Michael Joseph Garvey

EFFECTS OF A NANOPARTICULATE SILICA SUBSTRATE ON CELL ATTACHMENT OF CANDIDA ALBICANS

Aims:  To investigate the influence of silica nanoparticles on the attachment and growth of Candida albicans cells.

Increasing the extensional viscosity of silicone oil reduces the tendency for emulsification.

Purpose: The purpose was to study the emulsification of silicone oil tamponade agents that cause clinical complications. This study aimed to increase the emulsification resistance of silicone oil 1,000 to be at least as resistant as silicone oil 5,000 while maintaining the shear viscosity <5,000 mPa/s to aid injection and removal. Methods: High-molecular-weight (423 kDa) poly(dimethyl siloxane) was added to silicone oil 1,000 at 5% and 10% w/w concentration. The shear and extensional viscosity of 1,000 and 5,000, a 50:50 mixture of 1,000 and 5,000 and 5% and 10% w/w additive blends, respectively, of silicone oil were measured using capillary breakup extensional, rotational shear, and capillary extrusion rheometry. In vitro emulsification was assessed qualitatively after agitation using Pluronic F68 or a protein solution as the emulsion stabilizer. Results: The addition of high-molecular-weight polymer increased the extensional viscosity of the blends at high strain rates to levels equal to or greater than silicone oil 5,000. In all cases, the shear viscosity of the blends was lower than that of silicone oil 5,000. The additive blends were qualitatively as emulsification-resistant as silicone oil 5,000. Conclusion: The addition of low concentrations of very-high-molecular-weight polymers of the same chemistry as the bulk oil has the potential to increase the emulsification resistance of the tamponade agents while maintaining ease of injection and removal.

Emulsification of Silicone Oil and Eye Movements

PURPOSE Emulsification is an inherent problem of silicone oil used in vitreoretinal surgery. It has been shown that silicone oil can be made more resistant to emulsification and easier to inject by adding high-molecular-weight components (5% or 10% 423-kDa polydimethylsiloxane [PDMS]) to normal 1000 mPa · s silicone oil. The authors hypothesize that this might also reduce the movement of oil within an eye. METHODS A model eye chamber made of surface-modified poly(methyl methacrylate) was driven by a computer and a stepper motor to mimic saccadic eye movement. Seven silicone oils with different shear and extensional viscosities were tested. Two sets of eye movements were used: (amplitude 9°, angular velocity 390°/s, duration 50 ms) and (amplitude 90 °, angular velocity 360°/s, duration 300 ms). The movements were captured and analyzed by video recording. RESULTS The angular velocity of an oil bubble relative to the eye chamber appears to form an exponential relationship with its shear viscosity. Depending on the thickness of the film of aqueous between the eye wall and the oil bubble, the shear rate was estimated to be between 6 and 14 × 10(4) s(-1). The addition of 10% of 423-kDa PDMS to 1000 mPa · s silicone oil significantly reduced the peak relative velocity compared with the base oil of 1000 mPa · s but not 5000 mPa · s. CONCLUSIONS The addition of high molecular components to a base oil increases its extensional and shear viscosity. Although the extensional viscosity affected the ease with which the oil could be injected, the results showed that it was the shear viscosity that determined the relative velocity between the oil and the wall of the vitreous cavity, and thus the propensity to emulsify.

Injectability of silicone oil-based tamponade agents

Background/aims High viscosity silicone oils are used as tamponade agents to increase the resistance to emulsification; however, this makes the oils more difficult to inject. Increasing the extensional viscosity is one way to reduce emulsification. This study aimed to evaluate how silicone oils with increased extensional viscosity behave in terms of their ease of injection. Methods The shear viscosity and the length of time taken to inject 9 ml of Siluron 1000, Siluron 2000, Siluron 5000, SiliconMate, a 56/44 w/w blend of Siluron 1000/Siluron 5000 (Blend A) and a 90/10 w/w blend of Siluron 1000/PDMS 423kDa molecular weight (Blend B) were examined. Results The shear viscosity of Siluron 1000, Siluron 2000 and Siluron 5000 were within the expected ranges. The shear viscosity of Blend A was 2283 mPa s, Blend B was 4710 mPa s and SiliconMate was 995.3 mPa s. Siluron 1000 and SiliconMate had the shortest injection times as expected due to their lower shear viscosities. Comparison of Siluron 2000 and Blend A demonstrated that Siluron 2000 was easier to inject. Similarly, Blend B was easier to inject than Siluron 5000. Conclusion Silicone oil blends containing small percentages of a high molecular weight additive are easier to inject than single grade oils of the equivalent shear viscosity.

