Application of a Novel Film Sealant Technology for Penetrating Corneal Wounds: An Ex-Vivo Study

Adhesive and self-healing materials for central nervous system repair

The central nervous system (CNS) has a limited ability to regenerate after a traumatic injury or a disease due to the low capacity of the neurons to re-grow and the inhibitory environment formed in situ. Current therapies include the use of drugs and rehabilitation, which do not fully restore the CNS functions and only delay the pathology progression. Tissue engineering offers a simple and versatile solution for this problem through the use of bioconstructs that promote nerve tissue repair by bridging cavity spaces. In this approach, the choice of biomaterial is crucial. Herein, we present recent advances in the design and development of adhesive and self-healing materials that support CNS healing. The adhesive materials have the advantage of promoting recovery without the use of needles or sewing, while the self-healing materials have the capacity to restore the tissue integrity without the need for external intervention. These materials can be used alone or in combination with cells and/or bioactive agents to control the inflammation, formation of free radicals, and proteases activity. We discuss the advantages and drawbacks of different systems. The remaining challenges that can bring these materials to clinical reality are also briefly presented.

New thin-film adhesive for sealing full-thickness corneal incisions in rabbits

PURPOSE

To compare the repair of penetrating corneal incisions in an in vivo rabbit model using a laser-activated thin-film adhesive, sutures, or self-seal.

SETTING

The University of Sydney, Camperdown, Australia.

DESIGN

Animal studies.

METHODS

Under an operating microscope, 2.0 mm penetrating incisions were created in 162 right eyes. Incisions in one group were repaired with the adhesive, the second group received a single 10-0 nylon suture, and the third group was left to self-seal. Rabbits were killed humanely at predetermined timepoints over 2 weeks, and wound healing was assessed using burst pressure and immunohistological studies. A modified McDonald-Shadduck scoring was used to assess eyes.

RESULTS

The mean burst pressure of the adhesive group was significantly higher than the sutured or self-sealed groups at all timepoints within the first 72 hours. At 0 hour, the burst pressure was 98.0 (±17.0) mm Hg, 30.6 (±2.1) mm Hg, and 3.8 (±0.6) mm Hg (P < .00001) for adhesive-treated (n = 5), sutured (n = 5), and self-sealed wounds (n = 5), respectively. These increased to 229.0 (±53.7) mm Hg, 12.4 (±2.9) mm Hg, and 27.3 (±4.0) mm Hg (P = .0011) at 72 hours. The modified McDonald-Shadduck score was significantly higher for eyes repaired using the adhesive than those sutured or left to self-seal for the first 72 hours. On histology and immunofluorescence, adhesive treatment demonstrated better wound approximation and higher myofibroblastic activation than the other groups.

CONCLUSIONS

The adhesive was efficacious in sealing penetrating corneal incisions and tolerated higher burst pressures than sutures or self-seal. The adhesive was biocompatible in rabbits, and incisions demonstrated a rapid gain in wound strength that sustained over the study period.

A paintable ophthalmic adhesive with customizable properties based on symmetrical/asymmetrical cross-linking

In situ and efficient incision sealing for ophthalmic surgery remains unresolved. Current commercially available gel adhesives often suffer from unsuitable gelation time, difficulty in micro-delivery, and mismatched degradation period, leading to difficulties for application in ocular tissue areas. Herein, a novel hydrogel adhesive was developed based on the simultaneous crosslinking of poly(lysine) (PLL) and lysine (Lys) with an end-modified active ester multi-arm polyethylene glycol (PEG) via the amidation reaction, where the residual terminal active ester of PEG can also bond to amino groups on tissue to provide strong adhesion. Due to the different molecular structures around their amino groups, PLL and Lys can crosslink with 4-arm-PEG-NHS (active ester) respectively, to form symmetrical and asymmetrical crosslinking networks, which exhibit various mechanical properties. Therefore, just by adjusting PLL/Lys ratios, the PEG-PLL-Lys hydrogel can easily possess a suitable gelation time, appropriate mechanical properties and matched degradation rate. As a result, a paintable, readily accessible and biocompatible ophthalmic tissue adhesive (sealant) is prepared for sealing ocular tissue incision. Considering the simple strategy and outstanding performance, the PEG-PLL-Lys hydrogel is promising for clinical transformation.

Laser-Activated Corneal Adhesive: Retinal Safety in Rabbit Model

Purpose

The purpose of this study was to investigate whether laser irradiation, used to activate an adhesive for sealing penetrating corneal incisions, causes any ophthalmoscopically or histologically visible retinal changes.

Methods

Baseline fundus assessment was conducted prior to laser irradiation of eyes of pigmented Dutch Belted rabbits. Treatment group was 18 eyes with the corneal adhesive activated in situ by a near infrared laser (125 mW for 45 seconds). The positive control group was 18 eyes, each irradiated for 60 seconds at 375, 500, 625, and 750 mW at different retinal locations. Unexposed regions of the retina were used as negative internal control. Ophthalmoscopic assessment was conducted immediately after laser exposure and prior to euthanasia. Retinas were histologically assessed at 0, 3, 72, and 168 hours after treatment.

Results

No ophthalmoscopically or histologically visible retinal changes were observed in the treatment group immediately, nor up to 168 hours after laser irradiation. In the positive control group, the incidences of ophthalmoscopically visible retinal lesions increased with irradiation power: 5.6% at 375 mW, 16.7% at 500 mW, 44.4% at 625 mW, and 50% at 750 mW. Histologically, retinal damage was observed as coagulative necrosis to all layers of the neural retina, including the retinal pigment epithelium.

Conclusions

The laser irradiation process used in the corneal adhesive technology did not cause any ophthalmoscopically or histologically visible retinal changes in the in vivo pigmented rabbit model. Prolonged exposure with this laser and at higher power can cause coagulative necrosis to the retina.

Translational Relevance

The corneal adhesive can be applied in humans without causing laser retinal damage.