Biomedical subjects

George Eng

Publications and source records attributed to George Eng.

17 recordsLinked to original sources

PubMed2007

Microfluidic patterning for fabrication of contractile cardiac organoids.

The development of in vitro methods of engineering three-dimensional cardiac tissues can be useful for tissue replacement, diagnostics and drug discovery. Here, we introduce the use of patterned hyaluronic acid (HA) substrates generated using microfluidic patterning as a method of fabricating 3D cardiac organoids. HA micropatterns served as inductive templates for organoid assembly. Upon seeding, cardiomyocytes elongated and aligned along the pattern direction attaching preferentially to the glass substrate and the interface between HA patterns and glass substrate. After 3 days in culture, the linearly aligned myocytes detached from the surface and formed contractile cardiac organoids. The procedure can be utilized to simply, rapidly and inexpensively create in vitro cardiac tissue models.

Animals↗

PubMed2006

Micromolding of photocrosslinkable hyaluronic acid for cell encapsulation and entrapment.

Micropatterning of hydrogels is potentially useful for a variety of applications, including tissue engineering, fundamental biological studies, diagnostics, and high-throughput screening. Although synthetic polymers have been developed for these applications, natural polymers such as polysaccharides may have advantages for biological samples and cell-based devices because they are natural components of the in vivo microenvironment. In this study, we synthesized and used hyaluronic acid (HA) modified with photoreactive methacrylates to fabricate microstructures as functional components of microfabricated devices. To demonstrate the universality of this approach, two types of microstructures were formed. In the first approach, HA microstructures were fabricated and used as docking templates to enable the subsequent formation of cell microarrays within low shear stress regions of the patterns. Cells within these microwells remained viable, could generate spheroids, and could be retrieved using mechanical disruption. In the second approach, cells were encapsulated directly within the HA hydrogels. Arrays of viable embryonic stem (ES) cells or fibroblasts were encapsulated within HA hydrogels and could later be recovered using enzymatic digestion of the microstructures. These results demonstrate that it is possible to incorporate photocrosslinkable HA, a natural, versatile, degradable, and biocompatible biopolymer, into micro-electromechanical systems.

Animals↗

PubMed2006

Micromolding of shape-controlled, harvestable cell-laden hydrogels.

Encapsulation of mammalian cells within hydrogels has great utility for a variety of applications ranging from tissue engineering to cell-based assays. In this work, we present a technique to encapsulate live cells in three-dimensional (3D) microscale hydrogels (microgels) of controlled shapes and sizes in the form of harvestable free standing units. Cells were suspended in methacrylated hyaluronic acid (MeHA) or poly(ethylene glycol) diacrylate (PEGDA) hydrogel precursor solution containing photoinitiator, micromolded using a hydrophilic poly(dimethylsiloxane) (PDMS) stamp, and crosslinked using ultraviolet (UV) radiation. By controlling the features on the PDMS stamp, the size and shape of the molded hydrogels were controlled. Cells within microgels were well distributed and remained viable. These shape-specific microgels could be easily retrieved, cultured and potentially assembled to generate structures with controlled spatial distribution of multiple cell types. Further development of this technique may lead to applications in 3D co-cultures for tissue/organ regeneration and cell-based assays in which it is important to mimic the architectural intricacies of physiological cell-cell interactions.

Animals↗

PubMed2006

Micromolding of photocrosslinkable chitosan hydrogel for spheroid microarray and co-cultures.

Bioengineering approaches, such as co-cultures of multiple cell types, that aim to mimic the physiological microenvironment may be beneficial for optimizing cell function and for engineering tissues in vitro. This study describes a novel method for preparing a spheroid microarray on microfabricated hydrogels, alone or in co-cultures. Photocrosslinkable chitosan was synthesized and utilized for fabricating hydrogel microstructures through a micromolding process. The chitosan surface was initially cell repellent but became increasingly cell adhesive over time. By using this unique property of chitosan hydrogels, it was possible to generate patterned co-cultures of spheroids and support cells. In this scheme, cells were initially microarrayed within low shear stress regions of microwells. Human hepatoblastoma cells, Hep G2, seeded in these wells formed spheroids with controlled sizes and shapes and stably secreted albumin during the culture period. The change of cell adhesive properties in the chitosan surface facilitated the adhesion and growth of a second cell type, NIH-3T3 fibroblast, and therefore enabled co-cultures of hepatocyte spheroids and fibroblast monolayers. This co-culture system could be a useful platform for studying heterotypic cell-cell interactions, for drug screening, and for developing implantable bioartificial organs.

