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| Application of collagen-chitosan/fibrin glue asymmetric scaffolds in skin tissue engineering.
July 2, 2010 at 6:14 AM
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| | Application of collagen-chitosan/fibrin glue asymmetric scaffolds in skin tissue engineering. J Zhejiang Univ Sci B. 2010 Jul;11(7):524-30 Authors: Han CM, Zhang LP, Sun JZ, Shi HF, Zhou J, Gao CY To create a scaffold that is suitable for the construction of tissue-engineered skin, a novel asymmetric porous scaffold with different pore sizes on either side was prepared by combining a collagen-chitosan porous membrane with fibrin glue. Tissue-engineered skin was fabricated using this asymmetric scaffold, fibroblasts, and a human keratinocyte line (HaCaT). Epidermal cells could be seen growing easily and achieved confluence on the fibrin glue on the upper surface of the scaffold. Scanning electron microscopy showed typical shuttle-like fibroblasts adhering to the wall of the scaffold and fluorescence microscopy showed them growing in the dermal layer of the scaffold. The constructed composite skin substitute had a histological structure similar to that of normal skin tissue after three weeks of culture. The results of our study suggest that the asymmetric scaffold is a promising biologically functional material for skin tissue engineering, with prospects for clinical applications. PMID: 20593518 [PubMed - in process] | | |
| All-trans retinoic acid promotes smooth muscle cell differentiation of rabbit bone marrow-derived mesenchymal stem cells.
July 2, 2010 at 6:14 AM
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| | All-trans retinoic acid promotes smooth muscle cell differentiation of rabbit bone marrow-derived mesenchymal stem cells. J Zhejiang Univ Sci B. 2010 Jul;11(7):489-96 Authors: Su ZY, Li Y, Zhao XL, Zhang M Bone marrow-derived mesenchymal stem cells are multipotent stem cells, an attractive resource for regenerative medicine. Accumulating evidence suggests that all-trans retinoic acid plays a key role in the development and differentiation of smooth muscle cells. In the present study, we demonstrate, for the first time, that rabbit bone marrow-derived mesenchymal stem cells differentiate into smooth muscle cells upon the treatment with all-trans retinoic acid. All-trans retinoic acid increased the expression of myocardin, caldesmon, 22-kDa smooth muscle cell-specific protein (SM22alpha), and SM-myosin heavy chains in rabbit bone marrow-derived mesenchymal stem cells, as detected by reverse transcription polymerase chain reaction (PCR). Immunostaining of SM22alpha and SM-myosin heavy chains using monoclonal antibodies also indicated smooth muscle cell differentiation of rabbit bone marrow-derived mesenchymal stem cells following the treatment with all-trans retinoic acid. In addition, more than 47% of bone marrow-derived mesenchymal stem cells demonstrated the contractile phenotype of smooth muscle cells. Western blot results showed that SM-1 and SM-2 were highly expressed in the differentiated cells. These results suggest that all-trans retinoic acid may serve as a potent agent for functional smooth muscle cell differentiation in tissue engineering. PMID: 20593513 [PubMed - in process] | | |
| Microstructure and cytocompatibility of electrospun nanocomposites based on poly(epsilon-caprolactone) and carbon nanostructures.
