Fluid shear stress in a logarithmic microfluidic device enhances cancer cell stemness marker expression.

Fluid shear stress (FSS) is crucial in cancer cell survival and tumor development. Noteworthily, cancer cells are exposed to several degrees of FSS in the tumor microenvironment and during metastasis. Consequently, the stemness marker expression in cancer cells changes with the FSS signal, although it is unclear how it varies with different magnitudes and during metastasis. The current work explores the stemness and drug resistance characteristics of the cervical cancer cell line HeLa in a microfluidic device with a wide range of physiological FSS. Hence, the microfluidic device was designed to achieve a logarithmic flow distribution in four culture chambers, realizing four orders of biological shear stress on a single chip. The cell cycle analysis demonstrated altered cell proliferation and mitotic arrest after FSS treatment. In addition, EdU staining revealed increased cell proliferation with medium to low FSS, whereas high shear had a suppressing effect. FSS increased competence to withstand higher intracellular ROS and mitochondrial membrane potential in HeLa. Furthermore, stemness-related gene (Sox2, N-cadherin) and cell surface marker (CD44, CD33, CD117) expressions were enhanced by FSS mechanotransduction in a magnitude-dependent manner. In summary, these stemness-like properties were concurrent with the drug resistance capability of HeLa towards doxorubicin. Overall, our microfluidic device elucidates cancer cell survival and drug resistance mechanisms during metastasis and in cancer relapse patients.

2-D simulation of atmospheric boundary layer in and around Delhi to determine air pollution scenarios during winter morning.

In this paper, a 2-D turbulent closure model, based on the pollutant mass conservation equation, is adopted to estimate the local and background pollutants in the predominant wind direction for the stable atmosphere during winter mornings. The background concentration of pollutants can severely affect the regional pollution level, and its monitoring is a challenging task. Here, the turbulent closure model is employed across three cities in India, viz., Patiala, Delhi, and Agra, to estimate SO2 and NOx concentration along the predominant wind direction to demonstrate the potential of numerical models. The direction of the prevailing wind in this area during January 2003 was NNW (330°). Patiala is followed by Delhi and then Agra in the predominant wind direction. The sensitivity analysis of surface temperature on pollutant concentration reveals that concentration would increase by its square as temperature dips. So, during low or no horizontal wind, pollution episodes will be inevitable. Thus, the pollution hotspots are also identified in these three cities. Delhi had a high pollution load. So, the impact of local pollution in Delhi, through dispersion, was found significant in Agra. NOx hot spots (exceed the 30 µg/m3 limit) are found all across Delhi, except IGI Airport and two other locations. However, no SO2 hotspot (exceed the 60 µg/m3 limit) is found in Delhi. The proposed model output is verified with the WRF-CFD model results. Compared to the WRF-CFD model, the proposed model has overestimated NOx and SO2 concentration maximum by 14.4% and 23.5%, respectively. The overestimation occurred primarily due to ignoring atmospheric chemical reactions (e.g., acid condensation, etc.) for which the atmospheric factors were not so conducive.

Low intermittent flow promotes rat mesenchymal stem cell differentiation in logarithmic fluid shear device.

Bone marrow mesenchymal stem cells are an ideal candidate for bone tissue engineering due to their osteogenic potential. Along with chemical, mechanical signals such as fluid shear stress have been found to influence their differentiation characteristics. But the range of fluid shear experienced in vivo is too wide and difficult to generate in a single device. We have designed a microfluidic device that could generate four orders of shear stresses on adherent cells. This was achieved using a unique hydraulic resistance combination and linear optimization to the lesser total length of the circuit, making the device compact and yet generating four logarithmically increasing shear stresses. Numerical simulation depicts that, at an inlet velocity of 160 µl/min, our device generated shear stresses from 1.03 Pa to 1.09 mPa. In this condition, we successfully cultured primary rat bone marrow mesenchymal stem cells (rBMSCs) in the device for a prolonged period of time in the incubator environment (four days). Higher cell proliferation rate was observed in the intermittent flow at 1.09 mPa. At 10 mPa, both upregulation of osteogenic genes and higher alkaline phosphatase activity were observed. These results suggest that the intermittent shear of the order of 10 mPa can competently enhance osteogenic differentiation of rBMSCs compared to static culture.