Animals↗

PubMed2005

Micropatterned cell co-cultures using layer-by-layer deposition of extracellular matrix components.

Micropatterned cellular co-cultures were fabricated using three major extracellular matrix components: hyaluronic acid (HA), fibronectin (FN) and collagen. To fabricate co-cultures with these components, HA was micropatterned on a glass substrate by capillary force lithography, and the regions of exposed glass were coated with FN to generate cell adhesive islands. Once the first cell type was immobilized on the adhesive islands, the subsequent electrostatic adsorption of collagen to HA patterns switched the non-adherent HA surfaces to adherent, thereby facilitating the adhesion of a second cell type. This technique utilized native extracellular matrix components and therefore affords high biological affinity and no cytotoxicity. This biocompatible co-culture system could potentially provide a new tool to study cell behavior such as cell-cell communication and cell-matrix interactions, as well as tissue-engineering applications.

Animals↗

PubMed2005

Cell docking inside microwells within reversibly sealed microfluidic channels for fabricating multiphenotype cell arrays.

We present a soft lithographic method to fabricate multiphenotype cell arrays by capturing cells within an array of reversibly sealed microfluidic channels. The technique uses reversible sealing of elastomeric polydimethylsiloxane (PDMS) molds on surfaces to sequentially deliver various fluids or cells onto specific locations on a substrate. Microwells on the substrate were used to capture and immobilize cells within low shear stress regions inside channels. By using an array of channels it was possible to deposit multiple cell types, such as hepatocytes, fibroblasts, and embryonic stem cells, on the substrates. Upon formation of the cell arrays on the substrate, the PDMS mold could be removed, generating a multiphenotype array of cells. In addition, the orthogonal alignment and subsequent attachment of a secondary array of channels on the patterned substrates could be used to deliver fluids to the patterned cells. The ability to position many cell types on particular regions within a two dimensional substrate could potentially lead to improved high-throughput methods applicable to drug screening and tissue engineering.

Cell Adhesion↗

PubMed2005

Microfluidic system for studying the interaction of nanoparticles and microparticles with cells.

Nanoparticles and microparticles have many potential biomedical applications ranging from imaging to drug delivery. Therefore, in vitro systems that can analyze and optimize the interaction of such particles with cells may be beneficial. Here, we report a microfluidic system that can be used to study these interactions. As a model system, we evaluated the interaction of polymeric nanoparticles and microparticles and similar particles conjugated to aptamers that recognize the transmembrane prostate specific membrane antigen (PSMA), with cells seeded in microchannels. The binding of particles to cells that expressed or did not express the PSMA (LNCaP or PC3, respectively) were evaluated with respect to changes in fluid shear stress, PSMA expression on target cells, and particle size. Nanoparticle-aptamer bioconjugates selectively adhered to LNCaP but not PC3 cells at static and low shear (<1 dyn/cm2) but not higher shear (approximately 4.5 dyn/cm2) conditions. Control nanoparticles and microparticles lacking aptamers and microparticle-aptamer bioconjugates did not adhere to LNCaP cells, even under very low shear conditions (approximately 0.28 dyn/cm2). These results demonstrate that the interaction of particles with cells can be studied under controlled conditions, which may aid in the engineering of desired particle characteristics. The scalability, low cost, reproducibility, and high-throughput capability of this technology is potentially beneficial to examining and optimizing a wide array of cell-particle systems prior to in vivo experiments.

Biosensing Techniques↗

PubMed2005

Synthesis, spectral and thermal studies of some organotin(IV) derivatives of 5-amino-3H-1,3,4-thiadiazole-2-thione.

