3D-Printing of Silk Nanofibrils Reinforced Alginate for Soft Tissue Engineering

Nano-fibrous biopolymers as building blocks for gel networks: Interactions, characterization, and applications

Biopolymers derived from natural resources are highly abundant, biodegradable, and biocompatible, making them promising candidates to replace non-renewable fossil fuels and mitigate environmental and health impacts. Nano-fibrous biopolymers possessing advantages of biopolymers entangle with each other through inter-/intra-molecular interactions, serving as ideal building blocks for gel construction. These biopolymer nanofibers often synergize with other nano-building blocks to enhance gels with desirable functions and eco-friendliness across various applications in biomedical, environmental, and energy sectors. The inter-/intra-molecular interactions directly affect the assembly of nano-building blocks, which determines the structure of gels, and the integrity of connected nano-building blocks, influencing the mechanical properties and the performance of gels in specific applications. This review focuses on four biopolymer nanofibers (cellulose, chitin, silk, collagen), commonly used in gel preparations, as representatives for polysaccharides and polypeptides. The covalent and non-covalent interactions between biopolymers and other materials have been categorized and discussed in relation to the resulting gel network structures and properties. Nanomechanical characterization techniques, such as surface forces apparatus (SFA) and atomic force microscopy (AFM), have been employed to precisely quantify the intermolecular interactions between biopolymers and other building blocks. The applications of these gels are classified and correlated to the functions of their building blocks. The inter-/intra-molecular interactions act as "sewing threads", connecting all nano-building blocks to establish suitable network structures and functions. This review aims to provide a comprehensive understanding of the interactions involved in gel preparation and the design principles needed to achieve targeted functional gels.

3D printed sodium Alginate-Gelatin hydrogel loaded with Santalum album oil as an antibacterial Full-Thickness wound healing and scar reduction Scaffold: In vitro and in vivo study

Managing wounds and accompanying consequences like exudation and microbiological infections is challenging in clinical practice. Bioactive compounds from traditional medicinal plants help heal wounds, although their bioavailability is low. This study uses sodium alginate (SA), gelatin (G), and Santalum album oil (SAL) to 3D print a polymeric hydrogel scaffold to circumvent these difficulties. The 3D printed scaffolds showed hydrophilicity, an average pore size of 221.30 ± 19.83 µm, adequate swelling, higher mechanical strength with tensile strength (σ) of 13.5 ± 1.08 MPa, a Young's modulus of 17.53 ± 1.61 MPa, andpotential antibacterial activity against skin infection causing bacteria viz. Staphylococcus aureus (87.7 ± 4 % growth inhibition) and Pseudomonas aeruginosa (i.e. 81.96 ± 3.94 % growth inhibition). The scaffolds showed hemocompatibility, biocompatibility, and moderate biodegradability. Cytotoxicity and scratch assay showed significantly improved fibroblast viability, proliferation, and migration. In the in vivo study, the scaffolds were applied to full-thickness wounds in rat models. After 7 and 14 days of treatment, the wounds treated with the 3D-printed SA-G-SAL scaffold showed higher closure rates, lower contraction, higher-regenerated epithelium with minimal inflammation, and less scar formation compared to control groups. Thus, the 3D-printed SA-G-SAL scaffold is a promising biomaterial for wound healing with reduced scar formation.

Optimizations of Placenta Extracellular Matrix-Loaded Silk Fibroin/Alginate 3D-Printed Scaffolds Structurally and Functionally for Bone Tissue Engineering