Governing Influence of Thermodynamic and Chemical Equilibria on the Interfacial Properties in Complex Fluids.

We propose a comprehensive analysis and a quasi-analytical mathematical formalism to predict the surface tension and contact angles of complex surfactant-infused nanocolloids. The model rests on the foundations of the interaction potentials for the interfacial adsorption-desorption dynamics in complex multicomponent colloids. Surfactant-infused nanoparticle-laden interface problems are difficult to deal with because of the many-body interactions and interfaces involved at the meso-nanoscales. The model is based on the governing role of thermodynamic and chemical equilibrium parameters in modulating the interfacial energies. The influence of parameters such as the presence of surfactants, nanoparticles, and surfactant-capped nanoparticles on interfacial dynamics is revealed by the analysis. Solely based on the knowledge of interfacial properties of independent surfactant solutions and nanocolloids, the same can be deduced for complex surfactant-based nanocolloids through the proposed approach. The model accurately predicts the equilibrium surface tension and contact angle of complex nanocolloids available in the existing literature and present experimental findings.

Non-Fourier thermal transport induced structural hierarchy and damage to collagen ultrastructure subjected to laser irradiation.

Comprehending the mechanism of thermal transport through biological tissues is an important factor for optimal ablation of cancerous tissues and minimising collateral tissue damage. The present study reports detailed mapping of the rise in internal temperature within the tissue mimics due to NIR (1064 nm) laser irradiation, both for bare mimics and with gold nanostructures infused. Gold nanostructures such as mesoflowers and nanospheres have been synthesised and used as photothermal converters to enhance the temperature rise, resulting in achieving the desired degradation of malignant tissue in targeted region. Thermal history was observed experimentally and simulated considering non-Fourier dual phase lag (DPL) model incorporated Pennes bio-heat transfer equation using COMSOL Multiphysics software. The gross deviation in temperature i.e. rise from the classical Fourier model for bio-heat conduction suggests additional effects of temperature rise on the secondary structures and morphological and physico-chemical changes to the collagen ultrastructures building the tissue mass. The observed thermal denaturation in the collagen fibril morphologies have been explained based on the physico-chemical structure of collagen and its response to thermal radiation. The large shift in frequency of amides A and B is pronounced at a depth of maximum temperature rise compared with other positions in tissue phantom. Observations for change in band of amide I, amide II, and amide III are found to be responsible for damage to collagen ultra-structure. Variation in the concentration of gold nanostructures shows the potentiality of localised hyperthermia treatment subjected to NIR radiation through a proposed free radical mechanism.

Effect of Interaction of Nanoparticles and Surfactants on the Spreading Dynamics of Sessile Droplets.

While a body of literature on the spreading dynamics of surfactants and a few studies on the spreading dynamics of nanocolloids exist, to the best of the authors' knowledge, there are no reports on the effect of presence of surfactants on the spreading dynamics of nanocolloidal suspensions. For the first time the present study reports an extensive experimental and theoretical study on the effect of surfactant impregnated nanocolloidal complex fluids in modulating the spreading dynamics. A segregation analysis of the effect of surfactants alone, nanoparticle alone, and the combined effect of nanoparticle and surfactants in altering the spreading dynamics have been studied in detail. The spreading dynamics of nanocolloidal solutions alone and of the surfactant impregnated nanocolloidal solutions are found to be grossly different, and particle morphology is found to play a predominant role. For the first time the present study experimentally proves that the classical Tanner's law is disobeyed by the complex fluids in the case of particle alone and combined particle and surfactant case. We also discuss the role of imbibitions across the particle wedge in the precursor film in tuning spreading dynamics. We propose an analytical model to predict the nature of dependency of contact radius on time for the complex colloids. A detailed theoretical examination of the governing factors, the interacting forces at the three phase contact line, and the effects of interplay of surfactants and the nanoparticles at the precursor film in modulating the spreading dynamics has been presented for such complex colloids.

