Exploring Hydrogels: Key Materials for Biomedical Applications

Section Overview

• Introduction
• Key Material Types
• Crosslinking Methods
• Key Applications
• Recent Advances
• Additives for Hydrogel
• Related Products

Introduction

Hydrogels are three-dimensional networks of hydrophilic polymers with the ability to retain a large amount of water, closely mimicking the properties of natural tissue. Another key property of these materials is their biocompatibility, ensuring minimal adverse reactions when in contact with biological tissues¹. These distinctive properties render them highly useful in biomedical applications.  Hydrogels can be derived from natural sources like collagen and alginate or can be chemically produced from polymers such as PEG and PVA. The natural versatility in composition and structure permits the customization of mechanical strength, biodegradability, and bioactivity to meet the requirements for targeted applications.

Key Material Types

Based on the source, hydrogels can be broadly classified into natural and synthetic categories. Each type has unique properties, advantages, and applications in biomedical fields. Comparative properties of natural and synthetic hydrogel polymers are summarized in Table 1. 

Natural Polymers

Natural polymers such as collagen, gelatin, and alginate are favored for biomedical applications due to their excellent biocompatibility and biodegradability. Collagen supports cell growth and is widely used in tissue engineering; gelatin offers easy modification and gelation properties for drug delivery; and alginate forms biocompatible hydrogels ideal for cell encapsulation and wound healing.

Synthetic Polymers

Polyethylene glycol (PEG) is renowned for its biocompatibility and hydrophilicity and is widely used in drug delivery and tissue engineering hydrogels. Polyvinyl alcohol (PVA) offers excellent mechanical strength, biocompatibility, and moisture retention, making it ideal for wound dressings and scaffolds. Polyacrylic acid (PAA) is valued for its water absorption and pH-responsive gelation, suited for controlled drug release and tissue regeneration.

Crosslinking Methods

Hydrogels can be crosslinked using physical methods (e.g., hydrogen bonding) or chemical methods (e.g., covalent bonds), depending on the desired application. These advances enhance the applicability of hydrogels through improved interaction with biological systems, making them more effective in therapeutic and regenerative medicine. Representative hydrogel recipes with monomers, cross-linkers, initiators, and key biomedical applications are presented in Table 2. 

Key Applications

Hydrogels offer versatile solutions across the biomedical field due to their unique ability to retain water and adapt to biological environments. They enable developments in wound healing, medical devices, and tissue engineering by supporting advanced therapies, drug delivery, and 3D cell culture solutions.

Medical Devices

Wound Healing

Hydrogels support wound healing by maintaining moisture, promoting cell growth, and delivering antimicrobial agents. Integrating smart polymers allows continuous health monitoring, enabling real-time tracking of metrics like pH, glucose, or infection status for better care².

Contact Lenses and Dental Applications

Hydrogels are used in contact lenses for their oxygen permeability, softness, and ability to retain moisture—enhancing comfort during wear. In dentistry, the durability of hydrogels supports sustained drug release, stable tissue regeneration support, and periodontal repair with structural integrity and therapeutic function retained over long-term clinical use. Their biocompatibility and versatility make them valuable in both optical and oral care fields³.

Tissue Engineering

Hydrogels provide a scaffold that supports cell attachment, growth, and differentiation, crucial for tissue regeneration. They mimic the extracellular matrix (ECM) structure, allowing for the integration of cells and growth factors to form new tissues. Applications include cartilage repair, bone regeneration, and vascular tissue engineering.

3D Bioprinting

Hydrogels play a crucial role in 3D bioprinting as bioinks due to their high water content, biocompatibility, and customizable properties. They support cell encapsulation, maintain viability, and mimic the extracellular matrix. This facilitates the precise construction of tissues and organs, aiding regenerative medicine and personalized therapeutic solutions⁴. 

Controlled Release Mechanisms

Hydrogels can encapsulate drugs and release them in a controlled manner, improving therapeutic efficacy and reducing side effects. They are particularly useful for localized delivery, where the drug is released at the target site over an extended period⁵.  By regulating the drug's half-life, hydrogels enable sustained delivery for applications like cancer therapy or chronic wound management, improving therapeutic efficacy and patient compliance.

Personal Care – Cosmetic Industry

Hydrogels play a pivotal role in personal care due to their hydration, biocompatibility, and tunable properties. With respect to formulations, they stabilize and control the release of active ingredients in creams and serums. Dermal fillers, which are primarily hyaluronic acid-based hydrogels, provide volume restoration, elasticity, and long-lasting effects. A key factor behind their durability is 1,4-butanediol diglycidyl ether (BDDE), the gold-standard crosslinking agent.⁶ BDDE covalently links HA chains, strengthening the hydrogel structure, improving elasticity, and reducing enzymatic breakdown. This translates to longer-lasting fillers, fewer retreatments, and enhanced patient satisfaction. Beyond fillers, BDDE-crosslinked hydrogels are enabling next-generation cosmetic solutions. They provide a stable matrix for smart, responsive systems that deliver antioxidants, peptides, or UV filters precisely when needed, supporting skin health and rejuvenation. In high-end plastic surgery, injectable hydrogels support tissue regeneration and contouring with minimal invasiveness. Advanced personal care solutions utilize smart hydrogels, which are responsive to pH, temperature, or enzymes, enabling targeted delivery of antioxidants, peptides, or UV filters for enhanced skin health and rejuvenation.

Recent Advances

Recent innovations in hydrogel technology focus on enhancing their functional properties and are summarized in Table 3. 

Additives for Hydrogel

Additives are widely employed in hydrogel systems to enhance their performance and expand the functionality of hydrogel-based contact lenses. For instance, incorporating photo-absorbers like 2-(4-Benzoyl-3-hydroxyphenoxy)ethyl acrylate into the hydrogel matrix can regulate light penetration during photopolymerization. This not only improves crosslinking control, spatial resolution, and mechanical robustness of the hydrogel but also enables the integration of UV and blue light filtering capabilities. Such enhancements are particularly valuable for protecting the eyes from harmful radiation, reducing digital eye strain, and improving overall comfort and safety for users in both medical and personal care applications.

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