Novel bioadhesive hyaluronan-itaconic acid crosslinked films for ocular therapy

Tamarind seed polysaccharide-metformin insert: Higher ocular retention, slow-release, and efficacy against corneal burn

Metformin (MET) can be an alternative therapeutic strategy for managing ocular burn primarily because of its pleiotropic mechanism. Longer retention on the ocular surface and sustained release are necessary to ensure the efficacy of MET for ocular application. Although the high aqueous solubility of MET is good for formulation and biocompatibility, it makes MET prone to high nasolacrimal drainage. This limits ocular residence and may be a challenge in its application. To address this, polymers approved for ophthalmic application with natural origin were analyzed through in silico methods to determine their ability to bind to mucin and interact with MET. An ocular insert of MET (3 mg/6 mm) was developed using a scalable solvent casting method without using preservatives. The relative composition of the insert was 58 ± 2.06 %w/w MET with approximately 14 %w/w tamarind seed polysaccharide (TSP), and 28 %w/w propylene glycol (PG). Its stability was demonstrated as per the ICH Q1A (R2) guidelines. Compatibility, ocular retention, drug release, and other functional parameters were evaluated. In rabbits, efficacy was demonstrated in the 'corneal alkali burn preclinical model'. TSP showed potential for mucoadhesion and interaction with MET. With adequate stability and sterility, the insert contributed to adequate retention of MET (10-12 h) in vivo and slow release (30 h) in vitro. This resulted in significant efficacy in vivo.

Matrix hyaluronic acid and bilayer poly-hydroxyethyl methacrylate-hyaluronic acid films as potential ocular drug delivery platforms

This study aimed to design hydrogel based films comprising hyaluronic acid (HA) to overcome limitations of currently used eye drops. Timolol-loaded crosslinked (X2) HA-based and bilayer (B2) (pHEMA/PVP-HA-based layers) films were designed and characterized. The films were transparent (UV, visual observation) with crosslinked (<80 %) films showing lower light transmittance than bilayer (>80 %) films. X2 showed significantly higher swelling capacity, tensile strength and elastic modulus (5491.6 %, 1539.8 Nmm-2, 1777.2 mPa) than B2 (1905.0 %, 170.0N mm-2, 67.3 mPa) respectively. However, X2 showed lower cumulative drug released and adhesive force (27.3 %, 6.2 N) than B2 (57.5 %, 8.6 N). UV sterilization did not significantly alter physical properties, while SEM and IR microscopy showed smooth surface morphology and homogeneous drug distribution. Timolol permeation (EpiCorneal™/porcine cornea) depended on the film matrix with erodible films showing similar permeation to commercial eyedrops. Drug permeation for porcine cornea (X2 = 549.0.2, B2 = 312.1 μgcm-2 h-1) was significantly faster than EpiCorneal™ (X2 = 55.2, B2 = 37.6 μgcm-2 h-1), but with a linear correlation between them. All the selected optimized films showed acceptable compatibility (MTT assay) with both HeLa cells and EpiCorneal™. In conclusion, crosslinked and bilayer HA based films showed ideal characteristics suitable for potential ocular drug delivery, though further work is required to further optimize these properties and confirm their efficacy including in vivo tests.

Hyaluronic Acid Aerogels Made Via Freeze-Thaw-Induced Gelation

The biodegradability, biocompatibility, and bioactivity of hyaluronic acid (HA), a natural polysaccharide, combined with the low density, high porosity, and high specific surface area of aerogels attract interest for biomedical applications such as wound dressings. In this work, physically cross-linked HA aerogels were prepared via the freeze-thaw (FT) induced gelation method, solvent exchange, and drying with supercritical CO2. The morphology and properties of HA aerogels (volume shrinkage, density, and specific surface area) were investigated as a function of several process parameters: HA concentration, solution pH, number of FT cycles, and type of nonsolvent used during solvent exchange. We demonstrate that the HA solution pH plays a key role in the aerogel formation, as not all conditions result in materials with high specific surface area. HA aerogels were of low density (<0.2 g/cm3), high specific surface area (up to 600 m2/g), and high porosity (≥90%). Scanning electron microscopy pictures revealed that HA aerogels present a porous structure with meso- and small macropores. The results show that HA aerogels are promising biomaterials with tunable properties and internal structure that offer high potential as, e.g., wound dressings.

