Integration of layered chondrocyte-seeded alginate hydrogel scaffolds

Stochastic to Deterministic: A straightforward approach to create serially perfusable multiscale capillary beds

Generation of in vitro tissue models with serially perfused hierarchical vasculature would allow greater control of fluid perfusion throughout the network and enable direct mechanistic investigation of vasculogenesis, angiogenesis, and vascular remodeling. In this work, we have developed a method to produce a closed, serially perfused, multiscale vessel network embedded within an acellular hydrogel. We confirmed that the acellular and cellular gel-gel interface was functionally annealed without preventing or biasing cell migration and endothelial self-assembly. Multiscale connectivity of the vessel network was validated via high-resolution microscopy techniques to confirm anastomosis between self-assembled and patterned vessels. Lastly, using fluorescently labeled microspheres, the multiscale network was serially perfused to confirm patency and barrier function. Directional flow from inlet to outlet man-dated flow through the capillary bed. This method for producing closed, multiscale vascular networks was developed with the intention of straightforward fabrication and engineering techniques so as to be a low barrier to entry for researchers who wish to investigate mechanistic questions in vascular biology. This ease of use offers a facile extension of these methods for incorporation into organoid culture, organ-on-a-chip (OOC) models, and bioprinted tissues.

A straightforward cell culture insert model to incorporate biochemical and biophysical stromal properties into transplacental transport studies

Introduction

The placental extracellular matrix (ECM) dynamically remodels over pregnancy and in disease. How these changes impact placental barrier function is poorly understood as there are limited in vitro models of the placenta with a modifiable stromal compartment to mechanistically investigate these extracellular factors. We developed a straightforward method to incorporate uniform hydrogels into standard cell culture inserts for transplacental transport studies.

Methods

Uniform polyacrylamide (PAA) gels were polymerized within cell culture inserts by (re)using the insert packaging to create a closed, controllable environmental chamber. PAA pre-polymer solution was added dropwise via a syringe to the cell culture insert and the atmosphere was purged with an inert gas. Transport and cell culture studies were conducted to validate the model.

Results

We successfully incorporated and ECM functionalized uniform PAA gels to cell culture inserts enable cell adhesion and monolayer formation. Imaging and analyte transport studies validated gel formation and expected mass transport results and successful cell studies confirmed cell viability, monolayer formation, and that the model could be used transplacental transport studies. Detailed methods and validation protocols are included.

Discussion

It is well appreciated that ECM biophysical and biochemical properties impact cell phenotype and cell signaling in many tissues including the placenta. The incorporation of a PAA gel within a cell culture insert enables independent study of placental ECM biophysical and biochemical properties in the context of transplacental transport. These straightforward and low-cost methods to build three dimensional cellular models are readily adoptable by the wider scientific community.

Enhancing the mechanical strength of 3D printed GelMA for soft tissue engineering applications

Gelatin methacrylate (GelMA) hydrogels have gained significant traction in diverse tissue engineering applications through the utilization of 3D printing technology. As an artificial hydrogel possessing remarkable processability, GelMA has emerged as a pioneering material in the advancement of tissue engineering due to its exceptional biocompatibility and degradability. The integration of 3D printing technology facilitates the precise arrangement of cells and hydrogel materials, thereby enabling the creation of in vitro models that simulate artificial tissues suitable for transplantation. Consequently, the potential applications of GelMA in tissue engineering are further expanded. In tissue engineering applications, the mechanical properties of GelMA are often modified to overcome the hydrogel material's inherent mechanical strength limitations. This review provides a comprehensive overview of recent advancements in enhancing the mechanical properties of GelMA at the monomer, micron, and nano scales. Additionally, the diverse applications of GelMA in soft tissue engineering via 3D printing are emphasized. Furthermore, the potential opportunities and obstacles that GelMA may encounter in the field of tissue engineering are discussed. It is our contention that through ongoing technological progress, GelMA hydrogels with enhanced mechanical strength can be successfully fabricated, leading to the production of superior biological scaffolds with increased efficacy for tissue engineering purposes.

Human Chondrocytes, Metabolism of Articular Cartilage, and Strategies for Application to Tissue Engineering

Hyaline cartilage, which is characterized by the absence of vascularization and innervation, has minimal self-repair potential in case of damage and defect formation in the chondral layer. Chondrocytes are specialized cells that ensure the synthesis of extracellular matrix components, namely type II collagen and aggregen. On their surface, they express integrins CD44, α1β1, α3β1, α5β1, α10β1, αVβ1, αVβ3, and αVβ5, which are also collagen-binding components of the extracellular matrix. This article aims to contribute to solving the problem of the possible repair of chondral defects through unique methods of tissue engineering, as well as the process of pathological events in articular cartilage. In vitro cell culture models used for hyaline cartilage repair could bring about advanced possibilities. Currently, there are several variants of the combination of natural and synthetic polymers and chondrocytes. In a three-dimensional environment, chondrocytes retain their production capacity. In the case of mesenchymal stromal cells, their favorable ability is to differentiate into a chondrogenic lineage in a three-dimensional culture.

Manufacture of Bilayered Composite Hydrogels with Strong, Elastic, and Tough Properties for Osteochondral Repair Applications

Layered composite hydrogels have been considered attractive materials for use in osteochondral repair and regeneration. These hydrogel materials should be mechanically strong, elastic, and tough besides fulfilling some basic requirements such as biocompatibility and biodegradability. A novel type of bilayered composite hydrogel with multi-network structures and well-defined injectability was thus developed for osteochondral tissue engineering using chitosan (CH), hyaluronic acid (HA), silk fibroin (SF), CH nanoparticles (NPs), and amino-functionalized mesoporous bioglass (ABG) NPs. CH was combined with HA and CH NPs to build the chondral phase of the bilayered hydrogel, and CH, SF, and ABG NPs were used together to construct the subchondral phase of the bilayer hydrogel. Rheological measurements showed that the optimally achieved gels assigned to the chondral and subchondral layers had their elastic moduli of around 6.5 and 9.9 kPa, respectively, with elastic modulus/viscous modulus ratios higher than 36, indicating that they behaved like strong gels. Compressive measurements further demonstrated that the bilayered hydrogel with an optimally formulated composition had strong, elastic, and tough characteristics. Cell culture revealed that the bilayered hydrogel had the capacity to support the in-growth of chondrocytes in the chondral phase and osteoblasts in the subchondral phase. Results suggest that the bilayered composite hydrogel can act as an injective biomaterial for osteochondral repair applications.

