Mohammad Asif Hussain

Cytoskeletal changes of mesenchymal stem cells during differentiation.

Mesenchymal stem cells (MSCs) are progenitors for tissues such as bone and cartilage. In this report, the actin cytoskeleton and nanomechanobiology of human mesenchymal stem cells (hMSCs) were studied using fluorescence microscopy and atomic force microscopy (AFM). Human MSCs were differentiated into chondrocytes and osteoblasts as per previous approaches. Cytochalasin D (CytD) was used to temporarily disrupt cytoskeleton in hMSCs, hMSC-chondrocytes (hMSC-Cys) and hMSC-osteoblasts (hMSC-Obs). Fluorescence microscopy revealed a dose-dependent response to CytD. Removal of CytD from the media of cytoskeleton-disrupted cells led to the recovery of the cytoskeletal structures, as confirmed by both fluorescence microscopy and AFM. Force-volume imaging by AFM evaluated the nanomechanics of all three cell types before, during, and after CytD treatment. Cytochalasin D disruption of cytoskeleton had marked effects on hMSCs and hMSC-Cys, in comparison with limited cytoskeleton disruption in hMSC-Obs, as confirmed qualitatively by fluorescence microscopy and quantitatively by AFM. Treatment with CytD resulted in morphology changes of all cell types, with significant decreases in the observed Young’s Moduli of hMSCs and hMSC-Cys. These data suggest human mesenchymal stem cells alter their cytoskeletal components during differentiation. Additional studies will address the mechanisms of cytoskeletal changes using biochemical and biophysical methods.

Relationship between power law coefficients and major blood constituents affecting the whole blood viscosity

The present work concerns a quantitative analysis of parameters that affect apparent blood viscosity at different low shear rates, i.e, between 1 s−1 and, 100 s−1. Viscosity profile of a large number of blood samples from thromboembolic stroke cases and age and sex matched healthy controls were studied which confirmed non-Newtonian power law behaviour of blood. The power law coefficients,n andk, which are unique to each blood sample, were related with blood viscosity parameters in the form of a mathematical equation by performing non-linear regression analysis. It was possible to calculaten andk of power law model by supplying the values of major blood constituents in the equation obtained for stroke and controls. The calculation ofn andk of a blood sample using the equation obtained, provided a quick information on its apparent viscosity values at any given shear rate without viscometry. The calculated and the experimental viscosity were found in good agreement within a permissible error range. The relation obtained between power law coefficients and major blood constituents in the present investigation would give a quantification of different blood viscosity parameters contributing to the resistance to flow of blood. Such an analysis may be considered as a scientific basis for the study of blood fluidity in different disease conditions.

Gold Nanocomposite Bioink for Printing 3D Cardiac Constructs

Bioprinting is the most convenient microfabrication method to create biomimetic three-dimensional (3D) cardiac tissue constructs, which can be used to regenerate damaged tissue and provide platforms for drug screening. However, existing bioinks, which are usually composed of polymeric biomaterials, are poorly conductive and delay efficient electrical coupling between adjacent cardiac cells. To solve this problem, we developed a gold nanorod (GNR) incorporated gelatin methacryloyl (GelMA)-based bioink for printing 3D functional cardiac tissue constructs. The GNR concentration was adjusted to create a proper microenvironment for the spreading and organization of cardiac cells. At optimized concentration of GNR, the nanocomposite bioink had a low viscosity, similar to pristine inks, which allowed for the easy integration of cells at high densities. As a result, rapid deposition of cell-laden fibers at a high resolution was possible, while reducing shear stress on the encapsulated cells. In the printed GNR constructs, cardiac cells showed improved cell adhesion and organization when compared to the constructs without GNRs. Furthermore, the incorporated GNRs bridged the electrically resistant pore walls of polymers, improved the cell-to-cell coupling, and promoted synchronized contraction of the bioprinted constructs. Given its advantageous properties, this gold nanocomposite bioink may find wide application in cardiac tissue engineering.