July 2, 2010 at 6:14 AM
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| | Microstructure and cytocompatibility of electrospun nanocomposites based on poly(epsilon-caprolactone) and carbon nanostructures. Int J Artif Organs. 2010 Jul 1;33(5):271-282 Authors: Bianco A, Del Gaudio C, Baiguera S, Armentano I, Bertarelli C, Dottori M, Bultrini G, Lucotti A, Kenny JM, Folin M Carbon nanostructures (CNSs) are attractive and promising nanomaterials for the next generation of tissue engineering scaffolds, especially in neural prosthesis. Optimizing scaffold vascularization may be an important strategy to promote the repair of damaged brain tissue. In this context, the idea was to evaluate the cell response of electrospun nanohybrid scaffolds loaded with CNSs. Fibrous composites based on poly(epsilon-caprolactone) (PCL) and CNSs were fabricated by means of electrospinning technique. High-purity carbon nanofibers (CNFs) and single-wall carbon nanotubes (SWNTs) were studied. A detailed microstructural characterization was performed to evaluate the most favorable experimental conditions for the realization of fibrous PCL/CNS fabrics. Electrospun mats comprised of rather uniform and homogeneous submicrometric fibers were obtained starting from 1:1 v/v mixture of tetrahydrofuran (THF) and N,N dimethylformamide (DMF). In vitro cytocompatibility tests were performed using rat cerebro-microvascular endothelial cells (CECs). Acquired results showed an increased cell viability for PCL/CNS nanocomposites, suggesting these materials as a suitable environment for endothelial cells. These results are indicative of the promising potential of CNS-based nanocomposites in biomedical devices for tissue engineering applications where endothelial functional properties are required. PMID: 20593348 [PubMed - as supplied by publisher] | | |
| Advancing stem cell research with microtechnologies: opportunities and challenges.
July 2, 2010 at 6:14 AM
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| | Advancing stem cell research with microtechnologies: opportunities and challenges. Integr Biol (Camb). 2010 Jul 1; Authors: Toh YC, Blagović K, Voldman J Stem cells provide unique opportunities for understanding basic biology, for developing tissue models for drug testing, and for clinical applications in regenerative medicine. Despite the promise, the field faces significant challenges in identifying stem cell populations, controlling their fate, and characterizing their phenotype. These challenges arise because stem cells are ultimately functionally defined, and thus can often be identified only retrospectively. New technologies are needed that can provide surrogate markers of stem cell identity, can maintain stem cell state in vitro, and can better direct differentiation. In this review, we discuss the opportunities that microtechnologies, in particular, can provide to the unique qualities of stem cell biology. Microtechnology, by allowing organization and manipulation of cells and molecules at biologically relevant length scales, enables control of the cellular environment and assessment of cell functions and phenotypes with cellular resolution. This provides opportunities to, for instance, create more realistic stem cell niches, perform multi-parameter profiling of single cells, and direct the extracellular signals that control cell fate. All these features take place in an environment whose small size naturally conserves reagent and allows for multiplexing of experiments. By appropriately applying micro-scale engineering principles to stem cell research, we believe that significant breakthroughs can be made in stem cell research. PMID: 20593104 [PubMed - as supplied by publisher] | | |
| Variations of x chromosome inactivation occur in early passages of female human embryonic stem cells.
July 2, 2010 at 6:14 AM
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| | Variations of x chromosome inactivation occur in early passages of female human embryonic stem cells. PLoS One. 2010;5(6):e11330 Authors: Dvash T, Lavon N, Fan G X chromosome inactivation (XCI) is a dosage compensation mechanism essential for embryonic development and cell physiology. Human embryonic stem cells (hESCs) derived from inner cell mass (ICM) of blastocyst stage embryos have been used as a model system to understand XCI initiation and maintenance. Previous studies of undifferentiated female hESCs at intermediate passages have shown three possible states of XCI; 1) cells in a pre-XCI state, 2) cells that already exhibit XCI, or 3) cells that never undergo XCI even upon differentiation. In this study, XCI status was assayed in ten female hESC lines between passage 5 and 15 to determine whether XCI variations occur in early passages of hESCs. Our results show that three different states of XCI already exist in the early passages of hESC. In addition, we observe one cell line with skewed XCI and preferential expression of X-linked genes from the paternal allele, while another cell line exhibits random XCI. Skewed XCI in undifferentiated hESCs may be due to clonal selection in culture instead of non-random XCI in ICM cells. We also found that XIST promoter methylation is correlated with silencing of XIST transcripts in early passages of hESCs, even in the pre-XCI state. In conclusion, XCI variations already take place in early passages of hESCs, which may be a consequence of in vitro culture selection during the derivation process. Nevertheless, we cannot rule out the possibility that XCI variations in hESCs may reflect heterogeneous XCI states in ICM cells that stochastically give rise to hESCs. PMID: 20593031 [PubMed - in process] | | |
| Isolating adipose-derived mesenchymal stem cells from lipoaspirate blood and saline fraction.
