Deposition of triamcinolone acetonide and its effect on soft tissue topography.

Bimodal imaging is utilized to characterize the topography of human tissue samples. The deposition of triamcinolone acetonide (TA) on various surfaces - including surgical human inner limiting membrane (ILM) samples and collagen fibrillar sheets - was studied. Changes in composition were well defined with bimodal imaging when TA deposition was examined on mica. TA sedimentation resulted in observable changes in ILM topography when compared to collagen fibrillar sheets. The heterogeneous chemical and topographical features of the ILM tissues promoted the TA crystallization compared to the flatter and homogeneous collagen surfaces. Higher spatial resolution was achieved by imaging ILM samples in the new bimodal imaging mode. The most apparent difference was observed in the imaging of ILM samples which had been exposed to the steroid TA. The study demonstrated the usefulness of bimodal imaging to evaluate tissue samples.

Surface modification of vitreoretinal surgical instruments with layer-by-layer films.

Commercially available vitreoretinal surgical forceps were modified with layer-by-layer (LbL) films designed to render them the ability to specifically adhere human the inner limiting membrane. Surgical forceps with two different geometries were etched, polished, and silanized before deposition of the films composed of poly (allylamine hydrochloride), poly (styrene sulfonate), and cationic gold nanoparticles. Stability and integrity of the LbL films was scrutinized by exposing the modified forceps to commercial disinfectant Cidex-OPA and then placing the instruments in a physiological-like HEPES buffer (pH 7.4, 5 mM, 154 mM NaCl). Surface topography analysis with scanning electron microscopy revealed that the geometry of the surgical instrument may affect the integrity of the film. Analysis of the HEPES buffer with inductively coupled plasma mass spectrometry demonstrated that gold nanoparticles did not leach from the LbL film after 60 min.

Tuning the adhesion of layer-by-layer films to the physicochemical properties of inner limiting membranes using nanoparticles.

Retinal trauma is a serious concern for patients undergoing inner limiting membrane (ILM) peeling to correct for various vitreoretinal interface conditions. This mechanical trauma can be prevented by modifying the surface of surgical instruments to increase adhesion to the ILM. To this effect, we have studied the effects of roughness and surface charge on the adhesive properties of ILMs by utilizing layer-by-layer (LbL) films with embedded gold nanoparticles (LbL-AuNP films). LbL films were assembled on atomic force microscopy (AFM) tipless cantilevers. Topographical analysis of these films, with and without nanoparticles, showed that LbL films with nanoparticles had a higher rms roughness compared to films alone or unmodified cantilevers. Nanoparticle-modified LbL films significantly increased the adhesion forces at the cantilever-ILM interface, compared to LbL films without particles. Surprisingly, adsorption of gold nanoparticles onto the AFM cantilevers caused increases in adhesion forces greater than those measured with LbL-AuNP films. These results have important implications for the design of surface modifications for vitreoretinal surgical instruments.

Quantitative analysis of human internal limiting membrane extracted from patients with macular holes.

We report the study of the morphology, topography, and adhesion properties of internal limiting membrane (ILM) from patients with macular holes. The quantitative analysis of human ILM could provide essential information toward the improvement of existing surgical instruments for more efficient and safer surgical removal of ILM. Imaging in air revealed the presence of globular structures in most of the samples analyzed which were coupled with fibrillar structures in some of the samples. Modification of silicon nitride AFM tips with oppositely charged functional groups showed changes in adhesion force at the membrane-tip interface. Defining the surface characteristics of the human ILM is an initial step in the development of improved surgical tools that may allow nontraumatic stripping of ILM during surgery.

The effect of pre-polymeric solution and subsequent encapsulation in hydrogel membranes on the stability and biological activity of horse myoglobins.

Proteins are biological macromolecules which have a unique spatial conformation. Once this 3D spatial conformation is affected the protein's biological stability and activity can be severely limited. For these reasons, this investigation focuses on the effects of pre-polymeric solution components on the behavior of proteins to be encapsulated by the entrapment technique in anionic, cationic, and neutral hydrogel membranes. Equine skeletal muscle myoglobin (MMb), and equine heart myoglobin (HMb) were employed as model molecules. Three hydrogel morphologies were examined: methacrylic acid-poly(ethylene glycol) dimethacrylate (n=1000) (MAA-PEGDMA1000), dimethylaminoethyl methacrylate-poly(ethylene glycol) dimethacrylate (n=1000) (DMAEM-PEGDMA1000), and poly(ethylene glycol) (200) monomethyl ether methacrylate-poly(ethylene glycol) di-methacrylate (n=1000) (PEGDMA200-PEGDMA1000). Stability of the proteins in the pre-polymeric solution was assessed by UV-vis spectroscopy and the optimized morphologies were synthesized and the biological activity of both heme-proteins was assessed by oxidation-reduction reactions of the heme group. It was observed that while there was no displacement of the Soret bands of the proteins in the pre-polymeric solution, significant blue shifts were observed for the encapsulated proteins. Subsequent oxidation-reduction of the proteins caused shifts of the Soret bands as would be expected. However, the displaced peaks were not at their anticipated wavelengths. Other analyses will be performed on the membranes to better comprehend these results.