Instabilities induced by mechanical loading determine the viability of chondrocytes grown on porous scaffolds

Tissue-engineered cartilage constructs have shown promise to treat focal cartilage defects in multiple clinical studies. Notably, products in clinical use or in late-stage clinical trials often utilize porous collagen scaffolds to provide mechanical support and attachment sites for chondrocytes. Under loading, both the local mechanical responses of collagen scaffolds and the corresponding cellular outcomes are poorly understood, despite their wide use. As such, the architecture of collagen scaffolds varies significantly among tissue-engineered cartilage products, but the effects of such architectures on construct mechanics and cell viability are not well understood. This study investigated the effects of local mechanical responses of collagen scaffolds on chondrocyte viability in tissue-engineered cartilage constructs. We utilized fast confocal microscopy combined with a strain mapping technique to analyze the architecture-dependent instabilities under quasi-static loading and subsequent chondrocyte death in honeycomb and sponge scaffolds. More specifically, we compared the isotropic and the orthotropic planes for each type of collagen scaffold. Under compression, both planes exhibited elastic, buckled, and densified deformation modes. In both loading directions, cell death was minimal in regions that experienced elastic deformation mode and a trend of increase in buckled mode. More interestingly, we saw a significant increase in cell death in densified mode. Overall, this study suggests that local instabilities are directly correlated to chondrocyte death in tissue-engineered cartilage constructs, highlighting the importance of understanding the architecture-dependent local mechanical responses under loading.

Cell-Cell Interactions Enhance Cartilage Zonal Development in 3D Gradient Hydrogels

Cartilage tissue is characterized by zonal organization with gradual transitions of biochemical and mechanical cues from superficial to deep zones. We previously reported that 3D gradient hydrogels made of polyethylene glycol and chondroitin sulfate can induce zonal-specific responses of chondrocytes, resulting in zonal cartilage formation that mimics native tissues. While the role of cell-matrix interactions has been studied extensively, how cell-cell interactions across different zones influence cartilage zonal development remains unknown. The goal of this study is to harness gradient hydrogels as a tool to elucidate the role of cell-cell interactions in driving cartilage zonal development. When encapsulated in intact gradient hydrogels, chondrocytes exhibited strong zonal-specific responses that mimic native cartilage zonal organization. However, the separate culture of each zone of gradient hydrogels resulted in a significant decrease in cell proliferation and cartilage matrix deposition across all zones, while the trend of zonal dependence remains. Unexpectedly, mixing the coculture of all five zones of hydrogels in the same culture well largely abolished the zonal differences, with all zones behaving similarly to the softest zone. These results suggest that paracrine signal exchange among cells in different zones is essential in driving cartilage zonal development, and a spatial organization of zones is required for proper tissue zonal development. Intact, separate, or coculture groups resulted in distinct gene expression patterns in mechanosensing and cartilage-specific markers, suggesting that cell-cell interactions can also modulate mechanosensing. We further showed that 7 days of priming in intact gradient culture was sufficient to instruct the cells to complete the zonal development, and the separate or mixed coculture after 7 days of intact culture had minimal effects on cartilage formation. This study highlights the important role of cell-cell interactions in driving cartilage zonal development and validates gradient hydrogels as a useful tool to elucidate the role of cell-matrix and cell-cell interactions in driving zonal development during tissue morphogenesis and regeneration.

Predatory bacterial hydrogels for topical treatment of infected wounds

Wound infection is becoming a considerable healthcare crisis due to the abuse of antibiotics and the substantial production of multidrug-resistant bacteria. Seawater immersion wounds usually become a mortal trouble because of the infection of Vibrio vulnificus. Bdellovibrio bacteriovorus, one kind of natural predatory bacteria, is recognized as a promising biological therapy against intractable bacteria. Here, we prepared a B. bacteriovorus-loaded polyvinyl alcohol/alginate hydrogel for the topical treatment of the seawater immersion wounds infected by V. vulnificus. The B. bacteriovorus-loaded hydrogel (BG) owned highly microporous structures with the mean pore size of 90 μm, improving the rapid release of B. bacteriovorus from BG when contacting the aqueous surroundings. BG showed high biosafety with no L929 cell toxicity or hemolysis. More importantly, BG exhibited excellent in vitro anti-V. vulnificus effect. The highly effective infected wound treatment effect of BG was evaluated on mouse models, revealing significant reduction of local V. vulnificus, accelerated wound contraction, and alleviated inflammation. Besides the high bacterial inhibition of BG, BG remarkably reduced inflammatory response, promoted collagen deposition, neovascularization and re-epithelization, contributing to wound healing. BG is a promising topical biological formulation against infected wounds.

Effect of viscoelastic properties of cellulose nanocrystal/collagen hydrogels on chondrocyte behaviors

Cartilage tissue engineering technology provides a solution for treating osteoarthritis. Based on the viscoelastic nature of articular cartilage, many viscoelastic hydrogel scaffolds have been developed for investigating the effects on chondrocyte behaviors. However, cellulose nanocrystal/collagen (CNC/COL) hydrogels have not been used as a viscoelastic microenvironment to study chondrocyte growth. Here, we prepared CNC/COL hydrogels with tunable viscoelastic properties and investigated their influences on chondrocyte behaviors. The results showed that CNC and COL within the hydrogels are bonded by hydrogen bonds. The hydrogels had a microporous structure, and the viscoelastic properties were enhanced by increasing the concentration of CNC. Moreover, enhancing the hydrogel viscoelastic properties, including stress relaxation, creep, storage modulus, and loss modulus, promoted the cell shape change, proliferation, and matrix deposition and reduced the IL-1β level. Using a principal component analysis (PCA), stress relaxation was assessed to have the strongest correlation with chondrocytes behaviors, with an authority weight value of 62.547%. More importantly, FAK and YAP were involved in the chondrocytes’ response to the rapid relaxing hydrogel by immunofluorescence staining.

