Polyethylene Glycol-Based Synthetic Hydrogel Sealant for Closing Vitrectomy Wounds: An In Vivo and Histological Study

Progress in the Application of Hydrogels in Intervertebral Disc Repair: A Comprehensive Review

PURPOSE OF REVIEW

Intervertebral disc degeneration (IVDD) is a common orthopaedic disease and an important cause of lower back pain, which seriously affects the work and life of patients and causes a large economic burden to society. The traditional treatment of IVDD mainly involves early pain relief and late surgical intervention, but it cannot reverse the pathological course of IVDD. Current studies suggest that IVDD is related to the imbalance between the anabolic and catabolic functions of the extracellular matrix (ECM). Anti-inflammatory drugs, bioactive substances, and stem cells have all been shown to improve ECM, but traditional injection methods face short half-life and leakage problems.

RECENT FINDINGS

The good biocompatibility and slow-release function of polymer hydrogels are being noticed and explored to combine with drugs or bioactive substances to treat IVDD. This paper introduces the pathophysiological mechanism of IVDD, and discusses the advantages, disadvantages and development prospects of hydrogels for the treatment of IVDD, so as to provide guidance for future breakthroughs in the treatment of IVDD.

Formulation and characterization of ionically crosslinked gellan gum hydrogels using trilysine at low temperatures for antibody delivery

Research of the nontraditional polysaccharide gellan gum (GG) is a growing space for the development of novel drug delivery systems due to its tunable physic-mechanical properties, biocompatibility, and stability in a wide range of environments. Unfortunately, high temperature crosslinking is often required, representing a limiting factor for the incorporation of thermosensitive therapeutic agents. Here, we demonstrated that GG can be crosslinked at a low temperature (38 °C) using a simple fabrication process that utilizes trilysine as an alternative to traditional mono- or divalent ion crosslinkers. While elevated temperature mixing is still required to form a clear GG solution, crosslinking of 0.5 - 1 % GG (w/v) in the presence of trilysine (0.03 % - 0.05 % w/v) was achieved at 38 °C resulting in hydrogels with suitable working formulations to facilitate syringe loading. Low injection forces (< 20 N), and biocompatibility was evaluated with normal human dermal fibroblast (cell viability > 90 %). Frequency sweep showed a transition from purely liquid-like behavior to gel-like behavior with increased trilysine concentration. A temperature dependent behavior was lost with higher trilysine concentrations, indicating stable hydrogel formation. NMR results suggest that trilysine participates in gelation via both ionic interactions between the primary amines of trilysine and the carboxylate residues of glucuronic acid and hydrogen bonding. Released studies showed that GG hydrogels can entrap and provide sustained release of IgG in relation to the crosslinker, and antibody concentration used, with a burst release within the first 24 h (∼80 % cumulative released) followed by a sustained released for up to 5 days. Overall, findings demonstrate a promising nontoxic injectable hydrogel that requires lower crosslinking temperatures, is simple to manufacture and serves as a carrier of thermosensitive therapeutic agents.

NONPERFORATING INTRASCLERAL STABBING FOR SUTURELESS 23G SCLEROTOMY CLOSURE

PURPOSE

The need for suturing leaking sclerotomies have not been eliminated completely in transconjunctival sutureless vitrectomy (TSV). This study aims to describe a novel technique for 23-gauge (G) sclerotomy closure in TSV surgery and discuss its effectiveness.

MATERIALS AND METHODS

Two hundred and thirty cases of 180 patients who underwent 23G TSV with various diagnoses were included to the study. Cases with connective tissue diseases, thin sclera, and significant conjunctival and scleral scarring were excluded. Nonperforating intrascleral stabbing (NIS) was performed to leaking 23G sclerotomies (n = 650) and 27G chandeliers (n = 84). Demographics, rate of sclerotomy closure with NIS procedure, the need for suturing, and complications of the procedure were recorded.

RESULTS

The overall success of NIS was found to be 91.0% in sclerotomies. Although 9.1% of sclerotomies required sutures, 592 of the 650 sclerotomies could be closed with NIS procedure ( P < 0.001). Nonperforating intrascleral stabbing procedure helped close 98.8% of leaking 27G chandeliers. An average of 1.28 ± 0.52 NIS attempts were needed for successful sclerotomy closure. Closure of sclerotomies with the NIS technique were somewhat related to the location of the sclerotomy, history of TSV and NIS, duration of TSV, and type of endotamponade. Hypotonia and choroidal detachment were seen in one case. No additional interventions were needed to normalize intraocular pressure in any case. Subconjunctival hemorrhage happened to be the leading complication of the procedure.

CONCLUSION

NIS procedure seems as a practical, reproducible, cost-effective, and uncomplicated approach, which significantly reduces the need to suture 23G sclerotomies. Further studies are required.

