Name: fabricating superhydrophobic polymeric materials for biomedical applications
Uploaded: 2015-08-28T14:00:00.000+00:00
Duration: 9 min 22 s
Description: Watch this Scientific Journal Video about Fabricating Superhydrophobic Polymeric Materials for Biomedical Applications at JoVE.com

Funding was provided in part by BU and the NIH R01CA149561. The authors wish to thank the electrospinning/electrospraying team including Stefan Yohe, Eric Falde, Joseph Hersey, and Julia Wang for their helpful discussions and contributions to the preparation and characterization of superhydrophobic biomaterials.

1. Synthesizing Functionalizable poly(1,3-glycerol carbonate-co-caprolactone)29 and poly(1,3-glycerol carbonate-co-lactide)27,28.
<ol>
	<li>Monomer synthesis.
	<ol>
		<li>Dissolve cis-2-Phenyl-1,3-dioxan-5-ol (50 g, 0.28 mol, 1 eq.) in 500 ml dry tetrahydrofuran (THF) and stir on ice under nitrogen. Add potassium hydroxide (33.5 g, 0.84 mol, 3 eq.), finely crushed with a mortar and pestle. Place flask in ice bath.</li>
		<li>Add 49.6 ml benzyl bromide (71.32 g, 0.42 mol, 1.5 eq.) drop-wise with stirring on ice. Allow the reaction to warm to room temperature with stirring for 24 hr, under nitrogen.</li>
		<li>Add 150 ml distilled water to dissolve potassium hydroxide and remove the THF by rotary evaporation.</li>
		<li>Extract the remaining material with 200 ml dichloromethane (DCM) in a 1-L separatory funnel. Repeat the extraction twice.</li>
		<li>Dry the organic phase on sodium sulfate.</li>
		<li>Crystallize the product by adding 600 ml absolute ethanol to the solution, mixing well, and storing overnight at -20 &#176;C. The product can be stored at -20 &#176;C for several days before performing subsequent steps.</li>
		<li>Isolate product by vacuum-filtration through a B&#252;chner funnel and dry on high-vacuum. The product can be stored for several days before performing subsequent steps. A typical yield for this step is ~80%.</li>
		<li>In a 1-L round-bottom flask, suspend the product obtained in step 1.1.7. in methanol (300 ml). Add 150 ml of 2 N hydrochloric acid. Reflux at 80 &#176;C for 2 hr.</li>
		<li>Evaporate solvent and place under high-vacuum for 24 hr. The yield for this step is typically &#62;98%.</li>
		<li>Dissolve product of 1.1.9 in THF (650 ml) and transfer to a 2-L round-bottom flask. Place flask on ice bath and stir under nitrogen. Add 22.4 ml ethyl chloroformate (25.6 g, 0.29 mol, 2 eq.) to flask under nitrogen.</li>
		<li>Add 32.8 ml triethylamine (0.29 mol, 2 eq.) to an addition funnel. Mix with an equal volume of THF. Place addition funnel on round-bottom flask and keep under nitrogen.</li>
		<li>With vigorous stirring, carefully dispense triethyamine/THF mixture drop-wise to the round-bottom flask on ice. CAUTION: this is an exothermic reaction. To prevent rapid temperature increase, add the triethylamine/THF solution no faster than 1 drop per second. After adding the full volume, stir the reaction for 4 hr, warming up to room temperature, or for 24 hr.</li>
		<li>Filter out the triethylamine hydrochloride salt using a B&#252;chner funnel. Evaporate the solvent on a rotary evaporator.</li>
		<li>Add dichloromethane (200 ml) to the flask and heat gently until the residue is dissolved. Add 120 ml of diethyl ether while swirling. Store at -20 &#176;C overnight to crystallize the product.</li>
		<li>Filter monomer crystals and re-crystallize before polymerizing. The monomer product can be stored sealed at room temperature for 2 weeks or at -20 &#176;C indefinitely. Confirm product by 1H NMR, mass spectrometry, and elemental analysis. A typical yield for this final step in the monomer synthesis is between 40-60%.</li>
	</ol>
	</li>
	<li>Copolymerization of D,L-lactide/&#949;-caprolactone with 5-benzyloxy-1,3-dioxan-2-one.
	<ol>
		<li>Heat silicone oil bath to 140 &#176;C.</li>
		<li>Measure 2.1 g of 5-benzyloxy-1,3-dioxan-2-one (prepared in 1.1) and add it to a dry 100-ml round-bottom flask. If copolymerizing D,L-lactide, measure out 5.7 g and add to the flask now. Add a magnetic stir bar and seal the flask with a rubber stopper.
		<ol>
			<li>Also measure 240 mg (an excess) of tin(II) ethylhexanoate in a small pear-shaped flask. This polymerization will result in a 20 mol% glycerol carbonate monomer composition. Adjust the masses of monomers to achieve different monomer compositions.</li>
		</ol>
		</li>
		<li>Flush both flasks with nitrogen on a Schlenk manifold for 5 min&#160;and add 4.24 ml &#949;-caprolactone under nitrogen. Evacuate flasks&#8217; atmosphere by applying high-vacuum (300 mTorr) for 15 min&#160;to remove trace water.</li>
		<li>Recharge the flasks&#8217; atmosphere with nitrogen; repeat this cycle twice more.</li>
		<li>Mix 500 &#181;l dry toluene with the tin catalyst under nitrogen.</li>
		<li>Place the monomer flask in the 140 &#176;C oil bath and add catalyst once all solids have melted. The total volume of catalyst mixture delivered should be ~100 &#181;l. Keep at 140 &#176;C for no more than 24 hr, then cool the molten polymer to room temperature. Perform the subsequent steps immediately or at least 24 hr&#160;later.</li>
		<li>Dissolve the polymer in dichloromethane (50 ml) and precipitate into cold methanol (200 ml). Decant supernatant and dry under high-vacuum. The subsequent steps can be performed immediately or at any point. Store polymers in the freezer until further use. The typical polymerization yield/conversion is between 80-95%.</li>
		<li>Perform 1H NMR analysis to determine the co-monomer molar ratios. Dissolve polymer in deuterated chloroform (CDCl3) and integrate the benzylic proton shift of the carbonate monomer at 4.58-4.68 ppm; compare this peak area with that of the methylene peak at 2.3 ppm (PCL) and methyne peak at 5.2 ppm (PLGA).</li>
	</ol>
	</li>
	<li>Polymer modification: deprotection and grafting.
	<ol>
		<li>Dissolve polymer (~7 g) in 120 ml tetrahydrofuran (THF) in a high-pressure hydrogenation vessel. Weigh and add palladium-carbon catalyst (~2 g).</li>
		<li>Add hydrogen to the vessel using a hydrogenation apparatus. Hydrogenate at 50 psi for 4 hr. CAUTION: hydrogen gas is extremely flammable. Seek assistance from persons familiar with this procedure and always inspect the supply lines for possible leaks before performing this experiment.</li>
		<li>Filter out palladium-carbon catalyst using a packed bed of diatomaceous earth. Concentrate the polymer to ~50 ml under rotary evaporation and precipitate into cold methanol. CAUTION: Dry palladium particulates can spontaneously ignite. Keep a wet towel nearby in the event of a flare-up for smothering the flames. Add water to the palladium/carbon filter cake to keep it clumped and to prevent its ignition. Seek assistance from persons familiar with this procedure.</li>
		<li>Decant the supernatant and dry under high-vacuum. Confirm total conversion to free hydroxyl by noting the peak disappearance at 4.65 ppm (1H NMR in CDCl3). These polymers can be used immediately or saved for later use. Yields for this step are &#62;90%.</li>
		<li>Dissolve the polymer and stearic acid (1.5 eq.) in 500 ml dry dichloromethane (DCM). Add N,N&#8217;-dicyclohexylcarbodiimide (DCC, 2.0 eq.) and 3 flakes of 4-dimethylaminopyridine. Stir under nitrogen at room temperature for 24 hr.</li>
		<li>Remove insoluble N,N&#8217;-dicyclohexylcarbourea through a series of repeated filtrations and concentrations. At the end, concentrate the solution to 50 ml.</li>
		<li>Precipitate polymer into cold methanol (~175 ml) and decant the supernatant. Dry the polymer under high-vacuum overnight. Subsequent use of these polymers can be performed at any time, but keep polymers in the freezer for long-term storage. The yield for this final modification step is generally between 85-90%.</li>
	</ol>
	</li>
</ol>

