Hyaluronan and CD44: strategic players for cell-matrix interactions during chondrogenesis and matrix assembly

3D Bioprinting of Biomimetic Alginate/Gelatin/Chondroitin Sulfate Hydrogel Nanocomposites for Intrinsically Chondrogenic Differentiation of Human Mesenchymal Stem Cells

3D-printed hydrogel scaffolds biomimicking the extracellular matrix (ECM) are key in cartilage tissue engineering as they can enhance the chondrogenic differentiation of mesenchymal stem cells (MSCs) through the presence of active nanoparticles such as graphene oxide (GO). Here, biomimetic hydrogels were developed by cross-linking alginate, gelatin, and chondroitin sulfate biopolymers in the presence of GO as a bioactive filler, with excellent processability for developing bioactive 3D printed scaffolds and for the bioprinting process. A novel bioink based on our hydrogel with embedded human MSCs presented a cell survival rate near 100% after the 3D bioprinting process. The effects of processing and filler concentration on cell differentiation were further quantitatively evaluated. The nanocomposited hydrogels render high MSC proliferation and viability, exhibiting intrinsic chondroinductive capacity without any exogenous factor when used to print scaffolds or bioprint constructs. The bioactivity depended on the GO concentration, with the best performance at 0.1 mg mL-1. These results were explained by the rational combination of the three biopolymers, with GO nanoparticles having carboxylate and sulfate groups in their structures, therefore, biomimicking the highly negatively charged ECM of cartilage. The bioactivity of this biomaterial and its good processability for 3D printing scaffolds and 3D bioprinting techniques open up a new approach to developing novel biomimetic materials for cartilage repair.

Sweet but Challenging: Tackling the Complexity of GAGs with Engineered Tailor-Made Biomaterials

Glycosaminoglycans (GAGs) play a crucial role in tissue homeostasis by regulating the activity and diffusion of bioactive molecules. Incorporating GAGs into biomaterials has emerged as a widely adopted strategy in medical applications, owing to their biocompatibility and ability to control the release of bioactive molecules. Nevertheless, immobilized GAGs on biomaterials can elicit distinct cellular responses compared to their soluble forms, underscoring the need to understand the interactions between GAG and bioactive molecules within engineered functional biomaterials. By controlling critical parameters such as GAG type, density, and sulfation, it becomes possible to precisely delineate GAG functions within a biomaterial context and to better mimic specific tissue properties, enabling tailored design of GAG-based biomaterials for specific medical applications. However, this requires access to pure and well-characterized GAG compounds, which remains challenging. This review focuses on different strategies for producing well-defined GAGs and explores high-throughput approaches employed to investigate GAG-growth factor interactions and to quantify cellular responses on GAG-based biomaterials. These automated methods hold considerable promise for improving the understanding of the diverse functions of GAGs. In perspective, the scientific community is encouraged to adopt a rational approach in designing GAG-based biomaterials, taking into account the in vivo properties of the targeted tissue for medical applications.

Chitosan/Hyaluronan and Alginate-Nanohydroxyapatite Biphasic Scaffold as a Promising Matrix for Osteoarthritis Disorders

Purpose

Regenerative medicine offers new techniques for osteoarthritis (OA) disorders, especially while considering simultaneous chondral and subchondral regenerations.

Methods

Chitosan and hyaluronan were chemically bound as the chondral phase and the osteogenic layer was prepared with alginate and nano-hydroxyapatite (nHAP). These scaffolds were fixed by fibrin glue as a biphasic scaffold and then examined.

Results

Scanning electron microscopy (SEM) confirmed the porosity of 61.45±4.51 and 44.145±2.81 % for the subchondral and chondral layers, respectively. The composition analysis by energy dispersive X-ray (EDAX) indicated the various elements of both hydrogels. Also, their mechanical properties indicated that the highest modulus and resistance values corresponded to the biphasic hydrogel as 108.33±5.56 and 721.135±8.21 kPa, despite the same strain value as other groups. Their individual examinations demonstrated the proteoglycan synthesis of the chondral layer and also, the alkaline phosphatase (ALP) activity of the subchondral layer as 13.3±2.2 ng. After 21 days, the cells showed a mineralized surface and a polygonal phenotype, confirming their commitment to bone and cartilage tissues, respectively. Immunostaining of collagen I and II represented greater extracellular matrix (ECM) secretion in the biphasic composite group due to the paracrine effect of the two cell types on each other.

Conclusion

For the first time, the ability of this biphasic scaffold to regenerate both tissue types was evaluated and the results showed satisfactory cellular commitment to bone and cartilage tissues. Thus, this scaffold can be considered a new strategy for the preparation of implants for OA.

Subcutaneous Application of a Gelatin/Hyaluronic Acid Hydrogel Induces the Production of Skin Extracellular Matrix

The development of injectable hydrogels with natural biopolymers such as gelatin (Ge) and hyaluronic acid (Ha) is widely performed due to their biocompatibility and biodegradability. The combination of both polymers crosslinked with N-Ethyl-N'-(3-dimethyl aminopropyl) carbodiimide hydrochloride (EDC) can be used as an innovative dermal filler that stimulates fibroblast activity and increases skin elasticity and tightness. Thus, crosslinked Ge/Ha hydrogels with different concentrations of EDC were administered subcutaneously to test their efficacy in young and old rats. At higher EDC concentrations, the viscosity decreases while the particle size of the hydrogels increases. At all concentrations of EDC, amino and carboxyl groups are present. The histological analysis shows an acute inflammatory response, which disappears seven days after application. At one and three months post-treatment, no remains of the hydrogels are found, and the number of fibroblasts increases in all groups in comparison with the control. In addition, the elastic modulus of the skin increases after three months of treatment. Because EDC-crosslinked Ge/Ha hydrogels are biocompatible and induce increased skin tension, fibroblast proliferation, and de novo extracellular matrix production, we propose their use as a treatment to attenuate wrinkles and expression lines.

A review of advanced hydrogels for cartilage tissue engineering

With the increase in weight and age of the population, the consumption of tobacco, inappropriate foods, and the reduction of sports activities in recent years, bone and joint diseases such as osteoarthritis (OA) have become more common in the world. From the past until now, various treatment strategies (e.g., microfracture treatment, Autologous Chondrocyte Implantation (ACI), and Mosaicplasty) have been investigated and studied for the prevention and treatment of this disease. However, these methods face problems such as being invasive, not fully repairing the tissue, and damaging the surrounding tissues. Tissue engineering, including cartilage tissue engineering, is one of the minimally invasive, innovative, and effective methods for the treatment and regeneration of damaged cartilage, which has attracted the attention of scientists in the fields of medicine and biomaterials engineering in the past several years. Hydrogels of different types with diverse properties have become desirable candidates for engineering and treating cartilage tissue. They can cover most of the shortcomings of other treatment methods and cause the least secondary damage to the patient. Besides using hydrogels as an ideal strategy, new drug delivery and treatment methods, such as targeted drug delivery and treatment through mechanical signaling, have been studied as interesting strategies. In this study, we review and discuss various types of hydrogels, biomaterials used for hydrogel manufacturing, cartilage-targeting drug delivery, and mechanosignaling as modern strategies for cartilage treatment.

Bone Scaffold Materials in Periodontal and Tooth-supporting Tissue Regeneration: A Review

BACKGROUND AND OBJECTIVES

Periodontium is an important tooth-supporting tissue composed of both hard (alveolar bone and cementum) and soft (gingival and periodontal ligament) sections. Due to the multi-tissue architecture of periodontium, reconstruction of each part can be influenced by others. This review focuses on the bone section of the periodontium and presents the materials used in tissue engineering scaffolds for its reconstruction.

MATERIALS AND METHODS

The following databases (2015 to 2021) were electronically searched: ProQuest, EMBASE, SciFinder, MRS Online Proceedings Library, Medline, and Compendex. The search was limited to English-language publications and in vivo studies.

RESULTS

Eighty-three articles were found in primary searching. After applying the inclusion criteria, seventeen articles were incorporated into this study.

CONCLUSION

In complex periodontal defects, various types of scaffolds, including multilayered ones, have been used for the functional reconstruction of different parts of periodontium. While there are some multilayered scaffolds designed to regenerate alveolar bone/periodontal ligament/cementum tissues of periodontium in a hierarchically organized construct, no scaffold could so far consider all four tissues involved in a complete periodontal defect. The progress and material considerations in the regeneration of the bony part of periodontium are presented in this work to help investigators develop tissue engineering scaffolds suitable for complete periodontal regeneration.

