Design and Characterization of an Injectable Tendon Hydrogel: A Novel Scaffold for Guided Tissue Regeneration in the Musculoskeletal System

Human-Derived collagen hydrogel as an antibiotic vehicle for topical treatment of bacterial biofilms

The complexity of chronic wounds creates difficulty in effective treatments, leading to prolonged care and significant morbidity. Additionally, these wounds are incredibly prone to bacterial biofilm development, further complicating treatment. The current standard treatment of colonized superficial wounds, debridement with intermittent systemic antibiotics, can lead to systemic side-effects and often fails to directly target the bacterial biofilm. Furthermore, standard of care dressings do not directly provide adequate antimicrobial properties. This study aims to assess the capacity of human-derived collagen hydrogel to provide sustained antibiotic release to disrupt bacterial biofilms and decrease bacterial load while maintaining host cell viability and scaffold integrity. Human collagen harvested from flexor tendons underwent processing to yield a gellable liquid, and subsequently was combined with varying concentrations of gentamicin (50-500 mg/L) or clindamycin (10-100 mg/L). The elution kinetics of antibiotics from the hydrogel were analyzed using liquid chromatography-mass spectrometry. The gel was used to topically treat Methicillin-resistant Staphylococcus aureus (MRSA) and Clostridium perfringens in established Kirby-Bauer and Crystal Violet models to assess the efficacy of bacterial inhibition. 2D mammalian cell monolayers were topically treated, and cell death was quantified to assess cytotoxicity. Bacteria-enhanced in vitro scratch assays were treated with antibiotic-embedded hydrogel and imaged over time to assess cell death and mobility. Collagen hydrogel embedded with antibiotics (cHG+abx) demonstrated sustained antibiotic release for up to 48 hours with successful inhibition of both MRSA and C. perfringens biofilms, while remaining bioactive up to 72 hours. Administration of cHG+abx with antibiotic concentrations up to 100X minimum inhibitory concentration was found to be non-toxic and facilitated mammalian cell migration in an in vitro scratch model. Collagen hydrogel is a promising pharmaceutical delivery vehicle that allows for safe, precise bacterial targeting for effective bacterial inhibition in a pro-regenerative scaffold.

Decellularization and Their Significance for Tissue Regeneration in the Era of 3D Bioprinting

Three-dimensional bioprinting is an emerging technology that has high potential application in tissue engineering and regenerative medicine. Increasing advancement and improvement in the decellularization process have led to an increase in the demand for using a decellularized extracellular matrix (dECM) to fabricate tissue engineered products. Decellularization is the process of retaining the extracellular matrix (ECM) while the cellular components are completely removed to harvest the ECM for the regeneration of various tissues and across different sources. Post decellularization of tissues and organs, they act as natural biomaterials to provide the biochemical and structural support to establish cell communication. Selection of an effective method for decellularization is crucial, and various factors like tissue density, geometric organization, and ECM composition affect the regenerative potential which has an impact on the end product. The dECM is a versatile material which is added as an important ingredient to formulate the bioink component for constructing tissue and organs for various significant studies. Bioink consisting of dECM from various sources is used to generate tissue-specific bioink that is unique and to mimic different biometric microenvironments. At present, there are many different techniques applied for decellularization, and the process is not standardized and regulated due to broad application. This review aims to provide an overview of different decellularization procedures, and we also emphasize the different dECM-derived bioinks present in the current global market and the major clinical outcomes. We have also highlighted an overview of benefits and limitations of different decellularization methods and various characteristic validations of decellularization and dECM-derived bioinks.

Biocompatibility of hydrogel derived from equine tendon extracellular matrix in horses subcutaneous tissue

Tendinopathies account for a substantial proportion of musculoskeletal injuries. To improve treatment outcomes for partial and total tendon ruptures, new therapies are under investigation. These include the application of mesenchymal stem cells (MSCs) and biocompatible scaffolds derived from the Extracellular Matrix (ECM). Synthetic polymer hydrogels have not demonstrated results as promising as those achieved with ECM hydrogels sourced from the original tissue. This study aimed to evaluate the biocompatibility of a hydrogel formulated from equine tendon ECM. Six horses were administered three subcutaneous doses of the hydrogel, with a saline solution serving as a control. Biopsies were conducted on days 7, 14, and 56 post-application to gauge the hydrogel's impact. Throughout the experiment, the horse's physical condition remained stable. Thermographic analyses revealed a temperature increase in the treated groups compared to the control group within the initial 12 h. The von Frey test, used to measure the mechanical nociceptive threshold, also showed significant differences between the treated group and the control group at 6 h, 21 days, and 28 days. Histopathological analyses identified an inflammatory response on day 7, which was absent on days 14 and 56. Transmission electron microscopy indicated a decrease in inflammatory cellularity, while immunohistochemistry staining suggested an increased presence of inflammatory factors on day 14. In summary, the hydrogel is easily injectable, triggers a temporary local inflammatory response, and integrates into the adjacent tissue from day 14 onwards.

Characterisation of Matrix-Bound Nanovesicles (MBVs) Isolated from Decellularised Bovine Pericardium: New Frontiers in Regenerative Medicine

Matrix-bound nanovesicles (MBVs) are a recently discovered type of extracellular vesicles (EVs), and they are characterised by a strong adhesion to extracellular matrix structural proteins (ECM) and ECM-derived biomaterials. MBVs contain a highly bioactive and tissue-specific cargo that recapitulates the biological activity of the source ECM. The rich content of MBVs has shown to be capable of potent cell signalling and of modulating the immune system, thus the raising interest for their application in regenerative medicine. Given the tissue-specificity and the youthfulness of research on MBVs, until now they have only been isolated from a few ECM sources. Therefore, the objective of this research was to isolate and identify the presence of MBVs in decellularised bovine pericardium ECM and to characterise their protein content, which is expected to play a major role in their biological potential. The results showed that nanovesicles, corresponding to the definition of recently described MBVs, could be isolated from decellularised bovine pericardium ECM. Moreover, these MBVs were composed of numerous proteins and cytokines, thus preserving a highly potential biological effect. Overall, this research shows that bovine pericardium MBVs show a rich and tissue-specific biological potential.

Exploring polysaccharide and protein-enriched decellularized matrix scaffolds for tendon and ligament repair: A review

Tissue engineering (TE) has become a primary research topic for the treatment of diseased or damaged tendon/ligament (T/L) tissue. T/L injuries pose a severe clinical burden worldwide, necessitating the development of effective strategies for T/L repair and tissue regeneration. TE has emerged as a promising strategy for restoring T/L function using decellularized extracellular matrix (dECM)-based scaffolds. dECM scaffolds have gained significant prominence because of their native structure, relatively high bioactivity, low immunogenicity, and ability to function as scaffolds for cell attachment, proliferation, and differentiation, which are difficult to imitate using synthetic materials. Here, we review the recent advances and possible future prospects for the advancement of dECM scaffolds for T/L tissue regeneration. We focus on crucial scaffold properties and functions, as well as various engineering strategies employed for biomaterial design in T/L regeneration. dECM provides both the physical and mechanical microenvironments required by cells to survive and proliferate. Various decellularization methods and sources of allogeneic and xenogeneic dECM in T/L repair and regeneration are critically discussed. Additionally, dECM hydrogels, bio-inks in 3D bioprinting, and nanofibers are briefly explored. Understanding the opportunities and challenges associated with dECM-based scaffold development is crucial for advancing T/L repairs in tissue engineering and regenerative medicine.

