Department of Food Processing Technology and Management

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TWO DISTINCT FLUORESCENT QUANTUM CLUSTERS OF GOLD STARTING FROM METALLIC NANOPARTICLES BY PH-DEPENDENT LIGAND ETCHING
(Springer Link, 2008) Madathumpady, Abubaker Habeeb Muhammed; Subramani, Ramesh; Sudarson, Sekhar Sinha; Samir Kumar, Pal; Thalappil, Pradeep
Two fluorescent quantum clusters of gold, namely Au25 and Au8, have been synthesized from mercaptosuccinic acid-protected gold nanoparticles of 4–5 nm core diameter by etching with excess glutathione. While etching at pH ∼3 yielded Au25, that at pH 7–8 yielded Au8. This is the first report of the synthesis of two quantum clusters starting from a single precursor. This simple method makes it possible to synthesize well-defined clusters in gram quantities. Since these clusters are highly fluorescent and are highly biocompatible due to their low metallic content, they can be used for diagnostic applications.
SELF-ASSEMBLY OF A NANOSCALE DNA BOX WITH A CONTROLLABLE LID
(Nature Publishing Group UK, 2009-05-07) Ebbe S, Andersen; Mingdong, Dong; Morten M, Nielsen; Kasper, Jahn; Ramesh, Subramani; Wael, Mamdouh; Monika M, Golas; Bjoern, Sander; Holger, Stark; Cristiano L. P, Oliveira; Jan, Skov Pedersen; Victoria, Birkedal; Flemming, Besenbacher; Kurt V, Gothelf; Jørgen, Kjems
The unique structural motifs and self-recognition properties of DNA can be exploited to generate self-assembling DNA nanostructures of specific shapes using a ‘bottom-up’ approach1. Several assembly strategies have been developed for building complex three-dimensional (3D) DNA nanostructures2,3,4,5,6,7,8. Recently, the DNA ‘origami’ method was used to build two-dimensional addressable DNA structures of arbitrary shape9 that can be used as platforms to arrange nanomaterials with high precision and specificity9,10,11,12,13. A long-term goal of this field has been to construct fully addressable 3D DNA nanostructures14,15. Here we extend the DNA origami method into three dimensions by creating an addressable DNA box 42 × 36 × 36 nm3 in size that can be opened in the presence of externally supplied DNA ‘keys’. We thoroughly characterize the structure of this DNA box using cryogenic transmission electron microscopy, small-angle X-ray scattering and atomic force microscopy, and use fluorescence resonance energy transfer to optically monitor the opening of the lid. Controlled access to the interior compartment of this DNA nanocontainer could yield several interesting applications, for example as a logic sensor for multiple-sequence signals or for the controlled release of nanocargos
SINGLE-MOLECULE CHEMICAL REACTIONS ON DNA ORIGAMI
(Nature Nanotechnology, 2010-02-28) Niels V, Voigt; Thomas, Tørring; Alexandru, Rotaru; Mikkel F, Jacobsen; Jens B, Ravnsbæk; Ramesh, Subramani; Wael, Mamdouh; Jørgen, Kjems; Andriy, Mokhir; Flemming, Besenbacher; Kurt, Vesterager Gothelf
DNA nanotechnology1,2 and particularly DNA origami3, in which long, single-stranded DNA molecules are folded into predetermined shapes, can be used to form complex self-assembled nanostructures4,5,6,7,8,9,10. Although DNA itself has limited chemical, optical or electronic functionality, DNA nanostructures can serve as templates for building materials with new functional properties. Relatively large nanocomponents such as nanoparticles and biomolecules can also be integrated into DNA nanostructures and imaged11,12,13. Here, we show that chemical reactions with single molecules can be performed and imaged at a local position on a DNA origami scaffold by atomic force microscopy. The high yields and chemoselectivities of successive cleavage and bond-forming reactions observed in these experiments demonstrate the feasibility of post-assembly chemical modification of DNA nanostructures and their potential use as locally addressable solid supports.