Fabrication and characterization of porous, degradable, biocompatible poly(vinyl alcohol)/tannic acid/gelatin/hyaluronic acid hydrogels with good mechanical properties for cartilage tissue engineering

At present, articular cartilage repair and regeneration remain still one of the most concerned problems due to its poor self-healing capacity. Among the tissue engineering materials, hydrogel is considered an ideal candidate due to its similarity to extracellular matrices. Despite the good biocompatibility of gelatin and hyaluronic acid hydrogels, they are still limited to serve as tissue engineering materials by fast degradation rate and poor mechanical performances. In order to solve these problems, novel polyvinyl alcohol/tannic acid/gelatin/hyaluronic acid (PTGH) hydrogels are prepared by a facile physical crosslinked method. The PTGH hydrogels exhibit a high moisture content (85%) and porosity (87%). Meanwhile, the porous microstructures and mechanical properties (compressive strength: 0.85-2.59 MPa; compressive modulus: 57.88-124.27 kPa) can be controlled by adjusting the mass ratio of PT/GH. In vitro degradation analysis shows that the PTGH hydrogels can be degraded gradually in PBS solution with the presence of lysozyme. For this gel system, based on the hydrogen bonds among molecules, it improved the mechanical properties of gelatin and hyaluronic acid hydrogels. With the degradation of PTGH hydrogels, the release of gelatin and hyaluronic acid can have a continuous effort for the cartilage tissue regeneration and repair. In addition, in vitro cell culture results show that the PTGH hydrogels have no negative effects on chondrocytes growth and proliferation. In all, the PTGH hydrogels exhibit potential applications for articular cartilage tissue repair and regeneration.

An injectable and 3D printable pro-chondrogenic hyaluronic acid and collagen type II composite hydrogel for the repair of articular cartilage defects

Current treatments for repairing articular cartilage defects are limited. However, pro-chondrogenic hydrogels formulated using articular cartilage matrix components (such as hyaluronic acid (HA) and collagen type II (Col II)), offer a potential solution if they could be injected into the defect via minimally invasive arthroscopic procedures, or used as bioinks to 3D print patient-specific customised regenerative scaffolds-potentially combined with cells. However, HA and Col II are difficult to incorporate into injectable/3D printable hydrogels due to poor physicochemical properties. This study aimed to overcome this by developing an articular cartilage matrix-inspired pro-chondrogenic hydrogel with improved physicochemical properties for both injectable and 3D printing (3DP) applications. To achieve this, HA was methacrylated to improve mechanical properties and mixed in a 1:1 ratio with Col I, a Col I/Col II blend or Col II. Col I possesses superior mechanical properties to Col II and so was hypothesised to enhance hydrogel mechanical properties. Rheological analysis showed that the pre-gels had viscoelastic and shear thinning properties. Subsequent physicochemical analysis of the crosslinked hydrogels showed that Col II inclusion resulted in a more swollen and softer polymer network, without affecting degradation time. While all hydrogels exhibited exemplary injectability, only the Col I-containing hydrogels had sufficient mechanical stability for 3DP applications. To facilitate 3DP of multi-layered scaffolds using methacrylated HA (MeHA)-Col I and MeHA-Col I/Col II, additional mechanical support in the form of a gelatin slurry support bath freeform reversible embedding of suspended hydrogels was utilised. Biological analysis revealed that Col II inclusion enhanced hydrogel-embedded MSC chondrogenesis, thus MeHA-Col II was selected as the optimal injectable hydrogel, and MeHA-Col I/Col II as the preferred bioink. In summary, this study demonstrates how tailoring biomaterial composition and physicochemical properties enables development of pro-chondrogenic hydrogels with potential for minimally invasive delivery to injured articular joints or 3DP of customised regenerative implants for cartilage repair.

Alterations of bovine nucleus pulposus cells with aging

Aging is one of the major etiological factors driving intervertebral disc (IVD) degeneration, the main cause of low back pain. The nucleus pulposus (NP) includes a heterogeneous cell population, which is still poorly characterized. Here, we aimed to uncover main alterations in NP cells with aging. For that, bovine coccygeal discs from young (12 months) and old (10-16 years old) animals were dissected and primary NP cells were isolated. Gene expression and proteomics of fresh NP cells were performed. NP cells were labelled with propidium iodide and analysed by flow cytometry for the expression of CD29, CD44, CD45, CD146, GD2, Tie2, CD34 and Stro-1. Morphological cell features were also dissected by imaging flow cytometry. Elder NP cells (up-regulated bIL-6 and bMMP1 gene expression) presented lower percentages of CD29+, CD44+, CD45+ and Tie2+ cells compared with young NP cells (upregulated bIL-8, bCOL2A1 and bACAN gene expression), while GD2, CD146, Stro-1 and CD34 expression were maintained with age. NP cellulome showed an upregulation of proteins related to endoplasmic reticulum (ER) and melanosome independently of age, whereas proteins upregulated in elder NP cells were also associated with glycosylation and disulfide bonds. Flow cytometry analysis of NP cells disclosed the existence of 4 subpopulations with distinct auto-fluorescence and size with different dynamics along aging. Regarding cell morphology, aging increases NP cell area, diameter and vesicles. These results contribute to a better understanding of NP cells aging and highlighting potential anti-aging targets that can help to mitigate age-related disc disease.

3D Bioprinting of Hyaline Articular Cartilage: Biopolymers, Hydrogels, and Bioinks

The musculoskeletal system, consisting of bones and cartilage of various types, muscles, ligaments, and tendons, is the basis of the human body. However, many pathological conditions caused by aging, lifestyle, disease, or trauma can damage its elements and lead to severe disfunction and significant worsening in the quality of life. Due to its structure and function, articular (hyaline) cartilage is the most susceptible to damage. Articular cartilage is a non-vascular tissue with constrained self-regeneration capabilities. Additionally, treatment methods, which have proven efficacy in stopping its degradation and promoting regeneration, still do not exist. Conservative treatment and physical therapy only relieve the symptoms associated with cartilage destruction, and traditional surgical interventions to repair defects or endoprosthetics are not without serious drawbacks. Thus, articular cartilage damage remains an urgent and actual problem requiring the development of new treatment approaches. The emergence of biofabrication technologies, including three-dimensional (3D) bioprinting, at the end of the 20th century, allowed reconstructive interventions to get a second wind. Three-dimensional bioprinting creates volume constraints that mimic the structure and function of natural tissue due to the combinations of biomaterials, living cells, and signal molecules to create. In our case-hyaline cartilage. Several approaches to articular cartilage biofabrication have been developed to date, including the promising technology of 3D bioprinting. This review represents the main achievements of such research direction and describes the technological processes and the necessary biomaterials, cell cultures, and signal molecules. Special attention is given to the basic materials for 3D bioprinting-hydrogels and bioinks, as well as the biopolymers underlying the indicated products.

Biomaterials and tissue engineering approaches using glycosaminoglycans for tissue repair: Lessons learned from the native extracellular matrix

Glycosaminoglycans (GAGs) are an important component of the extracellular matrix as they influence cell behavior and have been sought for tissue regeneration, biomaterials, and drug delivery applications. GAGs are known to interact with growth factors and other bioactive molecules and impact tissue mechanics. This review provides an overview of native GAGs, their structure, and properties, specifically their interaction with proteins, their effect on cell behavior, and their mechanical role in the ECM. GAGs' function in the extracellular environment is still being understood however, promising studies have led to the development of medical devices and therapies. Native GAGs, including hyaluronic acid, chondroitin sulfate, and heparin, have been widely explored in tissue engineering and biomaterial approaches for tissue repair or replacement. This review focuses on orthopaedic and wound healing applications. The use of GAGs in these applications have had significant advances leading to clinical use. Promising studies using GAG mimetics and future directions are also discussed. STATEMENT OF SIGNIFICANCE: Glycosaminoglycans (GAGs) are an important component of the native extracellular matrix and have shown promise in medical devices and therapies. This review emphasizes the structure and properties of native GAGs, their role in the ECM providing biochemical and mechanical cues that influence cell behavior, and their use in tissue regeneration and biomaterial approaches for orthopaedic and wound healing applications.