Pushing the Natural Frontier: Progress on the Integration of Biomaterial Cues toward Combinatorial Biofabrication and Tissue Engineering

The engineering of fully functional, biological-like tissues requires biomaterials to direct cellular events to a near-native, 3D niche extent. Natural biomaterials are generally seen as a safe option for cell support, but their biocompatibility and biodegradability can be just as limited as their bioactive/biomimetic performance. Furthermore, integrating different biomaterial cues and their final impact on cellular behavior is a complex equation where the outcome might be very different from the sum of individual parts. This review critically analyses recent progress on biomaterial-induced cellular responses, from simple adhesion to more complex stem cell differentiation, looking at the ever-growing possibilities of natural materials modification. Starting with a discussion on native material formulation and the inclusion of cell-instructive cues, the roles of shape and mechanical stimuli, the susceptibility to cellular remodeling, and the often-overlooked impact of cellular density and cell-cell interactions within constructs, are delved into. Along the way, synergistic and antagonistic combinations reported in vitro and in vivo are singled out, identifying needs and current lessons on the development of natural biomaterial libraries to solve the cell-material puzzle efficiently. This review brings together knowledge from different fields envisioning next-generation, combinatorial biomaterial development toward complex tissue engineering.

Application of Alginate Hydrogels for Next-Generation Articular Cartilage Regeneration

The articular cartilage has insufficient intrinsic healing abilities, and articular cartilage injuries often progress to osteoarthritis. Alginate-based scaffolds are attractive biomaterials for cartilage repair and regeneration, allowing for the delivery of cells and therapeutic drugs and gene sequences. In light of the heterogeneity of findings reporting the benefits of using alginate for cartilage regeneration, a better understanding of alginate-based systems is needed in order to improve the approaches aiming to enhance cartilage regeneration with this compound. This review provides an in-depth evaluation of the literature, focusing on the manipulation of alginate as a tool to support the processes involved in cartilage healing in order to demonstrate how such a material, used as a direct compound or combined with cell and gene therapy and with scaffold-guided gene transfer procedures, may assist cartilage regeneration in an optimal manner for future applications in patients.

Evaluation of Polycaprolactone Electrospun Nanofiber-Composites for Artificial Skin Based on Dermal Fibroblast Culture

The study’s aim was to develop a dermal equivalent scaffold that can mimic the architecture and biological performance of the human dermis. Poly ε-caprolactone (PCL) electrospun nanofiber material (ENF) was assembled with polyethylene glycol diacrylate (PEGDA), sodium alginate (SA) and type I collagen (CG1) to develop three groups of dermal equivalent scaffolds. These scaffolds were named PEGDA-PCL, SA-PCL and CG1-PCL. Scanning electron microscopy (SEM) images of cell-free scaffolds’ top and cross-sectional surface were collected and analyzed to examine internal morphology, specifically the adhesiveness of PCL fibers with the different scaffolds. Human dermal fibroblasts were cultured on each of the scaffolds. Cell viability studies including cell adhesion, cell differentiation and stress fiber production were conducted on each scaffold. Furthermore, the architectural integrity of each scaffold was verified by degradation analysis for 2 weeks by soaking each scaffold in phosphate-buffered saline (PBS) solution. Finally, we conducted rheological characteristics of each scaffold. Based on our results from the above analysis, the study concluded that CG1-PCL is best suitable for the dermal equivalent model and has potential to be used as a graft for skin repair.

Construction of Lung Tumor Model for Drug Screening Based on 3D Bio-Printing Technology

As is known to all, the biological characteristics of two-dimensional (2D) cultured cells are quite different from those in vivo, so the 2D screening model can no longer meet people’s needs. With the development of tissue engineering, people are committed to developing 3D tissue models that can better reflect the biology in vivo, and tend to be mass and miniaturized. In this study, three-dimensional (3D) bio-printing was used to develop an appropriate 3D model for screening sensitive anti-lung cancer drugs in vitro. A549 lung cancer cells were mixed with 8% sodium alginate and 5% gelatin as bio-printing ink to fabricate a cell-laden hydrogel grid scaffold structure. The sensitivity of the printed 3D model to drugs was evaluated with eight anti-tumor traditional Chinese medicines. A fluorescent live/dead staining was carried out at different time to assess the cell survival rate in the 3D scaffolds. MTT assay was used to determine the inhibitory rate of eight antitumor traditional Chinese medicines on A549 cell proliferation in 3D-printed lung tumor models and conventional 2D culture models.

Modified hyaluronic acid hydrogels with chemical groups that facilitate adhesion to host tissues enhance cartilage regeneration

Stable integration of hydrogel implants with host tissues is of critical importance to cartilage tissue engineering. Designing and fabricating hydrogels with high adhesive strength, stability and regeneration potential are major challenges to be overcome. This study fabricated injectable adhesive hyaluronic acid (HA) hydrogel modified by aldehyde groups and methacrylate (AHAMA) on the polysaccharide backbone with multiple anchoring mechanisms (amide bond through the dynamic Schiff base reaction, hydrogen bond and physical interpenetration). AHAMA hydrogel exhibited significantly improved durability and stability within a humid environment (at least 7 days), together with higher adhesive strength (43 KPa to skin and 52 KPa to glass), as compared to commercial fibrin glue (nearly 10 KPa) and HAMA hydrogel (nearly 20 KPa). The results showed that AHAMA hydrogel was biocompatible and could be easily and rapidly prepared in situ. In vitro cell culture experiments showed that AHAMA hydrogel could enhance proliferation (1.2-folds after 3 days) and migration (1.5-folds after 12 h) of bone marrow stem cells (BMSCs), as compared to cells cultured in a culture dish. Furthermore, in a rat osteochondral defect model, implanted AHAMA hydrogel significantly promoted integration between neo-cartilage and host tissues, and significantly improved cartilage regeneration (modified O'Driscoll histological scores of 16.0 ± 4.1 and 18.3 ± 4.6 after 4 and 12-weeks of post-implantation in AHAMA groups respectively, 12.0 ± 2.7 and 12.2 ± 2.8 respectively in HAMA groups, 9.8 ± 2.4 and 11.5 ± 2.1 respectively in untreated groups). Hence, AHAMA hydrogel is a promising adhesive biomaterial for clinical cartilage regeneration and other biomedical applications.

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Adhesive hydrogel composed of single natural polymer component.

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The single component enhance stable and easy to use in surgical operation of hydrogel.

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Adhesive hydrogel exhibited strong adhesive strength through multiple anchoring mechanisms.

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Adhesive hydrogel promoted integration between neo-cartilage and host tissues, drastically improved cartilage regeneration.

