3D bioprinting of a biomimetic meniscal scaffold for application in tissue engineering

Advancements in Tissue Engineering: A Review of Bioprinting Techniques, Scaffolds, and Bioinks

Tissue engineering is a multidisciplinary field that uses biomaterials to restore tissue function and assist with drug development. Over the last decade, the fabrication of three-dimensional (3D) multifunctional scaffolds has become commonplace in tissue engineering and regenerative medicine. Thanks to the development of 3D bioprinting technologies, these scaffolds more accurately recapitulate in vivo conditions and provide the support structure necessary for microenvironments conducive to cell growth and function. The purpose of this review is to provide a background on the leading 3D bioprinting methods and bioink selections for tissue engineering applications, with a specific focus on the growing field of developing multifunctional bioinks and possible future applications.

[Construction of a novel tissue engineered meniscus scaffold based on low temperature deposition three-dimenisonal printing technology]

Objective

To investigate the construction of a novel tissue engineered meniscus scaffold based on low temperature deposition three-dimenisonal (3D) printing technology and evaluate its biocompatibility.

Methods

The fresh pig meniscus was decellularized by improved physicochemical method to obtain decellularized meniscus matrix homogenate. Gross observation, HE staining, and DAPI staining were used to observe the decellularization effect. Toluidine blue staining, safranin O staining, and sirius red staining were used to evaluate the retention of mucopolysaccharide and collagen. Then, the decellularized meniscus matrix bioink was prepared, and the new tissue engineered meniscus scaffold was prepared by low temperature deposition 3D printing technology. Scanning electron microscopy was used to observe the microstructure. After co-culture with adipose-derived stem cells, the cell compatibility of the scaffolds was observed by cell counting kit 8 (CCK-8), and the cell activity and morphology were observed by dead/live cell staining and cytoskeleton staining. The inflammatory cell infiltration and degradation of the scaffolds were evaluated by subcutaneous experiment in rats.

Results

The decellularized meniscus matrix homogenate appeared as a transparent gel. DAPI and histological staining showed that the immunogenic nucleic acids were effectively removed and the active components of mucopolysaccharide and collagen were remained. The new tissue engineered meniscus scaffolds was constructed by low temperature deposition 3D printing technology and it had macroporous-microporous microstructures under scanning electron microscopy. CCK-8 test showed that the scaffolds had good cell compatibility. Dead/live cell staining showed that the scaffold could effectively maintain cell viability (>90%). Cytoskeleton staining showed that the scaffolds were benefit for cell adhesion and spreading. After 1 week of subcutaneous implantation of the scaffolds in rats, there was a mild inflammatory response, but no significant inflammatory response was observed after 3 weeks, and the scaffolds gradually degraded.

Conclusion

The novel tissue engineered meniscus scaffold constructed by low temperature deposition 3D printing technology has a graded macroporous-microporous microstructure and good cytocompatibility, which is conducive to cell adhesion and growth, laying the foundation for the in vivo research of tissue engineered meniscus scaffolds in the next step.

A comprehensive review on the biomedical frontiers of nanowire applications

This comprehensive review examines the immense capacity of nanowires, nanostructures characterized by unbounded dimensions, to profoundly transform the field of biomedicine. Nanowires, which are created by combining several materials using techniques such as electrospinning and vapor deposition, possess distinct mechanical, optical, and electrical properties. As a result, they are well-suited for use in nanoscale electronic devices, drug delivery systems, chemical sensors, and other applications. The utilization of techniques such as the vapor-liquid-solid (VLS) approach and template-assisted approaches enables the achievement of precision in synthesis. This precision allows for the customization of characteristics, which in turn enables the capability of intracellular sensing and accurate drug administration. Nanowires exhibit potential in biomedical imaging, neural interfacing, and tissue engineering, despite obstacles related to biocompatibility and scalable manufacturing. They possess multifunctional capabilities that have the potential to greatly influence the intersection of nanotechnology and healthcare. Surmounting present obstacles has the potential to unleash the complete capabilities of nanowires, leading to significant improvements in diagnostics, biosensing, regenerative medicine, and next-generation point-of-care medicines.

Meticulously engineered three-dimensional-printed scaffold with microarchitecture and controlled peptide release for enhanced bone regeneration

The repair of large load-bearing bone defects requires superior mechanical strength, a feat that a single hydrogel scaffold cannot achieve. The objective is to seamlessly integrate optimal microarchitecture, mechanical robustness, vascularisation, and osteoinductive biological responses to effectively address these critical load-bearing bone defects. To confront this challenge, three-dimensional (3D) printing technology was employed to prepare a polycaprolactone (PCL)-based integrated scaffold. Within the voids of 3D printed PCL scaffold, a methacrylate gelatin (GelMA)/methacrylated silk fibroin (SFMA) composite hydrogel incorporated with parathyroid hormone (PTH) peptide-loaded mesoporous silica nanoparticles (PTH@MSNs) was embedded, evolving into a porous PTH@MSNs/GelMA/SFMA/PCL (PM@GS/PCL) scaffold. The feasibility of fabricating this functional scaffold with a customised hierarchical structure was confirmed through meticulous chemical and physical characterisation. Compression testing unveiled an impressive strength of 17.81 ± 0.83 MPa for the composite scaffold. Additionally, in vitro angiogenesis potential of PM@GS/PCL scaffold was evaluated through Transwell and tube formation assays using human umbilical vein endothelium, revealing the superior cell migration and tube network formation. The alizarin red and alkaline phosphatase staining assays using bone marrow-derived mesenchymal stem cells clearly illustrated robust osteogenic differentiation properties within this scaffold. Furthermore, the bone repair potential of the scaffold was investigated on a rat femoral defect model using micro-computed tomography and histological examination, demonstrating enhanced osteogenic and angiogenic performance. This study presents a promising strategy for fabricating a microenvironment-matched composite scaffold for bone tissue engineering, providing a potential solution for effective bone defect repair.

Current advances in engineering meniscal tissues: insights into 3D printing, injectable hydrogels and physical stimulation based strategies

The knee meniscus is the cushioning fibro-cartilage tissue present in between the femoral condyles and tibial plateau of the knee joint. It is largely avascular in nature and suffers from a wide range of tears and injuries caused by accidents, trauma, active lifestyle of the populace and old age of individuals. Healing of the meniscus is especially difficult due to its avascularity and hence requires invasive arthroscopic approaches such as surgical resection, suturing or implantation. Though various tissue engineering approaches are proposed for the treatment of meniscus tears, three-dimensional (3D) printing/bioprinting, injectable hydrogels and physical stimulation involving modalities are gaining forefront in the past decade. A plethora of new printing approaches such as direct light photopolymerization and volumetric printing, injectable biomaterials loaded with growth factors and physical stimulation such as low-intensity ultrasound approaches are being added to the treatment portfolio along with the contemporary tear mitigation measures. This review discusses on the necessary design considerations, approaches for 3D modeling and design practices for meniscal tear treatments within the scope of tissue engineering and regeneration. Also, the suitable materials, cell sources, growth factors, fixation and lubrication strategies, mechanical stimulation approaches, 3D printing strategies and injectable hydrogels for meniscal tear management have been elaborated. We have also summarized potential technologies and the potential framework that could be the herald of the future of meniscus tissue engineering and repair approaches.

Cartilage-on-a-chip with magneto-mechanical transformation for osteoarthritis recruitment

Osteoarthritis (OA) is a prevalent joint disease primarily induced by overstrain, leading to disability and significantly impacting patients' quality of life. However, current OA studies lack an ideal in vitro model, which can recapitulate the high peripheral strain of the joint and precisely model the disease onset process. In this paper, we propose a novel cartilage-on-a-chip platform that incorporates a biohybrid hydrogel comprising Neodymium (NdFeB)/Poly-GelMA-HAMA remote magneto-control hydrogel film. This platform facilitates chondrocyte culture and stress loading, enabling the investigation of chondrocytes under various stress stimuli. The Neodymium (NdFeB)/Poly-GelMA-HAMA hydrogel film exhibits magneto-responsive shape-transition behavior, further dragging the chondrocytes cultured in hydrogels under magnetic stimulation. It was investigated that inflammation-related genes and proteins in chondrocytes are changed with mechanical stress stimulation in the cartilage-on-a-chip. Especially, MMP-13 and the proportion of collagen secretion are upregulated, showing a phenotype similar to that of real human osteoarthritis. Therefore, we believed that this cartilage-on-a-chip platform provides a desired in vitro model for osteoarthritis, which is of great significance in disease research and drug development.