Atherosclerosis and Inflammation: Insights from the Theory of General Pathological Processes

Recent advances have greatly improved our understanding of the molecular mechanisms behind atherosclerosis pathogenesis. However, there is still a need to systematize this data from a general pathology perspective, particularly with regard to atherogenesis patterns in the context of both canonical and non-classical inflammation types. In this review, we analyze various typical phenomena and outcomes of cellular pro-inflammatory stress in atherosclerosis, as well as the role of endothelial dysfunction in local and systemic manifestations of low-grade inflammation. We also present the features of immune mechanisms in the development of productive inflammation in stable and unstable plaques, along with their similarities and differences compared to canonical inflammation. There are numerous factors that act as inducers of the inflammatory process in atherosclerosis, including vascular endothelium aging, metabolic dysfunctions, autoimmune, and in some cases, infectious damage factors. Life-critical complications of atherosclerosis, such as cardiogenic shock and severe strokes, are associated with the development of acute systemic hyperinflammation. Additionally, critical atherosclerotic ischemia of the lower extremities induces paracoagulation and the development of chronic systemic inflammation. Conversely, sepsis, other critical conditions, and severe systemic chronic diseases contribute to atherogenesis. In summary, atherosclerosis can be characterized as an independent form of inflammation, sharing similarities but also having fundamental differences from low-grade inflammation and various variants of canonical inflammation (classic vasculitis).

Non-hypertrophic chondrogenesis of mesenchymal stem cells through mechano-hypoxia programing

Cartilage tissue engineering aims to generate functional replacements to treat cartilage defects from damage and osteoarthritis. Human bone marrow-derived mesenchymal stem cells (hBM-MSC) are a promising cell source for making cartilage, but current differentiation protocols require the supplementation of growth factors like TGF-β1 or -β3. This can lead to undesirable hypertrophic differentiation of hBM-MSC that progress to bone. We have found previously that exposing engineered human meniscus tissues to physiologically relevant conditions of the knee (mechanical loading and hypoxia; hence, mechano-hypoxia conditioning) increased the gene expression of hyaline cartilage markers, SOX9 and COL2A1, inhibited hypertrophic marker COL10A1, and promoted bulk mechanical property development. Adding further to this protocol, we hypothesize that combined mechano-hypoxia conditioning with TGF-β3 growth factor withdrawal will promote stable, non-hypertrophic chondrogenesis of hBM-MSC embedded in an HA-hydrogel. We found that the combined treatment upregulated many cartilage matrix- and development-related markers while suppressing many hypertrophic- and bone development-related markers. Tissue level assessments with biochemical assays, immunofluorescence, and histochemical staining confirmed the gene expression data. Further, mechanical property development in the dynamic compression treatment shows promise toward generating functional engineered cartilage through more optimized and longer culture conditions. In summary, this study introduced a novel protocol to differentiate hBM-MSC into stable, cartilage-forming cells.

3D printing of skin equivalents with hair follicle structures and epidermal-papillary-dermal layers using gelatin/hyaluronic acid hydrogels

Recent advances in three-dimensional (3D) bioprinting technologies enabled the fabrication of sophisticated live 3D tissue analogs. Although various hydrogel-based bioink has been reported, the development of advanced bioink materials that can reproduce the composition of native extracellular matrix (ECM) accurately and mimic the intrinsic property of laden cells is still challenging. In this work, 3D printed skin equivalents incorporating hair follicle structures and epidermal-papillary-dermal layers are fabricated with gelatin methacryloyl (GelMA)/hyaluronic acid (HA) MA (HAMA) hydrogel (GelMA/HAMA) bioink. The composition of collagen and glycosaminoglycan (GAG) of native skin was recapitulated by adjusting the combination of GelMA and HAMA. The GelMA/HAMA bioink was proven to have excellent viscoelastic and physicochemical properties, 3D printability, cytocompatibility, and functionality to maintain the hair inductive potency and facilitated spontaneous hair pore development. Overall, we suggest that the GelMA/HAMA hydrogels can be promising candidates as bioinks for the 3D printing of skin equivalents with epidermal-papillary-dermal multi-layers and hair follicle structures, and they might serve as a useful model in skin tissue engineering and regeneration.

An Overview of Extracellular Matrix-Based Bioinks for 3D Bioprinting

As a microenvironment where cells reside, the extracellular matrix (ECM) has a complex network structure and appropriate mechanical properties to provide structural and biochemical support for the surrounding cells. In tissue engineering, the ECM and its derivatives can mitigate foreign body responses by presenting ECM molecules at the interface between materials and tissues. With the widespread application of three-dimensional (3D) bioprinting, the use of the ECM and its derivative bioinks for 3D bioprinting to replicate biomimetic and complex tissue structures has become an innovative and successful strategy in medical fields. In this review, we summarize the significance and recent progress of ECM-based biomaterials in 3D bioprinting. Then, we discuss the most relevant applications of ECM-based biomaterials in 3D bioprinting, such as tissue regeneration and cancer research. Furthermore, we present the status of ECM-based biomaterials in current research and discuss future development prospects.

A review on alginate-based bioinks, combination with other natural biomaterials and characteristics

The advent of three-dimensional (3D) Bioprinting increased the need for a suitable bioink in which Cells can live, proliferate and generate specific tissue and organ. Therefore, bioinks must have several physical and chemical characteristics that depend on the bioprinting modality and the target tissue. Alginate is considered a promising biomaterial for bioprinting due to its distinct physicochemical properties and diverse biological functions. However, some characteristics, such as cell adherence and biodegradability, are lacking, which can compensate when combined with other biomaterials, for example, gelatin, gelatin methacryloyl (GelMa), cellulose, silk fibroin, and hyaluronic acid. The alginate-gelatin blend receives considerable attention since gelatin has Arginine, Glycine, and Aspartate, the tripeptide Arg-Gly-Asp (RGD) sequence that could sustain cell attachment. Some parameters assist the optimization of bioink features like temperature, biomaterials' concentration, and crosslinking time. For instance, the viscosity of alginate increases by enhancing its concentration, and while it exhibits shear thinning property, it will be printed correctly. This review interprets the alginate-based bioink, focusing on its composite with other natural biomaterials, especially gelatin. Also, it discusses the parameters that affect bioink functionality and cell viability.

DEVELOPMENT OF FUNCTIONAL HYBRID SCAFFOLDS FOR WOUND HEALING APPLICATIONS

Hybrid hydrogels composed of chitosan (CS) and hyaluronic acid (HA) and collagen (Coll) were prepared by polyelectrolyte complex self-assembly. These scaffolds displayed a good intermingling of the polymeric chains, with porosities above 80% and good interconnected structures with pore sizes lying between 30–115 μm. The ionic interactions between CS and HA make the scaffolds have larger storage modulus and longer LVR regions than their pure counterparts. Both quantities progressively decrease as the HA and Coll concentrations in the formulation rise. These hybrid hydrogels showed good swelling extents from ca. 420 to ca. 690% and suitable resistance to enzymatic degradation, which was slightly lower for scaffolds containing CS to larger extents or Coll in the formulation. All scaffolds were largely cytocompatible and allowed the proliferation of both mouse fibroblast and human keratinocytes with their infiltration inside, thus becoming optimal matrices for intended tissue engineering applications as well as transdermal drug delivery depots.

•

Hybrid scaffolds were obtained by polyelectrolyte ionic self-assembly

•

Scaffolds were largely porous with suitable pore sizes for cell proliferation

•

Scaffolds showed exceptional swelling and good resistance to enzymatic attack

•

They were nontoxic and enabled cell proliferation and infiltration inside the scaffold

Chondroinductive/chondroconductive peptides and their-functionalized biomaterials for cartilage tissue engineering

The repair of articular cartilage defects is still challenging in the fields of orthopedics and maxillofacial surgery due to the avascular structure of articular cartilage and the limited regenerative capacity of mature chondrocytes. To provide viable treatment options, tremendous efforts have been made to develop various chondrogenically-functionalized biomaterials for cartilage tissue engineering. Peptides that are derived from and mimic the functions of chondroconductive cartilage extracellular matrix and chondroinductive growth factors, represent a unique group of bioactive agents for chondrogenic functionalization. Since they can be chemically synthesized, peptides bear better reproducibility, more stable efficacy, higher modifiability and yielding efficiency in comparison with naturally derived biomaterials and recombinant growth factors. In this review, we summarize the current knowledge in the designs of the chondroinductive/chondroconductive peptides, the underlying molecular mechanisms and their-functionalized biomaterials for cartilage tissue engineering. We also systematically compare their in-vitro and in-vivo efficacies in inducing chondrogenesis. Our vision is to stimulate the development of novel peptides and their-functionalized biomaterials for cartilage tissue engineering.

