S.N. was supported by a Postdoctoral Fellowship Grant from the Pittsburgh Tissue Engineering Initiative. D.O.Z. is supported by a grant awarded from The Geneva Foundation.

<ol>
	<li>Natesan, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+bilayer+construct+controls+adipose-derived+stem+cell+differentiation+into+endothelial+cells+and+pericytes+without+growth+factor+stimulation.">A bilayer construct controls adipose-derived stem cell differentiation into endothelial cells and pericytes without growth factor stimulation.</a> Tissue Eng. Part A. 17, 941-953 (2011).</li><li>Nuttelman, C. R., Tripodi, M. C., Anseth, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthetic+hydrogel+niches+that+promote+hMSC+viability.">Synthetic hydrogel niches that promote hMSC viability.</a> Matrix Biol. 24, 208-218 (2005).</li><li>Benoit, D. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Integrin-linked+kinase+production+prevents+anoikis+in+human+mesenchymal+stem+cells.">Integrin-linked kinase production prevents anoikis in human mesenchymal stem cells.</a> J Biomed Mater Res A. 81, 259-268 (2007).</li><li>Willerth, S. M., Sakiyama-Elbert, S. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Combining+stem+cells+and+biomaterial+scaffolds+for+constructing+tissues+and+cell+delivery.">Combining stem cells and biomaterial scaffolds for constructing tissues and cell delivery.</a> , (2008).</li><li>Natesan, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adipose-derived+stem+cell+delivery+into+collagen+gels+using+chitosan+microspheres.">Adipose-derived stem cell delivery into collagen gels using chitosan microspheres.</a> Tissue Eng. Part A. 16, 1369-1384 (2010).</li><li>Bubnis, W. A., Ofner, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+determination+of+epsilon-amino+groups+in+soluble+and+poorly+soluble+proteinaceous+materials+by+a+spectrophotometric+method+using+trinitrobenzenesulfonic+acid.">The determination of epsilon-amino groups in soluble and poorly soluble proteinaceous materials by a spectrophotometric method using trinitrobenzenesulfonic acid.</a> Anal. Biochem. 207, 129-133 (1992).</li><li>Zhang, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+PEGylated+fibrin+patch+for+mesenchymal+stem+cell+delivery.">A PEGylated fibrin patch for mesenchymal stem cell delivery.</a> Tissue Eng. 12, 9-19 (2006).</li><li>Bornstein, M. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reconstituted+rattail+collagen+used+as+substrate+for+tissue+cultures+on+coverslips+in+Maximow+slides+and+roller+tubes.">Reconstituted rattail collagen used as substrate for tissue cultures on coverslips in Maximow slides and roller tubes.</a> Lab Invest. 7, 134-137 (1958).</li><li>Zhang, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vascular+differentiation+of+bone+marrow+stem+cells+is+directed+by+a+tunable+three-dimensional+matrix.">Vascular differentiation of bone marrow stem cells is directed by a tunable three-dimensional matrix.</a> Acta Biomater. 6, 3395-3403 (2010).</li><li>Rochon, M. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Normal+human+epithelial+cells+regulate+the+size+and+morphology+of+tissue-engineered+capillaries.">Normal human epithelial cells regulate the size and morphology of tissue-engineered capillaries.</a> Tissue Eng. Part A. 16, 1457-1468 (2010).</li><li>Liu, H., Collins, S. F., Suggs, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-dimensional+culture+for+expansion+and+differentiation+of+mouse+embryonic+stem+cells.">Three-dimensional culture for expansion and differentiation of mouse embryonic stem cells.</a> Biomaterials. 27, 6004-6014 (2006).</li></ol>

No competing financial interests exist. 
Disclaimers 
The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or reflecting the views of the Department of Defense or the U.S. Government. The authors are employees of the U.S. Government, and this work was prepared as part of their official duties. All work was supported by the U.S. Army Medical Research and Materiel Command. This study was conducted under a protocol reviewed and approved by the U.S. Army Medical Research and Materiel Command Institutional Review Board and in accordance with the approved protocol.

