Polymeric hydrogel as a vitreous substitute: current research, challenges, and future directions

Risk Factors and Management of Intraocular Pressure Elevation After Vitrectomy Combined with Silicone Oil Tamponade

Silicone oil has emerged as the common option for intraocular tamponade during complicated retina vitrectomy. However, the postoperative elevation of intraocular pressure (IOP), influenced by numerous factors, remains a significant and frequently encountered complication that poses a potential threat to vision. Extensive research has been conducted to investigate the risk factors associated with elevated IOP following silicone oil tamponade, including silicone oil viscosity, preoperative high IOP, diabetes, and lens status. This comprehensive review aims to gather and summarize the current research findings regarding the risk factors contributing to IOP elevation following silicone oil tamponade, as well as the optimal management strategies for secondary glaucoma. The analysis includes the physicochemical properties of silicone oil, preoperative and intraoperative risk factors, and the effective management of secondary glaucoma. Enhancing our understanding of the primary factors associated with silicone oil-induced IOP elevation will facilitate the guidance of timely and appropriate interventions.

Forward Light Scattering of First to Third Generation Vitreous Body Replacement Hydrogels after Surgical Application Compared to Conventional Silicone Oils and Vitreous Body

To treat certain vitreoretinal diseases, the vitreous body, a hydrogel composed of mostly collagen and hyaluronic acid, must be removed. After vitrectomy surgery, the vitreous cavity is filled with an endotamponade. Previously, pre-clinical hydrogel-based vitreous body substitutes either made from uncrosslinked monomers (1st generation), preformed crosslinked polymers (2nd generation), or in situ gelating polymers (3rd generation) have been developed. Forward light scattering is a measure of Stray light induced by optical media, when increased, causing visual disturbance and glare. During pinhole surgery, the hydrogels are injected into the vitreous cavity through a small 23G-cannula. The aim of this study was to assess if and to what extent forward light scattering is induced by vitreous body replacement hydrogels and if Stray light differs between different generations of vitreous body hydrogel replacements due to the different gelation mechanisms and fragmentation during injection. A modified C-Quant setup was used to objectively determine forward light scattering. In this study, we found that the 1st and 3rd generation vitreous body replacements show very low stray light levels even after injection (2.8 +/- 0.4 deg2/sr and 0.2 +/- 0.2 deg2/sr, respectively) as gel fragmentation and generation of interfaces is circumvented. The 2nd generation preformed hydrogels showed a permanent increase in stray light after injection that will most likely lead to symptoms such as glare when used in patients (11.9 +/- 0.9 deg2/sr). Stray light of the 2nd generation hydrogels was 3- and 2-fold increased compared to juvenile and aged vitreous bodies, respectively. In conclusion, this significant downside in the forward light scattering of the 2nd generation hydrogels should be kept in mind when developing vitreous body replacement strategies, as any source of stray light should be minimized in patients with retinal comorbidities.

Innovative Strategies for Drug Delivery to the Ocular Posterior Segment

Innovative and new drug delivery systems (DDSs) have recently been developed to vehicle treatments and drugs to the ocular posterior segment and the retina. New formulations and technological developments, such as nanotechnology, novel matrices, and non-traditional treatment strategies, open new perspectives in this field. The aim of this mini-review is to highlight promising strategies reported in the current literature based on innovative routes to overcome the anatomical and physiological barriers of the vitreoretinal structures. The paper also describes the challenges in finding appropriate and pertinent treatments that provide safety and efficacy and the problems related to patient compliance, acceptability, effectiveness, and sustained drug delivery. The clinical application of these experimental approaches can help pave the way for standardizing the use of DDSs in developing enhanced treatment strategies and personalized therapeutic options for ocular pathologies.

Recent Advances of Intraocular Lens Materials and Surface Modification in Cataract Surgery

Advances in cataract surgery have increased the demand for intraocular lens (IOL) materials. At present, the progress of IOL materials mainly contains further improving biocompatibility, providing better visual quality and adjustable ability, reducing surgical incision, as well as dealing with complications such as posterior capsular opacification (PCO) and ophthalmitis. The purpose of this review is to describe the research progress of relevant IOL materials classified according to different clinical purposes. The innovation of IOL materials is often based on the common IOL materials on the market, such as silicon and acrylate. Special properties and functions are obtained by adding extra polymers or surface modification. Most of these studies have not yet been commercialized, which requires a large number of clinical trials. But they provide valuable thoughts for the optimization of the IOL function.

