Multifunctional silk vinyl sulfone-based hydrogel scaffolds for dynamic material-cell interactions

Photocurable cellulose nanofibers and their copolymers with polyacrylamide as microgels to support 3D cell cultivation

Cellulose nanofibers (CNFs) are renewable bionanomaterials with great utilization potential in future biomedicals. However, conventional CNF hydrogels are limited by low structural flexibility and insufficiently tunable mechanical properties, restricting their use in 3D cell culture systems. To address these limitations, we developed granular hydrogel platforms using photocurable and ionically crosslinkable methacrylated CNFs (CNFMAs) and their copolymers with polyacrylamide via a dual cross-linking mechanism. By employing this bottom-up approach, mechanically fragmented microgels were reassembled into granular hydrogels via calcium ion crosslinking. This assembly of methacrylated CNF-based microgels successfully supported long-term 3D cell culture and demonstrated the capability to provide biomechanical cues that facilitate different cellular responses. The granular hydrogel of CNFMA alone promoted clustering and migration of human pancreatic cancer cells (PANC-1), while the copolymerization of CNFMA with polyacrylamide introduced stiffness variations into the hybrid granular hydrogel system that enhanced the spreading of preosteoblasts (MC3T3-E1) and facilitated spheroid formation in the culture of PANC-1. These findings underscore the versatility of photocurable nanocellulose in constructing biomaterial platforms. Overall, this study establishes a foundation for advancing in vitro models for tissue engineering and cancer research using CNFMA-derived microgel systems.

Fabrication of a transforming growth factor β1 functionalized silk sericin hydrogel through genetical engineering to repair alveolar bone defects in rabbit

Cleft palate is one of the most prevalent congenital craniofacial birth defects in human congenital facial anomaly. Severe cleft palate is usually accompanied by alveolar bone defects (ABDs). Growth factors (GFs) are considered as desirable opportunity to promote the craniofacial healing post the surgery. However, limited resource, susceptibility to degradation, and lack of appropriate delivery systems greatly hinder the clinic application of GFs in the ABDs repair. In this study, a transforming growth factor β1 variant (eTGF-β1) with enhanced extracellular matrix (ECM) binding efficiency was engineered to generate transgenic silkworm using the silk gland biosynthesizing system for cost effective and massive bio-synthesis of the eTGF-β1 functionalized silk fibers. The eTGF-β1 achieved a highly-efficient expression in the middle silk gland (MSG) cells of transgenic silkworm, and secretion and distribution in the sericin layer of silk fiber which accounted for approximately 5.57 ± 0.72 % of the cocoon shell weight. The eTGF-β1 functionalized silk sericin hydrogel (eTGF-β1 SH) was then fabricated with excellent mechanical and processing properties, injectability, biocompatibility, biodegradability, sustained release of eTGF-β1, and capability to promote cell proliferation, which significantly accelerated the bone defect repair particularly the osteoblast maturation and new bone formation through regulating the expressions of the bone formation-related genes in a rabbit alveolar process cleft model. This study provides a valuable strategy for future the treatments of ABDs in rabbit with cleft palate using the genetically engineered eTGF-β1 silk sericin hydrogel.

Engineered Protein Hydrogels as Biomimetic Cellular Scaffolds

The biochemical and biophysical properties of the extracellular matrix (ECM) play a pivotal role in regulating cellular behaviors such as proliferation, migration, and differentiation. Engineered protein-based hydrogels, with highly tunable multifunctional properties, have the potential to replicate key features of the native ECM. Formed by self-assembly or crosslinking, engineered protein-based hydrogels can induce a range of cell behaviors through bioactive and functional domains incorporated into the polymer backbone. Using recombinant techniques, the amino acid sequence of the protein backbone can be designed with precise control over the chain-length, folded structure, and cell-interaction sites. In this review, the modular design of engineered protein-based hydrogels from both a molecular- and network-level perspective are discussed, and summarize recent progress and case studies to highlight the diverse strategies used to construct biomimetic scaffolds. This review focuses on amino acid sequences that form structural blocks, bioactive blocks, and stimuli-responsive blocks designed into the protein backbone for highly precise and tunable control of scaffold properties. Both physical and chemical methods to stabilize dynamic protein networks with defined structure and bioactivity for cell culture applications are discussed. Finally, a discussion of future directions of engineered protein-based hydrogels as biomimetic cellular scaffolds is concluded.