Recent advances in 3D bioprinted cartilage-mimicking constructs for applications in tissue engineering

Human cartilage tissue can be categorized into three types: hyaline cartilage, elastic cartilage and fibrocartilage. Each type of cartilage tissue possesses unique properties and functions, which presents a significant challenge for the regeneration and repair of damaged tissue. Bionics is a discipline in which humans study and imitate nature. A bionic strategy based on comprehensive knowledge of the anatomy and histology of human cartilage is expected to contribute to fundamental study of core elements of tissue repair. Moreover, as a novel tissue-engineered technology, 3D bioprinting has the distinctive advantage of the rapid and precise construction of targeted models. Thus, by selecting suitable materials, cells and cytokines, and by leveraging advanced printing technology and bionic concepts, it becomes possible to simultaneously realize multiple beneficial properties and achieve improved tissue repair. This article provides an overview of key elements involved in the combination of 3D bioprinting and bionic strategies, with a particular focus on recent advances in mimicking different types of cartilage tissue.

Advances in 3D Bioprinting of Biomimetic and Engineered Meniscal Grafts

The meniscus plays a crucial role in loads distribution and protection of articular cartilage. Meniscal injury can result in cartilage degeneration, loss of mechanical stability in the knee joint and ultimately lead to arthritis. Surgical interventions provide only short-term pain relief but fail to repair or regenerate the injured meniscus. Emerging tissue engineering approaches based on 3D bioprinting provide alternatives to current surgical methods for meniscus repair. In this review, the current bioprinting techniques employed in developing engineered meniscus grafts are summarized and discuss the latest strategies for mimicking the gradient structure, composition, and viscoelastic properties of native meniscus. Recent progress is highlighted in gene-activated matrices for meniscus regeneration as well. Finally, a perspective is provided on the future development of 3D bioprinting for meniscus repair, emphasizing the potential of this technology to revolutionize meniscus regeneration and improve patient outcomes.

Preclinical Studies and Clinical Trials on Cell-Based Treatments for Meniscus Regeneration

This study aims at performing a thorough review of cell-based treatment strategies for meniscus regeneration in preclinical and clinical studies. The PubMed, Embase, and Web of Science databases were searched for relevant studies (both preclinical and clinical) published from the time of database construction to December 2022. Data related to cell-based therapies for in situ regeneration of the meniscus were extracted independently by two researchers. Assessment of risk of bias was performed according to the Cochrane Handbook for Systematic Reviews of Interventions. Statistical analyses based on the classification of different treatment strategies were performed. A total of 5730 articles were retrieved, of which 72 preclinical studies and 6 clinical studies were included in this review. Mesenchymal stem cells (MSCs), especially bone marrow MSCs (BMSCs), were the most commonly used cell type. Among preclinical studies, rabbit was the most commonly used animal species, partial meniscectomy was the most commonly adopted injury pattern, and 12 weeks was the most frequently chosen final time point for assessing repair outcomes. A range of natural and synthetic materials were used to aid cell delivery as scaffolds, hydrogels, or other morphologies. In clinical trials, there was large variation in the dose of cells, ranging from 16 × 106 to 150 × 106 cells with an average of 41.52 × 106 cells. The selection of treatment strategy for meniscus repair should be based on the nature of the injury. Cell-based therapies incorporating various "combination" strategies such as co-culture, composite materials, and extra stimulation may offer greater promise than single strategies for effective meniscal tissue regeneration, restoring natural meniscal anisotropy, and eventually achieving clinical translation. Impact Statement This review provides an up-to-date and comprehensive overview of preclinical and clinical studies that tested cell-based treatments for meniscus regeneration. It presents novel perspectives on studies published in the past 30 years, giving consideration to the cell sources and dose selection, delivery methods, extra stimulation, animal models and injury patterns, timing of outcome assessment, and histological and biomechanical outcomes, as well as a summary of findings for individual studies. These unique insights will help to shape future research on the repair of meniscus lesions and inform the clinical translation of new cell-based tissue engineering strategies.

Photocrosslinked methacrylated natural macromolecular hydrogels for tissue engineering: A review

A hydrogel is a three-dimensional (3D) network structure formed through polymer crosslinking, and these have emerged as a popular research topic in recent years. Hydrogel crosslinking can be classified as physical, chemical, or enzymatic, and photocrosslinking is a branch of chemical crosslinking. Compared with other methods, photocrosslinking can control the hydrogel crosslinking initiation, crosslinking time, and crosslinking strength using light. Owing to these properties, photocrosslinked hydrogels have important research prospects in tissue engineering, in situ gel formation, 3D bioprinting, and drug delivery. Methacrylic anhydride modification is a common method for imparting photocrosslinking properties to polymers, and graft-substituted polymers can be photocrosslinked under UV irradiation. In this review, we first introduce the characteristics of common natural polysaccharide- and protein-based hydrogels and the processes used for methacrylate group modification. Next, we discuss the applications of methacrylated natural hydrogels in tissue engineering. Finally, we summarize and discuss existing methacrylated natural hydrogels in terms of limitations and future developments. We expect that this review will help researchers in this field to better understand the synthesis of methacrylate-modified natural hydrogels and their applications in tissue engineering.

3D Bioprinting of a Bioactive Composite Scaffold for Cell Delivery in Periodontal Tissue Regeneration

Hydrogels have been widely applied to the fabrication of tissue engineering scaffolds via three-dimensional (3D) bioprinting because of their extracellular matrix-like properties, capacity for living cell encapsulation, and shapeable customization depending on the defect shape. However, the current hydrogel scaffolds show limited regeneration activity, especially in the application of periodontal tissue regeneration. In this study, we attempted to develop a novel multi-component hydrogel that possesses good biological activity, can wrap living cells for 3D bioprinting and can regenerate periodontal soft and hard tissue. The multi-component hydrogel consisted of gelatin methacryloyl (GelMA), sodium alginate (SA) and bioactive glass microsphere (BGM), which was first processed into hydrogel scaffolds by cell-free 3D printing to evaluate its printability and in vitro biological performances. The cell-free 3D-printed scaffolds showed uniform porous structures and good swelling capability. The BGM-loaded scaffold exhibited good biocompatibility, enhanced osteogenic differentiation, apatite formation abilities and desired mechanical strength. The composite hydrogel was further applied as a bio-ink to load with mouse bone marrow mesenchymal stem cells (mBMSCs) and growth factors (BMP2 and PDGF) for the fabrication of a scaffold for periodontal tissue regeneration. The cell wrapped in the hydrogel still maintained good cellular vitality after 3D bioprinting and showed enhanced osteogenic differentiation and soft tissue repair capabilities in BMP2- and PDGF-loaded scaffolds. It was noted that after transplantation of the cell- and growth factor-laden scaffolds in Beagle dog periodontal defects, significant regeneration of gingival tissue, periodontal ligament, and alveolar bone was detected. Importantly, a reconstructed periodontal structure was established in the treatment group eight weeks post-transplantation of the scaffolds containing the cell and growth factors. In conclusion, we developed a bioactive composite bio-ink for the fabrication of scaffolds applicable for the reconstruction and regeneration of periodontal tissue defects.

Chondroitinase ABC Treatment Improves the Organization and Mechanics of 3D Bioprinted Meniscal Tissue

The meniscus is a fibrocartilage tissue that is integral to the correct functioning of the knee joint. The tissue possesses a unique collagen fiber architecture that is integral to its biomechanical functionality. In particular, a network of circumferentially aligned collagen fibers function to bear the high tensile forces generated in the tissue during normal daily activities. The limited regenerative capacity of the meniscus has motivated increased interest in meniscus tissue engineering; however, the in vitro generation of structurally organized meniscal grafts with a collagen architecture mimetic of the native meniscus remains a significant challenge. Here we used melt electrowriting (MEW) to produce scaffolds with defined pore architectures to impose physical boundaries upon cell growth and extracellular matrix production. This enabled the bioprinting of anisotropic tissues with collagen fibers preferentially oriented parallel to the long axis of the scaffold pores. Furthermore, temporally removing glycosaminoglycans (sGAGs) during the early stages of in vitro tissue development using chondroitinase ABC (cABC) was found to positively impact collagen network maturation. Specially we found that temporal depletion of sGAGs is associated with an increase in collagen fiber diameter without any detrimental effect on the development of a meniscal tissue phenotype or subsequent extracellular matrix production. Moreover, temporal cABC treatment supported the development of engineered tissues with superior tensile mechanical properties compared to empty MEW scaffolds. These findings demonstrate the benefit of temporal enzymatic treatments when engineering structurally anisotropic tissues using emerging biofabrication technologies such as MEW and inkjet bioprinting.

