nomic losses, and a reduction in natural fossil resources. With the current recycling infrastructure, only 14% of current plastic-packaging waste is collected, and even with this recycling, 4% is lost during the process and 8% is redirected for the fabrication of lower-value applications. [5] The long degradation half-lives of synthetic plastics, which break down in the environment over decades or centuries, is the central problem of sustainability. [4,6] Therefore, seeking sustainable and biodegradable alternatives to synthetic plastics have become a pressing task. Developing biodegradable products from renewable resources (e.g., natural biopolymers) represents the best option by fitting material design, production, use, and disposal into a circular materials lifecycle approach (Figure 1b). [7] Instead of losing fossil fuel resources into landfills and causing environmental burdens, natural biopolymers offer options for composting/degradation, thus, recycling the carbon back to environmental cycles for the regeneration of feedstocks. Besides being sustainable and biodegradable, fibrous structural biopolymers from plants (e.g., cellulose) and animals (e.g., silk, chitin) have unique hierarchical structures, with structural integrity, flexibility, and toughness. Therefore, fibrous structural biopolymers represent a class of material that could help to supplement or replace some conventional synthetic plastics. Additionally, the inherent biocompatibility of most natural biopolymers makes them important candidates for added-value applications, such as in regenerative medicine, drug delivery, and tissueimplantable devices. Among these natural biopolymers, cellulose, chitin, and silk fibroin represent the most abundant and investigated biopolymers in the categories of polysaccharides and proteins (Table 1).The first step in this progression toward sustainability is to process fibrous biopolymers into material formats suitable for targeted applications. The sophisticated hierarchical structure of fibrous biopolymers, which consists of well-organized structural features from molecular to nano-to macroscopic length scales, employ extensive hydrogen bonding networks embedded within semicrystalline structures across all structural levels. This structural stability endows fibrous biopolymers with exceptional mechanical properties, but also generates challenges with the direct processing of the fibrous materials into useful material formats via traditional thermal processing methods that are widely used for synthetic polymer processing Some of the most abundant biomass on earth is sequestered in fibrous biopolymers like cellulose, chitin, and silk. These types of natural materials offer unique and striking mechanical and functional features that have driven strong interest in their utility for a range of applications, while also matching environmental sustainability needs. However, these material systems are challenging to process in cost-competitive ways to compete with synthetic plastics due to the limited options for ther...
Volumetric additive manufacturing (VAM) enables fast photopolymerization of three-dimensional constructs by illuminating dynamically evolving light patterns in the entire build volume. However, the lack of bioinks suitable for VAM is a critical limitation. This study reports rapid volumetric (bio)printing of pristine, unmodified silk-based (silk sericin (SS) and silk fibroin (SF)) (bio)inks to form sophisticated shapes and architectures. Of interest, combined with post-fabrication processing, the (bio)printed SS constructs reveal properties including reversible as well as repeated shrinkage and expansion, or shape-memory; whereas the (bio)printed SF constructs exhibit tunable mechanical performances ranging from a few hundred Pa to hundreds of MPa. Both types of silk-based (bio)inks are cytocompatible. This work supplies expanded bioink libraries for VAM and provides a path forward for rapid volumetric manufacturing of silk constructs, towards broadened biomedical applications.
Silk fibroin protein is a biomaterial with excellent biocompatibility and low immunogenicity. These properties have catapulted the material as a leader for extensive use in stents, catheters, and wound dressings. Modulation of hydrophobicity of silk fibroin protein to further expand the scope and utility however has been elusive. We report that installing perfluorocarbon chains on the surface of silk fibroin transforms this water‐soluble protein into a remarkably hydrophobic polymer that can be solvent‐cast. A clear relationship emerged between fluorine content of the modified silk and film hydrophobicity. Water contact angles of the most decorated silk fibroin protein exceeded that of Teflon®. We further show that water uptake in prefabricated silk bars is dramatically reduced, extending their lifetimes, and maintaining mechanical integrity. These results highlight the power of chemistry under moderate conditions to install unnatural groups onto the silk fibroin surface and will enable further exploration into applications of this versatile biomaterial.
Carboxylated cellulose nanocrystals (cCNC) can be used to make cellulose microbeads by spray drying from aqueous suspension. The rescaling of cCNC to micrometer-size particle agglomerates yields a type of biodegradable cellulose microbead with potential for dye removal for water purification. The present study offers insight into small molecule transport properties that are important to design and assess the performance of cCNC microbeads in this context. In our study, cationic methylene blue (MB) dye was used as a model compound to probe uptake kinetics and diffusion. The study goes beyond the framework of pseudo-first-order or pseudo-second-order kinetics in that it explicitly engages the problem of diffusion. We introduce a two-resistance model based on film–pore diffusion that is conditioned by choice of an adsorption isotherm. The numerical study is combined with experiment to give more detailed insight into mass transport of MB in the cCNC microbeads. Langmuir, Temkin, and Freundlich isotherms were investigated. Film–pore diffusion based on Langmuir adsorption suggests how trafficking of MB molecules in the microbeads depends on pH and ionic strength. A “gating” mechanism is proposed to account for how MB uptake, release, or inhibition of binding depends on pH and ionic strength. At neutral pH, the effective diffusion coefficient, D eff, is 7.5 × 10–11 m2/s. Thermodynamic parameters were determined. The process is spontaneous but slightly endothermic with activation energy of about 20 kJ/mol.
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