Mechanical Properties of Double Network Poly (Acrylic Acid) Based Hydrogels for Potential Use as a Biomaterial

Load-bearing applications of hydrogels include soft robots, tissue engineering, and stretchable electronics. This paper presents an extensive study of double network poly (acrylic acid) based hydrogel on stress relaxation, compression fatigue, shear stress, and shock absorption properties as a potential load-bearing soft tissue replacement biomaterial. Double network poly (acrylic acid) hydrogel was selected due to simple processing and availability. The optimized formulation of poly (acrylic acid) hydrogel was used for samples preparation. The compression modulus varied with hydrogel formulation, crosshead speed and swelled amount of the hydrogel. Stress relaxation and shock absorption properties of hydrogel were compared with polyurethane gel used in soft insoles (Shore 5A). Developed hydrogel displayed good fatigue properties up to 10,000 loading cycle at maximum stress of 390±30 kPa and at 84±4% strain. Further, maximum average shear stress and shear modulus of 80 kPa and 140 kPa respectively were observed at 84% strain before fracture.

Mechanical confinement regulates cartilage matrix formation by chondrocytes

Cartilage tissue equivalents formed from hydrogels containing chondrocytes could provide a solution for replacing damaged cartilage. Previous approaches have often utilized elastic hydrogels. However, elastic stresses may restrict cartilage matrix formation and alter the chondrocyte phenotype. Here we investigated the use of viscoelastic hydrogels, in which stresses are relaxed over time and which exhibit creep, for three-dimensional (3D) culture of chondrocytes. We found that faster relaxation promoted a striking increase in the volume of interconnected cartilage matrix formed by chondrocytes. In slower relaxing gels, restriction of cell volume expansion by elastic stresses led to increased secretion of IL-1β, which in turn drove strong up-regulation of genes associated with cartilage degradation and cell death. As no cell-adhesion ligands are presented by the hydrogels, these results reveal cell sensing of cell volume confinement as an adhesion-independent mechanism of mechanotransduction in 3D culture, and highlight stress relaxation as a key design parameter for cartilage tissue engineering.

Mechanical stimulations on human bone marrow mesenchymal stem cells enhance cells differentiation in a three-dimensional layered scaffold

Scaffolds laden with stem cells are a promising approach for articular cartilage repair. Investigations have shown that implantation of artificial matrices, growth factors or chondrocytes can stimulate cartilage formation, but no existing strategies apply mechanical stimulation on stratified scaffolds to mimic the cartilage environment. The purpose of this study was to adapt a spraying method for stratified cartilage engineering and to stimulate the biosubstitute. Human mesenchymal stem cells from bone marrow were seeded in an alginate (Alg)/hyaluronic acid (HA) or Alg/hydroxyapatite (Hap) gel to direct cartilage and hypertrophic cartilage/subchondral bone differentiation, respectively, in different layers within a single scaffold. Homogeneous or composite stratified scaffolds were cultured for 28 days and cell viability and differentiation were assessed. The heterogeneous scaffold was stimulated daily. The mechanical behaviour of the stratified scaffolds were investigated by plane-strain compression tests. Results showed that the spraying process did not affect cell viability. Moreover, cell differentiation driven by the microenvironment was increased with loading: in the layer with Alg/HA, a specific extracellular matrix of cartilage, composed of glycosaminoglycans and type II collagen was observed, and in the Alg/Hap layer more collagen X was detected. Hap seemed to drive cells to a hypertrophic chondrocytic phenotype and increased mechanical resistance of the scaffold. In conclusion, mechanical stimulations will allow for the production of a stratified biosubstitute, laden with human mesenchymal stem cells from bone marrow, which is capable in vivo to mimic all depths of chondral defects, thanks to an efficient combination of stem cells, biomaterial compositions and mechanical loading.

3D Bioprinting of Highly Thixotropic Alginate/Methylcellulose Hydrogel with Strong Interface Bonding

A robust alginate/methylcellulose (Alg/MC) blend hydrogel, with a strategy to improve adhesion between printed layers, has been fabricated for the first time for three-dimensional (3D) bioprinting. The optimized Alg/MC blend hydrogel exhibits a highly thixotropic property, great extrudability, and stackability. With treatment by a trisodium citrate (TSC) solution, the interfacial bonding between the printed layers is significantly improved. The TSC solution acts as a chelating agent to remove the superficial calcium ions at each layer. Post-cross-linking in a CaCl₂ bath after 3D printing further enhances the adhesion strength between the layers. The key parameters affecting the interfacial strength of the Alg/MC hydrogel are found to be the concentration of TSC, the volume of TSC, and the concentration of CaCl₂ in the bath. The Alg/MC hydrogel with the aid of TSC demonstrates superior printability, high stackability (150 layers can be printed), and high shape fidelity. A good cell viability of >95% is obtained for a freshly 3D-bioprinted Alg/MC construct. The novel Alg/MC hydrogel with the aid of TSC has been shown to have a great potential as an advanced 3D bioprinting material.

Biodegradable polymer scaffolds

Tissue engineering aims to repair the damaged tissue by transplantation of cells or introducing bioactive factors in a biocompatible scaffold. In recent years, biodegradable polymer scaffolds mimicking the extracellular matrix have been developed to promote the cell proliferation and extracellular matrix deposition. The biodegradable polymer scaffolds thus act as templates for tissue repair and regeneration. This article reviews the updated information regarding various types of natural and synthetic biodegradable polymers as well as their functions, physico-chemical properties, and degradation mechanisms in the development of biodegradable scaffolds for tissue engineering applications, including their combination with 3D printing.

Layered Alginate Constructs: A Platform for Co-culture of Heterogeneous Cell Populations

Many load bearing tissues possess structurally and functionally distinct regions, typically accompanied by different cell phenotypes with differential mechanosensing characteristics. Engineering and analysis of these tissue types remain a challenge. Layered hydrogel constructs provide an opportunity for investigating the interactions among multiple cell populations within single constructs. Alginate hydrogels are both biocompatible and allow for easy isolation of cells after experimentation. Here, we describe a method for the development of small sized dual layered alginate hydrogel discs. This process maintains high cell viability of human mesenchymal stem cells during the formation process and these layered discs can withstand unconfined cyclic compression, commonly used for stimulation of hMSCs undergoing chondrogenesis. These layered constructs can potentially be scaled up to include additional levels, and also be used to segregate cell populations initially after layering. This dual layer alginate hydrogel culture platform can be used for many different applications including engineering and analysis of cells of load bearing tissues and co-cultures of other cell types.

