Core-Shell Microfibers via Bioorthogonal Layer-by-Layer Assembly

Bio-orthogonal tuning of matrix properties during 3D cell culture to induce morphological and phenotypic changes

Described herein is a protocol for producing a synthetic extracellular matrix that can be modified in situ during three-dimensional cell culture. The hydrogel platform is established using modular building blocks employing bio-orthogonal tetrazine (Tz) ligation with slow (norbornene, Nb) and fast (trans-cyclooctene, TCO) dienophiles. A cell-laden gel construct is created via the slow, off-stoichiometric Tz/Nb reaction. After a few days of culture, matrix properties can be altered by supplementing the cell culture media with TCO-tagged molecules through the rapid reaction with the remaining Tz groups in the network at the gel-liquid interface. As the Tz/TCO reaction is faster than molecular diffusion, matrix properties can be modified in a spatiotemporal fashion simply by altering the identity of the diffusive species and the diffusion time/path. Our strategy does not interfere with native biochemical processes nor does it require external triggers or a second, independent chemistry. The biomimetic three-dimensional cultures can be analyzed by standard molecular and cellular techniques and visualized by confocal microscopy. We have previously used this method to demonstrate how in situ modulation of matrix properties induces epithelial-to-mesenchymal transition, elicits fibroblast transition from mesenchymal stem cells and regulates myofibroblast differentiation. Following the detailed procedures, individuals with a bachelor's in science and engineering fields can successfully complete the protocol in 4-5 weeks. This protocol can be applied to model tissue morphogenesis and disease progression and it can also be used to establish engineered constructs with tissue-like anisotropy and tissue-specific functions.

Surface-induced self-assembly of peptides turns superhydrophobic surface of electrospun fibrous into superhydrophilic one

Current surface modification strategies for electrospun materials always require covalent conjugation technology, which is relatively inefficient and might damage the bioactivity and structure of peptides and proteins. Here we introduce the use of surface-induced self-assembly technology to modify electrospun materials, which is a simple but efficient noncovalent-based process. Results show that the peptide NapFFGRGD forms burr-like structures on the surface of PCL fibers, reducing the water contact angle of the fibers. Adjusting the peptide sequence and salt concentration affects the self-assembly and surface properties of modified PCL fibers. Additionally, we demonstrate the potential application of this surface modification technique for enhancing cellular responses in tissue engineering applications. The research provides valuable insights into the surface modification of PCL fibers and offers a new method for improving the biological compatibility of materials in tissue engineering.

Trends in Injectable Biomaterials for Vocal Fold Regeneration and Long-Term Augmentation

Human vocal folds (VF), a pair of small, soft tissues in the larynx, have a layered mucosal structure with unique mechanical strength to support high-level tissue deformation by phonation. Severe pathological changes to VF have causes including surgery, trauma, age-related atrophy, and radiation, and lead to partial or complete communication loss and difficulty in breathing and swallowing. VF glottal insufficiency requires injectable VF biomaterials such as hyaluronan, calcium hydroxyapatite, and autologous fat to augment VF functions. Although these biomaterials provide an effective short-term solution, significant variations in patient response and requirements of repeat reinjection remain notable challenges in clinical practice. Tissue engineering strategies have been actively explored in the search of an injectable biomaterial that possesses the capacity to match native tissue's material properties while promoting permanent tissue regeneration. This review aims to assess the current status of biomaterial development in VF tissue engineering. The focus will be on examining state-of-the-art techniques including modification with bioactive molecules, cell encapsulation, composite materials, as well as, in situ crosslinking with click chemistry. We will discuss potential opportunities that can further leverage these engineering techniques in the advancement of VF injectable biomaterials.

Cleaner and Sustainable Production of Core-Sheath Polymer Fibres

The amalgamation of sustainable practises throughout the fabrication process with advanced material engineering holds promise not only for eco-conscious manufacturing but also for promoting technological advancements in versatile material design and application. Moreover, technological innovation serves as a catalyst for sustainability initiatives, driving innovation and enabling the adoption of greener practises across industries. This study investigates redefining the production protocol of pressure spinning to produce core-sheath polymer fibres, deepening sustainable practises. It aims to explore innovative approaches such as modifying spinning parameters, optimising polymer solvent configurations and understanding fluid behaviour to curtail material wastage and maintain minimal energy consumption without compromising production efficiency. Utilising Polyvinylpyrrolidone (PVP) for the core and Polyethylene oxide (PEO) for the sheath, production rates of up to 64 g/h were achieved with a fibre diameter range of 3.2 ± 1.7 µm to 4.6 ± 2.0 µm. Energy consumption per mass of fibres produced showed a decreasing trend overall with increasing applied gas pressure. These findings highlight the potential for the efficient and scalable production of core-sheath fibres with applications in various advanced materials fields.