July 2, 2010 at 6:14 AM
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| | Isolating adipose-derived mesenchymal stem cells from lipoaspirate blood and saline fraction. Organogenesis. 2010 Jan;6(1):11-4 Authors: Francis MP, Sachs PC, Elmore LW, E Holt S Isolation of adipose-derived stem cells (ASCs) typically involves 8+ hours of intense effort, requiring specialized equipment and reagents. Here, we present an improved technique for isolating viable populations of mesenchymal stem cells from lipoaspirate saline fractions within 30 minutes. Importantly, the cells exhibit remarkable similarities to those obtained using the traditional isolation protocols, in terms of their multipotent differentiation potential and immunophenotype. Reducing the acquisition time of ASCs is critical for advancing regenerative medicine therapeutics, and our approach provides rapid and simple techniques for enhanced isolation and expansion of patient-derived mesenchymal stem cells. PMID: 20592860 [PubMed - in process] | | |
| Fabrication of highly porous tissue-engineering scaffolds using selective spherical porogens.
July 2, 2010 at 6:14 AM
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| | Fabrication of highly porous tissue-engineering scaffolds using selective spherical porogens. Biomed Mater Eng. 2010 Jan;20(2):107-18 Authors: Johnson T, Bahrampourian R, Patel A, Mequanint K Tissue engineering holds great promise as an alternative strategy to current treatment modalities of diseased or otherwise failed tissues. Most strategies of tissue engineering rely on three-dimensional porous scaffolds to mimic the natural extracellular matrix (ECM) as templates onto which cells attach, multiply, migrate and function. When cells are harvested from a donor and seeded, scaffolds facilitate the organization of these cells into a three-dimensional architecture, control cell behavior and subsequently direct the formation of organ-specific tissue. In view of its role, scaffold fabrication methods target the creation of highly porous and interconnected pore structures. Among the different scaffolds fabrication methods explored, solvent casting followed by precipitation or particulate leaching is one of the most straightforward methods. In this paper, we conducted a comparative study of two methods to prepare spherical porogens using poly(vinyl pyrrolidone) (PVP) and poly(vinyl alcohol) (PVA) as dispersing agents and we used these porogens to fabricate cylindrical porous scaffolds using a combination of pressure differential and solvent casting/particulate leaching method. Porogen particle size analyses showed that at 0.6% dispersing agent concentration, PVP produced smaller particles with narrower distribution (100-300 mum) than poly(vinyl alcohol) (100-500 mum) presumably due to the fast adsorption kinetics of the former. Scaffolds fabricated from PVP-stabilized porogens had higher open porosities and high pore interconnectivity than those based on porogens prepared using PVA stabilizer. Preliminary cell culture work also showed that scaffolds fabricated using PVP-stabilized porogens support attachment and spreading of human coronary artery smooth muscle cells (HCASMC) better than the PVA counterparts. This is the first time that such direct comparative studies on the porogen preparation methods and its effect on the scaffold porosity and cell attachment property is reported. PMID: 20592448 [PubMed - in process] | | |
| Preparation of arrays of cell spheroids and spheroid-monolayer cocultures within a microfluidic device.
July 2, 2010 at 6:14 AM
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| | Preparation of arrays of cell spheroids and spheroid-monolayer cocultures within a microfluidic device. J Biosci Bioeng. 2010 Jun 28; Authors: Okuyama T, Yamazoe H, Mochizuki N, Khademhosseini A, Suzuki H, Fukuda J This study describes a novel method for generation of an array of three-dimensional (3D) multicellular spheroids within a microchannel in patterned cultures containing one or multiple cell types. This method uses a unique property of a cross-linked albumin coated surface in which the surface can be switched from non-adhesive to cell adhesive upon electrostatic adsorption of a polycation. Introduction of a solution containing albumin and a cross-linking agent into a microchannel with an array of microwells caused the entire surface, with the exception of the interior of the microwells, to become coated with the cross-linked albumin layer. Cells that were seeded within the microchannel did not adhere to the surface of the microchannel and became entrapped in the microwells. HepG2 cells seeded in the microwells formed 3D spheroids with controlled sizes and shapes depending upon the dimensions of the microwells. When the albumin coated surface was subsequently exposed to an aqueous solution containing poly(ethyleneimine) (PEI), adhesion of secondary cells, fibroblasts, occurred in the regions surrounding the arrayed spheroids. This coculture system can be coupled with spatially controlled fluids such as gradients and focused flow generators for various biological and tissue engineering applications. PMID: 20591731 [PubMed - as supplied by publisher] | | |
| The long-term survival of in vitro engineered nervous tissue derived from the specific neural differentiation of mouse embryonic stem cells.
