I am a Postdoctoral Fellow in the Bioengineering Dept. and work with Professor Manu Prakash. I am currently involved in the research of frugal science and development of instrumentation with applications in biophysics and global health.
My background is in soft matter, particularly rheology, thin-film dynamics, and soft biological materials. I received my PhD in Chemical Engineering from Stanford (2015). My thesis advisor was Professor Gerry Fuller.
My past work has been primarily experimental in nature, with some theoretical modeling, and has found successful applications in the healthcare industry. My thesis centers around the design, patent, and implementation of a new instrument, the Interfacial Dewetting and Drainage Optical Platform (i-DDrOP), which enables dynamic measurement of thin films possessing viscoelastic interfacial properties, such as the human tear film and lung surfactants.
I received my Bachelors degree in Chemical Engineering from the Indian Institute of Technology, Madras (2010).
Honors & Awards
Innovation in MedTech Award, American India Foundation and Stanford Medicine (2016)
Dean’s Postdoctoral Fellowship, School of Medicine, Stanford University (2016)
People’s Choice Award, Art of Science Competition, Materials Research Society (MRS) (2014)
Centennial Teaching Assistant Award, Stanford University (2015)
Milton van Dyke Award, American Physical Society, Division of Fluid Dynamics (2015)
Accel Innovation Scholar, Stanford Technology Ventures Program (2014)
DARE: Diversifying Academia, Recruiting Excellence Fellowship Alternate, Stanford University (2013)
Summer Research Fellowship, Indian National Academy of Engineering (INAE) (2009)
Summer Research Fellowship, Indian Academy of Sciences (IAS) (2008)
Doctor of Philosophy, Stanford University, CHEME-PHD (2015)
PhD, Stanford University, Chemical Engineering (2015)
Master of Science, Stanford University, CHEME-MS (2014)
Bachelor of Technology, Indian Institute of Technology, Madras, Chemical Engineering (2010)
Manu Prakash, Postdoctoral Research Mentor
Mohammed Saad Bhamla, Gerald G. Fuller. "United States Patent 9,265,413 i-DDrOP: Interfacial Dewetting and Drainage Optical Platform", Leland Stanford Junior University, Feb 23, 2016
Current Research and Scholarly Interests
soft matter, fluid dynamics, global health, instrumentation, biological fluid mechanics
- Placing Marangoni instabilities under arrest PHYSICAL REVIEW FLUIDS 2016; 1 (5)
Instability and Breakup of Model Tear Films
INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE
2016; 57 (3): 949-958
An experimental platform to replicate the human tear film on a contact lens is presented. The influence of interfacial viscoelasticity in stabilizing in vitro model tear films against breakup and dewetting is investigated using this instrument.Model tear films consisting of bovine meibomian lipids (meibum) spread on either PBS or artificial tear solution (ATS) are created. The interfacial shear rheology of these films is measured as a function of temperature. The dewetting dynamics of these films is then investigated using the Interfacial Dewetting and Drainage Optical Platform (i-DDrOP) on top of silicone hydrogel (SiHy) contact lenses at 23 and 35°C. The film breakup times are evaluated using two parameters: onset of film breakup, Tonset for thick films (∼100 μm), and tear breakup times, TBU for thin films (∼1 μm). Thin film thinning rates as a result of evaporation are also calculated.The ATS/meibum films have the largest surface rheology and correspondingly show the largest Tonset times at both 23 and 35°C. The parameter TBU is also significantly larger for ATS/meibum (TBU ∼ 40 seconds) compared with that of ATS and PBS/meibum films (TBU ∼ 30 seconds) at room temperature. However, at 35°C, all three model tear films exhibit similar TBU ∼ 17 seconds and average rate of thinning of -4 μm/minute.Tear film stability is influenced by both surface rheology and evaporation. The in vitro tear breakup times and thinning rates of model tear films at 35°C are in good agreement with in vivo measurements previously reported, highlighting the utility of the i-DDrOP for in vitro tear film breakup research.
View details for DOI 10.1167/iovs.15-18064
View details for Web of Science ID 000374860600026
View details for PubMedID 26943158
Dewetting and deposition of thin films with insoluble surfactants from curved silicone hydrogel substrates.
Journal of colloid and interface science
2015; 449: 428-435
We investigate the stabilizing effect of insoluble surfactant monolayers on thin aqueous films. We first describe an experimental platform that enables the formation of aqueous films laden with dipalmitoylphosphatidylcholine (DPPC) monolayers on curved silicone hydrogel (SiHy) substrates. We show that these surfactant layers extend the lifetime of the aqueous films. The films eventually "dewet" by the nucleation and growth of dry areas and the onset of this dewetting can be controlled by the surface rheology of the DPPC layer. We thus demonstrate that increasing the interfacial rheology of the DPPC layer leads to stable films that delay dewetting. We also show that dewetting can be exploited to controllably pattern the underlying curved SiHy substrates with DPPC layers.