Hyaluronic acid hydrogels crosslinked via blue light-induced thiol-ene reaction for the treatment of rat corneal alkali burn

To assess corneal inflammation from alkali chemical burns, we examined the therapeutic effects of in situ-forming hyaluronic acid (HA) hydrogels crosslinked via blue light-induced thiol-ene reaction on a rat corneal alkali burn model. Animals were divided into three groups (n = 7 rats per group): untreated, treated with 0.1% HA eye drops, and treated with crosslinked HA hydrogels. Crosslinking of HA hydrogel followed by the administration of HA eye drops and crosslinked HA hydrogels were carried out once a day from days 0–4. Corneal re-epithelialization, opacity, neovascularization, thickness, and histology were evaluated to compare the therapeutic effects of the three groups. Further investigation was conducted on the transparency of HA hydrogels to acquire the practical capabilities of hydrogel as a reservoir for drug delivery. Compared to untreated animals, animals treated with crosslinked HA hydrogels exhibited greater corneal re-epithelialization on days 1, 2, 4, and 7 post-injury (p = 0.004, p = 0.007, p = 0.008, and p = 0.034, respectively) and the least corneal neovascularization (p = 0.008). Histological analysis revealed lower infiltration of stromal inflammatory cells and compact collagen structure in crosslinked HA hydrogel-treated animals than in untreated animals. These findings corresponded with immunohistochemical analyses indicating that the expression of inflammatory markers such as α-SMA, MMP9, and IL1-β was lower in animals treated with crosslinked HA hydrogels than untreated animals and animals treated only with 0.1% HA eye drops. With beneficial pharmacological effects such as re-epithelization and anti-inflammation, in situ-forming hyaluronic acid (HA) hydrogels may be a promising approach to effective drug delivery in cases of corneal burn injuries.

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Corneal chemical injuries can induce corneal opacification, limbal ischemia, and loss of vision.

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Limitations for using topical eye drops includes maintaining the optimal concentration of the drug on the ocular surface.

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Crosslinked HA hydrogels achieved rapid corneal re-epithelialization and low-grade neovascularization after chemical injury.

Chemical Modification of Hyaluronan and Their Biomedical Applications

Hyaluronan, the extracellular matrix glycosaminoglycan, is an important structural component of many tissues playing a critical role in a variety of biological contexts. This makes hyaluronan, which can be biotechnologically produced in large scale, an attractive starting polymer for chemical modifications. This review provides a broad overview of different synthesis strategies used for modulating the biological as well as material properties of this polysaccharide. We discuss current advances and challenges of derivatization reactions targeting the primary and secondary hydroxyl groups or carboxylic acid groups and the N-acetyl groups after deamidation. In addition, we give examples for approaches using hyaluronan as biomedical polymer matrix and consequences of chemical modifications on the interaction of hyaluronan with cells via receptor-mediated signaling. Collectively, hyaluronan derivatives play a significant role in biomedical research and applications indicating the great promise for future innovative therapies.

Toxicity Assessment of a Single Dose of Poly(ethylene glycol) Diglycidyl Ether (PEGDE) Administered Subcutaneously in Mice

Poly(ethylene glycol) diglycidyl ether (PEGDE) is widely used to cross-link polymers, particularly in the pharmaceutical and biomaterial sectors. However, the subcutaneous toxicity of PEGDE has not yet been assessed. PEGDE samples (500–40,000 μg/mouse) were subcutaneously injected into the paraspinal dorsum of BALB/c male mice. Cage-side observations were carried out with measurement of organ weight, body weight variation, and feed intake, as well as histopathological characterization on day 28 post-exposure. Mice that received 40,000 μg of PEGDE showed severe toxic response and had to be euthanized. Subcutaneous injection of PEGDE did not alter feed intake and organ weight; however, the body weight variation of mice injected with 20,000 μg of PEGDE was significantly lower than that of the other groups. Exposure to 10,000 and 20,000 μg of PEGDE induced epidermal ulcer formation and hair loss. The histology of skin tissue in mice administered with 20,000 μg of PEGDE showed re-epithelialized or unhealed wounds. However, the liver, spleen, and kidneys were histologically normal. Collectively, PEGDE, particularly above 10,000 μg/mouse, caused subcutaneous toxicity with ulceration, but no toxicity in the other organs. These results may indicate the optimal concentration of subcutaneously injected PEGDE.

