Intraocular Bioadhesives in Vitreoretinal Surgeries: A Systematic Review

BACKGROUND

Bioadhesion is the ability of materials to adhere to biological surfaces. Bioadhesives are substances which induce or promote bioadhesion. The internal application of bioadhesives is gaining popularity in recent years and is being increasingly utilized in vitreoretinal surgeries. The aim of this review is to discuss the various bioadhesives and their applications in vitreoretinal surgeries.

METHODS

PubMed, Google Scholar, ePub and Cochrane library database were used for literature selection. Keywords such as vitreoretinal surgery, bioadhesives, intraocular bioadhesives, glue, fibrin glue, cyanoacrylate glue and transforming growth factor were used individually and in differing combinations to perform a comprehensive systematic literature search.

RESULTS

A total of 47 papers were retrieved and included in this review. Cyanoacrylate glue was the first bioadhesive to be utilized for vitreoretinal surgery in human eyes in 1976. The most common indications for the use of bioadhesives were in optic disc pit maculopathy, macular holes and rhegmatogenous retinal detachments.

CONCLUSION

The use of intraocular bioadhesives in vitreoretinal surgery represents a significant and evolving area of interest within ophthalmic research. While the pioneering use of cyanoacrylate glue, fibrin glue and transforming growth factor beta demonstrated the possible use of intraocular adhesives, fibrin glue is the most widely used intraocular bioadhesive in vitreoretinal surgery.

Bioinspired Asymmetric-Adhesion Janus Hydrogel Patch Regulating by Zwitterionic Polymers for Wet Tissues Adhesion and Postoperative Adhesion Prevention

Asymmetrically adhesive hydrogel patch with robust wet tissue adhesion simultaneously anti-postoperative adhesion is essential for clinical applications in internal soft-tissue repair and postoperative anti-adhesion. Herein, inspired by the lubricative role of serosa and the underwater adhesion mechanism of mussels, an asymmetrically adhesive hydrogel Janus patch is developed with adhesion layer (AL) and anti-adhesion layer (anti-AL) through an in situ step-by-step polymerization process in the mold. The AL exhibits excellent adhesion to internal soft-tissues. In contrast, the anti-AL demonstrated ultralow fouling property against protein and fibroblasts, which hinders the early and advanced stages of development of the adhesion. Moreover, the Janus patch simultaneously promotes tissue regeneration via ROS clearance capability of catechol moieties in the AL. Results from in vivo experiments with rabbits and rats demonstrate that the AL strongly adheres to traumatized tissue, while the anti-AL surface demonstrate efficacy in preventing of post-abdominal surgery adhesions in contrast to clinical patches. Considering the advantages in terms of therapeutic efficacy and off the shelf, the Janus patch developed in this work presents a promise for preventing postoperative adhesions and promoting regeneration of internal tissue defects.

Functionalized chitosan based antibacterial hydrogel sealant for simultaneous infection eradication and tissue closure in ocular injuries

Management of infections at ocular injury often requires prolonged and high dose of antibiotic, which is associated with challenges of antibiotic resistance and bacterial biofilm formation. Tissue glues are commonly used for repairing ocular tissue defects and tissue regeneration, but they are ineffective in curing infection. There is a critical need for antibacterial ocular bio-adhesives capable of both curing infection and aiding wound closure. Herein, we present the development of an imine crosslinked N-(2-hydroxypropyl)-3-trimethylammonium chitosan chloride (HTCC)‑silver chloride nanocomposites (QAm1-Agx) and poly-dextran aldehyde (PDA) based bactericidal sealant (BacSeal). BacSeal exhibited potent bactericidal activity against a broad spectrum of bacteria including their planktonic and stationary phase within a short duration of 4 h. BacSeal effectively reduced biofilm-embedded MRSA and Pseudomonas aeruginosa by ∼99.99 %. In ex-vivo human cornea infection model, BacSeal displayed ∼99 % reduction of ocular infection. Furthermore, the hydrogel exhibited excellent sealing properties by maintaining ocular pressure up to 75 mm-Hg when applied to human corneal trauma. Cytotoxicity assessment and hydrogel-treated human cornea with a retained tissue structure, indicate its non-toxic nature. Collectively, BacSeal represents a promising candidate for the development of an ocular sealant that can effectively mitigate infections and may assist in tissue regeneration by sealing ocular wounds.