ASCs are well-known for their ease of isolation and ability to differentiate toward various cell types. With the techniques described in this manuscript, we are able to exploit the plasticity of ASCs by exposing these cells to multiple biomatrices simultaneously. As cells migrate away from their CSM base and enter their surrounding extracellular environment, the cells take cue from the scaffold and can either maintain "stemness" (collagen) or be induced to differentiate toward vascular- and vascular-supportive cell types...

<table border="1">
 <tbody>
 <tr>
 <td>Name of the reagent/equipment</td>
 <td>Company</td>
 <td>Catalogue number</td>
 <td>Comments</td>
 </tr>
 <tr>
 <td>Hanks Balanced Salt Solution (HBSS)</td>
 <td>Gibco</td>
 <td>14175</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>Fetal Bovine Serum</td>
 <td>Hyclone</td>
 <td>SH30071.03</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>Collagenase Type II</td>
 <td>Sigma-Aldrich</td>
 <td>C6685</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>70-&mu;m Nylon Mesh Filter</td>
 <td>BD Biosciences</td>
 <td>352350</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>100-&mu;m Nylon Mesh Filter</td>
 <td>BD Biosciences</td>
 <td>352360</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>MesenPRO Growth Medium System</td>
 <td>Invitrogen</td>
 <td>12746-012</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>L-Glutamine</td>
 <td>Gibco</td>
 <td>25030</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>CaCl2.2H2O</td>
 <td>Sigma</td>
 <td>C8106</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>T75 Tissue Culture Flask</td>
 <td>BD Biosciences</td>
 <td>137787</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>Chitosan</td>
 <td>Sigma-Aldrich</td>
 <td>448869</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>Acetic Acid</td>
 <td>Sigma-Aldrich</td>
 <td>320099</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>N-Octanol</td>
 <td>Acros Organics</td>
 <td>150630025 </td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>Sorbitan-Mono-Oleate</td>
 <td>Sigma-Aldrich</td>
 <td>S6760</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>Potassium Hydroxide</td>
 <td>Sigma-Aldrich</td>
 <td>P1767</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>Acetone</td>
 <td>Fisher Scientific</td>
 <td>L-4859</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>Ethanol</td>
 <td>Sigma-Aldrich</td>
 <td>270741</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>Trinitro Benzenesulfonic Acid</td>
 <td>Sigma-Aldrich</td>
 <td>P2297</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>Hydrochloric Acid</td>
 <td>Sigma-Aldrich</td>
 <td>320331</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>Ethyl Ether</td>
 <td>Sigma-Aldrich</td>
 <td>472-484</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>8-&mu;m Tissue Culture Plate Inserts</td>
 <td>BD Biosciences</td>
 <td>353097</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>1.5-ml Microcentrifuge Tubes</td>
 <td>Fisher</td>
 <td>05-408-129</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>MTT Reagent</td>
 <td>Invitrogen</td>
 <td>M6494</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>Dimethyl Sulfoxide</td>
 <td>Sigma-Aldrich</td>
 <td>D8779</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>Qtracker Cell Labeling Kit(Q Tracker 655)</td>
 <td>Molecular probes</td>
 <td>Q2502PMP</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>Type 1 Collagen</td>
 <td>Travigen</td>
 <td>3447-020-01</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>Sodium Hydroxide</td>
 <td>Sigma-Aldrich</td>
 <td>S8045</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>12-Well Tissue Culture Plates</td>
 <td>BD Biosciences</td>
 <td>353043</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>Fibrinogen</td>
 <td>Sigma</td>
 <td>F3879</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>Thrombin</td>
 <td>Sigma</td>
 <td>T6884</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>Benztriazole Derivative of Polyethylene</td>
 <td>Sunbio</td>
 <td>DE-034GS</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>Tris Buffer Tablet (pH 7.6)</td>
 <td>Sigma</td>
 <td>T5030</td>
 <td>Consumable</td>
 </tr>
 <tr>
 <td>Centrifuge</td>
 <td>Eppendorf</td>
 <td>5417R</td>
 <td>Equipment</td>
 </tr>
 <tr>
 <td>Orbital Shaker</td>
 <td>New Brunswick Scienctific</td>
 <td>C24</td>
 <td>Equipment</td>
 </tr>
 <tr>
 <td>Humidified Incubator with Air-5% CO2</td>
 <td>Thermo Scientific</td>
 <td>Model 370</td>
 <td>Equipment</td>
 </tr>
 <tr>
 <td>Overhead Stirrer</td>
 <td>IKA</td>
 <td>Visc6000</td>
 <td>Equipment</td>
 </tr>
 <tr>
 <td>Magnetic Stirrer</td>
 <td>Corning</td>
 <td>PC-210 </td>
 <td>Equipment</td>
 </tr>
 <tr>
 <td>Vacuum Desiccator</td>
 <td>-</td>
 <td>-</td>
 <td>Equipment</td>
 </tr>
 <tr>
 <td>Particle Size Analyzer</td>
 <td>Malvern</td>
 <td>STP2000 Spraytec</td>
 <td>Equipment</td>
 </tr>
 <tr>
 <td>Water Bath</td>
 <td>Fisher Scientific</td>
 <td>Isotemp210</td>
 <td>Equipment</td>
 </tr>
 <tr>
 <td>Spectrophotometer</td>
 <td>Beckman</td>
 <td>Beckman Coulter DU 800UV/Visible Spectrophotometer</td>
 <td>Equipment</td>
 </tr>
 <tr>
 <td>Vortex</td>
 <td>Diagger</td>
 <td>3030a</td>
 <td>Equipment</td>
 </tr>
 <tr>
 <td>Microplate Reader</td>
 <td>Molecular Devices</td>
 <td>SpectraMax M2</td>
 <td>Equipment</td>
 </tr>
 <tr>
 <td>Light/Fluorescence Microscope</td>
 <td>Olympus</td>
 <td>IX71</td>
 <td>Equipment</td>
 </tr>
 <tr>
 <td>Confocal Microscope</td>
 <td>Olympus</td>
 <td>FV-500 Laser Scanning Confocal Microscope</td>
 <td>Equipment</td>
 </tr>
 <tr>
 <td>Scanning Electron Microscope</td>
 <td>Carl Zeiss MicroImaging</td>
 <td>Leo 435 VP</td>
 <td>Equipment</td>
 </tr>
 <tr>
 <td>Transmission Electron Microscope</td>
 <td>JEOL</td>
 <td>JEOL 1230</td>
 <td>Equipment</td>
 </tr>
 </tbody>
</table>