Unraveling of Advances in 3D-Printed Polymer-Based Bone Scaffolds

The repair of large-area irregular bone defects is one of the complex problems in orthopedic clinical treatment. The bone repair scaffolds currently studied include electrospun membrane, hydrogel, bone cement, 3D printed bone tissue scaffolds, etc., among which 3D printed polymer-based scaffolds Bone scaffolds are the most promising for clinical applications. This is because 3D printing is modeled based on the im-aging results of actual bone defects so that the printed scaffolds can perfectly fit the bone defect, and the printed components can be adjusted to promote Osteogenesis. This review introduces a variety of 3D printing technologies and bone healing processes, reviews previous studies on the characteristics of commonly used natural or synthetic polymers, and clinical applications of 3D printed bone tissue scaffolds, analyzes and elaborates the characteristics of ideal bone tissue scaffolds, from t he progress of 3D printing bone tissue scaffolds were summarized in many aspects. The challenges and potential prospects in this direction were discussed.

Articulation inspired by nature: A review of biomimetic and biologically active 3D printed scaffolds for cartilage tissue engineering

In the human body, articular cartilage facilitates the frictionless movement of synovial joints. However, due to its avascular and aneural nature, it has a limited ability to self-repair when damaged due to injury or wear and tear over time. Current surgical treatment options for cartilage defects often lead to the formation of fibrous, non-durable tissue and thus a new solution is required. Nature is the best innovator and so recent advances in the field of tissue engineering have aimed to recreate the microenvironment of native articular cartilage using biomaterial scaffolds. However, the inability to mirror the complexity of native tissue has hindered the clinical translation of many products thus far. Fortunately, the advent of 3D printing has provided a potential solution. 3D printed scaffolds, fabricated using biomimetic biomaterials, can be designed to mimic the complex zonal architecture and composition of articular cartilage. The bioinks used to fabricate these scaffolds can also be further functionalised with cells and/or bioactive factors or gene therapeutics to mirror the cellular composition of the native tissue. Thus, this review investigates how the architecture and composition of native articular cartilage is inspiring the design of biomimetic bioinks for 3D printing of scaffolds for cartilage repair. Subsequently, we discuss how these 3D printed scaffolds can be further functionalised with cells and bioactive factors, as well as looking at future prospects in this field.

The tissue engineering triad of biomaterials, cells and therapeutics as it applies to the formulation of biomimetic bioinks for cartilage repair. These bioinks can be functionalised with cells or cellular therapeutics to promote cartilage repair.

Hyaluronan size alters chondrogenesis of mesenchymal stem cells cultured on tricalcium phosphate-collagen-hyaluronan scaffolds

Hyaluronan (HA) provides a favorable environment for chondrogenesis of bone marrow mesenchymal stem cells (BMSCs). A previous report from our group indicated that addition of HA increases the chondro-inductive capacity of scaffolds. Therefore, this study aimed to investigate whether the Mw of the HA could affect chondrogenesis of BMSCs seeded on TCP-COL-HA scaffolds. Human BMSCs (hBMSCs) and rabbit BMSCs (rBMSCs) were isolated and expanded. TCP-COL scaffolds and TCP-COL-HA scaffolds with two different HA Mws were assessed for their capacity to induce cartilage regeneration from hBMSCs in vitro and in vivo. The results showed that about 96.96% of hBMSCs expressed CD44. Moreover, Hyal-1 and chondrogenic marker genes expressions were increased in hMSCs seeded on TCP-COL-HA scaffolds, and blocking the HA-CD44 interaction with an anti-CD44 antibody reduced the expression levels of Hyal-1 and chondrogenic marker genes. Additionally, TCP-COL-HA scaffolds with 2000 kDa Mw showed greater induction of BMSC chondrogenesis induction compared with those with 80 kDa Mw. Similar results were observed in an ectopic implantation nude mouse model. In a rabbit osteochondral defect repair model, rBMSCs seeded on TCP-COL-HA scaffolds with 2000 kDa Mw showed greater cartilage regeneration than those seeded with 80 kDa Mw. In addition, hBMSC-seeded TCP-COL-HA scaffolds with 2000 kDa Mw showed a significantly higher mechanical strength than those with 80 kDa Mw. Collectively, these results indicate that the Mw of HA could affect chondrogenesis of BMSCs seeded on TCP-COL-HA scaffolds. The TCP-COL-HA scaffolds might be used as allogenic off the shelf products in cartilage tissue engineering in future.

Collagen- and hyaluronic acid-based hydrogels and their biomedical applications

Hydrogels have been widely investigated in biomedical fields due to their similar physical and biochemical properties to the extracellular matrix (ECM). Collagen and hyaluronic acid (HA) are the main components of the ECM in many tissues. As a result, hydrogels prepared from collagen and HA hold inherent advantages in mimicking the structure and function of the native ECM. Numerous studies have focused on the development of collagen and HA hydrogels and their biomedical applications. In this extensive review, we provide a summary and analysis of the sources, features, and modifications of collagen and HA. Specifically, we highlight the fabrication, properties, and potential biomedical applications as well as promising commercialization of hydrogels based on these two natural polymers.

Protective Effects of a Hyaluronan-Binding Peptide (P15-1) on Mesenchymal Stem Cells in an Inflammatory Environment

Mesenchymal stem cells (MSCs) obtained from various sources, including bone marrow, have been proposed as a therapeutic strategy for the improvement of tissue repair/regeneration, including the repair of cartilage defects or lesions. Often the highly inflammatory environment after injury or during diseases, however, greatly diminishes the therapeutic and reparative effectiveness of MSCs. Therefore, the identification of novel factors that can protect MSCs against an inflammatory environment may enhance the effectiveness of these cells in repairing tissues, such as articular cartilage. In this study, we investigated whether a peptide (P15-1) that binds to hyaluronan (HA), a major component of the extracellular matrix of cartilage, protects bone-marrow-derived MSCs (BMSCs) in an inflammatory environment. The results showed that P15-1 reduced the mRNA levels of catabolic and inflammatory markers in interleukin-1beta (IL-1β)-treated human BMSCs. In addition, P15-1 enhanced the attachment of BMSCs to HA-coated tissue culture dishes and stimulated the chondrogenic differentiation of the multipotential murine C3H/10T1/2 MSC line in a micromass culture. In conclusion, our findings suggest that P15-1 may increase the capacity of BMSCs to repair cartilage via the protection of these cells in an inflammatory environment and the stimulation of their attachment to an HA-containing matrix and chondrogenic differentiation.

Hyaluronan and the Fascial Frontier

The buzz about hyaluronan (HA) is real. Whether found in face cream to increase water volume loss and viscoelasticity or injected into the knee to restore the properties of synovial fluid, the impact of HA can be recognized in many disciplines from dermatology to orthopedics. HA is the most abundant polysaccharide of the extracellular matrix of connective tissues. HA can impact cell behavior in specific ways by binding cellular HA receptors, which can influence signals that facilitate cell survival, proliferation, adhesion, as well as migration. Characteristics of HA, such as its abundance in a variety of tissues and its responsiveness to chemical, mechanical and hormonal modifications, has made HA an attractive molecule for a wide range of applications. Despite being discovered over 80 years ago, its properties within the world of fascia have only recently received attention. Our fascial system penetrates and envelopes all organs, muscles, bones and nerve fibers, providing the body with a functional structure and an environment that enables all bodily systems to operate in an integrated manner. Recognized interactions between cells and their HA-rich extracellular microenvironment support the importance of studying the relationship between HA and the body’s fascial system. From fasciacytes to chronic pain, this review aims to highlight the connections between HA and fascial health.

