Name: transport properties of ibuprofen encapsulated in cyclodextrin nanosponge hydrogels: a proton hr-mas nmr spectroscopy study
Uploaded: 2016-08-15T13:00:00
Description: Watch this Scientific Journal Video about Transport Properties of Ibuprofen Encapsulated in Cyclodextrin Nanosponge Hydrogels: A Proton HR-MAS NMR Spectroscopy Study at JoVE.com

The authors gratefully acknowledge PRIN 2010-2011 NANOMED prot. 2010 FPTBSH and PRIN 2010-2011 PROxy prot. 2010PFLRJR_005 for funding.

1. Synthesis of CDNSEDTA Polymers
<ol>
	<li>Dry &#946;-cyclodextrin (&#946;-CD) in oven at 80 &#176;C for 4 hr before use. Dry 500 ml of dimethylsulfoxide (DMSO) and 100 ml of triethylamine (Et3N) over molecular sieves (4 &#197;) for 24 hr before using them in the protocol.</li>
	<li>Introduce 25 ml of DMSO into a 50 ml one-neck round-bottom flask. Under magnetic stirring, add 5.675 g of &#946;-CD (5 mmol). In order to reduce the formation of lumps, add the &#946;-CD powder in small portions to DMSO.</li>
	<...

<ol>
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Chem. 56, 209-213 (2006).</li><li>Trotta, F., 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=Cyclodextrin-based+nanosponges+as+a+vehicle+for+antitumoral+drugs.">Cyclodextrin-based nanosponges as a vehicle for antitumoral drugs.</a> Patent WO. , (2009).</li><li>Vyas, A., Shailendra, S., Swarnlata, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cyclodextrin+based+novel+drug+delivery+systems.">Cyclodextrin based novel drug delivery systems.</a> J. Incl. Phenom. Macrocycl. Chem. 62, 23-42 (2008).</li><li>Swaminathan, S., Vavia, P. 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Biot. 82, 382-388 (2007).</li><li>Lehmann, S., Seiffert, S., Richtering, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spatially+Resolved+Tracer+Diffusion+in+Complex+Responsive+Hydrogels.">Spatially Resolved Tracer Diffusion in Complex Responsive Hydrogels.</a> J. Am. Chem. Soc. 134, 15963-15969 (2012).</li><li>Ferrer, G. G., Pradas, M. M., Ribelles, J. L. G., Colomer, F. R., Castilla-Cortazar, I., Vidaurre, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Influence+of+the+nature+of+the+porous+confining+network+on+the+sorption,+diffusion+and+mechanical+properties+of+hydrogel+IPNs.">Influence of the nature of the porous confining network on the sorption, diffusion and mechanical properties of hydrogel IPNs.</a> Eur. Polym. J. 46, 774-782 (2010).</li><li>Santoro, M., Marchetti, P., Rossi, F., Perale, G., Castiglione, F., Mele, A., Masi, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Smart+approach+to+evaluate+drug+diffusivity+in+injectable+agar-carbomer+hydrogels+for+drug+delivery.">Smart approach to evaluate drug diffusivity in injectable agar-carbomer hydrogels for drug delivery.</a> J. Phys. Chem B. 115, 2503-2510 (2011).</li><li>Johnson, C. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diffusion+ordered+nuclear+magnetic+resonance+spectroscopy:+principles+and+applications.">Diffusion ordered nuclear magnetic resonance spectroscopy: principles and applications.</a> Prog. Nucl. Magn. Reson. Spectroscopy. 34, 203-256 (1999).</li><li>Viel, S., Ziarelli, F., Caldarelli, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhanced+diffusion-edited+NMR+spectroscopy+of+mixtures+using+chromatographic+stationary+phases.">Enhanced diffusion-edited NMR spectroscopy of mixtures using chromatographic stationary phases.</a> Proc. Natl. Acad. Sci. U. S. A. 100, 9696-9698 (2003).</li><li>Alam, T. M., Hibbs, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+heterogeneous+solvent+diffusion+environments+in+anion+exchange+membranes.">Characterization of heterogeneous solvent diffusion environments in anion exchange membranes.</a> Macromolecules. 47, 1073-1084 (2014).</li><li>Ferro, M., Castiglione, F., Punta, C., Melone, L., Panzeri, W., Rossi, B., Trotta, F., Mele, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anomalous+diffusion+of+Ibuprofen+in+cyclodextrin+nanosponges+hydrogels:+an+HR-MAS+NMR+study.">Anomalous diffusion of Ibuprofen in cyclodextrin nanosponges hydrogels: an HR-MAS NMR study.</a> Beilstein J. Org. Chem. 10, 2715-2723 (2014).</li><li>Wolf, G., Kleinpeter, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pulsed+Field+Gradient+NMR+Study+of+Anomalous+Diffusion+in+a+Lecithin-Based+Microemulsion.">Pulsed Field Gradient NMR Study of Anomalous Diffusion in a Lecithin-Based Microemulsion.</a> Langmuir. 21, 6742-6752 (2005).</li><li>Rossi, F., Castiglione, F., Ferro, M., Marchini, P., Mauri, E., Moioli, M., Mele, A., Masi, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Drug-Polymer+interactions+in+hydrogel-based+drug-delivery+systems:+an+experimental+and+theoretical+study.">Drug-Polymer interactions in hydrogel-based drug-delivery systems: an experimental and theoretical study.</a> Chem. Phys. Chem. , (2015).</li></ol>