Recent interest has been focused on extracellular matrix (ECM)-based scaffolds totreat critical-sized bone injuries. In this study, urea was used to decellularize and solubilize human placenta tissue. Then, different concentrations of ECM were composited with 8% alginate (Alg) and 12% silk fibroin (SF) for printing in order to produce a natural 3D construct that resembled bone tissue. The physical and biological features of the printed structures were evaluated entirely in vitro. Finally, a rat model was employed to examine the optimal 3D printed scaffold (5% ECM) as a bone transplant for the healing of cranial bone lesions. The present investigation demonstrated that decellularizing placental tissue fragments led to efficient removal of cell debris. In addition, a remarkable improvement in the printed scaffolds' mechanical and biological properties was observed by increasing the ECM concentration. The histology studies and real-time PCR results demonstrated the acceleration of bone regeneration in the bone lesions treated with 5%ECM-SF/Alg at 4 and 8 weeks after implantation. Overall, these results proved that the placental ECM-printed scaffolds could potentially construct biomimetic grafts to reconstruct significant bone defects and now promise to proceed with clinical studies.

Alginate-gelatin based nanocomposite hydrogel scaffold incorporated with bioactive glass nanoparticles and fragmented nanofibers promote osteogenesis: From design to in vitro studies

The current study proposes fragmented nanofibers of polycaprolactone (FNF) with bioactive glass nanoparticles (nBG) incorporated into a polymeric matrix of alginate-gelatin for the creation of a hydrogel scaffold. Four groups were prepared: control, bioactive glass containing scaffold (BG), fragmented nanofibers with bioactive glass scaffold (FNF(PCL) + BG), and fragmented composite nanofibers scaffold (FNF (PCL + BG)). FNF (PCL + BG) scaffolds revealed a more controlled degradation rate, with approximately 20 % degradation occurring after 28 compared. The FNF(PCL) + BG scaffolds had the highest compressive strength in both dry and wet states. Following 14 days of incubation in simulated body fluid, hydroxyapatite formation had occurred on the surface of scaffolds containing nBG, and after 28 days on other groups tested. Cell studies revealed that the FNF(PCL) + BG scaffolds had superior cell viability without inhibiting cell proliferation. The FNF(PCL) + BG and FNF(PCL + BG) scaffolds had the highest alkaline phosphatase (ALP) activity and FNF(PCL) + BG scaffolds showed to support osteogenic differentiation.

Bioprinting: Mechanical Stabilization and Reinforcement Strategies in Regenerative Medicine

Bioprinting describes the printing of biomaterials and cell-laden or cell-free hydrogels with various combinations of embedded bioactive molecules. It encompasses the precise patterning of biomaterials and cells to create scaffolds for different biomedical needs. There are many requirements that bioprinting scaffolds face, and it is ultimately the interplay between the scaffold's structure, properties, processing, and performance that will lead to its successful translation. Among the essential properties that the scaffolds must possess-adequate and appropriate application-specific chemical, mechanical, and biological performance-the mechanical behavior of hydrogel-based bioprinted scaffolds is the key to their stable performance in vivo at the site of implantation. Hydrogels that typically constitute the main scaffold material and the medium for the cells and biomolecules are very soft, and often lack sufficient mechanical stability, which reduces their printability and, therefore, the bioprinting potential. The aim of this review article is to highlight the reinforcement strategies that are used in different bioprinting approaches to achieve enhanced mechanical stability of the bioinks and the printed scaffolds. Enabling stable and robust materials for the bioprinting processes will lead to the creation of truly complex and remarkable printed structures that could accelerate the application of smart, functional scaffolds in biomedical settings. Impact statement Bioprinting is a powerful tool for the fabrication of 3D structures and scaffolds for biomedical applications. It has gained tremendous attention in recent years, and the bioink library is expanding to include more and more material combinations. From the practical application perspective, different properties need to be considered, such as the printed structure's chemical, mechanical, and biological performances. Among these, the mechanical behavior of the printed constructs is critical for their successful translation into the clinic. The aim of this review article is to explore the different reinforcement strategies used for the mechanical stabilization of bioinks and bioprinted structures.