Chitin nanocrystal-assisted 3D bioprinting of gelatin methacrylate scaffolds

In recent years, there has been an increasing focus on the application of hydrogels in tissue engineering. The integration of 3D bioprinting technology has expanded the potential applications of hydrogels. However, few commercially available hydrogels used for 3D biological printing exhibit both excellent biocompatibility and mechanical properties. Gelatin methacrylate (GelMA) has good biocompatibility and is widely used in 3D bioprinting. However, its low mechanical properties limit its use as a standalone bioink for 3D bioprinting. In this work, we designed a biomaterial ink composed of GelMA and chitin nanocrystal (ChiNC). We explored fundamental printing properties of composite bioinks, including rheological properties, porosity, equilibrium swelling rate, mechanical properties, biocompatibility, effects on the secretion of angiogenic factors and fidelity of 3D bioprinting. The results showed that adding 1% (w/v) ChiNC to 10% (w/v) GelMA improved the mechanical properties and printability of the GelMA hydrogels, promoted cell adhesion, proliferation and vascularization and enabled the printing of complex 3D scaffolds. This strategy of incorporating ChiNC to enhance the performance of GelMA biomaterials could potentially be applied to other biomaterials, thereby expanding the range of materials available for use. Furthermore, in combination with 3D bioprinting technology, this approach could be leveraged to bioprint scaffolds with complex structures, further broadening the potential applications in tissue engineering.

3D bioprinted liver tissue and disease models: Current advances and future perspectives

Three-dimensional (3D) bioprinting is a promising technology for fabricating complex tissue constructs with biomimetic biological functions and stable mechanical properties. In this review, the characteristics of different bioprinting technologies and materials are compared, and development in strategies for bioprinting normal and diseased hepatic tissue are summarized. In particular, features of bioprinting and other bio-fabrication strategies, such as organoids and spheroids are compared to demonstrate the strengths and weaknesses of 3D printing technology. Directions and suggestions, such as vascularization and primary human hepatocyte culture, are provided for the future development of 3D bioprinting.

3D and 4D Bioprinting Technologies: A Game Changer for the Biomedical Sector?

Bioprinting is an innovative and emerging technology of additive manufacturing (AM) and has revolutionized the biomedical sector by printing three-dimensional (3D) cell-laden constructs in a precise and controlled manner for numerous clinical applications. This approach uses biomaterials and varying types of cells to print constructs for tissue regeneration, e.g., cardiac, bone, corneal, cartilage, neural, and skin. Furthermore, bioprinting technology helps to develop drug delivery and wound healing systems, bio-actuators, bio-robotics, and bio-sensors. More recently, the development of four-dimensional (4D) bioprinting technology and stimuli-responsive materials has transformed the biomedical sector with numerous innovations and revolutions. This issue also leads to the exponential growth of the bioprinting market, with a value over billions of dollars. The present study reviews the concepts and developments of 3D and 4D bioprinting technologies, surveys the applications of these technologies in the biomedical sector, and discusses their potential research topics for future works. It is also urged that collaborative and valiant efforts from clinicians, engineers, scientists, and regulatory bodies are needed for translating this technology into the biomedical, pharmaceutical, and healthcare systems.

Strategies for improving the 3D printability of decellularized extracellular matrix bioink

3D bioprinting is a revolutionary technology capable of replicating native tissue and organ microenvironments by precisely placing cells into 3D structures using bioinks. However, acquiring the ideal bioink to manufacture biomimetic constructs is challenging. A natural extracellular matrix (ECM) is an organ-specific material that provides physical, chemical, biological, and mechanical cues that are hard to mimic using a small number of components. Organ-derived decellularized ECM (dECM) bioink is revolutionary and has optimal biomimetic properties. However, dECM is always "non-printable" owing to its poor mechanical properties. Recent studies have focused on strategies to improve the 3D printability of dECM bioink. In this review, we highlight the decellularization methods and procedures used to produce these bioinks, effective methods to improve their printability, and recent advances in tissue regeneration using dECM-based bioinks. Finally, we discuss the challenges associated with manufacturing dECM bioinks and their potential large-scale applications.

Decellularized-disc based allograft and xenograft prosthesis for the long-term precise reconstruction of temporomandibular joint disc

Currently, no effective disc reconstruction treatment strategy is clinically available for temporomandibular joint (TMJ) disc-related diseases. To address this, we developed a prosthesis construct with laser-drilled decellularized natural disc reinforced by polycaprolactone, which mimics the natural morphology, and structural, biomechanical and biological property of the TMJ disc. The construct demonstrated good biocompatibility, safety and immunological tolerance both in vitro, and in a rat subcutaneous model. During 6 months implantation in an allogeneic rabbit TMJ disc reconstruction model, the disc prosthesis maintained its integrity, collagen fiber-orientation, mechanical property, joint structural stability and prevented articular cartilage and bone from damage. Furthermore, the "upgraded" disc prosthesis obtained from decellularized porcine disc was implanted into a goat TMJ disc reconstruction model. The xenograft prosthesis, with strength and viscoelasticity similar to a natural TMJ disc, was able to restore the structure and function of TMJ up to 20 weeks. These results demonstrate the translational feasibility of an allogeneic or xenogeneic decellularized disc prosthesis for treatment of advanced TMJ disc-related diseases. STATEMENT OF SIGNIFICANCE: This study makes a significant contribution to TMJ disc disease treatment both in theory and in clinics, because: (1) it provided an innovative approach to prepare an artificial TMJ disc with decent mechanical properties and long-term condyle-protecting effect; (2) it specified an advanced decellularized method for fibrocartilage decellularization and xenograft application; (3) it developed a facile and reproducible TMJ disc reconstruction model not only for middle size animal but also for large animal study; (4) the comprehensive and unreported biomechanical tests on the natural TMJ discs would act as a valuable reference for further research in the field of artificial TMJ disc materials or TMJ disc tissue engineering; (5) it suggested a potential treatment for patients with severe TMJ diseases that were commonly met but difficult to treat in clinics.

Bioprinting EphrinB2-Modified Dental Pulp Stem Cells with Enhanced Osteogenic Capacity for Alveolar Bone Engineering

Bioprinting, a technology that allows depositing living cells and biomaterials together into a complex tissue architecture with desired pattern, becomes a revolutionary technology for fabrication of engineered constructs. Previously, we have demonstrated that EphrinB2-modified dental pulp stem cells (DPSCs) are expected to be promising seed cells with enhanced osteogenic differentiation capability for alveolar bone regeneration. In this study, we aimed to bioprint EphrinB2-overexpressing DPSCs with low-concentrated Gelatin methacrylate (GelMA) hydrogels into three-dimensional (3D) constructs. The printability of GelMA (5% w/v) and the structural fidelity of bioprinted constructs were examined. Then, viability, proliferation, morphology, and osteogenic differentiation of DPSCs in bioprinted constructs were measured. Finally, the effect of EphrinB2 overexpression on osteogenic differentiation of DPSCs in bioprinted constructs was evaluated. Our results demonstrated that GelMA (5% w/v) in a physical gel form was successfully bioprinted into constructs with various shapes and patterns using optimized printing parameters. Embedded DPSCs showed round-like morphology, and had a high viability (91.93% ± 8.38%) and obvious proliferation (∼1.9-fold increase) 1 day after printing. They also showed excellent osteogenic potential in bioprinted constructs. In bioprinted 3D constructs, EphrinB2-overexpressing DPSCs expressed upregulated osteogenic markers, including ALP, BMP2, RUNX2, and SP7, and generated more mineralized nodules, as compared with Vector-DPSCs. Taken together, this study indicated that fabrication of bioprinted EphrinB2-DPSCs-laden constructs with enhanced osteogenic potential was possible, and 3D bioprinting strategy combined with EphrinB2 gene modification was a promising way to create bioengineered constructs for alveolar bone regeneration.

