Name: automated lipid bilayer membrane formation using a polydimethylsiloxane thin film
Uploaded: 2016-07-10T13:00:00
Description: Watch this Scientific Journal Video about Automated Lipid Bilayer Membrane Formation Using a Polydimethylsiloxane Thin Film at JoVE.com

This work was supported by the Pioneer Research Center Program (NRF-2012-0009575) and National Research Foundation Grants (NRF-2012R1A1B4002413, NRF-2014R1A1A2059341) from the National Research Foundation of Korea. This work was also partially supported by the Inha University Research Grant.

1. Solution Preparation
<ol>
	<li>Preparation of buffer solution:
	<ol>
		<li>To formulate buffer solution, dissolve 1 M KCl (Potassium chloride), 10 mM Tris-HCl (Tris-hydrochloride), and 1 mM EDTA (Ethylenediaminetetraacetic acid) in distilled water and adjust pH to 8.0.</li>
		<li>Filter the solution using a 0.20 &#181;m filter. To sterilize, autoclave the solution at 121 &#176;C for 15 min.</li>
	</ol>
	</li>
	<li>Preparation of lipid solution for pre-painting:
	<ol>
		<li>To formulate the lipid solution for pre-pai...

<ol>
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J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Patch+clamping+by+numbers.">Patch clamping by numbers.</a> Drug. Discov. Today. 9 (10), 434-441 (2004).</li><li>Mueller, P., Rudin, D. O., Tien, H. T., Wescott, W. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reconstitution+of+cell+membrane+structure+in+vitro+and+its+transformation+into+an+excitable+system.">Reconstitution of cell membrane structure in vitro and its transformation into an excitable system.</a> Nature. 194, 979-980 (1962).</li><li>Montal, M., Mueller, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Formation+of+bimolecular+membranes+from+lipid+monolayers+and+a+study+of+their+electrical+properties.">Formation of bimolecular membranes from lipid monolayers and a study of their electrical properties.</a> Proc. Natl. Acad. Sci. U. S. A. 69, 3561-3566 (1972).</li><li>Baaken, G., Sondermann, M., Schlemmer, C., Ruhe, J., Behrends, J. 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Electron. 8 (2), 47-52 (1998).</li><li>Ide, T., Yanagida, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+artificial+lipid+bilayer+formed+on+an+agarose-coated+glass+for+simultaneous+electrical+and+optical+measurement+of+single+ion+channels.">An artificial lipid bilayer formed on an agarose-coated glass for simultaneous electrical and optical measurement of single ion channels.</a> Biochem. Biophys. Res. Commun. 265 (2), 595-599 (1999).</li><li>Jeon, T. J., Malmstadt, N., Schmidt, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrogel-encapsulated+lipid+membranes.">Hydrogel-encapsulated lipid membranes.</a> J Am Chem Soc. 128 (1), 42-43 (2006).</li><li>Malmstadt, N., Jeon, T. J., Schmidt, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Long-Lived+Planar+Lipid+Bilayer+Membranes+Anchored+to+an+In+Situ+Polymerized+Hydrogel.">Long-Lived Planar Lipid Bilayer Membranes Anchored to an In Situ Polymerized Hydrogel.</a> Adv. Mater. 20 (1), 84-89 (2008).</li><li>Jeon, T. J., Poulos, J. L., Schmidt, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Long-term+storable+and+shippable+lipid+bilayer+membrane+platform.">Long-term storable and shippable lipid bilayer membrane platform.</a> Lab. Chip. 8 (10), 1742-1744 (2008).</li><li>Ryu, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Automated+Lipid+Membrane+Formation+Using+a+Polydimethylsiloxane+Film+for+Ion+Channel+Measurements.">Automated Lipid Membrane Formation Using a Polydimethylsiloxane Film for Ion Channel Measurements.</a> Anal. Chem. 86 (18), 8910-8915 (2014).</li><li>Yaws, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Chemical Properties Handbooks: Physical, Thermodynamic, Environmental, Transport, Safety, and Health Related Properties for Organic and Inorganic Chemicals. , (1999).</li><li>Windholz, M., Budavari, S., Stroumtsos, L. Y., Fertig, M. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The Merck index. An encyclopedia of chemicals and drugs. , (1976).</li><li>Miller, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Ion Channel Reconstitution. , (1986).</li><li>Miller, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Open-state+substructure+of+single+chloride+channels+from+Torpedo+electroplax.">Open-state substructure of single chloride channels from Torpedo electroplax.</a> Philos. Trans. R. Soc. Lond. B. Biol. Sci. 299 (1097), 401-411 (1982).</li><li>Benz, R., Frohlich, O., Lauger, P., Montal, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrical+capacity+of+black+lipid+films+and+of+lipid+bilayers+made+from+monolayers.">Electrical capacity of black lipid films and of lipid bilayers made from monolayers.</a> Biochim. Biophys. Acta. 394 (3), 323-334 (1975).</li><li>Priel, A., Gil, Z., Moy, V. T., Magleby, K. L., Silberberg, S. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ionic+requirements+for+membrane-glass+adhesion+and+giga+seal+formation+in+patch-clamp+recording.">Ionic requirements for membrane-glass adhesion and giga seal formation in patch-clamp recording.</a> Biophys. J. 92 (11), 3893-3900 (2007).</li></ol>

Our BLM formation technique provides a powerful tool for cell membrane and ion channel studies, in contrast to conventional techniques that have limited potential for industrial use. We developed a membrane precursor using a PDMS thin film, and devised a frozen membrane precursor with expedited self-assembly.
As opposed to conventional membrane formation methods with hydrophobic films, where membrane formation only occurs via surface interactions between the film and the lipid solution,20...