We present an experimental methodology to determine the diffusion regime of a small drug molecule encapsulated inside two representative formulations of CDNSEDTA hydrogels. HR-MAS PGSE NMR allows the determination of the mean square displacement of small molecules in a given diffusion time (in the range of a few milliseconds up to second), then monitoring distances in the micrometer scales. In the range observed (50 - 170 msec) only one type of motion is observed for each studied system. It should be stressed, however, t...

There is a growing interest in the design and formulation of polymeric systems capable of entrapping, via non-covalent interactions, small molecules with potential biochemical activity. Such materials are expected to find applications in the transport of the active principle to selective target and release upon the action of external stimuli, such as pH variations, temperature, etc. In this context, hydrogels turned out to be versatile and powerful materials for nanomedicine in view of controlled release of drugs1. The formation of polymeric hydrogels can be achieved by interconnecting the macromolecular chains by i) physical, non-covalent interactions such as hydrogen bonds, ii) covalent cross-linking of the chains leading to a three-dimensional network able to swell in the presence of an aqueous solution or iii) a combination of the two mentioned methods2-4.
A particularly versatile class of three-dimensional, swellable polymers for the encapsulation of organic and inorganic species can be obtained starting from natural &#946;-cyclodextrin (&#946;-CD) via condensation with suitable, activated derivatives of a tetracarboxylic acid5-8 giving rise to cyclodextrin nanosponges (CDNS). The synthesis, characterization and application of CDNS is a consolidated research theme of our group. The past few years&#39; results indicate that CDNS show intriguing properties of swelling, absorption/inclusion of chemicals, and release of small drug molecules, with applications in controlled release of pharmaceutical active ingredients9-11 and environmental chemistry12-14.
Given these premises, two major issues to be addressed concern the efficient loading of the active compound in the polymeric gel and an improved understanding of solutes mobility in the gel matrices15. The literature provides both experimental studies and theories related to diffusion mechanisms of small molecules in macromolecular networks16,17. Pulsed field-gradient spin-echo (PGSE) NMR spectroscopy is a well-established structural method widely used to study the translational diffusion of small molecules in solvents18 or the self-diffusion of pure liquids. The recent developments of high resolution magic angle spinning (HR-MAS) NMR technology made it possible to collect high resolution NMR data of mobile molecules in heterogeneous suspensions19, gels and swellable polymers20,21. Indeed, the experimental setup combining HR-MAS NMR spectroscopy and the PGSE pulse sequence provides a unique opportunity to observe the solute molecules in the host&#39;s molecular environment. Important data on the transport properties of the entrapped drug molecule within a gel matrix can thus be obtained. High quality experimental data can thus be obtained allowing a more rational design of nanostructured host-guest systems.
In the present work we describe the detailed protocols for the following steps: i) synthesis and purification of two different formulation of CDNS cross-linked with EDTA polymers (Figure 1), referred to as CDNSEDTA, and characterized by different CD/cross linker molar ratio: 1:4 (CDNSEDTA 1:4) and 1:8 (CDNSEDTA 1:8); ii) the preparation of drug-loaded hydrogels for both CDNSEDTA 1:4 and CDNSEDTA 1:8. In this step we used, as model drug molecule, the popular non-steroidal anti-inflammatory ibuprofen sodium salt (IP); iii) the thorough investigation of the transport properties of IP within the CDNSEDTA hydrogels via PGSE-HRMAS NMR spectroscopy. The method we propose here is based on the measurement of the mean square displacement (MSD) of the encapsulated drug within the hydrogel followed by the analysis of the time dependence of the MSD.
We wish to stress that the methodology outlined above - which is focused on the time dependence of the drug&#39;s MDS in the matrix - provides a broader spectrum of information compared to the consolidated methodology based on the determination of the drug&#39;s diffusion coefficient only. We recently demonstrated21 that this approach allowed for the discrimination of normal and anomalous diffusion regimes experienced by IP confined in CDNS hydrogels.
We thus believe that the step-by-step description of polymer synthesis/purification, formation of the drug-loaded hydrogels, HR-MAS NMR characterization and data processing of MDS data, is a powerful toolkit for scientists interested in characterizing nanostructured systems for the confinement and release of small molecules.

