Hyaluronic acid/PEO electrospun tube reduces tendon adhesion to levels comparable to native tendons - An in vitro and in vivo study

A major problem after tendon injury is adhesion formation to the surrounding tissue leading to a limited range of motion. A viable strategy to reduce adhesion extent is the use of physical barriers that limit the contact between the tendon and the adjacent tissue. The purpose of this study was to fabricate an electrospun bilayered tube of hyaluronic acid/polyethylene oxide (HA/PEO) and biodegradable DegraPol® (DP) to improve the anti-adhesive effect of the implant in a rabbit Achilles tendon full laceration model compared to a pure DP tube. Additionally, the attachment of rabbit tenocytes on pure DP and HA/PEO containing scaffolds was tested and Scanning Electron Microscopy, Fourier-transform Infrared Spectroscopy, Differential Scanning Calorimetry, Water Contact Angle measurements, and testing of mechanical properties were used to characterize the scaffolds. In vivo assessment after three weeks showed that the implant containing a second HA/PEO layer significantly reduced adhesion extent reaching levels comparable to native tendons, compared with a pure DP implant that reduced adhesion formation only by 20 %. Tenocytes were able to attach to and migrate into every scaffold, but cell number was reduced over two weeks. Implants containing HA/PEO showed better mechanical properties than pure DP tubes and with the ability to entirely reduce adhesion extent makes this implant a promising candidate for clinical application in tendon repair.

Combining biomimetic collagen/hyaluronan hydrogels with discogenic growth factors promotes mesenchymal stroma cell differentiation into Nucleus Pulposus like cells

Based on stem cell injection into degenerated Nucleus Pulposus (NP), novel treatments for intervertebral disc (IVD) regeneration were disappointing because of cell leakage or inappropriate cell differentiation. In this study, we hypothesized that mesenchymal stromal cells encapsulated within injectable hydrogels possessing adequate physico-chemical properties would differentiate into NP like cells. Composite hydrogels consisting of type I collagen and tyramine-substituted hyaluronic acid (THA) were prepared to mimic the NP physico-chemical properties. Human bone marrow derived mesenchymal stromal cells (BM-MSCs) were encapsulated within hydrogels and cultivated in proliferation medium (supplemented with 10% fetal bovine serum) or differentiation medium (supplemented with GDF5 and TGFβ1) over 28 days. Unlike pure collagen, collagen/THA composite hydrogels were stable over 28 days in culture. In proliferation medium, the cell viability within pure collagen hydrogels was high, whereas that in composite and pure THA hydrogels was lower due to the weaker cell adhesion. Nonetheless, BM-MSCs proliferated in all hydrogels. In composite hydrogels, cells exhibited a rounded morphology similar to NP cells. The differentiation medium did not impact the hydrogel stability and cell morphology but negatively impacted the cell viability in pure collagen hydrogels. A high THA content within hydrogels promoted the gene expression of NP markers such as collagen II, aggrecan, SOX9 and cytokeratin 18 at day 28. The differentiation medium potentialized this effect with an earlier and higher expression of these NP markers. Taken together, these results show that the physico-chemical properties of collagen/THA composite hydrogels and GDF5/TGFβ1 act in synergy to promote the differentiation of BM-MSCs into NP like cells.

Hybrid Networks of Hyaluronic Acid and Poly(trimethylene carbonate) for Tissue Regeneration

To improve the mechanical performance of hyaluronic acid (HA)-based hydrogels, we prepared novel hybrid hydrogels consisting of hydrophilic HA and hydrophobic poly(trimethylene carbonate) (PTMC). Both polymers were functionalized with methacrylic anhydride, yielding HAMA and PTMC-tMA. Hybrid networks with different ratios of PTMC-tMA:HAMA were prepared by photo-cross-linking, using DMSO pH 2.7 as a common solvent for both macromers. The hybrid networks had high gel contents. The hydrophilicity of the networks increased with increasing HAMA content. The networks consisted of the intended amounts of both macromers. The suture retention strength and compression modulus of the networks increased with increasing PTMC-tMA content. While the 100% HAMA network could not be sutured, the 50:50 PTMC-tMA:HAMA network had a suture retention strength of 5.3 N/mm. This is comparable to that of natural vascular tissues. Also the compression modulus (867 kPa) was significantly higher than that of the 100% HAMA network (13 kPa). Moreover, the networks were compatible with human mesenchymal stem cells. In conclusion, these resilient PTMC-tMA:HAMA networks are promising new biomaterials for tissue regeneration.