Comparative Evaluation of Autologous Fibrin Glue and Conventional Sutures in the Treatment of Gingival Recession Using Connective Tissue Graft - A Randomised Controlled Clinical Trial

BACKGROUND

The combination of the coronally positioned flap with connective tissue grafting in treating gingival recession defects has been shown to demonstrate the highest success rate.

AIM

The aim of the present study was to compare and evaluate the efficiency between autologous fibrin glue (AFG) and conventional absorbable sutures in the treatment of marginal tissue recessions using connective tissue grafts (CTGs) and the coronally advanced flap (CAF) technique.

METHODS

Twenty Miller's class I and II recession sites in maxillary or mandibular areas in chronic periodontitis patients were treated as group I (test): CTG + CAF + AFG; and group II (control): CTG + CAF with conventional absorbable sutures. Clinical parameters in both groups were recorded at baseline (t0) and six months (t1) postoperatively in terms of gingival recession height (RH), root coverage esthetic score (RCES), visual analogue scale (VAS), and healing index (HI).

RESULTS

The RH, RCES, VAS, and HI were significantly reduced at the end of six months compared to baseline ( P < 0.005) in both groups; however, there was no statistical difference between the groups, indicating the equivalent efficacy of AFG and conventional sutures in healing.

CONCLUSION

All the treated sites were found to have appreciable root coverage with satisfactory post-operative healing. Hence, it may be suggested that both AFG and absorbable sutures are equally efficient in post-surgical soft tissue healing.

Photocurable and Temperature-Sensitive Bioadhesive Hydrogels for Sutureless Sealing of Full-Thickness Corneal Wounds

Penetrating corneal wounds can cause severe vision impairment and require prompt intervention to restore globe integrity and minimize the risk of infection. Tissue adhesives have emerged as a promising alternative to suturing for mitigating postoperative complications. However, conventional water-soluble adhesives suffer formidable challenges in sealing penetrating corneal wounds due to dilution or loss in a moist environment. Inspired by the robust adhesion of mussels in aquatic conditions, an injectable photocurable bioadhesive hydrogel (referred to as F20HD5) composed of polyether F127 diacrylate and dopamine-modified hyaluronic acid methacrylate is developed for sutureless closure of corneal full-thickness wounds. F20HD5 exhibits high transparency, wound-sealing ability, proper viscosity, biodegradability, and excellent biocompatibility. It allows in situ cross-linking via visible light, thereby providing sufficient mechanical strength and adhesiveness. In vivo, the adhesive hydrogel effectively closed penetrating linear corneal incisions and corneal injuries with minimal tissue loss in rabbits. During the 56-day follow-up, the hydrogel facilitates the repair of the injured corneas, resulting in more symmetrical curvatures and less scarring in distinction to the untreated control. Thus, bioinspired hydrogel holds promise as an effective adhesive for sealing full-thickness corneal wounds.

Human cornea-derived extracellular matrix hydrogel for prevention of post-traumatic corneal scarring: A translational approach

Corneal scarring and opacification are a significant cause of blindness affecting millions worldwide. The current standard of care for corneal blindness is corneal transplantation, which suffers from several drawbacks. One alternative approach that has shown promise is the use of xenogeneic corneal extracellular matrix (ECM), but its clinical applicability is challenging due to safety concerns. This study reports the innovative use of human cornea-derived ECM to prevent post-traumatic corneal scarring. About 30 - 40% of corneas donated to the eye banks do not meet the standards defined for clinical use and are generally discarded, although they are completely screened for their safety. In this study, human cornea-derived decellularized ECM hydrogel was prepared from the non-transplantation grade human cadaveric corneas obtained from an accredited eye-bank. The prepared hydrogel was screened for its efficacy against corneal opacification following an injury in an animal model. Our in vivo study revealed that, the control collagen-treated group developed corneal opacification, while the prophylactic application of human cornea-derived hydrogel effectively prevented corneal scarring and opacification. The human hydrogel-treated corneas were indistinguishable from healthy corneas and comparable to those treated with the xenogeneic bovine corneal hydrogel. We also demonstrated that the application of the hydrogel retained the biological milieu including cell behavior, protein components, optical properties, curvature, and nerve regeneration by remodeling the corneal wound after injury. The hydrogel application is also sutureless, resulting in faster corneal healing. We envision that this human cornea-derived ECM-based hydrogel has potential clinical application in preventing scarring from corneal wounding. STATEMENT OF SIGNIFICANCE: There are significant challenges surrounding corneal regeneration after injury due to extensive scarring. Although there is substantial research on corneal regeneration, much of it uses synthetic materials with chemical cross-linking methods or xenogeneic tissue-based material devices which have to undergo exhaustive safety analysis before clinical trials. Herein, we demonstrate the potential application of a human corneal extracellular matrix hydrogel without any additional materials for scarless corneal tissue regeneration, and a method to reduce the wasting of donated allogenic corneal tissue from eye banks. We found no difference in efficacy between the usage of human tissues compared to xenogeneic sources. This may help ease clinical translation and can be used topically without sutures as an outpatient procedure.