engineering a bilayered hydrogel to control asc differentiation

Natural polymers over the years have gained more importance because of their host biocompatibility and ability to interact with cells in vitro and in vivo. An area of research that holds promise in regenerative medicine is the combinatorial use of novel biomaterials and stem cells. A fundamental strategy in the field of tissue engineering is the use of three-dimensional scaffold (e.g., decellularized extracellular matrix, hydrogels, micro/nano particles) for directing cell function. This technology has evolved from the discovery that cells need a substrate upon which they can adhere, proliferate, and express their differentiated cellular phenotype and function 2-3. More recently, it has also been determined that cells not only use these substrates for adherence, but also interact and take cues from the matrix substrate (e.g., extracellular matrix, ECM)4. Therefore, the cells and scaffolds have a reciprocal connection that serves to control tissue development, organization, and ultimate function. Adipose-derived stem cells (ASCs) are mesenchymal, non-hematopoetic stem cells present in adipose tissue that can exhibit multi-lineage differentiation and serve as a readily available source of cells (i.e. pre-vascular endothelia and pericytes). Our hypothesis is that adipose-derived stem cells can be directed toward differing phenotypes simultaneously by simply co-culturing them in bilayered matrices1. Our laboratory is focused on dermal wound healing. To this end, we created a single composite matrix from the natural biomaterials, fibrin, collagen, and chitosan that can mimic the characteristics and functions of a dermal-specific wound healing ECM environment.

Watch this Scientific Journal Video about Engineering a Bilayered Hydrogel to Control ASC Differentiation at JoVE.com

Engineering a Bilayered Hydrogel to Control ASC Differentiation

This protocol focuses on utilizing the inherent ability of stem cells to take cue from their surrounding extracellular matrix and be induced to differentiate into multiple phenotypes. This methods manuscript extends our description and characterization of a model utilizing a bilayered hydrogel, composed of PEG-fibrin and collagen, to simultaneously co-differentiate adipose-derived stem cells1.