July 2, 2010 at 6:14 AM
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| | The long-term survival of in vitro engineered nervous tissue derived from the specific neural differentiation of mouse embryonic stem cells. Biomaterials. 2010 Jun 28; Authors: Dubois-Dauphin ML, Toni N, Julien SD, Charvet I, Sundstrom LE, Stoppini L Embryonic stem cells (ESCs) offer attractive prospective as potential source of neurons for cell replacement therapy in human neurodegenerative diseases. Besides, ESCs neural differentiation enables in vitro tissue engineering for fundamental research and drug discovery aimed at the nervous system. We have established stable and long-term three-dimensional (3D) culture conditions which can be used to model long latency and complex neurodegenerative diseases. Mouse ESCs-derived neural progenitor cells generated by MS5 stromal cells induction, result in strictly neural 3D cultures of about 120-mum thick, whose cells expressed mature neuronal, astrocytes and myelin markers. Neurons were from the glutamatergic and gabaergic lineages. This nervous tissue was spatially organized in specific layers resembling brain sub-ependymal (SE) nervous tissue, and was maintained in vitro for at least 3.5 months with great stability. Electron microscopy showed the presence of mature synapses and myelinated axons, suggesting functional maturation. Electrophysiological activity revealed biological signals involving action potential propagation along neuronal fibres and synaptic-like release of neurotransmitters. The rapid development and stabilization of this 3D cultures model result in an abundant and long-lasting production that is compatible with multiple and productive investigations for neurodegenerative diseases modeling, drug and toxicology screening, stress and aging research. PMID: 20591476 [PubMed - as supplied by publisher] | | |
| Branched vascular network architecture: A new approach to lung assist device technology.
July 2, 2010 at 6:14 AM
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| | Branched vascular network architecture: A new approach to lung assist device technology. J Thorac Cardiovasc Surg. 2010 Jun 28; Authors: Hoganson DM, Anderson JL, Weinberg EF, Swart EJ, Orrick BK, Borenstein JT, Vacanti JP OBJECTIVE: A lung assist device would serve an important clinical need as a bridge to transplant or destination therapy for patients with end-stage lung disease. A new lung assist device has been developed that incorporates a branched network of vascular channels adjacent to a gas chamber, separated by a thin, gas-permeable membrane. This study investigated 2 potential gas exchange membranes within this new architecture. METHODS: Oxygen and carbon dioxide exchange within the device was tested in vitro using 3 gas-permeable membranes. Two of the membranes, silicone only and silicone-coated microporous polymer, were plasma impermeable. The third, a microporous polymer, was used as a control. Gas exchange testing was done using anticoagulated porcine blood over a range of flow rates. RESULTS: Oxygen and carbon dioxide transfer was demonstrated in the device and increased nearly linearly from 0.6 to 8.0 mL/min blood flow for all of the membranes. There was no significant difference in the gas transfer between the silicone and the silicone-coated microporous polymer membranes. The transfer of oxygen and carbon dioxide in the device was similar to existing hollow fiber oxygenators controlling for surface area. CONCLUSION: The silicone and silicone-coated microporous polymer membranes both show promise as gas-permeable membranes in a new lung assist device design. Further optimization of the device by improving the membranes and reducing the channel diameter in the vascular network will improve gas transfer. The current device may be scaled up to function as an adult lung assist device. PMID: 20591445 [PubMed - as supplied by publisher] | | |
| In vitro organogenesis using multipotent cells.