TWO-DIMENSIONAL NETWORK STABILITY OF NUCLEOBASES AND AMINO ACIDS ON GRAPHITE UNDER AMBIENT CONDITIONS: ADENINE, L-SERINE AND L-TYROSINE
(Royal Society of Chemistry, 2010-03-09) Ilko, Bald; Sigrid, Weigelt; Xiaojing, Ma; Pengyang, Xie; Ramesh, Subramani; Mingdong, Dong; Chen, Wang; Wael, Mamdouh; Jianguo, Wang; Flemming, Besenbacher
We have investigated the stability of two-dimensional self-assembled molecular networks formed upon co-adsorption of the DNA base, adenine, with each of the amino acids, L-serine and L-tyrosine, on a highly oriented pyrolytic graphite (HOPG) surface by drop-casting from a water solution. L-serine and L-tyrosine were chosen as model systems due to their different interaction with the solvent molecules and the graphite substrate, which is reflected in a high and low solubility in water, respectively, compared with adenine. Combined scanning tunneling microscopy (STM) measurements and density functional theory (DFT) calculations show that the self-assembly process is mainly driven by the formation of strong adenine–adenine hydrogen bonds. We find that pure adenine networks are energetically more stable than networks built up of either pure L-serine, pure L-tyrosine or combinations of adenine with L-serine or L-tyrosine, and that only pure adenine networks are stable enough to be observable by STM under ambient conditions.
TWO DISTINCT FLUORESCENT QUANTUM CLUSTERS OF GOLD STARTING FROM METALLIC NANOPARTICLES BY PH-DEPENDENT LIGAND ETCHING
(Springer Link, 2010-04-08) Madathumpady Abubaker, Habeeb Muhammed; Subramani, Ramesh; Sudarson, Sekhar Sinha; Samir Kumar, Pal; Thalappil, Pradeep
Two fluorescent quantum clusters of gold, namely Au25 and Au8, have been synthesized from mercaptosuccinic acid-protected gold nanoparticles of 4 5 nm core diameter by etching with excess glutathione. While etching at pH ~3 yielded Au25, that at pH 7 8 yielded Au8. This is the fi rst report of the synthesis of two quantum clusters starting from a single precursor. This simple method makes it possible to synthesize well-defined clusters in gram quantities. Since these clusters are highly fl uorescent and are highly biocompatible due to their low metallic content, they can be used for diagnostic applications.
A NOVEL SECONDARY DNA BINDING SITE IN HUMAN TOPOISOMERASE I UNRAVELLED BY USING A 2D DNA ORIGAMI PLATFORM
(ACS Publications, 2010-09-09) Ramesh, Subramani; Sissel, Juul; Alexandru, Rotaru; Felicie F, Andersen; Kurt V., Gothelf; Wael, Mamdouh; Flemming, Besenbacher; Mingdong, Dong; Birgitta R, Knudsen
The biologically and clinically important nuclear enzyme human topoisomerase I relaxes both positively and negatively supercoiled DNA and binds consequently DNA with supercoils of positive or negative sign with a strong preference over relaxed DNA. One scheme to explain this preference relies on the existence of a secondary DNA binding site in the enzyme facilitating binding to DNA nodes characteristic for plectonemic DNA. Here we demonstrate the ability of human topoisomerase I to induce formation of DNA synapses at protein containing nodes or filaments using atomic force microscopy imaging. By means of a two-dimensional (2D) DNA origami platform, we monitor the interactions between a single human topoisomerase I covalently bound to one DNA fragment and a second DNA fragment protruding from the DNA origami. This novel single molecule origami-based detection scheme provides direct evidence for the existence of a secondary DNA interaction site in human topoisomerase I and lends further credence to the theory of two distinct DNA interaction sites in human topoisomerase I, possibly facilitating binding to DNA nodes characteristic for plectonemic supercoils.