Natural polymers over the years have gained more importance because of their host biocompatibility and ability to interact with cells in vitro and in ...

engineering-a-bilayered-hydrogel-to-control-asc-differentiation

Research

JoVE Journal

Bioengineering

13.8K Views.  United States Army Institute of Surgical Research. Questo protocollo si concentra sulla utilizzando la capacità intrinseca delle cellule staminali a prendere spunto dalla loro matrice extracellulare che circonda ed essere indotte a differenziarsi in fenotipi multipli. Questo manoscritto metodi estende la nostra descrizione e caratterizzazione di un modello utilizzando un idrogel doppo strato, costituito da PEG-fibrina e collagene, contemporaneamente alla co-differenziare derivate da tessuto adiposo cellule staminali

Video: Engineering a Bilayered Hydrogel to Control ASC Differentiation

Procedure for Lung Engineering

Lung tissue, including lung cancer and chronic lung diseases such as chronic obstructive pulmonary disease, cumulatively account for some 280,000 deaths annually; chronic obstructive pulmonary disease is currently the fourth leading cause of death in the United States1. Contributing to this mortality is the fact that lungs do not generally repair or regenerate beyond the microscopic, cellular level. Therefore, lung tissue that is damaged by degeneration or infection, or lung tissue that is surgically resected is not functionally replaced in vivo. To explore whether lung tissue can be generated in vitro, we treated lungs from adult rats using a procedure that removes cellular components to produce an acellular lung extracellular matrix scaffold. This scaffold retains the hierarchical branching structures of airways and vasculature, as well as a largely intact basement membrane, which comprises collagen IV, laminin, and fibronectin. The scaffold is mounted in a bioreactor designed to mimic critical aspects of lung physiology, such as negative pressure ventilation and pulsatile vascular perfusion. By culturing pulmonary epithelium and vascular endothelium within the bioreactor-mounted scaffold, we are able to generate lung tissue that is phenotypically comparable to native lung tissue and that is able to participate in gas exchange for short time intervals (45-120 minutes). These results are encouraging, and suggest that repopulation of lung matrix is a viable strategy for lung regeneration. This possibility presents an opportunity not only to work toward increasing the supply of lung tissue for transplantation, but also to study respiratory cell and molecular biology in vitro for longer time periods and in a more accurate microenvironment than has previously been possible.

We have developed a decellularized lung extracellular matrix and novel biomimetic bioreactor that can be used to generate functional lung tissue. By seeding cells into the matrix and culturing in the bioreactor, we generate tissue that demonstrates effective gas exchange when transplanted in vivo for short periods of time.

Lung tissue, including lung cancer and chronic lung diseases such as chronic obstructive pulmonary disease, cumulatively account for some 280,000 deaths ...

Encapsulation of Cardiomyocytes in a Fibrin Hydrogel for Cardiac Tissue Engineering

Culturing cells in a three dimensional hydrogel environment is an important technique for developing constructs for tissue engineering as well as studying cellular responses under various culture conditions in vitro. The three dimensional environment more closely mimics what the cells observe in vivo due to the application of mechanical and chemical stimuli in all dimensions 1. Three-dimensional hydrogels can either be made from synthetic polymers such as PEG-DA 2 and PLGA 3 or a number of naturally occurring proteins such as collagen 4, hyaluronic acid 5 or fibrin 6,7. Hydrogels created from fibrin, a naturally occurring blood clotting protein, can polymerize to form a mesh that is part of the body's natural wound healing processes 8. Fibrin is cell-degradable and potentially autologous 9, making it an ideal temporary scaffold for tissue engineering.
Here we describe in detail the isolation of neonatal cardiomyocytes from three day old rat pups and the preparation of the cells for encapsulation in fibrin hydrogel constructs for tissue engineering. Neonatal myocytes are a common cell source used for in vitro studies in cardiac tissue formation and engineering 4. Fibrin gel is created by mixing fibrinogen with the enzyme thrombin. Thrombin cleaves fibrinopeptides FpA and FpB from fibrinogen, revealing binding sites that interact with other monomers 10. These interactions cause the monomers to self-assemble into fibers that form the hydrogel mesh. Because the timing of this enzymatic reaction can be adjusted by altering the ratio of thrombin to fibrinogen, or the ratio of calcium to thrombin, one can injection mold constructs with a number of different geometries 11,12. Further we can generate alignment of the resulting tissue by how we constrain the gel during culture 13.
After culturing the engineered cardiac tissue constructs for two weeks under static conditions, the cardiac cells have begun to remodel the construct and can generate a contraction force under electrical pacing conditions 6. As part of this protocol, we also describe methods for analyzing the tissue engineered myocardium after the culture period including functional analysis of the active force generated by the cardiac muscle construct upon electrical stimulation, as well as methods for determining final cell viability (Live-Dead assay) and immunohistological staining to examine the expression and morphology of typical proteins important for contraction (Myosin Heavy Chain or MHC) and cellular coupling (Connexin 43 or Cx43) between myocytes.