Tissue Adhesives for the Management of Corneal Perforations and Challenging Corneal Conditions

Corneal perforations are ophthalmological emergencies which can have serious and detrimental consequences, if not managed timely and appropriately. These are a significant cause of ocular morbidity and can result in decreased vision, blindness, and even loss of the eye. Corneal perforations can be managed using a range of treatment approaches, including temporary solutions such as the application of corneal glue and bandage contact lens, as well as definitive treatment such as corneal transplantation. Tissue glues/adhesives were developed as substitutes for sutures in ophthalmic surgery. Unlike sutures, these glues are associated with shorter overall surgical times and reduced inflammation, thus improving postoperative comfort without compromising wound strength. The available tissue adhesives can be broadly classified into two types: synthetic (eg, cyanoacrylate derivatives) and biological (eg, fibrin glue). Cyanoacrylate glue is chiefly used as a corneal patch to manage acute corneal perforations and improve visual outcomes. Fibrin glue can be used instead of cyanoacrylate glue in many conditions with the benefits of reduced conjunctival and corneal inflammation and reaction. Apart from this, each type of adhesive is distinct in terms of its benefits as well as limitations and is accordingly used for different indications. The present review focuses on the two main types of tissue adhesives, their applications in the management of corneal perforations, the associated complications, safety and efficacy data related to their use available in the literature and the need for newer adhesives in this field.

Instant and Tough Adhesives for Rapid Gastric Perforation and Traumatic Pneumothorax Sealing

Hydrogel adhesives are hot spots due to their ubiquity and practical relevance. However, achieving a robust wet adhesion is still a challenge due to the preferential formation of hydrogen bonds between interfacial fluids and bulk hydrogel, as well as targeted substrates. Herein, a half-dry adhesive consisting of a silk fibroin (SF) semi-interpenetrating network and poly(acrylic acid) covalent network, which can allow a rapid liquid adsorption and repulsion process encountering a wet tissue, is reported. The remaining water enables excellent hydrogel flexibility to a dynamic surface, while the β-sheet fold endows its tough bulk strength under the peeling-off process. Notably, the wet adhesion energy versus porcine skin is 1440 J m^-2 due to the combination of hydrogen bonds, electrostatic interactions, and chain entanglement derived from SF. In particular, both in vitro and in vivo outcomes indicate excellent hemostatic effects and result in incision closure of skin, artery, gastric perforation, and lung. After the first-stage closure, polyacrylic-silk fibroin adhesive (PSA) sealants can detach from the lung surface, fitting well to the healing period. By virtue of the reliable adhesion and good noncytotoxicity, PSA may be a prospective candidate for tissue sealant and drug carrier applications.

Strong and bioactive bioinspired biomaterials, next generation of bone adhesives

The bone adhesive is a clinical requirement for complicated bone fractures always articulated by surgeons. Applying glue is a quick and easy way to fix broken bones. Adhesives, unlike conventional fixation methods such as wires and sutures, improve healing conditions and reduce postoperative pain by creating a complete connection at the fractured joint. Despite many efforts in the field of bone adhesives, the creation of a successful adhesive with robust adhesion and appropriate bioactivity for the treatment of bone fractures is still in its infancy. Because of the resemblance of the body's humid environment to the underwater environment, in the latest decades, researchers have pursued inspiration from nature to develop strong bioactive adhesives for bone tissue. The aim of this review article is to discuss the recent state of the art in bone adhesives with a specific focus on biomimetic adhesives, their action mechanisms, and upcoming perspective. Firstly, the adhesive biomaterials with specific affinity to bone tissue are introduced and their rational design is studied. Consequently, various types of synthetic and natural bioadhesives for bone tissue are comprehensively overviewed. Then, bioinspired-adhesives are described, highlighting relevant structures and examples of biomimetic adhesives mainly made of DOPA and the complex coacervates inspired by proteins secreted in mussel and sandcastle worms, respectively. Finally, this article overviews the challenges of the current bioadhesives and the future research for the improvement of the properties of biomimetic adhesives for use as bone adhesives.

