Biomedical subjects

S Ramakrishna

Publications and source records attributed to S Ramakrishna.

At least 19 recordsLinked to original sources

PubMed2006

Coherent spectroscopy in dissipative media: time-domain studies of channel phase and signal interferometry.

We extend a recently formulated coherence spectroscopy of dissipative media [J. Chem. Phys. 122, 084502 (2005)] from the stationary excitation limit to the time domain. Our results are based on analytical and numerical solutions of the quantum Liouville equation within the Bloch framework. It is shown that the short pulse introduces a new, controllable time scale that allows better insight into the relation between the coherence signal and the phase properties of the material system. We point to the relation between the time-domain coherence spectroscopy and the method of interferometric two-photon photoemission spectroscopy, and propose a variant of the latter method, where the two time-delayed excitation pathways are distinguishable, rather than identical. In particular, we show that distinguishability of the two excitation pathways introduces the new possibility of disentangling decoherence from population relaxation.

Chemistry, Physical↗

PubMed2006

Dissipative dynamics of laser induced nonadiabatic molecular alignment.

Nonadiabatic alignment induced by short, moderately intense laser pulses in molecules coupled to dissipative environments is studied within a nonperturbative density matrix theory. We focus primarily on exploring and extending a recently proposed approach [Phys. Rev. Lett. 95, 113001 (2005)], wherein nonadiabatic laser alignment is used as a coherence spectroscopy that probes the dissipative properties of the solvent. To that end we apply the method to several molecular collision systems that exhibit sufficiently varied behavior to represent a broad variety of chemical environments. These include molecules in low temperature gas jets, in room temperature gas cells, and in dense liquids. We examine also the possibility of prolonging the duration of the field free (post-pulse) alignment in dissipative media by a proper choice of the system parameters.

Journal Article↗

PubMed2006

Coaxial electrospinning of (fluorescein isothiocyanate-conjugated bovine serum albumin)-encapsulated poly(epsilon-caprolactone) nanofibers for sustained release.

As an aim toward developing biologically mimetic and functional nanofiber-based tissue engineering scaffolds, we demonstrated the encapsulation of a model protein, fluorescein isothiocyanate-conjugated bovine serum albumin (fitcBSA), along with a water-soluble polymer, poly(ethylene glycol) (PEG), within the biodegradable poly(epsilon-caprolactone) (PCL) nanofibers using a coaxial electrospinning technique. By variation of the inner flow rates from 0.2 to 0.6 mL/h with a constant outer flow rate of 1.8 mL/h, fitcBSA loadings of 0.85-2.17 mg/g of nanofibrous membranes were prepared. Variation of flow rates also resulted in increases of fiber sizes from ca. 270 nm to 380 nm. The encapsulation of fitcBSA/PEG within PCL was subsequently characterized by laser confocal scanning microscopy, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) analysis. In vitro release studies were conducted to evaluate sustained release potential of the core-sheath-structured composite nanofiber PCL-r-fitcBSA/PEG. As a negative control, composite nanofiber PCL/fitcBSA/PEG blend was prepared from a normal electrospinning method. It was found that core-sheath nanofibers PCL-r-fitcBSA/PEG pronouncedly alleviated the initial burst release for higher protein loading and gave better sustainability compared to that of PCL/fitcBSA/PEG nanofibers. The present study would provide a basis for further design and optimization of processing conditions to control the nanostructure of core-sheath composite nanofibers and ultimately achieve desired release kinetics of bioactive proteins (e.g., growth factors) for practical tissue engineering applications.

Animals↗

PubMed2006

PCL-PGLA composite tubular scaffold preparation and biocompatibility investigation.

The objective of this paper was to fabricate a biodegradable tubular scaffold for small diameter (d<6 mm) blood vessel tissue engineering. The tube scaffold needed a porous wall for cell attachment, proliferation and tissue regeneration with its degradation. A novel method given in this paper was to coat a porous layer of poly (epsilon-caprolactone) (PCL) on the outside of a poly (glycolic-co-lactic acid) (PGLA with GA:LA=90:10) fiber braided tube to give a PCL-PGLA composite. The PGLA tube was fabricated using a braiding machine by inserting a Teflon tube with the desired diameter in center of the 20 spindles, which are the carriers of PGLA fibers. Changing the diameter of the Teflon tube can vary the inner diameter of a braided PGLA tube. Thermally induced phase separation method was used for PCL solution coating on the surface of the PGLA braided tube. Controlling the polymer concentration, non-solvent addition and quenching temperature generated the pore structures, with pore sizes ranging from 10-30 microm. The fibroblast cells were seeded on the tubular scaffold and cultured in vitro for the biocompatibility investigation. Histology results showed that the fibroblast cells proliferated on the interconnected pore of the PCL porous layer in 1 week.

