Name: Fabricating Superhydrophobic Polymeric Materials for Biomedical Applications (Video) | JoVE Journal
Uploaded: 2015-08-28T14:00:00.000+00:00
Duration: 9 min 22 s
Description: Learn to fabricate superhydrophobic biodegradable fibrous meshes and nanoparticle coatings using electrospinning and electrospraying techniques. This method enables tunable wetting properties for controlled drug delivery applications.

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5 minutes

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

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 ε-caprolactone using a tin-catalyzed ring opening reaction at 140 °C. After purification by precipitation, the polymer composition is d...

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 ...

The overall goal of the following experiment is to fabricate biodegradable fibrous meshes and nano or microparticle coatings from blends of biomedical polymers and to tune the wet ability of these materials by varying the co-polymer blend. This is achieved by first synthesizing functionable copolymers in a ring opening polymerization, and subsequently grafting on hydrocarbon C 18 chains. As a second step, the copolymers are dissolved along with polycaprolactone or lactide cog glycoside in an organic solvent, and subsequently electros spun or electro sprayed, which results in three dimensional microfiber meshes or nano microparticle coatings respectively.Contact angle goniometry studies are then performed on the meshes and coatings in order to understand how fiber diameter co-polymer composition and blend composition affect surface wet ability and lead to super hydrophobic biomaterials. The results show how hydrophobicity is enhanced by increasing the concentration of co-polymer in the electros fun blend as determined by advancing and receding water contact angle studies. The implications of this technique extend towards situations such as chemotherapy because these materials can serve as local drug delivery depots for sustained release of entrapped agents with the related drug release being controllable by polymer composition and surface roughness.To begin synthesize the monomer required for the experiment by following the instructions in the accompanying text protocol. Then preheat a silicone oil bath to 140 degrees Celsius. Measure out two portions, 2.1 grams each, a five benzel oxy one three dioxin to own, and add it to separate dry 100 milliliter round bottom flasks.Next, measure out 5.7 grams of DL lactide and add it to only one of these flasks. Add a magnetic stir bar to both flasks and seal the flasks with rubber stoppers. Next, measure 240 milligrams of tin two ethyl H, no eight in a small pear shaped flask.Flush both flasks containing the monomer with nitrogen on a flank manifold for five minutes, and then at 4.24 milliliters of epsilon capralactone to the flask containing only five benzo oxy one three dioxin, two own while under nitrogen, evacuate all three flasks atmospheres by applying high vacuum of about 300 millitorr for 15 minutes to remove any trace water. Then recharge the flask atmosphere with nitrogen, and again, pull a high vacuum. Repeat this cycle for a total of three times.Once purged and under nitrogen for the last time, place the monomer flasks in the 140 degrees Celsius oil bath. Next, add 500 microliters of dry toluene to the pear-shaped flask with the tin catalyst while under nitrogen at about 100 microliters of the catalyst solution to the monomer mixtures. Once all solids have melted, keep the mixture at 140 degrees Celsius for no more than 24 hours.Then cool the molten polymer to room temperature. Once cooled, dissolve the polymers in 50 milliliters of di chloro methane, and then precipitate the solution into 200 milliliters of cold methanol. Decant the supernatant and dry the remaining polymer under high vacuum.Store the dried polymers in the minus 20 degrees Celsius freezer until further. Use further dissolve about six grams of the polymer into 120 milliliters of tetrahedran in a high pressure hydrogenation vessel. Then add two grams of a palladium carbon catalyst.Next, add hydrogen to the vessel using a hydrogenation apparatus. Hydrogenate the vessel at 50 PSI for four hours. Once complete, filter out the palladium carbon catalyst using a packed bed of diatomaceous earth.Then concentrate the polymer to about 50 milliliters under rotary of aberration. Precipitate the remaining volume into cold methanol. Next, decant the supernatant, and then dry the remaining volume under high vacuum, dissolve the dried polymer along with 1.5 equivalents of steric acid into 500 milliliters of dry dye chloral methane.Then add two equivalents of DCC and three flakes of four dimethyl amino paridine. Stir the mixture under nitrogen at room temperature for 24 hours. Remove the insoluble material through a series of three repeated filtrations and concentrations.At the end, concentrate the solution to 50 milliliters. Finally precipitate the concentrated polymer into 175 milliliters of cold methanol and filter the polymer using a boar funnel. Then dry the polymer under high vacuum overnight for electro spinning, dissolve the polymer overnight at 10 to 40%in a five to one mixture of chloroform and methanol for polycaprolactone, or a seven to three mixture of tetrahedran and NN dimethylformamide for PLGA for electro spraying.Prepare the polymer solutions at a lower concentration in the range of two to 10%in a solvent such as chloroform. Next, load approximately 4.5 milliliters of the solution into a glass syringe equipped with an 18 gauge needle, and place the syringe onto the syringe pump. Then set the rate at which to dispense this solution to five milliliters per hour.Cover the collector plate with aluminum foil and secure the foil with masking tape along the outer edges. Attach the high voltage DC supply wire to the needle tip and the ground to the collector drum. As a first attempt.Set the tip to collector distance at 15 centimeters to cover a large area. Turn on the rotating and translating collector drum at 45 RPMs. Then start the syringe pump and turn on the high voltage source set.At five kilovolts, initially adjust the voltage if necessary to achieve an acceptable tailor cone. Once the syringe pump stops, turn off the high voltage source, followed by the syringe pump and the motorized drum. Allow the electro spinning enclosure to continue ventilating for at least 30 minutes.Then remove the collected polymer from the drum and allow trace solvents to evaporate in a hood overnight. PGLA sheets can be stored at room temperature for at least two weeks, and polycaprolactone sheets can be stored at room temperature for up to two months. Cut 0.5 centimeter by three centimeter strips of the mesh or coated material, and place the thin strip on the stage of a contact angle.Goniometer then dispense a five microliter droplet of water using a 24 gauge needle and to make contact with the material surface, continue to slowly add an additional 20 to 25 microliters of water and capture the droplet image. This represents the advancing water contact angle. Next, slowly withdraw this same drop while simultaneously capturing its drop profile.Repeat this process 10 times on several discrete surface locations to report an average value. SEM imaging reveals that the electro spun meshes are the result of entangled microfibers and the electros sprayed coatings are a collection of particles of varying sizes. Electro spinning and electro spraying blends reveal that copolymer dopamine concentration affects hydrophobicity.Additionally, copolymer composition affects hydrophobicity with greater PG C 18 content yielding higher contact angles as shown here, the bulk wetting of submerged electros spun meshes can be tracked non-destructively over time using micro computed tomography. In the top set of images. The pure polycaprolactone mesh rapidly wets as water infiltrates the bulk material in the first day.In contrast, the mesh is dod with 30%P-C-L-P-G-C 18 remain non wetted for more than 75 days with air remaining within the bulk structure. These results illustrate the importance of super hydrophobic bulk materials for their use in non-wetting applications. Once mastered, the polymer chemistry procedure can be performed as little as three to four days with careful planning.Furthermore, once suitable electro spinning or electro spraying parameters have been identified, the fabrication of meshes and particle coatings can be performed in one to three hours depending on the desired thickness of these materials.