The molecular mechanisms of extracellular matrix-derived hydrogel therapy in idiopathic pulmonary fibrosis models

Idiopathic Pulmonary Fibrosis (IPF) is a progressively debilitating lung condition characterized by oxidative stress, cell phenotype shifts, and excessive extracellular matrix (ECM) deposition. Recent studies have shown promising results using decellularized ECM-derived hydrogels produced through pepsin digestion in various lung injury models and even a human clinical trial for myocardial infarction. This study aimed to characterize the composition of ECM-derived hydrogels, assess their potential to prevent fibrosis in bleomycin-induced IPF models, and unravel their underlying molecular mechanisms of action. Porcine lungs were decellularized and pepsin-digested for 48 h. The hydrogel production process, including visualization of protein molecular weight distribution and hydrogel gelation, was characterized. Peptidomics analysis of ECM-derived hydrogel contained peptides from 224 proteins. Probable bioactive and cell-penetrating peptides, including collagen IV, laminin beta 2, and actin alpha 1, were identified. ECM-derived hydrogel treatment was administered as an early intervention to prevent fibrosis advancement in rat models of bleomycin-induced pulmonary fibrosis. ECM-derived hydrogel concentrations of 1 mg/mL and 2 mg/mL showed subtle but noticeable effects on reducing lung inflammation, oxidative damage, and protein markers related to fibrosis (e.g., alpha-smooth muscle actin, collagen I). Moreover, distinct changes were observed in macroscopic appearance, alveolar structure, collagen deposition, and protein expression between lungs that received ECM-derived hydrogel and control fibrotic lungs. Proteomic analyses revealed significant protein and gene expression changes related to cellular processes, pathways, and components involved in tissue remodeling, inflammation, and cytoskeleton regulation. RNA sequencing highlighted differentially expressed genes associated with various cellular processes, such as tissue remodeling, hormone secretion, cell chemotaxis, and cytoskeleton engagement. This study suggests that ECM-derived hydrogel treatment influence pathways associated with tissue repair, inflammation regulation, cytoskeleton reorganization, and cellular response to injury, potentially offering therapeutic benefits in preventing or mitigating lung fibrosis.

Advances Focusing on the Application of Decellularized Extracellular Matrix in Periodontal Regeneration

The decellularized extracellular matrix (dECM) is capable of promoting stem cell proliferation, migration, adhesion, and differentiation. It is a promising biomaterial for application and clinical translation in the field of periodontal tissue engineering as it most effectively preserves the complex array of ECM components as they are in native tissue, providing ideal cues for regeneration and repair of damaged periodontal tissue. dECMs of different origins have different advantages and characteristics in promoting the regeneration of periodontal tissue. dECM can be used directly or dissolved in liquid for better flowability. Multiple ways were developed to improve the mechanical strength of dECM, such as functionalized scaffolds with cells that harvest scaffold-supported dECM through decellularization or crosslinked soluble dECM that can form injectable hydrogels for periodontal tissue repair. dECM has found recent success in many periodontal regeneration and repair therapies. This review focuses on the repairing effect of dECM in periodontal tissue engineering, with variations in cell/tissue sources, and specifically discusses the future trend of periodontal regeneration and the future role of soluble dECM in entire periodontal tissue regeneration.

Writing 3D In Vitro Models of Human Tendon within a Biomimetic Fibrillar Support Platform

Tendinopathies are poorly understood diseases for which treatment remains challenging. Relevant in vitro models to study human tendon physiology and pathophysiology are therefore highly needed. Here we propose the automated 3D writing of tendon microphysiological systems (MPSs) embedded in a biomimetic fibrillar support platform based on cellulose nanocrystals (CNCs) self-assembly. Tendon decellularized extracellular matrix (dECM) was used to formulate bioinks that closely recapitulate the biochemical signature of tendon niche. A monoculture system recreating the cellular patterns and phenotype of the tendon core was first developed and characterized. This system was then incorporated with a vascular compartment to study the crosstalk between the two cell populations. The combined biophysical and biochemical cues of the printed pattern and dECM hydrogel were revealed to be effective in inducing human-adipose-derived stem cells (hASCs) differentiation toward the tenogenic lineage. In the multicellular system, chemotactic effects promoted endothelial cells migration toward the direction of the tendon core compartment, while the established cellular crosstalk boosted hASCs tenogenesis, emulating the tendon development stages. Overall, the proposed concept is a promising strategy for the automated fabrication of humanized organotypic tendon-on-chip models that will be a valuable new tool for the study of tendon physiology and pathogenesis mechanisms and for testing new tendinopathy treatments.

Detergent-Free Decellularization Preserves the Mechanical and Biological Integrity of Murine Tendon

Tissue decellularization has demonstrated widespread applications across numerous organ systems for tissue engineering and regenerative medicine applications. Decellularized tissues are expected to retain structural and/or compositional features of the natural extracellular matrix (ECM), enabling investigation of biochemical factors and cell-ECM interactions that drive tissue homeostasis, healing, and disease. However, the dense collagenous tendon matrix has limited the efficacy of traditional decellularization strategies without the aid of harsh chemical detergents and/or physical agitation that disrupt tissue integrity and denature proteins involved in regulating cell behavior. In this study, we adapted and established the advantages of a detergent-free decellularization method that relies on latrunculin B actin destabilization, alternating hypertonic-hypotonic salt and water incubations, nuclease-assisted elimination of cellular material, and protease inhibitor supplementation under aseptic conditions. Our method maintained the collagen molecular structure (i.e., minimal extent of denaturation), while adequately removing cells and preserving bulk mechanical properties. Furthermore, we demonstrated that decellularized tendon ECM-derived coatings isolated from different mouse strains, injury states (i.e., naive and acutely injured/"provisional"), and anatomical sites harness distinct biochemical cues and robustly maintain tendon cell viability in vitro. Together, our work provides a simple and scalable decellularization method to facilitate mechanistic studies that will expand our fundamental understanding of tendon ECM and cell biology. Impact statement In this study, we present a decellularization method for tendon that does not rely on any detergent or physical processing techniques. We assessed the impact of detergent-free decellularization using tissue, cellular, and molecular level analyses and validated the preservation of gross fiber architecture, collagen molecular structure, and extracellular matrix (ECM)-associated biological cues that are essential for studying physiological cell-ECM interactions. Finally, we demonstrated the applicability of this method for healthy and injured tendon environments, across mouse strains, and for different types of tendons, illustrating the utility of this approach for isolating the contributions of biochemical cues within unique tendon ECM microenvironments.

Construction of antibacterial nano-silver embedded bioactive hydrogel to repair infectious skin defects

Background

Hydrogels loaded with antimicrobial agents have been widely used for treating infected wound defects. However, hydrogels derived from a porcine dermal extracellular matrix (PADM), containing silver nanoparticles (AgNPs), have not yet been studied. Therefore, we investigated the therapeutic effect of an AgNP-impregnated PADM (AgNP–PADM) hydrogel on the treatment of infected wounds.

Methods

An AgNP–PADM hydrogel was synthesized by embedding AgNPs into a PADM hydrogel. We examined the porosity, moisture retention, degradation, antibacterial properties, cytotoxicity, antioxidant properties, and ability of the PADM and AgNP–PADM hydrogels to treat infected wounds in animals.

Results

The PADM and AgNP–PADM hydrogels were pH sensitive, which made them flow dynamically and solidify under acidic and neutral conditions, respectively. The hydrogels also exhibited porous network structures, satisfactory moisture retention, and slow degradation. Additionally, the AgNP–PADM hydrogel showed a slow and sustained release of AgNPs for at least 7 days without the particle size changing. Thus, the AgNPs exhibited adequate antibacterial ability, negligible toxicity, and antioxidant properties in vitro. Moreover, the AgNP–PADM hydrogel promoted angiogenesis and healed infected skin defects in vivo.

Conclusions

The AgNP–PADM hydrogel is a promising bioderived antibacterial material for clinical application to infected wound dressings.

A decellularized flowable placental connective tissue matrix supports cellular functions of human tenocytes in vitro

Purpose

Injectable connective tissue matrices (CTMs) may promote tendon healing, given their minimally invasive properties, structural and biochemical extracellular matrix components, and capacity to fill irregular spaces. The purpose of this study is to evaluate the effects of placental CTMs on the cellular activities of human tenocytes. Decellularization, the removal of cells, cell fragments, and DNA from CTMs, has been shown to reduce the host’s inflammatory response. Therefore, the authors hypothesize that a decellularized CTM will provide a more cell-friendly matrix to support tenocyte functions.