<table border="0" cellpadding="0" cellspacing="0" width="657">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">HR-MAS probe</td>
			<td style="width:113px;">BRUKER</td>
			<td style="width:161px;">N/A</td>
			<td style="width:167px;">Probe for NMR measurements on semi-solid samples</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">NMR Spectrometer</td>
			<td style="width:113px;">BRUKER</td>
			<td style="width:161px;">DRX 500</td>
			<td>FT NMR spectrometer for liquid ans semi-solis state</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">&#946;-cyclodextrin (&#946;-CD)</td>
			<td style="width:113px;">Alfa-Aesar</td>
			<td style="width:161px;">J63161</td>
			<td>Reagent</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Ethylenediaminetetracetic (EDTA) dianhydride</td>
			<td style="width:113px;">Sigma-Aldrich</td>
			<td align="right" style="width:161px;">332046</td>
			<td>Reagent</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Dimethylsulfoxide (DMSO)</td>
			<td style="width:113px;">Alfa-Aesar</td>
			<td style="width:161px;">D0798</td>
			<td>Solvent</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Triethylamine</td>
			<td style="width:113px;">Sigma-Aldrich</td>
			<td align="right" style="width:161px;">471283</td>
			<td>Base (reagent)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Ibuprofen (IP) sadium salt</td>
			<td style="width:113px;">Sigma-Aldrich</td>
			<td style="width:161px;">I1892</td>
			<td>Antinflammatory drug</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Excel 2010</td>
			<td style="width:113px;">Microsoft</td>
			<td style="width:161px;">N/A</td>
			<td>speadsheet for data analysis</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Origin 8 SR0</td>
			<td style="width:113px;">OriginLab Co.</td>
			<td style="width:161px;"></td>
			<td>speadsheet for data analysis</td>
		</tr>
	</tbody>
</table>

transport properties of ibuprofen encapsulated in cyclodextrin nanosponge hydrogels: a proton hr-mas nmr spectroscopy study

The chemical cross-linking of &#946;-cyclodextrin (&#946;-CD) with ethylenediaminetetraacetic dianhydride (EDTA) led to branched polymers referred to as cyclodextrin nanosponges (CDNSEDTA). Two different preparations are described with 1:4 and 1:8 CD-EDTA molar ratios. The corresponding cross-linked polymers were contacted with 0.27 M aqueous solution of ibuprofen sodium salt (IP) leading to homogeneous, colorless, drug loaded hydrogels.
The systems were characterized by high resolution magic angle spinning (HR-MAS) NMR spectroscopy. Pulsed field gradient spin echo (PGSE) NMR spectroscopy was used to determine the mean square displacement (MSD) of IP inside the polymeric gel at different observation times td. The data were further processed in order to study the time dependence of MSD: MSD = f(td). The proposed methodology is useful to characterize the different diffusion regimes that, in principle, the solute may experience inside the hydrogel, namely normal or anomalous diffusion. The full protocols including the polymer preparation and purification, the obtainment of drug-loaded hydrogels, the NMR sample preparation, the measurement of MSD by HR-MAS NMR spectroscopy and the final data processing to achieve the time dependence of MSD are here reported and discussed. The presented experiments represent a paradigmatic case and the data are discussed in terms of innovative approach to the characterization of the transport properties of an encapsulated guest within a polymeric host of potential application for drug delivery.

We first applied this methodology to the IP drug molecule dissolved in water solution in order to verify the viability of this approach. A full description of the representative results can be found in ref. 21. Rather, we will focus here on the methodological aspects and the nuts-and-bolts approach to data collection and data analysis. Figure 3 shows, on a semi-logarithmic scale, the normalized experimental signal decays I(q, td)/I(0, td) as a functi...

Watch this Scientific Journal Video about Transport Properties of Ibuprofen Encapsulated in Cyclodextrin Nanosponge Hydrogels: A Proton HR-MAS NMR Spectroscopy Study at JoVE.com

Transport Properties of Ibuprofen Encapsulated in Cyclodextrin Nanosponge Hydrogels: A Proton HR-MAS NMR Spectroscopy Study

The motion regimes of ibuprofen encapsulated in &#946;-cyclodextrin nanosponges polymer network are investigated using pulsed-field-gradient spin-echo (PGSE) NMR technique. Synthesis, purification, drug loading, implementation of the NMR pulse sequence and data analysis to work out the mean square displacement of the drug at several observation times are described in detail.

The chemical cross-linking of &#946;-cyclodextrin (&#946;-CD) with ethylenediaminetetraacetic dianhydride (EDTA) led to branched polymers referred to as ...