Simvastatin Enhances the Chondrogenesis But Not the Osteogenesis of Adipose-Derived Stem Cells in a Hyaluronan Microenvironment

Directing adipose-derived stem cells (ADSCs) toward chondrogenesis is critical for ADSC-based articular cartilage regeneration. Simvastatin (SIM) was reported to promote both chondrogenic and osteogenic differentiation of ADSCs by upregulating bone morphogenetic protein-2 (BMP-2). We previously found that ADSC chondrogenesis is initiated and promoted in a hyaluronan (HA) microenvironment (HAM). Here, we further hypothesized that SIM augments HAM-induced chondrogenesis but not osteogenesis of ADSCs. ADSCs were treated with SIM in a HAM (SIM plus HAM) by HA-coated wells or HA-enriched fibrin (HA/Fibrin) hydrogel, and chondrogenic differentiation of ADSCs was evaluated. SIM plus HAM increased chondrogenesis more than HAM or SIM alone, including cell aggregation, chondrogenic gene expression (collagen type II and aggrecan) and cartilaginous tissue formation (collagen type II and sulfated glycosaminoglycan). In contrast, SIM-induced osteogenesis in ADSCs was reduced in SIM plus HAM, including mRNA expression of osteogenic genes, osteocalcin and alkaline phosphatase (ALP), ALP activity and mineralization. SIM plus HAM also showed the most effective increases in the mRNA expression of BMP-2 and transcription factors of SOX-9 and RUNX-2 in ADSCs, while these effects were reversed by CD44 blockade. HAM suppressed the levels of JNK, p-JNK, P38 and p-P38 in ADSCs, and SIM plus HAM also decreased SIM-induced phosphorylated JNK and p38 levels. In addition, SIM enhanced articular cartilage regeneration, as demonstrated by implantation of an ADSCs/HA/Fibrin construct in an ex vivo porcine articular chondral defect model. The results from this study indicate that SIM may be an enhancer of HAM-initiated MSC-based chondrogenesis and avoid osteogenesis.

Narrative review of the choices of stem cell sources and hydrogels for cartilage tissue engineering

Stem cell-based therapy is a promising treatment for cartilage defects due to the pluripotency, abundant sources and low immunogenicity of stem cells. Hydrogels are a promising class of biomaterials for cartilage engineering and are characterized by bioactivity, degradability and elasticity as well as provide water content and mechanical support. The combination of stem cells and hydrogels opens new possibilities for cartilage tissue engineering. However, the selection of suitable types of stem cells and hydrogels is difficult. Currently, various types of stem cells, such as embryonic stem cells (ESCs), mesenchymal stem cells (MSCs), induced pluripotent stem cells (iPSCs), and peripheral blood mononuclear cells (PBMSCs), and various types of hydrogels, including natural polymers, chemically modified natural polymers and synthetic polymers, have been explored based on their potential for cartilage tissue engineering. These materials are used independently or in combination; however, there is no clear understanding of their merits and disadvantages with regard to their suitability for cartilage repair. In this article, we aim to review recent progress in the use of stem cell-hydrogel hybrid constructs for cartilage tissue engineering. We focus on the effects of stem cell types and hydrogel types on efficient chondrogenesis from cellular, preclinical and clinical perspectives. We compare and analyze the advantages and disadvantages of these cells and hydrogels with the hope of increasing discussion of their suitability for cartilage repair and present our perspective on their use for the improvement of physical and biological properties for cartilage tissue engineering.

Activated hyaluronic acid/collagen composite hydrogel with tunable physical properties and improved biological properties

Self-crosslinkable and injectable hydrogels were fabricated with collagen type I (Col I) and N-hydroxy sulfosuccinimide activated hyaluronic acid (HA-sNHS) at physiological conditions without any initiators or crosslinkers. The physical properties of hydrogels, such as gelation time, swelling property, degradation property and mechanical property could be regulated by adjusting the substitution degree (DS) of HA-sNHS. Chondrocytes were encapsulated into hydrogels and their proliferation, phenotype maintenance and matrix secretion were characterized. The results demonstrated that chondrocytes in hydrogel Col I/HA-sNHS32% in which the DS of HA-sNHS was 32% secreted more cartilage specific matrix than others. The results of animal experiment demonstrated that hydrogels Col I and Col I/HA-sNHS32% both had good biodegradability and cytocompatibility. This study provided a novel and simple method for fabrication of self-crosslinkable and injectable hydrogels with tunable physical properties. It implied that these hydrogels could find some applications in the fields of cell encapsulation and tissue engineering.

Evaluation of Glycerylphytate Crosslinked Semi- and Interpenetrated Polymer Membranes of Hyaluronic Acid and Chitosan for Tissue Engineering

In the present study, semi- and interpenetrated polymer network (IPN) systems based on hyaluronic acid (HA) and chitosan using ionic crosslinking of chitosan with a bioactive crosslinker, glycerylphytate (G1Phy), and UV irradiation of methacrylate were developed, characterized and evaluated as potential supports for tissue engineering. Semi- and IPN systems showed significant differences between them regarding composition, morphology, and mechanical properties after physicochemical characterization. Dual crosslinking process of IPN systems enhanced HA retention and mechanical properties, providing also flatter and denser surfaces in comparison to semi-IPN membranes. The biological performance was evaluated on primary human mesenchymal stem cells (hMSCs) and the systems revealed no cytotoxic effect. The excellent biocompatibility of the systems was demonstrated by large spreading areas of hMSCs on hydrogel membrane surfaces. Cell proliferation increased over time for all the systems, being significantly enhanced in the semi-IPN, which suggested that these polymeric membranes could be proposed as an effective promoter system of tissue repair. In this sense, the developed crosslinked biomimetic and biodegradable membranes can provide a stable and amenable environment for hMSCs support and growth with potential applications in the biomedical field.

The tissues and regulatory pattern of limb chondrogenesis

Initial limb chondrogenesis offers the first differentiated tissues that resemble the mature skeletal anatomy. It is a developmental progression of three tissues. The limb begins with undifferentiated mesenchyme-1, some of which differentiates into condensations-2, and this tissue then transforms into cartilage-3. Each tissue is identified by physical characteristics of cell density, shape, and extracellular matrix composition. Tissue specific regimes of gene regulation underlie the diagnostic physical and chemical properties of these three tissues. These three tissue based regimes co-exist amid a background of other gene regulatory regimes within the same tissues and time-frame of limb development. The bio-molecular indicators of gene regulation reveal six identifiable patterns. Three of these patterns describe the unique bio-molecular indicators of each of the three tissues. A fourth pattern shares bio-molecular indicators between condensation and cartilage. Finally, a fifth pattern is composed of bio-molecular indicators that are found in undifferentiated mesenchyme prior to any condensation differentiation, then these bio-molecular indicators are upregulated in condensations and downregulated in undifferentiated mesenchyme. The undifferentiated mesenchyme that remains in between the condensations and cartilage, the interdigit, contains a unique set of bio-molecular indicators that exhibit dynamic behaviour during chondrogenesis and therefore argue for its own inclusion as a tissue in its own right and for more study into this process of differentiation.

Cartilage Tissue-Mimetic Pellets with Multifunctional Magnetic Hyaluronic Acid-Graft-Amphiphilic Gelatin Microcapsules for Chondrogenic Stimulation

Articular cartilage defect is a common disorder caused by sustained mechanical stress. Owing to its nature of avascular, cartilage had less reconstruction ability so there is always a need for other repair strategies. In this study, we proposed tissue-mimetic pellets composed of chondrocytes and hyaluronic acid-graft-amphiphilic gelatin microcapsules (HA-AGMCs) to serve as biomimetic chondrocyte extracellular matrix (ECM) environments. The multifunctional HA-AGMC with specific targeting on CD44 receptors provides excellent structural stability and demonstrates high cell viability even in the center of pellets after 14 days culture. Furthermore, with superparamagnetic iron oxide nanoparticles (SPIOs) in the microcapsule shell of HA-AGMCs, it not only showed sound cell guiding ability but also induced two physical stimulations of static magnetic field(S) and magnet-derived shear stress (MF) on chondrogenic regeneration. Cartilage tissue-specific gene expressions of Col II and SOX9 were upregulated in the present of HA-AGMC in the early stage, and HA-AGMC+MF+S held the highest chondrogenic commitments throughout the study. Additionally, cartilage tissue-mimetic pellets with magnetic stimulation can stimulate chondrogenesis and sGAG synthesis.

