Hydrogels for Ocular Gene Therapy: Sustained-Release Designs and the Promise and Limits of Preclinical Research
Delivery systems that keep nucleic acids in the eye longer
Hydrogels are being studied as a strategy for protecting nucleic acids and controlling their local release in ocular gene therapy. A review in Regenerative Biomaterials surveys exploratory studies in corneal and fundus diseases and notes that release control, long-term safety, and manufacturing reproducibility must be validated before clinical use. It does not newly establish efficacy in patients for any individual therapy.
Tear flow, blinking, and the corneal barrier impede topically applied therapeutic agents from reaching target tissues. The low stability of nucleic acids and their limited tissue penetration are additional challenges. A hydrogel is a water-rich, three-dimensional polymer network that can retain nucleic acids or carriers containing them, extending local residence time. However, gel residence in tissue and delivery of nucleic acids into cells are distinct evaluation measures.
The review covers delivery of DNA and RNA, as well as gene silencing and editing. In addition to directly loading nucleic acids, it includes approaches that combine gels with nanoparticles or viral vectors.
Release designs based on binding and stimulus responses
When nucleic acids are entrapped by mixing them into a gel precursor, release rates are influenced by diffusion driven by concentration gradients and by factors such as the cross-link density of the polymer network. Covalently linking nucleic acids can reduce their tendency to detach readily, but the linking process may also damage their structure. Releasing nucleic acids efficiently by breaking the bonds at the required place and time remains a design challenge. Covalent attachment alone does not guarantee a constant release rate.
The mechanisms of stimulus-responsive formulations also vary. Thermoresponsive formulations use gelation caused by temperature changes to promote local retention. Among photoresponsive formulations, some form cross-links upon exposure to light, while others undergo degradation of the polymer network to release their contents. The review considers applications of pH-responsive formulations in ocular gene therapy to remain limited.
One hydrogel contact lens described in the review was designed to deliver recombinant adeno-associated virus (rAAV) carrying the human insulin-like growth factor-1 (hIGF-I) gene. It was reported to release rAAV over 14 days while retaining gene-delivery capacity. However, therapeutic effects were not evaluated in a disease model in live animals, and comfort during wear and changes to the tear film remain to be assessed.
For fundus diseases, the review describes a photoresponsive hydrogel containing aflibercept and an antagomir that inhibits the action of miR-21-3p, a microRNA (miRNA). According to the review, drug release was observed for up to 45 days after in vivo photocrosslinking. This is a result from a preclinical formulation; it does not establish treatment duration or dosing intervals in patients.
Delivery efficiency and long-term safety as determinants of clinical translation
Hydrogels are a candidate platform for reducing the burden of repeated dosing. However, the review points out that passage across the blood-retinal barrier and nucleic-acid delivery efficiency in the posterior segment remain limited. On the ocular surface, tears, blinking, and pH changes also affect release, so adhesion and residence time need further adjustment.
The safety of materials that remain for long periods and of their degradation products is another key challenge for clinical translation. Inflammation associated with residual components, clearance of degradation products, and long-term effects on visual function have not been adequately assessed. Reproducibility of structure and release properties must also be confirmed when manufacturing is scaled up. Whether sustained release translates into an actual therapeutic benefit depends on formulation-specific validation of delivery performance and safety.
Specific design strategies and limitations of individual studies are described in the full review and the article citation.
Hydrogel-mediated gene therapy has achieved significant progress in the field of ophthalmology in recent years. As three-dimensional polymeric networks with high water content, hydrogels exhibit excellent biocompatibility, localized targeting capability and sustained-release properties. These characteristics make them ideal carriers for nucleic acid-based drugs, including DNA, RNA and gene editing systems. They can significantly improve the therapeutic efficacy and delivery kinetics of ocular drug administration, demonstrating unique advantages in the special ocular environment. This review systematically examines the current state of hydrogel-based gene therapy research in ophthalmology. First, recent advances in gene therapy are summarized, and the involved gene types and technical strategies are categorized. Second, various categories of hydrogels are outlined, including photo-responsive, temperature-sensitive and pH-responsive hydrogels. Their key characteristics for ocular gene delivery are also summarized. Furthermore, this article focuses on analyzing the design strategies for hydrogel-mediated gene therapy. Key design considerations include gene encapsulation, stability control and release kinetics. In addition, various gene-hydrogel integration strategies are discussed, including covalent conjugation and physical loading methods. Their impacts on transfection efficiency and therapeutic outcomes are also analyzed. Additionally, cutting-edge applications of hydrogel-based gene therapy in treating ocular diseases are systematically introduced, covering both anterior segment and fundus diseases. Finally, the limitations and future development prospects of these gene therapy hydrogel systems in ophthalmic research are discussed.
For developers of nucleic-acid delivery systems for corneal injury, this review can inform comparisons of release duration, surface adhesion, transparency, and residence under tear flow and blinking. Formulations for fundus diseases also need assessment of the administration route, retinal delivery efficiency, material degradation and clearance, and effects on visual function. When viruses or nanoparticles are combined with a gel, their contributions to nucleic-acid protection and cellular delivery should also be assessed separately. The 14-day and 45-day release examples provide reference evidence for formulation development, but cannot be interpreted as clinical evidence of reduced repeat injections or preserved vision in people.