Hydrolytic (In)stability of Methacrylate Esters in Covalently Cross-Linked Hydrogels Based on Chondroitin Sulfate and Hyaluronic Acid Methacrylate

Comparative Bioactivities of Chemically Modified Fucoidan and λ-Carrageenan toward Cells Encapsulated in Covalently Cross-Linked Hydrogels

The sulfated marine polysaccharides, fucoidan and λ-carrageenan, are known to possess anti-inflammatory, immunomodulatory, and cellular protective properties. Although they hold considerable promise for tissue engineering constructs, their covalent cross-linking in hydrogels and comparative bioactivities to cells are absent from the literature. Thus, fucoidan and λ-carrageenan were modified with methacrylate groups and were covalently cross-linked with the synthetic polymer poly(vinyl alcohol)-methacrylate (PVA-MA) to form 20 wt % biosynthetic hydrogels. Identical degrees of methacrylation were confirmed by 1H NMR, and covalent conjugation was determined by using a colorimetric 1,9-dimethyl-methylene blue (DMMB) assay. Pancreatic beta cells were encapsulated in the hydrogels, followed by culturing in the 3D environment for a prolonged period of 32 days and evaluation of the cellular functionality by live/dead, adenosine 5'-triphosphate (ATP) level, and insulin secretion. The results confirmed that fucoidan and λ-carrageenan exhibited ∼12% methacrylate substitution, which generated hydrogels with stable conjugation of the polysaccharides with PVA-MA. The cells encapsulated in the PVA-fucoidan hydrogels demonstrated consistently high ATP levels over the culture period. Furthermore, only cells in the PVA-fucoidan hydrogels retained glucose responsiveness, demonstrating comparatively higher insulin secretion in response to glucose. In contrast, cells in the PVA-λ-carrageenan and the PVA control hydrogels lost all glucose responsiveness. The present work confirms the superior effects of chemically modified fucoidan over λ-carrageenan on pancreatic beta cell survival and function in covalently cross-linked hydrogels, thereby illustrating the importance of differential polysaccharide structural features on their biological effects.

Plasma-treated collagen functionalized with chondroitin sulfate as bioactive and nanostructured extracellular matrix mimics

Aim: Cell microenvironment contains a plethora of information that influences cell modulation. Indeed, the extracellular matrix plays a central role in tissue development. Reproducing the cell-extracellular matrix crosstalk able to recapitulate both physical and biochemical signals is crucial to obtain functional tissue models or regenerative strategies. Materials & methods: Here, a combined method is proposed to easily functionalize collagen surface films, tailoring morphological properties. Oxygen nonthermal plasma treatment and glyco-conjugation with chondroitin sulfate are used to modify surface properties. Results: It results in higher adhesion, proliferation and morphological organization of U87 glioblastoma cells. Conclusion: Our finding suggests new promising strategies for the development of collagen-based biomaterials, which can be employed for advanced in vitro models.

Preclinical characterization of macrophage-adhering gadolinium micropatches for MRI contrast after traumatic brain injury in pigs

The choroid plexus (ChP) of the brain plays a central role in orchestrating the recruitment of peripheral leukocytes into the central nervous system (CNS) through the blood-cerebrospinal fluid (BCSF) barrier in pathological conditions, thus offering a unique niche to diagnose CNS disorders. We explored whether magnetic resonance imaging of the ChP could be optimized for mild traumatic brain injury (mTBI). mTBI induces subtle, yet influential, changes in the brain and is currently severely underdiagnosed. We hypothesized that mTBI induces sufficient alterations in the ChP to cause infiltration of circulating leukocytes through the BCSF barrier and developed macrophage-adhering gadolinium [Gd(III)]-loaded anisotropic micropatches (GLAMs), specifically designed to image infiltrating immune cells. GLAMs are hydrogel-based discoidal microparticles that adhere to macrophages without phagocytosis. We present a fabrication process to prepare GLAMs at scale and demonstrate their loading with Gd(III) at high relaxivities, a key indicator of their effectiveness in enhancing image contrast and clarity in medical imaging. In vitro experiments with primary murine and porcine macrophages demonstrated that GLAMs adhere to macrophages also under shear stress and did not affect macrophage viability or functions. Studies in a porcine mTBI model confirmed that intravenously administered macrophage-adhering GLAMs provide a differential signal in the ChP and lateral ventricles at Gd(III) doses 500- to 1000-fold lower than those used in the current clinical standard Gadavist. Under the same mTBI conditions, Gadavist did not offer a differential signal at clinically used doses. Our results suggest that macrophage-adhering GLAMs could facilitate mTBI diagnosis.

Granular Disulfide-Crosslinked Hyaluronic Hydrogels: A Systematic Study of Reaction Conditions on Thiol Substitution and Injectability Parameters

Granular polymer hydrogels based on dynamic covalent bonds are attracting a great deal of interest for the design of injectable biomaterials. Such materials generally exhibit shear-thinning behavior and properties of self-healing/recovery after the extrusion that can be modulated through the interactions between gel microparticles. Herein, bulk macro-hydrogels based on thiolated-hyaluronic acid were produced by disulphide bond formation using oxygen as oxidant at physiological conditions and gelation kinetics were monitored. Three different thiol substitution degrees (SD%: 65%, 30% and 10%) were selected for hydrogel formation and fully characterized as to their stability in physiological medium and morphology. Then, extrusion fragmentation technique was applied to obtain hyaluronic acid microgels with dynamic disulphide bonds that were subsequently sterilized by autoclaving. The resulting granular hyaluronic hydrogels were able to form stable filaments when extruded through a syringe. Rheological characterization and cytotoxicity tests allowed to assess the potential of these materials as injectable biomaterials. The application of extrusion fragmentation for the formation of granular hyaluronic hydrogels and the understanding of the relation between the autoclaving processes and the resulting particle size and rheological properties should expand the development of injectable materials for biomedical applications.