3T3 Cells↗

PubMed2006

Influence of microencapsulation method and peptide loading on formulation of poly(lactide-co-glycolide) insulin nanoparticles.

Insulin stability during microencapsulation and subsequent release is essential for retaining its biological activity. Therefore we investigated a novel solid/oil/water anhydrous encapsulation method with a combination of stabilizers for maintaining the integrity of insulin during formulation and delivery. Two methods were used for preparation of nanoparticles, namely water/oil/water solvent evaporation and s/o/w anhydrous encapsulation to study the influence of the microencapsulation method on nanoparticle characteristics such as size and morphology, drug content, encapsulation efficiency, and in vitro and in vivo release profile. Poly (lactic-co-glycolic) acid (PLGA) with co-polymer ratio 50:50 was selected to prepare drug-loaded nanoparticles. When nanoparticles were prepared by solvent evaporation higher encapsulation efficiencies could be obtained, e.g. 74 +/- 13 with 5% target loading, whereas with 12% target loading, encapsulation efficiency was 27 +/- 8.6. The s/o/w method has a direct influence on the evaluation parameters where very poor encapsulation efficiencies 11 +/- 6.8 (max) were observed. The presence of stabilizers in the nanoparticles resulted in an increase in particle size but a reduction of encapsulation efficiency. Insulin release rate was comparatively higher for the batches prepared by the w/o/w method containing stabilizers than the s/o/w method. Also the presence of stabilizers resulted in sustained release of insulin resulting in prolonged reduction of blood glucose levels in streptozotocin induced diabetic rats. From the in vitro and in vivo studies, it can be concluded that careful selection of processing conditions and combination of stabilizers also result in beneficial effects without compromising the advantages of these delivery systems.

Animals↗

PubMed2005

Determination of DPPH free radical scavenging activity by reversed-phase HPLC: a sensitive screening method for polyherbal formulations.

The colorimetric method of evaluation of antioxidant activity by scavenging 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical is with certain shortcomings like failure to indicate antioxidant activity of certain drugs and interference from color pigments of natural products. A specific HPLC method was developed for evaluating the DPPH free radical scavenging activity of commercial polyherbal formulations using a LiChrospher 100 RP-18e column (250 mm x 4 mm, 5 microM). The mobile phase was a mixture of methanol and water (80:20, v/v) pumped at a flow rate of 1 mL/min. The DPPH peaks were monitored at 517 nm. The method was standardized using known antioxidants such as ascorbic acid, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (trolox), probucol and alpha-tocopherol. The 50% radical scavenging activity (IC50) determined by the HPLC method correlated well with that of colorimetry. This HPLC method was applied for the estimation of free radical scavenging activity of Silymarin and a few commercial hepatoprotective polyherbal formulations. While the colorimetric method failed to estimate the free radical scavenging activity of polyherbal formulations, HPLC method was free from interferences and was specific. The HPLC method is sensitive and can be used as a quality control tool for the rapid determination of free radical scavenging activity of variety of products including plant extracts, foods, drugs and polyherbal formulations.

Antioxidants↗

PubMed2005

Production of ultra-fine bioresorbable carbonated hydroxyapatite.

Ionic-substituted hydroxyapatite (HAp) based materials may be a better choice than pure HAp owing to their similarity in chemical composition with biological apatite. The present study reports a process for the production of carbonated hydroxyapatite (CHAp) using microwaves. The CHAp was evaluated for its phase purity, chemical homogeneity, functionality, morphology, and solubility. The CHAp thus obtained was compared with a pure HAp and a biological apatite, which provides quite an interesting insight into the carbonate substitution. The in vitro ionic dissolution rates determined under physiological conditions clearly demonstrate the soluble nature of CHAp compared to HAp. The overall results indicate that the processed CHAp has increased resorption relative to pure HAp and has a chemical composition corresponding to some extent with that of biological apatite.