BUILDING LAYER-BY-LAYER 3D SUPRAMOLECULAR NANOSTRUCTURES AT THE TEREPHTHALIC ACID/STEARIC ACID INTERFACE
(Royal Society of Chemistry, 2011-07-14) Yinli, Li; Lei, Liu; Ramesh, Subramani; Yunxiang, Pan; Bo, Liu; Yanlian, Yang; Chen, Wang; Wael, Mamdouh; Flemming, Besenbacher; Mingdong, Dong
By using the layer-by-layer deposition method, we build three dimensional (3D) supramolecular nanostructures by stacking small molecular species on top of the first buffer layer, which can be utilized to fabricate novel 3D supramolecular functional nanostructures.
PLASMODIUM FALCIPARUM-INFECTED ERYTHROCYTE KNOB DENSITY IS LINKED TO THE PFEMP1 VARIANT EXPRESSED
(ASM Journals, 2015-10-06) Ramesh, Subramani; Katharina, Quadt; Anine E, Jeppesen; Casper, Hempel; Jens, Emil Vang Petersen; Tue, Hassenkam; Lars, Hviid; Lea, Barfod
Members of the clonally variant Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) family mediate adhesion of infected erythrocytes (IEs) to vascular receptors. PfEMP1 expression is normally confined to nanoscale knob protrusions on the IE surface membrane. To investigate the relationship between the densities of these IE surface knobs and the PfEMP1 variant expressed, we used specific antibody panning to generate three sublines of the P. falciparum clone IT4, which expresses the PfEMP1 variants IT4VAR04, IT4VAR32b, and IT4VAR60. The knob density in each subline was then determined by atomic force microscopy (AFM) and scanning electron microscopy (SEM) and compared to PfEMP1 and knob-associated histidine-rich protein (KAHRP) expression. Selection for uniform expression of IT4VAR04 produced little change in knob density, compared to unselected IEs. In contrast, selection for IT4VAR32b expression increased knob density approximately 3-fold, whereas IEs selected for IT4VAR60 expression were essentially knobless. When IT4VAR60+ IEs were subsequently selected to express IT4VAR04 or IT4VAR32b, they again displayed low and high knob densities, respectively. All sublines expressed KAHRP regardless of the PfEMP1 expressed. Our study documents for the first time that knob density is related to the PfEMP1 variant expressed. This may reflect topological requirements to ensure optimal adhesive properties of the IEs.
IMMERSED BOUNDARY MODELS FOR QUANTIFYING FLOW-INDUCED MECHANICAL STIMULI ON STEM CELLS SEEDED ON 3D SCAFFOLDS IN PERFUSION BIOREACTORS
(PLOS Computational Biology, 2016-09-22) Yann, Guyot; Bart, Smeets; Tim, Odenthal; Ramesh, Subramani; Frank P, Luyten; Herman, Ramon; Ioannis, Papantoniou; Liesbet, Geris
Perfusion bioreactors regulate flow conditions in order to provide cells with oxygen, nutrients and flow-associated mechanical stimuli. Locally, these flow conditions can vary depending on the scaffold geometry, cellular confluency and amount of extra cellular matrix deposition. In this study, a novel application of the immersed boundary method was introduced in order to represent a detailed deformable cell attached to a 3D scaffold inside a perfusion bioreactor and exposed to microscopic flow. The immersed boundary model permits the prediction of mechanical effects of the local flow conditions on the cell. Incorporating stiffness values measured with atomic force microscopy and micro-flow boundary conditions obtained from computational fluid dynamics simulations on the entire scaffold, we compared cell deformation, cortical tension, normal and shear pressure between different cell shapes and locations. We observed a large effect of the precise cell location on the local shear stress and we predicted flow-induced cortical tensions in the order of 5 pN/μm, at the lower end of the range reported in literature. The proposed method provides an interesting tool to study perfusion bioreactors processes down to the level of the individual cell’s micro-environment, which can further aid in the achievement of robust bioprocess control for regenerative medicine applications.