The overall goal of this work is to show the synthesis of cyclodextrin nanosponges, convert them into drug-loaded hydrogels, and to study the drug diffusivity inside the hydrogel by high-resolution magic angle spinning, nuclear magnetic resonance spectroscopy. Cyclodextrin nanosponge are prepared by step-growth polymerization between cyclodextrins, or CDs, and the EDTA DNA dried. If we don't mention, our network of CD units is formic, capable to absorb and release organic and inorganic species.The main advantage of high-resolution magic angle spinning NMR is to monitor the transfer property of the encapsulated drug within a polymeric host with potential interest for drug delivery. The synthetic approach is very simple, and it is performed at room temperature. The step-growth polymerization reaction takes place in about 10 minutes.We have chosen ibuprofen as an example of a drug trapped in polymeric hydrogen metrics, representative of a really six car fold down delivery. Dry beta cyclodextrin in an oven at 100 degrees Celsius up to a constant weight. Also, dry 250 milliliters of DMSO, and 100 milliliters of triethylamine over four Angstrom molecular sieves for 24 hours before using them in the protocol.Introduce 25 milliliters of DMSO into a 50-milliliter, one-neck round bottom flask. Under magnetic stirring, add 5.675 grams of beta-cyclodextrin. Add the beta-cyclodextrin powder in small portions to DMSO to reduce the formation of lumps.After about 30 minutes, add six milliliters of triethylamine to the homogenous solution using a 10 milliliter graduated pipette. Plunge the flask into a water bath maintained at room temperature, and keep the mixture under stirring for 15 minutes. For preparation of cyclodextrin nanosponge one-four, add 5.124 grams of EDTA dianhydride under intense stirring.And for preparation of cyclodextrin nanosponge one-eight, add 10.248 grams of EDTA dianhydride under intense stirring. After three hours, remove the solid material, which is the cyclodextrin nanosponge, from the flask using a spatula and crush it grossly with a mortar and pestle. Wash the solid material in an acetone bath, then wash and filter the solid material on filter paper.After drying all the solid material in the air at room temperature for 48 hours, crush the dried material finely using a mortar and pestle. Then, keep it under vacuum for two hours at 45 degrees Celsius. For high-resolution magic angle spinning NMR sample preparation, first prepare a solution of 0.27 molar ibuprofen sodium salt in deuterated water.Add 20 milligrams of cyclodextrin nanosponge one-four, and two milligrams of anhydrous sodium carbonate to 150 microliters of the solution in a two milliliter glass vial. Mix the contents of the vial with a small spatula to homogenize it. Repeat this process for the cyclodextrin nanosponge one-eight polymer.Obtaining a homogenous, perfectly swollen hydrogel is the first key step for a good HR mass NMR spectrum. The hydrogel should be placed in the NMR rotor very carefully, avoiding bubbles which may cause incorrect rotor spinning. Insert the gel into a five millimeter NMR rotor suitable for HR mass experiments using a small spatula.Then, insert the rotor into the magnet of the NMR spectrometer. Once in the magnet, set the rotor in rotation by a pneumatic unit up to 4, 000 hertz. To perform HR mass proton NMR experiments, set up the instrumental parameters with a rotor spinning speed of four kilohertz at the mass pneumatic control unit, and a sample temperature at 305 kelvin in the variable temperature unit.Run a one-dimensional spectrum, quire the diffusion HR mass spectra of ibuprofen in cyclodextrin nanosponge one-Four and cyclodextrin nanosponge one-eight hydrogels by using the pulsed gradient spin-echo pulse sequence on the proton resonance. The diffusion experiments are performed by using the BP led pulse sequence. This is a pseudo two-dimensional experiment with a gradient ramp increasing linearly from 2%to 100%gradient strength in the indirect dimension.The signal intensity is attenuated depending on the diffusion time and gradient pulse P30. The optimization of these parameters is required before properly running an experiment. The optimization is done by running two one-dimensional measurements, in which the diffusion time is kept constant while P30 is varied.Variable diffusion time measurements are carried out by incrementing the diffusion time in the range of 50 to 200 milliseconds. For each experiment, an array of 32 spectra is collected. Then, process the data as described in the text protocol.The basic pulsed field gradient spin-echo experiment allows for measurement of the molecular mean-squared displacement of ibuprofen in the hydrogels. The NMR signal intensity decays as the gradient strength increases. The decay fitting provides the molecular mean-squared displacement, indicated as Z-squared.In turn, the mean-squared displacement is related to the type of diffusion regime. The alpha exponent is obtained experimentally by a log-log linear regression of the mean-squared displacement as a function of the diffusion time. The value of the alpha exponent is a descriptor of the diffusive regime observed for ibuprofen in the hydrogel matrix.Isotropic unrestricted diffusion exists when alpha equals one. A subdiffusive regime is indicated for an alpha value of less than one. And a superdiffusive regime is represented by an alpha value of greater than one.Ibuprofen entrapped in the hydrogel matrix shows two different diffusion regimes according to the polymer preparation. Hydrogels of nanosponges one-four are represented by a subdiffusive regime. Conversely, hydrogels of nanosponges one-eight are characterized by a slightly superdiffusive regime.Once mastered, this reaction can be done in high-yield and purity in one hour if it is performed properly. The materials show interesting capability of water uptake by forming viscous hydrogels, in which, biologically active molecules can be easily incorporated. The molecular state in the transfer properties of a biologically active molecule encapsulated in such polymeric matrixes can be studied experimentally by using HMS NMR techniques.The NMR results on the diffusion of ibuprofen in the hydrogels prepared from cyclodextrine nanosponges indicate that the diffusion can be modulated by a suitable preparation of the polymers. Ibuprofen shows both subdiffusive and superdiffusive regime in cyclodextrin nanosponges hydrogels. This finding can be exploited for original design of the release properties of cyclodextrin nanosponges hydrogen scaffold.