Modulating design parameters to drive cell invasion into hydrogels for osteochondral tissue formation

Background

The use of acellular hydrogels to repair osteochondral defects requires cells to first invade the biomaterial and then to deposit extracellular matrix for tissue regeneration. Due to the diverse physicochemical properties of engineered hydrogels, the specific properties that allow or even improve the behaviour of cells are not yet clear. The aim of this study was to investigate the influence of various physicochemical properties of hydrogels on cell migration and related tissue formation using in vitro, ex vivo and in vivo models.

Methods

Three hydrogel platforms were used in the study: Gelatine methacryloyl (GelMA) (5% wt), norbornene hyaluronic acid (norHA) (2% wt) and tyramine functionalised hyaluronic acid (THA) (2.5% wt). GelMA was modified to vary the degree of functionalisation (DoF 50% and 80%), norHA was used with varied degradability via a matrix metalloproteinase (MMP) degradable crosslinker and THA was used with the addition of collagen fibrils. The migration of human mesenchymal stromal cells (hMSC) in hydrogels was studied in vitro using a 3D spheroid migration assay over 48h. In addition, chondrocyte migration within and around hydrogels was investigated in an ex vivo bovine cartilage ring model (three weeks). Finally, tissue repair within osteochondral defects was studied in a semi-orthotopic in vivo mouse model (six weeks).

Results

A lower DoF of GelMA did not affect cell migration in vitro (p ​= ​0.390) and led to a higher migration score ex vivo (p ​< ​0.001). The introduction of a MMP degradable crosslinker in norHA hydrogels did not improve cell infiltration in vitro or in vivo. The addition of collagen to THA resulted in greater hMSC migration in vitro (p ​= ​0.031) and ex vivo (p ​< ​0.001). Hydrogels that exhibited more cell migration in vitro or ex vivo also showed more tissue formation in the osteochondral defects in vivo, except for the norHA group. Whereas norHA with a degradable crosslinker did not improve cell migration in vitro or ex vivo, it did significantly increase tissue formation in vivo compared to the non-degradable crosslinker (p ​< ​0.001).

Conclusion

The modification of hydrogels by adapting DoF, use of a degradable crosslinker or including fibrillar collagen can control and improve cell migration and tissue formation for osteochondral defect repair. This study also emphasizes the importance of performing both in vitro and in vivo testing of biomaterials, as, depending on the material, the results might be affected by the model used.The translational potential of this article: This article highlights the potential of using acellular hydrogels to repair osteochondral defects, which are common injuries in orthopaedics. The study provides a deeper understanding of how to modify the properties of hydrogels to control cell migration and tissue formation for osteochondral defect repair. The results of this article also highlight that the choice of the used laboratory model can affect the outcome. Testing hydrogels in different models is thus advised for successful translation of laboratory results to the clinical application.

Injectable enzyme-catalyzed crosslinking hydrogels as BMSCs-laden tunable scaffold for osteogenic differentiation

Bone defects caused by trauma or tumor are a significant challenge in clinical practice. Hydrogel-based tissue engineering has been considered an effective strategy. This study successfully formed a series of injectable hydrogels by enzyme-catalyzed crosslinking hyaluronic acid-tyramine (HA-TA) and sodium alginate-tyramine (ALG-TA) under physiological conditions in the presence of both horseradish peroxidase and hydrogen peroxide. The morphology, mechanical properties, swelling properties, and biodegradation properties of hydrogels were investigated. The results showed that the mechanical properties, swelling properties and biodegradation of HA/ALG hydrogels varied with the precursor solution concentration. Furthermore, the proliferation and osteogenic differentiation of BMSCs within the HA/ALG hydrogels were evaluated in vitro. The results illustrated that the hydrogels could offer an excellent microenvironment for BMSCs growth and promote osteogenic differentiation. Therefore, the injectable hydrogels can be used as an effective 3 D scaffold for bone repair and regeneration.

New hyaluronan-based biomatrix for 3-D follicle culture yields functionally competent oocytes

BACKGROUND

Encapsulation of follicles within a biomatrix is one approach to maintaining 3-D follicle architecture during culture. Hyaluronan is one component of the natural extracellular matrix (ECM) that provides support to cells in vivo. This report describes the application of a novel tyramine-linked hyaluronan for 3-D in vitro follicle culture and the production of developmentally competent metaphase II oocytes.