The effect of HydroSpacer implant placement on the wear of opposing and adjacent cartilage

A HydroSpacer implant, that is, a swelling hydrogel confined by a spacer fabric, was developed to repair focal cartilage defects and to prevent progression into osteoarthritis. The present study evaluated the effect of implant placement height in an osteochondral (OC) plug on wear of the opposing and adjacent cartilage. Three-dimensional warp-knitted spacer fabrics, polycaprolactone with poly(4-hydroxybutyrate) pile yarns, were filled with a hyaluronic acid methacrylate and chondroitin sulfate methacrylate hydrogel. After polymerization of the hydrogel, these HydroSpacers were implanted in OC defects (ø 6 mm) created in bovine OC plugs (ø 10 mm) and allowed to swell to equilibrium. A custom-made pin-on-plate wear apparatus was used to apply simultaneous compression and sliding against bovine cartilage. Cartilage damage, visualized with Indian ink, was only seen for the group in which the HydroSpacer was placed flush with the surrounding cartilage. A significant increase on average surface roughness of the sliding path compared to the adjacent cartilage confirmed surface damage for this group. When the implants were recessed (with and without extra hydrogel layer on top of the implant), this damage was not observed, but the cartilage surrounding the implants was compressed (without damage) indicating substantial load sharing with the implant. Furthermore, it was shown that all defects treated with a HydroSpacer implant resulted in shear forces comparable to intact cartilage. Clinical significance: The present study suggests that placing a HydroSpacer implant recessed into the surrounding cartilage would decrease wear of the opposing cartilage. Altogether, this study supports the development of textile-constraining hydrogels for cartilage replacement.

Creating a Functional Biomimetic Cartilage Implant Using Hydrogels Based on Methacrylated Chondroitin Sulfate and Hyaluronic Acid

The load-bearing function of articular cartilage tissue contrasts with the poor load-bearing capacity of most soft hydrogels used for its regeneration. The present study explores whether a hydrogel based on the methacrylated natural polymers chondroitin sulfate (CSMA) and hyaluronic acid (HAMA), injected into warp-knitted spacer fabrics, could be used to create a biomimetic construct with cartilage-like mechanical properties. The swelling ratio of the combined CSMA/HAMA hydrogels in the first 20 days was higher for hydrogels with a higher CSMA concentration, and these hydrogels also degraded quicker, whereas those with a 1.33 wt% of HAMA were stable for more than 120 days. When confined by a polyamide 6 (PA6) spacer fabric, the volumetric swelling of the combined CSMA/HAMA gels (10 wt%, 6.5 × CSMA:HAMA ratio) was reduced by ~53%. Both the apparent peak and the equilibrium modulus significantly increased in the PA6-restricted constructs compared to the free-swelling hydrogels after 28 days of swelling, and no significant differences in the moduli and time constant compared to native bovine cartilage were observed. Moreover, the cell viability in the CSMA/HAMA PA6 constructs was comparable to that in gelatin–methacrylamide (GelMA) PA6 constructs at one day after polymerization. These results suggest that using a HydroSpacer construct with an extracellular matrix (ECM)-like biopolymer-based hydrogel is a promising approach for mimicking the load-bearing properties of native cartilage.

Viscoelastic Chondroitin Sulfate and Hyaluronic Acid Double-Network Hydrogels with Reversible Cross-Links

Viscoelastic hydrogels are gaining interest as they possess necessary requirements for bioprinting and injectability. By means of reversible, dynamic covalent bonds, it is possible to achieve features that recapitulate the dynamic character of the extracellular matrix. Dually cross-linked and double-network (DN) hydrogels seem to be ideal for the design of novel biomaterials and bioinks, as a wide range of properties required for mimicking advanced and complex tissues can be achieved. In this study, we investigated the fabrication of chondroitin sulfate/hyaluronic acid (CS/HA)-based DN hydrogels, in which two networks are interpenetrated and cross-linked with the dynamic covalent bonds of very different lifetimes. Namely, Diels-Alder adducts (between methylfuran and maleimide) and hydrazone bonds (between aldehyde and hydrazide) were chosen as cross-links, leading to viscoelastic hydrogels. Furthermore, we show that viscoelasticity and the dynamic character of the resulting hydrogels could be tuned by changing the composition, that is, the ratio between the two types of cross-links. Also, due to a very dynamic nature and short lifetime of hydrazone cross-links (∼800 s), the DN hydrogel is easily processable (e.g., injectable) in the first stages of gelation, allowing the material to be used in extrusion-based 3D printing. The more long-lasting and robust Diels-Alder cross-links are responsible for giving the network enhanced mechanical strength and structural stability. Being highly charged and hydrophilic, the cross-linked CS and HA enable a high swelling capacity (maximum swelling ratio ranging from 6 to 12), which upon confinement results in osmotically stiffened constructs, able to mimic the mechanical properties of cartilage tissue, with the equilibrium moduli ranging from 0.3 to 0.5 MPa. Moreover, the mesenchymal stromal cells were viable in the presence of the hydrogels, and the effect of the degradation products on the macrophages suggests their safe use for further translational applications. The DN hydrogels with dynamic covalent cross-links hold great potential for the development of novel smart and tunable viscoelastic materials to be used as biomaterial inks or bioinks in bioprinting and regenerative medicine.