2. Characterizing the Synthesized Copolymers
<ol>
	<li>Weigh out ~10 mg polymer (record the actual mass) and add to aluminum sample pan, then hermetically seal it. Load sample pan and an unloaded (reference) pan into the differential scanning calorimeter.</li>
	<li>Program a temperature ramp and cooling (&#8220;heat/cool/heat&#8221;) cycle: 1) heat from 20 &#176;C to 225 &#176;C at 10 &#176;C/min, 2) cool to -75 &#176;C at 5 &#176;C/min, 3) heat to 225 &#176;C at 10 &#176;C/min.</li>
	<li>Determine melting point (Tm), crystallization (Tc) and glass transition temperatures (Tg), and heat of fusion (&#916;Hf) from the thermal traces (if applicable).</li>
	<li>Dissolve each synthesized copolymer in THF (1 mg/ml) and filter through a 0.02-&#181;m PTFE filter. Inject the solution into a gel permeation chromatography system and compare retention time versus a range of polystyrene standards.</li>
</ol>
3. Preparing Polymer Solutions for Electrospinning/electrospraying27,31
<ol>
	<li>Dissolve polymer(s) at 10-40 wt% in suitable solvent, such as chloroform/methanol (5:1) for PCL or tetrahydrofuran/N,N-dimethylformamide (7:3) for PLGA, overnight. The mass of polymer required for this step will depend on the dimensions of the desired mesh. 
	Note: For example, to produce a 10 cm x 10 cm mesh of approximately 300-micron thickness, 1 gram will typically be required. It is worth noting that material losses may occur in subsequent steps of this protocol, such as during solution transfer to the syringe (especially for viscous solutions), and from dead volumes present in the optional connector tubing and the needle housing itself, which will reduce the yield of the electrospinning process. These reductions in yield may result in up to 20% loss of material, and it is recommended to scale up 1.5-fold to anticipate these losses, and also those losses associated with optimizing the electrospinning parameters when attempting this procedure for the first time.
	<ol>
		<li>Control fiber size by varying the total polymer concentration, with larger fibers expected from more concentrated solutions. For a modest enhancement of hydrophobicity, use 10% (by total polymer mass) superhydrophobic dopant. For extremely hydrophobic/superhydrophobic materials, use 30-50% dopant and/or reduce the total polymer concentration (i.e., reduce fiber size). Subsequent work with these solutions may be performed the next day or within one week thereafter.</li>
		<li>For electrospraying, prepare solutions at lower concentrations (i.e., 2-10%) in a suitable solvent such as chloroform. Like electrospinning, modulate particle size by varying the polymer concentration.</li>
	</ol>
	</li>
	<li>Vortex polymer solution to thoroughly mix. Allow large air bubbles to subside (5 min).</li>
	<li>Load solution into a glass syringe. Depending on solution viscosity, it may be easiest to remove the plunger and pour the solution directly into the syringe. A piece of inert, flexible tubing may aid maneuverability within the electrospinning setup. Invert the syringe to displace air through the hose/needle assembly.</li>
</ol>
4. Electrospinning/electrospraying Polymer Solutions
<ol>
	<li>Load syringe onto syringe pump, set total volume (e.g., 4.5 ml) and the rate (e.g., 5 ml/hr) at which to dispense this solution.</li>
	<li>Cover the collector plate with aluminum foil to ease subsequent removal and transport. Secure the foil with masking tape along the outer edges.</li>
	<li>Attach the high voltage DC (HVDC) supply wire to needle tip. The distance of this needle tip to the collector is an important variable to consider because it 1) affects the electric field at a given voltage, and 2) impacts the evaporation of solvent and consequent drying of fibers during their collection.
	<ol>
		<li>As a first attempt, use a tip-to-collector distance of 15 cm. CAUTION: High voltages and flammable solvents are involved in electrospinning/electrospraying. Provide adequate ventilation to outside exhaust, and never touch the syringe/needle or open the enclosure until absolutely certain the HVDC supply is off.</li>
	</ol>
	</li>
	<li>If electrospinning/electrospraying a large area of coverage, turn on rotating and translating collector drum. Otherwise, proceed to the next step.</li>
	<li>Start the syringe pump.</li>
	<li>Turn on and adjust the high voltage source to achieve an acceptable Taylor Cone. If the solution at the needle tip is sagging, increase the voltage. If multiple jets are forming, reduce the voltage. In addition to these adjustments, it may be necessary to adjust the tip-to-collector distance if the fibers/particles appear wet or if adjusting the voltage does not adequately solve a dragging droplet at the needle tip. 
	Note: For detailed troubleshooting, see the comprehensive electrospinning optimization process by Leach and co-workers47. Electrospraying will generally involve higher voltages and lower solution concentrations than electrospinning.</li>