Artificial lipid bilayer membrane, or black lipid membrane (BLM), is an important tool for elucidating mechanisms of cell membranes and ion channels, as well as for understanding interactions between ion channels and ions/molecules.1-7 Although the patch-clamp method is often considered the gold standard for cell membrane studies, it is laborious and requires highly skilled operators for ion channel measurements.8 While artificially reconstituted lipid bilayer membranes have emerged as alternative tools for ion channel studies,9,10 they are also associated with laborious processes and specific expertise. Moreover, membranes are susceptible to mechanical perturbations. Hence, lipid bilayer technologies introduced to date have limited practical applications.11
In order to enhance robustness and longevity of lipid bilayer membranes, Costello et al.12, and Ide and Yanagida13 have devised a free-standing lipid bilayer supported by hydrogels. Despite enhanced longevity however (&#60; 24 hr), bilayer robustness was not improved. Jeon et al.14 devised a hydrogel encapsulated membrane (HEM) with intimate hydrogel-lipid bilayer contact, resulting in enhanced longevity (up to several days). To further increase the lifetime of the HEM, Malmstadt and Jeon et al. created a hydrogel-encapsulated membrane with hydrogel-lipid binding via in-situ covalent conjugation (cgHEM).15 In both systems, membrane lifetimes increased substantially (&#62; 10 days). However, the membrane formation systems were not sufficiently robust, and could not be stored or delivered where required to liberate expertise for use of the lipid bilayers.
The development of a lipid bilayer platform has primarily revolved around increasing robustness and longevity of BLMs. Although the longevity of BLMs has been substantially enhanced recently, their applications have been limited due to a lack of transportability and storability. To overcome these issues, Jeon et al. created a storable membrane system and introduced a membrane precursor (MP).16 To construct an MP, they prepared a mixture of n-decane and hexadecane containing 3% DPhPC (1,2-diphytanoyl-sn-glycero-3-phosphatidylcholine) to control the freezing point of the lipid solution such that it would freeze at ~14 &#176;C (below room temperature, above typical refrigerator temperature). In this experiment, the MP was spread over a small aperture on a polytetrafluoroethylene (PTFE) film and subsequently frozen in a refrigerator at 4 &#176;C. When the MP was brought to room temperature, the MP thawed and a lipid bilayer was automatically formed, eliminating the expertise typically associated with membrane formation. However, the success rate of BLM made from the MP was as low as ~27%, and membrane formation time was inconsistent (30 min to 24 hr), limiting its practical applications.
In this study, a polydimethylsiloxane (PDMS) thin film is used instead of a conventional hydrophobic thin films (PTFE, polyoxymethylene, polystyrene) to (a) control fabrication time and (b) increase the success rate of BLM formation as previously reported by Ryu et al.17 Herein, membrane formation was facilitated by extraction of solvents due to the porous nature of PDMS, and the time required for membrane formation was successfully controlled in this study. In this system, as the lipid solution was absorbed into the PDMS thin film, a consistent membrane formation time was achieved. Moreover, membrane lifetime was prolonged due to slow absorption of solvents into the PDMS thin film, a result of the addition of squalene to the lipid solution. We conducted optical and electrical measurements to verify that membranes formed using this technique are suitable for ion channels studies.