Soft Devices for High-Resolution Neuro-Stimulation: The Interplay Between Low-Rigidity and Resolution

The field of neurostimulation has evolved over the last few decades from a crude, low-resolution approach to a highly sophisticated methodology entailing the use of state-of-the-art technologies. Neurostimulation has been tested for a growing number of neurological applications, demonstrating great promise and attracting growing attention in both academia and industry. Despite tremendous progress, long-term stability of the implants, their large dimensions, their rigidity and the methods of their introduction and anchoring to sensitive neural tissue remain challenging. The purpose of this review is to provide a concise introduction to the field of high-resolution neurostimulation from a technological perspective and to focus on opportunities stemming from developments in materials sciences and engineering to reduce device rigidity while optimizing electrode small dimensions. We discuss how these factors may contribute to smaller, lighter, softer and higher electrode density devices.

Assessment of the Retinal Toxicity and Sealing Strength of Tissue Adhesives

PURPOSE

The purpose of this in vitro prospective nonrandomized study is to compare the toxicity and strength of cyanoacrylate and hydrogel adhesives on human retinal pigment epithelium (RPE) cells and porcine retina, respectively.

METHODS

The toxicity of cyanoacrylate (histoacryl, dermabond, superglue), ReSure PEG, and Tisseel fibrin glue on human RPE cells was determined by growing RPE cells in vitro, applying the different adhesives to the cells, and monitoring for disruption of growth over 3 days. The relative strength of these adhesives was tested by gluing a 3 mm piece of foam to a porcine retina and determining the amount of force needed to break the attachment.

RESULTS

0.085 N of force was required to break the porcine retinal tissue (p = .913). Histoacryl adhesive exhibited high strength (0.247 N) and high RPE toxicity (0.55 mm inhibition zone after 24 hrs). The strength of Tisseel fibrin glue was 0.078 N while that of ReSure was only 0.053 N. Both Tisseel and ReSure were nontoxic to the RPE cells.

CONCLUSIONS

Tisseel VH fibrin sealant may provide the best option for sealing retinal breaks because of its high strength and low retinal toxicity.

In vivo biocompatibility evaluation of in situ-forming polyethylene glycol-collagen hydrogels in corneal defects

The available treatment options include corneal transplantation for significant corneal defects and opacity. However, shortage of donor corneas and safety issues in performing corneal transplantation are the main limitations. Accordingly, we adopted the injectable in situ-forming hydrogels of collagen type I crosslinked via multifunctional polyethylene glycol (PEG)-N-hydroxysuccinimide (NHS) for treatment and evaluated in vivo biocompatibility. The New Zealand White rabbits (N = 20) were randomly grouped into the keratectomy-only and keratectomy with PEG-collagen hydrogel-treated groups. Samples were processed for immunohistochemical evaluation. In both clinical and histologic observations, epithelial cells were able to migrate and form multilayers over the PEG-collagen hydrogels at the site of the corneal stromal defect. There was no evidence of inflammatory or immunological reactions or increased IOP for PEG-collagen hydrogel-treated corneas during the four weeks of observation. Immunohistochemistry revealed the presence of α-smooth muscle actin (α-SMA) in the superior corneal stroma of the keratectomy-only group (indicative of fibrotic healing), whereas low stromal α-SMA expression was detected in the keratectomy with PEG-collagen hydrogel-treated group. Taken together, we suggest that PEG-collagen may be used as a safe and effective alternative in treating corneal defect in clinical setting.

Emerging bioadhesives: from traditional bioactive and bioinert to a new biomimetic protein-based approach

Bioadhesives have reached significant milestones over the past two decades. Research has shown not only to produce adhesives capable of adhering to dry tissue but recently wet tissue as well. However, most bioadhesives developed have exhibited high adhesion strength yet lack other properties required for versatility in application, such as elasticity, biocompatibility and biodegradability. Adapting from limitations met from early bioadhesives and meeting the current demand allows novel bioadhesives to reach new milestones for the future. In this review, we overview the progression and variations of bioadhesives, current trends, characterisation techniques and conclude with future perspectives for bioadhesives for tissue engineering applications.