Bio-inspired hydrogel composed of hyaluronic acid and alginate as a potential bioink for 3D bioprinting of articular cartilage engineering constructs

Bioprinting is a promising tool to fabricate well-organized cell-laden constructs for repair and regeneration of articular cartilage. The selection of a suitable bioink, in terms of composition and mechanical properties, is crucial for the development of viable cartilage substitutes. In this study, we focused on the use of one of the main cartilage components, hyaluronic acid (HA), to design and formulate a new bioink for cartilage tissue 3D bioprinting. Major characteristics required for this application such as printability, biocompatibility, and biodegradability were analyzed. To produce cartilage constructs with optimal mechanical properties, HA-based bioink was co-printed with polylactic acid (PLA). HA-based bioink was found to improve cell functionality by an increase in the expression of chondrogenic gene markers and specific matrix deposition and, therefore, tissue formation. These results indicate that it is a promising bioink candidate for cartilage tissue engineering based in 3D bioprinting. STATEMENT OF SIGNIFICANCE: The recent appearance of 3D printing technology has enabled great advances in the treatment of osteochondral disorders by fabrication of cartilage tissue constructs that restore and/or regenerate damaged tissue. In this attempt, the selection of a suitable biomaterial, in terms of composition and mechanical properties, is crucial. In this study, we describe for first time the development of a bioink based on the main component of cartilage, HA, with suitable biological and mechanical properties, without involving toxic procedure, and its application  in cartilage tissue bioprinting. Hybrid constructs prepared by co-printing  this  bioink and thermoplastic polymer PLA provided an optimal niche for chondrocyte growth and maintenance as well as mechanical properties necessary to support load forces exerted in native tissue. We highlight the translation potential of this HA-based bioink in the clinical arena.

Effect of CD44 on differentiation of human amniotic mesenchymal stem cells into chondrocytes via Smad and ERK signaling pathways

CD44 antigen (CD44) is a transmembrane protein found in cell adhesion molecules and is involved in the regulation of various physiological processes in cells. It was hypothesized that CD44 directly affected the chondrogenic differentiation of human amniotic mesenchymal stem cells (hAMSCs). In the present study, the expression of chondrocyte-associated factors was detected in the absence and presence of the antibody blocker anti-CD44 antibody during the chondrogenic differentiation of hAMSCs. Following inhibition of CD44 expression, the transcriptional levels of chondrocyte-associated genes SRY-box transcription factor 9, aggrecan and collagen type II α 1 chain, as well as the production of chondrocyte markers type II collagen and aggrecan were significantly decreased in hAMSCs. Further investigation indicated that there was no significant change in total ERK1/2 expression following inhibition of CD44 expression; however, phosphorylated (p)-ERK1/2 expression was decreased. The expression of p-Smad2/3 was also upregulated following CD44 inhibition. These data indicated that CD44 may affect the differentiation of hAMSCs into chondrocytes by regulating the Smad2/3 and ERK1/2 signaling pathway.

Injectable dual cross-linked adhesive hyaluronic acid multifunctional hydrogel scaffolds for potential applications in cartilage repair

A double crosslinked hydrogels was designed and prepared by combining the Diels–Alder click reaction and possessed good mechanical strength, injectability and adhesion.

Frequency of CD44 positive cells in MKN45 cell line after treatment with docetaxel in two and three-dimensional cell cultures

Three-dimensional (3D) cell culture is more similar to in vivo studies and suitable for studies of interactions between cells and extracellular matrix. CD44 is a cell surface receptor that can relate with the extracellular matrix molecules. CD44 in gastric cancer (GC) is a metastatic and drug resistance marker. In this study the quantity of CD44⁺ cells in MKN-45 cell line in response to half maximal inhibitory concentration (IC₅₀) dose of Docetaxel (DOC) was measured in 2D and 3D cultures. MKN-45 cell line was cultured in 2D and 3D environments. For 3D culture, rat gastric tissue was separated and decellularized and MKN-45 cells were injected and cultured in the prepared matrix. The frequency of CD44⁺ cells in 2D and 3D cultures were analyzed before and after treatment with IC₅₀ of DOC by flow cytometry and immunohistochemistry. Despite different environmental conditions, The frequency of CD44⁺ cells increased significantly in 2D and 3D environments after treatment with IC₅₀ of DOC (P < 0.05). Given the advantages of 3D, this environment seems more appropriate for study about CD44⁺ cells and drug resistance in GC.

Hyaluronic acid as a macromolecular crowding agent for production of cell-derived matrices

Cell-derived matrices (CDMs) provide an exogenous source of human extracellular matrix (ECM), with applications as cell delivery vehicles, substrate coatings for cell attachment and differentiation, and as biomaterial scaffolds. However, commercial application of CDMs has been hindered due to the prolonged culture time required for sufficient ECM accumulation. One approach to increasing matrix deposition in vitro is macromolecular crowding (MMC), which is a biophysical phenomenon that limits the diffusion of ECM precursor proteins, resulting in increased ECM accumulation at the cell layer. Hyaluronic acid (HA), a natural MMC highly expressed in vivo during fetal development, has been shown to play a role in ECM production, but has not been investigated as a macromolecule for increasing cell-mediated ECM deposition in vitro. In the current study, we hypothesized that HA can act as a MMC, and increase cell-mediated ECM production. Human dermal fibroblasts were cultured for 3, 7, or 14 days with 0%, 0.05%, or 0.5% high molecular weight HA. Ficoll 70/400 was used as a positive control. SDS-PAGE, Sircol, and hydroxyproline assays indicated that 0.05% HA-treated cultures had significantly higher mean collagen deposition at 14 days, whereas Ficoll 70/400-treated cultures had significantly lower collagen production compared to the HA and untreated controls. However, fluorescent immunostaining of ECM proteins and quantification of mean gray values did not indicate statistically significant differences in ECM production in HA or Ficoll 70/400-treated cultures compared to untreated controls. Raman imaging (a marker-free spectral imaging method) indicated that HA increased ECM deposition in human dermal fibroblasts. These results are consistent with decreases in CDM stiffness observed in Ficoll 70/400-treated cultures by atomic force microscopy. Overall, these results indicate that there are macromolecule- and cell type- dependent effects on matrix assembly, turnover, and stiffness in cell-derived matrices. STATEMENT OF SIGNIFICANCE: Cell-derived matrices (CDMs) are versatile biomaterials with many regenerative medicine applications, including as cell and drug delivery vehicles and scaffolds for wound healing and tissue regeneration. While CDMs have several advantages, their commercialization has been limited due to the prolonged culture time required to achieve CDM synthesis in vitro. In this study, we explored the use of hyaluronic acid (HA) as a macromolecular crowder in human fibroblast cell cultures to support production of CDM biomaterials. Successful application of macromolecular crowding will allow development of human cell-derived, xeno-free biomaterials that re-capitulate the native human tissue microenvironment.

Prechondrogenic ATDC5 Cell Attachment and Differentiation on Graphene Foam; Modulation by Surface Functionalization with Fibronectin

Graphene foam holds promise for tissue engineering applications. In this study, graphene foam was used as a three-dimension scaffold to evaluate cell attachment, cell morphology, and molecular markers of early differentiation. The aim of this study was to determine if cell attachment and elaboration of an extracellular matrix would be modulated by functionalization of graphene foam with fibronectin, an extracellular matrix protein that cells adhere well to, prior to the establishment of three-dimensional cell culture. The molecular dynamic simulation demonstrated that the fibronectin-graphene interaction was stabilized predominantly through interaction between the graphene and arginine side chains of the protein. Quasi-static and dynamic mechanical testing indicated that fibronectin functionalization of graphene altered the mechanical properties of graphene foam. The elastic strength of the scaffold increased due to fibronectin, but the viscoelastic mechanical behavior remained unchanged. An additive effect was observed in the mechanical stiffness when the graphene foam was both coated with fibronectin and cultured with cells for 28 days. Cytoskeletal organization assessed by fluorescence microscopy demonstrated a fibronectin-dependent reorganization of the actin cytoskeleton and an increase in actin stress fibers. Gene expression assessed by quantitative real-time polymerase chain reaction of 9 genes encoding cell attachment proteins (Cd44, Ctnna1, Ctnnb1, Itga3, Itga5, Itgav, Itgb1, Ncam1, Sgce), 16 genes encoding extracellular matrix proteins (Col1a1, Col2a1, Col3a1, Col5a1, Col6a1, Ecm1, Emilin1, Fn1, Hapln1, Lamb3, Postn, Sparc, Spp1, Thbs1, Thbs2, Tnc), and 9 genes encoding modulators of remodeling (Adamts1, Adamts2, Ctgf, Mmp14, Mmp2, Tgfbi, Timp1, Timp2, Timp3) indicated that graphene foam provided a microenvironment conducive to expression of genes that are important in early chondrogenesis. Functionalization of graphene foam with fibronectin modified the cellular response to graphene foam, demonstrated by decreases in relative gene expression levels. These findings illustrate the combinatorial factors of microscale materials properties and nanoscale molecular features to consider in the design of three-dimensional graphene scaffolds for tissue engineering applications.