	<li>Turn off the high voltage source and then the syringe pump and motorized drum (if applicable). Allow the electrospinning enclosure to continue ventilating for 30 min.</li>
	<li>Remove meshes/coatings from collector. Allow trace solvents to evaporate in a hood overnight. Materials can be stored at room temperature for at least two weeks (PLGA) or two months (PCL). Steps 4.5-4.8 may be performed in any order.</li>
</ol>
5. Characterizing Fiber and Particle Size by Light and Scanning Electron Microscopy
<ol>
	<li>Light microscopy
	<ol>
		<li>If producing an electrospun mesh, cut and mount thin portions of it on a glass slide.</li>
		<li>Observe fiber diameter, node characteristics (blobs or discrete), and fiber shape (i.e., beaded, flat, straight/wavy). Ideal electrospun mesh fibers are uniform, straight or wavy, and bead-free.</li>
	</ol>
	</li>
	<li>Scanning electron microscopy (SEM)
	<ol>
		<li>Cut and mount meshes or coated surfaces on aluminum SEM stubs using conductive copper tape. Electrospun fibers and electrosprayed coatings can also be observed by SEM by directly depositing fibers/particles onto the tape in advance.</li>
		<li>Coat the meshes/coatings with a thin (~4 nm) layer of Au/Pd through sputter coating.</li>
		<li>Load stubs into SEM chamber and observe at 1-2 keV. A 250X magnification provides a general topographical assessment of the material, while higher magnifications reveal additional fiber and particle features such as hierarchal patterns for extremely superhydrophobic fibers and interconnectivity for particle coatings.</li>
	</ol>
	</li>
</ol>
6. Determining Non-wetting Properties
<ol>
	<li>Advancing and receding water contact angle measurements using the volume variation method
	<ol>
		<li>Cut thin (0.5 cm x 5 cm) strips of mesh or coated material (if possible) and place on the stage of a contact angle goniometer.</li>
		<li>Capture the water drop profile while dispensing it (from a 24 AWG syringe needle) on the material surface.
		<ol>
			<li>To do this, start with an approximate 5-&#181;l drop, and make contact with the material surface. Continue to slowly add volume (20-25 &#181;l) and capture the droplet image, which represents the advancing water contact angle. The needle tip should be small compared to the droplet, and the capillary length should be greater than the droplet to minimize distortion of droplet shape.</li>
		</ol>
		</li>
		<li>Withdraw this same drop while simultaneously capturing its drop profile. Repeat on discrete surface locations of several samples to report an average value&#8212;typically, 10 measurements of both advancing and receding contact angles are sufficient to characterize these materials.</li>
	</ol>
	</li>
	<li>Determine critical surface tension of materials by modifying probing liquids.
	<ol>
		<li>Prepare solutions varying in ethanol, propylene glycol, or ethylene glycol content, as these mixtures have known surface tensions99-101.
		<ol>
			<li>Alternatively, use solvents with varying surface tensions&#8212;for example, water (72 mN/m), glycerol (64 mN/m), dimethyl sulfoxide (44 mN/m), benzyl alcohol (39 mN/m), 1,4-dioxane (33 mN/m), 1-octanol (28 mN/m), and acetone (25 mN/m). It is important to use solvents that will not dissolve the polymers, as these will confound results. Additionally, it is important to note that, in addition to surface tension, these liquids have different viscosities, which may impact contact angle measurements and is a limitation of this technique.</li>
			<li>Measure the contact angle of these solutions probed on the material surface. Plot contact angle as a function of surface tension.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
7. Detecting Bulk Wetting of Meshes31
<ol>
	<li>Observe water infiltration into 3D meshes using micro-computed tomography (&#181;CT).
	<ol>
		<li>Prepare an 80 mg/ml solution of Ioxaglate (an iodinated contrast agent) in water.</li>
		<li>Submerge meshes in these solutions and incubate at 37 &#176;C; periodically measure contrast agent (water) infiltration by &#181;CT (18 &#181;m3 voxel resolution) using a 70 kVP tube voltage, 114 &#181;A current, and a 300 msec integration time.</li>
		<li>Using image processing software, measure pixel intensity throughout the thickness of the mesh, where bright pixels represent water infiltration. Select a pixel threshold value (~1500) for which higher intensity represents water infiltration.</li>
	</ol>
	</li>
</ol>
8. Testing the Mechanical Properties of Meshes
<ol>
	<li>Cut meshes to 1 cm x 7 cm and place between the grips of a tensile testing apparatus. Measure the exact width, length, and thickness.</li>
	<li>Perform a ramp test of extension on three samples. Plot a stress-strain curve using these data to determine the elastic modulus, ultimate tensile strength, and elongation-at-break.</li>
</ol>