<table border="0" cellpadding="0" cellspacing="0" width="1448">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Potassium Chloride</td>
			<td style="width:172px;">Sigma-Aldrich</td>
			<td style="width:199px;">P9333</td>
			<td style="width:743px;">For buffer solution</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Tris-hydrochloride</td>
			<td style="width:172px;">Sigma-Aldrich</td>
			<td style="width:199px;">1185-53-1</td>
			<td>For buffer solution</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Ethylenediaminetetraacetic acid</td>
			<td style="width:172px;">Sigma-Aldrich</td>
			<td style="width:199px;">60-00-4</td>
			<td>For buffer solution</td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:335px;">n-decane</td>
			<td style="width:172px;">Sigma-Aldrich</td>
			<td style="width:199px;">44074-U</td>
			<td>For lipid solution</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Hexadecane</td>
			<td style="width:172px;">Sigma-Aldrich</td>
			<td style="width:199px;">544-76-3</td>
			<td>For lipid solution</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Squalene</td>
			<td style="width:172px;">Sigma-Aldrich</td>
			<td style="width:199px;">S3626</td>
			<td>For lipid solution</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Gramicidin A</td>
			<td style="width:172px;">Sigma-Aldrich</td>
			<td style="width:199px;">11029-61-1</td>
			<td>Membrane protein</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">1,2-diphytanoyl-sn-glycero-3-phosphocholine</td>
			<td style="width:172px;">Avanti Polar Lipids, Inc.</td>
			<td style="width:199px;">850356</td>
			<td>For membrae formation</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Sylgard 184a and 184b elastromer kit</td>
			<td style="width:172px;">Dow Corning Asia</td>
			<td style="width:199px;"></td>
			<td>To produce PDMS thin film</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">0.2 &#956;m filter</td>
			<td style="width:172px;">Satorius stedim</td>
			<td style="width:199px;">16534----------K</td>
			<td>To filter buffer solution</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Rotator</td>
			<td style="width:172px;">FinePCR</td>
			<td style="width:199px;">AG</td>
			<td>To dissolve lipid homogeneously</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Autoclave</td>
			<td style="width:172px;">Biofree</td>
			<td style="width:199px;">BF-60AC</td>
			<td>To sterilize buffer solution</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Spin coater</td>
			<td style="width:172px;">Shinu Mst</td>
			<td style="width:199px;">SP-60P</td>
			<td>To spread PDMS prepolymer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Vaccum dessiccator</td>
			<td style="width:172px;">Welch</td>
			<td style="width:199px;">2042-22</td>
			<td>To remove air bubble in PDMS prepolymer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">500 &#956;m&#160; punch</td>
			<td style="width:172px;">Harris Uni-Core</td>
			<td style="width:199px;">0.5</td>
			<td>To create an aperture on the PDMS thin film</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">CNC machine</td>
			<td style="width:172px;">SME trading</td>
			<td style="width:199px;">SME 2518</td>
			<td>To fabricate membrane formation chamber</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Halogen fiber optic illuminator</td>
			<td style="width:172px;">Motic</td>
			<td style="width:199px;">MLC-150C</td>
			<td>To illuminate the aperture of PDMS thin film for optical observation</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Digital microscope</td>
			<td style="width:172px;">Digital blue</td>
			<td style="width:199px;">QX-5</td>
			<td>To optically observe lipid bilayer membrane formation</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Electrode</td>
			<td style="width:172px;">A-M Systems</td>
			<td style="width:199px;"></td>
			<td>To electrically observe membrane formation</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:335px;">Microelectrode amplifier (Axopatch amplifier)</td>
			<td style="width:172px;">Axon Instruments</td>
			<td>Axopatch 200B Amplifier</td>
			<td>To measure capacitance of the membrane (described as microelectrode amplifier in the manuscript)</td>
		</tr>
	</tbody>
</table>

automated lipid bilayer membrane formation using a polydimethylsiloxane thin film

An artificial lipid bilayer, or black lipid membrane (BLM), is a powerful tool for studying ion channels and protein interactions, as well as for biosensor applications. However, conventional BLM formation techniques have several drawbacks and they often require specific expertise and laborious processes. In particular, conventional BLMs suffer from low formation success rates and inconsistent membrane formation time. Here, we demonstrate a storable and transportable BLM formation system with controlled thinning-out time and enhanced BLM formation rate by replacing conventionally used films (polytetrafluoroethylene, polyoxymethylene, polystyrene) to polydimethylsiloxane (PDMS). In this experiment, a porous-structured polymer such as PDMS thin film is used. In addition, as opposed to conventionally used solvents with low viscosity, the use of squalene permitted a controlled thinning-out time via slow solvent absorption by PDMS, prolonging membrane lifetime. In addition, by using a mixture of squalene and hexadecane, the freezing point of the lipid solution was increased (~16 &#176;C), in addition, membrane precursors were produced that can be indefinitely stored and readily transported. These membrane precursors have reduced BLM formation time of &#60; 1 hr and achieved a BLM formation rate of ~80%. Moreover, ion channel experiments with gramicidin A demonstrated the feasibility of the membrane system.

Optimization of MPES Solution Composition 
Different compositions of lipids and solvents were tested to successfully reconstitute lipid bilayer membranes from MPES. The MP system with a mixture of n-decane and hexadecane containing 3% DPhPC14 exhibited a low success rate of membrane formation (~27%). In addition, as the PDMS film continuously extracted lipid solution, it was necessary to optimize solvent composition to maintain an intact lipid bil...

Watch this Scientific Journal Video about Automated Lipid Bilayer Membrane Formation Using a Polydimethylsiloxane Thin Film at JoVE.com

Automated Lipid Bilayer Membrane Formation Using a Polydimethylsiloxane Thin Film

We demonstrate a storable, transportable lipid bilayer formation system. A lipid bilayer membrane can be formed within 1 hr with over 80% success rate when a frozen membrane precursor is brought to ambient temperature. This system will reduce laborious processes and expertise associated with ion channels.

An artificial lipid bilayer, or black lipid membrane (BLM), is a powerful tool for studying ion channels and protein interactions, as well as for ...

