On Feb 17, 2025, Petit and colleagues from the Royal College of Surgeons in Ireland and CÚRAM, Research Ireland Centre for Medical Devices, published an article in Mater Today Bio entitled "Hyaluronic acid as a versatile building block for the development of biofunctional hydrogels: In vitro models and preclinical innovations." The core finding is that targeted chemical modifications are essential to leverage the inherent biocompatibility of Hyaluronic Acid (HA), transforming it from a simple extracellular matrix (ECM) component into a robust, mechanically stable, and highly bioactive scaffold. This engineered glycan platform enables precise control over material properties like stiffness, degradation, and self-healing, opening pathways for highly advanced in vitro models and complex preclinical therapeutic interventions. The review thoroughly explores the chemical diversity of HA derivatives—including methacrylate, acrylate, and norbornene modifications—and their profound impact across diverse tissue repair applications, encompassing cartilage, bone, muscle, and neural tissue regeneration. It emphasizes that rational polymer design is the critical determinant for successful clinical outcomes.

Overview

HA, a non-sulfated glycosaminoglycan, is naturally abundant throughout the body's extracellular matrix. Its intrinsic bioactivity is strongly correlated with its molecular weight (MW): high MW HA acts as an immunosuppressive and anti-inflammatory agent, while lower MW fragments can promote pro-inflammatory phenotypes. This inherent versatility, combined with its established biocompatibility and low toxicity, positions HA as the leading choice among natural biopolymers for biomaterial development. The driving necessity for the research detailed in this paper is the fact that native HA, despite its biological advantages, degrades too rapidly and lacks the mechanical rigidity required to form stable scaffolds for complex tissue engineering or sustained drug delivery applications, thus demanding strategic chemical modification. Crucially, HA is a natural ligand for key cellular receptors, most notably CD44, which is expressed on many cell types, including stem cells and immune cells. The way HA interacts with CD44 is highly dependent on its MW, explaining the differential signaling observed in biological systems. Therefore, the manufacturing process ensures the modified HA retains critical binding epitopes while simultaneously achieving the desired mechanical strength and stability, bridging the gap between molecular glycobiology and macro-scale biomaterial functionality.

Research Results

• Tuneable Synthesis for Controlled Network Stability

To overcome the native HA's rapid turnover and structural fragility, specific chemical modifications are employed to facilitate controlled crosslinking. Techniques such as the introduction of maleate groups (MAHA) or norbornene groups (NorHA) allow the saccharide backbone to undergo reactions like Michael addition or thiol-ene photopolymerization, respectively. This precise degree of substitution (DS) during synthesis is paramount for manufacturing. Solvent-based protocols often achieve the highest efficiency (up to 88.2% DS), offering stringent control over the final hydrogel's crosslinking density, which directly governs its stiffness and mesh size—parameters critical for regulating encapsulated cell behavior.

Fig.1 Chemical structure of HA, chemical groups for modification, and resulting HA hydrogel precursors. (Petit, et al., 2025)

• Engineering Dynamic, Injectable Glycan Scaffolds

A major innovation highlighted is the move toward hydrogels with dynamic mechanical properties that more accurately mimic the native ECM. This is achieved using supramolecular chemistry, specifically host-guest interactions (e.g., adamantane/cyclodextrin pairs). By modifying HA with these reversible binding moieties, the resulting hydrogels exhibit shear-thinning and self-healing capabilities. These features are critical for clinical translation, allowing the hydrogel precursor solution to be easily injected in situ through a narrow-gauge needle, followed by rapid, non-toxic reformation of the scaffold network. This process ensures high cell viability during delivery and allows the scaffold to dynamically remodel under physiological stress.

Fig.2 Graphical depiction of bioactive moieties that have been conjugated to enhance the bioactivity of modified HA hydrogels. (Petit, et al., 2025)

• Biofunctionalization and Cellular Programming

The transformation of HA into a true Biofunctional Material is achieved by covalently conjugating biomolecules, effectively programming the scaffold to modulate cellular responses. By attaching cell-adhesion peptides (such as RGD sequences), growth factors (e.g., VEGF or BMP-2), or specific proteins, the hydrogel can be tailored to direct cellular behavior. This biochemical customization allows the HA platform to regulate stem cell differentiation, promote tissue-specific regeneration (like cartilage or bone), and influence the local inflammatory environment. This level of control is essential for creating sophisticated in vitro models for disease progression and for developing high-efficacy regenerative therapies.

Conclusion

The comprehensive review strongly reinforces that Chemical Modification and functionalization are not merely optional steps but mandatory protocols in advanced HA biomaterial manufacturing. The central conclusion is the ability of these engineered glycans to act as highly tunable materials where mechanical properties can be precisely decoupled from biochemical signaling. This enables the design of complex, multi-functional therapeutic systems. Looking forward, the most innovative application lies in the development of dynamic, immunomodulatory HA-based hydrogels. Future work must prioritize integrating molecules that actively suppress or guide the immune response, ensuring a favorable microenvironment for tissue integration and regeneration, thereby solidifying HA's role as an enabling technology for next-generation medicine. Furthermore, the detailed control over the HA matrix is paving the way for sophisticated in vitro models, such as high-content screening platforms and multi-organ-on-a-chip systems. These models, built on precisely defined HA scaffolds, offer unprecedented opportunities to study disease mechanisms and screen new drugs in a physiologically relevant 3D environment, dramatically accelerating both fundamental glycobiology research and the development of new regenerative treatments.