Cartilage synthesis in hyaluronic acid-tyramine constructs

Enzymatically cross-linked hyaluronic acid hydrogels as in situ forming carriers of platelet-rich plasma: Mechanical properties and bioactivity levels evaluation

New studies have shown the great potential of the combination of in situ enzymatically cross-linked hydrogels based on tyramine derivative of hyaluronic acid (HA-TA) with platelet-rich plasma (PRP) and platelet lysate in regenerative medicine. This study describes how the presence of PRP and platelet lysate affects the kinetics of gelation, viscoelastic properties, swelling ratio, and the network structure of HA-TA hydrogels and how the encapsulation of PRP in hydrogels affects the bioactivity of released PRP determined as the ability to induce cell proliferation. The properties of hydrogels were tuned by a degree of substitution and concentration of HA-TA derivatives. The addition of platelet derivatives to the reaction mixture slowed down the cross-linking reaction and reduced elastic modulus (G') and thus cross-linking efficiency. However, low-swellable hydrogels (7-190%) suitable for soft tissue engineering with G' 200-1800 Pa were prepared with a gelation time within 1 min. It was confirmed that tested cross-linking reaction conditions are suitable for PRP incorporation because the total bioactivity level of PRP released from HA-TA hydrogels was ≥87% and HA-TA content in the hydrogels and thus mesh size (285-482 nm) has no significant effect on the bioactivity level of released PRP.

Designing functional hyaluronic acid-based hydrogels for cartilage tissue engineering

Damage to cartilage tissues is often difficult to repair owing to chronic inflammation and a lack of bioactive factors. Therefore, developing bioactive materials, such as hydrogels acting as extracellular matrix mimics, that can inhibit the inflammatory microenvironment and promote cartilage repair is crucial. Hyaluronic acid, which exists in cartilage and synovial fluid, has been extensively investigated for cartilage tissue engineering because of its promotion of cell adhesion and proliferation, regulation of inflammation, and enhancement of cartilage regeneration. However, hyaluronic acid-based hydrogels have poor degradation rates and unfavorable mechanical properties, limiting their application in cartilage tissue engineering. Recently, various multifunctional hyaluronic acid-based hydrogels, including alkenyl, aldehyde, thiolated, phenolized, hydrazide, and host–guest group-modified hydrogels, have been extensively studied for use in cartilage tissue engineering. In this review, we summarize the recent progress in the multifunctional design of hyaluronic acid-based hydrogels and their application in cartilage tissue engineering. Moreover, we outline the future research prospects and directions in cartilage tissue regeneration. This would provide theoretical guidance for developing hyaluronic acid-based hydrogels with specific properties to satisfy the requirements of cartilage tissue repair.

Hyaluronic Acid: A Key Ingredient in the Therapy of Inflammation

Hyaluronic acid (HA) is a natural polymer, produced endogenously by the human body, which has unique physicochemical and biological properties, exhibiting desirable biocompatibility and biodegradability. Therefore, it has been widely studied for possible applications in the area of inflammatory diseases. Although exogenous HA has been described as unable to restore or replace the properties and activities of endogenous HA, it can still provide satisfactory pain relief. This review aims to discuss the advances that have been achieved in the treatment of inflammatory diseases using hyaluronic acid as a key ingredient, essentially focusing on studies carried out between the years 2017 and 2021.

Prediction of Viscoelastic Properties of Enzymatically Crosslinkable Tyramine-Modified Hyaluronic Acid Solutions Using a Dynamic Monte Carlo Kinetic Approach