Nanoengineered biomimetic hydrogels for guiding human stem cell osteogenesis in three dimensional microenvironments

The ability to modulate stem cell differentiation in a three dimensional (3D) microenvironment for bone tissue engineering in absence of exogenous pharmaceutical agents such as bone morphogenic protein (BMP-2) remains a challenge. In this study, we introduce extracellular matrix (ECM)-mimicking nanocomposite hydrogels to induce osteogenic differentiation of human mesenchymal stem cells (hMSCs) for bone regeneration in absence of any osteoinducting factors. In particular, we have reinforced photocrosslinkable collagen-based matrix (gelatin methacryloyl, GelMA) used disk-shaped nanosilicates (nSi), a new class of two-dimensional (2D) nanomaterials. We show that nanoengineered hydrogels supported migration and proliferation of encapsulated hMSCs, with no signs of cell apoptosis or inflammatory cytokine responses. The addition of nSi significantly enhances osteogenic differentiation of encapsulated hMSCs as evident by the increase in alkaline phosphates (ALP) activity and deposition of biomineralized matrix compared to GelMA without nSi. We also show that microfabricated nanoengineered microgels can be used to pattern and control cellular behaviour. Furthermore, we also show that nanoengineered hydrogel have high biocompatibility as determined by in vivo experiments using immunocompetent rat model. Specifically, the hydrogels showed minimum localized immune responses, indicating it ability for tissue engineering applications. Overall, we showed the ability of nanoengineered hydrogels loaded with 2D nanosilicates for osteogenic differentiation of stem cells in vitro, in absence of any growth factors such as BMP-2. Our in vivo studies show high biocompatibility of nanocomposites and show the potential for growth factor free bone regeneration.

Elastomeric nanocomposite scaffolds made from poly(glycerol sebacate) chemically crosslinked with carbon nanotubes

Carbon nanotube (CNT)-based nanocomposites often possess properties such as high stiffness, electrical conductivity, and thermal stability and have been studied for various biomedical and biotechnological applications. However, the current design approaches utilize CNTs as physical filler, and thus, the true potential of CNT-based nanocomposites has not been achieved. Here, we introduce a general approach of fabricating stiff, elastomeric nanocomposites from poly(glycerol sebacate) (PGS) and CNTs. The covalent crosslinking between the nanotubes and polymer chains resulted in novel property combinations that are not observed in conventional nanocomposites. The addition of 1% CNTs resulted a five-fold increase in the tensile modulus and a six-fold increase in compression modulus compared with PGS alone, which is far superior to the previously reported studies for CNT-based nanocomposites. Despite significant increase in mechanical stiffness, the elasticity of the network was not compromised and the resulting nanocomposites showed more than 94% recovery. This study demonstrates that the chemical conjugation of CNTs to a PGS backbone results in stiff and elastomeric nanocomposites. Additionally, in vitro studies using human mesenchymal stem cells (hMSCs) indicated that the incorporation of CNTs to PGS network significantly enhanced the differentiation potential of the seeded hMSCs rendering them potentially suitable for applications ranging from scaffolding in musculoskeletal tissue engineering to biosensors in biomedical devices.

Double-Channel AlGaN/GaN High Electron Mobility Transistor With Back Barriers

We have developed a double-channel high electron mobility transistor with back barriers for carrier confinement. We have observed that the double-channel devices may suffer from the lack of gate control particularly for the lower channel. However, the problem can be contained by using a suitable back barrier for the lower channel. The double-channel back-barrier devices show good current gain and power gain cutoff frequencies. These devices can be operated with excellent gain linearity up to a larger value for input power and frequency.