The authors declare that they have no competing financial interests.

Our approach to constructing superhydrophobic materials from biomedical polymers combines synthetic polymer chemistry with the polymer processing techniques of electrospinning and electrospraying. These techniques provide either fibers or particles, respectively. Specifically, polycaprolactone and poly(lactide-co-glycolide) based superhydrophobic materials are prepared using this strategy. By varying the hydrophobic copolymer composition, percent copolymer in the final polymer blend, fiber/particle size, overall...

Superhydrophobic surfaces are generally categorized as exhibiting apparent water contact angles greater than 150&#176; with low contact angle hysteresis. These surfaces are fabricated by introducing high surface roughness on low surface energy materials to establish a resulting air-liquid-solid interface that resists wetting1-6. Depending on the fabrication method, thin or multilayered superhydrophobic surfaces, multilayered superhydrophobic substrate coatings, or even bulk superhydrophobic structures can be prepared. This permanent or semi-permanent water repellency is a useful property that is employed to prepare self-cleaning surfaces7, microfluidic devices8, anti-fouling cell/protein surfaces9,10, drag-reducing surfaces11, and drug delivery devices12-15. Recently, stimuli-responsive superhydrophobic materials are described where the non-wetted to wetted state is triggered by chemical, physical, or environmental cues (e.g., light, pH, temperature, ultrasound, and applied electrical potential/current)14,16-20, and these materials are finding use for additional applications21-25.
The first synthetic superhydrophobic surfaces were prepared by treating material surfaces with methyldihalogenosilanes26, and were of limited value for biomedical applications, as the materials used were not suitable for in vivo use. Herein we describe the preparation of surface and bulk superhydrophobic materials from biocompatible polymers. Our approach entails electrospinning or electrospraying a polymer mixture containing a biodegradable, biocompatible aliphatic polyester as the major component, doped with a hydrophobic copolymer composed of the polyester and a stearate-modified poly(glycerol carbonate)27-30. The fabrication techniques provide the enhanced surface roughness and porosity on and within the fibers or the particles, respectively, while the use of a copolymer dopant provides a low surface energy polymer that blends with the polyester and can be stably electrospun or electrosprayed27,31,32.
Aliphatic biodegradable polyesters such as poly(lactic acid) (PLA), poly(glycolic acid) (PGA), poly(lactic acid-co-glycolic acid) (PLGA), and polycaprolactone (PCL) are polymers used in clinically-approved devices and prominent in biomedical materials research because of their non-toxicity, biodegradability, and ease of synthesis33. PGA and PLGA debuted in the clinic as bioresorbable sutures in the 1960&#8217;s and early 1970&#8217;s, respectively34-37. Since then, these poly(hydroxy acids) have been processed into a variety of other application-specific form factors, such as micro-38,39 and nanoparticles40,41, wafers/discs42, meshes27,43, foams44, and films45.
Aliphatic polyesters, as well as other polymers of biomedical interest, can be electrospun to produce nano- or microfiber mesh structures possessing a high surface area and porosity as well as tensile strength. Table 1 lists the synthetic polymers electrospun for various biomedical applications and their corresponding references. Electrospinning and electrospraying are rapid and commercially-scalable techniques. These two similar techniques rely on applying high voltage (electrostatic repulsion) to overcome surface tension of a polymer solution/melt in a syringe pump setup as it is directed toward a grounded target46,47. When this technique is used in conjunction with low surface energy polymers (hydrophobic polymers such as poly(caprolactone-co-glycerol monostearate)), the resulting materials exhibit superhydrophobicity.
To illustrate this general synthetic and materials processing approach to constructing superhydrophobic materials from biomedical polymers, we describe the synthesis of superhydrophobic polycaprolactone- and poly(lactide-co-glycolide)-based materials as representative examples. The respective copolymer dopants poly(caprolactone-co-glycerol monostearate) and poly(lactide-co-glycerol monostearate) are first synthesized, then blended with polycaprolactone and poly(lactide-co-glycolide), respectively, and finally electrospun or electrosprayed. The resulting materials are characterized by SEM imaging and contact angle goniometry, and tested for in vitro and in vivo biocompatibility. Finally, bulk wetting through three-dimensional superhydrophobic meshes is examined using contrast-enhanced microcomputed tomography.

