Morgana M. Trexler

Structure and properties of collagen vitrigel membranes for ocular repair and regeneration applications

The frequency of ocular injuries on the battlefield has been steadily increasing during recent conflicts. Combat-related eye injuries are difficult to treat and solutions requiring donor tissue are not ideal and are often not readily available. Collagen vitrigels have previously been developed for corneal reconstruction, but increased transparency and mechanical strength are desired for improved vision and ease of handling. In this study, by systematically varying vitrification temperature, relative humidity and time, the collagen vitrigel synthesis conditions were optimized to yield the best combination of high transparency and high mechanical strength. Optical, mechanical, and thermal properties were characterized for each set of conditions to evaluate the effects of the vitrification parameters on material properties. Changes in denaturing temperature and collagen fibril morphology were evaluated to correlate properties with structure. Collagen vitrigels with transmittance up to 90%, tensile strength up to 12 MPa, and denaturing temperatures that significantly exceed the eye/body temperature have been synthesized at 40 °C and 40% relative humidity for one week. This optimal set of conditions enabled improvements of 100% in tensile strength and 11% in transmittance, compared to the previously developed collagen vitrigels.

Synthesis and properties of regenerated cellulose-based hydrogels with high strength and transparency for potential use as an ocular bandage

Cellulose is a biologically derived material with excellent wound-healing properties. The high strength of cellulose fibers and the ability to synthesize gels with high optical transparency make these materials suitable for ocular applications. In this study, cellulose materials derived from wood pulp, cotton, and bacterial sources were dissolved in lithium chloride/N,N-dimethylacetamide to form regenerated cellulose hydrogels. Material properties of the resulting hydrogels, including water content, optical transparency, and tensile and tear strengths, were evaluated. Synthesis parameters, including activation time, dissolution time, relative humidity, and cellulose concentration, were found to impact the material properties of the resulting hydrogels. Overnight activation time improves the optical transparency of the hydrogels from 77% to 97% at 550 nm, whereas controlling cellulose concentration improves their tear strength by as much as 200%. On the basis of the measured transmittance and strength values of the regenerated hydrogels prepared via the optimized synthesis parameters, Avicel PH 101, Sigma-Aldrich microcrystalline cellulose 435236, and bacterial cellulose types were prioritized for future biocompatibility testing and potential clinical investigation.

Regeneration of corneal epithelium utilizing a collagen vitrigel membrane in rabbit models for corneal stromal wound and limbal stem cell deficiency.

This study was performed to evaluate the potential of a collagen‐based membrane, collagen vitrigel (CV), for reconstructing corneal epithelium in the stromal wound and limbal stem cell deficiency (LSCD) models.

Evaluation of the biocompatibility of regenerated cellulose hydrogels with high strength and transparency for ocular applications

Prompt emergency treatment for ocular injury, particularly in a battlefield setting, is essential to preserve vision, reduce pain, and prevent secondary infection. A bandage contact lens that could be applied in the field, at the time of injury, would protect the injured ocular surface until hospital treatment is available. Cellulose, a natural polymer, is widely used in biomedical applications including bandage materials. Hydrogels synthesized from different cellulose sources, such as plants, cotton, and bacteria, can have the optical transparency and mechanical strength of contact lenses, by tailoring synthesis parameters. Thus, we optimized the fabrication of cellulose-based hydrogels and evaluated their in vivo biocompatibility and related physical properties. Our data demonstrate that along with tailorable physical properties, our novel cellulose-based hydrogels could be made with contact lens geometry, exhibit no significant signs of material toxicity after 22 days of in vivo testing, and show significant promise for use as a corneal bandage immediately following ocular trauma.

Application of a Collagen-Based Membrane and Chondroitin Sulfate-Based Hydrogel Adhesive for the Potential Repair of Severe Ocular Surface Injuries

This study was performed to evaluate the potential of a chondroitin sulfate-polyethylene glycol (CS-PEG) adhesive and collagen-based membrane (collagen vitrigel, CV) combination as a method to treat penetrating ocular injuries on the battlefield and to improve this method with two technologies: an antibiotic releasing CS-PEG adhesive and a corneal shaped CV. Burst testing using porcine cadaveric eyes, high-performance liquid chromatography, the Kirby-Bauer bacterial inhibition test, and CV implantations on the live and cadaveric rabbit eyes were performed. The ocular burst test showed CS-PEG adhesive could successfully repair 5-mm to 6-mm length wounds in the corneal and corneoscleral regions but would require CS-PEG + CV to treat larger wounds similar to those seen on the battlefield. In addition, high performance liquid chromatography and the Kirby-Bauer bacterial inhibition test presented evidence suggesting the vancomycin incorporated CS-PEG could inhibit Staphylococcus infection for 9 days. Furthermore, the curved CV showed an advantage by matching the corneal contour without any wrinkle formation. Although this pilot study showed a limited range of possible applications, we demonstrated that the combination of CS-PEG adhesive + CV is a promising method and the 2 technologies improve their applicability to the special demands of the battlefield.