IMMERSED BOUNDARY MODELSFOR QUANTIFYING FLOW-INDUCED MECHANICAL STIMULI ON STEM CELLS SEEDED ON 3D SCAFFOLDS IN PERFUSION BIOREACTORS
(PLOS Computational Biology, 2016-09-22) Yann, Guyot; Bart, Smeets; Tim, Odentha; Ramesh, Subramani; Frank P, Luyten; Herman, Ramon; Ioannis, Papantoniou; Liesbet, Geris
Perfusion bioreactors regulate flow conditions in order to provide cells with oxygen, nutrients and flow-associated mechanical stimuli. Locally, these flow conditions can vary depending on the scaffold geometry, cellular confluency and amount of extra cellular matrix deposition. In this study, a novel application of the immersed boundary method was introduced in order to represent a detailed deformable cell attached to a 3D scaffold inside a perfusion bioreactor and exposed to microscopic flow. The immersed boundary model permits the prediction of mechanical effects of the local flow conditions on the cell. Incorporating stiffness values measured with atomic force microscopy and micro-flow boundary conditions obtained from computational fluid dynamics simulations on the entire scaffold, we compared cell deformation, cortical tension, normal and shear pressure between different cell shapes and locations. We observed a large effect of the precise cell location on the local shear stress and we predicted flow-induced cortical tensions in the order of 5 pN/μm, at the lower end of the range reportedin literature. The proposed method provides an interesting tool to study perfusion bioreactors processes down to the level of the individual cell’s micro-environment, which can furtheraid in the achievement of robust bioprocess control for regenerative medicine applications.
GREEN SYNTHESIZED SILVER NANOPARTICLES: TOXICITY AGAINST POECILIA RETICULATA FISHES AND CERIODAPHNIA CORNUTA CRUSTACEANS
(Springer Link, 2016-11-30) Ramachandran, Ishwarya; Baskaralingam, Vaseeharan; Sathappan, Shanthi; Subramani, Ramesh; Pitchaimani, Manogari,; Kannan, Dhanalakshmi; Sekar, Vijayakumar; Giovanni, Benelli
Recently, the green synthesis of silver nanoparticles gained increasing attention due to interesting properties for optical, antimicrobial and pest control applications. However, their toxicity against micro-crustaceans and fishes has been scarcely explored, while most of the research efforts focused on mosquito control with the green-synthesized nanocomposites. In this study, we investigated the toxic effects of AgNO3, Cissus quadrangularis (Cq)-synthesized AgNPs and Cq extract in two different study models, the larvae of Poecilia reticulata fishes and adults of the micro-crustacean Ceriodaphnia cornuta. In both species, AgNO3 and Cq-AgNPs showed high mortality rates even if tested at very low doses. Molecular analysis revealed high DNA damages induced by Cq-AgNPs on both aquatic organisms. Furthermore, light microscopy studies evidenced lesions in the gills and vacuolization in the gills and in the abdomen of P. reticulata larvae. Overall, our research pointed out that the exposure of aquatic organisms to AgNO3 or green-fabricated AgNPs can damage fishes and crustaceans, posing noteworthy risks to the aquatic ecosystems.
THE INFLUENCE OF SWELLING ON LOCAL ELASTIC PROPERTIES OF POLYACRYLAMIDE HYDROGELS
(Open Science Framework, 2017) Ramesh, Subramani; Alicia, Izquierdo-Alvarez; Pinaki, Bhattacharya; Mathieu, Meerts; Paula, Moldenaers; Herman, Ramon; Hans Van, Oosterwyck
Polyacrylamide (PAM)hydrogelsarecommonly usedas soft cell culture substrates for cell mechanical and mechanobiological studiesbecause oftheir tunable stiffness,easeof handling, transparent natureand surface functionalization to promote cell adhesion. The dependence of bulk rheological and local elastic properties (for example, as assessed by means of Atomic Force Microscopyor AFM) of PAM hydrogels onmonomer and cross-linkerconcentrationsand on polymerization temperature havebeen extensively investigated.PAM hydrogels are known to swell, which may affect their elastic properties and therefore may complicate the interpretation ofcell culturingexperiments because of a lack of control of substrate stiffness. Direct measurements of the effect of swelling on PAM elastic properties are scarce. We report here, for the first time, the direct observation of swelling (by measuring the volumetric swelling ratio) and its influence onlocal elastic properties, as measuredby AFM. Bulk rheological measurements were performed as well to enable the comparison between local and global elastic properties during and after hydrogel polymerization. Four PAM hydrogel compositions were considered,with corresponding storage shear moduliof 4530 Pa(termed stiffest), 2900 Pa(stiff), 538 Pa(soft)and 260 Pa(softest) as measured