Mucus-coated, magnetically-propelled fecal surrogate to mimic fecal shear forces on colonic epithelium

The relationship between the mechanical forces associated with bowel movement and colonic mucosal physiology is understudied. This is partly due to the limited availability of physiologically relevant fecal models that can exert these mechanical stimuli in in vitro colon models in a simple-to-implement manner. In this report, we created a mucus-coated fecal surrogate that was magnetically propelled to produce a controllable sweeping mechanical stimulation on primary intestinal epithelial cell monolayers. The mucus layer was derived from purified porcine stomach mucins, which were first modified with reactive vinyl sulfone (VS) groups followed by reaction with a thiol crosslinker (PEG-4SH) via a Michael addition click reaction. Formation of mucus hydrogel network was achieved at the optimal mixing ratio at 2.5 % w/v mucin-VS and 0.5 % w/v PEG-4SH. The artificial mucus layer possessed similar properties as the native mucus in terms of its storage modulus (66 Pa) and barrier function (resistance to penetration by 1-μm microbeads). This soft, but mechanically resilient mucus layer was covalently linked to a stiff fecal hydrogel surrogate (based on agarose and magnetic particles, with a storage modulus of 4600 Pa). The covalent bonding between the mucus and agarose ensured its stability in the subsequent fecal sliding movement when tested at travel distances as long as 203 m. The mucus layer served as a lubricant and protected epithelial cells from the moving fecal surrogate over a 1 h time without cell damage. To demonstrate its utility, this mucus-coated fecal surrogate was used to mechanically stimulate a fully differentiated, in vitro primary colon epithelium, and the physiological stimulated response of mucin-2 (MUC2), interleukin-8 (IL-8) and serotonin (5HT) secretion was quantified. Compared with a static control, mechanical stimulation caused a significant increase in MUC2 secretion into luminal compartment (6.4 × ), a small but significant increase in IL-8 secretion (2.5 × and 3.5 × , at both luminal and basal compartments, respectively), and no detectable alteration in 5HT secretion. This mucus-coated fecal surrogate is expected to be useful in in vitro colon organ-on-chips and microphysiological systems to facilitate the investigation of feces-induced mechanical stimulation on intestinal physiology and pathology.

Designed modular protein hydrogels for biofabrication

Designing proteins that fold and assemble over different length scales provides a way to tailor the mechanical properties and biological performance of hydrogels. In this study, we designed modular proteins that self-assemble into fibrillar networks and, as a result, form hydrogel materials with novel properties. We incorporated distinct functionalities by connecting separate self-assembling (A block) and cell-binding (B block) domains into single macromolecules. The number of self-assembling domains affects the rigidity of the fibers and the final storage modulus G' of the materials. The mechanical properties of the hydrogels could be tuned over a broad range (G' = 0.1 - 10 kPa), making them suitable for the cultivation and differentiation of multiple cell types, including cortical neurons and human mesenchymal stem cells. Moreover, we confirmed the bioavailability of cell attachment domains in the hydrogels that can be further tailored for specific cell types or other biological applications. Finally, we demonstrate the versatility of the designed proteins for application in biofabrication as 3D scaffolds that support cell growth and guide their function. STATEMENT OF SIGNIFICANCE: Designed proteins that enable the decoupling of biophysical and biochemical properties within the final material could enable modular biomaterial engineering. In this context, we present a designed modular protein platform that integrates self-assembling domains (A blocks) and cell-binding domains (B blocks) within a single biopolymer. The linking of assembly domains and cell-binding domains this way provided independent tuning of mechanical properties and inclusion of biofunctional domains. We demonstrate the use of this platform for biofabrication, including neural cell culture and 3D printing of scaffolds for mesenchymal stem cell culture and differentiation. Overall, this work highlights how informed design of biopolymer sequences can enable the modular design of protein-based hydrogels with independently tunable biophysical and biochemical properties.

Chitin Nanofibrils Enabled Core-Shell Microcapsules of Alginate Hydrogel

An engineered 3D architectural network of the biopolymeric hydrogel can mimic the native cell environment that promotes cell infiltration and growth. Among several bio-fabricated hydrogel structures, core-shell microcapsules inherit the potential of cell encapsulation to ensure the growth and transport of cells and cell metabolites. Herein, a co-axial electrostatic encapsulation strategy is used to create and encapsulate the cells into chitin nanofibrils integrated alginate hydrogel microcapsules. Three parameters that are critical in the electrostatic encapsulation process, hydrogel composition, flow rate, and voltage were optimized. The physicochemical characterization including structure, size, and stability of the core-shell microcapsules was analyzed by scanning electron microscope (SEM), FTIR, and mechanical tests. The cellular responses of the core-shell microcapsules were evaluated through in vitro cell studies by encapsulating NIH/3T3 fibroblast cells. Notably, the bioactive microcapsule showed that the cell viability was found excellent for more than 2 weeks. Thus, the results of this core-shell microcapsule showed a promising approach to creating 3D hydrogel networks suitable for different biomedical applications such as in vitro tissue models for toxicity studies, wound healing, and tissue repair.