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Bioengineering

Tracking Hypoxic Signaling within Encapsulated Cell Aggregates

In Diabetes mellitus type 1, autoimmune destruction of the pancreatic &beta;-cells results in loss of insulin production and potentially lethal hyperglycemia. As an alternative treatment option to exogenous insulin injection, transplantation of functional pancreatic tissue has been explored1,2. This approach offers the promise of a more natural, long-term restoration of normoglycemia. Protection of the donor tissue from the host's immune system is required to prevent rejection and encapsulation is a method used to help achieve this aim.
Biologically-derived materials, such as alginate3 and agarose4, have been the traditional choice for capsule construction but may induce inflammation or fibrotic overgrowth5 which can impede nutrient and oxygen transport. Alternatively, synthetic poly(ethylene glycol) (PEG)-based hydrogels are non-degrading, easily functionalized, available at high purity, have controllable pore size, and are extremely biocompatible,6,7,8. As an additional benefit, PEG hydrogels may be formed rapidly in a simple photo-crosslinking reaction that does not require application of non-physiological temperatures6,7. Such a procedure is described here. In the crosslinking reaction, UV degradation of the photoinitiator, 1-[4-(2-Hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one (Irgacure 2959), produces free radicals which attack the vinyl carbon-carbon double bonds of dimethacrylated PEG (PEGDM) inducing crosslinking at the chain ends. Crosslinking can be achieved within 10 minutes. PEG hydrogels constructed in such a manner have been shown to favorably support cells7,9, and the low photoinitiator concentration and brief exposure to UV irradiation is not detrimental to viability and function of the encapsulated tissue10. While we methacrylate our PEG with the method described below, PEGDM can also be directly purchased from vendors such as Sigma.
An inherent consequence of encapsulation is isolation of the cells from a vascular network. Supply of nutrients, notably oxygen, is therefore reduced and limited by diffusion. This reduced oxygen availability may especially impact &beta;-cells whose insulin secretory function is highly dependent on oxygen11-13. Capsule composition and geometry will also impact diffusion rates and lengths for oxygen. Therefore, we also describe a technique for identifying hypoxic cells within our PEG capsules. Infection of the cells with a recombinant adenovirus allows for a fluorescent signal to be produced when intracellular hypoxia-inducible factor (HIF) pathways are activated14. As HIFs are the primary regulators of the transcriptional response to hypoxia, they represent an ideal target marker for detection of hypoxic signaling15. This approach allows for easy and rapid detection of hypoxic cells. Briefly, the adenovirus has the sequence for a red fluorescent protein (Ds Red DR from Clontech) under the control of a hypoxia-responsive element (HRE) trimer. Stabilization of HIF-1 by low oxygen conditions will drive transcription of the fluorescent protein (Figure 1). Additional details on the construction of this virus have been published previously15. The virus is stored in 10% glycerol at -80&deg; C as many 150 &mu;L aliquots in 1.5 mL centrifuge tubes at a concentration of 3.4 x 1010 pfu/mL. 
Previous studies in our lab have shown that MIN6 cells encapsulated as aggregates maintain their viability throughout 4 weeks of culture in 20% oxygen. MIN6 aggregates cultured at 2 or 1% oxygen showed both signs of necrotic cells (still about 85-90% viable) by staining with ethidium bromide as well as morphological changes relative to cells in 20% oxygen. The smooth spherical shape of the aggregates displayed at 20% was lost and aggregates appeared more like disorganized groups of cells. While the low oxygen stress does not cause a pronounced drop in viability, it is clearly impacting MIN6 aggregation and function as measured by glucose-stimulated insulin secretion15. Western blot analysis of encapsulated cells in 20% and 1% oxygen also showed a significant increase in HIF-1&alpha; for cells cultured in the low oxygen conditions which correlates with the expression of the DsRed DR protein.

A method for photo-encapsulation of cells in a crosslinked PEG hydrogel is described. Hypoxic signaling within encapsulated murine insulinoma (MIN6) aggregates is tracked using a fluorescent marker system. This system allows serial examination of cells within a hydrogel scaffold and correlation of hypoxic signaling with changes in cell phenotype.

In Diabetes mellitus type 1, autoimmune destruction of the pancreatic &beta;-cells results in loss of insulin production and potentially lethal ...

