A Tunable, Three-Dimensional In Vitro Culture Model of Growth Plate Cartilage Using Alginate Hydrogel Scaffolds

Whey Protein Isolate Composites as Potential Scaffolds for Cultivated Meat

Modern food technology has given rise to numerous alternative protein sources in response to a growing human population and the negative environmental impacts of current food systems. To aid in achieving global food security, one such form of alternative protein being investigated is cultivated meat, which applies the principles of mechanical and tissue engineering to produce animal proteins and meat products from animal cells. Herein, nonmodified and methacrylated whey protein formed hydrogels with methacrylated alginate as potential tissue engineering scaffolds for cultivated meat. Whey protein is a byproduct of dairy processing and was selected because it is an approved food additive and cytocompatible and has shown efficacy in other biomaterial applications. Whey protein and alginate scaffolds were formed via visible light cross-linking in aqueous solutions under ambient conditions. The characteristics of the precursor solution and the physical-mechanical properties of the scaffolds were quantified; while gelation occurred within the homo- and copolymer hydrogels, the integrity of the network was significantly altered with varying components. Qualitatively, the scaffolds exhibited a three-dimensional (3D) interconnected porous network. Whey protein isolate (WPI)-based scaffolds were noncytotoxic and supported in vitro myoblast adhesion and proliferation. The data presented support the hypothesis that the composition of the hydrogel plays a significant role in the scaffold's performance.

Advancements and Challenges in Hydrogel Engineering for Regenerative Medicine

This manuscript covers the latest advancements and persisting challenges in the domain of tissue engineering, with a focus on the development and engineering of hydrogel scaffolds. It highlights the critical role of these scaffolds in emulating the native tissue environment, thereby providing a supportive matrix for cell growth, tissue integration, and reducing adverse reactions. Despite significant progress, this manuscript emphasizes the ongoing struggle to achieve an optimal balance between biocompatibility, biodegradability, and mechanical stability, crucial for clinical success. It also explores the integration of cutting-edge technologies like 3D bioprinting and biofabrication in constructing complex tissue structures, alongside innovative materials and techniques aimed at enhancing tissue growth and functionality. Through a detailed examination of these efforts, the manuscript sheds light on the potential of hydrogels in advancing regenerative medicine and the necessity for multidisciplinary collaboration to navigate the challenges ahead.

3D bioprinted hydrogel/polymer scaffold with factor delivery and mechanical support for growth plate injury repair

Introduction: Growth plate injury is a significant challenge in clinical practice, as it could severely affect the limb development of children, leading to limb deformity. Tissue engineering and 3D bioprinting technology have great potential in the repair and regeneration of injured growth plate, but there are still challenges associated with achieving successful repair outcomes. Methods: In this study, GelMA hydrogel containing PLGA microspheres loaded with chondrogenic factor PTH(1-34) was combined with BMSCs and Polycaprolactone (PCL) to develop the PTH(1-34)@PLGA/BMSCs/GelMA-PCL scaffold using bio-3D printing technology. Results: The scaffold exhibited a three-dimensional interconnected porous network structure, good mechanical properties, biocompatibility, and was suitable for cellchondrogenic differentiation. And a rabbit model of growth plate injury was appliedto validate the effect of scaffold on the repair of injured growth plate. The resultsshowed that the scaffold was more effective than injectable hydrogel in promotingcartilage regeneration and reducing bone bridge formation. Moreover, the addition ofPCL to the scaffold provided good mechanical support, significantly reducing limbdeformities after growth plate injury compared with directly injected hydrogel. Discussion: Accordingly, our study demonstrates the feasibility of using 3D printed scaffolds for treating growth plate injuries and could offer a new strategy for the development of growth plate tissue engineering therapy.

Roles of Local Soluble Factors in Maintaining the Growth Plate: An Update

The growth plate is a cartilaginous tissue found at the ends of growing long bones, which contributes to the lengthening of bones during development. This unique structure contains at least three distinctive layers, including resting, proliferative, and hypertrophic chondrocyte zones, maintained by a complex regulatory network. Due to its soft tissue nature, the growth plate is the most susceptible tissue of the growing skeleton to injury in childhood. Although most growth plate damage in fractures can heal, some damage can result in growth arrest or disorder, impairing leg length and resulting in deformity. In this review, we re-visit previously established knowledge about the regulatory network that maintains the growth plate and integrate current research displaying the most recent progress. Next, we highlight local secretary factors, such as Wnt, Indian hedgehog (Ihh), and parathyroid hormone-related peptide (PTHrP), and dissect their roles and interactions in maintaining cell function and phenotype in different zones. Lastly, we discuss future research topics that can further our understanding of this unique tissue. Given the unmet need to engineer the growth plate, we also discuss the potential of creating particular patterns of soluble factors and generating them in vitro.