Tissue engineering in otology: a review of achievements

Tissue engineering application in otology spans a distance from the pinna to auditory nerve covered with specialized tissues and functions such as sense of hearing and aesthetics. It holds the potential to address the barriers of lack of donor tissue, poor tissue match, and transplant rejection through provision of new and healthy tissues similar to the host and possesses the capacity to renew, to regenerate, and to repair in-vivo and was shown to be a bypasses for any need to immunosuppression. This review aims to investigate the application of tissue engineering in otology and to evaluate the achievements and challenges in external, middle and inner ear sections. Since gaining the recent knowledge and training on use of different scaffolds is essential for otology specialists and who look for the recovery of ear function and aesthetics of patients, it is shown in this review how utilizing tissue engineering and cell transplantation, regenerative medicine can provide advancements in hearing and ear aesthetics to fit different patients' needs.

Nanofibrous Material-Reinforced Printable Ink for Enhanced Cell Proliferation and Tissue Regeneration

The three-dimensional (3D) printing of biomaterials, cells, and bioactive components, including growth factors, has gained interest among researchers in the field of tissue engineering (TE) with the aim of developing many scaffolds to sustain size, shape fidelity, and structure and retain viable cells inside a network. The biocompatible hydrogel employed in 3D printing should be soft enough to accommodate cell survival. At the same time, the gel should be mechanically strong to avoid the leakage of cells into the surrounding medium. Considering these basic criteria, researchers have developed nanocomposite-based printable inks with suitable mechanical and electroconductive properties. These nanomaterials, including carbon family nanomaterials, transition metal dichalcogenides, and polymeric nanoparticles, act as nanofillers and dissipate stress across polymeric networks through their electroactive interactions. Nanofiber-reinforced printable ink is one kind of nanocomposite-based ink that comprises dispersed nanofiber components in a hydrogel matrix. In this current review, we compile various TE applications of nanofiber-reinforced printable ink and describe the 3D-printing parameters, classification, and impact of cross-linkage. Furthermore, we discuss the challenges and future perspectives in this field.

Photo-/thermo-responsive bioink for improved printability in extrusion-based bioprinting

Extrusion-based bioprinting has demonstrated significant potential for manufacturing constructs, particularly for 3D cell culture. However, there is a greatly limited number of bioink candidates exploited with extrusion-based bioprinting, as they meet the opposing requirements for printability with indispensable rheological features and for biochemical functionality with desirable microenvironment. In this study, a blend of silk fibroin (SF) and iota-carrageenan (CG) was chosen as a cell-friendly printable material. The SF/CG ink exhibited suitable viscosity and shear-thinning properties, coupled with the rapid sol-gel transition of CG. By employing photo-crosslinking of SF, the printability with Pr value close to 1 and structural integrity of the 3D constructs were significantly improved within a matter of seconds. The printed constructs demonstrated a Young's modulus of approximately 250 kPa, making them suitable for keratinocyte and myoblast cell culture. Furthermore, the high cell adhesiveness and viability (maximum >98%) of the loaded cells underscored the considerable potential of this 3D culture scaffold applied for skin and muscle tissues, which can be easily manipulated using an extrusion-based bioprinter.

Biopolymers for Tissue Engineering: Crosslinking, Printing Techniques, and Applications

Currently, tissue engineering has been dedicated to the development of 3D structures through bioprinting techniques that aim to obtain personalized, dynamic, and complex hydrogel 3D structures. Among the different materials used for the fabrication of such structures, proteins and polysaccharides are the main biological compounds (biopolymers) selected for the bioink formulation. These biomaterials obtained from natural sources are commonly compatible with tissues and cells (biocompatibility), friendly with biological digestion processes (biodegradability), and provide specific macromolecular structural and mechanical properties (biomimicry). However, the rheological behaviors of these natural-based bioinks constitute the main challenge of the cell-laden printing process (bioprinting). For this reason, bioprinting usually requires chemical modifications and/or inter-macromolecular crosslinking. In this sense, a comprehensive analysis describing these biopolymers (natural proteins and polysaccharides)-based bioinks, their modifications, and their stimuli-responsive nature is performed. This manuscript is organized into three sections: (1) tissue engineering application, (2) crosslinking, and (3) bioprinting techniques, analyzing the current challenges and strengths of biopolymers in bioprinting. In conclusion, all hydrogels try to resemble extracellular matrix properties for bioprinted structures while maintaining good printability and stability during the printing process.