Fluorescence-quenching of a Liposomal-encapsulated Near-infrared Fluorophore as a Tool for In Vivo Optical Imaging

Optical imaging offers a wide range of diagnostic modalities and has attracted a lot of interest as a tool for biomedical imaging. Despite the enormous number of imaging techniques currently available and the progress in instrumentation, there is still a need for highly sensitive probes that are suitable for in vivo imaging. One typical problem of available preclinical fluorescent probes is their rapid clearance in vivo, which reduces their imaging sensitivity. To circumvent rapid clearance, increase number of dye molecules at the target site, and thereby reduce background autofluorescence, encapsulation of the near-infrared fluorescent dye, DY-676-COOH in liposomes and verification of its potential for in vivo imaging of inflammation was done. DY-676 is known for its ability to self-quench at high concentrations. We first determined the concentration suitable for self-quenching, and then encapsulated this quenching concentration into the aqueous interior of PEGylated liposomes. To substantiate the quenching and activation potential of the liposomes we use a harsh freezing method which leads to damage of liposomal membranes without affecting the encapsulated dye. The liposomes characterized by a high level of fluorescence quenching were termed Lip-Q. We show by experiments with different cell lines that uptake of Lip-Q is predominantly by phagocytosis which in turn enabled the characterization of its potential as a tool for in vivo imaging of inflammation in mice models. Furthermore, we use a zymosan-induced edema model in mice to substantiate the potential of Lip-Q in optical imaging of inflammation in vivo. Considering possible uptake due to inflammation-induced enhanced permeability and retention (EPR) effect, an always-on liposome formulation with low, non-quenched concentration of DY-676-COOH (termed Lip-dQ) and the free DY-676-COOH were compared with Lip-Q in animal trials.

Fluorescence-quenching of a Liposomal-encapsulated Near-infrared Fluorophore as a Tool for In Vivo Optical Imaging

The use of fluorophores for in vivo imaging can be greatly limited by opsonization, rapid clearance, low detection sensitivity and cytotoxic effects on the host. Encapsulation of fluorophores in liposomes by film hydration and extrusion leads to fluorescence quenching and protection which enables in vivo imaging with high detection sensitivity.

Optical imaging offers a wide range of diagnostic modalities and has attracted a lot of interest as a tool for biomedical imaging. Despite the enormous ...

Light-mediated Formation and Patterning of Hydrogels for Cell Culture Applications

Click chemistries have been investigated for use in numerous biomaterials applications, including drug delivery, tissue engineering, and cell culture. In particular, light-mediated click reactions, such as photoinitiated thiol&#8722;ene and thiol&#8722;yne reactions, afford spatiotemporal control over material properties and allow the design of systems with a high degree of user-directed property control. Fabrication and modification of hydrogel-based biomaterials using the precision afforded by light and the versatility offered by these thiol&#8722;X photoclick chemistries are of growing interest, particularly for the culture of cells within well-defined, biomimetic microenvironments. Here, we describe methods for the photoencapsulation of cells and subsequent photopatterning of biochemical cues within hydrogel matrices using versatile and modular building blocks polymerized by a thiol&#8722;ene photoclick reaction. Specifically, an approach is presented for constructing hydrogels from allyloxycarbonyl (Alloc)-functionalized peptide crosslinks and pendant peptide moieties and thiol-functionalized poly(ethylene glycol) (PEG) that rapidly polymerize in the presence of lithium acylphosphinate photoinitiator and cytocompatible doses of long wavelength ultraviolet (UV) light. Facile techniques to visualize photopatterning and quantify the concentration of peptides added are described. Additionally, methods are established for encapsulating cells, specifically human mesenchymal stem cells, and determining their viability and activity. While the formation and initial patterning of thiol-alloc hydrogels are shown here, these techniques broadly may be applied to a number of other light and radical-initiated material systems (e.g., thiol-norbornene, thiol-acrylate) to generate patterned substrates.

We describe a sequential process for light-mediated formation and subsequent biochemical patterning of synthetic hydrogel matrices for three-dimensional cell culture applications. The construction and modification of hydrogels with cytocompatible photoclick chemistry is demonstrated. Additionally, facile techniques to quantify and observe patterns and determine cell viability within these hydrogels are presented.

Click chemistries have been investigated for use in numerous biomaterials applications, including drug delivery, tissue engineering, and cell culture. In ...

Tunable Hydrogels from Pulmonary Extracellular Matrix for 3D Cell Culture

Here we present a method for establishing multiple component cell culture hydrogels for in vitro lung cell culture. Beginning with healthy en bloc lung tissue from porcine, rat, or mouse, the tissue is perfused and submerged in subsequent chemical detergents to remove the cellular debris. Histological comparison of the tissue before and after processing confirms removal of over 95% of double stranded DNA and alpha galactosidase staining suggests the majority of cellular debris is removed. After decellularization, the tissue is lyophilized and then cryomilled into a powder. The matrix powder is digested for 48 hr in an acidic pepsin digestion solution and then neutralized to form the pregel solution. Gelation of the pregel solution can be induced by incubation at 37 &#176;C and can be used immediately following neutralization or stored at 4 &#176;C for up to two weeks. Coatings can be formed using the pregel solution on a non-treated plate for cell attachment. Cells can be suspended in the pregel prior to self-assembly to achieve a 3D culture, plated on the surface of a formed gel from which the cells can migrate through the scaffold, or plated on the coatings. Alterations to the strategy presented can impact gelation temperature, strength, or protein fragment sizes. Beyond hydrogel formation, the hydrogel stiffness may be increased using genipin.