Adhesive Tissue Engineered Scaffolds: Mechanisms and Applications

A variety of suture and bioglue techniques are conventionally used to secure engineered scaffold systems onto the target tissues. These techniques, however, confront several obstacles including secondary damages, cytotoxicity, insufficient adhesion strength, improper degradation rate, and possible allergic reactions. Adhesive tissue engineering scaffolds (ATESs) can circumvent these limitations by introducing their intrinsic tissue adhesion ability. This article highlights the significance of ATESs, reviews their key characteristics and requirements, and explores various mechanisms of action to secure the scaffold onto the tissue. We discuss the current applications of advanced ATES products in various fields of tissue engineering, together with some of the key challenges for each specific field. Strategies for qualitative and quantitative assessment of adhesive properties of scaffolds are presented. Furthermore, we highlight the future prospective in the development of advanced ATES systems for regenerative medicine therapies.

Photo Cross-linkable Biopolymers for Cornea Tissue Healing

Light can act as an effective and strong agent for the cross-linking of biomaterials and tissues and is recognized as a safe substitute for chemical cross-linkers to modify mechanical and physical properties and promote biocompatibility. This review focuses on the research about cross-linked biomaterials with different radiation sources such as Laser or Ultraviolet (UV) that can be applied as scaffolds, controlled release systems, and tissue adhesives for cornea healing and tissue regeneration.

An Intrinsically-Adhesive Family of Injectable and Photo-Curable Hydrogels with Functional Physicochemical Performance for Regenerative Medicine

Attaching hydrogels to soft internal tissues is crucial for the development of various biomedical devices. Tough sticky hydrogel patches present high adhesion, yet with lack of injectability and the need for treatment of contacting surface. On the contrary, injectable and photo-curable hydrogels are highly attractive owing to their ease of use, flexibility of filling any shape, and their minimally invasive character, compared to their conventional preformed counterparts. Despite recent advances in material developments, a hydrogel that exhibits both proper injectability and sufficient intrinsic adhesion is yet to be demonstrated. Herein, a paradigm shift is proposed toward the design of intrinsically adhesive networks for injectable and photo-curable hydrogels. The bioinspired design strategy not only provides strong adhesive contact, but also results in a wide window of physicochemical properties. The adhesive networks are based on a family of polymeric backbones where chains are modified to be intrinsically adhesive to host tissue and simultaneously form a hydrogel network via a hybrid cross-linking mechanism. With this strategy, adhesion is achieved through a controlled synergy between the interfacial chemistry and bulk mechanical properties. The functionalities of the bioadhesives are demonstrated for various applications, such as tissue adhesives, surgical sealants, or injectable scaffolds.

Prevention of Corneal Myofibroblastic Differentiation In Vitro Using a Biomimetic ECM Hydrogel for Corneal Tissue Regeneration

Corneal scarring is one of the major causes of blindness, affecting millions worldwide. Despite recent advancements in surgical strategies, there is an unmet need for a clinically feasible material and methods to prevent scarring following corneal injury. In this study, we report the potential utility of a hydrogel derived from cadaveric animal corneas, using a decellularized corneal matrix hydrogel (abbreviated as dCMH), which is prepared by a simple method. This hydrogel is easily injectable, biocompatible, and has the ability to maintain good shape-retention properties at 37 °C, which make it suitable for in vivo applications. Furthermore, our gene expression studies and immunofluorescence studies indicate that dCMH maintains the morphology and function of keratocytes in vitro and prevents their transdifferentiation to myofibroblasts. From the above results, it is evident that dCMH maintains the keratocytes with the ability to regenerate the corneal defect without scar. We thus suggest a simple yet effective approach for corneal tissue decellularization and that dCMH can be a promising material for prophylaxis against blinding scar formation in an injured cornea.