MATERIALS AND METHODS

Enzymatically isolated mouse preantral follicles or follicle clusters (FL-C) from fresh or vitrified ovaries were encapsulated in 3 mg/ml of hyaluronan gel (HA). Follicle growth, antrum formation and meiotic maturation to metaphase II oocytes was monitored. Chromatin staining was used to assess GV oocyte progression towards meiotic competence. Functional competence of in vitro matured (IVM) oocytes was evaluated by in vitro fertilization and ability to develop to blastocyst. Modifying the HA gel by inclusion of laminin (HA-LM), mouse sarcoma extracellular matrix (Matrigel;HA-MG) or placental extracellular matrix (HA-PM) was also tested to see if this might further enhance IVM outcomes.

RESULTS

A total of 402 preantral follicles were cultured in HA gel. After hCG trigger, 314 oocyte-cumulus complexes ovulated from the embedded follicles. Meiotic maturation rate to the metaphase II stage was 73% (228/314). After insemination 83% (188/228) of IVM oocytes fertilized with a subsequent blastulation rate of 46% (87/188). A pilot transfer study with 3 recipient mice resulted in the birth of a single pup. HA gel supported individually isolated follicles as well ovarian tissue fragments containing clusters of 6-8 preantral follicles. Meiotic maturation was lower with FL-clusters from vitrified versus fresh ovaries (34% and 55%, respectively; p < 0.007). Modification of the HA gel with ECMs or laminin affected antrum formation and follicle retention. Maturation rates to the metaphase II stage were however not significantly different: 74% for HA gel alone as compared to HA-LM (67%), HA-MG (56%) and HA-PM (58%).

CONCLUSION

Hyaluronan gel is an effective and versatile extracellular matrix based biomaterial for 3-D culture of ovarian follicles. This culture model allowed ovulation of functionally competent metaphase II oocytes, capable of fertilization, genomic activation and blastulation. Future testing with human follicles that require longer in vitro culture times should be considered.

Stereolithographic Visible-Light Printing of Poly(l-glutamic acid) Hydrogel Scaffolds

Bioprinting is a promising fabrication technique aimed at developing biologically functional, tissue-like constructs for various biomedical applications. Among the different bioprinting approaches, vat polymerization-based techniques offer the highest feature resolution compared to more commonly used extrusion-based methods and therefore have greater potential to be utilized for printing complex hierarchical tissue architectures. Although significant efforts have been directed toward harnessing digital light processing techniques for high-resolution bioprinting, the use of stereolithography (SLA) setups for producing distinct hydrogel filaments smaller than 20 μm has received less attention. Improving the bioprinting resolution is still a technical challenge that must consider both the practical limitations of the bioprinter apparatus and the formulation of the cytocompatible bioresin. In this study, we developed a novel bioresin compatible with SLA and capable of printing high-resolution features. This resin, composed of a biosynthetic polypeptide poly(l-glutamic acid) functionalized with tyramine moieties (PLGA-Tyr), was crosslinked using a visible-light photoinitiator system. Varying concentrations of PLGA-Tyr and the co-photoinitiator were evaluated for the hydrogel system's gelation ability, swelling characteristics, degradation profiles, mechanical properties, and cell viability post-encapsulation. This study introduces a custom-built, cost-effective, visible-light SLA bioprinting system named the "MicroNC". Using the newly developed visible-light bioresin, we demonstrated for the first time the ability to fabricate hydrogel scaffolds with well-resolved filaments (less than 8 μm in width) capable of supporting cell viability and proliferation and directing cellular morphology at the single-cell level for up to 14 days. Overall, these experiments have underscored the exciting potential of using the visible-light-photoinitiated PLGA-Tyr material system for developing physiologically relevant in vitro hydrogel scaffolds with feature resolutions comparable to the dimensions of individual human cells for a wide range of biomedical applications.

Optimization of hyaluronic acid-tyramine/silk-fibroin composite hydrogels for cartilage tissue engineering and delivery of anti-inflammatory and anabolic drugs