Apatites↗

PubMed2005

Intense laser alignment in dissipative media as a route to solvent dynamics.

We extend the concept of alignment by short intense pulses to dissipative environments within a density matrix formalism and illustrate the application of this method as a probe of the dissipative properties of dense media. In particular, we propose a means of disentangling rotational population relaxation from decoherence effects via strong laser alignment. We illustrate also the possibility of suppressing rotational relaxation to prolong the alignment lifetime through choice of the field parameters. Implications to several disciplines and a number of potential applications are proposed.

Journal Article↗

PubMed2005

Coherence spectroscopy in dissipative media: a Liouville space pathway approach.

We address the possibility of using coherent control tools to extract useful information about the interaction of a system with a dissipative environment. To that end we extend previous work, which developed a coherence spectroscopy based on two-pathway excitation phase control, from the isolated molecule limit to dense media. Specifically, we explore the properties of the channel phase, an observable of energy-domain two-pathway excitation experiments that was shown in the isolated molecule limit to carry information about the phase properties of the material system. Our analysis is based on the combination of steady state and time-dependent analytical perturbative approaches within the density matrix formalism, complemented by nonperturbative numerical simulations. We find that the channel phase carries significantly richer information in the presence of decoherence mechanisms than in their absence. In particular, rescattering events in the structured continuum introduce new features in the channel phase spectrum, whose structure conveys information about both the molecular continuum and the system bath interaction.

Journal Article↗

PubMed2005

Development of fibrous biodegradable polymer conduits for guided nerve regeneration.

The technique of microbraiding with modification was employed as a novel method for the fabrication of fibrous tubular scaffolds for nerve tissue engineering purposes. The biodegradable polymers used in this study were poly(L-lactide-co-glycolide) (10:90) and chitosan. The polymeric fibers were microbraided around a Teflon mandrel to make it as a tubular construct. The conduits were then studied for their surface morphology, swelling behaviour and biocompatibility. The surface morphology was analysed by scanning electron microscope, swelling behaviour by weight increase due to water uptake and biocompatibility by in vitro cytotoxicity assessment in terms of cell morphology and cell viability by the MTT assay of polymer extract treated cells. These conduits may also be used for regeneration of tissues, which require tubular scaffolds such as blood vessel, spinal cord, intestine etc.

Absorbable Implants↗

PubMed2005

Inhibition of ATPases enzyme activities on brain disturbing normal oestrous cycle.

Wistar rats treated with alpha-methyl-DL-p-tyrosine methylester showed significant level of inhibition in the activity of Na+, K+ -ATPase, Mg2+ -ATPase and Ca2+ -ATPase enzymes in different regions of the brain. The enzyme activity was assayed in cerebral hemispheres, hypothalamus, thalamus, hippocampus, amygdala and septum at proestrous (12 h), estrous (25 h), metestrous (38 h) and diestrous periods (92 h) of the rat. The Na+, K+ -ATPase activity was significantly inhibited in most of the brain regions after treated with alpha-methyl-DL-p-tyrosine methylester (MPT) and this indicated that MPT affected the active transport system and nerve impulse transmission. Mg2+ -ATPase and Ca2+ -ATPase was also significantly (P < 0.001) reduced in different regions of the brain. The results revealed that MPT affected active transport system and nerve impulse transmission by inhibiting Na+, K+ -ATPase and Ca2+ -ATPase. It has induced energy crisis by inhibiting Mg2+ -ATPase and all these cumulative effects of MPT have adversely affected the female Wistar rats. These effects have been manifested in the form of aberrations in the behavior of MPT treated female rats, which have shown their inability to perform their normal sexual activity.

Adenosine Triphosphatases↗

PubMed2005

Electrospinning of nano/micro scale poly(L-lactic acid) aligned fibers and their potential in neural tissue engineering.