Label-Free and Regenerative Electrochemical Microfluidic Biosensors for Continual Monitoring of Cell Secretomes

Development of an efficient sensing platform capable of continual monitoring of biomarkers is needed to assess the functionality of the in vitro organoids and to evaluate their biological responses toward pharmaceutical compounds or chemical species over extended periods of time. Here, a novel label‐free microfluidic electrochemical (EC) biosensor with a unique built‐in on‐chip regeneration capability for continual measurement of cell‐secreted soluble biomarkers from an organoid culture in a fully automated manner without attenuating the sensor sensitivity is reported. The microfluidic EC biosensors are integrated with a human liver‐on‐a‐chip platform for continual monitoring of the metabolic activity of the organoids by measuring the levels of secreted biomarkers for up to 7 d, where the metabolic activity of the organoids is altered by a systemically applied drug. The variations in the biomarker levels are successfully measured by the microfluidic regenerative EC biosensors and agree well with cellular viability and enzyme‐linked immunosorbent assay analyses, validating the accuracy of the unique sensing platform. It is believed that this versatile and robust microfluidic EC biosensor that is capable of automated and continual detection of soluble biomarkers will find widespread use for long‐term monitoring of human organoids during drug toxicity studies or efficacy assessments of in vitro platforms.

Hemorheological profiles in cancer patients

This study was undertaken to assess the hemorheological changes due to the presence of malignancy in human subjects and to find the usefulness of the hemorheological changes for the diagnosis and prognosis of malignancy and metastasis. 55 (40 males and 15 fem~les) freshly detected head & neck cancer patients, of age group 30-70 years, were considered for this study. Head and neck cancers are a group of cancers having similar characteristics, hence analysed together. Parameters studied include whole blood viscosity (WBV), plasma viscosity (PV), red cell aggregation (RCA), red cell rigidity (RG), hematocrit (HCT), and concentrations of cholesterol (CHOL), total protein (PRTN), albumin (ALBN), triglyceride (TRG) and fibrinogen (FIBRN) in plasma. 80 (55 males & 25 females) blood samples from age and sex matched normal controls were also analysed for comparison. Cases were divided into two groups. One with moderate whole blood viscosity (Group-I) while the other with high whole blood viscosity (Group-II). The results show that there is significant increase in RCA, PV, RG and FIBRN in cancer patients. It was very interesting to note that in spite of significant elevation of whole blood viscosity in Group-II cases, the hematocrit values were within the normal range. Since HCT is the main factor influencing whole blood viscosity, we suspect the role of some other factor(s) in elevating the WBV. It is likely that tumour cells or their products are present in the blood causing increased WBV. It is also observed that patients with high whole blood viscosity were having the disease at a higher stage (stage IV).

Electrical spin injection using GaCrN in a GaN based spin light emitting diode

We have demonstrated electrical spin-injection from GaCrN dilute magnetic semiconductor (DMS) in a GaN-based spin light emitting diode (spin-LED). The remanent in-plane magnetization of the thin-film semiconducting ferromagnet has been used for introducing the spin polarized electrons into the non-magnetic InGaN quantum well. The output circular polarization obtained from the spin-LED closely follows the normalized in-plane magnetization curve of the DMS. A saturation circular polarization of ∼2.5% is obtained at 200 K.

Effect of electrospinning parameters on nanofiber diameter made of poly (vinyl alcohol) as determined by Atomic Force Microscopy

A solution of poly (vinyl alcohol) (PVA) in water was electrospun into ultrafine nanofibers using a commercially available electrospinning set-up. Some major electrospinning parameters such as the concentration of polymer solution, flow rate, spinning voltage and distance between the needle tip and collection target were chosen to investigate its effect on the topological morphology as well as the average diameter of the electronspun PVA nanofibers using Atomic Force Microscopy (AFM). Diameters of the nanofibers obtained ranged from 150 nm to 900 nm. The diameters of electrospun nanofibers were most significantly affected by the concentration of polymer solution. While lower concentration always gave rise to the formation of discontinuous nanofibers with beads, an increasing concentration yielded smooth and uniform nanofibers with increasing diameters and beaded morphology was found disappearing. Keeping solution concentration constant at a higher value that yielded smooth nanofibers, an increase in the flow rate again changed the morphology from smooth to beaded morphology of nanofibers obtained. Spinning voltage did not show any specific trend of diameter change at a wider range (10 to 25 kV) selected in this study.