We describe the isolation of neonatal cardiomyocytes and the preparation of the cells for encapsulation in fibrin hydrogel constructs for tissue engineering. We describe methods for analyzing the tissue engineered myocardium after the culture period including active force generated upon electrical stimulation and cell viability and immunohistological staining.

Culturing cells in a three dimensional hydrogel environment is an important technique for developing constructs for tissue engineering as well as studying ...

Design of a Cyclic Pressure Bioreactor for the Ex Vivo Study of Aortic Heart Valves

The aortic valve, located between the left ventricle and the aorta, allows for unidirectional blood flow, preventing backflow into the ventricle. Aortic valve leaflets are composed of interstitial cells suspended within an extracellular matrix (ECM) and are lined with an endothelial cell monolayer. The valve withstands a harsh, dynamic environment and is constantly exposed to shear, flexion, tension, and compression. Research has shown calcific lesions in diseased valves occur in areas of high mechanical stress as a result of endothelial disruption or interstitial matrix damage1-3. Hence, it is not surprising that epidemiological studies have shown high blood pressure to be a leading risk factor in the onset of aortic valve disease4. 
The only treatment option currently available for valve disease is surgical replacement of the diseased valve with a bioprosthetic or mechanical valve5. Improved understanding of valve biology in response to physical stresses would help elucidate the mechanisms of valve pathogenesis. In turn, this could help in the development of non-invasive therapies such as pharmaceutical intervention or prevention. Several bioreactors have been previously developed to study the mechanobiology of native or engineered heart valves6-9. Pulsatile bioreactors have also been developed to study a range of tissues including cartilage10, bone11 and bladder12. The aim of this work was to develop a cyclic pressure system that could be used to elucidate the biological response of aortic valve leaflets to increased pressure loads. 
The system consisted of an acrylic chamber in which to place samples and produce cyclic pressure, viton diaphragm solenoid valves to control the timing of the pressure cycle, and a computer to control electrical devices. The pressure was monitored using a pressure transducer, and the signal was conditioned using a load cell conditioner. A LabVIEW program regulated the pressure using an analog device to pump compressed air into the system at the appropriate rate. The system mimicked the dynamic transvalvular pressure levels associated with the aortic valve; a saw tooth wave produced a gradual increase in pressure, typical of the transvalvular pressure gradient that is present across the valve during diastole, followed by a sharp pressure drop depicting valve opening in systole. The LabVIEW program allowed users to control the magnitude and frequency of cyclic pressure. The system was able to subject tissue samples to physiological and pathological pressure conditions. This device can be used to increase our understanding of how heart valves respond to changes in the local mechanical environment.

Design of a Cyclic Pressure Bioreactor for the Ex Vivo Study of Aortic Heart Valves

A cyclic pressure bioreactor capable of subjecting heart valve tissue to physiological and pathological pressure conditions has been designed. A LabVIEW program allows users to control pressure magnitude, amplitude and frequency. This device can be used to study the mechanobiology of heart valve tissue or isolated cells.

The aortic valve, located between the left ventricle and the aorta, allows for unidirectional blood flow, preventing backflow into the ventricle. Aortic ...

