Rheological and Adhesive Properties to Identify Cohesive and Dispersive Ophthalmic Viscosurgical Devices

Injectable in situ cross-linking hyaluronan hydrogel for easier removal of posterior vitreous cortex in vitrectomy

PURPOSE

Removing transparent vitreous tissues, such as a residual vitreous cortex (VC) or proliferative membrane, without damaging the retina is often problematic in vitrectomy. We examined the feasibility of an injectable in situ cross-linking hyaluronan hydrogel (XL-HA) for vitrectomy.

STUDY DESIGN

Experiments using ex vivo and in vivo animal models.

METHODS

HA-dibenzocyclooctyne and HA-azidoethylamine solutions were mixed to form XL-HA, which then gradually formed a hydrogel. We tested the function of XL-HA in ex vivo porcine eyes. We then examined the performance of XL-HA in in vivo rabbit models of posterior vitreous detachment, posterior VC removal, and proliferative vitreoretinopathy.

RESULTS

The ex vivo study showed that XL-HA rapidly embedded triamcinolone acetonide, mimicking VC attached to the retina, and became hard enough to be pinched with tweezers within 3 minutes, allowing us to remove only the triamcinolone acetonide without impairing the internal limiting membrane. In the in vivo rabbit models, XL-HA injection improved posterior vitreous detachment, and the thin and fragile posterior VC or fibrous proliferative membrane was readily peeled off without any damage to the underlying retina as compared with untreated controls. A short-term intraocular biocompatibility test demonstrated that the intraocular pressure remained normal with XL-HA injected into the eye. In addition, transmission electron microscopy showed no obvious abnormalities in the cornea or in the inner and outer retina.

CONCLUSION

The results indicate that XL-HA is a potential adjunctive device to help make vitrectomy safe, effective, and successful.

Development of in situ crosslinked hyaluronan as an adjunct to vitrectomy surgery

Ophthalmologists have used hyaluronan (HA) products as adjuncts to ocular surgery since the 1970s. However, HA products are not always functional in surgeries of the posterior eye segment due to their lack of biomechanical strength. In this study, we developed an in situ crosslinked HA (XL-HA) and evaluated its potential as an adjunct to vitrectomy surgery in an in vitro model with a triamcinolone acetonide (TA) layer used as a pseudo residual vitreous cortex (RVC). Within a few minutes at concentrations over 0.9%, XL-HA, generated by the click chemistry of HA-dibenzocyclooctyne and HA-azidoethylamine, formed a hydrogel with the appropriate hardness for tweezers peeling. XL-HA (concentration, 0.76-1.73%) without dispersion successfully entered the TA layer and removed more than 45% of the total TA. Dynamic viscoelasticity helps to explain the rheological behavior of hydrogels, and the assessment results for XL-HA indicated that suitable concentrations were between 0.97% and 1.30%. For example, 1.30% XL-HA hydrogel reached sufficient hardness at 3 min for tweezers peeling, and the TA removal ability exceeded 70%. These results demonstrated that XL-HA was a potential adjunct to successful vitrectomy.

Comparative evaluation of the results of phacoemulsification using domestic and foreign viscoelastics

BACKGROUND: Phacoemulsification, being the safest technique, is the golden standard of cataract surgery worldwide. However, as any surgery, it is accompanied by inevitable damage to intraocular structures. The most prevalent among them is the loss of corneal endothelial cells. In order to prevent these complications, various viscoelastics with particular features and characteristics are widely used. AIM: To compare the anatomical and functional state of ocular structures after standard phacoemulsification with monofocal posterior chamber intraocular lens (IOL) implantation using domestic (Kogevisc and Adgevisc) and foreign (Viscoat and Amvisc Plus) viscoelastics. MATERIALS AND METHODS: 60 cataract patients (60 eyes) were included in the clinical study, which were divided into two equal groups. In the first group (30 patients, 30 eyes), Adgevisc and Kogevisc (Solofarm, Russia) were used during the procedure. The mean age of the patients was 66 11 years. In the second group (30 patients, 30 eyes), Viscoat (Alcon) and Amvisc Plus (BauschLomb) were used. The mean age of the patients was 69.03 10.44 years. All patients underwent phacoemulsification with the implantation of the AcrySof IOL (model SA60AT, Alcon) according to the standard technique. Visual acuity, IOP level, CCT, corneal endothelial cell density were assessed. All studies were performed before surgery, the next day, 7 days and 1 month after surgery. RESULTS: In patients of the second group, on the 1st (p 0.05) and 7th day (p 0.01) after surgery, a statistically significant increase in IOP was revealed compared to the first group. The central cornea thickness in the early postoperative period was higher in patients of the second group, however, it was not statistically significant. The loss of corneal endothelial cells 1 month after surgery was 8.5 7.0% (p 0.01) in the first group and 6.6 6.4% in the second group (p 0.01). The mean value of endothelial cell loss in patients of the first group was higher, however, it was not statistically significant. The best corrected visual acuity in both groups at all stages of follow-up after surgery (days 1, 7 and 30) was comparable, there was no significant difference between the groups. CONCLUSIONS: The clinical efficacy of domestic adhesive and cohesive viscoelastics Adgevisc and Kogevisc (Solofarm, Russia) in phacoemulsification using the soft-shell technique is comparable to the foreign analogues Viscoat (Alcon) and Amvisc Plus (Bausch Lomb), which is confirmed by the absence of statistically significant differences in the studied parameters of the postoperative state of ocular structures and explained by their similar composition, molecular weight and viscosity.