Some tri- and diorganotin(IV) compounds of the general formula, RnSnL4-n (where n=2, R=Me, n-Bu and Ph; n=3, R=Me, n-Bu, n-Pr and Ph; HL=5-amino-3H-1,3,4-thiadiazole-2-thione) have been synthesized by the reaction of RnSnCl4-n (where n=2 or 3, R=Me, n-Bu, n-Pr and Ph) and the sodium salt of the ligand. Oct2SnL2 was obtained by the reaction of Oct2SnO with HL in a 1:2 molar ratio under azeotropic removal of water. The bonding and coordination behavior in these derivatives are discussed on the basis of IR, Far-IR, multinuclear (1H, 13C and 119Sn) NMR and 119Sn Mössbauer spectroscopic studies. These investigations suggest that in all the compounds the ligand acts as monoanionic bidentate coordinating through ring N(3) and exocyclic S. Thermal studies of five compounds, viz., Ph3SnL, Me2SnL2, n-Bu2SnL2, Oct2SnL2 and Ph2SnL2 have been carried out in the temperature range 25-1000 degrees C using TG, DTG and DTA techniques under an atmosphere of dry nitrogen.

Alkenes↗

PubMed2005

Synthesis, spectral characterization and biological studies of some organotin(IV) complexes of L-proline, trans-hydroxy-L-proline and L-glutamine.

New organotin(IV) complexes of the general formula R3Sn(L) (where R=Me, n-Bu and HL=L-proline; R=Me, Ph and HL=trans-hydroxy-L-proline and L-glutamine) and R2Sn(L)2 (where R=n-Bu, Ph and HL=L-proline; R=Ph, HL=trans-hydroxy-L-proline) have been synthesized by the reaction of RnSnCl(4-n) (where n=2 or 3) with sodium salt of the amino acid (HL). n-Bu2Sn(Pro)2 was synthesized by the reaction of n-Bu2SnO with L-proline under azeotropic removal of water. The bonding and coordination behavior in these complexes have been discussed on the basis of IR and 119Sn Mössbauer spectroscopic studies in the solid-state. Their coordination behavior in solution has been discussed with the help of multinuclear (1H, 13C and 119Sn) NMR spectral studies. The 119Sn Mössbauer and IR studies indicate that L-proline and trans-hydroxy-L-proline show similar coordination behavior towards organotin(IV) compounds. Pentacoordinate trigonal-bipyramidal and hexacoordinate octahedral structures, respectively, have been proposed for the tri- and diorganotin(IV) complexes of L-proline and trans-hydroxy-L-proline, in which the carboxylate group acts as bidentate group. L-glutamine shows different coordination behavior towards organotin(IV) compounds, it acts as monoanionic bidentate ligand coordinating through carboxylate and amino group. The triorganotin(IV) complexes of L-glutamine have been proposed to have trigonal-bipyramidal environment around tin. The newly synthesized complexes have been tested for their antiinflammatory and cardiovascular activities. Their LD50 values are >1000 mg kg-1.

Animals↗

PubMed2005

New triorganotin (IV) derivatives of dipeptides as models for metal-protein interactions: synthesis, structural characterization and biological studies.

New non-electrolytic triorganotin(IV) derivatives of dipeptides with general formulae R3Sn(HL), where R = Ph and HL = monoanion of glycylisoleucine (H2L-1), valylvaline (H2L-2), alanylvaline (H2L-3), leucylalanine (H2L-4), leucylleucine (H2L-5); R = n-Bu and HL = monoanion of glycylisoleucine (H2L-1) and leucylalanine (H2L-4); and R = Me and HL = monoanion of leucylalanine (H2L-4) have been synthesized and characterized on the basis of infrared, multinuclear 1H, 13C and 119Sn NMR and 119Sn Mössbauer spectroscopic studies. These investigations suggest that all the ligands in R3Sn(HL) act as monoanionic bidentates coordinating through the COO- and NH2 groups. The 119Sn Mössbauer studies, together with the NMR data, indicate that, for these polymeric derivatives, the polyhedron around tin in R3Sn(HL) is a trigonal-bipyramid with the three organic groups in the equatorial positions, while the axial positions are occupied by a carboxylic oxygen and the amino nitrogen atom from the adjacent molecule. The anti-inflammatory and cardiovascular activities and toxicity of all these compounds have been determined. Four of the complexes have also been screened against some of the chosen bacterial and fungal strains. The Ph3Sn(IV) compounds exhibit better anti-inflammatory and cardiovascular activities in comparison to the Me3Sn(IV) and n-Bu3Sn(IV) analogues. n-Bu3Sn(Gly-Ile) and Ph3Sn(Ala-Val) exhibit good antibacterial activity against all the chosen strains.

Animals↗

PubMed2005

New triorganotin(IV) derivatives of dipeptides as anti-inflammatory-antimicrobial agents.

