the interface between alanine and fumed silica nanoparticles were probed with a combination of 1 H, 13 C, and 15 N one-and two-dimensional (2D) magic angle spinning (MAS) solid-state NMR methods at different alanine surface coverages and hydration levels. It is illustrated at high surface coverages both crystalline and adsorbed states of alanine exist in the samples while only adsorbed alanine is observed at low surface coverage (approximately a monolayer). At high hydration levels, the adsorbed alanine exhibits enhanced mobility, and both the carboxyl and amine group interact with mobile water molecules on the silica nanoparticle surface. At low hydration levels, the adsorbed alanine interacts with surface silanols via the protonated amine group and the carboxylate group. The thermal condensation of alanine on fumed silica nanoparticles was also investigated, and the results indicate that alanine can undergo thermal condensation at ∼170 °C at the interface of fumed silica nanoparticles as confirmed by a battery of 13 C and 15 N 2D MAS solid-state NMR experiments. By combining the adsorption and thermal condensation results, a possible mechanism for the silica surface-catalyzed thermal condensation reaction of alanine is proposed.

The adsorption of amino acids on silica surfaces has attracted considerable interest since it has a broad range of applications in various fields such as drug delivery, solid-phase peptide synthesis and biocompatible materials synthesis. In this work, we systematically study lysine adsorption on fumed silica nanoparticles with thermal analysis and solid-state NMR. Thermal-gravimetric analysis (TGA) results show that the adsorption behavior of lysine in low concentration aqueous solutions is well described by the Langmuir isotherm. With ultrafast magic-angle-spinning (MAS) 1 H NMR and multinuclear and multi-dimensional 13 C and 15 N solid-state NMR, we successfully determine the protonation state of bulk lysine and find that lysine is adsorbed on silica nanoparticles surfaces through the sidechain amine groups. Density functional theory (DFT) calculations carried out on lysine and lysinesilanol complex structures further confirm that the side-chain amine groups interact with the silica surface hydroxyl groups via strong hydrogen bonding. Furthermore, we find that lysine preferentially has monolayer coverage on silica surfaces in high salt concentration solutions because of the ionic complexes formed with surface bound lysine molecules.

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