Effects of interplay of nanoparticles, surfactants and base fluid on the surface tension of nanocolloids.

A systematically designed study has been conducted to understand and demarcate the degree of contribution by the constituting elements to the surface tension of nanocolloids. The effects of elements such as surfactants, particles and the combined effects of these on the surface tension of these complex fluids are studied employing the pendant drop shape analysis method by fitting the Young-Laplace equation. Only the particle has shown an increase in the surface tension with particle concentration in a polar medium like DI water, whereas only a marginal effect of particles on surface tension in weakly polar mediums like glycerol and ethylene glycol has been demonstrated. Such behaviour has been attributed to the enhanced desorption of particles to the interface and a theory has been presented to quantify this. The combined particle and surfactant effect on the surface tension of a complex nanofluid system showed a decreasing behaviour with respect to the particle and surfactant concentration with a considerably feeble effect of particle concentration. This combined colloidal system recorded a surface tension value below the surface tension of an aqueous surfactant system at the same concentration, which is a counterintuitive observation as only the particle results in an increase in the surface tension and only the surfactant results in a decrease in the surface tension. The possible physical mechanism behind such an anomaly happening at the complex fluid air interface has been explained. Detailed analyses based on thermodynamic, mechanical and chemical equilibrium of the constituents and their adsorption-desorption characteristics as extracted from the Gibbs adsorption analysis have been provided. The present paper conclusively explains several physical phenomena observed, yet hitherto unexplained, in the case of the surface tension of such complex fluids by segregating the individual contributions of each component of the colloidal system.

Interplay of chemical and thermal gradient on bacterial migration in a diffusive microfluidic device.

Living systems are constantly under different combinations of competing gradients of chemical, thermal, pH, and mechanical stresses allied. The present work is about competing chemical and thermal gradients imposed on E. coli in a diffusive stagnant microfluidic environment. The bacterial cells were exposed to opposing and aligned gradients of an attractant (1 mM sorbitol) or a repellant (1 mM NiSO4) and temperature. The effects of the repellant/attractant and temperature on migration behavior, migration rate, and initiation time for migration have been reported. It has been observed that under competing gradients of an attractant and temperature, the nutrient gradient (gradient generated by cells itself) initiates directed migration, which, in turn, is influenced by temperature through the metabolic rate. Exposure to competing gradients of an inhibitor and temperature leads to the imposed chemical gradient governing the directed cell migration. The cells under opposing gradients of the repellant and temperature have experienced the longest decision time (∼60 min). The conclusion is that in a competing chemical and thermal gradient environment in the range of experimental conditions used in the present work, the migration of E. coli is always initiated and governed by chemical gradients (either generated by the cells in situ or imposed upon externally), but the migration rate and percentage of migration of cells are influenced by temperature, shedding insights into the importance of such gradients in deciding collective dynamics of such cells in physiological conditions.

Role and significance of wetting pressures during droplet impact on structured superhydrophobic surfaces.

The impact dynamics and spreading behavior of droplets impinging on structured superhydrophobic surfaces are dependent on both the droplet initial conditions and the surface texture. The equivalence of wetting and dewetting pressures is classically known to be a critical factor in determining the state of a droplet during the contact and spreading phases. The present study extensively examines the underlying physics behind this pressure balance during the impact process and its direct role in determining the wetting process. Extensive three-dimensional simulations employing droplet impact on a structured superhydrophobic surface has been performed to reveal the intricacies of the interactivities of the fluid with the microstructure. Insight onto the acute role of wetting pressures and the implications of the same on determining the wetting dynamics, with internal fluidics of the droplet during the impact process, has been discussed. The phenomenon of state transition from the Cassie-Baxter to the Wenzel up on impact is also investigated and the intricate flow mechanics at play within the posts has been presented. Knowledge of pressure distribution and internal flow structures within the droplet during its interaction with the surface at different instances of time reveals the root mechanism behind the impalement of the droplet to a fully wetting state. Analysis of the internal pressure and flow distribution also presents necessary justification for the existence of a partially impaled state. The time evolution of spread for different scenarios is in agreement with experimental results and the article provides insight onto the role of wetting pressure in determining fluidic interactions on such surfaces.