Efficacy of aligned poly(l-lactic acid) (PLLA) nano/micro fibrous scaffolds for neural tissue engineering is described and their performance with random PLLA scaffolds is compared as well in this study. Perfectly aligned PLLA fibrous scaffolds were fabricated by an electrospinning technique under optimum condition and the diameter of the electrospun fibers can easily be tailored by adjusting the concentration of polymer solution. As the structure of PLLA scaffold was intended for neural tissue engineering, its suitability was evaluated in vitro using neural stem cells (NSCs) as a model cell line. Cell morphology, differentiation and neurite outgrowth were studied by various microscopic techniques. The results show that the direction of NSC elongation and its neurite outgrowth is parallel to the direction of PLLA fibers for aligned scaffolds. No significant changes were observed on the cell orientation with respect to the fiber diameters. However, the rate of NSC differentiation was higher for PLLA nanofibers than that of micro fibers and it was independent of the fiber alignment. Based on the experimental results, the aligned nanofibrous PLLA scaffold could be used as a potential cell carrier in neural tissue engineering.

Animals↗

PubMed2005

Guided bone regeneration membrane made of polycaprolactone/calcium carbonate composite nano-fibers.

In this study, new type of guided bone regeneration (GBR) membranes were fabricated by polycaprolactone (PCL)/CaCO3 composite nano-fibers with two different PCL to calcium carbonate (CaCO3) ratios (PCL:CaCO3=75:25 wt% and 25:75 wt%). The composite nano-fibers were successfully fabricated by electrospinning method and CaCO3 nano-particles on the surface of nano-fibers were confirmed by energy disperse X-ray (EDX) analysis. In order to achieve mechanical stability of GBR membranes, composite nano-fibers were spun on PCL nano-fibrous membranes which has high tensile strength, i.e., the membranes consist of two layers of functional layer (PCL/CaCO3) and mechanical support layer (PCL). Two different GBR membranes were prepared, i.e., GBR membrane (A)=PCL:CaCO3=75:25 wt%+PCL, GBR membrane (B)=PCL:CaCO3=25:75 wt%+PCL. Osteoblast attachment and proliferation of GBR membrane (A) and (B) were discussed by MTS assay and scanning electron microscope (SEM) observation. As a result, absorbance intensity of GBR membrane (A) and tissue culture polystyrene (TCPS) increased during 5 days seeding time. In contrast, although absorbance intensity of GBR membrane (B) also increased, its value was lower than membrane (A). SEM observation showed that no significant difference in osteoblast attachment manner was seen on GBR membrane (A) and (B). Because of good cell attachment manner, there is a potential to utilize PCL/CaCO3 composite nano-fibers to GBR membranes.

Biocompatible Materials↗

PubMed2005

In vitro study of smooth muscle cells on polycaprolactone and collagen nanofibrous matrices.

Biodegradable polycaprolactone and collagen nanofibers were produced by electrospinning, with fiber diameters of around 300-700nm and features similar to the extracellular matrix of natural tissue. Human coronary artery smooth muscle cells (SMCs) seeded on nanofibrous matrices tend to maintain normal phenotypic shape and growth tends to be guided by the nanofiber orientation. The SMC and nanofibrous matrix interaction was observed by SEM, MTS assay, trypan blue exclusion method and laser scanning confocal microscopy. The results showed that the proliferation and growth rate of SMCs were not different on polycaprolactone (PCL) nanofibrous matrices coated with collagen or tissue culture plates. PCL nanofibrous matrices coated with collagen showed that the SMCs migrated towards inside the nanofibrous matrices and formed smooth muscle tissue. This approach may be useful for engineering a variety of tissues in various structures and shapes, and also to demonstrate the importance of matching both the initial mechanical properties and degradation rate of nanofibrous matrices to the specific tissue engineering.

Actins↗

PubMed2005

Applications of polymer nanofibers in biomedicine and biotechnology.