Supramolecular host-guest hyaluronic acid hydrogels enhance corneal wound healing through dynamic spatiotemporal effects

Severe corneal wounds can lead to ulceration and scarring if not promptly and adequately treated. Hyaluronic acid (HA) has been investigated for the treatment of corneal wounds due to its remarkable biocompatibility, transparency and mucoadhesive properties. However, linear HA has low retention time on the cornea while many chemical moieties used to crosslink HA can cause toxicity, which limits their clinical ocular applications. Here, we used supramolecular non-covalent host-guest interactions between HA-cyclodextrin and HA-adamantane to form shear-thinning HA hydrogels and evaluated their impact on corneal wound healing. Supramolecular HA hydrogels facilitated adhesion and spreading of encapsulated human corneal epithelial cells ex vivo and improved corneal wound healing in vivo as an in situ-formed, acellular therapeutic membrane. The HA hydrogels were absorbed within the corneal stroma over time, modulated mesenchymal cornea stromal cell secretome production, reduced cellularity and inflammation of the anterior stroma, and significantly mitigated corneal edema compared to treatment with linear HA and untreated control eyes. Taken together, our results demonstrate supramolecular HA hydrogels as a promising and versatile biomaterial platform for corneal wound healing.

Ophthalmic Viscosurgical Devices (OVDs) in Challenging Cases: a Review

Ophthalmic viscoelastic devices (OVDs) are currently used in cataract surgery and have significantly improved the safety and effectiveness of this surgical procedure. OVDs are classified according to the zero-shear viscosity and the cohesion-dispersion index in cohesive, dispersive, and viscoadaptives. OVDs create and maintain anterior chamber depth and visibility, protecting the corneal endothelium and other intraocular tissues during surgery. The selection of the most adequate OVD is especially relevant when performing cataract surgery in challenging cases, such as in hard, mature cataracts, flat anterior chamber, pseudoexfoliation syndrome, intraoperative floppy iris syndrome, or glaucoma surgery. In such cases, OVD is crucial for facilitating the surgical procedure and the associated minimal complication rate. The use of a combination of OVDs (soft-shell technique and modifications), the use of blue-colored OVDs, and the combination of sodium hyaluronate with lidocaine have also been described as useful tools in some of these challenging cases.

Advances in Understanding the Mechanism of Ophthalmic Viscosurgical Device Retention in the Anterior Chamber or on the Corneal Surface during Ocular Surgery

Retention durability, especially in the eye, is one of the most important properties of ophthalmic viscosurgical devices (OVDs) during ocular surgery. However, the information on the physical properties of OVDs is insufficient to explain their retention durability. The purpose of this study is to clarify the mechanism of OVD retention to improve understanding of the behavior of OVDs during ocular surgery. To elucidate the mechanism of OVD retention, we have developed a new test method for measuring repulsive force. As a result, the maximum repulsive force of OVDs was positively and well correlated with the retention durability of investigated OVDs. Consequently, we demonstrated that the repulsive force could be used as an index of retention durability on the ocular surface and in the eye. We directly compared the intraocular retention durability of three OVDs (Shellgan, Viscoat, and Opegan-Hi) in ex vivo porcine eyes. Opegan-Hi was immediately removed from the anterior chamber, but Shellgan and Viscoat remained largely in the anterior chamber as determined by fluorescence imaging. These results showed that the intraocular retention behavior of OVDs was similar to their ocular surface behavior in our previous report, suggesting that retention durability is dependent on the OVD itself. The retention durability of Shellgan seemed to be higher than that of Viscoat, and the maximum repulsive force of Shellgan was 1.35-fold higher than that of Viscoat. Therefore, the repulsive force might be a useful index for assessing the difference in the retention durability between OVDs such as Shellgan and Viscoat.

Quantitative Assessment of Ophthalmic Viscosurgical Devices on Visibility, Spreadability, and Durability as Corneal Wetting Agents for the Wet Shell Technique

Purpose

To evaluate ophthalmic viscosurgical devices (OVDs) as corneal wetting agents for the wet shell technique, a common procedure in Japan to maintain the wettability of corneal surfaces.

Methods

We surveyed Japanese ophthalmologists to determine the current state of the wet shell technique. After developing three ex vivo testing methods, we evaluated the corneal wetting properties of OVDs including 3% hyaluronic acid (HA) solution and OVD products, Opegan, Opelead, Viscoat, Shellgan, Discovisc, and Opegan-Hi.