Hyaline Articular Matrix Formed by Dynamic Self-Regenerating Cartilage and Hydrogels

Injuries to the articular cartilage surface are challenging to repair because cartilage possesses a limited capacity for self-repair. The outcomes of current clinical procedures aimed to address these injuries are inconsistent and unsatisfactory. We have developed a novel method for generating hyaline articular cartilage to improve the outcome of joint surface repair. A suspension of 10(7) swine chondrocytes was cultured under reciprocating motion for 14 days. The resulting dynamic self-regenerating cartilage (dSRC) was placed in a cartilage ring and capped with fibrin and collagen gel. A control group consisted of chondrocytes encapsulated in fibrin gel. Constructs were implanted subcutaneously in nude mice and harvested after 6 weeks. Gross, histological, immunohistochemical, biochemical, and biomechanical analyses were performed. In swine patellar groove, dSRC was implanted into osteochondral defects capped with collagen gel and compared to defects filled with osteochondral plugs, collagen gel, or left empty after 6 weeks. In mice, the fibrin- and collagen-capped dSRC constructs showed enhanced contiguous cartilage matrix formation over the control of cells encapsulated in fibrin gel. Biochemically, the fibrin and collagen gel dSRC groups were statistically improved in glycosaminoglycan and hydroxyproline content compared to the control. There was no statistical difference in the biomechanical data between the dSRC groups and the control. The swine model also showed contiguous cartilage matrix in the dSRC group but not in the collagen gel and empty defects. These data demonstrate the survivability and successful matrix formation of dSRC under the mechanical forces experienced by normal hyaline cartilage in the knee joint. The results from this study demonstrate that dSRC capped with hydrogels successfully engineers contiguous articular cartilage matrix in both nonload-bearing and load-bearing environments.

Fabrication of hASCs-laden structures using extrusion-based cell printing supplemented with an electric field

In this study, we proposed a hybrid cell-printing technique that combines a conventional extrusion-based cell-printing process with an electrohydrodynamic jet. The electric field stabilized the extruded struts of cell-embedding-hydrogel and reduced the damage to dispensed cells caused by the high wall shear stress in the dispensing nozzle. The new cell-printing process was optimized in terms of various processing parameters, applied electric field strength, nozzle movement speed, and distance between the nozzle tip and working stage. Using the optimal cell-embedding hydrogel composition (1×10(6)cellsmL(-1) in 4wt% alginate) and cell-printing process parameters (applied voltage, 1kV; nozzle movement speed, 12mms(-1); distance, 0.7mm; current, 10.67±1.1nA), we achieved rapid and stable fabrication of a cell-laden structure without loss of cell viability or proliferation, the values of which were similar to those of the process without an electric field. Furthermore, by applying the same pneumatic pressure to fabricate cell-laden structures, considerably higher volume flow rate and cell viability at the same volume flow rate were achieved by the modified process compared with conventional extrusion-based cell-printing processes. To assess the feasibility of the method, the hydrogel containing human adipose stem cells (hASCs) and alginate (4wt%) was fabricated into a cell-laden porous structure in a layer-by-layer manner. The cell-laden structure exhibited reasonable initial hASC viability (87%), which was similar to that prior to processing of the cell-embedding-hydrogel.

STATEMENT OF SIGNIFICANCE

The extrusion-based cell-printing process has shortcomings, such as unstable flow and potential loss of cell viability. The unsteady flow can occur due to the high cell concentration, viscosity, and surface tension of bioinks. Also, cell viability post extrusion can be significantly reduced by damage of the cells due to the high wall shear stress in the extrusion nozzle. To overcome these limitations, we suggested an innovative cell-printing process that combines a conventional extrusion-based cellprinting process with an electric field. The electric field in the cell-printing process stabilized the extruded struts of bioink and dramatically reduced the damage to dispensed cells caused by the high wall shear stress in the dispensing nozzle.

Seaweed polysaccharide-based hydrogels used for the regeneration of articular cartilage

This manuscript provides an overview of the in vitro and in vivo studies reported in the literature focusing on seaweed polysaccharides based hydrogels that have been proposed for applications in regenerative medicine, particularly, in the field of cartilage tissue engineering. For a better understanding of the main requisites for these specific applications, the main aspects of the native cartilage structure, as well as recognized diseases that affect this tissue are briefly described. Current available treatments are also presented to emphasize the need for alternative techniques. The following part of this review is centered on the description of the general characteristics of algae polysaccharides, as well as relevant properties required for designing hydrogels for cartilage tissue engineering purposes. An in-depth overview of the most well known seaweed polysaccharide, namely agarose, alginate, carrageenan and ulvan biopolymeric gels, that have been proposed for engineering cartilage is also provided. Finally, this review describes and summarizes the translational aspect for the clinical application of alternative systems emphasizing the importance of cryopreservation and the commercial products currently available for cartilage treatment.

Rheological characterization of an injectable alginate gel system

Background

This work investigates a general method for producing alginate gel matrices using an internal mode of gelation that depends solely on soluble alginate and alginate/gelling ion particles. The method involves the formulation of two-component kits comprised of soluble alginate and insoluble alginate/gelling ion particles. Gelling kinetics, elastic and Young’s moduli were investigated for selected parameters with regard to soluble alginate guluronate content, molecular weight, calcium or strontium gelling ions and alginate gelling ion particle sizes in the range between 25 and 125 micrometers.

Results

By mixing the two components and varying the parameters mentioned above, alginate gel matrices with tailor-made viscoelastic properties and gelling kinetics were obtained. Final gel elasticity depended on alginate type, concentration and gelling ion. The gelling rate could be manipulated, e.g. through selection of the alginate type and molecular weight, particle sizes and the concentration of non-gelling ions.

Conclusions

Formulations of the injectable and moldable alginate system presented have recently been used within specific medical applications and may have potential within regenerative medicine or other fields.