immediately after polymerization. These values as well as values obtained during hydrogel polymerization were found to be in good agreement with the local elastic moduli derived from AFM and assuming hydrogel incompressibility. After polymerization, the hydrogels were subjected to swelling conditions over six days in phosphate buffered salineand swelling ratios and local elastic moduli were measured each day.Additional short term measurements (at 0, 3, 6, 9, 12 and 24 hours) were performed for the soft and softest gelsto study their swelling kinetics in more detail. Swelling ratio and local elastic modulus did not change with time for the stiffest and stiff gels, while for the soft and softest gels substantialchanges between Day 0 and Day 1were found for both swelling ratio (21.6%and 133% increase for soft and softest gel respectively) and local elastic modulus (33.7%and 33.3% decrease for soft and softest gel respectively). Experimental data werefurther analysed theoretically by combining models of ideal elastomeric gels with a poroelastic swelling kinetics model, which confirmed the validity of observed trends with respect to literature data. The results demonstrate that swelling can have an important effect on PAM elastic properties and must be taken into account when using PAM as a cell culture substrate, particularly for PAM gels with low monomer and cross-linker concentrations
SPATIOTEMPORAL ANALYSES OF CELLULAR TRACTIONS DESCRIBE SUBCELLULAR EFFECT OF SUBSTRATE STIFFNESS AND COATING
(Springer Link, 2018-11-08) Alicia, Izquierdo-Álvarez; Diego A, Vargas; Álvaro, Jorge-Peñas; Ramesh, Subramani; Marie-Mo, Vaeyens; Hans, Van Oosterwyck
Cells interplay with their environment through mechanical and chemical interactions. To characterize this interplay, endothelial cells were cultured on polyacrylamide hydrogels of varying stiffness, coated with either fibronectin or collagen. We developed a novel analysis technique, complementary to traction force microscopy, to characterize the spatiotemporal evolution of cellular tractions: We identified subpopulations of tractions, termed traction foci, and tracked their magnitude and lifetime. Each focus consists of tractions associated with a local single peak of maximal traction. Individual foci were spread over a larger area in cells cultured on collagen relative to those on fibronectin and exerted higher tractions on stiffer hydrogels. We found that the trends with which forces increased with increasing hydrogel stiffness were different for foci and whole-cell measurements. These differences were explained by the number of foci and their average strength. While on fibronectin multiple short-lived weak foci contributed up to 30% to the total traction on hydrogels with intermediate stiffness, short-lived foci in such a number were not observed on collagen despite the higher tractions. Our approach allows for the use of existing traction force microscopy data to gain insight at the subcellular scale without molecular probes or spatial constraining of cellular tractions.
SPATIOTEMPORAL ANALYSES OF CELLULAR TRACTIONS DESCRIBE SUBCELLULAR EFFECT OF SUBSTRATE STIFFNESS AND COATING
(Springer Link, 2019) Alicia, Izquierdo-Álvarez; Diego A, Vargas; Álvaro, Jorge-Peñas; Ramesh, Subramani; Marie-Mo, Vaeyens; Hans Van, Oosterwyck
Cells interplay with their environment through mechanical and chemical interactions. To characterize this interplay, endothelial cells were cultured on polyacrylamide hydrogels of varying stiffness, coated with either fibronectin or collagen. We developed a novel analysis technique, complementary to traction force microscopy, to characterize the spatiotemporal evolution of cellular tractions: We identified subpopulations of tractions, termed traction foci, and tracked their magnitude and lifetime. Each focus consists of tractions associated with a local single peak of maximal traction. Individual foci were spread over a larger area in cells cultured on collagen relative to those on fibronectin and exerted higher tractions on stiffer hydrogels. We found that the trends with which forces increased with increasing hydrogel stiffness were different for foci and whole-cell measurements. These differences were explained by the number of foci and their average strength. While on fibronectin multiple short-lived weak foci contributed up to 30% to the total traction on hydrogels with intermediate stiffness, short-lived foci in such a number were not observed on collagen despite the higher tractions. Our approach allows for the use of existing traction force microscopy data to gain insight at the subcellular scale without molecular probes or spatial constraining of cellular tractions.