Penetrating-peptide-mediated non-invasive Axitinib delivery for anti-neovascularisation

The unique physiological makeup of the eye limits the use of small-molecule drugs for treating the posterior segment of the eye. Nevertheless, transmembrane-peptide-mediated non-invasive drug delivery can serve as an ideal treatment strategy, as it is capable of delivering small-molecule drugs across the membrane in the form of eye drops, thereby achieving the effective treatment of neovascularisation in the posterior cavity. In this study, we screened and compared the posterior segment distribution of two poly(ethylene glycol)-distearoylphosphatidylethanolamine carriers modified using targeting-peptides. Thereafter, a transmembrane peptide (i.e., PENE) with a greater ability of transmembrane delivery was selected for delivering the anti-vascular drug (i.e., Axitinib) to the posterior segment of the eye. Using two different mouse models with fundus neovascular diseases, the complete non-invasive delivery of Axitinib to the posterior segment of the eye was confirmed using the targeted system; the designed eye drops (i.e., PENE-nanoparticles) could achieve drug distribution to the retina and veins of the eye as well as good drug permeability for renewal. Moreover, using the eye-drop treatment, neovascularisation was substantially reduced, demonstrating the high efficacy of this drug delivery system. This study, which combines nanodrug-loading technology and the transmembrane delivery of penetrating-peptides to achieve the goal of the non-invasive delivery of small-molecule drugs through the dense blood vessels of the sclera, shows wide applicability and considerably expands the use of ocular drugs. Thus, this study is expected to help develop a more acceptable drug administration strategy for the drug treatment of the posterior segment of the eye.

Long-Term Biocompatibility of a Highly Viscously Thiol-Modified Cross-Linked Hyaluronate as a Novel Vitreous Body Substitute

Purpose: In surgical ophthalmology, the treatment of complicated retinal and vitreous diseases is one of the central challenges. For this purpose, the vitreous body is removed as part of the standard therapy and replaced by a temporary tamponade to stabilize the position of the retina. Since the tamponading properties of previous materials such as silicone oils, gases, or semi-fluorinated alkanes are a combination of their surface tension and their buoyancy vector, they cannot completely fill the vitreous cavity. The aim of this work was to test in vivo a novel vitreous body substitute (ViBos strong) based on cross-linked hyaluronic acid for its compatibility.

Methods: A pars plana vitrectomy with posterior vitreous detachment was performed in the right eye of 18 pigmented rabbits, with subsequent injection of ViBos strong. Follow-up examination included slit-lamp examination, funduscopy, intraocular pressure measurements (IOP), optical coherence tomography (OCT), and electroretinogram (ERG) measurements. The rabbits were sacrificed at three different time points (1, 3, and 6 months; each 6 animals) and examined macroscopically and prepared for histological examination (HE staining) and immunohistochemistry (Brn3a and glial fibrillary acidic protein (GFAP)).

Results: ViBos strong demonstrated good intraoperative handling and remained stable for at least 1 month and degraded slowly over 6 months. IOP was within clinical acceptable values at all follow-up examinations. Retinal function was well preserved after instillation of the hydrogel and comparable to the untreated eye after 6 months in OCT, ERG, and histological examinations. An increase in the GFAP expression was found in the surgery eyes, with a peak in the 3-month group. The Brn3a expression was not significantly affected by vitrectomy with ViBos strong.

Conclusion: Highly viscously thiol-modified cross-linked hyaluronate showed a good biocompatibility in rabbit eyes over 6 months after vitrectomy, making it a promising potential as a vitreous substitute.

Super-fast in situ formation of hydrogels based on multi-arm functional polyethylene glycols as endotamponade substitutes

Polymer-based hydrogels used in the vitreous cavity could lead to an unsatisfactory gel-forming state, uncontrollable swelling, and potential cytotoxicity. Their application can significantly impair the filling effect and cause severe side effects in the surrounding tissues. To address the concerns, a poly(ethylene glycol)-engineered hydrogel capable of fast in situ gel formation (less than 1 min), with an ultralow swelling ratio and no cytotoxicity in the rabbits' eyes, was constructed as a vitreous substitute. The multi-arm polyethylene glycols (PEGs) modified with functional groups (thiol and maleimide) possess high reaction efficiency in the vitreous cavity and present excellent biomimetic characteristics of the natural vitreous humor in vitro. After injection with a double syringe via a 25-gauge needle in the eyes of rabbits for 6 months, the hydrogel functioned as an artificial vitreous body that could highly promote retinal detachment repair, with excellent biocompatibility and high transparency, and without bio-degradation or ocular complications. Collectively, the fast in situ forming hydrogel could achieve quick and good filling in the vitreous cavity without cytotoxicity, which makes it a promising long-term endotamponade substitute.