The Effect of Chondroitin Sulphate and Hyaluronic Acid on Chondrocytes Cultured within a Fibrin-Alginate Hydrogel

Osteoarthritis is a painful degenerative joint disease that could be better managed if tissue engineers can develop methods to create long-term engineered articular cartilage tissue substitutes. Many of the tissue engineered cartilage constructs currently available lack the chemical stimuli and cell-friendly environment that promote the matrix accumulation and cell proliferation needed for use in joint cartilage repair. The goal of this research was to test the efficacy of using a fibrin-alginate hydrogel containing hyaluronic acid (HA) and/or chondroitin sulphate (CS) supplements for chondrocyte culture. Neonatal porcine chondrocytes cultured in fibrin-alginate hydrogels retained their phenotype better than chondrocytes cultured in monolayer, as evidenced by analysis of their relative expression of type II versus type I collagen mRNA transcripts. HA or CS supplementation of the hydrogels increased matrix glycosaminoglycan (GAG) production during the first week of culture. However, the effects of these supplements on matrix accumulation were not additive and were no longer observed after two weeks of culture. Supplementation of the hydrogels with CS or a combination of both CS and HA increased the chondrocyte cell population after two weeks of culture. Statistical analysis indicated that the HA and CS treatment effects on chondrocyte numbers may be additive. This research suggests that supplementation with CS and/or HA has positive effects on cartilage matrix production and chondrocyte proliferation in three-dimensional (3D) fibrin-alginate hydrogels.

Cartilage repair using mesenchymal stem cell (MSC) sheet and MSCs-loaded bilayer PLGA scaffold in a rabbit model

PURPOSE

The integration of regenerated cartilage with surrounding native cartilage is a major challenge for the success of cartilage tissue-engineering strategies. The purpose of this study is to investigate whether incorporation of the power of mesenchymal stem cell (MSC) sheet to MSCs-loaded bilayer poly-(lactic-co-glycolic acid) (PLGA) scaffolds can improve the integration and repair of cartilage defects in a rabbit model.

METHODS

Rabbit bone marrow-derived MSCs were cultured and formed cell sheet. Full-thickness cylindrical osteochondral defects (4 mm in diameter, 3 mm in depth) were created in the patellar groove of 18 New Zealand white rabbits and the osteochondral defects were treated with PLGA scaffold (n = 6), PLGA/MSCs (n = 6) or MSC sheet-encapsulated PLGA/MSCs (n = 6). After 6 and 12 weeks, the integration and tissue response were evaluated histologically.

RESULTS

The MSC sheet-encapsulated PLGA/MCSs group showed significantly more amounts of hyaline cartilage and higher histological scores than PLGA/MSCs group and PLGA group (P < 0.05). In addition, the MSC sheet-encapsulated PLGA/MCSs group showed the best integration between the repaired cartilage and surrounding normal cartilage and subchondral bone compared to other two groups.

CONCLUSIONS

The novel method of incorporation of MSC sheet to PLGA/MCSs could enhance the ability of cartilage regeneration and integration between repair cartilage and the surrounding cartilage. Transplantation of autologous MSC sheet combined with traditional strategies or cartilage debris might provide therapeutic opportunities for improving cartilage regeneration and integration in humans.

Cell-laden biphasic scaffolds with anisotropic structure for the regeneration of osteochondral tissue

Sufficient treatment of chondral and osteochondral defects to restore function of the respective tissue remains challenging in regenerative medicine. Biphasic scaffolds that mimic properties of bone and cartilage are appropriate to regenerate both tissues at the same time. The present study describes the development of biphasic, but monolithic scaffolds based on alginate, which are suitable for embedding of living cells in the chondral part. Scaffolds are fabricated under sterile and cell-compatible conditions according to the principle of diffusion-controlled, directed ionotropic gelation, which leads to the formation of channel-like, parallel aligned pores, running through the whole length of the biphasic constructs. The synthesis process leads to an anisotropic structure, as it is found in many natural tissues. The two different layers of the scaffolds are characterized by different microstructure and mechanical properties which provide a suitable environment for cells to form the respective tissue. Human chondrocytes and human mesenchymal stem cells were embedded within the chondral layer of the biphasic scaffolds during hydrogel formation and their chondrogenic (re)differentiation was successfully induced. Whereas viability of non-induced human mesenchymal stem cells decreased during culture, cell viability of human chondrocytes and chondrogenically induced human mesenchymal stem cells remained high within the scaffolds over the whole culture period of 3 weeks, demonstrating successful fabrication of cell-laden centimetre-scaled constructs for potential application in regenerative treatment of osteochondral defects. Copyright © 2014 John Wiley & Sons, Ltd.

Construction of self-assembled cartilage tissue from bone marrow mesenchymal stem cells induced by hypoxia combined with GDF-5

It is widely known that hypoxia can promote chondrogenesis of human bone marrow derived mesenchymal stem cells (hMSCs) in monolayer cultures. However, the direct impact of oxygen tension on hMSC differentiation in three-dimensional cultures is still unknown. This research was designed to observe the direct impact of oxygen tension on the ability of hMSCs to "self assemble" into tissue-engineered cartilage constructs. hMSCs were cultured in chondrogenic medium (CM) containing 100 ng/mL growth differentiation factor 5 (GDF-5) at 5% (hypoxia) and 21% (normoxia) O2 levels in monolayer cultures for 3 weeks. After differentiation, the cells were digested and employed in a self-assembly process to produce tissue-engineered constructs under hypoxic and normoxic conditions in vitro. The aggrecan and type II collagen expression, and type X collagen in the self-assembled constructs were assessed by using immunofluorescent and immunochemical staining respectively. The methods of dimethylmethylene blue (DMMB), hydroxyproline and PicoGreen were used to measure the total collagen content, glycosaminoglycan (GAG) content and the number of viable cells in each construct, respectively. The expression of type II collagen and aggrecan under hypoxic conditions was increased significantly as compared with that under normoxic conditions. In contrast, type X collagen expression was down-regulated in the hypoxic group. Moreover, the constructs in hypoxic group showed more significantly increased total collagen and GAG than in normoxic group, which were more close to those of the natural cartilage. These findings demonstrated that hypoxia enhanced chondrogenesis of in vitro, scaffold-free, tissue-engineered constructs generated using hMSCs induced by GDF-5. In hypoxic environments, the self-assembled constructs have a Thistological appearance and biochemical parameters similar to those of the natural cartilage.