This is a method to create a 3-dimensional cell culture scaffold from pulmonary extracellular matrix. Intact lung is processed into hydrogels that can support the growth of cells in three-dimensions.

Here we present a method for establishing multiple component cell culture hydrogels for in vitro lung cell culture. Beginning with healthy en bloc lung ...

Targeted Plasma Membrane Delivery of a Hydrophobic Cargo Encapsulated in a Liquid Crystal Nanoparticle Carrier

The controlled delivery of drug/imaging agents to cells is critical for the development of therapeutics and for the study of cellular signaling processes. Recently, nanoparticles (NPs) have shown significant promise in the development of such delivery systems. Here, a liquid crystal NP (LCNP)-based delivery system has been employed for the controlled delivery of a water-insoluble dye, 3,3&#8242;-dioctadecyloxacarbocyanine perchlorate (DiO), from within the NP core to the hydrophobic region of a plasma membrane bilayer. During the synthesis of the NPs, the dye was efficiently incorporated into the hydrophobic LCNP core, as confirmed by multiple spectroscopic analyses. Conjugation of a PEGylated cholesterol derivative to the NP surface (DiO-LCNP-PEG-Chol) enabled the binding of the dye-loaded NPs to the plasma membrane in HEK 293T/17 cells. Time-resolved laser scanning confocal microscopy and F&#246;rster resonance energy transfer (FRET) imaging confirmed the passive efflux of DiO from the LCNP core and its insertion into the plasma membrane bilayer. Finally, the delivery of DiO as a LCNP-PEG-Chol attenuated the cytotoxicity of DiO; the NP form of DiO exhibited ~30-40% less toxicity compared to DiOfree delivered from bulk solution. This approach demonstrates the utility of the LCNP platform as an efficient modality for the membrane-specific delivery and modulation of hydrophobic molecular cargos.

A liquid crystal nanoparticle (LCNP) nanocarrier is exploited as a vehicle for the controlled delivery of a hydrophobic cargo to the plasma membrane of living cells.

The controlled delivery of drug/imaging agents to cells is critical for the development of therapeutics and for the study of cellular signaling processes. ...

Synthesis of Hydrogels with Antifouling Properties As Membranes for Water Purification

Hydrogels have been widely utilized to enhance the surface hydrophilicity of membranes for water purification, increasing the antifouling properties and thus achieving stable water permeability through membranes over time. Here, we report a facile method to prepare hydrogels based on zwitterions for membrane applications. Freestanding films can be prepared from sulfobetaine methacrylate (SBMA) with a crosslinker of poly(ethylene glycol) diacrylate (PEGDA) via photopolymerization. The hydrogels can also be prepared by impregnation into hydrophobic porous supports to enhance the mechanical strength. These films can be characterized by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) to determine the degree of conversion of the (meth)acrylate groups, using goniometers for hydrophilicity and differential scanning calorimetry (DSC) for polymer chain dynamics. We also report protocols to determine the water permeability in dead-end filtration systems and the effect of foulants (bovine serum albumin, BSA) on membrane performance.

This paper reports practical methods to prepare hydrogels in freestanding films and impregnated membranes and to characterize their physical properties, including water transport properties.

Hydrogels have been widely utilized to enhance the surface hydrophilicity of membranes for water purification, increasing the antifouling properties and ...

Production of Elastin-like Protein Hydrogels for Encapsulation and Immunostaining of Cells in 3D

Two-dimensional (2D) tissue culture techniques have been essential for our understanding of fundamental cell biology. However, traditional 2D tissue culture systems lack a three-dimensional (3D) matrix, resulting in a significant disconnect between results collected in vitro and in vivo. To address this limitation, researchers have engineered 3D hydrogel tissue culture platforms that can mimic the biochemical and biophysical properties of the in vivo cell microenvironment. This research has motivated the need to develop material platforms that support 3D cell encapsulation and downstream biochemical assays. Recombinant protein engineering offers a unique toolset for 3D hydrogel material design and development by allowing for the specific control of protein sequence and therefore, by extension, the potential mechanical and biochemical properties of the resultant matrix. Here, we present a protocol for the expression of recombinantly-derived elastin-like protein (ELP), which can be used to form hydrogels with independently tunable mechanical properties and cell-adhesive ligand concentration. We further present a methodology for cell encapsulation within ELP hydrogels and subsequent immunofluorescent staining of embedded cells for downstream analysis and quantification.

Recombinant protein-engineered hydrogels are advantageous for 3D cell culture as they allow for complete tunability of the polymer backbone and therefore, the cell microenvironment. Here, we describe the process of recombinant elastin-like protein purification and its application in 3D hydrogel cell encapsulation.

Two-dimensional (2D) tissue culture techniques have been essential for our understanding of fundamental cell biology. However, traditional 2D tissue ...