<table><tbody><tr><td>Silicone oil</td><td>Sigma-Aldrich</td><td>85409</td><td></td></tr><tr><td>Cis-2-Phenyl-1,3-dioxan-5-ol</td><td>Sigma-Aldrich</td><td>13468</td><td></td></tr><tr><td>Benzyl bromide</td><td>Sigma-Aldrich</td><td>B17905</td><td>Toxic, lacrymator/eye irritant, use in chemical fume hood</td></tr><tr><td>Potassium hydroxide</td><td>Sigma-Aldrich</td><td>221473</td><td>Corrosive</td></tr><tr><td>Rotary evaporator</td><td>Buchi</td><td>R-124</td><td></td></tr><tr><td>High-vacuum pump</td><td>Welch</td><td>8907</td><td></td></tr><tr><td>Nitrogen, ultra high purity</td><td>Airgas</td><td>NI UHP300</td><td>Compressed gas</td></tr><tr><td>Tetrahydrofuran, stabilized with BHT</td><td>Pharmaco-Aaper</td><td>346000</td><td>Flammable. Dried through column of XXX</td></tr><tr><td>Dichloromethane</td><td>Pharmaco-Aaper</td><td>313000</td><td>Flammable, toxic.</td></tr><tr><td>Separatory funnel (1 L)</td><td>Fisher Scientific</td><td>13-678-606</td><td></td></tr><tr><td>Sodium sulfate</td><td>Sigma-Aldrich</td><td>239313</td><td></td></tr><tr><td>Ethanol, absolute</td><td>Pharmaco-Aaper</td><td>111USP200</td><td>Flammable, toxic.</td></tr><tr><td>Buchner funnel</td><td>Fisher Scientific</td><td>FB-966-F</td><td></td></tr><tr><td>Methanol</td><td>Pharmaco-Aaper</td><td>339000ACS</td><td>Flammable, toxic.</td></tr><tr><td>Hydrochloric acid</td><td>Sigma-Aldrich</td><td>320331</td><td>Corrosive. Diluted to 2N in distilled water.</td></tr><tr><td>Ethyl chloroformate, 97%</td><td>Sigma-Aldrich</td><td>185892</td><td>Toxic, flammable, harmful to environment</td></tr><tr><td>Triethylamine (anhydrous)</td><td>Sigma-Aldrich</td><td>471283</td><td>Toxic, flammable, harmful to environment</td></tr><tr><td>Diethyl ether</td><td>Pharmaco-Aaper</td><td>373ANHACS</td><td>Highly flammable. Purified through XXX column.</td></tr><tr><td>3,6-Dimethyl-1,4-dioxane-2,5-dione (D,L-lactide)</td><td>Sigma-Aldrich</td><td>303143</td><td></td></tr><tr><td>Tin (II) ethylhexanoate</td><td>Sigma-Aldrich</td><td>S3252</td><td>Toxic.</td></tr><tr><td>&amp;epsilon;-caprolactone (97%)</td><td>Sigma-Aldrich</td><td>704067</td><td></td></tr><tr><td>Toluene, anhydrous</td><td>Sigma-Aldrich</td><td>244511</td><td>Flammable, toxic.</td></tr><tr><td>Glass syringe</td><td>Hamilton Company</td><td>1700-series</td><td></td></tr><tr><td>Deuterated chloroform</td><td>Cambridge Isotopes Laboratories, Inc.</td><td>DLM-29-10</td><td>Toxic</td></tr><tr><td>Nuclear magnetic resonance instrument</td><td>Varian</td><td>V400</td><td></td></tr><tr><td>Palladium on carbon catalyst</td><td>Strem Chemicals, Inc.</td><td>46-1707</td><td></td></tr><tr><td>Hydrogenator unit</td><td>Parr</td><td>3911</td><td></td></tr><tr><td>Hydrogenator shaker vessel</td><td>Parr</td><td>66CA</td><td></td></tr><tr><td>Hydrogen</td><td>Airgas</td><td>HY HP300</td><td>Highly flammable.</td></tr><tr><td>Diatomaceous earth</td><td>Sigma-Aldrich</td><td>22140</td><td></td></tr><tr><td>2H,2H,3H,3H-perflurononanoic acid</td><td>Oakwood Products, Inc.</td><td>10519</td><td>Toxic.</td></tr><tr><td>Stearic acid</td><td>Sigma-Aldrich</td><td>S4751</td><td></td></tr><tr><td>N,N&amp;rsquo;-dicyclohexylcarbodiimide</td><td>Sigma-Aldrich</td><td>D80002</td><td>Toxic, irritant.</td></tr><tr><td>4-(dimethylamino) pyridine</td><td>Sigma-Aldrich</td><td>107700</td><td>Toxic.</td></tr><tr><td>Hexanes</td><td>Pharmaco-Aaper</td><td>359000ACS</td><td>Toxic, flammable.</td></tr><tr><td>Gel permeation chromatography (GPC) system</td><td>Rainin</td><td></td><td></td></tr><tr><td>GPC column</td><td>Waters</td><td>WAT044228</td><td></td></tr><tr><td>Differential scanning calorimeter</td><td>TA Instruments</td><td>Q100</td><td></td></tr><tr><td>Chloroform</td><td>Pharmaco-Aaper</td><td>309000ACS</td><td>Toxic.</td></tr><tr><td>N,N-dimethylformamide</td><td>Sigma-Aldrich</td><td>227056</td><td>Toxic, flammable.</td></tr><tr><td>Polycaprolactone, MW 70-90 kg/mol</td><td>Sigma-Aldrich</td><td>440744</td><td></td></tr><tr><td>Poly(lactide-co-glycolide), MW 136 kg/mol</td><td>Evonik Industries</td><td>LP-712</td><td></td></tr><tr><td>10 ml glass syringe</td><td>Hamilton Company</td><td>81620</td><td></td></tr><tr><td>18 AWG blunt needle</td><td>BRICO Medical Supplies</td><td>BN1815</td><td></td></tr><tr><td>Electrospinner enclosure box</td><td>Custom-built</td><td>N/A</td><td>Made of acrylic panels</td></tr><tr><td>High voltage DC supply</td><td>Glassman High Voltage, Inc.</td><td>PS/EL30R01.5</td><td>High voltages, electrocution hazard</td></tr><tr><td>Linear (translating) stage</td><td>Servo Systems Co.</td><td>LPS-12-20-0.2</td><td>Optional</td></tr><tr><td>Programmable motor &amp;amp; power supply</td><td>Intelligent Motion Systems, Inc.</td><td>MDrive23 Plus</td><td>Optional</td></tr><tr><td>24V DC motor &amp;amp; power supply</td><td>McMaster-Carr</td><td>6331K32</td><td>Optional</td></tr><tr><td>Aluminum collector drum</td><td>Custom-built</td><td></td><td>Optional</td></tr><tr><td>Syringe pump</td><td>Fisher Scientific</td><td>78-0100I</td><td></td></tr><tr><td>Inverted optical microscope</td><td>Olympus</td><td>IX70</td><td></td></tr><tr><td>Scanning electron microscope</td><td>Carl Zeiss</td><td>Supra V55</td><td></td></tr><tr><td>Conductive copper tape</td><td>3M</td><td>16072</td><td></td></tr><tr><td>Aluminum SEM stubs</td><td>Electron Microscopy Sciences</td><td>75200</td><td></td></tr><tr><td>Contact angle goniometer</td><td>Kruss</td><td>DSA100</td><td></td></tr><tr><td>Propylene glycol</td><td>Sigma-Aldrich</td><td>W294004</td><td>Toxic.</td></tr><tr><td>Ethylene glycol</td><td>Sigma-Aldrich</td><td>324558</td><td>Toxic.</td></tr><tr><td>Ioxaglate</td><td>Guerbet</td><td></td><td></td></tr><tr><td>Fetal bovine serum</td><td>American Type Culture Collection</td><td>30-2020</td><td></td></tr><tr><td>Micro-computed tomography instrument</td><td>Scanco</td><td></td><td></td></tr><tr><td>Image analysis software (Analyze)</td><td>Mayo Clinic</td><td></td><td></td></tr><tr><td>Tensile tester</td><td>Instron</td><td>5848</td><td></td></tr><tr><td>Micrometer</td><td>Multitoyo</td><td>293-340</td><td></td></tr><tr><td>Calipers</td><td>Fisher Scientific</td><td>14-648-17</td><td></td></tr></tbody></table>