Methods

Three human placental CTMs were selected for comparison: AmnioFill® (A-CTM), a minimally manipulated, non-viable cellular particulate, BioRenew™ (B-CTM), a liquid matrix, and Interfyl® (I-CTM), a decellularized flowable particulate. Adhesion and proliferation were evaluated using cell viability assays and tenocyte migration using a transwell migration assay. Gene expression of tenocyte markers, cytokines, growth factors, and matrix metalloprotease (MMP) in tenocytes were assessed using quantitative polymerase chain reaction.

Results

Although A-CTM supported more tenocyte adhesion, I-CTM promoted significantly more tenocyte proliferation compared with A-CTM and B-CTM. Unlike A-CTM, tenocyte migration was higher in I-CTM than the control. The presence of I-CTM also prevented the loss of tenocyte phenotype, attenuated the expression of pro-inflammatory cytokines, growth factors, and MMP, and promoted the expression of antifibrotic growth factor, TGFβ3.

Conclusion

Compared with A-CTM and B-CTM, I-CTM interacted more favorably with human tenocytes in vitro. I-CTM supported tenocyte proliferation with reduced de-differentiation and attenuation of the inflammatory response, suggesting that I-CTM may support tendon healing and regeneration in vivo.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40634-022-00509-4.

Comparison of three different acidic solutions in tendon decellularized extracellular matrix bio-ink fabrication for 3D cell printing

Decellularized extracellular matrix (dECM) hydrogels are being increasingly investigated for use in bio-inks for three-dimensional cell printing given their good cytocompatibility and biomimetic properties. The osmotic pressure and stiffness of bio-ink are important factors affecting the biological functions of printed cells. However, little attention has been given to the osmotic pressure and stiffness of the dECM bio-inks. Here, we compared three types of commonly used acidic solutions in the bio-fabrication of a tendon derived dECM bio-ink for 3D cell printing (0.5 M acetic acid, 0.1 M hydrochloric acid and 0.02 M hydrochloric acid). We found that low pH value of 0.1 M hydrochloric acid could accelerate the digestion process for dECM powders. This could lead to a much softer dECM hydrogel with storage modulus less than 100 Pa. This soft dECM hydrogel facilitated the spreading and proliferation of stem cells encapsulated within it. It also showed better tendon-inducing ability compared with two others much stiffer dECM hydrogels. However, this over-digested dECM hydrogel was more unstable as it could shrink with the culture time going on. For 0.5 M acetic acid made dECM bio-ink, the hyperosmotic state of the bio-ink led to much lower cellular viability rates. Postprocess (Dilution or dialysis) to tailor the osmotic pressure of hydrogels could be a necessary step before mixed with cells. Thus, kindly choosing the type and concentration of acidic solution is necessary for dECM bio-ink preparation. And a balance should be made between the digestion period, strength of acidic solution, as well as the size and concentration of the dECM powders. STATEMENT OF SIGNIFICANCE: The dECM bio-ink has been widely used in 3D cell printing for tissue engineering and organ modelling. In this study, we found that different types of acid have different digestion and dissolution status for the dECM materials. A much softer tendon derived dECM hydrogel with lower stiffness could facilitate the cellular spreading, proliferation and tendon differentiation. We also demonstrated that the osmotic pressure should be taken care of in the preparation of dECM bio-ink with 0.5 M acetic acid. Thus, kindly choosing the type and concentration of acidic solution is necessary for dECM bio-ink preparation.

Properties Regulation and Biological Applications of Decellularized Peripheral Nerve Matrix Hydrogel

Decellularized peripheral nerve matrix hydrogel (DNM-G) has drawn increasing attention in the field of neural tissue engineering, owing to its high tissue-specific bioactivity, drug/cell delivery capability, and multifunctional processability. However, the mechanisms and influencing factors of DNM-G formation have been rarely reported. To enable potential biological applications, the relationship between gelation conditions (including digestion time and gel concentration) and mechanical properties/stability (sol-gel transition temperature, gelation time, nanotopology, and storage modulus) of the DNM-G were systematically investigated in this study. The adequate-digested decellularized nerve matrix solution exhibited higher mechanical property, shorter gelation time, and a lower gelation temperature. A noteworthy increase of β-sheet proportion was identified through Fourier-transform infrared spectroscopy (FTIR) and circular dichroism (CD) characterizations, which suggested the possible major secondary structure formation during the phase transition. Besides, the DNM-G degraded fast that over 70% mass loss was noted after 4 weeks when immersing in PBS. A natural cross-linking agent, genipin, was gently introduced into DNM-G to enhance its mechanical properties and stability without changing its microstructure and biological performance. As a prefabricated scaffold, DNM-G remarkably increased the length and penetration depth of dorsal root ganglion (DRG) neurites compared to collagen gel. Furthermore, the DNM-G promoted the myelination and facilitated the formation of the morphological neural network. Finally, we demonstrated the feasibility of applying DNM-G in support-free extrusion-based 3D printing. Overall, the mechanical and biological performance of DNM-G can be manipulated by tuning the processing parameters, which is key to the versatile applications of DNM-G in regenerative medicine.

Protective Effects of Extracellular Matrix-Derived Hydrogels in Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive disease with significant gas exchange impairment owing to exaggerated extracellular matrix (ECM) deposition and myofibroblast activation. IPF has no cure, and although nintedanib and pirfenidone are two approved medications for symptom management, the total treatment cost is exuberant and prohibitive to a global uninsured patient population. New therapeutic alternatives with moderate costs are needed to treat IPF. ECM hydrogels derived from decellularized lungs are cost-effective therapeutic candidates to treat pulmonary fibrosis because of their reported antioxidant properties. Oxidative stress contributes to IPF pathophysiology by damaging macromolecules, interfering with tissue remodeling, and contributing to myofibroblast activation. Thus, preventing oxidative stress has beneficial outcomes in IPF. For this purpose, this review describes ECM hydrogel's properties to regulate oxidative stress and tissue remodeling in IPF.

A comparative study on fabrication techniques of gelable bone matrix derived from porcine tibia

Recently, several types of native tissues have been enzymatically digested to prepare hydrogels that have natural-mimic extracellular matrix (ECM) proteins, architecture, and biologic activities. However, the residual detergents and salts remaining in the hydrogel may cause some undesirable effects on compatibility, functionality, and bioactivity of the material. In this study, we enzymatically digested the demineralized and decellularized bone matrix (DDBM) and adopted two common methods that included dialysis against distilled water and acetone precipitation for sample desalting. Efficiency in salt removal, protein preservation, gelation ability, and in vivo biocompatibility and function were compared to the DDBM digest without a desalting treatment. After lyophilization, the dialyzed, precipitated, and non-desalted DDBM digests all exhibited cotton-like texture and were water-soluble; however, only the precipitated DDBM digest could be gelled. We also found that the method of acetone precipitation could effectively remove salt from the DDBM digest while preserving of multiple proteins from the native bone and internal porous structure. A total of 57 proteins were identified by mass spectrometry in the precipitated DDBM digest and the majority of these proteins are critical to overall protein assembly, scaffold structure and stability, and cell-activities. Additionally, the precipitated DDBM digest possessed enhanced biocompatibility and osteointegration in repairing a cranial bone defect in Sprague-Dawley (SD) rat. In conclusion, the soluble, biodegradable, and biocompatible natures of the precipitated DDBM digest allow its usage in bone tissue engineering as a protein carrier because of its resemblance to native bone-like protein composite and operative flexibility.