Simulating and Predicting the Part Warping in Fused Deposition Modeling by Thermal-Structural Coupling Analysis

As the most commonly used additive manufacturing technology, fused deposition modeling (FDM) still faces some technical issues caused by temperature change-induced unsteady thermal stress and warping. These issues can further lead to the deformation of printed parts and even terminate the printing process. In response to these issues, this article established a numerical model of temperature field and thermal stress field for FDM by finite element modeling and "birth-death element" technique to predict the deformation of the part. What makes sense in this process is that the logic of elements sort based on ANSYS Parametric Design Language (APDL) was proposed to sort the meshed elements, which was aimed to perform FDM simulation quickly on the model. In this work, the effects of the sheets shape and infill line directions (ILDs) on the distortion during FDM were simulated and verified. From the analysis of stress field and deformation nephogram, the simulation results indicated that ILD had greater effects on the distortion. Moreover, the sheet warping became most serious when the ILD was aligned with the diagonal of the sheet. The simulation results matched well with the experimental results. Thus, the proposed method in this work can be used to optimize the printing parameters for FDM process.

Recent advances in GelMA hydrogel transplantation for musculoskeletal disorders and related disease treatment

Increasing data reveals that gelatin that has been methacrylated is involved in a variety of physiologic processes that are important for therapeutic interventions. Gelatin methacryloyl (GelMA) hydrogel is a highly attractive hydrogels-based bioink because of its good biocompatibility, low cost, and photo-cross-linking structure that is useful for cell survivability and cell monitoring. Methacrylated gelatin (GelMA) has established itself as a typical hydrogel composition with extensive biomedical applications. Recent advances in GelMA have focused on integrating them with bioactive and functional nanomaterials, with the goal of improving GelMA's physical, chemical, and biological properties. GelMA's ability to modify characteristics due to the synthesis technique also makes it a good choice for soft and hard tissues. GelMA has been established to become an independent or supplementary technology for musculoskeletal problems. Here, we systematically review mechanism-of-action, therapeutic uses, and challenges and future direction of GelMA in musculoskeletal disorders. We give an overview of GelMA nanocomposite for different applications in musculoskeletal disorders, such as osteoarthritis, intervertebral disc degeneration, bone regeneration, tendon disorders and so on.

A Universal and Simple Method to Obtain Hydrogels with Combined Extreme Mechanical Properties and Their Application as Tendon Substitutes

With the development of biomedical engineering, the preparation of hydrogels with combined extreme mechanical properties similar to those of some biological hydrogels becomes an important research topic for scientists. In this work, a single-network hydrogel with combined extreme mechanical properties is prepared through a simple and universal method, wherein the strength, elongation at break, toughness, and fracture energy of the hydrogel WPU-3PAAm-6PAN are achieved at 24.7 MPa, 544.0%, 68.9 MJ m^-3, and 37.2 kJ m^-2, respectively. Herein, a series of photosensitive resins in emulsion form are synthesized, and due to the water-oil diphasic characteristic, hydrophobic monomers and high-efficient hydrophobic photo-initiators are adopted into the resins, which can significantly improve the mechanical properties of the hydrogels due to the hydrophobic association effect and solve the biggest barrier of low curing rate in digital light processing (DLP) fabrication of hydrogels, respectively. Moreover, the simple and facile method to obtain robust and tough hydrogels can be universally applied to other polymer systems. Combined with the excellent mechanical properties and printing ability, the hydrogels with optimized structures are fabricated through DLP printing technology and applied as tendon substitutes. The tendon substitutes exhibit superior performance for mechanical connection and regeneration of collagen fibers. Although further clinical research is required, the hydrogels have great potential applications in various biological areas.

3D Bioprinting Technology and Hydrogels Used in the Process

3D bioprinting has gained visibility in regenerative medicine and tissue engineering due to its applicability. Over time, this technology has been optimized and adapted to ensure a better printability of bioinks and biomaterial inks, contributing to developing structures that mimic human anatomy. Therefore, cross-linked polymeric materials, such as hydrogels, have been highly targeted for the elaboration of bioinks, as they guarantee cell proliferation and adhesion. Thus, this short review offers a brief evolution of the 3D bioprinting technology and elucidates the main hydrogels used in the process.

Microtissue-Based Bioink as a Chondrocyte Microshelter for DLP Bioprinting

Bioprinting specific tissues with robust viability is a great challenge, requiring a delicate balance between a densely cellular distribution and hydrogel network crosslinking density. Microtissues composed of tissue-specific mesenchymal stem cells and extra cellular matrix (ECM) particles provide an alternative scheme for realizing biomimetic cell density and microenvironment. Nevertheless, due to their instability during manufacturing, scarce efforts have been made to date to assemble them using rapid prototyping methods. Here, a novel microtissue bioink with good printability and cellular viability maintenance for digital light processing (DLP) bioprinting is introduced. Generally, the microtissue bioink is prepared by crosslinking acellular matrix microparticles and GelMA hydrogel with a specific proportion. The microtissue bioink exhibits the desired mechanical properties, swelling ratio, and has almost no influences on printability. For instance, a DLP bioprinted ear with a precise auricle structure using microtia chondrocytes microtissue boink is created. Additionally, the chondrocytes in the printed ears show obvious advantages in cell proliferation in vitro and auricular cartilage regeneration in vivo. The microtissue composite bioink for DLP printing not only enables accurate assembly of organ building blocks but also provides a 3D shelter to ensure printed cells' viability.

Formulation and evaluation of a bioink composed of alginate, gelatin, and nanocellulose for meniscal tissue engineering

1The necessity to preserve meniscal function prompts the research and development of novel treatment options, like three-dimensional (3D) bioprinting. However, bioinks for meniscal 3D bioprinting have not been extensively explored. Therefore, in this study, a bioink composed of alginate, gelatin, and carboxymethylated cellulose nanocrystal (CCNC) was formulated and evaluated. Firstly, bioinks with varying concentrations of the aforementioned components were subjected to rheological analysis (amplitude sweep test, temperature sweep test, and rotation). The optimal bioink formulation of 4.0% gelatin, 0.75% alginate, and 1.4% CCNC dissolved in 4.6% D-mannitol was further used for printing accuracy analysis, followed by 3D bioprinting with normal human knee articular chondrocytes (NHAC-kn). The encapsulated cells' viability was > 98%, and collagen II expression was stimulated by the bioink. The formulated bioink is printable, stable under cell culture conditions, biocompatible, and able to maintain the native phenotype of chondrocytes. Aside from meniscal tissue bioprinting, it is believed that this bioink could serve as a basis for the development of bioinks for various tissues.

Graded-Three-Dimensional Cell-Encapsulating Hydrogel as a Potential Biologic Scaffold for Disc Tissue Engineering

BACKGROUND

Intervertebral disk (IVD) degeneration, which can cause lower back pain, is a major predisposing factor for disability and can be managed through multiple approaches. However, there is no satisfactory strategy currently available to reconstruct and recover the natural properties of IVDs after degeneration. As tissue engineering develops, scaffolds with embedded cell cultures have proved critical for the successful regeneration of IVDs.

METHODS

In this study, an integrated scaffold for IVD replacement was developed. Through scanning electron microscopy and other mechanical measurements, we characterized the physical properties of different hydrogels. In addition, we simulated the physiological structure of natural IVDs. Nucleus pulposus (NP) cells and annulus fibrosus-derived stem cells (AFSCs) were seeded in gelatin methacrylate (GelMA) hydrogel at different concentrations to evaluate cell viability and matrix expression.

RESULTS

It was found that different concentrations of GelMA hydrogel can provide a suitable environment for cell survival. However, hydrogels with different mechanical properties influence cell adhesion and extracellular matrix component type I collagen, type II collagen, and aggrecan expression.

CONCLUSION

This tissue-engineered IVD implant had a similar structure and function as the native IVD, with the inner area mimicking the NP tissue and the outer area mimicking the stratified annulus fibrosus tissue. The new integrated scaffold demonstrated a good simulation of disc structure. The preparation of efficient and regeneration-promoting tissue-engineered scaffolds is an important issue that needs to be explored in the future. It is hoped that this work will provide new ideas and methods for the further construction of functional tissue replacement discs.