Induction of Articular Chondrogenesis by Chitosan/Hyaluronic-Acid-Based Biomimetic Matrices Using Human Adipose-Derived Stem Cells

Cartilage repair using tissue engineering is the most advanced clinical application in regenerative medicine, yet available solutions remain unsuccessful in reconstructing native cartilage in its proprietary form and function. Previous investigations have suggested that the combination of specific bioactive elements combined with a natural polymer could generate carrier matrices that enhance activities of seeded stem cells and possibly induce the desired matrix formation. The present study sought to clarify this by assessing whether a chitosan-hyaluronic-acid-based biomimetic matrix in conjunction with adipose-derived stem cells could support articular hyaline cartilage formation in relation to a standard chitosan-based construct. By assessing cellular development, matrix formation, and key gene/protein expressions during in vitro cultivation utilizing quantitative gene and immunofluorescent assays, results showed that chitosan with hyaluronic acid provides a suitable environment that supports stem cell differentiation towards cartilage matrix producing chondrocytes. However, on the molecular gene expression level, it has become apparent that, without combinations of morphogens, in the chondrogenic medium, hyaluronic acid with chitosan has a very limited capacity to stimulate and maintain stem cells in an articular chondrogenic state, suggesting that cocktails of various growth factors are one of the key features to regenerate articular cartilage, clinically.

Influence of hyaluronic acid modification on CD44 binding towards the design of hydrogel biomaterials

Hyaluronic acid (HA) is a linear polysaccharide of d-glucuronic acid and N-acetyl-d-glucosamine that is native to many tissues and interacts with cells via cell-surface receptors (e.g., CD44). HA has been extensively explored as a chemically-modified macromer for crosslinking into biomaterials, such as hydrogels and macroporous scaffolds. However, the influence of the extent and type of HA modification on its binding to CD44 is not well understood or quantified. To address this, we modified HA at either the carboxylic acid or the primary alcohol with various chemical groups (e.g., norbornenes, methacrylates) and magnitudes (~10, 20, or 40% of disaccharides) and then characterized binding in both soluble and hydrogel forms. HA binding to CD44 immobilized on plates or presented by cells was influenced by the extent and type of its modification, where increased modification (i.e., ~40%) generally decreased binding. The adhesion of CD44-modified beads to hydrogels as measured by atomic force microscopy revealed a similar trend, particularly with decreased adhesion with hydrophobic modifications to the carboxylic acid. Further, the chondrogenesis of mesenchymal stromal cells when encapsulated in hydrogels fabricated from modified HA macromers was reduced at high modification, behaving similarly to inert hydrogel controls. This work suggests that the types and extents of modification of polysaccharides are important factors that should be considered in preserving their biological function when processed as hydrogels.

In Vitro Analysis of the Differentiation Capacity of Postmortally Isolated Human Chondrocytes Influenced by Different Growth Factors and Oxygen Levels

OBJECTIVE

In the present in vitro study, we analyzed the chondrogenic differentiation capacity of human chondrocytes postmortally isolated from unaffected knee cartilage by the addition of transforming growth factor-β1 (TGF-β1) and/or insulin-like growth factor-1 (IGF-1) and different oxygen levels.

DESIGN

After 14 and 35 days, DNA concentrations and protein contents of Col1, Col2, aggrecan as well as glycosaminoglycans (GAGs) of chondrocytes cultivated as pellet cultures were analyzed. Additionally, expression rates of mesenchymal stem cell (MSC)-associated differentiation markers were assessed in monolayer cultures.

RESULTS

All cultivated chondrocytes were found to be CD29⁺/CD44⁺/CD105⁺/CD166⁺. Chondrocytic pellets stimulated with TGF-β1 showed enhanced synthesis rates of hyaline cartilage markers and reduced expression of the non-hyaline cartilage marker Col1 under hypoxic culture conditions.

CONCLUSIONS

Our results underline the substantial chondrogenic potential of human chondrocytes postmortally isolated from unaffected articular knee cartilage especially in case of TGF-β1 administration.

Biofabrication of human articular cartilage: a path towards the development of a clinical treatment

Cartilage injuries cause pain and loss of function, and if severe may result in osteoarthritis (OA). 3D bioprinting is now a tangible option for the delivery of bioscaffolds capable of regenerating the deficient cartilage tissue. Our team has developed a handheld device, the Biopen, to allow in situ additive manufacturing during surgery. Given its ability to extrude in a core/shell manner, the Biopen can preserve cell viability during the biofabrication process, and it is currently the only biofabrication tool tested as a surgical instrument in a sheep model using homologous stem cells. As a necessary step toward the development of a clinically relevant protocol, we aimed to demonstrate that our handheld extrusion device can successfully be used for the biofabrication of human cartilage. Therefore, this study is a required step for the development of a surgical treatment in human patients. In this work we specifically used human adipose derived mesenchymal stem cells (hADSCs), harvested from the infra-patellar fat pad of donor patients affected by OA, to also prove that they can be utilized as the source of cells for the future clinical application. With the Biopen, we generated bioscaffolds made of hADSCs laden in gelatin methacrylate, hyaluronic acid methacrylate and cultured in the presence of chondrogenic stimuli for eight weeks in vitro. A comprehensive characterisation including gene and protein expression analyses, immunohistology, confocal microscopy, second harmonic generation, light sheet imaging, atomic force mycroscopy and mechanical unconfined compression demonstrated that our strategy resulted in human hyaline-like cartilage formation. Our in situ biofabrication approach represents an innovation with important implications for customizing cartilage repair in patients with cartilage injuries and OA.

Hyaluronic acid, CD44 and RHAMM regulate myoblast behavior during embryogenesis

Hyaluronic acid (HA) is an extracellular matrix (ECM) component that has been shown to play a significant role in regulating muscle cell behavior during repair and regeneration. For instance, ECM remodeling after muscle injury involves an upregulation in HA expression that is coupled with skeletal muscle precursor cell recruitment. However, little is known about the role of HA during skeletal muscle development. To gain insight into the way in which HA mediates embryonic myogenesis, we first determined the spatial distribution and gene expression of CD44, RHAMM and other HA related proteins in embryonic day (E)10.5 to E12.5 murine forelimbs. While HA and CD44 expression remained high, RHAMM decreased at both the protein (via immunohistochemistry) and RNA (via qPCR) levels. Next, we determined that 4-methylumbelliferone-mediated knockdown of HA synthesis inhibited the migration and proliferation of E11.5/E12.5 forelimb-derived cells. Then, the influence of CD44 and RHAMM on myoblast and connective tissue cell behavior was investigated using antibodies against these receptors. Anti-RHAMM, but not anti-CD44, significantly decreased the total distance myogenic progenitors migrated over 24 h, whereas both inhibited connective tissue cell migration. In contrast, anti-CD44 inhibited the proliferation of connective tissue cells and muscle progenitors, but anti-RHAMM had no effect. However, when myoblasts and connective tissue cells were depleted of CD44 and RHAMM by shRNA, motility and proliferation were significantly inhibited in both cells indicating that blocking cell surface-localized CD44 and RHAMM does not have as pronounced effect as global shRNA-mediated depletion of these receptors. These results show, for the first time, the distribution and activity of RHAMM in the context of skeletal muscle. Furthermore, our data indicate that HA, through interactions with CD44 and RHAMM, promotes myogenic progenitor migration and proliferation. Confirmation of the role of HA and its receptors in directing myogenesis will be useful for the design of regenerative therapies that aim to promote the restoration of damaged or diseased muscle.

Dose and Timing of N-Cadherin Mimetic Peptides Regulate MSC Chondrogenesis within Hydrogels

The transmembrane glycoprotein N-cadherin (NCad) mediates cell-cell interactions found during mesenchymal condensation and chondrogenesis. Here, NCad-derived peptides (i.e., HAV) are incorporated into hyaluronic acid (HA) hydrogels with encapsulated mesenchymal stem cells (MSCs). Since the dose and timing of NCad signaling are dynamic, HAV peptide presentation is tuned via alterations in peptide concentration and incorporation of an ADAM10-cleavable domain between the hydrogel and the HAV motif, respectively. HA hydrogels functionalized with HAV result in dose-dependent increases in early chondrogenesis of encapsulated MSCs and resultant cartilage matrix production. For example, type II collagen and glycosaminoglycan production increase ≈9- and 2-fold with the highest dose of HAV (i.e., 2 × 10^-3 m), respectively, when compared to unmodified hydrogels, while incorporation of an efficient ADAM10-cleavable domain between the HAV peptide and hydrogel abolishes increases in chondrogenesis and matrix production. Treatment with a small-molecule ADAM10 inhibitor restores the functional effect of the HAV peptide, indicating that timing and duration of HAV peptide presentation is crucial for robust chondrogenesis. This study demonstrates a nuanced approach to the biofunctionalization of hydrogels to better emulate the complex cell microenvironment during embryogenesis toward stem-cell-based cartilage production.