Novel Heavy Tamponade for Vitreoretinal Surgery

PURPOSE The aim of this study was to produce a heavy tamponade with a specific gravity greater than 1.06 g/mL that was optically transparent, could be manufactured using simple processing, could be injected using standard clinical equipment, and would have appropriate biocompatibility. METHODS Aerosil silica was added to a phenyl trimethicone and mixed via a roller, overhead stirring, and ultrasonics. The refractive index, visible absorbance, and shear viscosity were measured. The injectability of the solutions was evaluated using the Accurus Viscous Fluid Injection system. The tamponade efficiency was assessed using a model eye chamber and compared with that of Densiron 68, Oxane HD, and F6H8. The biocompatibility was evaluated in vitro and in vivo in rabbits. RESULTS Tamponade agents were produced with specific gravities of 1.10, 1.11, 1.13, and 1.16 g/mL that had good optical clarity. Mixing using overhead stirring was sufficient to produce tamponade agents with shear viscosities in the range 1000 to 5000 mPa·s that were reproducible and stable during storage. The solutions were easier to inject using the Accurus Viscous Fluid Injection system than silicone oil 1000 mPa·s. The 11% silica solution had greater tamponade efficiency than Densiron 68 or Oxane HD. There was no evidence of cytotoxicity in vitro. Silica solution 11% induced cataract earlier than Polydimethylsiloxane 1000 (PDMS 1000). Silica solution 11% and phenyl trimethicone reduced the a-wave value at 1 week after vitrectomy, but recovery was observed at later time points. Silica solution 11% caused inner nuclear layer (INL) nuclei dropdown in inferior retina from 4 weeks postoperation. Polydimethylsiloxane 1000 induced a similar phenomenon in superior retina 12 weeks postoperation. CONCLUSIONS We have produced a heavy tamponade with good clarity that has appropriate shear viscosity, injectibility, enhanced tamponade efficiency, and biocompatibility similar to that of PDMS 1000.

Manufacturing a nanometre scale surface topography with varying surface chemistry to assess the combined effect on cell behaviour

Surface topography and surface chemistry can influence cell adhesion. This study evaluated how the combined effect of topography and chemistry can reduce cell spreading and proliferation. Silica nanoparticulate coatings ranging from 7, 14 and 21 nm in diameter were manufactured on glass substrates and chemically modified using organofunctional siloxanes bearing methyl (−CH3), sulphydryl (−SH), amine (−NH2), carboxyl (−COOH) and hydroxyl (−OH) terminal functional groups. Chemical modification of 7 nm silica induced changes in wettability with the advancing angle increasing for all modifications and the receding angle increasing for −CH3, −NH2 and −SH group modifications. X-ray Photoelectron Spectroscopy (XPS) revealed that the surface chemistry was altered for all chemically modified surfaces confirming the modification step. The Field Emission Scanning Electron Microscopy (FESEM) demonstrated that the nanoparticulate coating remained intact after each chemical treatment. Optical microscopy from tissue culture experiments revealed changes in the morphology of the cells that could be attributed to the surface topography of the nanoparticulate coatings irrespective of the surface chemistry.

Shear and Extensional Rheometry of PDMS Tamponade Agents Used in Vitroretinal Surgery

The emulsification of low molar mass silicone oil (PDMS)‐based tamponade agents used in the treatment of complex retinal detachments is a significant clinical problem leading to the patient suffering impairment of vision whilst the tamponade is in place. This is particularly the case in temporal postoperative applications where the tamponade can remain in the ocular cavity for several months. The majority of clinicians prefer to use a PDMS fluid of kinematic viscosity 1000 cS, which offers ease of manual injection. Work is progressing towards the development of tamponades with a reduced tendency to emulsify, through specific tailoring of rheology and interfacial properties. Greater knowledge of the mechanism of intraocular emulsification is being elucidated and has led to the development of ‘polymer modified’ tamponades with enhanced performance. Such materials are formulated by the addition of a high molecular weight PDMS to the base PDMS fluid. Measurement of the shear viscosity at moderate shear rates ...