Injury of articular cartilage leads to an imbalance in tissue homeostasis, and due to the poor self-healing capacity of cartilage the affected tissue often exhibits osteoarthritic changes. In recent years, injectable and highly tunable composite hydrogels for cartilage tissue engineering and drug delivery have been introduced as a desirable alternative to invasive treatments. In this study, we aimed to formulate injectable hydrogels for drug delivery and cartilage tissue engineering by combining different concentrations of hyaluronic acid-tyramine (HA-Tyr) with regenerated silk-fibroin (SF) solutions. Upon enzymatic crosslinking, the gelation and mechanical properties were characterized over time. To evaluate the effect of the hydrogel compositions and properties on extracellular matrix (ECM) deposition, bovine chondrocytes were embedded in enzymatically crosslinked HA-Tyr/SF composites (in further work abbreviated as HA/SF) or HA-Tyr hydrogels. We demonstrated that all hydrogel formulations were cytocompatible and could promote the expression of cartilage matrix proteins allowing chondrocytes to produce ECM, while the most prominent chondrogenic effects were observed in hydrogels with HA20/SF80 polymeric ratios. Unconfined mechanical testing showed that the compressive modulus for HA20/SF80 chondrocyte-laden constructs was increased almost 10-fold over 28 days of culture in chondrogenic medium which confirmed the superior production of ECM in this hydrogel compared to other hydrogels in this study. Furthermore, in hydrogels loaded with anabolic and anti-inflammatory drugs, HA20/SF80 hydrogel showed the longest and the most sustained release profile over time which is desirable for the long treatment duration typically necessary for osteoarthritic joints. In conclusion, HA20/SF80 hydrogel was successfully established as a suitable injectable biomaterial for cartilage tissue engineering and drug delivery applications.

A high molecular weight hyaluronic acid biphasic dispersion as potential therapeutics for interstitial cystitis

Interstitial cystitis (IC) is a progressive bladder disease characterized by increased urothelial permeability, inflammation of the bladder with abdominal pain. While there is no consensus on the etiology of the disease, it was believed that restoring the barrier between urinary solutes and (GAG) urothelium would interrupt the progression of this disease. Currently, several treatment options include intravesical delivery of hyaluronic acid (HA) and/or chondroitin sulfate solutions, through a catheter to restore the urothelial barrier, but have shown limited success in preclinical, clinical trials. Herein we report for the first time successful engineering and characterization of biphasic system developed by combining cross‐linked hyaluronic acid and naïve HA solution to decrease inflammation and permeability in an in vitro model of interstitial cystitis. The cross‐linking of HA was performed by 4‐arm‐polyethyeleneamine chemistry. The HA formulations were tested for their viscoelastic properties and the effects on cell metabolism, inflammatory markers, and permeability. Our study demonstrates the therapeutic effects of different ratios of the biphasic system and reports their ability to increase the barrier effect by decreasing the permeability and alteration of cell metabolism with respect to relative controls. Restoring the barrier by using biphasic system of HA therapy may be a promising approach to IC.

Tissue mimetic hyaluronan bioink containing collagen fibers with controlled orientation modulating cell migration and alignment

Biofabrication is providing scientists and clinicians the ability to produce engineered tissues with desired shapes and gradients of composition and biological cues. Typical resolutions achieved with extrusion-based bioprinting are at the macroscopic level. However, for capturing the fibrillar nature of the extracellular matrix (ECM), it is necessary to arrange ECM components at smaller scales, down to the micron and the molecular level. Herein, we introduce a bioink containing the tyramine derivative of hyaluronan (HA; henceforth known as THA) and collagen (Col) type 1. In this bioink, similar to connective tissues, Col is present in the fibrillar form, and HA functions as a viscoelastic space filler. THA was enzymatically cross-linked under mild conditions allowing simultaneous Col fibrillogenesis, thus achieving a homogeneous distribution of Col fibrils within the viscoelastic HA-based matrix. The THA-Col composite displayed synergistic properties in terms of storage modulus and shear thinning, translating into good printability. Shear-induced alignment of the Col fibrils along the printing direction was achieved and quantified via immunofluorescence and second-harmonic generation. Cell-free and cell-laden constructs were printed and characterized, analyzing the influence of the controlled microscopic anisotropy on human bone marrow-derived mesenchymal stromal cell (hMSC) migration. Anisotropic HA-Col showed cell-instructive properties modulating hMSC adhesion, morphology, and migration from micropellets stimulated by the presence and the orientation of Col fibers. Actin filament staining showed that hMSCs embedded in aligned constructs displayed increased cytoskeleton alignment along the fibril direction. Based on gene expression of cartilage/bone markers and ECM production, hMSCs embedded in the isotropic bioink displayed chondrogenic differentiation comparable with standard pellet culture by means of proteoglycan production (safranin O staining and proteoglycan quantification). The possibility of printing matrix components with control over microscopic alignment brings biofabrication one step closer to capturing the complexity of native tissues.