Regulation of hyaluronan biosynthesis and clinical impact of excessive hyaluronan production

The tightly regulated biosynthesis and catabolism of the glycosaminoglycan hyaluronan, as well as its role in organizing tissues and cell signaling, is crucial for the homeostasis of tissues. Overexpression of hyaluronan plays pivotal roles in inflammation and cancer, and markedly high serum and tissue levels of hyaluronan are noted under such pathological conditions. This review focuses on the complexity of the regulation at transcriptional and posttranslational level of hyaluronan synthetic enzymes, and the outcome of their aberrant expression and accumulation of hyaluronan in clinical conditions, such as systemic B-cell cancers, aggressive breast carcinomas, metabolic diseases and virus infection.

Hyaluronan size alters chondrogenesis of adipose-derived stem cells via the CD44/ERK/SOX-9 pathway

Hyaluronan (HA) is a natural linear polymer that is one of the main types of extracellular matrix during the early stage of chondrogenesis. We found that the chondrogenesis of adipose-derived stem cells (ADSCs) can be initiated and promoted by the application of HA to mimic the chondrogenic niche. The aim of this study is to investigate the optimal HA molecular weight (Mw) for chondrogenesis of ADSCs and the detailed mechanism. In this study, we investigated the relationships among HA Mw, CD44 clustering, and the extracellular signal-regulated kinase (ERK)/SOX-9 pathway during chondrogenesis of ADSCs. Human ADSCs (hADSCs) and rabbit ADSCs (rADSCs) were isolated and expanded. Chondrogenesis was induced in rADSCs by culturing cells in HA-coated wells (HA Mw: 80 kDa, 600 kDa and 2000 kDa) and evaluated by examining cell aggregation, chondrogenic gene expression (collagen type II and aggrecan) and sulfated glycosaminoglycan (sGAG) deposition in vitro. Cartilaginous tissue formation in vivo was confirmed by implanting HA/rADSCs into joint cavities. CD44 clustering, ERK phosphorylation, SOX-9 expression and SOX-9 phosphorylation in cultured hADSCs were further evaluated. Isolated and expanded rADSCs showed multilineage potential and anchorage-independent growth properties. Cell aggregation, chondrogenic gene expression, and sGAG deposition increased with increasing HA Mw in rADSCs. The 2000 kDa HA had the most pronounced chondrogenic effect on rADSCs in vitro, and implanted 2000 kDa HA/rADSCs exhibited marked cartilaginous tissue formation in vivo. CD44 clustering and cell aggregation of hADSCs were enhanced by an increase in HA Mw. In addition, higher HA Mws further enhanced CD44 clustering, ERK phosphorylation, and SOX-9 expression and phosphorylation in hADSCs. Inhibiting CD44 clustering in hADSCs reduced HA-induced chondrogenic gene expression. Inhibiting ERK phosphorylation also simultaneously attenuated HA-induced SOX-9 expression and phosphorylation and chondrogenic gene expression in hADSCs. Our results indicate that HA initiates ADSC chondrogenesis and that higher Mw HAs exhibit stronger effects, with 2000 kDa HA having the strongest effect. These effects may be mediated through increased CD44 clustering and the ERK/SOX-9 signaling pathway.

STATEMENT OF SIGNIFICANCE

HA-based biomaterials have been studied in stem cell-based articular cartilage tissue engineering. However, little is known about the optimal HA size for stem cell chondrogenesis and the mechanism of how HA size modulates stem cell chondrogenesis. Accordingly, we used HAs with various Mws (80-2000 kDa) as culture substrates and tested their chondrogenic effect on ADSCs. Our results demonstrated that HAs with a Mw of 2000 kDa showed the optimal effect for chondrogenesis of ADSCs. Moreover, we found that HA size can regulate ADSC chondrogenesis via the CD44/ERK/SOX-9 pathway. This finding provides new information regarding the biochemical control of chondrogenesis by HA substrates that may add value to the development of HA-based biomaterials for articular cartilage regeneration.

Establishing Early Functional Perfusion and Structure in Tissue Engineered Cardiac Constructs

Myocardial infarction (MI) causes massive heart muscle death and remains a leading cause of death in the world. Cardiac tissue engineering aims to replace the infarcted tissues with functional engineered heart muscles or revitalize the infarcted heart by delivering cells, bioactive factors, and/or biomaterials. One major challenge of cardiac tissue engineering and regeneration is the establishment of functional perfusion and structure to achieve timely angiogenesis and effective vascularization, which are essential to the survival of thick implants and the integration of repaired tissue with host heart. In this paper, we review four major approaches to promoting angiogenesis and vascularization in cardiac tissue engineering and regeneration: delivery of pro-angiogenic factors/molecules, direct cell implantation/cell sheet grafting, fabrication of prevascularized cardiac constructs, and the use of bioreactors to promote angiogenesis and vascularization. We further provide a detailed review and discussion on the early perfusion design in nature-derived biomaterials, synthetic biodegradable polymers, tissue-derived acellular scaffolds/whole hearts, and hydrogel derived from extracellular matrix. A better understanding of the current approaches and their advantages, limitations, and hurdles could be useful for developing better materials for future clinical applications.

Human Periodontal Ligament- and Gingiva-derived Mesenchymal Stem Cells Promote Nerve Regeneration When Encapsulated in Alginate/Hyaluronic Acid 3D Scaffold

Repair or regeneration of damaged nerves is still a challenging clinical task in reconstructive surgeries and regenerative medicine. Here, it is demonstrated that periodontal ligament stem cells (PDLSCs) and gingival mesenchymal stem cells (GMSCs) isolated from adult human periodontal and gingival tissues assume neuronal phenotype in vitro and in vivo via a subcutaneous transplantation model in nude mice. PDLSCs and GMSCs are encapsulated in a 3D scaffold based on alginate and hyaluronic acid hydrogels capable of sustained release of human nerve growth factor (NGF). The elasticity of the hydrogels affects the proliferation and differentiation of encapsulated MSCs within scaffolds. Moreover, it is observed that PDLSCs and GMSCs are stained positive for βIII-tubulin, while exhibiting high levels of gene expression related to neurogenic differentiation (βIII-tubulin and glial fibrillary acidic protein) via quantitative polymerase chain reaction (qPCR). Western blot analysis shows the importance of elasticity of the matrix and the presence of NGF in the neurogenic differentiation of encapsulated MSCs. In vivo, immunofluorescence staining for neurogenic specific protein markers confirms islands of dense positively stained structures inside transplanted hydrogels. As far as it is known, this study is the first demonstration of the application of PDLSCs and GMSCs as promising cell therapy candidates for nerve regeneration.

Alginate/hyaluronic acid hydrogel delivery system characteristics regulate the differentiation of periodontal ligament stem cells toward chondrogenic lineage

Cartilage tissue regeneration often presents a challenging clinical situation. Recently, it has been shown that Periodontal Ligament Stem Cells (PDLSCs) possess high chondrogenic differentiation capacity. In this study, we developed a stem cell delivery system based on alginate/hyaluronic acid (HA) loaded with TGF-β1 ligand, encapsulating PDLSCs; and investigated the chondrogenic differentiation of encapsulated cells in alginate/HA hydrogel microspheres in vitro and in vivo. The results showed that PDLSCs, as well as human bone marrow mesenchymal stem cells (hBMMSCs), as the positive control, were stained positive for both toluidine blue and alcian blue staining, while exhibiting high levels of gene expression related to chondrogenesis (Col II, Aggrecan and Sox-9), as assessed via qPCR. The quantitative PCR analyses exhibited that the chondrogenic differentiation of encapsulated MSCs can be regulated by the modulus of elasticity of hydrogel delivery system, confirming the vital role of the microenvironment, and the presence of inductive signals for viability and differentiation of MSCs. In vivo, histological and immunofluorescence staining for chondrogenic specific protein markers confirmed ectopic cartilage-like tissue regeneration inside transplanted hydrogels. PDLSCs presented significantly greater capability for chondrogenic differentiation than hBMMSCs (P < 0.05). Altogether, our findings confirmed that alginate/HA hydrogels encapsulating PDLSCs are a promising candidate for cartilage regeneration.