A Multifunctional 3D Bioprinting System for Construction of Complex Tissue Structure Scaffolds: Design and Application

Three-dimensional (3D) bioprinting offers a potentially powerful new approach to reverse engineering human pathophysiology to address the problem of developing more biomimetic experimental systems. Human tissues and organs are multiscale and multi-material structures. The greatest challenge for organ printing is the complexity of the structural elements, from the shape of the macroscopic structure to the details of the nanostructure. A highly bionic tissue-organ model requires the use of multiple printing processes. Some printers with multiple nozzles and multiple processes are currently reported. However, the bulk volume, which is inconvenient to move, and the high cost of these printing systems limits the expansion of their applications. Scientists urgently need a multifunctional miniaturized 3D bioprinter. In this study, a portable multifunctional 3D bioprinting system was built based on a modular design and a custom written operating application. Using this platform, constructs with detailed surface structures, hollow structures, and multiscale complex tissue analogs were successfully printed using commercial polymers and a series of hydrogel-based inks. With further development, this portable, modular, low-cost, and easy-to-use Bluetooth-enabled 3D printer promises exciting opportunities for resource-constrained application scenarios, not only in biomedical engineering but also in the education field, and may be used in space experiments.

The triply periodic minimal surface-based 3D printed engineering scaffold for meniscus function reconstruction

Background

The meniscus injury is a common disease in the area of sports medicine. The main treatment for this disease is the pain relief, rather than the meniscal function recovery. It may lead to a poor prognosis and accelerate the progression of osteoarthritis. In this study, we designed a meniscal scaffold to achieve the purposes of meniscal function recovery and cartilage protection.

Methods

The meniscal scaffold was designed using the triply periodic minimal surface (TPMS) method. The scaffold was simulated as a three-dimensional (3D) intact knee model using a finite element analysis software to obtain the results of different mechanical tests. The mechanical properties were gained through the universal machine. Finally, an in vivo model was established to evaluate the effects of the TPMS-based meniscal scaffold on the cartilage protection. The radiography and histological examinations were performed to assess the cartilage and bony structures. Different regions of the regenerated meniscus were tested using the universal machine to assess the biomechanical functions.

Results

The TPMS-based meniscal scaffold with a larger volume fraction and a longer functional periodicity demonstrated a better mechanical performance, and the load transmission and stress distribution were closer to the native biomechanical environment. The radiographic images and histological results of the TPMS group exhibited a better performance in terms of cartilage protection than the grid group. The regenerated meniscus in the TPMS group also had similar mechanical properties to the native meniscus.

Conclusion

The TPMS method can affect the mechanical properties by adjusting the volume fraction and functional periodicity. The TPMS-based meniscal scaffold showed appropriate features for meniscal regeneration and cartilage protection.

Lipid nanoparticle-encapsulated VEGFa siRNA facilitates cartilage formation by suppressing angiogenesis

Cartilage is an important tissue that is widely found in joints, ears, nose and other organs. The limited capacity to regenerate makes cartilage reconstruction an urgent clinical demand. Due to the avascular nature of cartilage, we hypothesized that inhibition of vascularization contributes to cartilage formation. Here, we used VEGFa siRNA to inhibit the infiltration of the local vascular system. Optimized lipid nanoparticles were prepared by microfluidics for the delivery of siRNA. Then, we constructed a tissue engineering scaffold. Both seed cells and VEGFa siRNA-LNPs were loaded in a GELMA hydrogel. Subcutaneous implantation experiments in nude mice indicate that this is a promising strategy for cartilage reconstruction. The regenerated cartilage was superior, with significant upregulation of SOX9, COL-II and ACAN. This is attributed to an environment deficient in oxygen and nutrients, which facilitates cartilage formation by upregulating HIF-1α and FOXO transcription factors. In conclusion, a GelMA/Cells+VEGFa siRNA-LNPs scaffold was constructed to achieve superior cartilage regeneration.

Integrated bioactive scaffold with aptamer-targeted stem cell recruitment and growth factor-induced pro-differentiation effects for anisotropic meniscal regeneration

Reconstruction of the knee meniscus remains a significant clinical challenge owing to its complex anisotropic tissue organization, complex functions, and limited healing capacity in the inner region. The development of in situ tissue-engineered meniscal scaffolds, which provide biochemical signaling to direct endogenous stem/progenitor cell (ESPC) behavior, has the potential to revolutionize meniscal tissue engineering. In this study, a fiber-reinforced porous scaffold was developed based on aptamer Apt19S-mediated mesenchymal stem cell (MSC)-specific recruitment and dual growth factor (GF)-enhanced meniscal differentiation. The aptamer, which can specifically recognize and recruit MSCs, was first chemically conjugated to the decellularized meniscus extracellular matrix (MECM) and then mixed with gelatin methacrylate (GelMA) to form a photocrosslinkable hydrogel. Second, connective tissue growth factor (CTGF)-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) and transforming growth factor-β3 (TGF-β3)-loaded PLGA microparticles (MPs) were mixed with aptamer-conjugated MECM to simulate anisotropic meniscal regeneration. These three bioactive molecules were delivered sequentially. Apt19S, which exhibited high binding affinity to synovium-derived MSCs (SMSCs), was quickly released to facilitate the mobilization of ESPCs. CTGF incorporated within PLGA NPs was released rapidly, inducing profibrogenic differentiation, while sustained release of TGF-β3 in PLGA MPs remodeled the fibrous matrix into fibrocartilaginous matrix. The in vitro results showed that the sequential release of Apt19S/GFs promoted cell migration, proliferation, and fibrocartilaginous differentiation. The in vivo results demonstrated that the sequential release system of Apt/GF-scaffolds increased neomeniscal formation in rabbit critical-sized meniscectomies. Thus, the novel delivery system shows potential for guiding meniscal regeneration in situ.

Methods for Biomaterials Printing: A Short Review and Perspective

Printing technologies have opened larger windows of innovation and creativity to biomaterials engineers by providing them with the ability to fabricate complex shapes in a reasonable time, cost, and weight. However, there has always been a trouble to function adjusting in printing technologies in view of the multiplicity of materials and apparatus parameters. 3D printing, also known as additive manufacturing, revolutionized biomaterials engineering by the realization of a digital subject into a printed object (implants, scaffolds, or diagnostics and drug delivery devices/systems).Inspired by the lessons learned from 3D printing, the concept of 4D printing (better called shape-morphing fabrication) was conceptualized and put into practice to reply on the need for responsiveness of printed platforms to an environmental stimulus (light, pH, temperature, voltage, humidity, etc.) in a programmable manner. Later, the next milestone in printing technology was reached by 5D printing, by which objects could be printed from five axes compared to one-point upward printing by 3D printers. 5D printers use ≈20-30% fewer materials comparatively, enabling the printing of curved surfaces. Nevertheless, all bioprinters need a bio-ink with qualifies characteristics for biomedical applications. Thus, we discussed briefly the cell viability, scaffold biomimicry, scaffold biodegradation and affordability.

Bioink Formulation and Machine Learning-Empowered Bioprinting Optimization

Bioprinting enables the fabrication of complex, heterogeneous tissues through robotically-controlled placement of cells and biomaterials. It has been rapidly developing into a powerful and versatile tool for tissue engineering. Recent advances in bioprinting modalities and biofabrication strategies as well as new materials and chemistries have led to improved mimicry and development of physiologically relevant tissue architectures constituted with multiple cell types and heterogeneous spatial material properties. Machine learning (ML) has been applied to accelerate these processes. It is a new paradigm for bioprinting. In this review, we explore current trends in bioink formulation and how ML has been used to accelerate optimization and enable real-time error detection as well as to reduce the iterative steps necessary for bioink formulation. We examined how rheometric properties, including shear storage, loss moduli, viscosity, shear-thinning property of biomaterials affect the printability of a bioink. Furthermore, we scrutinized the interplays between yield shear stress and the printability of a bioink. Moreover, we systematically surveyed the application of ML in precision in situ surgical site bioprinting, closed-loop AI printing, and post-printing optimization.