fabricating superhydrophobic polymeric materials for biomedical applications

Superhydrophobic materials, with surfaces possessing permanent or metastable non-wetted states, are of interest for a number of biomedical and industrial applications. Here we describe how electrospinning or electrospraying a polymer mixture containing a biodegradable, biocompatible aliphatic polyester (e.g., polycaprolactone and poly(lactide-co-glycolide)), as the major component, doped with a hydrophobic copolymer composed of the polyester and a stearate-modified poly(glycerol carbonate) affords a superhydrophobic biomaterial. The fabrication techniques of electrospinning or electrospraying provide the enhanced surface roughness and porosity on and within the fibers or the particles, respectively. The use of a low surface energy copolymer dopant that blends with the polyester and can be stably electrospun or electrosprayed affords these superhydrophobic materials. Important parameters such as fiber size, copolymer dopant composition and/or concentration, and their effects on wettability are discussed. This combination of polymer chemistry and process engineering affords a versatile approach to develop application-specific materials using scalable techniques, which are likely generalizable to a wider class of polymers for a variety of applications.

Through a series of chemical transformations, the functional carbonate monomer 5-benzyloxy-1,3-dioxan-2-one is synthesized as a white crystalline solid (Figure 1A). 1H NMR confirms the structure (Figure 1B) and mass spectrometry and elemental analysis confirm the composition. This solid is then copolymerized with either D,L-lactide or &#949;-caprolactone using a tin-catalyzed ring opening reaction at 140 &#176;C. After purification by precipitation, the polymer compos...

Watch this Scientific Journal Video about Fabricating Superhydrophobic Polymeric Materials for Biomedical Applications at JoVE.com

Fabricating Superhydrophobic Polymeric Materials for Biomedical Applications

Two- and three-dimensional superhydrophobic polymeric materials are prepared by electrospinning or electrospraying biodegradable polymers blended with a lower surface energy polymer of similar composition.

Superhydrophobic materials, with surfaces possessing permanent or metastable non-wetted states, are of interest for a number of biomedical and industrial ...

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Synthetic Polymers

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19.1K Views.  Boston University. Two- and three-dimensional superhydrophobic polymeric materials are prepared by electrospinning or electrospraying biodegradable polymers blended with a lower surface energy polymer of similar composition. 

Video: Fabricating Superhydrophobic Polymeric Materials for Biomedical Applications

Microfabricated Platforms for Mechanically Dynamic Cell Culture

The ability to systematically probe in vitro cellular response to combinations of mechanobiological stimuli for tissue engineering, drug discovery or fundamental cell biology studies is limited by current bioreactor technologies, which cannot simultaneously apply a variety of mechanical stimuli to cultured cells. In order to address this issue, we have developed a series of microfabricated platforms designed to screen for the effects of mechanical stimuli in a high-throughput format. In this protocol, we demonstrate the fabrication of a microactuator array of vertically displaced posts on which the technology is based, and further demonstrate how this base technology can be modified to conduct high-throughput mechanically dynamic cell culture in both two-dimensional and three-dimensional culture paradigms.

In this protocol, we demonstrate the fabrication of a microactuator array of vertically displaced posts on which the technology is based, and how this base technology can be modified to conduct high-throughput mechanically dynamic cell culture in both two-dimensional and three-dimensional culture paradigms.

The ability to systematically probe in vitro cellular response to combinations of mechanobiological stimuli for tissue engineering, drug discovery or ...

Advanced Compositional Analysis of Nanoparticle-polymer Composites Using Direct Fluorescence Imaging

The fabrication of polymer-nanoparticle composites is extremely important in the development of many functional materials. Identifying the precise composition of these materials is essential, especially in the design of surface catalysts, where the surface concentration of the active component determines the activity of the material. Antimicrobial materials which utilize nanoparticles are a particular focus of this technology. Recently swell encapsulation has emerged as a technique for inserting antimicrobial nanoparticles into a host polymer matrix. Swell encapsulation provides the advantage of localizing the incorporation to the external surfaces of materials, which act as the active sites of these materials. However, quantification of this nanoparticle uptake is challenging. Previous studies explore the link between antimicrobial activity and surface concentration of the active component, but this is not directly visualized. Here we show a reliable method to monitor the incorporation of nanoparticles into a polymer host matrix via swell encapsulation. We show that the surface concentration of CdSe/ZnS nanoparticles can be accurately visualized through cross-sectional fluorescence imaging. Using this method, we can quantify the uptake of nanoparticles via swell encapsulation and measure the surface concentration of encapsulated particles, which is key in optimizing the activity of functional materials.

Here we present a reliable method to monitor the incorporation of nanoparticles into a polymer host matrix via swell encapsulation. We show that the surface concentration of cadmium selenide quantum dots can be accurately visualized through cross-sectional fluorescence imaging.

The fabrication of polymer-nanoparticle composites is extremely important in the development of many functional materials. Identifying the precise ...