View details for DOI 10.1016/j.jcis.2015.01.002
View details for PubMedID 25628055
Influence of Lipid Coatings on Surface Wettability Characteristics of Silicone Hydrogels
2015; 31 (13): 3820-3828
Insoluble lipids serve vital functions in our bodies and interact with biomedical devices, e.g., the tear film on a contact lens. Over a period of time, these naturally occurring lipids form interfacial coatings that modify the wettability characteristics of these foreign synthetic surfaces. In this study, we examine the deposition and consequences of tear film lipids on silicone hydrogel (SiHy) contact lenses. We use bovine meibum, which is a complex mixture of waxy esters, cholesterol esters, and lipids that is secreted from the meibomian glands located on the upper and lower eyelids of mammals. For comparison, we study two commercially available model materials: dipalmitoylphosphatidylcholine (DPPC) and cholesterol. Upon deposition, we find that DPPC and meibum remain closer to the SiHy surface than cholesterol, which diffuses further into the porous SiHy matrix. In addition, we also monitor the fate of unstable thin liquid films that consequently rupture and dewet on these lipid-decorated surfaces. This dewetting provides valuable qualitative and quantitative information about the wetting characteristics of these SiHy substrates. We observe that decorating the SiHy surface with simple model lipids such as DPPC and cholesterol increases the hydrophilicity, which consequently inhibits dewetting, whereas meibum behaves conversely.
View details for DOI 10.1021/la503437a
View details for Web of Science ID 000352660500007
View details for PubMedID 25280206
Lung surfactants and different contributions to thin film stability
2015; 11 (41): 8048-8057
The surfactant lining the walls of the alveoli in the lungs increases pulmonary compliance and prevents collapse of the lung at the end of expiration. In premature born infants, surfactant deficiency causes problems, and lung surfactant replacements are instilled to facilitate breathing. These pulmonary surfactants, which form complex structured fluid-fluid interfaces, need to spread with great efficiency and once in the alveolus they have to form a thin stable film. In the present work, we investigate the mechanisms affecting the stability of surfactant-laden thin films during spreading, using drainage flows from a hemispherical dome. Three commercial lung surfactant replacements Survanta, Curosurf and Infasurf, along with the phospholipid dipalmitoylphosphatidylcholine (DPPC), are used. The surface of the dome can be covered with human alveolar epithelial cells and experiments are conducted at the physiological temperature. Drainage is slowed down due to the presence of all the different lung surfactant replacements and therefore the thin films show enhanced stability. However, a scaling analysis combined with visualization experiments demonstrates that different mechanisms are involved. For Curosurf and Infasurf, Marangoni stresses are essential to impart stability and interfacial shear rheology does not play a role, in agreement with what is observed for simple surfactants. Survanta, which was historically the first natural surfactant used, is rheologically active. For DPPC the dilatational properties play a role. Understanding these different modes of stabilization for natural surfactants can benefit the design of effective synthetic surfactant replacements for treating infant and adult respiratory disorders.
View details for DOI 10.1039/c5sm01603g
View details for Web of Science ID 000363204000003
View details for PubMedID 26307946
Influence of interfacial rheology on drainage from curved surfaces.
2014; 10 (36): 6917-6925
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. We also present a simple theoretical model that offers qualitative support to our experimental findings.
View details for DOI 10.1039/c3sm52934g
View details for PubMedID 25140576
Autonomous Motility of Active Filaments due to Spontaneous Flow-Symmetry Breaking
PHYSICAL REVIEW LETTERS
2012; 109 (15)
We simulate the nonlocal Stokesian hydrodynamics of an elastic filament which is active due a permanent distribution of stresslets along its contour. A bending instability of an initially straight filament spontaneously breaks flow symmetry and leads to autonomous filament motion which, depending on conformational symmetry, can be translational or rotational. At high ratios of activity to elasticity, the linear instability develops into nonlinear fluctuating states with large amplitude deformations. The dynamics of these states can be qualitatively understood as a superposition of translational and rotational motion associated with filament conformational modes of opposite symmetry. Our results can be tested in molecular-motor filament mixtures, synthetic chains of autocatalytic particles, or other linearly connected systems where chemical energy is converted to mechanical energy in a fluid environment.
View details for DOI 10.1103/PhysRevLett.109.158302
View details for Web of Science ID 000309658300024
View details for PubMedID 23102372
- Extrudate swell of linear and branched polyethylenes: ALE simulations and comparison with experiments JOURNAL OF NON-NEWTONIAN FLUID MECHANICS 2011; 166 (1-2): 12-24