New Hydrogel Network Based on Alginate and a Spiroacetal Copolymer

This study reports a strategy for developing a biohybrid complex based on a natural/synthetic polymer conjugate as a gel-type structure. Coupling synthetic polymers with natural compounds represents an important approach to generating gels with superior properties and with potential for biomedical applications. The study presents the preparation of hybrid gels with tunable characteristics by using a spiroacetal polymer and alginate as co-partners in different ratios. The new network formation was tested, and the structure was confirmed by FTIR and SEM techniques. The physical properties of the new gels, namely their thermal stability and swelling behavior, were investigated. The study showed that the increase in alginate content caused a smooth increase in thermal stability due to the additional crosslinking bridges that appeared. Moreover, increasing the content of the synthetic polymer in the structure of the gel network ensures a slower release of carvacrol, the encapsulated bioactive compound.

Is hyaluronic acid the perfect excipient for the pharmaceutical need?

Hyaluronic acid has become an interesting and important polymer as an excipient for pharmaceutical products due to its beneficial properties, like solubility, biocompatibility and biodegradation. To improve the properties of hyaluronic acid, different possibilities for chemical modifications are presented, and the opportunities as novel systems for drug delivery are discussed. This review gives an overview over the production of hyaluronic acid, the possibilities of its chemical modification and the current state of in vitro and in vivo research. Furthermore, market approved and commercially available products are reviewed and derivatives undergoing clinical trials and applying for market approval are shown. In particular, hyaluronic acid has been studied for different administrations in rheumatology, ophthalmology, local anesthetics, cancer treatment and bioengineering of tissues. The present work concludes with perspectives for future administration of pharmaceuticals based on hyaluronic acid.

Significance of Crosslinking Approaches in the Development of Next Generation Hydrogels for Corneal Tissue Engineering

Medical conditions such as trachoma, keratoconus and Fuchs endothelial dystrophy can damage the cornea, leading to visual deterioration and blindness and necessitating a cornea transplant. Due to the shortage of donor corneas, hydrogels have been investigated as potential corneal replacements. A key factor that influences the physical and biochemical properties of these hydrogels is how they are crosslinked. In this paper, an overview is provided of different crosslinking techniques and crosslinking chemical additives that have been applied to hydrogels for the purposes of corneal tissue engineering, drug delivery or corneal repair. Factors that influence the success of a crosslinker are considered that include material composition, dosage, fabrication method, immunogenicity and toxicity. Different crosslinking techniques that have been used to develop injectable hydrogels for corneal regeneration are summarized. The limitations and future prospects of crosslinking strategies for use in corneal tissue engineering are discussed. It is demonstrated that the choice of crosslinking technique has a significant influence on the biocompatibility, mechanical properties and chemical structure of hydrogels that may be suitable for corneal tissue engineering and regenerative applications.

Inhibition of post-trabeculectomy fibrosis via topically instilled antisense oligonucleotide complexes co-loaded with fluorouracil

Trabeculectomy is the mainstay of surgical glaucoma treatment, while the success rate was unsatisfying due to postoperative scarring of the filtering blebs. Clinical countermeasures for scar prevention are intraoperative intervention or repeated subconjunctival injections. Herein, we designed a co-delivery system capable of transporting fluorouracil and anti-TGF-β2 oligonucleotide to synergistically inhibit fibroblast proliferation via topical instillation. This co-delivery system was built based on a cationic dendrimer core (PAMAM), which encapsulated fluorouracil within hydrophobic cavity and condensed oligonucleotide with surface amino groups, and was further modified with hyaluronic acid and cell-penetrating peptide penetratin. The co-delivery system was self-assembled into nanoscale complexes with increased cellular uptake and enabled efficient inhibition on proliferation of fibroblast cells. In vivo studies on rabbit trabeculectomy models further confirmed the anti-fibrosis efficiency of the complexes, which prolonged survival time of filtering blebs and maintained their height and extent during wound healing process, exhibiting an equivalent effect on scar prevention compared to intraoperative infiltration with fluorouracil. Qualitative observation by immunohistochemistry staining and quantitative analysis by Western blotting both suggested that TGF-β2 expression was inhibited by the co-delivery complexes. Our study provided a potential approach promising to guarantee success rate of trabeculectomy and prolong survival time of filtering blebs.

Cross-linked hyaluronan films loaded with acetazolamide-cyclodextrin-triethanolamine complexes for glaucoma treatment

AIM

This work aimed to design and characterize cross-linked hyaluronic acid-itaconic acid films loaded with acetazolamide-hydroxypropyl β cyclodextrin-triethanolamine complexes.

MATERIALS & METHODS

Films were cross-linked with itaconic acid and poly(ethyleneglycol)-diglycidylether. Biopharmaceutical properties were assessed by evaluating in vitro drug release rate, biocompatibility in a human corneal epithelial cell line, bioadhesiveness with pig gastric mucin, in vivo bioadhesion and efficacy.