Progress of Microfluidic Hydrogel-Based Scaffolds and Organ-on-Chips for the Cartilage Tissue Engineering

Cartilage degeneration is among the fundamental reasons behind disability and pain across the globe. Numerous approaches have been employed to treat cartilage diseases. Nevertheless, none have shown acceptable outcomes in the long run. In this regard, the convergence of tissue engineering and microfabrication principles can allow developing more advanced microfluidic technologies, thus offering attractive alternatives to current treatments and traditional constructs used in tissue engineering applications. Herein, the current developments involving microfluidic hydrogel-based scaffolds, promising structures for cartilage regeneration, ranging from hydrogels with microfluidic channels to hydrogels prepared by the microfluidic devices, that enable therapeutic delivery of cells, drugs, and growth factors, as well as cartilage-related organ-on-chips are reviewed. Thereafter, cartilage anatomy and types of damages, and present treatment options are briefly overviewed. Various hydrogels are introduced, and the advantages of microfluidic hydrogel-based scaffolds over traditional hydrogels are thoroughly discussed. Furthermore, available technologies for fabricating microfluidic hydrogel-based scaffolds and microfluidic chips are presented. The preclinical and clinical applications of microfluidic hydrogel-based scaffolds in cartilage regeneration and the development of cartilage-related microfluidic chips over time are further explained. The current developments, recent key challenges, and attractive prospects that should be considered so as to develop microfluidic systems in cartilage repair are highlighted.

Tissue engineering in growth plate cartilage regeneration: Mechanisms to therapeutic strategies

The repair of growth plate injuries is a highly complex process that involves precise spatiotemporal regulation of multiple cell types. While significant progress has been made in understanding the pathological mechanisms underlying growth plate injuries, effectively regulating this process to regenerate the injured growth plate cartilage remains a challenge. Tissue engineering technology has emerged as a promising therapeutic approach for achieving tissue regeneration through the use of functional biological materials, seed cells and biological factors, and it is now widely applied to the regeneration of bone and cartilage. However, due to the unique structure and function of growth plate cartilage, distinct strategies are required for effective regeneration. Thus, this review provides an overview of current research on the application of tissue engineering to promote growth plate regeneration. It aims to elucidates the underlying mechanisms by which tissue engineering promotes growth plate regeneration and to provide novel insights and therapeutic strategies for future research on the regeneration of growth plate.

Growing Pains: The Need for Engineered Platforms to Study Growth Plate Biology

Growth plates, or physis, are highly specialized cartilage tissues responsible for longitudinal bone growth in children and adolescents. Chondrocytes that reside in growth plates are organized into three distinct zones essential for proper function. Modeling key features of growth plates may provide an avenue to develop advanced tissue engineering strategies and perspectives for cartilage and bone regenerative medicine applications and a platform to study processes linked to disease progression. In this review, a brief introduction of the growth plates and their role in skeletal development is first provided. Injuries and diseases of the growth plates as well as physiological and pathological mechanisms associated with remodeling and disease progression are discussed. Growth plate biology, namely, its architecture and extracellular matrix organization, resident cell types, and growth factor signaling are then focused. Next, opportunities and challenges for developing 3D biomaterial models to study aspects of growth plate biology and disease in vitro are discussed. Finally, opportunities for increasingly sophisticated in vitro biomaterial models of the growth plate to study spatiotemporal aspects of growth plate remodeling, to investigate multicellular signaling underlying growth plate biology, and to develop platforms that address key roadblocks to in vivo musculoskeletal tissue engineering applications are described.