A Toolkit to Enable Hydrocarbon Conversion in Aqueous Environments

This work puts forward a toolkit that enables the conversion of alkanes by Escherichia coli and presents a proof of principle of its applicability. The toolkit consists of multiple standard interchangeable parts (BioBricks)9 addressing the conversion of alkanes, regulation of gene expression and survival in toxic hydrocarbon-rich environments.
A three-step pathway for alkane degradation was implemented in E. coli to enable the conversion of medium- and long-chain alkanes to their respective alkanols, alkanals and ultimately alkanoic-acids. The latter were metabolized via the native &beta;-oxidation pathway. To facilitate the oxidation of medium-chain alkanes (C5-C13) and cycloalkanes (C5-C8), four genes (alkB2, rubA3, rubA4and rubB) of the alkane hydroxylase system from Gordonia sp. TF68,21 were transformed into E. coli. For the conversion of long-chain alkanes (C15-C36), theladA gene from Geobacillus thermodenitrificans was implemented. For the required further steps of the degradation process, ADH and ALDH (originating from G. thermodenitrificans) were introduced10,11. The activity was measured by resting cell assays. For each oxidative step, enzyme activity was observed.
To optimize the process efficiency, the expression was only induced under low glucose conditions: a substrate-regulated promoter, pCaiF, was used. pCaiF is present in E. coli K12 and regulates the expression of the genes involved in the degradation of non-glucose carbon sources.
The last part of the toolkit - targeting survival - was implemented using solvent tolerance genes, PhPFD&alpha; and &beta;, both from Pyrococcus horikoshii OT3. Organic solvents can induce cell stress and decreased survivability by negatively affecting protein folding. As chaperones, PhPFD&alpha; and &beta; improve the protein folding process e.g. under the presence of alkanes. The expression of these genes led to an improved hydrocarbon tolerance shown by an increased growth rate (up to 50%) in the presences of 10% n-hexane in the culture medium were observed.
Summarizing, the results indicate that the toolkit enables E. coli to convert and tolerate hydrocarbons in aqueous environments. As such, it represents an initial step towards a sustainable solution for oil-remediation using a synthetic biology approach.

A sustainable auto regulating bacterial system for the remediation of oil pollutions was designed using standard interchangeable DNA parts (BioBricks). An engineered E. coli strain was used to degrade alkanes via &beta;-oxidation in toxic aqueous environments. The respective enzymes from different species showed alkane degradation activity. Additionally, an increased tolerance to n-hexane was achieved by introducing genes from alkane-tolerant bacteria.

This work puts forward a toolkit that enables the conversion of alkanes by Escherichia coli and presents a proof of principle of its applicability. The ...

Synthesis of an Intein-mediated Artificial Protein Hydrogel

We present the synthesis of a highly stable protein hydrogel mediated by a split-intein-catalyzed protein trans-splicing reaction. The building blocks of this hydrogel are two protein block-copolymers each containing a subunit of a trimeric protein that serves as a crosslinker and one half of a split intein. A highly hydrophilic random coil is inserted into one of the block-copolymers for water retention. Mixing of the two protein block copolymers triggers an intein trans-splicing reaction, yielding a polypeptide unit with crosslinkers at either end that rapidly self-assembles into a hydrogel. This hydrogel is very stable under both acidic and basic conditions, at temperatures up to 50 &#176;C, and in organic solvents. The hydrogel rapidly reforms after shear-induced rupture. Incorporation of a &#34;docking station peptide&#34; into the hydrogel building block enables convenient incorporation of &#34;docking protein&#34;-tagged target proteins. The hydrogel is compatible with tissue culture growth media, supports the diffusion of 20 kDa molecules, and enables the immobilization of bioactive globular proteins. The application of the intein-mediated protein hydrogel as an organic-solvent-compatible biocatalyst was demonstrated by encapsulating the horseradish peroxidase enzyme and corroborating its activity.

We present the synthesis of a split-intein-mediated protein hydrogel. The building blocks of this hydrogel are two protein copolymers each containing a subunit of a trimeric protein that serves as a crosslinker and one half of a split intein. Mixing of the two protein copolymers triggers an intein trans-splicing reaction, yielding a polypeptide unit that self-assembles into a hydrogel. This hydrogel is highly pH- and temperature-stable, compatible with organic solvents, and easily incorporates functional globular proteins.

We present the synthesis of a highly stable protein hydrogel mediated by a split-intein-catalyzed protein trans-splicing reaction. The building blocks of ...