Advances in biomaterials as a retinal patch for the repair of rhegmatogenous retinal detachment

Rhegmatogenous retinal detachment (RRD) is the most common retinological emergency that can cause blindness without surgical treatment. RRD occurs when liquefied vitreous accumulates between the neurosensory retina and the retinal pigment epithelium via retinal breaks, which are caused by the separation of the vitreous from the retina with aging. Currently, the main treatment option is pars plana vitrectomy, which involves surgical removal of the vitreous and laser photocoagulation around retinal breaks to generate firm chorioretinal adhesion, as well as subsequent filling of the vitreous cavity with long-lasting substitutes (expansile gas or silocone oil) to prevent the connection between the subretinal space and the vitreous cavity via the breaks before the chorioretinal adhesion firm enough. However, the postoperative face-down position and the not very satisfactory first retinal reattachment rate place a heavy burden on patients. With the development of technology and materials engineering, researchers have developed biomaterials that can be used as a retinal patch to seal retinal breaks and prevent the connection of subretinal space and vitreous cavity via breaks, thus replacing the long-lasting vitreous substitutes and eliminating the postoperative face-down position. Preclinical studies have demonstrated that biomaterial sealants have enough biocompatibility and efficacy in the in vitro and in vivo experiments. Some sealants have been used in clinical trials on a small scale, and the results indicate promising application prospects of the biomaterial sealants as retinal patches in the repair of RRD. Herein, we review the recent advances in biomaterials as retinal patches for the repair of RRD, focusing on the biomaterial categories, methods, and procedures for sealing retinal breaks, as well as their biocompatibility and efficacy, current limitations, and development perspectives.

Polyethylene Glycol-Based Synthetic Hydrogel Sealant for Filtration Bleb Leaks: An In Vivo and Histologic Study

Purpose

To evaluate the efficacy of polyethylene glycol (PEG)-based synthetic sealant for closing bleb leaks after glaucoma filtration surgery.

Methods

Tube shunt surgery that included implantation of a 22-gauge indwelling catheter and intraoperative mitomycin C was performed in the left eyes of 11 New Zealand white rabbits. Seven days postoperatively, all filtration blebs were perforated with an 18-gauge needle to create a bleb hole. In six rabbits, the holes were covered with the sealant and irradiated with blue-green light for 60 seconds; in the five control rabbits, the holes were untreated. For 3 weeks after the tube shunt surgery, the eyes were checked for bleb leaks, and the intraocular pressure (IOP) was measured in both eyes. Finally, the operated eyes were enucleated for histologic examination.

Results

The bleb leaks stopped in the eyes in which sealant was used and persisted in the other eyes. The sealant preserved the bleb function; the IOPs in these eyes were significantly (P < 0.05) lower than the right eyes that did not undergo surgery. Hematoxylin and eosin staining showed that the holes were closed and covered with conjunctival epithelial cells in the eyes in which sealant was applied; the holes were open in the control eyes. Immunohistochemical staining showed that the bleb holes in which the sealant was applied had fewer inflammatory cells.

Conclusions

The PEG sealant has the potential to seal bleb leaks effectively.

Translational Relevance

Application of the PEG sealant can be used as adjunct therapy for bleb leaks in glaucoma surgery.

Evaluation of leakage resistance improvement in transconjunctival sutureless vitrectomy sclerotomies closed with adhesives. an experimental study

Background

The purpose of this paper is to study the utility of adhesives (artificial-cyanoacrylate and biological-fibrin glue) for improving transconjunctival sutureless vitrectomy (TSV) sclerotomy closure competency.

Methods

Experimental and observer-masked study in which after performing TSV in cadaveric pig eyes, different adhesives were tested on sclerotomy entrances in order to determine if they improved closure competency in face of progressive intraocular pressure increase. In 76 eyes cyanoacrylate-treated sclerotomies were compared with sclerotomies in which no additional manoeuvre to aid closing was performed; in 76 eyes fibrin glue with no manoeuvre; and in the last 76 eyes, cyanoacrylate-treated sclerotomies were compared with fibrin glue-treated sclerotomies.

Results

A total of 228 eyes had a 23-gauge TSV performed. Both cyanoacrylate and fibrin glue treated sclerotomies achieved higher mean opening pressures when compared with nontreated sclerotomies in the same eye (p < 0.002). When cyanoacrylate was compared with biological adhesive in the same eye, no statistically significant differences were obtained (p = 0.216).

Discussions

This experimental study provides support for the possible role of adhesives in improving TSV sclerotomy closure competency in clinical practice.

Surgical adhesives in ophthalmology: history and current trends

Tissue adhesives are gaining popularity in ophthalmology, as they could potentially reduce the complications associated with current surgical methods. An ideal tissue adhesive should have superior tensile strength, be non-toxic and anti-inflammatory, improve efficiency and be cost-effective. Both synthetic and biological glues are available. The primary synthetic glues include cyanoacrylate and the recently introduced polyethylene glycol (PEG) derivatives, while most biological glues are composed of fibrin. Cyanoacrylate has a high tensile strength, but rapidly polymerises upon contact with any fluid and has been associated with histotoxicity. Fibrin induces less toxic and inflammatory reactions, and its polymerisation time can be controlled. Tensile strength studies have shown that fibrin is not as strong as cyanoacrylate. While more research is needed, PEG variants currently appear to have the most promise. These glues are non-toxic, strong and time-effective. Through MEDLINE and internet searches, this paper presents a systematic review of the current applications of surgical adhesives to corneal, glaucoma, retinal, cataract and strabismus surgeries. Our review suggests that surgical adhesives have promise to reduce problems in current ophthalmic surgical procedures.