A Quantitative Fluorescence Microscopy-based Single Liposome Assay for Detecting the Compositional Inhomogeneity Between Individual Liposomes

Most research employing liposomes as membrane model systems or drug delivery carriers relies on bulk read-out techniques and thus intrinsically assumes all liposomes of the ensemble to be identical. However, new experimental platforms able to observe liposomes at the single-particle level have made it possible to perform highly sophisticated and quantitative studies on protein-membrane interactions or drug carrier properties on individual liposomes, thus avoiding errors from ensemble averaging. Here we present a protocol for preparing, detecting, and analyzing single liposomes using a fluorescence-based microscopy assay, facilitating such single-particle measurements. The setup allows for imaging individual liposomes in a massive parallel manner and is employed to reveal intra-sample size and compositional inhomogeneities. Additionally, the protocol describes the advantages of studying liposomes at the single liposome level, the limitations of the assay, and the important features to be considered when modifying it to study other research questions.

This protocol describes the fabrication of liposomes and how these can be immobilized on a surface and imaged individually in a massive parallel manner using fluorescence microscopy. This allows for the quantification of the size and compositional inhomogeneity between single liposomes of the population.

Most research employing liposomes as membrane model systems or drug delivery carriers relies on bulk read-out techniques and thus intrinsically assumes ...

Characterization of Intra-Cartilage Transport Properties of Cationic Peptide Carriers

Several negatively charged tissues in the body, like cartilage, present a barrier to the targeted drug delivery due to their high density of negatively charged aggrecans and, therefore, require improved targeting methods to increase their therapeutic response. Because cartilage has a high negative fixed charge density, drugs can be modified with positively charged drug carriers to take advantage of electrostatic interactions, allowing for enhanced intra-cartilage drug transport. Studying the transport of drug carriers is, therefore, crucial towards predicting the efficacy of drugs in inducing a biological response. We show the design of three experiments which can quantify the equilibrium uptake, depth of penetration and non-equilibrium diffusion rate of cationic peptide carriers in cartilage explants. Equilibrium uptake experiments provide a measure of the solute concentration within the cartilage compared to its surrounding bath, which is useful for predicting the potential of a drug carrier in enhancing therapeutic concentration of drugs in cartilage. Depth of penetration studies using confocal microscopy allow for the visual representation of 1D solute diffusion from the superficial to deep zone of cartilage, which is important for assessing whether solutes reach their matrix and cellular target sites. Non-equilibrium diffusion rate studies using a custom-designed transport chamber enables the measurement of the strength of binding interactions with the tissue matrix by characterizing the diffusion rates of fluorescently labeled solutes across the tissue; this is beneficial for designing carriers of optimal binding strength with cartilage. Together, the results obtained from the three transport experiments provide a guideline for designing optimally charged drug carriers which take advantage of weak and reversible charge interactions for drug delivery applications. These experimental methods can also be applied to evaluate the transport of drugs and drug-drug carrier conjugates. Further, these methods can be adapted for the use in targeting other negatively charged tissues such as meniscus, cornea and the vitreous humor.

This protocol determines equilibrium uptake, depth of penetration and non-equilibrium diffusion rate for cationic peptide carriers in cartilage. Characterization of transport properties is critical for ensuring an effective biological response. These methods can be applied for designing an optimally charged drug carriers for targeting negatively charged tissues.

Several negatively charged tissues in the body, like cartilage, present a barrier to the targeted drug delivery due to their high density of negatively ...

Fragmenting Bulk Hydrogels and Processing into Granular Hydrogels for Biomedical Applications

Granular hydrogels are jammed assemblies of hydrogel microparticles (i.e., &#34;microgels&#34;). In the field of biomaterials, granular hydrogels have many advantageous properties, including injectability, microscale porosity, and tunability by mixing multiple microgel populations. Methods to fabricate microgels often rely on water-in-oil emulsions (e.g., microfluidics, batch emulsions, electrospraying) or photolithography, which may present high demands in terms of resources and costs, and may not be compatible with many hydrogels. This work details simple yet highly effective methods to fabricate microgels using extrusion fragmentation and to process them into granular hydrogels useful for biomedical applications (e.g., 3D printing inks). First, bulk hydrogels (using photocrosslinkable hyaluronic acid (HA) as an example) are extruded through a series of needles with sequentially smaller diameters to form fragmented microgels. This microgel fabrication technique is rapid, low-cost, and highly scalable. Methods to jam microgels into granular hydrogels by centrifugation and vacuum-driven filtration are described, with optional post-crosslinking for hydrogel stabilization. Lastly, granular hydrogels fabricated from fragmented microgels are demonstrated as extrusion printing inks. While the examples described herein use photocrosslinkable HA for 3D printing, the methods are easily adaptable for a wide variety of hydrogel types and biomedical applications.

This work describes straightforward, adaptable, and low-cost methods to fabricate microgels with extrusion fragmentation, process the microgels into injectable granular hydrogels, and apply the granular hydrogels as extrusion printing inks for biomedical applications.

Granular hydrogels are jammed assemblies of hydrogel microparticles (i.e., &#34;microgels&#34;). In the field of biomaterials, granular hydrogels have ...