fabricating-superhydrophobic-polymeric-materials-for-biomedical

Research

JoVE Journal

Bioengineering

Two adjacent fluids passing through a grooved microfluidic channel can be directed to form a sheath around a prepolymer core; thereby 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.

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

We present a protocol to synthesize Janus microhydrogels composed entirely of the same base material, poly(N-isopropylacrylamide) (PNIPAAm), with a clearly compartmentalized structure base on the phase separation of a supersaturated NIPAAm monomer solution. The synthesized Janus microhydrogels show unique properties such as anisotropic thermo-responsiveness and organophilic/hydrophilic loading capability.

Synthesis of Poly(N-isopropylacrylamide) Janus Microhydrogels for Anisotropic Thermo-responsiveness and Organophilic/Hydrophilic Loading Capability

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

Synthesis of Hydrogels with Antifouling Properties As Membranes for Water Purification

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.

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

An additive manufacturing strategy for processing UV-crosslinkable hydrogels has been developed. This strategy allows for the layer-by-layer assembly of microfabricated hydrogel structures as well as the assembly of independent components, yielding integrated devices containing moving components that are responsive to magnetic actuation.

An Additive Manufacturing Technique for the Facile and Rapid Fabrication of Hydrogel-based Micromachines with Magnetically Responsive Components

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

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

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

Fabrication of Superhydrophobic Metal Surfaces for Anti-Icing Applications

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.

Fabrication of Refractive-index-matched Devices for Biomedical Microfluidics

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.

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

This protocol presents a light-induced method for fabricating slippery three-dimensional structures via sequential digital patterning and grafting on silane-coated nanoporous surfaces. This approach enables the spatially controlled formation of slippery regions, enabling patterned liquid repellency and the quantitative analysis of interfacial slipperiness, with applications in fluid manipulation and surface engineering.

Light-induced Patterning and Grafting for Slippery Surfaces based on Silane-coated Nanoporous Structures

Learn to fabricate superhydrophobic biodegradable fibrous meshes and nanoparticle coatings using electrospinning and electrospraying techniques. This method enables tunable wetting properties for controlled drug delivery applications.

Fabricating Superhydrophobic Polymeric Materials for Biomedical Applications

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