Large electrorheological phenomena in graphene nano-gels.

Large-scale electrorheology (ER) response has been reported for dilute graphene nanoflake-based ER fluids that have been engineered as novel, readily synthesizable polymeric gels. Polyethylene glycol (PEG 400) based graphene gels have been synthesized and a very high ER response (∼125 000% enhancement in viscosity under influence of an electric field) has been observed for low concentration systems (∼2 wt.%). The gels overcome several drawbacks innate to ER fluids. The gels exhibit long term stability, a high graphene packing ratio which ensures very high ER response, and the microstructure of the gels ensures that fibrillation of the graphene nanoflakes under an electric field is undisturbed by thermal fluctuations, further leading to mega ER. The gels exhibit a large yield stress handling caliber with a yield stress observed as high as ∼13 kPa at 2 wt.% for graphene. Detailed investigations on the effects of graphene concentration, electric field strength, imposed shear resistance, transients of electric field actuation on the ER response and ER hysteresis of the gels have been performed. In-depth analyses with explanations have been provided for the observations and effects, such as inter flake lubrication/slip induced augmented ER response. The present gels show great promise as potential ER gels for various smart applications.

Analytical prediction of sub-surface thermal history in translucent tissue phantoms during plasmonic photo-thermotherapy (PPTT).

Knowledge of thermal history and/or distribution in biological tissues during laser based hyperthermia is essential to achieve necrosis of tumour/carcinoma cells. A semi-analytical model to predict sub-surface thermal distribution in translucent, soft, tissue mimics has been proposed. The model can accurately predict the spatio-temporal temperature variations along depth and the anomalous thermal behaviour in such media, viz. occurrence of sub-surface temperature peaks. Based on optical and thermal properties, the augmented temperature and shift of the peak positions in case of gold nanostructure mediated tissue phantom hyperthermia can be predicted. Employing inverse approach, the absorption coefficient of nano-graphene infused tissue mimics is determined from the peak temperature and found to provide appreciably accurate predictions along depth. Furthermore, a simplistic, dimensionally consistent correlation to theoretically determine the position of the peak in such media is proposed and found to be consistent with experiments and computations. The model shows promise in predicting thermal distribution induced by lasers in tissues and deduction of therapeutic hyperthermia parameters, thereby assisting clinical procedures by providing a priori estimates.

Subsurface thermal behaviour of tissue mimics embedded with large blood vessels during plasmonic photo-thermal therapy.

PURPOSE: The purpose of this study was to understand the subsurface thermal behaviour of a tissue phantom embedded with large blood vessels (LBVs) when exposed to near-infrared (NIR) radiation. The effect of the addition of nanoparticles to irradiated tissue on the thermal sink behaviour of LBVs was also studied. MATERIALS AND METHODS: Experiments were performed on a tissue phantom embedded with a simulated blood vessel of 2.2 mm outer diameter (OD)/1.6 mm inner diameter (ID) with a blood flow rate of 10 mL/min. Type I collagen from bovine tendon and agar gel were used as tissue. Two different nanoparticles, gold mesoflowers (AuMS) and graphene nanostructures, were synthesised and characterised. Energy equations incorporating a laser source term based on multiple scattering theories were solved using finite element-based commercial software. RESULTS: The rise in temperature upon NIR irradiation was seen to vary according to the position of the blood vessel and presence of nanoparticles. While the maximum rise in temperature was about 10 °C for bare tissue, it was 19 °C for tissue embedded with gold nanostructures and 38 °C for graphene-embedded tissues. The axial temperature distribution predicted by computational simulation matched the experimental observations. CONCLUSIONS: A different subsurface temperature distribution has been obtained for different tissue vascular network models. The position of LBVs must be known in order to achieve optimal tissue necrosis. The simulation described here helps in predicting subsurface temperature distributions within tissues during plasmonic photo-thermal therapy so that the risks of damage and complications associated with in vivo experiments and therapy may be avoided.