The overall goal of this procedure is to describe a method that can be used to study automated lipid bilayer formation using a polydimethylsiloxane thin film. This method can help answer key questions in the nanobiosensor field regarding membrane-protein interactions. The main advantage of this technique is that the lipid bilayer formation is automated and reproducible.To start, prepare the buffer solution by combining potassium chloride, tris hydrochloride, and EDTA in distilled water. Then, adjust the PH of the solution to 8.0. Then, filter the solution using a 0.2 micron filter, and autoclave the solution at 121 degrees celsius for 15 minutes.Next, prepare the lipid solution for pre-painting by dissolving 3%of the lipid in a mixture consisting of two parts undecane and eight parts hexadecane by volume. Stir the solution overnight using a rotator. Also, prepare the lipid solution for membrane formation by dissolving 0.1%of the lipid in the same mixture of two parts undecane and eight parts hexadecane by volume.Stir this solution overnight on a rotator as well. In order to prepare a PDMS thin film, mix nine parts prepolymer with one part curing agent in a mixing cup. Place five grams of this mixture into a petri dish, and spin coat the dish at 800 rpm for 10 seconds to form a film that is 200 to 250 microns thick.Next, place the petri dish into a vacuum desiccator and pull a vaccum of 100 millitorr for two hours to remove the residual air bubbles. Then, bake the thin film in an oven for five hours at 70 degrees celsius to polymerize the PDMS. Once cooled, cut the polymerized thin film into two centimeter by two centimeter squares, and use a 500 micron diameter punch to make a small aperture in the center of the square.Then, use a micropipette to prepaint the apertures with one microliter of the 3%lipid solution. To create the black lipid membrane chamber, design two symmetric blocks for the chamber using 3D drawing software. Then, fabricate the chamber using a block of PTFE and a CNC machine.To assemble the chamber, place the pre-painted PDMS thin film between the two PTFE blocks, such that the aperture on the PDMS thin film is centered with the hole in the chamber. Use cover glass and vacuum grease to seal the outer edges of the chamber. Once sealed, immobilize the assembled chamber using nuts and bolts.It is important to make sure the chamber's well sealed so that there is no liquid leakage. Using a pipette, deposit 0.5 microliters of the 0.1%lipid solution onto the aperture of the PDMS thin film, assembled with the chamber. Then, place the chamber in a cooled environment below 10 degrees celsius and store it until it is needed.To form a black lipid membrane with expedited self-assembly, withdraw the chamber from the refrigerator and add two milliliters of the buffer solution into each side of the chamber. Set the chamber aside for 10 minutes until the frozen membrane precursor thaws. Then, place the chamber onto a micro manipulator to precisely control the elevation with respect to the light source and the microscope.Using a halogen fiber optic illuminator, illuminate one side of the chamber to brighten the aperture of the PDMS thin film. On the other side, place a 20x objective in line with the aperture and observe the center where the color becomes brighter than the annulus. For electrical measurement, prepare silver chloride electrodes by placing a 208 micrometer thick silver wire in a solution of sodium hypochlorite for at least one minute.Next, connect the electrodes to a microelectrode amplifier. Then, place the silver chloride electrodes into each side of the chamber, so that they are in the buffer solution. Using electrophysiology software, apply a 10 millivolt triangular wave form across the membrane to acquire a square wave.Record the electrical properties of the membrane by clicking the record button. Continue recording until a uniform square wave is observed. Then, quit recording by clicking on the black square icon.Two methods can be employed to incorporate gramicidin A into the lipid bilayer. First, gramicidin A can be added directly to the lipid solution before spreading the lipid solution onto the aperture of the PDMS thin film. Second, gramicidin A solution can be added to the chamber when a lipid bilayer forms.To observe gramicidin A channel activities, apply 100 millivolts across the membrane at a sample rate of 5 kilohertz to measure the holding potential of the membrane. Record the electrical properties as previously done, by clicking the record button. As ion channel activities are shown, keep recording until various current jumps are observed to confirm ion channel incorporation.Once confirmed, quit the recording by clicking the black square icon. When the recording is finished, filter the data with a low pass bessel filter at 100 hertz using electrophysiology software. Observe the current jumps in the filtered holding potential data.These jumps represent the dimerization of a gramicidin A ion channel. When the frozen membrane precursor was brought in to room temperature to thaw, the lipid bilayer formation is facilitated due to extraction of hydrophobic solvent into the PDMS thin film. This sequence of images shows the formation of a lipid bilayer, which self assembles when warmed from its frozen form.Here, the electrical conductance illustrates the incorporation and dimerization of gramicidin A.Upon dimerization, the gramicidin A forms an ion channel and the conductance levels jump to 28 picosiemens, which is consistent with the results of previous reports and shows immediate incorporation of this antibiotic into the bilayer. Our membrane formation technique provides powerful tool for cell membrane and nanochannel studies in contrast to conventional techniques that have limited potentials for practical application. Our system requires no expertise for either membrane formation or ion channeling incorporation making it well suited for drug screening and bio sensing applications.