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

Aim: To compare the burst pressures of corneal wounds closed with a laser-activated, chitosan-based thin film adhesive against self-seal, sutures and cyanoacrylate. Methods: 2, 4 or 6 mm penetrating corneal wounds were created on 100 freshly enucleated bovine eyes. The wounds were closed using a laser-activated chitosan adhesive (n = 30), self-sealed (control) (n = 30), sutures (n = 20) or cyanoacrylate glue (Histoacryl®) (n = 20). The corneoscleral rim was dissected and mounted onto a custom burst pressure testing chamber. Water was pumped into the chamber at 9ml/hr. The fluid pressure prior to wound leakage was recorded as the ‘burst pressure’. Results: The burst pressure for the 2, 4 and 6 mm wounds were 239.2 mmHg (SD = ±102.4), 181.7 mmHg (SD = ±72.8) and 77.4 mmHg (SD = ±37.4) (p < 0.00001), respectively, for chitosan adhesive. Burst pressure was 36.4 mmHg (SD = ±14.7), 4.8 mmHg (SD = ±4.9) and 2.7 mmHg (SD = ±1.3) (p < 0.00001), respectively, for the self-sealed group. For 4 and 6mm wounds, burst pressures with sutures were 33.0 mmHg (SD = ±19) and 23.5 mmHg (SD = ±17.4) (p = 0.0087), respectively. For cyanoacrylate, burst pressures for 2 and 4 mm wounds were 698 mmHg (SD = ±240.3) and 494.3 mmHg (SD = ±324.6) (p = 0.020087), respectively. Conclusion: This laser-activated chitosan-based adhesive sealed bovine corneal wounds up to 6 mm in length. Burst pressure was higher for the adhesive than sutured or self-sealed wounds, but lower than for cyanoacrylate.

Comparison and application of commercially available fibrin sealants in ophthalmology

Fibrin glues carry many advantages over traditional suture as a tissue adhesive and have been increasingly used in a variety of ophthalmic procedures over the past 15 years. Several fibrin sealants are commercially available worldwide, each of which differs slightly in its composition and mechanism of delivery. The focus of our review is to briefly discuss the reported uses of fibrin in ophthalmic surgery and provide a broad overview of the properties associated with each commercially available fibrin sealant.

Ocular adhesives: Design, chemistry, crosslinking mechanisms, and applications

Closure of ocular wounds after an accident or surgery is typically performed by suturing, which is associated with numerous potential complications, including suture breakage, inflammation, secondary neovascularization, erosion to the surface and secondary infection, and astigmatism; for example, more than half of post-corneal transplant infections are due to suture related complications. Tissue adhesives provide promising substitutes for sutures in ophthalmic surgery. Ocular adhesives are not only intended to address the shortcomings of sutures, but also designed to be easy to use, and can potentially minimize post-operative complications. Herein, recent progress in the design, synthesis, and application of ocular adhesives, along with their advantages, limitations, and potential are discussed. This review covers two main classes of ocular adhesives: (1) synthetic adhesives based on cyanoacrylates, polyethylene glycol (PEG), and other synthetic polymers, and (2) adhesives based on naturally derived polymers, such as proteins and polysaccharides. In addition, different technologies to cover and protect ocular wounds such as contact bandage lenses, contact lenses coupled with novel technologies, and decellularized corneas are discussed. Continued advances in this area can help improve both patient satisfaction and clinical outcomes.

Sutureless repair of corneal injuries using naturally derived bioadhesive hydrogels

Corneal injuries are common causes of visual impairment worldwide. Accordingly, there is an unmet need for transparent biomaterials that have high adhesion, cohesion, and regenerative properties. Herein, we engineer a highly biocompatible and transparent bioadhesive for corneal reconstruction using a visible light cross-linkable, naturally derived polymer, GelCORE (gel for corneal regeneration). The physical properties of GelCORE could be finely tuned by changing prepolymer concentration and photocrosslinking time. GelCORE revealed higher tissue adhesion compared to commercial adhesives. Furthermore, in situ photopolymerization of GelCORE facilitated easy delivery to the cornea, allowing for bioadhesive curing precisely according to the required geometry of the defect. In vivo experiments, using a rabbit stromal defect model, showed that bioadhesive could effectively seal corneal defects and induce stromal regeneration and re-epithelialization. Overall, GelCORE has many advantages including low cost and ease of production and use. This makes GelCORE a promising bioadhesive for corneal repair.

