Electrohydrodynamic-direct-printed cell-laden microfibrous structure using alginate-based bioink for effective myotube formation

Enhancing volumetric muscle loss (VML) recovery in a rat model using super durable hydrogels derived from bacteria

Bacteria can be programmed to deliver natural materials with defined biological and mechanical properties for controlling cell growth and differentiation. Here, we present an elastic, resilient and bioactive polysaccharide derived from the extracellular matrix of Pantoea sp. BCCS 001. Specifically, it was methacrylated to generate a new photo crosslinkable hydrogel that we coined Pantoan Methacrylate or put simply PAMA. We have used it for the first time as a tissue engineering hydrogel to treat VML injuries in rats. The crosslinked PAMA hydrogel was super elastic with a recovery nearing 100 %, while mimicking the mechanical stiffness of native muscle. After inclusion of thiolated gelatin via a Michaelis reaction with acrylate groups on PAMA we could also guide muscle progenitor cells into fused and aligned tubes - something reminiscent of mature muscle cells. These results were complemented by sarcomeric alpha-actinin immunostaining studies. Importantly, the implanted hydrogels exhibited almost 2-fold more muscle formation and 50 % less fibrous tissue formation compared to untreated rat groups. In vivo inflammation and toxicity assays likewise gave rise to positive results confirming the biocompatibility of this new biomaterial system. Overall, our results demonstrate that programmable polysaccharides derived from bacteria can be used to further advance the field of tissue engineering. In greater detail, they could in the foreseeable future be used in practical therapies against VML.

Recent trends in 3D bioprinting technology for skeletal muscle regeneration

Skeletal muscle is a pro-regenerative tissue, that utilizes a tissue-resident stem cell system to effect repair upon injury. Despite the demonstrated efficiency of this system in restoring muscle mass after many acute injuries, in conditions of severe trauma such as those evident in volumetric muscle loss (VML) (>20 % by mass), this self-repair capability is unable to restore tissue architecture, requiring interventions which currently are largely surgical. As a possible alternative, the generation of artificial muscle using tissue engineering approaches may also be of importance in the treatment of VML and muscle diseases such as dystrophies. Three-dimensional (3D) bioprinting has been identified as a promising technique for regeneration of the complex architecture of skeletal muscle. This review discusses existing treatment strategies following muscle damage, recent progress in bioprinting techniques, the bioinks used for muscle regeneration, the immunogenicity of scaffold materials, and in vitro and in vivo maturation techniques for 3D bio-printed muscle constructs. The pros and cons of these bioink formulations are also highlighted. Finally, we present the current limitations and challenges in the field and critical factors to consider for bioprinting approaches to become more translationa and to produce clinically relevant engineered muscle. STATEMENT OF SIGNIFICANCE: This review discusses the physiopathology of muscle injuries and existing clinical treatment strategies for muscle damage, the types of bioprinting techniques that have been applied to bioprinting of muscle, and the bioinks commonly used for muscle regeneration. The pros and cons of these bioinks are highlighted. We present a discussion of existing gaps in the literature and critical factors to consider for the translation of bioprinting approaches and to produce clinically relevant engineered muscle. Finally, we provide insights into what we believe will be the next steps required before the realization of the application of tissue-engineered muscle in humans. We believe this manuscript is an insightful, timely, and instructive review that will guide future muscle bioprinting research from a fundamental construct creation approach, down a translational pathway to achieve the desired impact in the clinic.

The Innovative Biomaterials and Technologies for Developing Corneal Endothelium Tissue Engineering Scaffolds: A Review and Prospect

Corneal transplantation is the only treatment for corneal endothelial blindness. However, there is an urgent need to find substitutes for corneal endothelium grafts due to the global shortage of donor corneas. An emerging research field focuses on the construction of scaffold-based corneal endothelium tissue engineering (CETE). Long-term success in CETE transplantation may be achieved by selecting the appropriate biomaterials as scaffolds of corneal endothelial cells and adding bioactive materials to promote cell activity. This article reviews the research progress of CETE biomaterials in the past 20 years, describes the key characteristics required for corneal endothelial scaffolds, and summarizes the types of materials that have been reported. Based on these, we list feasible improvement strategies for biomaterials innovation. In addition, we describe the improved techniques for the scaffolds' surface topography and drug delivery system. Some promising technologies for constructing CETE are proposed. However, some questions have not been answered yet, and clinical trials and industrialization should be carried out with caution.