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Bioengineering

A Chitosan Based, Laser Activated Thin Film Surgical Adhesive, 'SurgiLux': Preparation and Demonstration

Sutures are a 4,000 year old technology that remain the 'gold-standard' for wound closure by virtue of their repair strength (~100 KPa). However, sutures can act as a nidus for infection and in many procedures are unable to effect wound repair or interfere with functional tissue regeneration.1 Surgical glues and adhesives, such as those based on fibrin and cyanoacrylates, have been developed as alternatives to sutures for the repair of such wounds. However, current commercial adhesives also have significant disadvantages, ranging from viral and prion transfer and a lack of repair strength as with the fibrin glues, to tissue toxicity and a lack of biocompatibility for the cyanoacrylate based adhesives. Furthermore, currently available surgical adhesives tend to be gel-based and can have extended curing times which limit their application.2 Similarly, the use of UV lasers to facilitate cross-linking mechanisms in protein-based or albumin 'solders' can lead to DNA damage while laser tissue welding (LTW) predisposes thermal damage to tissues.3 Despite their disadvantages, adhesives and LTW have captured approximately 30% of the wound closure market reported to be in excess of US $5 billion per annum, a significant testament to the need for sutureless technology.4
In the pursuit of sutureless technology we have utilized chitosan as a biomaterial for the development of a flexible, thin film, laser-activated surgical adhesive termed 'SurgiLux'. This novel bioadhesive uses a unique combination of biomaterials and photonics that are FDA approved and successfully used in a variety of biomedical applications and products. SurgiLux overcomes all the disadvantages associated with sutures and current surgical adhesives (see Table 1).
In this presentation we report the relatively simple protocol for the fabrication of SurgiLux and demonstrate its laser activation and tissue weld strength. SurgiLux films adhere to collagenous tissue without chemical modification such as cross-linking and through irradiation using a comparatively low-powered (120 mW) infrared laser instead of UV light. Chitosan films have a natural but weak adhesive attraction to collagen (~3 KPa), laser activation of the chitosan based SurgiLux films emphasizes the strength of this adhesion through polymer chain interactions as a consequence of transient thermal expansion.5 Without this 'activation' process, SurgiLux films are readily removed.6-9 SurgiLux has been tested both in vitro and in vivo on a variety of tissues including nerve, intestine, dura mater and cornea. In all cases it demonstrated good biocompatibility and negligible thermal damage as a consequence of irradiation.6-10

The fabrication of a novel, flexible thin film surgical adhesive from FDA approved ingredients, chitosan and indocyanine green is described. Bonding of this adhesive to collagenous tissue through a simple activation process with a low-powered infra-red laser is demonstrated.

Sutures are a 4,000 year old technology that remain the 'gold-standard' for wound closure by virtue of their repair strength (~100 KPa). However, sutures ...

Creating Transient Cell Membrane Pores Using a Standard Inkjet Printer

Bioprinting has a wide range of applications and significance, including tissue engineering, direct cell application therapies, and biosensor microfabrication.1-10 Recently, thermal inkjet printing has also been used for gene transfection.8,9 The thermal inkjet printing process was shown to temporarily disrupt the cell membranes without affecting cell viability. The transient pores in the membrane can be used to introduce molecules, which would otherwise be too large to pass through the membrane, into the cell cytoplasm.8,9,11
The application being demonstrated here is the use of thermal inkjet printing for the incorporation of fluorescently labeled g-actin monomers into cells. The advantage of using thermal ink-jet printing to inject molecules into cells is that the technique is relatively benign to cells.8, 12 Cell viability after printing has been shown to be similar to standard cell plating methods1,8. In addition, inkjet printing can process thousands of cells in minutes, which is much faster than manual microinjection. The pores created by printing have been shown to close within about two hours. However, there is a limit to the size of the pore created (~10 nm) with this printing technique, which limits the technique to injecting cells with small proteins and/or particles. 8,9,11
A standard HP DeskJet 500 printer was modified to allow for cell printing.3, 5, 8 The cover of the printer was removed and the paper feed mechanism was bypassed using a mechanical lever. A stage was created to allow for placement of microscope slides and coverslips directly under the print head. Ink cartridges were opened, the ink was removed and they were cleaned prior to use with cells. The printing pattern was created using standard drawing software, which then controlled the printer through a simple print command. 3T3 fibroblasts were grown to confluence, trypsinized, and then resuspended into phosphate buffered saline with soluble fluorescently labeled g-actin monomers. The cell suspension was pipetted into the ink cartridge and lines of cells were printed onto glass microscope cover slips. The live cells were imaged using fluorescence microscopy and actin was found throughout the cytoplasm. Incorporation of fluorescent actin into the cell allows for imaging of short-time cytoskeletal dynamics and is useful for a wide range of applications.13-15

A description of the methods used to convert an HP DeskJet 500 printer into a bioprinter. The printer is capable of processing living cells, which causes transient pores in the membrane. These pores can be utilized to incorporate small molecules, including fluorescent G-actin, into the printed cells.

Bioprinting has a wide range of applications and significance, including tissue engineering, direct cell application therapies, and biosensor ...