Fibre-reinforced hydrogels with high optical transparency

Abstract Fibre-reinforced hydrogels with high optical transparency are an emerging composite material with great promise to enable new applications, such as a transparent wound dressing with custom tuned mechanical properties that provides desirable mechanical and physical properties along with optical clarity for facile wound inspection. Stand-alone hydrogels are an important class of materials comprising a cross-linked polymer network surrounded by a water matrix. However, their mechanical properties are typically very modest compared with other materials. While significant research is going on in parallel in the fields of hydrogels and reinforcement fibres, researchers are only starting to scratch the surface of the possibilities of combining the two. This report provides a review of natural and synthetic reinforcement fibre research with special emphasis placed on nanofibres. These provide the added benefit of transparency by being much smaller than the wavelength of visible light. A review of hydrogel materials is also presented. The mechanical properties, optical properties and biological functionality of hydrogel systems are also described. Ocular, load-bearing tissue, wound management and sensing/device applications are all discussed. Transparent fibre-reinforced hydrogels provide a compelling potential solution to enable advanced functionality, in particular in the wound care and optical application areas.

Moxifloxacin in situ gelling microparticles-bioadhesive delivery system

Antibiotic use for ocular treatments has been largely limited by poor local bioavailability with conventional eyedrops formulations. Here, we developed a controlled delivery system composed of moxifloxacin-loaded poly(lactic-co-glycolic acid) (PLGA) microparticles encapsulated in a chondroitin sulfate-based, two-component bioadhesive hydrogel. Using a simple and fast electrohydrodynamic spray drying (electrospraying) technique, surfactant-free moxifloxacin-loaded microparticles were fabricated with diameters on the order of 1 μm. A mixed solvent system of methanol/dichloromethane (MeOH/DCM) was employed to prepare the microparticles for the electrospraying processing. Extended release of moxifloxacin using a series of MeOH/DCM mixed solvents was accomplished over 10 days with release concentrations higher than the minimum inhibitory concentration (MIC). In contrast, moxifloxacin loaded directly in hydrogels was released rapidly within 24 h. We observed a decrease of the drug release rate from the microparticles when using an increased percentage of methanol in the mixed solvent from 10% to 30% (v/v), which can be explained by the mixed solvent system providing a driving force to form a gradient of the drug concentrations inside the microparticles. In addition, the delivery system developed in this study, which incorporates a bioadhesive to localize drug release by in situ gelling, may potentially integrate antibiotic prophylaxis and wound healing in the eye.

Influence of collagen source on fibrillar architecture and properties of vitrified collagen membranes.

Collagen vitrigel membranes are transparent biomaterials characterized by a densely organized, fibrillar nanostructure that show promise in the treatment of corneal injury and disease. In this study, the influence of different type I collagen sources and processing techniques, including acid-solubilized collagen from bovine dermis (Bov), pepsin-solubilized collagen from human fibroblast cell culture (HuCC), and ficin-solubilized collagen from recombinant human collagen expressed in tobacco leaves (rH), on the properties of the vitrigel membranes was evaluated. Postvitrification carbodiimide crosslinking (CX) was also carried out on the vitrigels from each collagen source, forming crosslinked counterparts BovXL, HuCCXL, and rHXL, respectively. Collagen membrane ultrastructure and biomaterial properties were found to rely heavily on both collagen source and crosslinking. Bov and HuCC samples showed a random fibrillar organization of collagen, whereas rH vitrigels showed remarkable regional fibril alignment. After CX, light transmission was enhanced in all groups. Denaturation temperatures after CX increased in all membranes, of which the highest increase was seen in rH (14.71°C), suggesting improved thermal stability of the collagen fibrils in the membranes. Noncrosslinked rH vitrigels may be reinforced through CX to reach levels of mechanical strength and thermal stability comparable to Bov.

Crystal structure and optical properties of erbium- and neodymium-doped zirconia nanoparticles

We report the synthesis, characterization, and optical properties of high-temperature stable lanthanide-doped luminescent zirconia nanoparticles via a novel method using carbon black as template. Dopant concentrations were varied from 1 to 5% of Er 3+ or Nd 3+ and annealing temperatures were varied from 650 to 1100 °C. The effects of the dopant concentration on crystal structure and emission properties were evaluated using x-ray powder diffraction and fluorescence spectroscopy, respectively. The lanthanide cations were found to stabilize the tetragonal phase of zirconia over the monoclinic phase as dopant concentration was increased to 5%. Increasing the annealing temperature to 1100 °C had the opposite effect and was found to stabilize the monoclinic phase of zirconia. The luminescence intensity of the Nd-doped zirconia was enhanced by two orders of magnitude over the undoped or Er-doped zirconia. In all cases, the luminescence spectra revealed increasing intensity with increasing annealing temperature. Zirconia luminescence at near-infrared wavelengths is likely caused by oxygen vacancies. This work demonstrates that the spectral signatures of fluorescent zirconia nanoparticles can be modified with small lanthanide dopant concentration. These particles will have utility in fluorescent sensors and tags, as well as new in refractory materials.

Banded structures in collagen vitrigels for corneal injury repair.

There is a growing interest in using collagen vitrigels for corneal injury repair. We recently reported the synthesis and thermal denaturation behavior of these gels. In this paper, the banded structure in these vitrified gels is studied by small-angle X-ray scattering (SAXS) one-dimensional (1-D) correlation function analysis and transmission electron microscopy (TEM). Results demonstrate that the collagen vitrigel possess banded structures similar to those of the starting type I collagen, with an average D-spacing of 64nm (by SAXS) or 57nm (by TEM). A combination of SAXS 1-D correlation function analyses and TEM show that overlap and gap distances ranged from 30 to 33nm and from 23 to 25nm, respectively. Changing the vitrification condition does not impact on the banded structure significantly.