RESULTS

Showed good mechanical properties and oxygen permeability. Proliferation rate of corneal cells was affected by highest acetazolamide concentration. Bioadhesive interaction exhibited a water movement from pig mucin to the film; in vivo experiments showed strong bioadhesion for 8 h and hypotensive effect for almost 20 h.

CONCLUSION

Experimental set showed promising performance and encouraged future studies to optimize formulation. [Formula: see text].

Novel Artificial Tears Containing Cross-Linked Hyaluronic Acid: An In Vitro Re-Epithelialization Study

Dry eye syndrome is a common disease which can damage the corneal epithelium. It is treated with eye drops to stimulate tear production and hydrate the corneal surface. The most prescribed artificial tear remedies contain hyaluronic acid (HA), which enhances epithelial wound healing, improving tissue health. To the best of our knowledge, only a few recent studies have investigated cross-linked HA (HA-CL) in eye drops for human applications. This work consists in an in vitro evaluation of the re-epithelialization ability of two different preparations containing a recently synthetized HA cross-linked with urea: 0.02% (w/v) HA-CL (solution 1, S1), and 0.4% (w/v) HA-CL (solution 2, S2). The study was conducted on both 2D human corneal cells (HCEpiC) and 3D reconstructed tissues of human corneal epithelium (HCE). Viability by 3(4,5-dimethylthiazol-2)2,5-diphenyltetrazolium bromide (MTT) test, pro-inflammatory cytokine release (interleukin-8, IL-8) by ELISA, and morphology by hematoxylin and eosin (HE) staining were evaluated. In addition, to understand the molecular basis of the re-epithelialization properties, cyclin D1 levels were assessed by western blot. The results showed no cellular toxicity, a slight decrease in IL-8 release, and restoration of epithelium integrity when the wounded 3D model was treated with S1 and S2. In parallel, cyclin D1 levels increased in cells treated with both S1 and S2.

Preparation and Property Evaluation of Conductive Hydrogel Using Poly (Vinyl Alcohol)/Polyethylene Glycol/Graphene Oxide for Human Electrocardiogram Acquisition

Conductive hydrogel combined with Ag/AgCl electrode is widely used in the acquisition of bio-signals. However, the high adhesiveness of current commercial hydrogel causes human skin allergies and pruritus easily after wearing hydrogel for electrodes for a long time. In this paper, a novel conductive hydrogel with good mechanical and conductive performance was prepared using polyvinyl alcohol (PVA), polyethylene glycol (PEG), and graphene oxide (GO) nanoparticles. A cyclic freezing⁻thawing method was employed under processing conditions of -40 °C (8 h) and 20 °C (4 h) separately for three cycles in sequence until a strong conductive hydrogel, namely, PVA/PEG/GO gel, was obtained. Characterization (Fourier transform infrared spectroscopy, nuclear magnetic resonance, scanning electron microscopy) results indicated that the assembled hydrogel was successfully prepared with a three-dimensional network structure and, thereafter, the high strength and elasticity due to the complete polymeric net formed by dense hydrogen bonds in the freezing process. The as-made PVA/PEG/GO hydrogel was then composited with nonwoven fabric for electrocardiogram (ECG) electrodes. The ECG acquisition data indicated that the prepared hydrogel has good electro-conductivity and can obtain stable ECG signals for humans in a static state and in motion (with a small amount of drift). A comparison of results indicated that the prepared PVA/PEG/GO gel obtained the same quality of ECG signals with commercial conductive gel with fewer cases of allergies and pruritus in volunteer after six hours of wear.

Design and development of polysaccharide hemostatic materials and their hemostatic mechanism

The formation of stable blood clots or hemostasis is essential to prevent major blood loss and death from excessive bleeding.

Hyaluronan as a promising excipient for ocular drug delivery

Hyaluronan (HA) is a naturally occurring polysaccharide and well known for its exceptional properties such as high biocompatibility and biodegradability, along with a low immunogenicity. Besides its use for various biomedical applications it recently came into focus as a favorable excipient for the formulation of various ocular therapeutics. This review article summarizes the ocular distribution of HA and its most heavily investigated binding protein "cluster of differentiation 44" (CD44) which is the rationale for the clinical use of HA, primarily as an additive in ocular applications ranging from eye drops to contact lenses. Moreover, examples will be given for using HA in various pre-clinical approaches to generate entirely new therapeutics, most notably in the field of nanotechnology.