Lipid Bilayer Vesicle Generation Using Microfluidic Jetting

Bottom-up synthetic biology presents a novel approach for investigating and reconstituting biochemical systems and, potentially, minimal organisms. This emerging field engages engineers, chemists, biologists, and physicists to design and assemble basic biological components into complex, functioning systems from the bottom up. Such bottom-up systems could lead to the development of artificial cells for fundamental biological inquiries and innovative therapies1,2. Giant unilamellar vesicles (GUVs) can serve as a model platform for synthetic biology due to their cell-like membrane structure and size. Microfluidic jetting, or microjetting, is a technique that allows for the generation of GUVs with controlled size, membrane composition, transmembrane protein incorporation, and encapsulation3. The basic principle of this method is the use of multiple, high-frequency fluid pulses generated by a piezo-actuated inkjet device to deform a suspended lipid bilayer into a GUV. The process is akin to blowing soap bubbles from a soap film. By varying the composition of the jetted solution, the composition of the encompassing solution, and/or the components included in the bilayer, researchers can apply this technique to create customized vesicles. This paper describes the procedure to generate simple vesicles from a droplet interface bilayer by microjetting.

Microfluidic jetting against a droplet interface lipid bilayer provides a reliable way to generate vesicles with control over membrane asymmetry, incorporation of transmembrane proteins, and encapsulation of material. This technique can be applied to study a variety of biological systems where compartmentalized biomolecules are desired.

Bottom-up synthetic biology presents a novel approach for investigating and reconstituting biochemical systems and, potentially, minimal organisms. This ...

Biomembrane Fabrication by the Solvent-assisted Lipid Bilayer (SALB) Method

In order to mimic cell membranes, the supported lipid bilayer (SLB) is an attractive platform which enables in vitro investigation of membrane-related processes while conferring biocompatibility and biofunctionality to solid substrates. The spontaneous adsorption and rupture of phospholipid vesicles is the most commonly used method to form SLBs. However, under physiological conditions, vesicle fusion (VF) is limited to only a subset of lipid compositions and solid supports. Here, we describe a one-step general procedure called the solvent-assisted lipid bilayer (SALB) formation method in order to form SLBs which does not require vesicles. The SALB method involves the deposition of lipid molecules onto a solid surface in the presence of water-miscible organic solvents (e.g., isopropanol) and subsequent solvent-exchange with aqueous buffer solution in order to trigger SLB formation. The continuous solvent exchange step enables application of the method in a flow-through configuration suitable for monitoring bilayer formation and subsequent alterations using a wide range of surface-sensitive biosensors. The SALB method can be used to fabricate SLBs on a wide range of hydrophilic solid surfaces, including those which are intractable to vesicle fusion. In addition, it enables fabrication of SLBs composed of lipid compositions which cannot be prepared using the vesicle fusion method. Herein, we compare results obtained with the SALB and conventional vesicle fusion methods on two illustrative hydrophilic surfaces, silicon dioxide and gold. To optimize the experimental conditions for preparation of high quality bilayers prepared via the SALB method, the effect of various parameters, including the type of organic solvent in the deposition step, the rate of solvent exchange, and the lipid concentration is discussed along with troubleshooting tips. Formation of supported membranes containing high fractions of cholesterol is also demonstrated with the SALB method, highlighting the technical capabilities of the SALB technique for a wide range of membrane configurations.

Biomembrane Fabrication by the Solvent-assisted Lipid Bilayer SALB Method

We present an experimental protocol to form a supported lipid bilayer on solid substrates without using lipid vesicles. We demonstrate a one-step method to form a lipid bilayer on silicon dioxide and gold as well as supported membranes with cholesterol-enriched domain for various biological applications.

In order to mimic cell membranes, the supported lipid bilayer (SLB) is an attractive platform which enables in vitro investigation of membrane-related ...

Double Emulsion Generation Using a Polydimethylsiloxane (PDMS) Co-axial Flow Focus Device

Double emulsions are useful in a number of biological and industrial applications in which it is important to have an aqueous carrier fluid. This paper presents a polydimethylsiloxane (PDMS) microfluidic device capable of generating water/oil/water double emulsions using a coaxial flow focusing geometry that can be fabricated entirely using soft lithography. Similar to emulsion devices using glass capillaries, double emulsions can be formed in channels with uniform wettability and with dimensions much smaller than the channel sizes. Three dimensional flow focusing geometry is achieved by casting a pair of PDMS slabs using two layer soft lithography, then mating the slabs together in a clamshell configuration. Complementary locking features molded into the PDMS slabs enable the accurate registration of features on each of the slab surfaces. Device testing demonstrates formation of double emulsions from 14 &#181;m to 50 &#181;m in diameter while using large channels that are robust against fouling and clogging.

Double Emulsion Generation Using a Polydimethylsiloxane PDMS Co-axial Flow Focus Device

Microfluidic double emulsions generation typically involves devices with patterned wettability or custom-fabricated glass components. Here we describe the fabrication and testing of an all polydimethylsiloxane (PDMS) double emulsion generator that does not require surface treatment or complicated fabrication processes, and is capable of producing double emulsions down to 14 &#181;m.