Enhancement of Migration and Tenogenic Differentiation of Macaca Mulatta Tendon-Derived Stem Cells by Decellularized Tendon Hydrogel

Decellularized tendon hydrogel from human or porcine tendon has been manufactured and found to be capable of augmenting tendon repair in vivo. However, no studies have clarified the effect of decellularized tendon hydrogel upon stem cell behavior. In the present study, we developed a new decellularized tendon hydrogel (T-gel) from Macaca mulatta, and investigated the effect of T-gel on the proliferation, migration and tenogenic differentiation of Macaca mulatta tendon-derived stem cells (mTDSCs). The mTDSCs were first identified to have universal stem cell characteristics, including clonogenicity, expression of mesenchymal stem cell and embryonic stem cell markers, and multilineage differentiation potential. Decellularization of Macaca mulatta Achilles tendons was confirmed to be effective by histological staining and DNA quantification. The resultant T-gel exhibited highly porous structure or similar nanofibrous structure and approximately swelling ratio compared to the collagen gel (C-gel). Interestingly, stromal cell-derived factor-1 (SDF-1) and fibromodulin (Fmod) inherent in the native tendon extracellular matrix (ECM) microenvironment were retained and the values of SDF-1 and Fmod in the T-gel were significantly higher than those found in the C-gel. Compared with the C-gel, the T-gel was found to be cytocompatible with NIH-3T3 fibroblasts and displayed good histocompatibility when implanted into rat subcutaneous tissue. More importantly, it was demonstrated that the T-gel supported the proliferation of mTDSCs and significantly promoted the migration and tenogenic differentiation of mTDSCs compared to the C-gel. These findings indicated that the T-gel, with its retained nanofibrous structure and some bioactive factors of native tendon ECM microenvironment, represents a promising hydrogel for tendon regeneration.

A Natural Xenogeneic Endometrial Extracellular Matrix Hydrogel Toward Improving Current Human in vitro Models and Future in vivo Applications

Decellularization techniques support the creation of biocompatible extracellular matrix hydrogels, providing tissue-specific environments for both in vitro cell culture and in vivo tissue regeneration. We obtained endometrium derived from porcine decellularized uteri to create endometrial extracellular matrix (EndoECM) hydrogels. After decellularization and detergent removal, we investigated the physicochemical features of the EndoECM, including gelation kinetics, ultrastructure, and proteomic profile. The matrisome showed conservation of structural and tissue-specific components with low amounts of immunoreactive molecules. EndoECM supported in vitro culture of human endometrial cells in two- and three-dimensional conditions and improved proliferation of endometrial stem cells with respect to collagen and Matrigel. Further, we developed a three-dimensional endometrium-like co-culture system of epithelial and stromal cells from different origins. Endometrial co-cultures remained viable and showed significant remodeling. Finally, EndoECM was injected subcutaneously in immunocompetent mice in a preliminary study to test a possible hypoimmunogenic reaction. Biomimetic endometrial milieus offer new strategies in reproductive techniques and endometrial repair and our findings demonstrate that EndoECM has potential for in vitro endometrial culture and as treatment for endometrial pathologies.

Extracellular matrix grafts: From preparation to application (Review)

Recently, the increasing emergency of traffic accidents and the unsatisfactory outcome of surgical intervention are driving research to seek a novel technology to repair traumatic soft tissue injury. From this perspective, decellularized matrix grafts (ECM-G) including natural ECM materials, and their prepared hydrogels and bioscaffolds, have emerged as possible alternatives for tissue engineering and regenerative medicine. Over the past decades, several physical and chemical decellularization methods have been used extensively to deal with different tissues/organs in an attempt to carefully remove cellular antigens while maintaining the non-immunogenic ECM components. It is anticipated that when the decellularized biomaterials are seeded with cells in vitro or incorporated into irregularly shaped defects in vivo, they can provide the appropriate biomechanical and biochemical conditions for directing cell behavior and tissue remodeling. The aim of this review is to first summarize the characteristics of ECM-G and describe their major decellularization methods from different sources, followed by analysis of how the bioactive factors and undesired residual cellular compositions influence the biologic function and host tissue response following implantation. Lastly, we also provide an overview of the in vivoapplication of ECM-G in facilitating tissue repair and remodeling.

Extracellular matrix coating improves the biocompatibility of polymeric heart valves

Prosthetic heart valve replacement is an effective therapy for patients with valvular heart disease. New-type polymer materials provide potential choices of material for preparing prosthetic heart valves. In this study, we focused on enhancing the biocompatibility of polystyrene-block-isobutylene-block-styrene (SIBS) by surface modification with an extracellular matrix (ECM). Experimental results demonstrated that the ECM coating increased the adsorption resistance against protein and platelets. SIBS coated with an ECM adsorbed much less bovine serum albumin and fibrinogen (5.38 μg cm-2 and 31.53 μg cm-2, respectively) than the original material (90.84 μg cm-2 and 132.38 μg cm-2, respectively). The relative platelet adsorption of the ECM-modified SIBS was lower than that of SIBS (0.04 versus 0.10). Moreover, the surface coating could also reduce endothelial cytotoxicity, suppress the immune response, and potentially induce tissue regeneration. In conclusion, ECM coating improved the biocompatibility of SIBS effectively.

Homing of Adipose-Derived Stem Cells to a Tendon-Derived Hydrogel: A Potential Mechanism for Improved Tendon-Bone Interface and Tendon Healing

PURPOSE

Tendons are difficult to heal owing to their hypocellularity and hypovascularity. Our laboratory has developed a tendon-derived hydrogel (tHG) that significantly improves tendon healing in an animal model. We hypothesized that a potential mechanism for improved healing with tHG is through the attraction of systemic stem cells.

METHODS

Homing of systemic adipose-derived stem cells (ADSCs) to tendon injuries was assessed with acute and chronic injury models. Injury sites were treated with saline or tHG, and animals given a tail vein injection (TVI) of labeled ADSCs 1 week after treatment. One week following TVI, rats were harvested for histology. To further evaluate a potential difference in homing to tHG, a subcutaneous injection (SQI) model was used. Rats were treated with an SQI of saline, silicone, ADSCs in media, tHG, tHG + fibroblasts (FBs), or tHG + ADSCs on day 0. One week after SQI, rats underwent TVI with labeled ADSCs. Samples were harvested 2 or 3 weeks after SQI for analysis. Flow cytometry confirmed homing in the SQI model.

RESULTS

Systemically delivered ADSCs homed to both acute tendon and chronic tendon-bone interface (TBI) injury sites. Despite their presence at the injury site, there was no difference in the number of macrophages, amount of cell proliferation, or angiogenesis 1 week after stem cell delivery. In an SQI model, ADSCs homed to tHG. There was no difference in the number of ADSCs homing to tHG alone versus tHG + ADSCs. However, there was an increase in the number of living cells, general immune cells, and T-cells present at tHG + ADSC versus tHG alone.

CONCLUSIONS

The ADSCs home to tendon injury sites and tHG. We believe the attraction of additional systemic ADSCs is one mechanism for improved tendon and TBI healing with tHG.

CLINICAL RELEVANCE

Treatment of tendon and TBI injuries with tHG can augment healing via homing of systemic stem cells.

Potential of Soluble Decellularized Extracellular Matrix for Musculoskeletal Tissue Engineering - Comparison of Various Mesenchymal Tissues

Background

It is well studied that preparations of decellularized extracellular matrix (ECM) obtained from mesenchymal tissues can function as biological scaffolds to regenerate injured musculoskeletal tissues. Previously, we reported that soluble decellularized ECMs derived from meniscal tissue demonstrated excellent biocompatibility and produced meniscal regenerate with native meniscal anatomy and biochemical characteristics. We therefore hypothesized that decellularized mesenchymal tissue ECMs from various mesenchymal tissues should exhibit tissue-specific bioactivity. The purpose of this study was to test this hypothesis using porcine tissues, for potential applications in musculoskeletal tissue engineering.