Tissue Engineering of Tumor Stromal Microenvironment with Application to Cancer Cell Invasion

3D organotypic cultures of epithelial cells on a matrix embedded with mesenchymal cells are widely used to study epithelial cell differentiation and invasion. Rat tail type I collagen and/or matrix derived from Engelbreth-Holm-Swarm mouse sarcoma cells have been traditionally employed as the substrates to model the matrix or stromal microenvironment into which mesenchymal cells (usually fibroblasts) are populated. Although experiments using such matrices are very informative, it can be argued that due to an overriding presence of a single protein (such as in type I Collagen) or a high content of basement membrane components and growth factors (such as in matrix derived from mouse sarcoma cells), these substrates do not best reflect the contribution to matrix composition made by the stromal cells themselves. To study native matrices produced by primary dermal fibroblasts isolated from patients with a tumor prone, genetic blistering disorder (recessive dystrophic epidermolysis bullosa), we have adapted an existing native matrix protocol to study tumor cell invasion. Fibroblasts are induced to produce their own matrix over a prolonged period in culture. This native matrix is then detached from the culture dish and epithelial cells are seeded onto it before the entire coculture is raised to the air-liquid interface. Cellular differentiation and/or invasion can then be assessed over time. This technique provides the ability to assess epithelial-mesenchymal cell interactions in a 3D setting without the need for a synthetic or foreign matrix with the only disadvantage being the prolonged period of time required to produce the native matrix. Here we describe the application of this technique to assess the ability of a single molecule expressed by fibroblasts, type VII collagen, to inhibit tumor cell invasion.

Tissue engineered fibroblast-derived native matrix is an emerging tool to generate a stromal substrate which supports epithelial cell proliferation and differentiation. Here a protocol applying this methodology to assess the impact of different stromal cell types on tumor cell biology is presented.

3D organotypic cultures of epithelial cells on a matrix embedded with mesenchymal cells are widely used to study epithelial cell differentiation and ...

An Injectable and Drug-loaded Supramolecular Hydrogel for Local Catheter Injection into the Pig Heart

Regeneration of lost myocardium is an important goal for future therapies because of the increasing occurrence of chronic ischemic heart failure and the limited access to donor hearts. An example of a treatment to recover the function of the heart consists of the local delivery of drugs and bioactives from a hydrogel. In this paper a method is introduced to formulate and inject a drug-loaded hydrogel non-invasively and side-specific into the pig heart using a long, flexible catheter. The use of 3-D electromechanical mapping and injection via a catheter allows side-specific treatment of the myocardium. To provide a hydrogel compatible with this catheter, a supramolecular hydrogel is used because of the convenient switching from a gel to a solution state using environmental triggers. At basic pH this ureido-pyrimidinone modified poly(ethylene glycol) acts as a Newtonian fluid which can be easily injected, but at physiological pH the solution rapidly switches into a gel. These mild switching conditions allow for the incorporation of bioactive drugs and bioactive species, such as growth factors and exosomes as we present here in both in vitro and in vivo experiments. The in vitro experiments give an on forehand indication of the gel stability and drug release, which allows for tuning of the gel and release properties before the subsequent application in vivo. This combination allows for the optimal tuning of the gel to the used bioactive compounds and species, and the injection system.

Supramolecular hydrogelators based on ureido-pyrimidinones allow full control over the macroscopic gel properties and the sol&#8211;gel switching behavior using pH. Here, we present a protocol for formulating and injecting such a supramolecular hydrogelator via a catheter delivery system for local delivery directly in relevant areas in the pig heart.

Regeneration of lost myocardium is an important goal for future therapies because of the increasing occurrence of chronic ischemic heart failure and the ...