Chemical Modifications in Hyaluronic Acid-Based Electrospun Scaffolds

Hyaluronic acid (HA) is a natural, non-sulfated glycosaminoglycan (GAG) present in ECM. It is involved in different biological functions with appealing properties in cosmetics and pharmaceutical preparations as well as in tissue engineering. Generally, HA has been electrospun in blends with natural or synthetic polymers to produce fibers having diameters in the order of nano and micro-scale whose pores can host cells able to regenerate damaged tissues. In the last decade, a rich literature on electrospun HA-based materials arose. Chemical modifications were generally introduced in HA scaffolds to favour crosslinking or conjugation with bioactive molecules. Considering the high solubility of HA in water, HA-based electrospun scaffolds are cross-linked to increase the stability in biological fluids. Crosslinking is necessary also to avoid the release of HA from the hybrid scaffold when implanted in-vivo. Furthermore, to endow the HA based scaffolds with new chemical or biological properties, conjugation of bioactive molecules to HA was widely reported. Herein, we review the existing research classifying chemical modifications on HA and HA-based electrospun fibers into three categories: i) in-situ crosslinking of electrospun HA-based scaffolds ii) off-site crosslinking of electrospun HA-based scaffolds; iii) conjugation of biofunctional molecules to HA with focus on peptides.

Facile Fabrication of NIR-Responsive Alginate/CMC Hydrogels Derived through IEDDA Click Chemistry for Photothermal-Photodynamic Anti-Tumor Therapy

Novel chemically cross-linked hydrogels derived from carboxymethyl cellulose (CMC) and alginate (Alg) were prepared through the utilization of the norbornene (Nb)-methyl tetrazine (mTz) click reaction. The hydrogels were designed to generate reactive oxygen species (ROS) from an NIR dye, indocyanine green (ICG), for combined photothermal and photodynamic therapy (PTT/PDT). The cross-linking reaction between Nb and mTz moieties occurred via an inverse electron-demand Diels-Alder chemistry under physiological conditions avoiding the need for a catalyst. The resulting hydrogels exhibited viscoelastic properties (G' ~ 492-270 Pa) and high porosity. The hydrogels were found to be injectable with tunable mechanical characteristics. The ROS production from the ICG-encapsulated hydrogels was confirmed by DPBF assays, indicating a photodynamic effect (with NIR irradiation at 1-2 W for 5-15 min). The temperature of the ICG-loaded hydrogels also increased upon the NIR irradiation to eradicate tumor cells photothermally. In vitro cytocompatibility assessments revealed the non-toxic nature of CMC-Nb and Alg-mTz towards HEK-293 cells. Furthermore, the ICG-loaded hydrogels effectively inhibited the metabolic activity of Hela cells after NIR exposure.

Dynamic modulation of matrix adhesiveness induces epithelial-to-mesenchymal transition in prostate cancer cells in 3D

Synthetic matrices with dynamic presentation of cell guidance cues are needed for the development of physiologically relevant in vitro tumor models. Towards the goal of mimicking prostate cancer progression and metastasis, we engineered a tunable hyaluronic acid-based hydrogel platform with protease degradable and cell adhesive properties employing bioorthogonal tetrazine ligation with strained alkenes. The synthetic matrix was first fabricated via a slow tetrazine-norbornene reaction, then temporally modified via a diffusion-controlled method using trans-cyclooctene, a fierce dienophile that reacts with tetrazine with an unusually fast rate. The encapsulated DU145 prostate cancer single cells spontaneously formed multicellular tumoroids after 7 days of culture. In situ modification of the synthetic matrix via covalent tagging of cell adhesive RGD peptide induced tumoroid decompaction and the development of cellular protrusions. RGD tagging did not compromise the overall cell viability, nor did it induce cell apoptosis. In response to increased matrix adhesiveness, DU145 cells dynamically loosen cell-cell adhesion and strengthen cell-matrix interactions to promote an invasive phenotype. Characterization of the 3D cultures by immunocytochemistry and gene expression analyses demonstrated that cells invaded into the matrix via a mesenchymal like migration, with upregulation of major mesenchymal markers, and down regulation of epithelial markers. The tumoroids formed cortactin positive invadopodia like structures, indicating active matrix remodeling. Overall, the engineered tumor model can be utilized to identify potential molecular targets and test pharmacological inhibitors, thereby accelerating the design of innovative strategies for cancer therapeutics.