Three-Dimensional Bioprinting of Decellularized Extracellular Matrix-Based Bioinks for Tissue Engineering

Three-dimensional (3D) bioprinting is one of the most promising additive manufacturing technologies for fabricating various biomimetic architectures of tissues and organs. In this context, the bioink, a critical element for biofabrication, is a mixture of biomaterials and living cells used in 3D printing to create cell-laden structures. Recently, decellularized extracellular matrix (dECM)-based bioinks derived from natural tissues have garnered enormous attention from researchers due to their unique and complex biochemical properties. This review initially presents the details of the natural ECM and its role in cell growth and metabolism. Further, we briefly emphasize the commonly used decellularization treatment procedures and subsequent evaluations for the quality control of the dECM. In addition, we summarize some of the common bioink preparation strategies, the 3D bioprinting approaches, and the applicability of 3D-printed dECM bioinks to tissue engineering. Finally, we present some of the challenges in this field and the prospects for future development.

Bioink with cartilage-derived extracellular matrix microfibers enables spatial control of vascular capillary formation in bioprinted constructs

Microvasculature is essential for the exchange of gas and nutrient for most tissues in our body. Some tissue structures such as the meniscus presents spatially confined blood vessels adjacent to non-vascularized regions. In biofabrication, mimicking the spatial distribution of such vascular components is paramount, as capillary ingrowth into non-vascularized tissues can lead to tissue matrix alterations and subsequent pathology. Multi-material 3D bioprinting can potentially resolve anisotropic tissue features, although building complex constructs comprising stable vascularized and non-vascularized regions remains a major challenge. Here, we developed endothelial cell(EC)-laden pro- and anti-angiogenic bioinks, supplemented with bioactive matrix-derived microfibers (MFs) that were created from type I collagen sponges (col-1) and cartilage decellularized extracellular matrix (CdECM). EC-driven capillary network formation started two days after bioprinting. Supplementing cartilage-derived MFs to endothelial-cell laden bioinks reduced the total length of neo-microvessels by 29% after 14 days, compared to col-1 MFs-laden bioinks. As a proof of concept, the bioinks were bioprinted into an anatomical meniscus shape with a biomimetic vascularized outer and non-vascularized inner region, using a microgel suspension bath. The constructs were cultured up to 14 days, with in the outer zone the HUVEC-, mural cell-, and col-1 MF-laden pro-angiogenic bioink, and in the inner zone a meniscus progenitor cell (MPC)- and CdECM MF-laden anti-angiogenic bioink, revealing successful spatial confinement of the nascent vascular network only in the outer zone. Further, to co-facilitate both microvessel formation and MPC-derived matrix formation, we formulated cell culture medium conditions with a temporal switch. Overall, this study provides a new strategy that could be applied to develop zonal biomimetic meniscal constructs. Moreover, the use of ECM-derived MFs to promote or inhibit capillary networks opens new possibilities for the biofabrication of tissues with anisotropic microvascular distribution. These have potential for many applications including in vitro models, cancer progression, and testing anti-angiogenic therapies.

Transcriptome Analysis Revealed the Symbiosis Niche of 3D Scaffolds to Accelerate Bone Defect Healing

Three dimension (3D) printed scaffolds have been shown to be superior in promoting tissue repair, but the cell-level specific regulatory network activated by 3D printing scaffolds with different material components to form a symbiosis niche have not been systematically revealed. Here, three typical 3D printed scaffolds, including natural polymer hydrogel (gelatin-methacryloyl, GelMA), synthetic polymer material (polycaprolactone, PCL), and bioceramic (β-tricalcium phosphate, β-TCP), are fabricated to explore the regulating effect of the symbiotic microenvironment during bone healing. Enrichment analysis show that hydrogel promotes tissue regeneration and reconstruction by improving blood vessel generation by enhancing oxygen transport and red blood cell development. The PCL scaffold regulates cell proliferation and differentiation by promoting cellular senescence, cell cycle and deoxyribonucleic acid (DNA) replication pathways, accelerating the process of endochondral ossification, and the formation of callus. The β-TCP scaffold can specifically enhance the expression of osteoclast differentiation and extracellular space pathway genes to promote the differentiation of osteoclasts and promote the process of bone remodeling. In these processes, specific biomaterial properties can be used to guide cell behavior and regulate molecular network in the symbiotic microenvironment to reduce the barriers of regeneration and repair.

Bioprinting and regeneration of auricular cartilage using a bioactive bioink based on microporous photocrosslinkable acellular cartilage matrix

Tissue engineering provides a promising strategy for auricular reconstruction. Although the first international clinical breakthrough of tissue-engineered auricular reconstruction has been realized based on polymer scaffolds, this approach has not been recognized as a clinically available treatment because of its unsatisfactory clinical efficacy. This is mainly since reconstruction constructs easily cause inflammation and deformation. In this study, we present a novel strategy for the development of biological auricle equivalents with precise shapes, low immunogenicity, and excellent mechanics using auricular chondrocytes and a bioactive bioink based on biomimetic microporous methacrylate-modified acellular cartilage matrix (ACMMA) with the assistance of gelatin methacrylate (GelMA), poly(ethylene oxide) (PEO), and polycaprolactone (PCL) by integrating multi-nozzle bioprinting technology. Photocrosslinkable ACMMA is used to emulate the intricacy of the cartilage-specific microenvironment for active cellular behavior, while GelMA, PEO, and PCL are used to balance printability and physical properties for precise structural stability, form the microporous structure for unhindered nutrient exchange, and provide mechanical support for higher shape fidelity, respectively. Finally, mature auricular cartilage-like tissues with high morphological fidelity, excellent elasticity, abundant cartilage lacunae, and cartilage-specific ECM deposition are successfully regenerated in vivo, which provides new opportunities and novel strategies for the fabrication and regeneration of patient-specific auricular cartilage.

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Comprehensive proteomic characteristics of the acellular cartilage matrix.

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Bioactive bioink based on ACMMA, GelMA, and PEO promoted cell behavior.

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Bioactive bioink contained biomimetic ECM components and microporous structure.

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Higher biomechanics was provided by alternately bioactive bioink and PCL strands.

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Mature auricle cartilage with high shape fidelity and good mechanics was regenerated.

Recent Advances in Additive Manufacturing and 3D Bioprinting for Organs-On-A-Chip and Microphysiological Systems

The re-creation of physiological cellular microenvironments that truly resemble complex in vivo architectures is the key aspect in the development of advanced in vitro organotypic tissue constructs. Among others, organ-on-a-chip technology has been increasingly used in recent years to create improved models for organs and tissues in human health and disease, because of its ability to provide spatio-temporal control over soluble cues, biophysical signals and biomechanical forces necessary to maintain proper organotypic functions. While media supply and waste removal are controlled by microfluidic channel by a network the formation of tissue-like architectures in designated micro-structured hydrogel compartments is commonly achieved by cellular self-assembly and intrinsic biological reorganization mechanisms. The recent combination of organ-on-a-chip technology with three-dimensional (3D) bioprinting and additive manufacturing techniques allows for an unprecedented control over tissue structures with the ability to also generate anisotropic constructs as often seen in in vivo tissue architectures. This review highlights progress made in bioprinting applications for organ-on-a-chip technology, and discusses synergies and limitations between organ-on-a-chip technology and 3D bioprinting in the creation of next generation biomimetic in vitro tissue models.

Natural polymer-derived photocurable bioadhesive hydrogels for sutureless keratoplasty

Keratoplasty is the gold standard treatment for visual impairment caused by corneal damage. The use of suturing as the bonding method is the source of many complications following keratoplasty. Currently available corneal adhesives do not have both adequate adhesive strength and acceptable biocompatibility. Herein, we developed a photocurable bioadhesive hydrogel which was composed of gelatin methacryloyl and oxidized dextran for sutureless keratoplasty. The bioadhesive hydrogel exhibited high light transmittance, resistance to enzymatic degradation and excellent biocompatibility. It also had higher adhesive strength than commercial adhesives (fibrin glue). In a rabbit model of lamellar keratoplasty, donor corneal grafts could be closely bonded to the recipient corneal bed and remained attached for 56 days by using of this in situ photopolymerized bioadhesive hydrogel. The operated cornea maintained transparent and noninflamed. Sutureless keratoplasty using bioadhesive hydrogel allowed rapid graft re-epithelialization, typically within 7 days. In vivo confocal microscopic and histological evaluation of the operated cornea did not show any apparent abnormalities in terms of corneal cells and ultrastructure. Thus, this bioadhesive hydrogel is exhibited to be an appealing alternative to sutures for keratoplasty and other corneal surgeries.