Engineering

Microfluidic Fabrication of Polymeric and Biohybrid Fibers with Predesigned Size and Shape

A &#8220;sheath&#8221; fluid passing through a microfluidic channel at low Reynolds number can be directed around another &#8220;core&#8221; stream and used to dictate the shape as well as the diameter of a core stream.&#160;Grooves in the top and bottom of a microfluidic channel were designed to direct the sheath fluid and shape the core fluid.&#160;By matching the viscosity and hydrophilicity of the sheath and core fluids, the interfacial effects are minimized and complex fluid shapes can be formed.&#160;Controlling the relative flow rates of the sheath and core fluids determines the cross-sectional area of the core fluid.&#160;Fibers have been produced with sizes ranging from 300 nm to ~1 mm, and fiber cross-sections can be round, flat, square, or complex as in the case with double anchor fibers. Polymerization of the core fluid downstream from the shaping region solidifies the fibers.&#160;Photoinitiated click chemistries are well suited for rapid polymerization of the core fluid by irradiation with ultraviolet light.&#160;Fibers with a wide variety of shapes have been produced from a list of polymers including liquid crystals, poly(methylmethacrylate), thiol-ene and thiol-yne resins, polyethylene glycol, and hydrogel derivatives. Minimal shear during the shaping process and mild polymerization conditions also makes the fabrication process well suited for encapsulation of cells and other biological components.

Two adjacent fluids passing through a grooved microfluidic channel can be directed to form a sheath around a prepolymer core; thereby&#160;determining both shape and cross-section. Photoinitiated polymerization, such as thiol click chemistry, is well suited for rapidly solidifying the core fluid into a microfiber with predetermined size and shape.

A &#8220;sheath&#8221; fluid passing through a microfluidic channel at low Reynolds number can be directed around another &#8220;core&#8221; stream and ...

Preparation and High-temperature Anti-adhesion Behavior of a Slippery Surface on Stainless Steel

Anti-adhesion surfaces with high-temperature resistance have a wide application potential in electrosurgical instruments, engines, and pipelines. A typical anti-wetting superhydrophobic surface easily fails when exposed to a high-temperature liquid. Recently, Nepenthes-inspired slippery surfaces demonstrated a new way to solve the adhesion problem. A lubricant layer on the slippery surface can act as a barrier between the repelled materials and the surface structure. However, the slippery surfaces in previous studies rarely showed high-temperature resistance. Here, we describe a protocol for the preparation of slippery surfaces with high-temperature resistance. A photolithography-assisted method was used to fabricate pillar structures on stainless steel. By functionalizing the surface with saline, a slippery surface was prepared by adding silicone oil. The prepared slippery surface maintained the anti-wetting property for water, even when the surface was heated to 300 &#176;C. Also, the slippery surface exhibited great anti-adhesion effects on soft tissues at high temperatures. This type of slippery surface on stainless steel has applications in medical devices, mechanical equipment, etc.

Slippery surfaces provide a new way to solve the adhesion problem. This protocol describes how to fabricate slippery surfaces at high temperatures. The results demonstrate that the slippery surfaces showed anti-wetting for liquids and a remarkable anti-adhesion effect on soft tissues at high temperatures.

Anti-adhesion surfaces with high-temperature resistance have a wide application potential in electrosurgical instruments, engines, and pipelines. A ...

Fabrication of Superhydrophobic Metal Surfaces for Anti-Icing Applications

Several ways to produce superhydrophobic metal surfaces are presented in this work. Aluminum was chosen as the metal substrate due to its wide use in industry. The wettability of the produced surface was analyzed by bouncing drop experiments and the topography was analyzed by confocal microscopy. In addition, we show various methodologies to measure its durability and anti-icing properties. Superhydrophobic surfaces hold a special texture that must be preserved to keep their water-repellency. To fabricate durable surfaces, we followed two strategies to incorporate a resistant texture. The first strategy is a direct incorporation of roughness to the metal substrate by acid etching. After this surface texturization, the surface energy was decreased by silanization or fluoropolymer deposition. The second strategy is the growth of a ceria layer (after surface texturization) that should enhance the surface hardness and corrosion resistance. The surface energy was decreased with a stearic acid film.
The durability of the superhydrophobic surfaces was examined by a particle impact test, mechanical wear by lateral abrasion, and UV-ozone resistance. The anti-icing properties were explored by studying the ability to repeal subcooled water, freezing delay, and ice adhesion.

We illustrate several methodologies to produce superhydrophobic metal surfaces and to explore their durability and anti-icing properties.

Several ways to produce superhydrophobic metal surfaces are presented in this work. Aluminum was chosen as the metal substrate due to its wide use in ...

Thin Film Composite Silicon Elastomers for Cell Culture and Skin Applications: Manufacturing and Characterization

In this protocol, we present methods to fabricate thin elastomer composite films for advanced cell culture applications and for the development of skin adhesives. Two different poly-(dimethyl siloxanes) (PDMS and soft skin adhesive (SSA)), have been used for in depth investigation of biological effects and adhesive characteristics. The composite films consist of a flexible backing layer and an adhesive top coating. Both layers have been manufactured by doctor blade application technique. In the present investigation, the adhesive behavior of the composite films has been investigated as a function of the layer thickness or a variation of the Young&#39;s modulus of the top layer. The Young&#39;s modulus of PDMS has been changed by varying the base to crosslinker mixing ratio. In addition, the thickness of SSA films has been varied from approx. 16 &#181;m to approx. 320 &#181;m. Scanning electron microscopy (SEM) and optical microscopy have been used for thickness measurements. The adhesive properties of elastomer films depend strongly on the film thickness, the Young&#39;s modulus of the polymers and surface characteristics. Therefore, normal adhesion of these films on glass substrates exhibiting smooth and rough surfaces has been investigated. Pull-off stress and work of separation are dependent on the mixing ratio of silicone elastomers.
Additionally, the thickness of the soft skin adhesive placed on top of a supportive backing layer has been varied in order to produce patches for skin applications. Cytotoxicity, proliferation and cellular adhesion of L929 murine fibroblasts on PDMS films (mixing ratio 10:1) and SSA films (mixing ratio 50:50) have been conducted. We have shown here, for the first time, the side by side comparison of thin composite films manufactured of both polymers and present the investigation of their biological- and adhesive properties.

A protocol for the manufacturing process of polymeric thin film composite structures possessing either different Young&#39;s moduli or thicknesses is presented. Films are produced for advanced cell culture studies or as skin adhesives.

In this protocol, we present methods to fabricate thin elastomer composite films for advanced cell culture applications and for the development of skin ...