Role of plasma-derived fibrin on keratinocyte and fibroblast wound healing

Fibrin has excellent biocompatibility and biological properties to support tissue regeneration and promote wound healing. However, the role of diluted fibrin in wound healing has yet to be elucidated as it is commonly used in high concentration. This study was aimed to examine the effects of diluted plasma-derived fibrin (PDF) on keratinocyte and fibroblast wound healing in term of cell proliferation, migration, extracellular matrix (ECM) production and soluble factor secretion. Two PDF concentrations, 10 and 20% (v/v) were tested on keratinocytes and fibroblasts indirectly co-cultured in the transwell system. The control group was cultured with 5% FBS. Results showed that PDF reduced the keratinocyte growth rate and fibroblast migration, and increased the fibroblast ECM gene expression whereby significant differences were found between the 20% PDF group and the 5% FBS group. Similar trend was seen for the 10% PDF group but the differences were not significant. Comparison of the soluble factors between the PDF groups demonstrated that the level of growth-related oncogene alpha, interleukin-8 and epithelial neutrophil-activating peptide-78 were significantly higher in the 10% PDF group, whilst interleukin-1 alpha and granulocyte-macrophage colony stimulating factor were significantly more concentrated in the 20% PDF group. Our results suggested that PDF selectively elevated the expression of collagen type 1 and collagen type 3 in fibroblasts but slowed down the migration in concentration-dependent manner. These novel findings provide new insight into the role of PDF in wound healing and may have important implications for the use of fibrin in skin tissue engineering.

Optimization of Fibrin Glue Spray Systems for Ophthalmic Surgery

PURPOSE

To optimize fibrin glue (FG) spray for ophthalmic surgery using two spray applicators, EasySpray and DuploSpray systems, by varying the distance from point of application and the pressure/flow rate, and to compare the adhesive strength of sutured and sutureless (FG sprayed) conjunctival graft surgery in a rabbit model.

METHODS

FG was sprayed on a 0.2 mm-thick sheet of paper using EasySpray by variously combining application distances of 2.5, 5, 7.5, and 10 cm with pressures of 10, 15, and 20 psi. DuploSpray was used at the same distances but with varying flow rates of 1 and 2 L/min. Subsequently, FG was sprayed on porcine corneas and FG thickness was analyzed by histology. In addition, adhesive strength of the conjunctival graft (0.5 × 0.5 cm) attached to the rabbit cornea by sutured and sutureless surgery (FG spray) was compared using a tension meter.

RESULTS

Histology measurements revealed that the FG thickness decreased with increases in distance and pressure of spray using the EasySpray applicator on paper and porcine corneal sections. The adhesive strength of the sutured conjunctival graft (41 ± 4.85 [kilopascal] KPa) was found to be higher than the graft attached by spraying (10 ± 2.3 KPa) and the sequential addition of FG (6 ± 0.714 KPa).

CONCLUSIONS

The EasySpray applicator formed a uniform spread of FG at a distance-pressure combination of 5 cm and 20 psi. The conjunctival graft attached with sutures had higher adhesive strength compared with grafts glued with a spray applicator. Although the adhesive strength of FG applied through the applicator was similar to the drop-wise sequential technique, the former was more cost effective because more samples could be sprayed compared with the sequential manual technique.

TRANSLATIONAL RELEVANCE

The standardization of the spray system for the application of FG in ophthalmology will provide an economical method for delivering consistent healing results after surgery.

Effect of fibrin glue on the biomechanical properties of human Descemet's membrane

Background

Corneal transplantation has rapidly evolved from full-thickness penetrating keratoplasty (PK) to selective tissue corneal transplantation, where only the diseased portions of the patient's corneal tissue are replaced with healthy donor tissue. Descemet's membrane endothelial keratoplasty (DMEK) performed in patients with corneal endothelial dysfunction is one such example where only a single layer of endothelial cells with its basement membrane (10–15 µm in thickness), Descemet's membrane (DM) is replaced. It is challenging to replace this membrane due to its intrinsic property to roll in an aqueous environment. The main objective of this study was to determine the effects of fibrin glue (FG) on the biomechanical properties of DM using atomic force microscopy (AFM) and relates these properties to membrane folding propensity.

Methodology/Principal Findings

Fibrin glue was sprayed using the EasySpray applicator system, and the biomechanical properties of human DM were determined by AFM. We studied the changes in the “rolling up” tendency of DM by examining the changes in the elasticity and flexural rigidity after the application of FG. Surface topography was assessed using scanning electron microscopy (SEM) and AFM imaging. Treatment with FG not only stabilized and stiffened DM but also led to a significant increase in hysteresis of the glue-treated membrane. In addition, flexural or bending rigidity values also increased in FG-treated membranes.

Conclusions/Significance

Our results suggest that fibrin glue provides rigidity to the DM/endothelial cell complex that may aid in subsequent manipulation by maintaining tissue integrity.