Double emulsions are useful in a number of biological and industrial applications in which it is important to have an aqueous carrier fluid. This paper ...

Ligand Nano-cluster Arrays in a Supported Lipid Bilayer

Currently there is considerable interest in creating ordered arrays of adhesive protein islands in a sea of passivated surface for cell biological studies. In the past years, it has become increasingly clear that living cells respond, not only to the biochemical nature of the molecules presented to them but also to the way these molecules are presented. Creating protein micro-patterns is therefore now standard in many biology laboratories; nano-patterns are also more accessible. However, in the context of cell-cell interactions, there is a need to pattern not only proteins but also lipid bilayers. Such dual proteo-lipidic patterning has so far not been easily accessible. We offer a facile technique to create protein nano-dots supported on glass and propose a method to backfill the inter-dot space with a supported lipid bilayer (SLB). From photo-bleaching of tracer fluorescent lipids included in the SLB, we demonstrate that the bilayer exhibits considerable in-plane fluidity. Functionalizing the protein dots with fluorescent groups allows us to image them and to show that they are ordered in a regular hexagonal lattice. The typical dot size is about 800 nm and the spacing demonstrated here is 2 microns. These substrates are expected to serve as useful platforms for cell adhesion, migration and mechano-sensing studies.

We present a protocol to functionalize glass with nanometric protein patches surrounded by a fluid lipid bilayer. These substrates are compatible with advanced optical microscopy and are expected to serve as platform for cell adhesion and migration studies.

Currently there is considerable interest in creating ordered arrays of adhesive protein islands in a sea of passivated surface for cell biological ...

Spontaneous Formation and Rearrangement of Artificial Lipid Nanotube Networks as a Bottom-Up Model for Endoplasmic Reticulum

We present a convenient method to form a bottom-up structural organelle model for the endoplasmic reticulum (ER). The model consists of highly dense lipidic nanotubes that are, in terms of morphology and dynamics, reminiscent of ER. The networks are derived from phospholipid double bilayer membrane patches adhering to a transparent Al2O3 substrate. The adhesion is mediated by Ca2+ in the ambient buffer. Subsequent depletion of Ca2+ by means of BAPTA/EDTA causes retraction of the membrane, resulting in spontaneous lipid nanotube network formation. The method only comprises phospholipids and microfabricated surfaces for simple formation of an ER model and does not require the addition of proteins or chemical energy (e.g., GTP or ATP). In contrast to the 3D morphology of the cellular endoplasmic reticulum, the model is two-dimensional (albeit the nanotube dimensions, geometry, structure, and dynamics are maintained). This unique in vitro ER model consists of only a few components, is easy to construct, and can be observed under a light microscope. The resulting structure can be further decorated for additional functionality, such as the addition of ER-associated proteins or particles to study transport phenomena among the tubes. The artificial networks described here are suitable structural models for the cellular ER, whose unique characteristic morphology has been shown to be related to its biological function, whereas details regarding formation of the tubular domain and rearrangements within are still not completely understood. We note that this method uses Al2O3 thin-film-coated microscopy coverslips, which are commercially available but require special orders. Therefore, it is advisable to have access to a microfabrication facility for preparation.

Solid-supported, protein-free, double phospholipid bilayer membranes (DLBM) can be transformed into complex and dynamic lipid nanotube networks and can serve as 2D bottom-up models of the endoplasmic reticulum.

We present a convenient method to form a bottom-up structural organelle model for the endoplasmic reticulum (ER). The model consists of highly dense ...

Immobilization of Live Caenorhabditis elegans Individuals Using an Ultra-thin Polydimethylsiloxane Microfluidic Chip with Water Retention

Radiation is widely used for biological applications and for ion-beam breeding, and among these methods, microbeam irradiation represents a powerful means of identifying radiosensitive sites in living organisms. This paper describes a series of on-chip immobilization methods developed for the targeted microbeam irradiation of live individuals of Caenorhabditis elegans. Notably, the treatment of the polydimethylsiloxane (PDMS) microfluidic chips that we previously developed to immobilize C. elegans individuals without the need for anesthesia is explained in detail. This chip, referred to as a worm sheet, is resilient to allow the microfluidic channels to be expanded, and the elasticity allows animals to be enveloped gently. Also, owing to the self-adsorption capacity of the PDMS, animals can be sealed in the channels by covering the surface of the worm sheet with a thin cover film, in which animals are not pushed into the channels for enclosure. By turning the cover film over, we can easily collect the animals. Furthermore, the worm sheet shows water retention and allows C. elegans individuals to be subjected to microscopic observation for long periods under live conditions. In addition, the sheet is only 300 &#181;m thick, allowing heavy ions such as carbon ions to pass through the sheet enclosing the animals, thus allowing the ion particles to be detected and the applied radiation dose to be measured accurately. Because selection of the cover films used for enclosing the animals is very important for successful long-term immobilization, we conducted the selection of the suitable cover films and showed a recommended one among some films. As an application example of the chip, we introduced imaging observation of muscular activities of animals enclosing the microfluidic channel of the worm sheet, as well as the microbeam irradiation. These examples indicate that the worm sheets have greatly expanded the possibilities for biological experiments.