Methods

Nine types of porcine tissue, including cartilage, meniscus, ligament, tendon, muscle, synovium, fat pad, fat, and bone, were decellularized using established methods and solubilized. Although the current trend is to develop tissue specific decellularization protocols, we selected a simple standard protocol across all tissues using Triton X-100 and DNase/RNase after mincing to compare the outcome. The content of sulfated glycosaminoglycan (sGAG) and hydroxyproline were quantified to determine the biochemical composition of each tissue. Along with the concentration of several growth factors, known to be involved in tissue repair and/or maturation, including bFGF, IGF-1, VEGF, and TGF-β1. The effect of soluble ECMs on cell differentiation was explored by combining them with 3D collagen scaffold culturing human synovium derived mesenchymal stem cells (hSMSCs).

Results

The decellularization of each tissue was performed and confirmed both histologically [hematoxylin and eosin (H&E) and 4’,6-diamidino-2-phenylindole (DAPI) staining] and on the basis of dsDNA quantification. The content of hydroxyproline of each tissue was relatively unchanged during the decellularization process when comparing the native and decellularized tissue. Cartilage and meniscus exhibited a significant decrease in sGAG content. The content of hydroxyproline in meniscus-derived ECM was the highest when compared with other tissues, while sGAG content in cartilage was the highest. Interestingly, a tissue-specific composition of most of the growth factors was measured in each soluble decellularized ECM and specific differentiation potential was particularly evident in cartilage, ligament and bone derived ECMs.

Conclusion

In this study, soluble decellularized ECMs exhibited differences based on their tissue of origin and the present results are important going forward in the field of musculoskeletal regeneration therapy.

Differentially Expressed Proteins in Intra Synovial Compared to Extra Synovial Flexor Tendon Grafts in a Rabbit Tendon Transplantation Model

 Uncomplicated healing of grafts for tendon reconstruction remains an unsolved problem in hand surgery. Results are limited by adhesion formation and decreased strength properties, especially within the tight fibro-osseous sheath of the digits. This is especially problematic when an extra synovial tendon graft is used to replace an intra synovial flexor tendon. Compositional differences are likely to play an important role in these processes. The aim of this study was, therefore, to compare protein expression in pair-matched intra synovial tendon grafts with extra synovial tendon grafts, using a rabbit tendon injury model. We hypothesized that there would be significant differences in proteins critical for response to tensile loading and adhesion formation between the two groups. Using mass spectrometry and multivariate statistical data analysis, we found tissue-specific differences in 22 proteins, where 7 explained 93% (R2) of the variation, with a prediction of 81% (Q2). Among the highest discriminating proteins were Galectin, Histone H2A, and Periostin, which were found in a substantially larger amount in the extra synovial tendons compared to the intra synovial tendons. These findings may contribute to improved understanding of the differences in outcome seen after tendon reconstruction using tendon grafts with intra synovial and extra synovial grafts.

Analysis of Cell-seeded, Collagen-rich Hydrogel for Wound Healing

Our laboratory has previously developed a novel collagen-rich hydrogel (cHG), which significantly increases the speed of wound healing in diabetic rats.

Methods

In this study, we examine the in vitro survival and migration of fibroblasts, endothelial cells, and adipose-derived stem cells in a novel cHG. Furthermore, we test the ability of adipose-derived stem cell-seeded cHG to support cell survival and accelerate healing in vivo.

Results

In vitro, cell survival within the cHG was retained for 25 days. We were unable to detect cellular migration into, out of, or through cHG. In the in vivo model, bioluminescence of stem cells seeded within the cHG in diabetic rat wounds was detected until day 10. Rate of wound closure was higher for cHG plus adipose-derived stem cells versus control from day 2 until day 16 and significant on days 6, 8, and 12 (P < 0.05). This significant difference was also observed on day 16 by histology (P ≤ 0.05).

Conclusions

We conclude that cHG is a good candidate for delivering adipose-derived stem cells, endothelial cells, and fibroblasts to wounds. Future studies will determine whether the delivery of combinations of different cell lines in cHG further enhances wound healing.

Topical Antibiotic Elution in a Collagen-Rich Hydrogel Successfully Inhibits Bacterial Growth and Biofilm Formation In Vitro

Chronic wounds are a prominent concern, accounting for $25 billion of health care costs annually. Biofilms have been implicated in delayed wound closure, but they are susceptible to developing antibiotic resistance and treatment options continue to be limited. A novel collagen-rich hydrogel derived from human extracellular matrix presents an avenue for treating chronic wounds by providing appropriate extracellular proteins for healing and promoting neovascularization. Using the hydrogel as a delivery system for localized secretion of a therapeutic dosage of antibiotics presents an attractive means of maximizing delivery while minimizing systemic side effects. We hypothesize that the hydrogel can provide controlled elution of antibiotics leading to inhibition of bacterial growth and disruption of biofilm formation. The rate of antibiotic elution from the collagen-rich hydrogel and the efficacy of biofilm disruption was assessed with Pseudomonas aeruginosa Bacterial growth inhibition, biofilm disruption, and mammalian cell cytotoxicity were quantified using in vitro models. The antibiotic-loaded hydrogel showed sustained release of antibiotics for up to 24 h at therapeutic levels. The treatment inhibited bacterial growth and disrupted biofilm formation at multiple time points. The hydrogel was capable of accommodating various classes of antibiotics and did not result in cytotoxicity in mammalian fibroblasts or adipose stem cells. The antibiotic-loaded collagen-rich hydrogel is capable of controlled antibiotic release effective for bacteria cell death without native cell death. A human-derived hydrogel that is capable of eluting therapeutic levels of antibiotic is an exciting prospect in the field of chronic wound healing.

Extracellular matrix-derived biomaterials in engineering cell function

Extracellular matrix (ECM) derived components are emerging sources for the engineering of biomaterials that are capable of inducing desirable cell-specific responses. This review explores the use of biomaterials derived from naturally occurring ECM proteins and their derivatives in approaches that aim to regulate cell function. Biomaterials addressed are grouped into six categories: purified single ECM proteins, combinations of purified ECM proteins, cell-derived ECM, tissue-derived ECM, diseased and modified ECM, and ECM-polymer coupled biomaterials. Purified ECM proteins serve as a material coating for enhanced cell adhesion and biocompatibility. Cell-derived and tissue-derived ECM, generated by cell isolation and decellularization technologies, can capture the native state of the ECM environment and guide cell migration and alignment patterns as well as stem cell differentiation. We focus primarily on recent advances in the fields of soft tissue, cardiac, and dermal repair, and explore the utilization of ECM proteins as biomaterials to engineer cell responses.

Injectable hydrogels for tendon and ligament tissue engineering

The problem of tendon and ligament (T/L) regeneration in musculoskeletal diseases has long constituted a major challenge. In situ injection of formable biodegradable hydrogels, however, has been demonstrated to treat T/L injury and reduce patient suffering in a minimally invasive manner. An injectable hydrogel is more suitable than other biological materials due to the special physiological structure of T/L. Most other materials utilized to repair T/L are cell-based, growth factor-based materials, with few material properties. In addition, the mechanical property of the gel cannot reach the normal T/L level. This review summarizes advances in natural and synthetic polymeric injectable hydrogels for tissue engineering in T/L and presents prospects for injectable and biodegradable hydrogels for its treatment. In future T/L applications, it is necessary develop an injectable hydrogel with mechanics, tissue damage-specific binding, and disease response. Simultaneously, the advantages of various biological materials must be combined in order to achieve personalized precision therapy.

Decellularized Extracellular Matrix-based Bioinks for Engineering Tissue- and Organ-specific Microenvironments

Biomaterials-based biofabrication methods have gained much attention in recent years. Among them, 3D cell printing is a pioneering technology to facilitate the recapitulation of unique features of complex human tissues and organs with high process flexibility and versatility. Bioinks, combinations of printable hydrogel and cells, can be utilized to create 3D cell-printed constructs. The bioactive cues of bioinks directly trigger cells to induce tissue morphogenesis. Among the various printable hydrogels, the tissue- and organ-specific decellularized extracellular matrix (dECM) can exert synergistic effects in supporting various cells at any component by facilitating specific physiological properties. In this review, we aim to discuss a new paradigm of dECM-based bioinks able to recapitulate the inherent microenvironmental niche in 3D cell-printed constructs. This review can serve as a toolbox for biomedical engineers who want to understand the beneficial characteristics of the dECM-based bioinks and a basic set of fundamental criteria for printing functional human tissues and organs.