Mechanotransductive Mechanisms of Biomimetic Hydrogel Cues Modulating Meckel's Cartilage Degeneration

Meckel's cartilage, a cartilage rod present in the mandible during developmental stages, shows a unique developmental fate: while the anterior and posterior portions undergo ossification, the middle part degenerates. Previously, it was shown that a stiff environment promoted cartilage degeneration in the middle region, while a soft environment enhanced the mineralization in the anterior region of Meckel's cartilage. This study aims to elucidate the spatio-temporal changes in the mechanosensing properties of Meckel's cartilage during its early developmental stages and clarify the mechanotransduction-related mechanisms involved in its degeneration. The results show that the expression of Hippo pathway effector yes-associated protein (YAP) is only detectable in the Meckel's cartilage onward embryonic day (E)14.5, indicating that mechanosensing is dependent on the tissue developmental stage. Consistently, microenvironmental stiffness-induced cartilage degeneration can only be induced in cartilages onward E14.5, but not in those at earlier developmental stages. Expressions of integrin-β1 and cartilage matrix-degrading enzymes, matrix metalloproteinase 1 (MMP-1) and MMP-13, are significantly enhanced in the degeneration area. Moreover, verteporfin (YAP inhibitor) and integrin-β1 antibody block the substrate stiffness-induced degeneration by suppressing the expressions of MMP-1 and MMP-13. These data provide new insights into the interplay between biochemical and mechanical cues determining the fate of Meckel's cartilage.

Recent advances of natural biopolymeric culture scaffold: synthesis and modification

Traditionally existing 2D culture scaffold has been inappropriately validated due to the failure in generating the precise therapeutic response. Therefore, this leads to the fabrication of 3D culture scaffold resolving the limitations in the in vivo environment. In recent years, tissue engineering played an important role in the field of bio-medical engineering. Biopolymer material, a novel natural material with excellent properties of nontoxic and biodegradable merits can be served as culture scaffold. This review summarizes the modifications of natural biopolymeric culture scaffold with different crosslinkers and their application. In addition, this review provides the recent progress of natural biopolymeric culture scaffold mainly focusing on their properties, synthesizing and modification and application.

Enlightenment of Growth Plate Regeneration Based on Cartilage Repair Theory: A Review

The growth plate (GP) is a cartilaginous region situated between the epiphysis and metaphysis at the end of the immature long bone, which is susceptible to mechanical damage because of its vulnerable structure. Due to the limited regeneration ability of the GP, current clinical treatment strategies (e.g., bone bridge resection and fat engraftment) always result in bone bridge formation, which will cause length discrepancy and angular deformity, thus making satisfactory outcomes difficult to achieve. The introduction of cartilage repair theory and cartilage tissue engineering technology may encourage novel therapeutic approaches for GP repair using tissue engineered GPs, including biocompatible scaffolds incorporated with appropriate seed cells and growth factors. In this review, we summarize the physiological structure of GPs, the pathological process, and repair phases of GP injuries, placing greater emphasis on advanced tissue engineering strategies for GP repair. Furthermore, we also propose that three-dimensional printing technology will play a significant role in this field in the future given its advantage of bionic replication of complex structures. We predict that tissue engineering strategies will offer a significant alternative to the management of GP injuries.

3D printed alginate bead generator for high-throughput cell culture

Alginate hydrogel beads are a common platform for generating 3D cell cultures in biomedical research. Simple methods for bead generation using a manual pipettor or syringe are low-throughput and produce beads showing high variability in size and shape. To address these challenges, we designed a 3D printed bead generator that uses an airflow to cleave beads from a stream of hydrogel solution. The performance of the proposed alginate bead generator was evaluated by changing the volume flow rates of alginate (Q_Alg) and air (Q_A), the diameter of device nozzle (d) and the concentration of alginate gel solution (C). We identified that the diameter of beads (D = 0.9 -2.8 mm) can be precisely controlled by changing Q_A and d. Also the bead generation frequency (f) can be tuned by changing Q_Alg. Finally, we demonstrated that viability and biological function (pericellular matrix deposition) of chondrocytes were not adversely affected by high f using this bead generator. Because 3D printing is becoming a more accessible technique, our unique design will allow greater access to average biomedical research laboratories, STEM education and industries in cost- and time-effective manner.

A Microfluidic Platform for Stimulating Chondrocytes with Dynamic Compression

Mechanical stimuli are known to modulate biological functions of cells and tissues. Recent studies have suggested that compressive stress alters growth plate cartilage architecture and results in growth modulation of long bones of children. To determine the role of compressive stress in bone growth, we created a microfluidic device actuated by pneumatic pressure, to dynamically (or statically) compress growth plate chondrocytes embedded in alginate hydrogel cylinders. In this article, we describe detailed methods for fabricating and characterizing this device. The advantages of our protocol are: 1) Five different magnitudes of compressive stress can be generated on five technical replicates in a single platform, 2) It is easy to visualize cell morphology via a conventional light microscope, 3) Cells can be rapidly isolated from the device after compression to facilitate downstream assays, and 4) The platform can be applied to study mechanobiology of any cell type that can grow in hydrogels.