Preliminary characterization of dexamethasone-loaded cross-linked hyaluronic acid films for topical ocular therapy

The aim of this work was to design and characterize cross-linked hyaluronic acid (HA)-itaconic acid (IT) films loaded with dexamethasone sodium phosphate salt (DEX) for topical therapy of inflammatory ocular surface diseases. Films were chemically cross-linked with polyethylene glycol diglycidyl ether (PEGDE), then physical and mechanical characterization by stress-strain, X-ray diffraction, X-ray fluorescence spectrometry and swelling assays was conducted. A sequential in vitro therapeutic efficacy model was designed to assess changes in interleukin (IL)-6 production in an inflamed human corneal epithelial (HCE) cell line after film exposure. Changes in cell proliferation after film exposure were assessed using the alamarBlue(®) proliferation assay. Experimental findings showed desirable mechanical properties and in vitro efficacy to reduce cell inflammation. A moderately decreased proliferation rate was induced in HCE cells by DEX-loaded films, compared to commercial DEX eye drops. These results suggest that DEX and HA have opposite effects. The sequential in vitro therapeutic efficacy model arises as an efficient tool to study drug release from delivery systems by indirect measurement of a biological response.

Thiolated α-Cyclodextrin: The Invisible Choice to Prolong Ocular Drug Residence Time

It was the aim of this study to develop cysteamine-conjugated α-cyclodextrin (α-CD) enabled to form disulfide bonds with cysteine-rich substructures of the ocular mucus layer to provide a prolonged residence time of incorporated drugs at the site of action. Cysteamine was covalently attached to oxidized α-CD via reductive amination. The resulting α-CD-cysteamine conjugates (α-CD-Cys) were characterized regarding the amount of free thiol groups attached to the oligomer backbone via Ellman's reagent; resazurin assay was conducted for cytotoxicity, and mucoadhesive properties were evaluated on porcine intestinal and ocular mucosal tissues. Furthermore, albino rabbits were used for assessing the irritation-masking effects of α-CD-Cys. Free thiol groups attached to the backbone were in the range of 558 ± 24-1143 ± 92 μmol/g. None of these α-CD-Cys unduly affected the viability of Caco-2 cells in a concentration of 0.5%. Mucoadhesive properties of α-CD-Cys were up to 32-fold improved compared to unmodified α-CD. Encapsulation of cetirizine into α-CD-Cys resulted in significantly reduced local ocular mucosal irritation of this model drug. According to these results, α-CD-Cys is a promising new tool to prolong drug residence time on the ocular mucosal surface.

Hyaluronic acid concentration-mediated changes in structure and function of porous carriers for corneal endothelial cell sheet delivery

In this study, the effects of hyaluronic acid (HA) concentrations (0.05-1.25wt.%) on the properties of porous carriers for corneal endothelial tissue engineering were investigated. The pore size and porosity gradually increased with decreasing solid content. However, at relatively low HA concentration (i.e., 0.05wt.%), the material samples contained small interior pores and a dense surface skin layer, probably due to no gas bubble effect on the stirring processing of porous microstructures of freeze-dried polysaccharide hydrogels. The carriers prepared from 0.25wt.% HA solution had the highest freezable water content and oxygen and glucose permeability among the samples evaluated. Results of cell viability assays and quantitative real-time reverse transcription polymerase chain reaction analyses showed that the HA concentration-related alteration of porous microstructure dictates the compatibility of biopolymer carriers with corneal endothelial cell (CEC) cultures. In vivo studies demonstrated that the CEC sheet/HA carrier construct implants are therapeutically efficacious in the reconstruction of endothelial scrape-wounded corneas. It is concluded that the polysaccharide concentration is the major factor for affecting the processing of carriers and their structure and function. Porous hydrogels prepared from 0.25wt.% HA solution are capable of delivering bioengineered CEC sheets to the posterior surface of cornea.

Hyaluronan-Itaconic Acid-Glutaraldehyde Films for Biomedical Applications: Preliminary Studies

New hyaluronic acid–itaconic acid films were synthesized as potential materials with biomedical applications. In this work, we explored the homogeneous cross-linking reactions of hyaluronic acid using glutaraldehyde in the presence of itaconic acid and triacetin as plasticizers.

Biomechanical properties were assessed in terms of stability by measuring swelling in aqueous environments, investigating wettability using contact angle tests, and evaluating bioadhesive performance. The ductility of the materials was evaluated through stress-strain measurements and the morphology was explored by scanning electron microscopy.

The results show that the incorporation of itaconic acid improved most of the desirable properties, increasing adhesiveness and reducing wettability and swelling. The use of triacetin enhanced the strength, bioadhesiveness, and ductility of the material.