A Simplified Method for the Preparation of Highly Conductive and Flexible Silk Nanofibrils/MXene Membrane

Silk nanofibers (SNF) have great applications in high-performance functional nanocomposites due to their excellent mechanical properties, biocompatibility, and degradability. However, the preparation of SNF by traditional methods often requires the use of some environmentally harmful or toxic reagents, limiting its application in green chemistry. In this paper, we successfully prepared SNF using natural silk as raw material and solvent stripping technology by adjusting the solvent concentration and solution ratio (the diameter of about 120 nm). Using the above SNFs as raw materials, SNF membranes were prepared by vacuum filtration technology. In addition, we prepared an SNF/MXene nanocomposite material with excellent humidity sensitivity by simply coating MXene nanosheets with silk fibers. The conductivity of the material can approach 1400.6 S m-1 with excellent mechanical strength (51.34 MPa). The SNF/MXene nanocomposite material with high mechanical properties, high conductivity, and green degradability can be potentially applied in the field of electromagnetic interference (EMI) shielding, providing a feasible approach for the development of functional nanocomposite materials.

Kappa-carrageenan based hybrid hydrogel for soft tissue engineering applications

Biological materials such as cell-derived membrane vesicles have emerged as alternative sources for molecular delivery systems, owing to multicomponent features, the inherent functionalities and signaling networks, and easy-to-carry therapeutic agents with various properties. Herein, red blood cell membrane (RBCM) vesicle-laden methacrylate kappa-carrageenan (KaMA) composite hydrogel is introduced for soft tissue engineering. Results revealed that the characteristics of hybrid hydrogels were significantly modulated by changing the RBCM vesicle content. For instance, the incorporation of 20% (v/v) RBCM significantly enhanced compressive strength from 103 ± 26 kPa to 257 ± 18 kPa and improved toughness under the cyclic loading from 1.0 ± 0.4 kJ m-3to 4.0 ± 0.5 kJ m-3after the 5thcycle. RBCM vesicles were also used for the encapsulation of curcumin (CUR) as a hydrophobic drug molecule. Results showed a controlled release of CUR over three days of immersion in PBS solution. The RBCM vesicles laden KaMA hydrogels also supportedin vitrofibroblast cell growth and proliferation. In summary, this research sheds light on KaMA/RBCM hydrogels, that could reveal fine-tuned properties and hydrophobic drug release in a controlled manner.

Fabrication of Injectable Kartogenin-Conjugated Composite Hydrogel with a Sustained Drug Release for Cartilage Repair

Cartilage tissue engineering has attracted great attention in defect repair and regeneration. The utilization of bioactive scaffolds to effectively regulate the phenotype and proliferation of chondrocytes has become an elemental means for cartilage tissue regeneration. On account of the simultaneous requirement of mechanical and biological performances for tissue-engineered scaffolds, in this work we prepared a naturally derived hydrogel composed of a bioactive kartogenin (KGN)-linked chitosan (CS-KGN) and an aldehyde-modified oxidized alginate (OSA) via the highly efficient Schiff base reaction and multifarious physical interactions in mild conditions. On the basis of the rigid backbones and excellent biocompatibility of these two natural polysaccharides, the composite hydrogel demonstrated favorable morphology, easy injectability, good mechanical strength and tissue adhesiveness, low swelling ratio, long-term sustainable KGN release, and facilitated bone marrow mesenchymal stem cell activity, which could simultaneously provide the mechanical and biological supports to promote chondrogenic differentiation and repair the articular cartilage defects. Therefore, we believe this work can offer a designable consideration and potential alternative candidate for cartilage and other soft tissue implants.