Modulating gradients in regulatory signals within mesenchymal stem cell seeded hydrogels: a novel strategy to engineer zonal articular cartilage

Engineering organs and tissues with the spatial composition and organisation of their native equivalents remains a major challenge. One approach to engineer such spatial complexity is to recapitulate the gradients in regulatory signals that during development and maturation are believed to drive spatial changes in stem cell differentiation. Mesenchymal stem cell (MSC) differentiation is known to be influenced by both soluble factors and mechanical cues present in the local microenvironment. The objective of this study was to engineer a cartilaginous tissue with a native zonal composition by modulating both the oxygen tension and mechanical environment thorough the depth of MSC seeded hydrogels. To this end, constructs were radially confined to half their thickness and subjected to dynamic compression (DC). Confinement reduced oxygen levels in the bottom of the construct and with the application of DC, increased strains across the top of the construct. These spatial changes correlated with increased glycosaminoglycan accumulation in the bottom of constructs, increased collagen accumulation in the top of constructs, and a suppression of hypertrophy and calcification throughout the construct. Matrix accumulation increased for higher hydrogel cell seeding densities; with DC further enhancing both glycosaminoglycan accumulation and construct stiffness. The combination of spatial confinement and DC was also found to increase proteoglycan-4 (lubricin) deposition toward the top surface of these tissues. In conclusion, by modulating the environment through the depth of developing constructs, it is possible to suppress MSC endochondral progression and to engineer tissues with zonal gradients mimicking certain aspects of articular cartilage.

Effects of perfusion and dynamic loading on human neocartilage formation in alginate hydrogels

Dynamic loading and perfusion culture environments alone are known to enhance cartilage extracellular matrix (ECM) production in dedifferentiated articular chondrocytes. In this study, we explored whether a combination of these factors would enhance these processes over a free-swelling (FS) condition using adult human articular chondrocytes embedded in 2% alginate. The alginate constructs were placed into a bioreactor for perfusion (P) only (100 μL/per minute) or perfusion and dynamic compressive loading (PL) culture (20% for 1 h, at 0.5 Hz), each day. Control FS alginate gels were maintained in six-well static culture. Gene expression analysis was conducted on days 7 and 14, while cell viability, immunostaining, and mechanical property testing were performed on day 14 only. Total glycosaminoglycan (GAG) content and GAG synthesis were assessed after 14 days. Col2a1 mRNA expression levels were significantly higher (at least threefold; p<0.05) in both bioreactor conditions compared with FS by days 7 and 14. For all gene studies, no significant differences were seen between P and PL treatments. Aggrecan mRNA levels were not significantly altered in any condition although both GAG/DNA and (35)S GAG incorporation studies indicated higher GAG retention and synthesis in the FS treatment. Collagen type II protein deposition was low in all samples, link protein distribution was more diffuse in FS condition, and aggrecan deposition was located in the outer regions of the alginate constructs in both bioreactor conditions, yet more uniformly in the FS condition. Catabolic gene expression (matrix metalloproteinase 3 [MMP3] and inducible nitric oxide synthase [iNOS]) was higher in bioreactor conditions compared with FS, although iNOS expression levels decreased to approximately fourfold less than the FS condition by day 14. Our data indicate that conditions created in the bioreactor enhanced both anabolic and catabolic responses, similar to other loading studies. Perfusion was sufficient alone to promote this dual response. PL increased the deposition of aggrecan surrounding cells compared with the other conditions; however, overall low GAG retention in the bioreactor system was likely due to both perfusion and catabolic conditions created. Optimal conditions, which permit appropriate anabolic and catabolic processes for accumulation of ECM and tissue remodeling for neocartilage development, specifically for humans, are needed.

In situ tissue engineering using magnetically guided three-dimensional cell patterning

Manipulation of cell patterns in three dimensions in a manner that mimics natural tissue organization and function is critical for cell biological studies and likely essential for successfully regenerating tissues--especially cells with high physiological demands, such as those of the heart, liver, lungs, and articular cartilage.(1, 2) In the present study, we report on the feasibility of arranging iron oxide-labeled cells in three-dimensional hydrogels using magnetic fields. By manipulating the strength, shape, and orientation of the magnetic field and using crosslinking gradients in hydrogels, multi-directional cell arrangements can be produced in vitro and even directly in situ. We show that these ferromagnetic particles are nontoxic between 0.1 and 10 mg/mL; certain species of particles can permit or even enhance tissue formation, and these particles can be tracked using magnetic resonance imaging. Taken together, this approach can be adapted for studying basic biological processes in vitro, for general tissue engineering approaches, and for producing organized repair tissues directly in situ.

Physiological cartilage tissue engineering effect of oxygen and biomechanics

In vitro engineering of cartilaginous tissues has been studied for many years, and tissue-engineered constructs are sought to be used clinically for treating articular cartilage defects. Even though there is a plethora of studies and data available, no breakthroughs have been achieved yet that allow for implanting in vivo cultured articular cartilaginous tissues in patients. A review of contributions to cartilage tissue engineering over the past decades emphasizes that most of the studies were performed under environmental conditions neglecting the physiological situation. This is specifically pronounced in the use of bioreactor systems which neither allow for application of near physiomechanical stimulations nor for controlling a hypoxic environment as it is experienced in synovial joints. It is suspected that the negligence of these important parameters has slowed down progress and prevented major breakthroughs in the field. This review focuses on the main aspects of cartilage tissue engineering with emphasis on the relation and understanding of employing physiological conditions.

Potential of human embryonic stem cells in cartilage tissue engineering and regenerative medicine

The current surgical intervention of using autologous chondrocyte implantation (ACI) for cartilage repair is associated with several problems such as donor site morbidity, de-differentiation upon expansion and fibrocartilage repair following transplantation. This has led to exploration of the use of stem cells as a model for chondrogenic differentiation as well as a potential source of chondrogenic cells for cartilage tissue engineering and repair. Embryonic stem cells (ESCs) are advantageous, due to their unlimited self-renewal and pluripotency, thus representing an immortal cell source that could potentially provide an unlimited supply of chondrogenic cells for both cell and tissue-based therapies and replacements. This review aims to present an overview of emerging trends of using ESCs in cartilage tissue engineering and regenerative medicine. In particular, we will be focusing on ESCs as a promising cell source for cartilage regeneration, the various strategies and approaches employed in chondrogenic differentiation and tissue engineering, the associated outcomes from animal studies, and the challenges that need to be overcome before clinical application is possible.