Immobilization of Live Caenorhabditis elegans Individuals Using an Ultra-thin Polydimethylsiloxane Microfluidic Chip with Water Retention

A series of immobilization methods has been established to allow the targeted irradiation of live Caenorhabditis elegans individuals using a recently developed ultra-thin polydimethylsiloxane microfluidic chip with water retention. This novel on-chip immobilization is also adequate for imaging observations. The detailed treatment and application examples of the chip are explained.

Radiation is widely used for biological applications and for ion-beam breeding, and among these methods, microbeam irradiation represents a powerful means ...

An Automated Method to Perform The In Vitro Micronucleus Assay using Multispectral Imaging Flow Cytometry

The in vitro micronucleus (MN) assay is often used to evaluate cytotoxicity and genotoxicity but scoring the assay via manual microscopy is laborious and introduces uncertainty in results due to variability between scorers. To remedy this, automated slide-scanning microscopy as well as conventional flow cytometry methods have been introduced in an attempt to remove scorer bias and improve throughput. However, these methods have their own inherent limitations such as inability to visualize the cytoplasm of the cell and the lack of visual MN verification or image data storage with flow cytometry. Multispectral Imaging Flow Cytometry (MIFC) has the potential to overcome these limitations. MIFC combines the high resolution fluorescent imagery of microscopy with the statistical robustness and speed of conventional flow cytometry. In addition, all collected imagery can be stored in dose-specific files. This paper describes the protocol developed to perform a fully automated version of the MN assay on MIFC. Human lymphoblastoid TK6 cells were enlarged using a hypotonic solution (75 mM KCl), fixed with 4% formalin and the nuclear content was stained with Hoechst 33342. All samples were run in suspension on the MIFC, permitting acquisition of high resolution images of all key events required for the assay (e.g. binucleated cells with and without MN as well as mononucleated and polynucleated cells). Images were automatically identified, categorized and enumerated in the MIFC data analysis software, allowing for automated scoring of both cytotoxicity and genotoxicity. Results demonstrate that using MIFC to perform the in vitro MN assay allows statistically significant increases in MN frequency to be detected at several different levels of cytotoxicity when compared to solvent controls following exposure of TK6 cells to Mitomycin C and Colchicine, and that no significant increases in MN frequency are observed following exposure to Mannitol.

The in vitro micronucleus assay is a well-established method for evaluating genotoxicity and cytotoxicity but scoring the assay using manual microscopy is laborious and suffers from subjectivity and inter-scorer variability. This paper describes the protocol developed to perform a fully automated version of the assay using multispectral imaging flow cytometry.

The in vitro micronucleus (MN) assay is often used to evaluate cytotoxicity and genotoxicity but scoring the assay via manual microscopy is laborious and ...

Assembly of Cell Mimicking Supported and Suspended Lipid Bilayer Models for the Study of Molecular Interactions

Model cell membranes are a useful screening tool with applications ranging from early drug discovery to toxicity studies. The cell membrane is a crucial protective barrier for all cell types, separating the internal cellular components from the extracellular environment. These membranes are composed largely of a lipid bilayer, which contains outer hydrophilic head groups and inner hydrophobic tail groups, along with various proteins and cholesterol. The composition and structure of the lipids themselves play a crucial role in regulating biological function, including interactions between cells and the cellular microenvironment, which may contain pharmaceuticals, biological toxins, and environmental toxicants. In this study, methods to formulate uni-lipid and multi-lipid supported and suspended cell mimicking lipid bilayers are described. Previously, uni-lipid phosphatidylcholine (PC) lipid bilayers as well as multi-lipid placental trophoblast-inspired lipid bilayers were developed for use in understanding molecular interactions. Here, methods for achieving both types of bilayer models will be presented. For cell mimicking multi-lipid bilayers, the desired lipid composition is first determined via lipid extraction from primary cells or cell lines followed by liquid chromatography-mass spectrometry (LC-MS). Using this composition, lipid vesicles are fabricated using a thin-film hydration and extrusion method and their hydrodynamic diameter and zeta potential are characterized. Supported and suspended lipid bilayers can then be formed using quartz crystal microbalance with dissipation monitoring (QCM-D) and on a porous membrane for use in a parallel artificial membrane permeability assay (PAMPA), respectively. The representative results highlight the reproducibility and versatility of in vitro cell membrane lipid bilayer models. The methods presented can aid in rapid, facile assessment of the interaction mechanisms, such as permeation, adsorption, and embedment, of various molecules and macromolecules with a cell membrane, helping in the screening of drug candidates and prediction of potential cellular toxicity.

This protocol describes the formation of cell mimicking uni-lipid and multi-lipid vesicles, supported lipid bilayers, and suspended lipid bilayers. These in vitro models can be adapted to incorporate a variety of lipid types and can be used to investigate various molecule and macromolecule interactions.

Model cell membranes are a useful screening tool with applications ranging from early drug discovery to toxicity studies. The cell membrane is a crucial ...