July 2, 2010 at 6:14 AM
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| | In vitro organogenesis using multipotent cells. Hum Cell. 2010 Feb 1;23(1):1-14 Authors: Kurisaki A, Ito Y, Onuma Y, Intoh A, Asashima M Abstract The establishment of efficient methods for promoting stem cell differentiation into target cells is important not only in regenerative medicine, but also in drug discovery. In addition to embryonic stem (ES) cells and various somatic stem cells, such as mesenchymal stem cells derived from bone marrow, adipose tissue, and umbilical cord blood, a novel dedifferentiation technology that allows the generation of induced pluripotent stem (iPS) cells has been recently developed. Although an increasing number of stem cell populations are being described, there remains a lack of protocols for driving the differentiation of these cells. Regeneration of organs from stem cells in vitro requires precise blueprints for each differentiation step. To date, studies using various model organisms, such as zebrafish, Xenopus laevis, and gene-targeted mice, have uncovered several factors that are critical for the development of organs. We have been using X. laevis, the African clawed frog, which has developmental patterns similar to those seen in humans. Moreover, Xenopus embryos are excellent research tools for the development of differentiation protocols, since they are available in high numbers and are sufficiently large and robust for culturing after simple microsurgery. In addition, Xenopus eggs are fertilized externally, and all stages of the embryo are easily accessible, making it relatively easy to study the functions of individual gene products during organogenesis using microinjection into embryonic cells. In the present review, we provide examples of methods for in vitro organ formation that use undifferentiated Xenopus cells. We also describe the application of amphibian differentiation protocols to mammalian stem cells, so as to facilitate the development of efficient methodologies for in vitro differentiation. PMID: 20590914 [PubMed - in process] | | |
| Opposite Spectrum of Activity of Canonical Wnt Signaling in the Osteogenic Context of Undifferentiated and Differentiated Mesenchymal Cells: Implications for Tissue Engineering.
July 2, 2010 at 6:14 AM
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| | Opposite Spectrum of Activity of Canonical Wnt Signaling in the Osteogenic Context of Undifferentiated and Differentiated Mesenchymal Cells: Implications for Tissue Engineering. Tissue Eng Part A. 2010 Jun 30; Authors: Quarto N, Behr B, Longaker MT To delineate the competence window in which canonical wingless (Wnt)-signaling can either inhibit or promote osteogenic differentiation, we have analyzed cells with different status, specifically undifferentiated mesenchymal cells, such as adipose-derived stem cells and embryonic calvarial mesenchymal cells, and differentiated mesenchymal cells such as juvenile immature calvarial osteoblasts and adult calvarial osteoblasts. Our analysis indicated that undifferentiated mesenchymal cells and juvenile calvarial osteoblasts are endowed with higher levels of endogenous canonical Wnt signaling compared to fully differentiated adult calvarial osteoblasts, and that different levels of activation inversely correlated with expression levels of several Wnt antagonists. We have observed that activation of canonical Wnt signaling may elicit opposite biological activity in the context of osteogenic differentiation depending on the status of cell, the threshold levels of its activation, and Wnt ligands concentration. The results presented in this study indicate that treatment with Wnt3 and/or expression of constitutively activated beta-catenin inhibits osteogenic differentiation of undifferentiated mesenchymal cells, whereas expression of dominant negative transcription factor 4 (Tcf4) and/or secreted frizzled related protein 1 treatment enhances their osteogenic differentiation. Wnt3a treatment also inhibits osteogenesis in juvenile calvarial osteoblasts in a dose-dependent fashion. Conversely, Wnt3a treatment strongly induces osteogenesis in mature calvarial osteoblasts in a dose-dependent manner. Importantly, in vitro data correlated with in vivo results showing that Wnt3a treatment of calvarial defects, created in juvenile mice, promotes calvarial healing and bone regeneration only at low doses, whereas high doses of Wnt3a impairs tissue regeneration. In contrast, high doses of Wnt3a enhance bony tissue regeneration and calvarial healing in adult mice. Therefore, the knowledge of both endogenous activity of canonical Wnt signaling and appropriate concentrations of Wnt3a treatment may lead to significant improvement for bony tissue engineering, as well as for the efficient implement of adipose-derived stem cells in bone regeneration. Indeed, this study has important potential implications for tissue engineering, specifically for repair of juvenile bone defects. PMID: 20590472 [PubMed - as supplied by publisher] | | |
| Bi-Modular Flow Characterization in Tissue Engineering Scaffolds Using Computational Fluid Dynamics and Particle Imaging Velocimetry.