A highly organized three-dimensional alginate scaffold for cartilage tissue engineering prepared by microfluidic technology

Osteoarthritis is a degenerative disease and frequently involves the knee, hip and phalangeal joints. Current treatments used in small cartilage defects including multiple drilling, abrasion arthroplasty, mosaicplasty, and autogenous chondrocyte transplantation, however, there are problems needed to be solved. The standard treatment for severe osteoarthritis is total joint arthroplasty. The disadvantages of this surgery are the possibility of implant loosening. Therefore, tissue engineering for cartilage regeneration has become a promising topic. We have developed a new method to produce a highly organized single polymer (alginate) scaffold using microfluidic device. Scanning electron microscope and confocal fluoroscope examinations showed that the scaffold has a regular interconnected porous structure in the scale of 250 μm and high porosity. The scaffold is effective in chondrocyte culture; the cell viability test (WST-1 assay), cell toxicity (lactate dehydrogenase assay), cell survival rate, extracellular matrix production (glycosaminoglycans contents), cell proliferation (DNA quantification), and gene expression (real-time PCR) all revealed good results for chondrocyte culture. The chondrocytes can maintain normal phenotypes, highly express aggrecan and type II collagen, and secrete a great deal of extracellular matrix when seeded in the alginate scaffold. This study demonstrated that a highly organized alginate scaffold can be prepared with an economical microfluidic device, and this scaffold is effective in cartilage tissue engineering.

Optical properties of breast tumor phantoms containing carbon nanotubes and nanohorns

The degree by which optical properties of tumors are altered following introduction of carbon nanotubes (CNTs) of varying concentration and type is poorly understood, making it difficult to predict the impact of CNT inclusion on the photothermal response to laser therapies. Optical properties were measured of phantoms representative of breast tumor tissue incorporated with multiwalled carbon nanotubes (MWNTs), single-walled carbon nanotubes (SWNTs), and single-walled carbon nanohorns (SWNHs) of varying concentration (0.01-0.1 mg/ml). Tissue phantoms were made from sodium alginate (3 g/ml) incorporated with polystyrene microbeads (3 μm diam and 1 mg/ml) and talc-France powder (40 mg/ml). Absorption (μ(a)) and reduced scattering (μ's) coefficients of phantoms containing CNTs were determined by the inverse adding-doubling algorithm for the wavelength range of 400-1300 nm. Optical properties of phantoms without CNTs were in the range of μ(a) = 1.04-0.06 mm(-1) and μ's' = 0.05-0.07 mm(-1) at a wavelength of 900 nm, which corresponds with published data for human breast tumor tissue. Incorporating MWNTs, SWNTs, and SWNHs in phantoms with a concentration of 0.1 mg/ml increased (μ(a)) by 20- to 30-fold, 5- to 6-fold, and 9- to 14-fold, respectively, for the wavelength range of 800-1100 nm with minimal change in μ's (1.2- to 1.3-fold). Introduction of CNTs into tissue phantoms increased absorption, providing a means to enhance photothermal therapy.

Measurement of the thermal conductivity of carbon nanotube--tissue phantom composites with the hot wire probe method

Developing combinatorial treatments involving laser irradiation and nanoparticles require an understanding of the effect of nanoparticle inclusion on tissue thermal properties, such as thermal conductivity. This information will permit a more accurate prediction of temperature distribution and tumor response following therapy, as well as provide additional information to aid in the selection of the appropriate type and concentration of nanoparticles. This study measured the thermal conductivity of tissue representative phantoms containing varying types and concentrations of carbon nanotubes (CNTs). Multi-walled carbon nanotubes (MWNTs, length of 900-1200 nm and diameter of 40-60 nm), single-walled carbon nanotubes (SWNTs, length of 900-1200 nm and diameter <2 nm), and a novel embodiment of SWNTs referred to as single-walled carbon nanohorns (SWNHs, length of 25-50 nm and diameter of 3-5 nm) of varying concentrations (0.1, 0.5, and 1.0 mg/mL) were uniformly dispersed in sodium alginate tissue representative phantoms. The thermal conductivity of phantoms containing CNTs was measured using a hot wire probe method. Increasing CNT concentration from 0 to 1.0 mg/mL caused the thermal conductivity of phantoms containing SWNTs, SWNHs, and MWNTs to increase by 24, 30, and 66%, respectively. For identical CNT concentrations, phantoms containing MWNTs possessed the highest thermal conductivity.

In situ collagen polymerization of layered cell-seeded electrospun scaffolds for bone tissue engineering applications

Electrospun scaffolds have been studied extensively for their potential use in bone tissue engineering applications. However, inherent issues with the electrospinning approach limit the thickness of these scaffolds and constrain their use for repair of critical-sized bone defects. One method to increase overall scaffold thickness is to bond multiple electrospun scaffolds together with a biocompatible gel. The objective of this study was to determine whether multiple human adipose-derived stem cell (hASC-seeded electrospun, nanofibrous scaffolds could be layered via in situ collagen assembly and whether the addition of laser-ablated micron-sized pores within the electrospun scaffold layers was beneficial to the bonding process. Pores were created by a laser ablation technique. We hypothesized that the addition of micron-sized pores within the electrospun scaffolds would encourage collagen integration between scaffold layers, and promote osteogenic differentiation of hASCs seeded within the layered electrospun scaffolds. To evaluate the benefit of assembled scaffolds with and without engineered pores, hASCs were seeded on individual electrospun scaffolds, hASC-seeded scaffolds were bonded with type I collagen, and the assembled ∼3-mm-thick constructs were cultured for 3 weeks to examine their potential as bone tissue engineering scaffolds. Assembled electrospun scaffolds/collagen gel constructs using electrospun scaffolds with pores resulted in enhanced hASC viability, proliferation, and mineralization of the scaffolds after 3 weeks in vitro compared to constructs using electrospun scaffolds without pores. Scanning electron microscopy and histological examination revealed that the assembled constructs that included laser-ablated electrospun scaffolds were able to maintain a contracted structure and were not delaminated, unlike assembled constructs containing nonablated electrospun scaffolds. This is the first study to show that the introduction of engineered pores in electrospun scaffolds assists with multilayered scaffold integration, resulting in thick constructs potentially suitable for use as scaffolds for bone tissue engineering or repair of critical bone defects.