Surface- and Hydrogel-Mediated Delivery of Nucleic Acid Nanoparticles

Gene expression within a cell population can be directly altered through gene delivery approaches. Traditionally for nonviral delivery, plasmids or siRNA molecules, encoding or targeting the gene of interest, are packaged within nanoparticles. These nanoparticles are then delivered to the media surrounding cells seeded onto tissue culture plastic; this technique is termed bolus delivery. Although bolus delivery is widely utilized to screen for efficient delivery vehicles and to study gene function in vitro, this delivery strategy may not result in efficient gene transfer for all cell types or may not identify those delivery vehicles that will be efficient in vivo. Furthermore, bolus delivery cannot be used in applications where patterning of gene expression is needed. In this chapter, we describe methods that incorporate material surfaces (i.e., surface-mediated delivery) or hydrogel scaffolds (i.e., hydrogel-mediated delivery) to efficiently deliver genes. This chapter includes protocols for surface-mediated DNA delivery focusing on the simplest and most effective methods, which include nonspecific immobilization of DNA complexes (both polymer and lipid vectors) onto serum-coated cell culture polystyrene and self-assembled monolayers (SAMs) of alkanethiols on gold. Also, protocols for the encapsulation of DNA/cationic polymer nanoparticles into hydrogel scaffolds are described, including methods for the encapsulation of low amounts of DNA (<0.2 μg/μl) and high amounts of DNA (>0.2 μg/μl) since incorporation of high amounts of DNA pose significant challenges due to aggregation.

Mussel-Inspired Tissue-Adhesive Hydrogel Based on the Polydopamine-Chondroitin Sulfate Complex for Growth-Factor-Free Cartilage Regeneration

Glycosaminoglycan-based hydrogels are widely used for cartilage repair because glycosaminoglycans are the main component of the cartilage extracellular matrix and can maintain chondrocyte functions. However, most of the glycosaminoglycan-based hydrogels are negatively charged and cell-repellant, and they cannot host cells or favor tissue regeneration. Inspired by mussel chemistry, we designed a polydopamine-chondroitin sulfate-polyacrylamide (PDA-CS-PAM) hydrogel with tissue adhesiveness and super mechanical properties for growth-factor-free cartilage regeneration. Thanks to the abundant reactive catechol groups on the PDA, a cartilage-specific PDA-CS complex was formed by the self-assembly of PDA and CS, and then the PDA-CS complex was homogenously incorporated into an elastic hydrogel network. This catechol-group-enriched PDA-CS complex endowed the hydrogel with good cell affinity and tissue adhesiveness to facilitate cell adhesion and tissue integration. Compared with bare CS, the PDA-CS complex in the hydrogel was more effective in exerting its functions on adhered cells to upregulate chondrogenic differentiation. Because of the synergistic effects of noncovalent interactions caused by the PDA-CS complex and covalently cross-linked PAM network, the hydrogel exhibited super resilience and toughness, meeting the mechanical requirement of cartilage repair. Collectively, this tissue-adhesive and tough PDA-CS-PAM hydrogel with good cell affinity creates a growth-factor-free and biomimetic microenvironment for chondrocyte growth and cartilage regeneration and sheds light on the development of growth-factor-free biomaterials for cartilage repair.

Pneumatic microfluidic cell compression device for high-throughput study of chondrocyte mechanobiology

Hyaline cartilage is a specialized type of connective tissue that lines many moveable joints (articular cartilage) and contributes to bone growth (growth plate cartilage). Hyaline cartilage is composed of a single cell type, the chondrocyte, which produces a unique hydrated matrix to resist compressive stress. Although compressive stress has profound effects on transcriptional networks and matrix biosynthesis in chondrocytes, mechanistic relationships between strain, signal transduction, cell metabolism, and matrix production remain superficial. Here, we describe development and validation of a polydimethylsiloxane (PDMS)-based pneumatic microfluidic cell compression device which generates multiple compression conditions in a single platform. The device contained an array of PDMS balloons of different sizes which were actuated by pressurized air, and the balloons compressed chondrocytes cells in alginate hydrogel constructs. Our characterization and testing of the device showed that the developed platform could compress chondrocytes with various magnitudes simultaneously with negligible effect on cell viability. Also, the device is compatible with live cell imaging to probe early effects of compressive stress, and it can be rapidly dismantled to facilitate molecular studies of compressive stress on transcriptional networks. Therefore, the proposed device will enhance the productivity of chondrocyte mechanobiology studies, and it can be applied to study mechanobiology of other cell types.