Results

Overall, 214 ophthalmologists (70%) had performed the wet shell technique, and 91% of ophthalmologists who performed vitreous surgery had performed this technique. Using a questionnaire, we evaluated the performance of OVD as corneal wetting agents as follows: (i) visibility, smoothness of OVD surface; (ii) spreadability, coverage of the cornea; and (iii) retention durability, residual ratio of OVD on the corneal surface. The smoothness and spreadability of Opegan, Opelead, and 3% HA were superior to other OVDs. Adding an appropriate amount of balanced salt solution to the other OVDs improved smoothness and spreadability similar to that of Opelead or 3% HA. Shellgan and Viscoat, combination OVDs consisting of 3% HA and 4% chondroitin sulfate, showed high retention durability, resulting in remaining longer on the cornea compared with other OVDs.

Conclusions

Physical properties of OVDs tested in this study may provide useful information for ophthalmologists to select a suitable OVD when performing the wet shell technique.

Addition Of D-Sorbitol Improves The Usability Of Ophthalmic Viscosurgical Devices

Purpose

To evaluate the effects of D-sorbitol addition on changes in the extrusion force of ophthalmic viscosurgical devices (OVDs).

Methods

OVD formulations; the mixtures of 3% hyaluronic acid (HA) and 4% chondroitin sulfate (CS) containing 0%, 0.5%, or 1.0% D-sorbitol were prepared. Each prefilled syringe of OVD was stored at room temperature for 0, 15, 30, 60, or 120 mins after a small amount of viscoelastic agent was discharged from the needle. The extrusion force values (kgf) of these OVDs when reused after storage were measured with a texture analyzer. Moreover, 10 healthy adults (5 men and 5 women) used a pinch sensor to measure the extrusion force values for the HA/CS combination without D-sorbitol which was stored in the above manner, and used a 4-step scale to score the usability of OVD.

Results

For the HA/CS combination without D-sorbitol, the extrusion force value was increased from its initial value (storage duration, 0 min) as storage duration increased. However, for the HA/CS combination containing 0.5% or 1.0% D-sorbitol, this value remained almost unchanged over time. Likewise, the pinch sensor-determined extrusion force values of HA/CS combination without D-sorbitol increased, depending on storage duration.

Conclusion

The addition of D-sorbitol to viscoelastic agent may suppress the needle clogging that occurs with OVD storage, and may improve the usability of OVDs during surgery.

3D Bioprinting of the Sustained Drug Release Wound Dressing with Double-Crosslinked Hyaluronic-Acid-Based Hydrogels

Hyaluronic acid (HA)-based hydrogels are widely used in biomedical applications due to their excellent biocompatibility. HA can be Ultraviolet (UV)-crosslinked by modification with methacrylic anhydride (HA-MA) and crosslinked by modification with 3,3'-dithiobis(propionylhydrazide) (DTP) (HA-SH) via click reaction. In the study presented in this paper, a 3D-bioprinted, double-crosslinked, hyaluronic-acid-based hydrogel for wound dressing was proposed. The hydrogel was produced by mixing HA-MA and HA-SH at different weight ratios. The rheological test showed that the storage modulus (G') of the HA-SH/HA-MA hydrogel increased with the increase in the HA-MA content. The hydrogel had a high swelling ratio and a high controlled degradation rate. The in vitro degradation test showed that the hydrogel at the HA-SH/HA-MA ratio of 9:1 (S9M1) degraded by 89.91% ± 2.26% at 11 days. The rheological performance, drug release profile and the cytocompatibility of HA-SH/HA-MA hydrogels with loaded Nafcillin, which is an antibacterial drug, were evaluated. The wound dressing function of this hydrogel was evaluated by Live/Dead staining and CCK-8 assays. The foregoing results imply that the proposed HA-SH/HA-MA hydrogel has promise in wound repair applications.

[Evaluation of Rheological Properties of Cohesive Ophthalmic Viscosurgical Devices Composed of Sodium Hyaluronate with High Molecular Weight-2019]

Ophthalmic viscosurgical devices (OVDs), mainly containing sodium hyaluronate (HA), are used in cataract surgeries to protect the cornea endothelium. In this study, the rheological properties of 9 launched products (containing 1% HA) were evaluated. The molecular weights (MWs) of HA estimated based on intrinsic viscosity varied widely, between 1100-2500 kDa, and showed a particular value for each product. Of the 9 products, 6 are classified as cohesive OVDs and their product specifications show the same value for intrinsic viscosity (25-45 dL/g), with high MW HA (>2000 kDa); however, the MW of each HA showed a particular value (2200-2500 kDa) within the range of the product specification. As with the MW of HA, apparent viscosity and dynamic rheological parameters showed particular values for each OVD. The product Opegan-Hi exhibited the highest value of apparent viscosity at low shear rate, and a solid-like behavior among the OVDs. In a questionnaire survey among 198 cataract surgeons, 42% of surgeons had experienced a difference in ability to maintain the depth of anterior chamber during surgery among the different cohesive OVDs used. This suggested that surgeons select OVD properties based on surgical procedure and patient cases. In conclusion, we demonstrated that each OVD has particular rheological properties within the range of the product specification defined by the intrinsic viscosity. The results might provide useful information for surgeons in their selection of OVDs based on their experience.