Meniscus regeneration by 3D printing technologies: Current advances and future perspectives

Meniscal tears are a frequent orthopedic injury commonly managed by conservative strategies to avoid osteoarthritis development descending from altered biomechanics. Among cutting-edge approaches in tissue engineering, 3D printing technologies are extremely promising guaranteeing for complex biomimetic architectures mimicking native tissues. Considering the anisotropic characteristics of the menisci, and the ability of printing over structural control, it descends the intriguing potential of such vanguard techniques to meet individual joints’ requirements within personalized medicine. This literature review provides a state-of-the-art on 3D printing for meniscus reconstruction. Experiences in printing materials/technologies, scaffold types, augmentation strategies, cellular conditioning have been compared/discussed; outcomes of pre-clinical studies allowed for further considerations. To date, translation to clinic of 3D printed meniscal devices is still a challenge: meniscus reconstruction is once again clear expression of how the integration of different expertise (e.g., anatomy, engineering, biomaterials science, cell biology, and medicine) is required to successfully address native tissues complexities.

Hydrogel composite scaffolds achieve recruitment and chondrogenesis in cartilage tissue engineering applications

BACKGROUND

The regeneration and repair of articular cartilage remains a major challenge for clinicians and scientists due to the poor intrinsic healing of this tissue. Since cartilage injuries are often clinically irregular, tissue-engineered scaffolds that can be easily molded to fill cartilage defects of any shape that fit tightly into the host cartilage are needed.

METHOD

In this study, bone marrow mesenchymal stem cell (BMSC) affinity peptide sequence PFSSTKT (PFS)-modified chondrocyte extracellular matrix (ECM) particles combined with GelMA hydrogel were constructed.

RESULTS

In vitro experiments showed that the pore size and porosity of the solid-supported composite scaffolds were appropriate and that the scaffolds provided a three-dimensional microenvironment supporting cell adhesion, proliferation and chondrogenic differentiation. In vitro experiments also showed that GelMA/ECM-PFS could regulate the migration of rabbit BMSCs. Two weeks after implantation in vivo, the GelMA/ECM-PFS functional scaffold system promoted the recruitment of endogenous mesenchymal stem cells from the defect site. GelMA/ECM-PFS achieved successful hyaline cartilage repair in rabbits in vivo, while the control treatment mostly resulted in fibrous tissue repair.

CONCLUSION

This combination of endogenous cell recruitment and chondrogenesis is an ideal strategy for repairing irregular cartilage defects.

Comprehensive Review on Design and Manufacturing of Bio-scaffolds for Bone Reconstruction

Bio-scaffolds are synthetic entities widely employed in bone and soft-tissue regeneration applications. These bio-scaffolds are applied to the defect site to provide support and favor cell attachment and growth, thereby enhancing the regeneration of the defective site. The progressive research in bio-scaffold fabrication has led to identification of biocompatible and mechanically stable materials. The difficulties in obtaining grafts and expenditure incurred in the transplantation procedures have also been overcome by the implantation of bio-scaffolds. Drugs, cells, growth factors, and biomolecules can be embedded with bio-scaffolds to provide localized treatments. The right choice of materials and fabrication approaches can help in developing bio-scaffolds with required properties. This review mostly focuses on the available materials and bio-scaffold techniques for bone and soft-tissue regeneration application. The first part of this review gives insight into the various classes of biomaterials involved in bio-scaffold fabrication followed by design and simulation techniques. The latter discusses the various additive, subtractive, hybrid, and other improved techniques involved in the development of bio-scaffolds for bone regeneration applications. Techniques involving multimaterial printing and multidimensional printing have also been briefly discussed.

Three-Dimensional-Printed Scaffolds for Meniscus Tissue Engineering: Opportunity for the Future in the Orthopaedic World

The meniscus is a critical component of a healthy knee joint. It is a complex and vital fibrocartilaginous tissue that maintains appropriate biomechanics. Injuries of the meniscus, particularly in the inner region, rarely heal and usually progress into structural breakdown, followed by meniscus deterioration and initiation of osteoarthritis. Conventional therapies range from conservative treatment, to partial meniscectomy and even meniscus transplantation. All the above have high long-term failure rates, with recurrence of symptoms. This communication presents a brief account of in vitro and in vivo studies and describes recent developments in the field of 3D-printed scaffolds for meniscus tissue engineering. Current research in meniscal tissue engineering tries to combine polymeric biomaterials, cell-based therapy, growth factors, and 3D-printed scaffolds to promote the healing of meniscal defects. Today, 3D-printing technology represents a big opportunity in the orthopaedic world to create more specific implants, enabling the rapid production of meniscal scaffolds and changing the way that orthopaedic surgeons plan procedures. In the future, 3D-printed meniscal scaffolds are likely to be available and will also be suitable substitutes in clinical applications, in an attempt to imitate the complexity of the native meniscus.

Surface coating prolongs the degradation and maintains the mechanical strength of surgical suture in vivo

Biodegradable and absorbable sutures have been widely used in surgical procedures. However, for the repair of ligament and tendon injures, the biodegradable suture cannot provide sufficient mechanical support to close the wound for a long period of time which is important to completely heal the tissue. Herein, we develop a simple method that makes a surface coating to prolong the degradation of the suture in vivo. Polylactic acid (PLLA) and Polycaprolactone (PCL) were successfully coated to a commercial degradable polydioxanone (PDO) suture in this study, which was confirmed by Fourier transform infrared spectra (FTIR). Scanning electron microscopy (SEM) was used to observe the smooth surface of the coated sutures. Moreover, live/dead assay of human fibroblasts after co-culturing with the modified/unmodified sutures showed fairly good cellular activity. In vivo study demonstrates the degradation properties of sutures were significantly changed after the surface coating. The raw suture exhibited the fastest degradation in 12 weeks, showing significantly decline in mechanical strength. Interestingly, the PCL-coated suture was able to maintain more than 20% of its original tensile strength after 12 weeks' implantation. In addition, in vivo results of PCL-coated sutures also showed less inflammatory cell infiltration and less surface inflammation. These findings indicate the one step suture-coating method could be feasibly for the development of clinical equipment.

Biofabrication of cell-free dual drug-releasing biomimetic scaffolds for meniscal regeneration

Regenerating the meniscus remains challenging because of its avascular, aneural, and alymphatic nature. Three-dimensional (3D) printing technology provides a promising strategy to fabricate biomimetic meniscal scaffolds with an anisotropic architecture, a proper biomechanical microenvironment, and bioactive components. Herein, 3D printing technology is adopted by coencapsulating chemokines (platelet-derived growth factor-BB, PDGF-BB) and small chondroinductive molecules (kartogenin, KGN) within biomimetic polycaprolactone/hydrogel composite scaffolds. The incorporated PDGF-BB is expected to promote endogenous stem cell homing, and KGN in poly(lactic-co-glycolic) acid microspheres is employed to target the chondrogenesis of resident mesenchymal stem cells (MSCs). First, we chose basic bioinks composed of gelatin methacrylamide and hyaluronic acid methacrylate and then incorporated four concentrations (0%, 0.5%, 1.0%, and 2.0%) of meniscal extracellular matrix into the bioink to systematically study the superiority of these combinations and identify the optimally printable bioink. Next, we investigated the scaffold morphology and drug release profile. The effects of releasing the drugs in a sequentially controlled manner from the composite scaffolds on the fate of MSCs were also evaluated. The biofabricated scaffolds, with and without dual drug loading, were further studied in a rabbit model established with a critical-size medial meniscectomy. We found that meniscal scaffolds containing both drugs had combinational advantages in enhancing cell migration and synergistically promoted MSC chondrogenic differentiation. The dual drug-loaded scaffolds also significantly promotedin vivoneomeniscal regeneration three and six months after implantation in terms of histological and immunological phenotypes. The results presented herein reveal that this 3D-printed dual drug-releasing meniscal scaffold possesses the potential to act as an off-the-shelf product for the clinical treatment of meniscal injury and related joint degenerative diseases.