The present study deals with the mathematical modeling of crosslinking kinetics of polymer-phenol conjugates mediated by the Horseradish Peroxidase (HRP)-hydrogen peroxide (H₂O₂) initiation system. More specifically, a dynamic Monte Carlo (MC) kinetic model is developed to quantify the effects of crosslinking conditions (i.e., polymer concentration, degree of phenol substitution and HRP and H₂O₂ concentrations) on the gelation onset time; evolution of molecular weight distribution and number and weight average molecular weights of the crosslinkable polymer chains and gel fraction. It is shown that the MC kinetic model can faithfully describe the crosslinking kinetics of a finite sample of crosslinkable polymer chains with time, providing detailed molecular information for the crosslinkable system before and after the gelation point. The MC model is validated using experimental measurements on the crosslinking of a tyramine modified Hyaluronic Acid (HA-Tyr) polymer solution reported in the literature. Based on the rubber elasticity theory and the MC results, the dynamic evolution of hydrogel viscoelastic and molecular properties (i.e., number average molecular weight between crosslinks, M_c, and hydrogel mesh size, ξ) are calculated.

Recent advances in the design of injectable hydrogels for stem cell-based therapy

The recent advances in the design of injectable hydrogels for stem cell delivery, especially for in vivo applications, are overviewed in this review.

Alginate/poly(amidoamine) injectable hybrid hydrogel for cell delivery

A covalently cross-linked injectable hybrid hydrogel, namely, alginate/poly(amidoamine) (PAMAM), with the objective of cell delivery was innovatively designed and synthesized using tetra-amino-functional PAMAM dendrimer as the cross-linker. With the increase in percentage of PAMAM cross-linker, the pore size and swelling ratio of hydrogels were in the range of 57 ± 18 μm to 88 ± 25 μm and 110 ± 16 to 157 ± 20, respectively. The study of attachment and proliferation of MC3T3-E1 pre-osteoblasts using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay through indirect and direct contact methods indicated a continuous increase in metabolically active live cells with time, implying non-cytotoxicity of the synthesized hydrogel. The live–dead assay showed >95% of live cells for alginate/PAMAM hydrogels, suggesting viability of the encapsulated cells. When the percentage of PAMAM cross-linker in alginate/PAMAM hydrogel was increased from 5 to 25, the percentage degradation rate decreased from 1.1 to 0.29%/day. Given that the poly(ethylene glycol) is commonly used cross-linker for hydrogel syntheses, we compared the behavior with poly(ethylene glycol). The incorporation of poly(ethylene glycol) in alginate/PAMAM hydrogel reduced the activity of MC3T3-E1 cells and their viability compared to the alginate/PAMAM hydrogels. The protonation of amino groups in alginate/PAMAM injectables under physiological conditions led to the formation of cationic hydrogels. These cationic hydrogels showed enhanced cell encapsulation and attachment ability because of electrostatic interaction with negatively charged cell surface as determined by cell adhesion and extensions from scanning electron microscope and vinculin assay and ability of in situ calcium phosphate mineralization. These observations point toward the potential use as an injectable scaffold for cell delivery and tissue engineering applications.

Hydrogels for Cartilage Regeneration, from Polysaccharides to Hybrids

The aims of this paper are: (1) to review the current state of the art in the field of cartilage substitution and regeneration; (2) to examine the patented biomaterials being used in preclinical and clinical stages; (3) to explore the potential of polymeric hydrogels for these applications and the reasons that hinder their clinical success. The studies about hydrogels used as potential biomaterials selected for this review are divided into the two major trends in tissue engineering: (1) the use of cell-free biomaterials; and (2) the use of cell seeded biomaterials. Preparation techniques and resulting hydrogel properties are also reviewed. More recent proposals, based on the combination of different polymers and the hybridization process to improve the properties of these materials, are also reviewed. The combination of elements such as scaffolds (cellular solids), matrices (hydrogel-based), growth factors and mechanical stimuli is needed to optimize properties of the required materials in order to facilitate tissue formation, cartilage regeneration and final clinical application. Polymer combinations and hybrids are the most promising materials for this application. Hybrid scaffolds may maximize cell growth and local tissue integration by forming cartilage-like tissue with biomimetic features.

Liposomal delivery of horseradish peroxidase for thermally triggered injectable hyaluronic acid–tyramine hydrogel scaffolds

A thermally triggered injectable scaffold was developed by utilizing thermoresponsive liposomes to segregate the crosslinking agent from a polymer.