Hyaluronic Acid-Based Bioconjugate Systems, Scaffolds, and Their Therapeutic Potential

In recent years, the development of hyaluronic acid or hyaluronan (HA) based scaffolds, medical devices, bioconjugate systems have expanded into a broad range of research and clinical applications. Research findings over the last two decades suggest that the abundance of HA in most mammalian tissues with distinctive biological roles and chemical simplicity for modifications have made it an attractive material with a rapidly growing global market. Besides its use as native forms, HA has received much interest on so-called "HA-bioconjugates" and "modified-HA systems". In this review, the importance of chemical modifications of HA, underlying rationale approaches, and various advancements of bioconjugate derivatives with their potential physicochemical, and pharmacological advantages are summarized. This review also highlights the current and emerging HA-based conjugates of small molecules, macromolecules, crosslinked systems, and surface coating strategies with their biological implications, including their potentials and key challenges discussed in detail.

Scalable fabrication, compartmentalization and applications of living microtissues

Living microtissues are used in a multitude of applications as they more closely resemble native tissue physiology, as compared to 2D cultures. Microtissues are typically composed of a combination of cells and materials in varying combinations, which are dictated by the applications' design requirements. Their applications range wide, from fundamental biological research such as differentiation studies to industrial applications such as cruelty-free meat production. However, their translation to industrial and clinical settings has been hindered due to the lack of scalability of microtissue production techniques. Continuous microfluidic processes provide an opportunity to overcome this limitation as they offer higher throughput production rates as compared to traditional batch techniques, while maintaining reproducible control over microtissue composition and size. In this review, we provide a comprehensive overview of the current approaches to engineer microtissues with a focus on the advantages of, and need for, the use of continuous processes to produce microtissues in large quantities. Finally, an outlook is provided that outlines the required developments to enable large-scale microtissue fabrication using continuous processes.

Matrix Adhesiveness Regulates Myofibroblast Differentiation from Vocal Fold Fibroblasts in a Bio-orthogonally Cross-linked Hydrogel

Repeated mechanical and chemical insults cause an irreversible alteration of extracellular matrix (ECM) composition and properties, giving rise to vocal fold scarring that is refractory to treatment. Although it is well known that fibroblast activation to myofibroblast is the key to the development of the pathology, the lack of a physiologically relevant in vitro model of vocal folds impedes mechanistic investigations on how ECM cues promote myofibroblast differentiation. Herein, we describe a bio-orthogonally cross-linked hydrogel platform that recapitulates the alteration of matrix adhesiveness due to enhanced fibronectin deposition when vocal fold wound healing is initiated. The synthetic ECM (sECM) was established via the cycloaddition reaction of tetrazine (Tz) with slow (norbornene, Nb)- and fast (trans-cyclooctene, TCO)-reacting dienophiles. The relatively slow Tz-Nb ligation allowed the establishment of the covalent hydrogel network for 3D cell encapsulation, while the rapid and efficient Tz-TCO reaction enabled precise conjugation of the cell-adhesive RGDSP peptide in the hydrogel network. To mimic the dynamic changes of ECM composition during wound healing, RGDSP was conjugated to cell-laden hydrogel constructs via a diffusion-controlled bioorthognal ligation method 3 days post encapsulation. At a low RGDSP concentration (0.2 mM), fibroblasts residing in the hydrogel remained quiescent when maintained in transforming growth factor beta 1 (TGF-β1)-conditioned media. However, at a high concentration (2 mM), RGDSP potentiated TGF-β1-induced myofibroblast differentiation, as evidenced by the formation of an actin cytoskeleton network, including F-actin and alpha-smooth muscle actin. The RGDSP-driven fibroblast activation to myofibroblast was accompanied with an increase in the expression of wound healing-related genes, the secretion of profibrotic cytokines, and matrix contraction required for tissue remodeling. This work represents the first step toward the establishment of a 3D hydrogel-based cellular model for studying myofibroblast differentiation in a defined niche associated with vocal fold scarring.

Tunable Synthesis of Hydrogel Microfibers via Interfacial Tetrazine Ligation

Crosslinked, degradable, and cell-adhesive hydrogel microfibers were synthesized via interfacial polymerization employing tetrazine ligation, an exceptionally fast bioorthogonal reaction between strained trans-cyclooctene (TCO) and s-tetrazine (Tz). A hydrophobic trisTCO crosslinker and homo-difunctional poly(ethylene glycol) (PEG)-based macromers with the tetrazine group conjugated to PEG via a stable carbamate (PEG-bisTz1) bond or a labile hydrazone (PEG-bisTz2) linkage were synthesized. After laying an ethyl acetate solution of trisTCO over an aqueous solution of bisTz macromers, mechanically robust microfibers were continuously pulled from the oil-water interface. The resultant microfibers exhibited comparable mechanical and thermal properties but different aqueous stability. Combining PEG-bisTz2 and PEG-bisTz3 with a dangling arginine-glycine-aspartic acid (RGD) peptide in the aqueous phase yielded degradable fibers that supported the attachment and growth of primary vocal fold fibroblasts. The degradable and cell-adhesive hydrogel microfibers are expected to find utility in a wide array of tissue engineering applications.