July 2, 2010 at 6:14 AM
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| | Bi-Modular Flow Characterization in Tissue Engineering Scaffolds Using Computational Fluid Dynamics and Particle Imaging Velocimetry. Tissue Eng Part C Methods. 2010 Jun 30; Authors: De Boodt S, Truscello S, Ozcan SE, Leroy T, Van Oosterwyck H, Berckmans D, Schrooten J As part of a tissue engineering (TE) therapy, cell-seeded scaffolds can be cultured in perfusion bioreactors in which the flow-mediated wall shear stress and the nutrient transport are factors that influence in vitro proliferation and osteogenic differentiation of the seeded progenitor cells. In this study both computational fluid dynamics simulations on idealized boundary conditions and circumstances and microparticle image velocimetry measurements on realistic conditions were carried out to quantify the fluid dynamic microenvironment inside a bone TE construct. The results showed that differences between actual and designed geometry and time-dependent character of the fluid flow caused a 19% difference in average fluid velocity and a 27% difference in wall shear stress between simulations and measurements. The computational fluid dynamics simulation enabled higher resolution and three-dimensional fluid flow quantification that could be quantitatively compared with a microparticle image velocimetry measurement. The coupling of numerical and experimental analysis provides a reliable and high-resolution bi-modular tool for quantifying the fluid dynamics that represent the basis to determine the relation between the hydrodynamic environment and cell growth and differentiation within TE scaffolds. PMID: 20590471 [PubMed - as supplied by publisher] | | |
| Chitosan in Nanostructured Thin Films.
July 2, 2010 at 6:14 AM
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| | Chitosan in Nanostructured Thin Films. Biomacromolecules. 2010 Jun 30; Authors: Pavinatto FJ, Caseli L, Oliveira ON This review paper brings an overview of the use of chitosans in nanostructured films produced with the Langmuir-Blodgett (LB) or the electrostatic layer-by-layer (LbL) techniques, with emphasis on their possible applications. From a survey in the literature one may identify three main types of study with chitosan in nanostructured films. First, the interaction between chitosans and phospholipid Langmuir monolayers has been investigated for probing the mechanisms of chitosan action in their biological applications, with the monolayers serving as cell membrane models. In the second type, chitosan serves as a matrix for immobilization of biomolecules in LB as well as in LbL films, for which chitosan is suitable to help preserve the bioactivity of such biomolecules for long periods of time even in dry, solid films. An important application of these chitosan-containing films is in sensing and biosensing. The third type of study involves exploiting the mechanical and biocompatibility properties of chitosan in producing films with enhanced properties, for example, for tissue engineering. It is emphasized that chitosans have been proven excellent building blocks to produce films with controlled molecular architecture, allowing for synergy between distinct materials. We also discuss the prospects of the field, following a critical review of the latest developments in nanostructured chitosan films. PMID: 20590156 [PubMed - as supplied by publisher] | | |
| Sustained release of water-insoluble simvastatin from biodegradable hydrogel augments bone regeneration.