Multicomponent hydrogels for the formation of vascularized bone-like constructs in vitro

The native extracellular matrix (ECM) is a complex gel-like system with a broad range of structural features and biomolecular signals. Hydrogel platforms that can recapitulate the complexity and signaling properties of this ECM would have enormous impact in fields ranging from tissue engineering to drug discovery. Here, we report on the design, synthesis, and proof-of-concept validation of a microporous and nanofibrous hydrogel exhibiting multiple bioactive epitopes designed to recreate key features of the bone ECM. The material platform integrates self-assembly with orthogonal enzymatic cross-linking to create a supramolecular environment comprising hyaluronic acid modified with tyramine (HA-Tyr) and peptides amphiphiles (PAs) designed to promote cell adhesion (RGDS-PA), osteogenesis (Osteo-PA), and angiogenesis (Angio-PA). Through individual and co-cultures of human adipose derived mesenchymal stem cells (hAMSCs) and human umbilical vascular endothelial cells (HUVECs), we confirmed the capacity of the HA-Tyr/RGDS-PA/Osteo-PA/Angio-PA hydrogel to promote cell adhesion as well as osteogenic and angiogenic differentiation in both 2D and 3D setups. Furthermore, using immunofluorescent staining and reverse transcription-quantitative polymerase chain reaction (RT-qPCR), we demonstrated co-differentiation and organization of hAMSCs and HUVECs into 3D aggregates resembling vascularized bone-like constructs. STATEMENT OF SIGNIFICANCE: This body of work presents a new approach to develop more complex, yet functional, in vitro environments for cell culture while enabling a high level of control, tuneability, and reproducibility. The multicomponent self-assembling bioactive 2D and 3D hydrogels with nanofibrous architecture designed to recreate key molecular and macromolecular features of the native bone ECM and promote both osteogenesis and angiogenesis. The materials induce endothelial cells towards large vascular lumens and MSCs into bone cells on/within the same platform and form vascularized-bone like construct in vitro. This strategy looks encouraging for lifelike bone tissue engineering in vitro and bone tissue regeneration in vivo.

Extracellular matrix-mimetic composite hydrogels of cross-linked hyaluronan and fibrillar collagen with tunable properties and ultrastructure

A platform of enzymatically-crosslinked Collagen/Tyramine hyaluronan derivative (Col/HA-Tyr) hydrogels with tunable compositions and gelation conditions was developed to evaluate the impact of the preparation conditions on their physical, chemical and biological properties. At low HA-Tyr content, hydrogels exhibited a fibrillar structure, with lower mechanical properties compared to pure Col hydrogels. At high HA-Tyr and Horse Radish Peroxydase (HRP) content, a microfibrillar network was formed beside the banded Col fibrils and a synergistic effect of the hybrid structure on mechanical properties was observed. These hydrogels were highly resistant against enzymatic degradation while keeping a high degree of hydration. Unlike HA-Tyr hydrogels, encapsulation of human dermal fibroblasts within Col/HA-Tyr hydrogels allowed for high cell viability. These results showed that high HA-Tyr and HRP concentrations are required to positively impact the physical properties of hydrogels while preserving collagen fibrils. Those Col/HA-Tyr hydrogels appear promising for novel tissue engineering applications following a biomimetic approach.

An injectable enzymatically crosslinked tyramine-modified carboxymethyl chitin hydrogel for biomedical applications

The in-situ forming injectable hydrogels have received much attention as scaffolds in the biomedical field, providing a minimally invasive surgical procedure to fill the damaged area. In the present work, carboxymethyl chitin (CMCH) synthesized homogenously was further functionalized with tyramine, resulted in a new injectable enzymatically crosslinked in-situ forming hydrogel under physiological conditions. This new tyramine-modified carboxymethyl chitin (CMCH-Tyr) hydrogel showed much better mechanical properties than those of the thermosensitive in-situ forming physical-crosslinking CMCH hydrogel. The CMCH-Tyr hydrogels remained stable under physiological conditions and could be degraded by lysozyme. The gelation time, strength and biodegradation rate of the CMCH-Tyr hydrogels can be adjusted by varying the concentrations of the horseradish peroxidase and H₂O₂ in the certain range. In vitro cytotoxicity assays and in vivo in-situ injection study showed non-toxicity, favorable gel formation, and good tissue biocompatibility of the enzyme-catalyzed CMCH-Tyr hydrogel. Thus, the biodegradable and biocompatible CMCH-Tyr hydrogels may hold great potential for three dimensional cell culture and tissue engineering.

Horseradish peroxidase-catalyzed hydrogelation for biomedical applications

Hydrogels catalyzed by horseradish peroxidase (HRP) serve as an efficient and effective platform for biomedical applications due to their mild reaction conditions for cells, fast and adjustable gelation rate in physiological conditions, and an abundance of substrates as water-soluble biocompatible polymers.