A Human-Derived, Collagen-Rich Hydrogel Augments Wound Healing in a Diabetic Animal Model

BACKGROUND

Application of collagen products to wounds has been shown to improve wound healing. Using a collagen-based hydrogel (cHG) capable of cellular support previously developed by our laboratory, we hypothesize that our hydrogel will increase the speed of wound healing by providing a 3-dimensional framework for cellular support, increasing angiogenesis and cell-proliferation at the wound bed.

METHODS

Two, 10-mm excisional wounds were created over the dorsum of 12 male, genetically modified Zucker diabetic rats. Wounds were splinted open to limit healing by wound contracture. One wound was treated with an occlusive dressing (OD), whereas the adjacent wound was treated with an OD plus cHG. Occlusive dressings were changed every other day. Hydrogel was applied on day 2 and every 4 days after until complete wound closure. Rate of wound closure was monitored with digital photography every other day. Wounds were harvested at days 10 and 16 for histological and immunohistochemical analysis.

RESULTS

Wound closure was significantly faster in cHG-treated wounds compared with OD-treated wounds. By day 10, cHG-treated wounds achieved 63% wound closure, compared with 55% wound closure in OD-treated wounds (P < 0.05). By day 16, cHG-treated wounds achieved 84% wound closure, compared with 68% wound closure in OD-treated wounds (P < 0.05).Histologically, wound depth was not different between the cHG and OD groups on days 10 and 16. However, wound length was significantly less in the cHG group compared with the OD group (P < 0.05) consistent with digital photographic analysis. Immunohistochemical analysis for RECA-1 demonstrated that blood vessel density in the wound bed was 2.3 times higher in the cHG group compared with the OD group (P = 0.01) on day 16. Cell proliferation was 3.8 times higher in the cHG group versus the OD group (P < 0.05) on day 10.

CONCLUSIONS

Collagen-based hydrogel-treated wounds demonstrated significantly improved healing compared with control. The thermoresponsive feature of collagen hydrogel and its structural stability at body temperature demonstrate promising clinical potential as a vehicle for the delivery of therapeutic cells to the wound bed.

Thermosensitive injectable decellularized nucleus pulposus hydrogel as an ideal biomaterial for nucleus pulposus regeneration

Extracellular matrix loss is one of the early manifestations of intervertebral disc degeneration. Stem cell-based tissue engineering creates an appropriate microenvironment for long term cell survival, promising for NP regeneration. We created a decellularized nucleus pulposus hydrogel (DNPH) from fresh bovine nucleus pulposus. Decellularization removed NP cells effectively, while highly preserving their structures and major biochemical components, such as glycosaminoglycan and collagen II. DNPH could be gelled as a uniform grid structure in situ at 37°C for 30 min. Adding adipose marrow-derived mesenchymal stem cells into the hydrogel for three-dimensional culture resulted in good bioactivity and biocompatibility in vitro. Meanwhile, NP-related gene expression significantly increased without the addition of exogenous biological factors. In summary, the thermosensitive and injectable hydrogel, which has low toxicity and inducible differentiation, could serve as a bio-scaffold, bio-carrier, and three-dimensional culture system. Therefore, DNPH has an outstanding potential for intervertebral disc regeneration.

The impact of decellularization methods on extracellular matrix derived hydrogels

Tissue-derived decellularized biomaterials are ideal for tissue engineering applications as they mimic the biochemical composition of the native tissue. These materials can be used as hydrogels for cell encapsulation and delivery. The decellularization process can alter the composition of the extracellular matrix (ECM) and thus influence the hydrogels characteristics. The aim of this study was to examine the impact of decellularization protocols in ECM-derived hydrogels obtained from porcine corneas. Porcine corneas were isolated and decellularized with SDS, Triton X-100 or by freeze-thaw cycles. All decellularization methods decreased DNA significantly when measured by PicoGreen and visually assessed by the absence of cell nuclei. Collagen and other ECM components were highly retained, as quantified by hydroxyproline content and sGAG, by histological analysis and by SDS-PAGE. Hydrogels obtained by freeze-thaw decellularization were the most transparent. The method of decellularization impacted gelation kinetics assessed by turbidimetric analysis. All hydrogels showed a fibrillary and porous structure determined by cryoSEM. Human corneal stromal cells were embedded in the hydrogels to assess cytotoxicity. SDS decellularization rendered cytotoxic hydrogels, while the other decellularization methods produced highly cytocompatible hydrogels. Freeze-thaw decellularization produced hydrogels with the overall best properties.

Human Tendon-Derived Collagen Hydrogel Significantly Improves Biomechanical Properties of the Tendon-Bone Interface in a Chronic Rotator Cuff Injury Model

PURPOSE

Poor healing of the tendon-bone interface (TBI) after rotator cuff (RTC) tears leads to high rates of recurrent tear following repair. Previously, we demonstrated that an injectable, thermoresponsive, type I collagen-rich, decellularized human tendon-derived hydrogel (tHG) improved healing in an acute rat Achilles tendon injury model. The purpose of this study was to investigate whether tHG enhances the biomechanical properties of the regenerated TBI in a rat model of chronic RTC injury and repair.

METHODS

Tendon hydrogel was prepared from chemically decellularized human cadaveric flexor tendons. Eight weeks after bilateral resection of supraspinatus tendons, repair of both shoulders was performed. One shoulder was treated with a transosseous suture (control group) and the other was treated with a transosseous suture plus tHG injection at the repair site (tHG group). Eight weeks after repair, the TBIs were evaluated biomechanically, histologically, and via micro-computed tomography (CT).

RESULTS

Biomechanical testing revealed a larger load to failure, higher stiffness, higher energy to failure, larger strain at failure, and higher toughness in the tHG group versus control. The area of new cartilage formation was significantly larger in the tHG group. Micro-CT revealed no significant difference between groups in bone morphometry at the supraspinatus tendon insertion, although the tHG group was superior to the control.

CONCLUSIONS

Injection of tHG at the RTC repair site enhanced biomechanical properties and increased fibrocartilage formation at the TBI in a chronic injury model.

CLINICAL RELEVANCE

Treatment of chronic RTC injuries with tHG at the time of surgical treatment may improve outcomes after surgical repair.

An overview of decellularisation techniques of native tissues and tissue engineered products for bone, ligament and tendon regeneration

Decellularised tissues and organs have been successfully used in a variety of tissue engineering/regenerative medicine applications. Because of the complexity of each tissue (size, porosity, extracellular matrix (ECM) composition etc.), there is no standardised protocol and the decellularisation methods vary widely, thus leading to heterogeneous outcomes. Physical, chemical, and enzymatic methods have been developed and optimised for each specific application and this review describes the most common strategies utilised to achieve decellularisation of soft and hard tissues. While removal of the DNA is the primary goal of decellularisation, it is generally achieved at the expense of ECM preservation due to the harsh chemical or enzymatic processing conditions. As denaturation of the native ECM has been associated with undesired host responses, decellularisation conditions aimed at effectively achieving simultaneous DNA removal and minimal ECM damage will be highlighted. Additionally, the utilisation of decellularised matrices in regenerative medicine is explored, as are the most recent strategies implemented to circumvent challenges in this field. In summary, this review focusses on the latest advancements and future perspectives in the utilisation of natural ECM for the decoration of synthetic porous scaffolds.