Effect of gold nanoparticles on thermal gradient generation and thermotaxis of E. coli cells in microfluidic device.

Bacteria responds to changing chemical and thermal environment by moving towards or away from a particular location. In this report, we looked into thermal gradient generation and response of E. coli DH5α cells to thermal gradient in the presence and in the absence of spherical gold nanoparticles (size: 15 to 22 nm) in a static microfluidic environment using a polydimethylsiloxane (PDMS) made microfluidic device. A PDMS-agarose based microfluidic device for generating thermal gradient has been developed and the thermal gradient generation in the device has been validated with the numerical simulation. Our studies revealed that the presence of gold nanoparticles, AuNPs (0.649 µg/mL) has no effect on the thermal gradient generation. The E. coli DH5α cells have been treated with AuNPs of two different concentrations (0.649 µg/mL and 0.008 µg/mL). The thermotaxis behavior of cells in the presence of AuNPs has been studied and compared to the thermotaxis of E.coli DH5α cells in the absence of AuNPs. In case of thermotaxis, in the absence of the AuNPs, the E. coli DH5α cells showed better thermotaxis towards lower temperature range, whereas in the presence of AuNPs (0.649 µg/mL and 0.008 µg/mL) thermotaxis of the E. coli DH5α cells has been inhibited. The results show that the spherical AuNPs intervenes in the themotaxis of E. coli DH5α cells and inhibits the cell migration. The reason for the failure in thermotaxis response mechanism may be due to decreased F-type ATP synthase activity and collapse of membrane potential by AuNPs, which, in turn, leads to decreased ATP levels. This has been hypothesized since both thermotaxis and chemotaxis follows the same response mechanism for migration in which ATP plays critical role.

Coalescence Dynamics of PEDOT:PSS Droplets Impacting at Offset on Substrates for Inkjet Printing.

UNLABELLED: The dynamics of coalescence and consequent spreading of conducting polymer droplets on a solid substrate impacting at an offset are crucial in understanding the stability of inkjet printed patterns, which find application in organic flexible electronic devices. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PEDOT: PSS) dispersion in water is a widely used commercial conducting polymer for the fabrication of electron devices. The effects of droplet spacing, impact velocity, substrate hydrophilicity, polymer concentration, and charges on the coalescence of two sessile droplets have been experimentally investigated, and the characteristics of dynamic spreading during the coalescence process are determined through image processing. The equilibrium spreading length of the coalesced droplets decreases with concentration and spacing of the droplets, revealing the necessity of optimum fluid properties (viscosity and surface tension) for the stability of the desired pattern. The droplet's impact energy governs the maximum extent of spreading and receding dynamics, as the velocity gradients developed in polymer droplets during coalescence are a function of the inertia of the fluid elements. Hydrophilicity affects the maximum spreading extent but it has no influence on the equilibrium droplet diameter. The spreading length dynamics of charge-neutralized PEDOT: PSS is found similar to the charged droplets, which show that the charged nature of the polymer does not affect the coalescence behavior. Furthermore, different spreading regimes are identified and the governing forces in each regime are described using a semianalytical formulation derived for the coalescence of two droplets. The model has been found to accurately provide insight into the various mechanisms that play a role during the complex spreading event.

Anomalously augmented charge transport capabilities of biomimetically transformed collagen intercalated nanographene-based biocolloids.