Synthesis of Keratin-based Nanofiber for Biomedical Engineering

Electrospinning, due to its versatility and potential for applications in various fields, is being frequently used to fabricate nanofibers. Production of these porous nanofibers is of great interest due to their unique physiochemical properties. Here we elaborate on the fabrication of keratin containing poly (&#949;-caprolactone) (PCL) nanofibers (i.e., PCL/keratin composite fiber). Water soluble keratin was first extracted from human hair and mixed with PCL in different ratios. The blended solution of PCL/keratin was transformed into nanofibrous membranes using a laboratory designed electrospinning set up. Fiber morphology and mechanical properties of the obtained nanofiber were observed and measured using scanning electron microscopy and tensile tester. Furthermore, degradability and chemical properties of the nanofiber were studied by FTIR. SEM images showed uniform surface morphology for PCL/keratin fibers of different compositions. These PCL/keratin fibers also showed excellent mechanical properties such as Young&#39;s modulus and failure point. Fibroblast cells were able to attach and proliferate thus proving good cell viability. Based on the characteristics discussed above, we can strongly argue that the blended nanofibers of natural and synthetic polymers can represent an excellent development of composite materials that can be used for different biomedical applications.

Electrospun nanofibers have a high surface area to weight ratio, excellent mechanical integrity, and support cell growth and proliferation. These nanofibers have a wide range of biomedical applications. Here we fabricate keratin/ PCL nanofibers, using the electrospinning technique, and characterize the fibers for possible applications in tissue engineering.

Electrospinning, due to its versatility and potential for applications in various fields, is being frequently used to fabricate nanofibers. Production of ...

Tissue Engineering by Intrinsic Vascularization in an In Vivo Tissue Engineering Chamber

In reconstructive surgery, there is a clinical need for an alternative to the current methods of autologous reconstruction which are complex, costly and trade one defect for another. Tissue engineering holds the promise to address this increasing demand. However, most tissue engineering strategies fail to generate stable and functional tissue substitutes because of poor vascularization. This paper focuses on an in vivo tissue engineering chamber model of intrinsic vascularization where a perfused artery and a vein either as an arteriovenous loop or a flow-through pedicle configuration is directed inside a protected hollow chamber. In this chamber-based system angiogenic sprouting occurs from the arteriovenous vessels and this system attracts ischemic and inflammatory driven endogenous cell migration which gradually fills the chamber space with fibro-vascular tissue. Exogenous cell/matrix implantation at the time of chamber construction enhances cell survival and determines specificity of the engineered tissues which develop. Our studies have shown that this chamber model can successfully generate different tissues such as fat, cardiac muscle, liver and others. However, modifications and refinements are required to ensure target tissue formation is consistent and reproducible. This article describes a standardized protocol for the fabrication of two different vascularized tissue engineering chamber models in vivo.

Tissue Engineering by Intrinsic Vascularization in an In Vivo Tissue Engineering Chamber

This is a guideline for constructing in vivo vascularized tissue using a microsurgical arteriovenous loop or a flow-through pedicle configuration inside a tissue engineering chamber. The vascularized tissues generated can be employed for organ regeneration and replacement of tissue defects, as well as for drug testing and disease modeling.

In reconstructive surgery, there is a clinical need for an alternative to the current methods of autologous reconstruction which are complex, costly and ...

Dendrimer-based Uneven Nanopatterns to Locally Control Surface Adhesiveness: A Method to Direct Chondrogenic Differentiation

Cellular adhesion and differentiation is conditioned by the nanoscale disposition of the extracellular matrix (ECM) components, with local concentrations having a major effect. Here we present a method to obtain large-scale uneven nanopatterns of arginine-glycine-aspartic acid (RGD)-functionalized dendrimers that permit the nanoscale control of local RGD surface density. Nanopatterns are formed by surface adsorption of dendrimers from solutions at different initial concentrations and are characterized by water contact angle (CA), X-ray photoelectron spectroscopy (XPS), and scanning probe microscopy techniques such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The local surface density of RGD is measured using AFM images by means of probability contour maps of minimum interparticle distances and then correlated with cell adhesion response and differentiation. The nanopatterning method presented here is a simple procedure that can be scaled up in a straightforward manner to large surface areas. It is thus fully compatible with cell culture protocols and can be applied to other ligands that exert concentration-dependent effects on cells.

A method to obtain dendrimer-based uneven nanopatterns that permit the nanoscale control of local arginine-glycine-aspartic acid (RGD) surface density is described and applied for the study of cell adhesion and chondrogenic differentiation.

Cellular adhesion and differentiation is conditioned by the nanoscale disposition of the extracellular matrix (ECM) components, with local concentrations ...