Tissue Response and Biodistribution of Injectable Cellulose Nanocrystal Composite Hydrogels

Interest in cellulose nanocrystal (CNC)-based hydrogels for drug delivery, tissue engineering, and other biomedical applications has rapidly expanded despite the minimal in vivo research reported to date. Herein, we assess both in vitro protein adsorption and cell adhesion as well as in vivo subcutaneous tissue responses and CNC biodistribution of injectable CNC-poly(oligoethylene glycol methacrylate) (POEGMA) hydrogels. Hydrogels with different PEG side chain lengths, CNC loadings, and with or without in situ magnetic alignment of the CNCs are compared. CNC loading has a minimal impact on protein adsorption but significantly increases cell adhesion. In vivo, both CNC-only and CNC-POEGMA injections largely stay at their subcutaneous injection site over one month, with minimal bioaccumulation of CNCs in any typical clearance organ. CNC-POEGMA hydrogels exhibit mild acute and chronic inflammatory responses, although significant fibroblast penetration was observed with the magnetically aligned hydrogels. Collectively, these results suggest that CNC-POEGMA hydrogels offer promise in practical biomedical applications.

Augmentation of chronic rotator cuff healing using adipose-derived stem cell-seeded human tendon-derived hydrogel

Rotator cuff (RTC) repair outcomes are unsatisfactory due to the poor healing capacity of the tendon bone interface (TBI). In our preceding study, tendon hydrogel (tHG), which is a type I collagen rich gel derived from human tendons, improved biomechanical properties of the TBI in a rat chronic RTC injury model. Here we investigated whether adipose-derived stem cell (ASC)-seeded tHG injection at the repair site would further improve RTC healing. Rats underwent bilateral supraspinatus tendon detachment. Eight weeks later injured supraspinatus tendons were repaired with one of four treatments. In the control group, standard transosseous suture repair was performed. In the ASC, tHG, tHGASC groups, ASC in media, tHG, and ASC-seeded tHG were injected at repair site after transosseous suture repair, respectively. Eight weeks after repair, the TBI was evaluated biomechanically, histologically, and via micro CT. Implanted ASCs were detected in ASC and tHGASC groups 7 weeks after implantation. ACS implantation improved bone morphometry at the supraspinatus insertion on the humerus. Injection of tHG improved biomechanical properties of the repaired TBI. RTC healing in tHGASC group was significantly better than control but statistically equivalent to the tHG group based on biomechanical properties, fibrocartilage area at the TBI, and bone morphometry at the supraspinatus insertion. In a rat RTC chronic injury model, no biomechanical advantage was gained with ASC augmentation of tHG. Clinical Significance: Tendon hydrogel augmentation with adipose derived stem cells does not significantly improve TBI healing over tHG alone in a chronic rotator cuff injury model. © 2019 Orthopaedic Research Society. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Tissue-Engineered Grafts from Human Decellularized Extracellular Matrices: A Systematic Review and Future Perspectives

Tissue engineering and regenerative medicine involve many different artificial and biologic materials, frequently integrated in composite scaffolds, which can be repopulated with various cell types. One of the most promising scaffolds is decellularized allogeneic extracellular matrix (ECM) then recellularized by autologous or stem cells, in order to develop fully personalized clinical approaches. Decellularization protocols have to efficiently remove immunogenic cellular materials, maintaining the nonimmunogenic ECM, which is endowed with specific inductive/differentiating actions due to its architecture and bioactive factors. In the present paper, we review the available literature about the development of grafts from decellularized human tissues/organs. Human tissues may be obtained not only from surgery but also from cadavers, suggesting possible development of Human Tissue BioBanks from body donation programs. Many human tissues/organs have been decellularized for tissue engineering purposes, such as cartilage, bone, skeletal muscle, tendons, adipose tissue, heart, vessels, lung, dental pulp, intestine, liver, pancreas, kidney, gonads, uterus, childbirth products, cornea, and peripheral nerves. In vitro recellularizations have been reported with various cell types and procedures (seeding, injection, and perfusion). Conversely, studies about in vivo behaviour are poorly represented. Actually, the future challenge will be the development of human grafts to be implanted fully restored in all their structural/functional aspects.

Utility of extracellular matrix powders in tissue engineering

Extracellular matrix (ECM) materials have had remarkable success as scaffolds in tissue engineering (TE) and as therapies for tissue injury whereby the ECM microenvironment promotes constructive remodeling and tissue regeneration. ECM powder and solubilized derivatives thereof have novel applications in TE and RM afforded by the capacity of these constructs to be dynamically modulated. The powder form allows for effective incorporation and penetration of reagents; hence, ECM powder is an efficacious platform for 3D cell culture and vehicle for small molecule delivery. ECM powder offers minimally invasive therapy for tissue injury and successfully treatment for wounds refractory to first-line therapies. Comminution of ECM and fabrication of powder-derived constructs, however, may compromise the biological integrity of the ECM. The current lack of optimized fabrication protocols prevents a more extensive and effective clinical application of ECM powders. Further study on methods of ECM powder fabrication and modification is needed.

Extracellular matrix hydrogel therapies: In vivo applications and development

Decellularized extracellular matrix (ECM) has been widely used for tissue engineering applications and is becoming increasingly versatile as it can take many forms, including patches, powders, and hydrogels. Following additional processing, decellularized ECM can form an inducible hydrogel that can be injected, providing for new minimally-invasive procedure opportunities. ECM hydrogels have been derived from numerous tissue sources and applied to treat many disease models, such as ischemic injuries and organ regeneration or replacement. This review will focus on in vivo applications of ECM hydrogels and functional outcomes in disease models, as well as discuss considerations for clinical translation.

STATEMENT OF SIGNIFICANCE

Extracellular matrix (ECM) hydrogel therapies are being developed to treat diseased or damaged tissues and organs throughout the body. Many ECM hydrogels are progressing from in vitro models to in vivo biocompatibility studies and functional models. There is significant potential for clinical translation of these therapies since one ECM hydrogel therapy is already in a Phase 1 clinical trial.

Boosting tendon repair: interplay of cells, growth factors and scaffold-free and gel-based carriers

Background

Tendons are dense connective tissues and critical components for the integrity and function of the musculoskeletal system. Tendons connect bone to muscle and transmit forces on which locomotion entirely depends. Due to trauma, overuse and age-related degeneration, many people suffer from acute or chronic tendon injuries. Owing to their hypovascularity and hypocellularity, tendinopathies remain a substantial challenge for both clinicians and researchers. Surgical treatment includes suture or transplantation of autograft, allograft or xenograft, and these serve as the most common technique for rescuing tendon injuries. However, the therapeutic efficacies are limited by drawbacks including inevitable donor site morbidity, poor graft integration, adhesion formations and high rates of recurrent tearing. This review summarizes the literature of the past 10 y concerning scaffold-free and gel-based approaches for treating tendon injuries, with emphasis on specific advantages of such modes of application, as well as the obtained results regarding in vitro and in vivo tenogenesis.

Results

The search was focused on publications released after 2006 and 83 articles have been analysed. The main results are summarizing and discussing the clear advantages of scaffold-free and hydrogels carriers that can be functionalized with cells alone or in combination with growth factors.

Conclusion

The improved understanding of tissue resident adult stem cells has made a significant progress in recent years as well as strategies to steer their fate toward tendon lineage, with the help of growth factors, have been identified. The field of tendon tissue engineering is exploring diverse models spanning from hard scaffolds to gel-based and scaffold-free approaches seeking easier cell delivery and integration in the site of injury. Still, the field needs to consider a multifactorial approach that is based on the combination and fine-tuning of chemical and biomechanical stimuli. Taken together, tendon tissue engineering has now excellent foundations and enters the period of precision and translation to models with clinical relevance on which better treatment options of tendon injuries can be shaped up.