ROBUST SCALABLE SYNTHESIS OF A BIS-UREA DERIVATIVE FORMING THIXOTROPIC AND CYTOCOMPATIBLE SUPRAMOLECULAR HYDROGELS
(Royal Society of Chemistry, 2019-06-06) Laurens A J, Rutgeerts; Al, Halifa Soulta; Ramesh, Subramani; Burak, Toprakhisar; Herman, Ramon; Monissa C, Paderes; Wim M, De Borggraeve; Jennifer, Patterson
Synthetic hydrogels address a need for affordable, industrially scalable scaffolds for tissue engineering. Herein, a novel low molecular weight gelator is reported that forms self-healing supramolecular hydrogels. Its robust synthesis can be performed in a solvent-free manner using ball milling. Strikingly, encapsulated cells spread and proliferate without specific cell adhesion ligands in the nanofibrous material.
PHYSICO-CHEMICAL CHARACTERISTICS OF TWO VARIETIES OF PUMPKIN SEEDS
(2020) R, Santhiya; J, Sridevi
Pumpkin seed is one among the plant foods that contain high levels of bioactive components such as beta-carotene, unsaturated fatty acids, phenolic compounds, phytosterols and tocopherols. Pumpkin seeds are generally considered as waste product but it is rich in bioactive compounds with neutraceutical properties and considered as a healthy source. The nutritional factors of pumpkin seed comprises of nutrients such as carbohydrates, fats and proteins, as well as minor components such as minerals, vitamins, fibres. The chemical composition of pumpkin varies from one cultivar or species to other. The study aimed to characterize the physico-chemical characterization of Cucurbita maxima Dushesne- CUCURBITACEAE i.e. orange pumpkin seed (OPS) and Cucurbita pepo L. – CUCURBITACEAE i.e. white pumpkin seed (WPS).
3D NANOMANIPULATION: DESIGN AND APPLICATIONS OF FUNCTIONAL NANOSTRUCTURED BIO-MATERIALS
(IOP Science, 2020) Lega P V; Orlov A P; Frolov A V; Subramani R; Irzhak A V; Koledov V V; Smolovich A M; Shelyakov A V
Recent progress in the development of the new functional materials opens up exciting possibilities for designing reconfigurable micro- and nano-structures and for operating mechanical nanotools which are controlled by external fields or heat. The nanotools such as nanotweezers with an active layer thickness of about several tenths of nm, and whose overall size is of the order of 1 µm can be applied to different micro- and nanoobjects. The present report gives an overview of the application of mechanical nanotools in 3D nanomanipulation of bio-nano objects such as micro biofibers DNA etc. The future prospects of mechanical bottom up nanomanipulation for biomedical technology, food technology are discussed.
IN VITRO ANTI-ARTHRITIC ACTIVITY OF TWO VARIETIES OF PUMPKIN SEEDS
(INTERNATIONAL JOURNAL OF SCIENTIFIC DEVELOPMENT AND RESEARCH, 2020-06-06) Santhiya R; Sridevi J
The seeds of the orange pumpkin (OPS) and white pumpkin (WPS) belongs to the family of cucurbitaceae. This family is one of the largest family in plant kingdom comprising of highest number of edible plant species. Pumpkin seeds are generally considered as waste product but it is rich in bioactive compounds with neutraceutical properties and considered as a healthy source. The anti-arthritic activity of the OPS and WPS are done by various methods such as inhibition of protein denaturation, Proteinase inhibition in different concentrations with aqueous and ethanol extracts. The results from these studies concluded that the pumpkin seed varieties showed good anti-arthritic property and thus the OPS and WPS can be suggested as a potent inhibitor for occurrence of arthritis.