New triorganotin(IV) derivatives of dipeptides with general formulae R(3)Sn(HL), where R = Me and/or n-Bu and/or Ph and HL is the monoanion of glycylglycine (H(2)L-1), glycylvaline (H(2)L-2), glycylleucine (H(2)L-3), glycyltryptophane (H(2)L-4) and glycyltyrosine (H(2)L-5) have been synthesized and characterized on the basis of infrared, multinuclear NMR and (119)Sn Mossbauer spectroscopic studies. All the newly synthesized compounds were examined for their in vivo anti-inflammatory activity (using the carrageenan-induced paw edema bioassay in rats), acute toxicity (LD(50)) and cardiovascular activity. These compounds were also screened for their in vitro antimicrobial activity against Staphylococcus aureus Mau (29/58) and (78/71), Bacillus subtilis (18/64), Escherichia coli (326/71), Candida albicans (Pn-10), Microsporum gypseum and Euglena gracillis. The results revealed that triphenyltin(IV) derivatives exhibited anti-inflammatory activity comparable to that of phenylbutazone with high safety margin (LD(50) > 500 mg kg(-1)). Further Ph(3)Sn(Gly-Val) displays a potent cardiovascular activity. Moreover, most of the compounds displayed appreciable antibacterial activities when compared with ampicillin and norfloxacin. Compounds Ph(3)Sn(Gly-Gly) and Ph(3)Sn(Gly-Val) are the most distinctive derivatives identified in the present study because of their promising in vivo anti-inflammatory activity and in vitro antibacterial activity against gram-positive and -negative bacteria.

Animals↗

PubMed2005

New organotin(IV) ascorbates: synthesis, spectral characterization, biological and potentiometric studies.

New organotin(IV) ascorbates of the general formulae R(3)Sn(HAsc) (where R = Me , n-Pr, n-Bu and Ph) and R(2)Sn(Asc) (where R = n-Bu and Ph) have been synthesized by the reaction of R(n)SnCl(4-n) (where n = 2 or 3) with monosodium-l-ascorbate. The bonding and coordination behaviour in these complexes are discussed on the basis of UV-Vis, IR, Far-IR, (1)H and (13)C NMR, and (119)Sn Mossbauer spectroscopic studies. L-Ascorbic acid acts as a monoanionic bidentate ligand in R(3)Sn(HAsc) coordinating through O(1) and O(3). The Mossbauer studies together with IR and NMR studies suggest that for these polymeric derivatives, the polyhedron is trigonal bipyramidal around tin with three organic groups in the equatorial positions. In R(2)Sn(Asc), L-ascorbic acid acts as dianionic tetradentate ligand and a polymeric structure with octahedral geometry around tin with trans organic groups has been tentatively proposed. The complexes have been assayed for their anti-inflammatory and cardiovascular activity. Ph(2)Sn(Asc) has been found to show the highest activity among the studied complexes. It is suggested on the basis of potentiometric studies of Me(2)Sn(IV) and Me(3)Sn(IV) systems with L-ascorbic acid that under physiological conditions (pH = 7.0) Me(2)Sn(HAsc)(OH) (approximately 60%), Me(2)Sn(OH)(2) (approximately 40%) and Me(3)Sn(HAsc) (approximately 60%), Me(3)Sn(OH) (approximately 40%), respectively, are existing, which may be responsible for their biological activities.

Animals↗

PubMed2005

New diorganotin(IV) derivatives of 7-hydroxycoumarin (umbelliferone) and their adducts with 1,10-phenanthroline.

New diorganotin(IV) derivatives of the general formula R2Sn(Umb)2 (where R = n-Bu, n-Oct and Ph; Umb = umbelliferone anion) have been synthesized either by the reaction of R2SnO with umbelliferone under azeotropic removal of water or by the reaction of R2SnCl2 with sodium salt of umbelliferone. Further, the adducts of the general formula R2Sn(Umb)2.phen (where R = n-Bu and n-Oct; phen = 1,10-phenanthroline) have also been synthesized by the interaction of R2Sn(Umb)2 with 1,10-phenanthroline. The bonding and coordination behavior in these derivatives are discussed on the basis of IR and 119Sn Mössbauer spectroscopic studies in solid state. Their coordination behavior in solution is discussed by the multinuclear (1H, 13C and 119Sn) NMR spectral studies. The Mössbauer and IR studies indicate that umbelliferone acts as a monoanionic bidentate ligand in R2Sn(Umb)2 coordinating through O(7) and O(1). A distorted octahedral geometry around tin has been proposed for R2Sn(Umb)2 as well as for R2Sn(Umb)2.phen in solid state. The newly synthesized derivatives have been tested for their anti-inflammatory and cardiovascular activities. The average LD50 value >1000 mg kg(-1) of these compounds indicates their safety margin.

