Name: fabricating superhydrophobic polymeric materials for biomedical applications
Uploaded: 2015-08-28T14:00:00
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,...

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 border="0" cellpadding="0" cellspacing="0">
	<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 align="right">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 align="right">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 align="right">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 align="right">346000</td>
			<td>Flammable. Dried through column of XXX</td>
		</tr>
		<tr>
			<td>Dichloromethane</td>
			<td>Pharmaco-Aaper</td>
			<td align="right">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 align="right">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 align="right">320331</td>
			<td>Corrosive. Diluted to 2N in distilled water.</td>
		</tr>
		<tr>
			<td>Ethyl chloroformate, 97%</td>
			<td>Sigma-Aldrich</td>
			<td align="right">185892</td>
			<td>Toxic, flammable, harmful to environment</td>
		</tr>
		<tr>
			<td>Triethylamine (anhydrous)</td>
			<td>Sigma-Aldrich</td>
			<td align="right">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 align="right">303143</td>
			<td></td>
		</tr>
		<tr>
			<td>Tin (II) ethylhexanoate</td>
			<td>Sigma-Aldrich</td>
			<td>S3252</td>
			<td>Toxic.</td>
		</tr>
		<tr>
			<td>&#949;-caprolactone (97%)</td>
			<td>Sigma-Aldrich</td>
			<td align="right">704067</td>
			<td></td>
		</tr>
		<tr>
			<td>Toluene, anhydrous</td>
			<td>Sigma-Aldrich</td>
			<td align="right">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 align="right">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 align="right">22140</td>
			<td></td>
		</tr>
		<tr>
			<td>2H,2H,3H,3H-perflurononanoic acid</td>
			<td>Oakwood Products, Inc.</td>
			<td align="right">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&#8217;-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 align="right">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 align="right">227056</td>
			<td>Toxic, flammable.</td>
		</tr>
		<tr>
			<td>Polycaprolactone, MW 70-90 kg/mol</td>
			<td>Sigma-Aldrich</td>
			<td align="right">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 align="right">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 &#38; power supply</td>
			<td>Intelligent Motion Systems, Inc.</td>
			<td>MDrive23 Plus</td>
			<td>Optional</td>
		</tr>
		<tr>
			<td>24V DC motor &#38; 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 align="right">16072</td>
			<td></td>
		</tr>
		<tr>
			<td>Aluminum SEM stubs</td>
			<td>Electron Microscopy Sciences</td>
			<td align="right">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 align="right">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 align="right">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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