Collagen microfibrils biomimetically intercalate graphitic structures in aqueous media to form graphene nanoplatelet-collagen complexes (G-Cl). Synthesized G-Cl-based stable, aqueous bionanocolloids exhibit anomalously augmented charge transportation capabilities oversimple collagen or graphene based colloids. The concentration tunable electrical transport properties of synthesized aqueous G-Cl bionanocolloids has been experimentally observed, theoretically analyzed, and mathematically modeled. A comprehensive approach to mathematically predict the electrical transport properties of simple graphene and collagen based colloids has been presented. A theoretical formulation to explain the augmented transport characteristics of the G-Cl bionanocolloids based on the physicochemical interactions among the two entities, as revealed from extensive characterizations of the G-Cl biocomplex, has also been proposed. Physical interactions between the zwitterionic amino acid molecules within the collagen triple helix with the polar water molecules and the delocalized π electrons of graphene and subsequent formation of partially charged entities has been found to be the crux mechanism behind the augmented transport phenomena. The analysis has been observed to accurately predict the degree of enhancement in transport of the concentration tunable composite colloids over the base colloids. The electrically active G-Cl bionanocolloids with concentration tunability promises find dual utility in novel gel bioelectrophoresis-based protein separation techniques and advanced surface charge modulated drug delivery using biocolloids.

Near-field magnetostatics and Néel-Brownian interactions mediated magneto-rheological characteristics of highly stable nano-ferrocolloids.

Magnetic nanocolloids consisting of synthesized superparamagnetic iron(II,III) oxide nanoparticles (SPION) (5-15 nm) dispersed in poly(ethylene glycol) (PEG) and a nano-silica complex have been synthesized. The PEG-nano-silica complex physically encapsulates the SPIONs, ensuring that there is no phase separation under high magnetic fields (∼1.2 T). Exhaustive magneto-rheological investigations have been performed to understand the structural behavior and response of the ferrocolloids. Remarkable stability and reversibility have been observed under magnetic field for concentrated systems. The results show the impact of particle concentration, size and encapsulation efficiency on parameters such as shear viscosity, yield stress, viscoelastic moduli, magneto-viscous hysteresis, and so on. Analytical models to reveal the system mechanism and mathematically predict the magneto-viscosity and magneto-yield stress have been developed. The mechanistic approach based on near-field magnetostatics and Néel-Brownian interactivities could predict the colloidal properties under the effect of the magnetic field accurately. The colloid exhibits amplified storage and loss moduli together with a highly augmented linear viscoelastic region under magnetic stimuli. The transition of the colloidal state from the fluidic phase to the soft condensed phase and its viscoelastic stimuli under the influence of a magnetic field has been explained based on the mathematical analysis. The remarkable stability, magnetic properties and accurate physical models reveal promise for the colloids in transient situations, namely, magneto-microelectromechanical/nanoelectromechanical devices, anti-seismic damping, biomedical invasive treatments, and so on.

Long range microfluidic shear device for cellular mechanotransduction studies.

Cells sense external mechanical stimulus and respond to it through mechanotransduction mechanism. Fluid shear stress (FSS) has been found to be an important element among the mechanical stimuli. Recent advancements in microfluidics made mechanotransduction studies possible in near physiological conditions using microfluidic devices. FSS on human cells covers a broad range from very low level experienced due to interstitial flows (0.1 mPa) to very high level in aorta (10 Pa). In the present communication, we have designed a novel microfluidic device which can generate FSS on cells of five different orders with single inflow of fluid which can cover the whole range of physiological fluid shear stresses in one run. The dimensions of the device were calculated taking a resistance model for the micro channels. Flow velocities and wall shear stress were predicted through computer simulation. Shear stress values were analyzed for two different depths of channels and different inlet flow rates ranging from 50 to 0.5 µl/s. FSS was found to increase linearly with inlet flow rate and the stress profile was flatter for lesser depth of channel.