GC-MS ANALYSIS OF FATTY ACID COMPONENTS IN ETHANOL EXTRACTS OF TWO VARIETIES OF PUMPKIN SEEDS
(2020-06-06) Santhiya R; Sridevi J
The two varieties of pumpkin seeds such as orange pumpkin seed (OPS) and white pumpkin seed (WPS) were analyzed with their ethanol extracts for the estimation of fatty acid components through GC-MS analysis. 37 compounds were analyzed in total in both OPS and WPS where about 19 compounds were pinpointed to be present in OPS, 25 compounds in WPS and about 8 compounds to be present common in both OPS and WPS. The peak area % concentration obtained from analysis were compared with the known peak area % concentrations of WILEY8.LIB and the results were interpreted. Some of the compounds determined to be present in higher concentration in OPS include were Propane 1,1,3-triethoxy- (6.58 %), Hexadecanoic acid, 1-(hydroxymethyl)-1,2 ethanediyl ester (9.38 %), 9,12-Octadecadienoyl chloride, (Z,Z)- propanetriyl ester, (E,E,E)- (17.59 %), 9-Octadecenoic acid, 1,2,3-propanetriyl ester – (19.19 %), Squalene (21.33 %) and those identified in WPS include Beta.-Sitosterol (5.10%), 9-Octadecenoic acid,1,2,3-propanetriyl ester (E,E,E) (5.65%), Chondrillasterol (7.30%), Propane, 1, 1, 3- triethoxy- (7.50%), Bicyclo[10.1.0]tridec-1-ene (40.55%). Among them biological activities of some of the important compounds are suggested. This study thus offers the base for using OPS and WPS as an herbal supplement.
THE INFLUENCE OF SWELLING ON ELASTIC PROPERTIES OF POLYACRYLAMIDE HYDROGELS
(Frontiers in Materials, 2020-07-23) Ramesh, Subramani; Alicia, Izquierdo-Alvarez; Pinaki, Bhattacharya; Mathieu, Meerts; Paula, Moldenaers; Herman, Ramon; Hans, Van Oosterwyck
Polyacrylamide (PAM) hydrogels are commonly used as substrates for cell mechanical and mechanobiological studies because of their tunable stiffness and ease of handling. The dependence of bulk rheological and local elastic properties (assessed by Atomic Force Microscopy, or AFM) of PAM hydrogels on its composition and polymerization temperature has been extensively studied. PAM hydrogels swell when immersed in media, but the influence of swelling on local elastic properties is poorly characterized. Direct measurements of the effect of swelling on PAM elastic properties are scarce. We report here, for the first time, the direct measurements of volumetric swelling and local elastic properties of PAM gels throughout the post-polymerization swelling process until equilibrium. First, local and global elastic properties (measured by rheology), were obtained during polymerization in the absence of swelling, and showed good agreement with each other. Four PAM hydrogel compositions were characterized thus, with corresponding storage shear moduli (as measured immediately after polymerization) of 4,530 Pa (termed stiffest), 2,900 Pa (stiff), 538 Pa (soft), and 260 Pa (softest). Next, all compositions were subjected to swelling in phosphate buffered saline. Swelling ratios and local elastic moduli were measured at 0, 3, 6, 9, 12, and 24 h post-polymerization for the soft and softest compositions, and once daily till 6 days post-polymerization for all four compositions. For the stiffest and stiff gels, swelling ratio, and local elastic modulus changed negligibly with time, while for the soft and softest gels, substantial changes between Day 0 and Day 1 were found for both swelling ratio (increased by 21.6 and 133%, respectively), and local elastic modulus decreased (by 33.7 and 33.3%, respectively), substantially. Experimental data were analyzed by a model that combined ideal elastomer mechanics and poroelastic swelling kinetics model. Model predictions confirmed the validity of present measurements with respect to past studies where swelling and elastic properties were not measured simultaneously. The present study underlines the important effect swelling can have on PAM elastic properties and provides detailed quantitative data to guide the duration taken to reach equilibrium—a useful information for cell mechanics experiments. In addition, the simultaneous measurements of swelling and local elastic moduli provide novel data for the validation of theoretical models.