Recent advancements in the electrospinning method enable the production of ultrafine solid and continuous fibers with diameters ranging from a few nanometers to a few hundred nanometers with controlled surface and internal molecular structures. A wide range of biodegradable biopolymers can be electrospun into mats with specific fiber arrangement and structural integrity. Through secondary processing, the nanofiber surface can be functionalized to display specific biochemical characteristics. It is hypothesized that the large surface area of nanofibers with specific surface chemistry facilitates attachment of cells and control of their cellular functions. These features of nanofiber mats are morphologically and chemically similar to the extracellular matrix of natural tissue, which is characterized by a wide range of pore diameter distribution, high porosity, effective mechanical properties, and specific biochemical properties. The current emphasis of research is on exploiting such properties and focusing on determining appropriate conditions for electrospinning various polymers and biopolymers for eventual applications including multifunctional membranes, biomedical structural elements (scaffolds used in tissue engineering, wound dressing, drug delivery, artificial organs, vascular grafts), protective shields in specialty fabrics, and filter media for submicron particles in the separation industry. This has resulted in the recent applications for polymer nanofibers in the field of biomedicine and biotechnology.

Biocompatible Materials↗

PubMed2004

Beta-cyclodextrin complexes of celecoxib: molecular-modeling, characterization, and dissolution studies.

Celecoxib, a specific inhibitor of cycloxygenase-2 (COX-2) is a poorly water-soluble nonsteroidal anti-inflammatory drug with relatively low bioavailability. The effect of beta-cyclodextrin on the aqueous solubility and dissolution rate of celecoxib was investigated. The possibility of molecular arrangement of inclusion complexes of celecoxib and beta-cyclodextrin were studied using molecular modeling and structural designing. The results offer a better correlation in terms of orientation of celecoxib inside the cyclodextrin cavity. Phase-solubility profile indicated that the solubility of celecoxib was significantly increased in the presence of beta-cyclodextrin and was classified as A(L)-type, indicating the 1:1 stoichiometric inclusion complexes. Solid complexes prepared by freeze drying, evaporation, and kneading methods were characterized using differential scanning calorimetry, powder x-ray diffractometry, and scanning electron microscopy. In vitro studies showed that the solubility and dissolution rate of celecoxib were significantly improved by complexation with beta-cyclodextrin with respect to the drug alone. In contrast, freeze-dried complexes showed higher dissolution rate than the other complexes.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed2004

Peripheral nerve regeneration by microbraided poly(L-lactide-co-glycolide) biodegradable polymer fibers.

Tiny tubes with fiber architecture were developed by a novel method of fabrication upon introducing some modification to the microbraiding technique, to function as nerve guide conduit and the feasibility of in vivo nerve regeneration was investigated through several of these conduits. Poly(L-lactide-co-glycolide) (10:90) polymer fibers being biocompatible and biodegradable were used for the fabrication of the conduits. The microbraided nerve guide conduits (MNGCs) were characterized using scanning electron microscopy to study the surface morphology and fiber arrangement. Degradation tests were performed and the micrographs of the conduit showed that the degradation of the conduit is by fiber breakage indicating bulk hydrolysis of the polymer. Biological performances of the conduits were examined in the rat sciatic nerve model with a 12-mm gap. After implantation of the MNGC to the right sciatic nerve of the rat, there was no inflammatory response. One week after implantation, a thin tissue capsule was formed on the outer surface of the conduit, indicating good biological response of the conduit. Fibrin matrix cable formation was seen inside the MNGC after 1 week implantation. One month after implantation, 9 of 10 rats showed successful nerve regeneration. None of the implanted tubes showed tube breakage. The MNGCs were flexible, permeable, and showed no swelling apart from its other advantages. Thus, these new poly(L-lactide-co-glycolide) microbraided conduits can be effective aids for nerve regeneration and repair and may lead to clinical applications.

Animals↗

PubMed2004

Electrospun P(LLA-CL) nanofiber: a biomimetic extracellular matrix for smooth muscle cell and endothelial cell proliferation.

Poly(L-lactide-co-epsilon-caprolactone) [P(LLA-CL)] with L-lactide to epsilon-caprolactone ratio of 75 to 25 has been electrospun into nanofibers. The relationship between electrospinning parameters and fiber diameter has been investigated. The fiber diameter decreased with decreasing polymer concentration and with increasing electrospinning voltage. The X-ray diffractometer and differential scanning colorimeter results suggested that the electrospun nanofibers developed highly oriented structure in CL-unit sequences during the electrospinning process. The biocompatibility of the nanofiber scaffold has been investigated by culturing cells on the nanofiber scaffold. Both smooth muscle cell and endothelial cell adhered and proliferated well on the P(LLA-CL) nanofiber scaffolds.

Biocompatible Materials↗