E. coli DH5α cell response to a sudden change in microfluidic chemical environment.

Motile bacteria respond to changing chemical environment by moving towards or away from a particular location. Bacterial migration under chemical gradient is one of the most studied areas in biomedical field. In this work we looked into how bacterial cells respond to sudden change in the microfluidic chemical environment. E. coli DH5α cells were subjected to an attractant gradient (0.1 mM sorbitol--attractant to E. coli cells) and after 120 min the same cells were exposed to an inhibitor (0.1 mM NiSO4) gradient in the same microfluidic device. Our studies revealed that when the E. coli DH5α cells were exposed to 0.1 mM sorbitol, they showed faster chemotaxis towards the attractant (0.1 mM sorbitol) and achieved steady state by 60 min. When we replaced 0.1 mM sorbitol with 0.1 mM NiSO4 in the device we found that that the E. coli DH5α cells started responding to change in chemical environment within 10 min and achieved steady state at the end of 60 min. This shows that the bacterial cells respond to change in local chemical environment is within few minutes.

Temperature evolution in tissues embedded with large blood vessels during photo-thermal heating.

During laser-assisted photo-thermal therapy, the temperature of the heated tissue region must rise to the therapeutic value (e.g., 43°C) for complete ablation of the target cells. Large blood vessels (larger than 500 micron in diameter) at or near the irradiated tissues have a considerable impact on the transient temperature distribution in the tissue. In this study, the cooling effects of large blood vessels on temperature distribution in tissues during laser irradiation are predicted using finite element based simulation. A uniform flow is assumed at the entrance and three-dimensional conjugate heat transfer equations in the tissue region and the blood region are simultaneously solved for different vascular models. A volumetric heat source term based on Beer-Lambert law is introduced into the energy equation to account for laser heating. The heating pattern is taken to depend on the absorption and scattering coefficients of the tissue medium. Experiments are also conducted on tissue mimics in the presence and absence of simulated blood vessels to validate the numerical model. The coupled heat transfer between thermally significant blood vessels and their surrounding tissue for three different tissue-vascular networks are analyzed keeping the laser irradiation constant. A surface temperature map is obtained for different vascular models and for the bare tissue (without blood vessels). The transient temperature distribution is seen to differ according to the nature of the vascular network, blood vessel size, flow rate, laser spot size, laser power and tissue blood perfusion rate. The simulations suggest that the blood flow through large blood vessels in the vicinity of the photothermally heated tissue can lead to inefficient heating of the target.

Colloidal graphite/graphene nanostructures using collagen showing enhanced thermal conductivity.

In the present study, the exfoliation of natural graphite (GR) directly to colloidal GR/graphene (G) nanostructures using collagen (CL) was studied as a safe and scalable process, akin to numerous natural processes and hence can be termed "biomimetic". Although the exfoliation and functionalization takes place in just 1 day, it takes about 7 days for the nano GR/G flakes to stabilize. The predominantly aromatic residues of the triple helical CL forms its own special micro and nanoarchitecture in acetic acid dispersions. This, with the help of hydrophobic and electrostatic forces, interacts with GR and breaks it down to nanostructures, forming a stable colloidal dispersion. Surface enhanced Raman spectroscopy, X-ray diffraction, photoluminescence, fluorescence, and X-ray photoelectron spectroscopy of the colloid show the interaction between GR and CL on day 1 and 7. Differential interference contrast images in the liquid state clearly reveal how the GR flakes are entrapped in the CL fibrils, with a corresponding fluorescence image showing the intercalation of CL within GR. Atomic force microscopy of graphene-collagen coated on glass substrates shows an average flake size of 350 nm, and the hexagonal diffraction pattern and thickness contours of the G flakes from transmission electron microscopy confirm ≤ five layers of G. Thermal conductivity of the colloid shows an approximate 17% enhancement for a volume fraction of less than approximately 0.00005 of G. Thus, through the use of CL, this new material and process may improve the use of G in terms of biocompatibility for numerous medical applications that currently employ G, such as internally controlled drug-delivery assisted thermal ablation of carcinoma cells.