Animals↗

PubMed2004

Molded polyethylene glycol microstructures for capturing cells within microfluidic channels.

The ability to control the deposition and location of adherent and non-adherent cells within microfluidic devices is beneficial for the development of micro-scale bioanalytical tools and high-throughput screening systems. Here, we introduce a simple technique to fabricate poly(ethylene glycol)(PEG) microstructures within microfluidic channels that can be used to dock cells within pre-defined locations. Microstructures of various shapes were used to capture and shear-protect cells despite medium flow in the channel. Using this approach, PEG microwells were fabricated either with exposed or non-exposed substrates. Proteins and cells adhered within microwells with exposed substrates, while non-exposed substrates prevented protein and cell adhesion (although the cells were captured inside the features). Furthermore, immobilized cells remained viable and were stained for cell surface receptors by sequential flow of antibodies and secondary fluorescent probes. With its unique strengths in utility and control, this approach is potentially beneficial for the development of cell-based analytical devices and microreactors that enable the capture and real-time analysis of cells within microchannels, irrespective of cell anchorage properties.

Animals↗

PubMed2004

Single nanocrystal arrays on patterned poly(ethylene glycol) copolymer microstructures using selective wetting and drying.

Single nanocrystal arrays were fabricated on sub-microwells of poly(ethylene glycol) (PEG) copolymer using selective wetting on the hydrophilic regions of the exposed substrate surface and subsequent drying. Templates were produced by molding a thin film of a PEG-based random copolymer on hydrophilic substrates such as glass or silicon dioxide. The polymeric microstructures provide a topographical barrier around the well, which makes it possible to create nanocrystal arrays with controlled geometrical features. The size of the nanocrystal was found to decrease with decreasing well size and also decrease with decreasing topological height. A simple empirical equation was derived to predict the size of the crystal as a function of the pattern size and height, which is in good agreement with the experimental data.

Journal Article↗

PubMed2004

A soft lithographic approach to fabricate patterned microfluidic channels.

The control of surface properties and spatial presentation of functional molecules within a microfluidic channel is important for the development of diagnostic assays and microreactors and for performing fundamental studies of cell biology and fluid mechanics. Here, we present a simple technique, applicable to many soft lithographic methods, to fabricate robust microchannels with precise control over the spatial properties of the substrate. In this approach, the patterned regions were protected from oxygen plasma by controlling the dimensions of the poly(dimethylsiloxane) (PDMS) stamp and by leaving the stamp in place during the plasma treatment process. The PDMS stamp was then removed, and the microfluidic mold was irreversibly bonded to the substrate. The approach was used to pattern a nonbiofouling poly(ethylene glycol)-based copolymer or the polysaccharide hyaluronic acid within microfluidic channels. These nonbiofouling patterns were then used to fabricate arrays of fibronectin and bovine serum albumin as well as mammalian cells. In addition, further control over the deposition of multiple proteins onto multiple or individual patterns was achieved using laminar flow. Also, cells that were patterned within channels remained viable and capable of performing intracellular reactions and could be potentially lysed for analysis.

Animals↗

PubMed2004

Layer-by-layer deposition of hyaluronic acid and poly-L-lysine for patterned cell co-cultures.

A novel method for patterning cellular co-cultures that uses the layer-by-layer deposition of ionic biopolymers is described. Non-biofouling hyaluronic acid (HA) micropatterns were used to immobilize cells and proteins to glass substrates. Subsequent ionic adsorption of poly-L-lysine (PLL) to HA patterns was used to switch the HA surfaces from cell repulsive to adherent thereby facilitating the adhesion of a second cell type. The utility of this approach to pattern co-cultures of hepatocytes or embryonic stem cells with fibroblasts was demonstrated. In addition, the versatility of this approach to generate patterned co-cultures irrespective of the primary cell seeding and relative adhesion of the seeded cells was demonstrated. Thus, the proposed method may be a useful tool for fabricating controlled cellular co-cultures for cell-cell interaction studies and tissue engineering applications.

Adsorption↗