July 2, 2010 at 6:14 AM
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| | Sustained release of water-insoluble simvastatin from biodegradable hydrogel augments bone regeneration. J Control Release. 2010 Apr 19;143(2):201-6 Authors: Tanigo T, Takaoka R, Tabata Y Drug delivery technology is a practically promising way to enhance the therapeutic efficacy of drugs. However, there remain some properties of material to be improved for drug delivery, such as the biodegradability and biocompatibility. In this study, we demonstrate that a biodegradable hydrogel of gelatin can achieve the sustained release of water-insoluble simvastatin. Biologically active simvastatin can be released accompanied with the biodegradation of hydrogel. The biocompatibility issue of material remaining after drug release can be practically resolved. Simvastatin was water-solubilized by gelatin grafted with L-lactic acid oligomer and mixed with gelatin, followed by chemical crosslinking to obtain gelatin hydrogels incorporating simvastatin water-solubilized. The hydrogel augments the simvastatin-induced bone regeneration given biocompatible gelatin fragments and has its potential to deliver a wide range of water-insoluble drugs. PMID: 20060429 [PubMed - indexed for MEDLINE] | | |
| Enhanced external counterpulsation is a regenerative therapy.
July 2, 2010 at 6:14 AM
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| | Enhanced external counterpulsation is a regenerative therapy. Front Biosci (Elite Ed). 2010;2:111-21 Authors: Jewell CW, Houck PD, Watson LE, Dostal DE, Dehmer GJ Enhanced external counterpulsation (EECP) is used for the treatment of severe angina and heart failure in patients who are not candidates for revascularization. The clinical benefits of EECP extend well beyond the time period of any hemodynamic effects, but the cause of this prolonged effect is not understood. The prolonged clinical benefits suggest EECP could be a regenerative therapy. This study was performed to determine whether EECP increased circulating hematopoietic progenitor cells (HPCs) or endothelial progenitor cells (EPCs) and thus be a possible regenerative therapy. The proposed mechanism of the increase in regenerative circulating stem cells is the enhanced shear forces induced on the endothelial boundary by the flow reversal produced by the sequential inflation of the pneumatic cuffs during EECP therapy. PMID: 20036860 [PubMed - indexed for MEDLINE] | | |
| Hydrophobic-electrostatic balance driving the LCST offset aggregation-redissolution behavior of N-alkylacrylamide-based ionic terpolymers.
July 2, 2010 at 6:14 AM
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| | Hydrophobic-electrostatic balance driving the LCST offset aggregation-redissolution behavior of N-alkylacrylamide-based ionic terpolymers. Langmuir. 2010 Apr 20;26(8):5934-41 Authors: López-Pérez PM, da Silva RM, Pashkuleva I, Parra F, Reis RL, San Roman J A series of random terpolymers composed of N-isopropylacrylamide (NIPAAm), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), and N-tert-butylacrylamide (NTBAAm) monomers were synthesized by free radical polymerization. The molar fraction of the negatively charged monomer (AMPS) was maintained constant (0.05) for all studied terpolymer compositions. Turbidity measurements were used to evaluate the influence of the relative amount of NIPAAm and NTBAAm, polymer concentration, and solution ionic strength on the cloud point and redissolution temperatures (macroscopic phase separation). Dynamic light scattering (DLS) was employed to elucidate some aspects regarding the molecular scale mechanism of the temperature-induced phase separation and to determine the low critical solution temperature (LCST). The aqueous solutions of terpolymers remained clear at all studied temperatures; turbidity was only observed in the presence of NaCl. The cloud point temperature (CPT) determined by turbidimetry was found to be systematically much higher than the LCST determined by DLS; nanosized aggregates were observed at temperatures between the LCST and the CPT. Both CPT and LCST decreased when increasing the molar ratio of NTBAAm (increased hydrophobicity). It was found that above a critical molar fraction of NTBAAm (0.25-0.30) the aggregation rate suddenly decreased. Polymers with NTBAAm content lower than 0.25 showed a fast macroscopic phase separation, but the formed large aggregates are disaggregating during the cooling ramp at temperatures still higher than the LCST. On the contrary, polymers with NTBAAm contents above 0.30 showed a slow macroscopic phase separation, and the formed large aggregates only redissolved when LCST was reached. These differences were explained on the basis of a delicate balance between the electrostatic repulsion and the hydrophobic attractive forces, which contribute cooperatively to the formation of metastable nanosized aggregates. PMID: 19994868 [PubMed - indexed for MEDLINE] | | | | 
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