Enhanced hepatogenic differentiation of bone marrow derived mesenchymal stem cells on liver ECM hydrogel

Bone marrow derived mesenchymal stem cells (BM-MSC) is a promising alternative cell source to primary hepatocytes because of their ability to differentiate into hepatocyte-like cells. However, their inability to differentiate efficiently and potential to turn into myofibroblasts restrict their applications. This study developed a plate coating from the liver extracellular matrix (ECM) and investigated its ability in facilitating the BM-MSCs proliferation, hepatic differentiation, and hepatocyte-specific functions during in vitro culture. After 28-day culture, BM-MSCs on the ECM coating showed hepatocyte-like morphology, and certain cells took up low-density lipoprotein. Synthesis of albumin, urea, and anti-alpha-fetoprotein, as well as expression of certain hepatic markers, in cells cultured on ECM were higher than cells cultured on non-coated and Matrigel-coated plates. mRNA levels of CYP3A4, albumin, CK18, and CYP7A1 in cells on ECM coating were significantly higher than cells cultured on the non-coating environment. In conclusion, viability and hepatogenic differentiation of BM-MSCs cultured on both Matrigel and ECM coating were significantly enhanced compared with those cultured on non-coated plates. Moreover, the liver ECM coating induced additional metabolic functions relative to the Matrigel coating. The liver ECM hydrogel preserves the natural composition, promotes simple gelling, induces efficient stem cell hepatogenic differentiation, and may have uses as an injectable intermedium for hepatocytes. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 829-838, 2018.

Injectable Anisotropic Nanocomposite Hydrogels Direct in Situ Growth and Alignment of Myotubes

While injectable in situ cross-linking hydrogels have attracted increasing attention as minimally invasive tissue scaffolds and controlled delivery systems, their inherently disorganized and isotropic network structure limits their utility in engineering oriented biological tissues. Traditional methods to prepare anisotropic hydrogels are not easily translatable to injectable systems given the need for external equipment to direct anisotropic gel fabrication and/or the required use of temperatures or solvents incompatible with biological systems. Herein, we report a new class of injectable nanocomposite hydrogels based on hydrazone cross-linked poly(oligoethylene glycol methacrylate) and magnetically aligned cellulose nanocrystals (CNCs) capable of encapsulating skeletal muscle myoblasts and promoting their differentiation into highly oriented myotubes in situ. CNC alignment occurs on the same time scale as network gelation and remains fixed after the removal of the magnetic field, enabling concurrent CNC orientation and hydrogel injection. The aligned hydrogels show mechanical and swelling profiles that can be rationally modulated by the degree of CNC alignment and can direct myotube alignment both in two- and three-dimensions following coinjection of the myoblasts with the gel precursor components. As such, these hydrogels represent a critical advancement in anisotropic biomimetic scaffolds that can be generated noninvasively in vivo following simple injection.

In Vitro Characteristics of Porcine Tendon Hydrogel for Tendon Regeneration

PURPOSE

Previous work has characterized the development of a human tendon hydrogel capable of improving mechanical strength after tendon injury. Animal tendon hydrogel has not yet been described, but would prove beneficial due to the cost and ethical concerns associated with the use of human cadaveric tendon. This study details the manufacture and assesses the biocompatibility of porcine tendon hydrogel seeded with human adipoderived stem cells (ASCs).

MATERIALS AND METHODS

Porcine tendon was dissected from surrounding connective and muscle tissue and decellularized via 0.2% sodium dodecyl sulfate and 0.2% sodium dodecyl sulfate/ethylenediaminetetraacetic acid wash solutions before lyophilization. Tendon was milled and reconstituted by previously described methods. Decellularization was confirmed by hematoxylin-eosin staining, SYTO Green 11 nucleic acid dye, and DNeasy assay. The protein composition of milled tendon matrix before and after digestion was identified by mass spectrometry. Rheological properties were determined using an ARG2 rheometer. Biocompatibility was assessed by live/dead assay. The proliferation of human ASCs seeded in porcine and human hydrogel was measured by MTS assay. All experimental conditions were performed in triplicate.

RESULTS

Decellularization of porcine tendon was successful. Mass spectrometry showed that collagen composes one third of milled porcine tendon before and after pepsin digestion. Rheology demonstrated that porcine hydrogel maintains a fluid consistency over a range of temperatures, unlike human hydrogel, which tends to solidify. Live/dead staining revealed that human ASCs survive in hydrogel 7 days after seeding and retain spindle-like morphology. MTS assay at day 3 and day 5 showed that human ASC proliferation was marginally greater in human hydrogel.

CONCLUSIONS

After reconstitution and digestion, porcine hydrogel was capable of supporting growth of human ASCs. The minimal difference in proliferative capacity suggests that porcine tendon hydrogel may be an effective and viable alternative to human hydrogel for the enhancement of tendon healing.

Intratendinous Injection of Hydrogel for Reseeding Decellularized Human Flexor Tendons

BACKGROUND

Decellularized cadaveric tendons are a potential source for reconstruction. Reseeding to enhance healing is ideal; however, cells placed on the tendon surface result in inadequate delivery. The authors used an injection technique to evaluate intratendinous cell delivery.

METHODS

Decellularized tendons were reseeded with adipose-derived stem cells in culture, and injected with fetal bovine serum or hydrogel. PKH26-stained cells in cross-section were quantified. To evaluate cell viability, the authors delivered luciferase-labeled cells and performed bioluminescent imaging. To evaluate synthetic ability, the authors performed immunohistochemistry of procollagen. Adipose-derived stem cells' ability to attract tenocytes was assessed using transwell inserts. Cell-to-cell interaction was assessed by co-culturing, measuring proliferation and collagen production, and quantifying synergy. Finally, tensile strength was tested.

RESULTS

Both fetal bovine serum (p < 0.001) and hydrogel (p < 0.001) injection led to more cells inside the tendon compared with culturing. Hydrogel injection initially demonstrated greater bioluminescence than culturing (p < 0.005) and fetal bovine serum injection (p < 0.05). Injection groups demonstrated intratendinous procollagen staining correlating with the cells' location. Co-culture led to greater tenocyte migration (p < 0.05). Interaction index of proliferation and collagen production assays were greater than 1 for all co-culture ratios, demonstrating synergistic proliferation and collagen production compared with controls (p < 0.05). There were no differences in tensile strength.

CONCLUSIONS

Hydrogel injection demonstrated the greatest intratendinous seeding efficiency and consistency, without compromising tensile strength. Intratendinous cells demonstrated synthetic capabilities and can potentially attract tenocytes inside the tendon, where synergy would promote intrinsic tendon healing.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, V.

Efficacy of thermoresponsive, photocrosslinkable hydrogels derived from decellularized tendon and cartilage extracellular matrix for cartilage tissue engineering

Tissue engineering using adult mesenchymal stem cells (MSCs), a promising approach for cartilage repair, is highly dependent on the nature of the matrix scaffold. Thermoresponsive, photocrosslinkable hydrogels were fabricated by functionalizing pepsin-soluble decellularized tendon and cartilage extracellular matrices (ECM) with methacrylate groups. Methacrylated gelatin hydrogels served as controls. When seeded with human bone marrow MSCs and cultured in chondrogenic medium, methacrylated ECM hydrogels experienced less cell-mediated contraction, as compared against non-methacrylated ECM hydrogels. However, methacrylation slowed or diminished chondrogenic differentiation of seeded MSCs, as determined through analyses of gene expression, biochemical composition and histology. In particular, methacrylated cartilage hydrogels supported minimal due to chondrogenesis over 42 weeks, as hydrogel disintegration beginning at day 14 presumably compromised cell-matrix interactions. As compared against methacrylated gelatin hydrogels, MSCs cultured in non-methacrylated ECM hydrogels exhibited comparable expression of chondrogenic genes (Sox9, Aggrecan and collagen type II) but increased collagen type I expression. Non-methacrylated cartilage hydrogels did not promote chondrogenesis to a greater extent than either non-methacrylated or methacrylated tendon hydrogels. Whereas methacrylated gelatin hydrogels supported relatively homogeneous increases in proteoglycan and collagen type II deposition throughout the construct over 42 days, ECM hydrogels possessed greater heterogeneity of staining intensity and construct morphology. These results do not support the utility of pepsin-solubilized cartilage and tendon hydrogels for cartilage tissue engineering over methacrylated gelatin hydrogels. Methacrylation of tendon and cartilage ECM hydrogels permits thermal- and light-induced polymerization but compromises chondrogenic differentiation of seeded MSCs.