Development of Electro-Conductive Composite Bioinks for Electrohydrodynamic Bioprinting with Microscale Resolution

Bioprinting has attracted extensive attention in the field of tissue engineering due to its unique capability in constructing biomimetic tissue constructs in a highly controlled manner. However, it is still challenging to reproduce the physical and structural properties of native electroactive tissues due to the poor electroconductivity of current bioink systems as well as the limited printing resolution of conventional bioprinting techniques. In this work, an electro-conductive hydrogel is prepared by introducing poly (3,4-ethylene dioxythiophene): poly (styrene sulfonate) (PEDOT: PSS) into an RGD (GGGGRGDSP)-functionalized alginate and fibrin system (RAF), and then electrohydrodynamic (EHD)-bioprinted to form living tissue constructs with microscale resolution. The addition of 0.1 (w/v%) PEDOT: PSS increases the electroconductivity to 1.95 ± 0.21 S m-1 and simultaneously has little effect on cell viability. Compared with pure RAF bioink, the presence of PEDOT: PSS expands the printable parameters for EHD-bioprinting, and hydrogel filaments with the smallest feature size of 48.91 ± 3.44 µm can be obtained by further optimizing process parameters. Furthermore, the EHD-bioprinted electro-conductive living tissue constructs with improved resolution show good viability (>85%). The synergy of the advanced electro-conductive hydrogel and EHD-bioprinting presented here may provide a promising approach for engineering electro-conductive and cell-laden constructs for electroactive tissue engineering.

Biomaterials / bioinks and extrusion bioprinting

Bioinks are formulations of biomaterials and living cells, sometimes with growth factors or other biomolecules, while extrusion bioprinting is an emerging technique to apply or deposit these bioinks or biomaterial solutions to create three-dimensional (3D) constructs with architectures and mechanical/biological properties that mimic those of native human tissue or organs. Printed constructs have found wide applications in tissue engineering for repairing or treating tissue/organ injuries, as well as in vitro tissue modelling for testing or validating newly developed therapeutics and vaccines prior to their use in humans. Successful printing of constructs and their subsequent applications rely on the properties of the formulated bioinks, including the rheological, mechanical, and biological properties, as well as the printing process. This article critically reviews the latest developments in bioinks and biomaterial solutions for extrusion bioprinting, focusing on bioink synthesis and characterization, as well as the influence of bioink properties on the printing process. Key issues and challenges are also discussed along with recommendations for future research.

Prospect and retrospect of 3D bio-printing

3D bioprinting has become a popular medical technique in recent years. The most compelling rationale for the development of 3D bioprinting is the paucity of biological structures required for the rehabilitation of missing organs and tissues. They're useful in a multitude of domains, including disease modelling, regenerative medicine, tissue engineering, drug discovery with testing, personalised medicine, organ development, toxicity studies, and implants. Bioprinting requires a range of bioprinting technologies and bioinks to finish their procedure, that Inkjet-based bioprinting, extrusion-based bioprinting, laser-assisted bioprinting, stereolithography-based bioprinting, and in situ bioprinting are some of the technologies listed here. Bioink is a 3D printing material that is used to construct engineered artificial living tissue. It can be constructed solely for cells, but it usually includes a carrier substance that envelops the cells, then there's Agarose-based bioinks, alginate-based bioinks, collagen-based bioinks, and hyaluronic acid-based bioinks, to name a few. Here we presented about the different bioprinting methods with the use of bioinks in it and then Prospected over various applications in different fields.

Advanced Strategies for 3D Bioprinting of Tissue and Organ Analogs Using Alginate Hydrogel Bioinks

Alginate is a natural polysaccharide that typically originates from various species of algae. Due to its low cost, good biocompatibility, and rapid ionic gelation, the alginate hydrogel has become a good option of bioink source for 3D bioprinting. However, the lack of cell adhesive moieties, erratic biodegradability, and poor printability are the critical limitations of alginate hydrogel bioink. This review discusses the pivotal properties of alginate hydrogel as a bioink for 3D bioprinting technologies. Afterward, a variety of advanced material formulations and biofabrication strategies that have recently been developed to overcome the drawbacks of alginate hydrogel bioink will be focused on. In addition, the applications of these advanced solutions for 3D bioprinting of tissue/organ mimicries such as regenerative implants and in vitro tissue models using alginate-based bioink will be systematically summarized.

Engineered Myoblast-Laden Collagen Filaments Fabricated Using a Submerged Bioprinting Process to Obtain Efficient Myogenic Activities

The skeletal muscle tissue comprises a hierarchical fibrous structure with fully aligned myofibers. To obtain a unique aligned engineering construct for regenerating muscle tissue, we adopted a submerged bioprinting process. Here, 3 wt % collagen and 6 wt % alginate solutions were used as a matrix cell-encapsulating bioink and supporting solution in the printing bath, respectively. By manipulating the processing parameters (various alginate weight fractions in the bath, nozzle moving speed, and hydrostatic pressure), cell-laden filaments (∼50 μm in diameter) were successfully fabricated. They presented a high degree of alignment of the fibrillated collagen and meaningful initial viability (∼90%) of the C2C12 myoblasts. In vitro cellular responses indicated that fully aligned F-actin filaments of myoblasts were developed, resulting in a high degree of alignment/formation of myotubes, compared to that in the controls (>100 μm diameter of cell-laden filaments). Furthermore, the expression levels of various myogenic genes (Myod1, Myh2, and Myog) were measured using a reverse transcription polymerase chain reaction on day 21 of the cell culture, and the results showed that the cell-laden filaments with a small diameter had considerably greater gene expression levels (2.2-8-fold) than those with a relatively large diameter. Thus, the printing process described herein can provide a new potential biofabricating platform to obtain cell-laden engineering constructs for various tissues.