Developmental Biology

Fabrication of Refractive-index-matched Devices for Biomedical Microfluidics

The use of microfluidic devices has emerged as a defining tool for biomedical applications. When combined with modern microscopy techniques, these devices can be implemented as part of a robust platform capable of making simultaneous complementary measurements. The primary challenge created by the combination of these two techniques is the mismatch in refractive index between the materials traditionally used to make microfluidic devices and the aqueous solutions typically used in biomedicine. This mismatch can create optical artifacts near the channel or device edges. One solution is to reduce the refractive index of the material used to fabricate the device by using a fluorinated polymer such as MY133-V2000 whose refractive index is similar to that of water (n = 1.33). Here, the construction of a microfluidic device made out of MY133-V2000 using soft lithography techniques is demonstrated, using O2 plasma in conjunction with an acrylic holder to increase the adhesion between the MY133-V2000 fabricated device and the polydimethylsiloxane (PDMS) substrate. The device is then tested by incubating it filled with cell culture media for 24 h to demonstrate the ability of the device to maintain cell culture conditions during the course of a typical imaging experiment. Finally, quantitative phase microscopy (QPM) is used to measure the distribution of mass within the live adherent cells in the microchannel. This way, the increased precision, enabled by fabricating the device from a low index of refraction polymer such as MY133-V2000 in lieu of traditional soft lithography materials such as PDMS, is demonstrated. Overall, this approach for fabricating microfluidic devices can be readily integrated into existing soft lithography workflows in order to reduce optical artifacts and increase measurement precision.

This protocol describes the fabrication of microfluidic devices from MY133-V2000 to eliminate artifacts that often arise in microchannels due to the mismatching refractive indices between microchannel structures and an aqueous solution. This protocol uses an acrylic holder to compress the encapsulated device, improving adhesion both chemically and mechanically.

The use of microfluidic devices has emerged as a defining tool for biomedical applications. When combined with modern microscopy techniques, these devices ...

Rendering SiO2/Si Surfaces Omniphobic by Carving Gas-Entrapping Microtextures Comprising Reentrant and Doubly Reentrant Cavities or Pillars

We present microfabrication protocols for rendering intrinsically wetting materials repellent to liquids (omniphobic) by creating gas-entrapping microtextures (GEMs) on them comprising cavities and pillars with reentrant and doubly reentrant features. Specifically, we use SiO2/Si as the model system and share protocols for two-dimensional (2D) designing, photolithography, isotropic/anisotropic etching techniques, thermal oxide growth, piranha cleaning, and storage towards achieving those microtextures. Even though the conventional wisdom indicates that roughening intrinsically wetting surfaces (&#952;o &#60; 90&#176;) renders them even more wetting (&#952;r &#60; &#952;o &#60; 90&#176;), GEMs demonstrate liquid repellence despite the intrinsic wettability of the substrate. For instance, despite the intrinsic wettability of silica &#952;o &#8776; 40&#176; for the water/air system, and &#952;o &#8776; 20&#176; for the hexadecane/air system, GEMs comprising cavities entrap air robustly on immersion in those liquids, and the apparent contact angles for the droplets are &#952;r &#62; 90&#176;. The reentrant and doubly reentrant features in the GEMs stabilize the intruding liquid meniscus thereby trapping the liquid-solid-vapor system in metastable air-filled states (Cassie states) and delaying wetting transitions to the thermodynamically-stable fully-filled state (Wenzel state) by, for instance, hours to months. Similarly, SiO2/Si surfaces with arrays of reentrant and doubly reentrant micropillars demonstrate extremely high contact angles (&#952;r &#8776; 150&#176;&#8211;160&#176;) and low contact angle hysteresis for the probe liquids, thus characterized as superomniphobic. However, on immersion in the same liquids, those surfaces dramatically lose their superomniphobicity and get fully-filled within &#60;1 s. To address this challenge, we present protocols for hybrid designs that comprise arrays of doubly reentrant pillars surrounded by walls with doubly reentrant profiles. Indeed, hybrid microtextures entrap air on immersion in the probe liquids. To summarize, the protocols described here should enable the investigation of GEMs in the context of achieving omniphobicity without chemical coatings, such as perfluorocarbons, which might unlock the scope of inexpensive common materials for applications as omniphobic materials. Silica microtextures could also serve as templates for soft materials.

Rendering SiO2/Si Surfaces Omniphobic by Carving Gas-Entrapping Microtextures Comprising Reentrant and Doubly Reentrant Cavities or Pillars

This work presents microfabrication protocols for achieving cavities and pillars with reentrant and doubly reentrant profiles on SiO2/Si wafers using photolithography and dry etching. Resulting microtextured surfaces demonstrate remarkable liquid repellence, characterized by robust long-term entrapment of air under wetting liquids, despite the intrinsic wettability of silica.

We present microfabrication protocols for rendering intrinsically wetting materials repellent to liquids (omniphobic) by creating gas-entrapping ...

High-throughput Identification of Bacteria Repellent Polymers for Medical Devices

Medical devices are often associated with hospital-acquired infections, which place enormous strain on patients and the healthcare system as well as contributing to antimicrobial resistance. One possible avenue for the reduction of device-associated infections is the identification of bacteria-repellent polymer coatings for these devices, which would prevent bacterial binding at the initial attachment step. A method for the identification of such repellent polymers, based on the parallel screening of hundreds of polymers using a microarray, is described here. This high-throughput method resulted in the identification of a range of promising polymers that resisted binding of various clinically relevant bacterial species individually and also as multi-species communities. One polymer, PA13 (poly(methylmethacrylate-co-dimethylacrylamide)), demonstrated significant reduction in attachment of a number of hospital isolates when coated onto two commercially available central venous catheters. The method described could be applied to identify polymers for a wide range of applications in which modification of bacterial attachment is important.

A high-throughput microarray method for the identification of polymers which reduce bacterial surface binding on medical devices is described.

Medical devices are often associated with hospital-acquired infections, which place enormous strain on patients and the healthcare system as well as ...

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 ...