The Application of Polycaprolactone in Three-Dimensional Printing Scaffolds for Bone Tissue Engineering

Bone tissue engineering commonly encompasses the use of three-dimensional (3D) scaffolds to provide a suitable microenvironment for the propagation of cells to regenerate damaged tissues or organs. 3D printing technology has been extensively applied to allow direct 3D scaffolds manufacturing. Polycaprolactone (PCL) has been widely used in the fabrication of 3D scaffolds in the field of bone tissue engineering due to its advantages such as good biocompatibility, slow degradation rate, the less acidic breakdown products in comparison to other polyesters, and the potential for loadbearing applications. PCL can be blended with a variety of polymers and hydrogels to improve its properties or to introduce new PCL-based composites. This paper describes the PCL used in developing state of the art of scaffolds for bone tissue engineering. In this review, we provide an overview of the 3D printing techniques for the fabrication of PCL-based composite scaffolds and recent studies on applications in different clinical situations. For instance, PCL-based composite scaffolds were used as an implant surgical guide in dental treatment. Furthermore, future trend and potential clinical translations will be discussed.

Immune-Inflammatory Responses of an Acellular Cartilage Matrix Biomimetic Scaffold in a Xenotransplantation Goat Model for Cartilage Tissue Engineering

The rapid development of tissue engineering and regenerative medicine has introduced a new strategy for ear reconstruction, successfully regenerating human-ear-shaped cartilage and achieving the first clinical breakthrough using a polyglycolic acid/polylactic acid (PGA/PLA) scaffold. However, its clinical repair varies greatly among individuals, and the quality of regenerated cartilage is unstable, which seriously limits further clinical application. Acellular cartilage matrix (ACM), with a cartilage-specific microenvironment, good biocompatibility, and potential to promote cell proliferation, has been used to regenerate homogeneous ear-shaped cartilage in immunocompromised nude mice. However, there is no evidence on whether ACM will regenerate homogeneous cartilage tissue in large animals or has the potential for clinical transformation. In this study, xenogeneic ACM assisted with gelatin (GT) with or without autologous chondrocytes was implanted subcutaneously into goats to establish a xenotransplantation model and compared with a PGA/PLA scaffold to evaluate the immune-inflammatory response and quality of regenerated cartilage. The results confirmed the superiority of the ACM/GT, which has the potential capacity to promote cell proliferation and cartilage formation. Although there is a slight immune-inflammatory response in large animals, it does not affect the quality of the regenerated cartilage and forms homogeneous and mature cartilage. The current study provides detailed insights into the immune-inflammatory response of the xenogeneic ACM/GT and also provides scientific evidence for future clinical application of ACM/GT in cartilage tissue engineering.

3D printed chitosan/polycaprolactone scaffold for lung tissue engineering: hope to be useful for COVID-19 studies

To prevent or reduce mortality from lung diseases, new biological materials and scaffolds are needed to conduct more accurate research and support lung tissue regeneration. On the other hand, the outbreak of the COVID-19 virus and its targeting of the human lung has caused many deaths worldwide. The main aim of this study was to provide a biologically and mechanically suitable 3D printed scaffold using chitosan/polycaprolactone bioink for lung tissue engineering. Design-Expert software was employed for studying various compositions for 3D printing. The selected scaffolds underwent physiochemical, biological and mechanical studies to evaluate if they are capable of MRC-5 cell line growth, proliferation, and migration. Based on the results, the average diameter of the chitosan/polycaprolactone strands was measured at 360 μm. Chitosan concentration controlled the printability, while changes in polycaprolactone content did not affect printability. The scaffolds showed excellent potential in swelling, degradation, and mechanical behavior, although they can be modified by adjusting the polycaprolactone content. The scaffolds also revealed notable cell adhesion, nontoxicity, low apoptosis, high proliferation, and cell biocompatibility in vitro. To sum up, scaffold 3 (chitosan/polycaprolactone ratio: 4 : 1) revealed better activity for MRC-5 cell culture. Thereby, this scaffold can be a good candidate for lung tissue engineering and may be applicable for more studies on the COVID-19 virus.

3D printed hybrid bone constructs of PCL and dental pulp stem cells loaded GelMA

Fabrication of scaffolds using polymers and then cell seeding is a routine protocol of tissue engineering applications. Synthetic polymers have adequate mechanical properties to substitute for some bone tissue, but they are generally hydrophobic and have no specific cell recognition sites, which leads to poor cell affinity and adhesion. Some natural polymers, have high cell affinity but are mechanically weak and do not have the strength required as a bone supporting material. In the present study, 3D printed hybrid scaffolds were fabricated using PCL and GelMA carrying dental pulp stem cells (DPSCs), which is printed in the gaps between the PCL struts. This cell loaded GelMA was shown to support osteoinductivity, while the PCL provided mechanical strength needed to mimic the bone tissue. 3D printed PCL/GelMA and GelMA scaffolds were highly stable during 21 days of incubation in PBS. The compressive moduli of the hybrid scaffolds were in the range of the compressive moduli of trabecular bone. DPSCs were homogeneously distributed throughout the entire hydrogel component and exhibited high cell viability in both scaffolds during 21 days of incubation. Upon osteogenic differentiation DPSCs expressed two key matrix proteins, osteopontin and osteocalcin. Alizarin red staining showed mineralized nodules, which demonstrates osteogenic differentiation of DPSCs within GelMA. This construct yielded a very high cell viability, osteogenic differentiation and mineralization comparable to cell culture without compromising mechanical strength suitable for bone tissue engineering applications. Thus, 3D printed, cell loaded PCL/GelMA hybrid scaffolds have a great potential for use in bone tissue engineering applications.

Bladder muscle regeneration enhanced by sustainable delivery of heparin from bilayer scaffolds carrying stem cells in a rat bladder partial cystectomy model

In bladder tissue engineering, regeneration of muscle is of equal importance to epithelial regeneration. However, as yet there is no effective strategy for promoting bladder muscle regeneration. In this study we aim to promote bladder muscle regeneration by sustainably delivering heparin from a bilayer scaffold carrying stem cells. The bilayer scaffold [heparin-polycaprolactone (PCL)/bladder decellularized matrix (BAM) Hep-PB/PCL] comprises an electrospun layer (Hep-PB electrospun membrane) and a three-dimensional (3D) printed layer (PCL scaffold), fabricated via coaxial-electrospinning and 3D printing, respectively. Heparin was encapsulated into the core of the Hep-PB fibers with a core-shell structure to sustain its release. The morphology of the bilayer scaffold and the microstructure of the electrospun fibers were characterized. The release behavior of heparin from various electrospun membranes was evaluated. The role of Hep-PB in promoting myogenic differentiation of the adipose-derived stem cells (ADSCs) through sustainable release of heparin was also evaluated. After 7 d culture, Hep-PB/PCL scaffolds carrying ADSCs (defined as ASHP) were used for bladder reconstruction in a rat partial cystotomy model. The result shows that the PCL printed scaffold has ordered macropores (∼370 μm), unlike the compact microstructure of electrospun films. The Hep-PB membrane exhibits a sustained release behavior for heparin. This membrane also shows better growth and proliferation of ADSCs than the other membranes. The polymerase chain reaction results show that the expression of smooth muscle cell markers in ADSCs is enhanced by the Hep-PB scaffold. The results of retrograde urethrography and histological staining indicate that the bladder volume in the ASHP group recovers better, and the regenerated bladder muscle bundles are arranged in a more orderly fashion compared with the direct suture and bladder decellularized matrix groups. Therefore, findings from this study show that bladder muscle regeneration could be enhanced by bilayer scaffolds delivering heparin and carrying stem cells, which may provide a new strategy for bladder tissue engineering.

Emerging Biofabrication Techniques: A Review on Natural Polymers for Biomedical Applications

Natural polymers have been widely used for biomedical applications in recent decades. They offer the advantages of resembling the extracellular matrix of native tissues and retaining biochemical cues and properties necessary to enhance their biocompatibility, so they usually improve the cellular attachment and behavior and avoid immunological reactions. Moreover, they offer a rapid degradability through natural enzymatic or chemical processes. However, natural polymers present poor mechanical strength, which frequently makes the manipulation processes difficult. Recent advances in biofabrication, 3D printing, microfluidics, and cell-electrospinning allow the manufacturing of complex natural polymer matrixes with biophysical and structural properties similar to those of the extracellular matrix. In addition, these techniques offer the possibility of incorporating different cell lines into the fabrication process, a revolutionary strategy broadly explored in recent years to produce cell-laden scaffolds that can better mimic the properties of functional tissues. In this review, the use of 3D printing, microfluidics, and electrospinning approaches has been extensively investigated for the biofabrication of naturally derived polymer scaffolds with encapsulated cells intended for biomedical applications (e.g., cell therapies, bone and dental grafts, cardiovascular or musculoskeletal tissue regeneration, and wound healing).