Education B.Tech Chemical Engineering, Indian Institute of Technology, Madras (IITM), India (2010).
My thesis focuses on the dynamics of the tear film in the presence of contact lenses. The tear film covers the surface of the eye, protecting and lubricating the cornea. However, extended wear of contact lenses can often lead to ocular discomfort and irritation, and my work attempts to understand how the tear film is related to this process.
Influence of interfacial rheology on drainage:
Thin lubrication flows accompanying drainage from curved surfaces surround us (e.g., the drainage of the tear film on our eyes). These draining aqueous layers are normally covered with surface-active molecules that render the free surface viscoelastic. The non-Newtonian character of these surfaces fundamentally alters the dynamics of drainage. We show that increased film stability during drainage can occur as a consequence of enhanced surface rheology. Increasing the surfactant layer viscosity decreases the rate of drainage; however, this retarding influence is most pronounced when the insoluble surfactant layer has significant elasticity. A simple theoretical model that offers qualitative support to our experimental findings is also investigated.
Figure 1: Schematic of drainage on a contact lens
Figure 2: Photograph (L) and schematic (R) of the drainage setup.
A contact lens is placed on a titanium dome (inset). Both are initially submerged in the water filled Langmuir trough (white, Teflon container). Insoluble surfactants (DPPC, meibum) are then spread at the air–liquid interface and compressed using the barrier to the desired surface pressure. Surface pressure is monitored using a Wilhelmy plate connected to a surface pressure sensor (1). The lens is then elevated through the air–liquid interface using a computer controlled motorized stage (2) which captures a thin layer of fluid coated with the insoluble material. A high-speed interferometer (3) captures the thickness of the aqueous layer on the lens as a function of time at the apex of the lens (θ = 0).
|Influence of interfacial rheology on drainage from curved surfaces (M Saad Bhamla, Caroline E Giacomin, Caroline Balemans, Gerald G Fuller), In Soft Matter, The Royal Society of Chemistry, 2014. [bibtex] [pdf] [doi]|
Lipid Deposition on Silicone Hydrogel Contact Lenses
Insoluble lipids serve vital functions in our bodies and can interact with various biomedical devices, e.g. the tear film on a contact lens. Over a period of time, these naturally occurring lipids form interfacial coatings leading to a modification of the wettability characteristics of these foreign synthetic surfaces. To characterize these lipid-depositions and their consequences, we deposit insoluble phospholipid and cholesterol monolayers onto silicone hydrogel substrates using a modified Langmuir- Schaefer technique. Additionally, the dewetting instability of thin aqueous films is used to measure the wetting characteristics of these lipid-decorated surfaces.
Figure 3: Fluorescently tagged DPPC (6 mN/m) coated on a silicone hydrogel lens surface.
Figure 4:Photograph (L) and schematic (R) of the deposition/dewetting setup.
Tear Film Instability on Hydrogel Surfaces
The tear film undergoes thinning due to a combination of processes such as evaporation, capillary forces and osmotic driven fluxes. Eventually, at a critical thickness, the tear film becomes unstable and can break up, leading to dewetting of the substrate. We are currently investigating this phenomenon using a custom in-house optical setup.