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 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.
Superhydrophobic surfaces are generally categorized as exhibiting apparent water contact angles greater than 150° 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’s and early 1970’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.
1. Synthesizing Functionalizable poly(1,3-glycerol carbonate-co-caprolactone)29 and poly(1,3-glycerol carbonate-co-lactide)27,28.
2. Characterizing the Synthesized Copolymers
3. Preparing Polymer Solutions for Electrospinning/electrospraying27,31
4. Electrospinning/electrospraying Polymer Solutions
5. Characterizing Fiber and Particle Size by Light and Scanning Electron Microscopy
6. Determining Non-wetting Properties
7. Detecting Bulk Wetting of Meshes31
8. Testing the Mechanical Properties of Meshes
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 determined using 1H NMR analysis by integrating the benzylic proton chemical shift at 4.58-4.68 ppm and the characteristic methylene peak of caprolactone or methyne peak of lactide (2.3 or 5.2 ppm, respectively). Selective removal of the benzyl protecting group is achieved by Pd/C-catalyzed hydrogenolysis. Complete deprotection is confirmed by noting the disappearance of the benzyl peak in the 1H NMR spectra. Subsequent grafting of stearic acid onto the free hydroxyl group renders the final copolymers hydrophobic. These copolymers are white solids at room temperature (Figure 1C), and they are capable of being processed into films, electrospun meshes, and electrosprayed coatings (Figure 1D).
The copolymer composition (i.e., lactide/caprolactone to glycerol carbonate) is tuned by varying the corresponding monomer feed ratios. Varying the composition provides a means to synthesize copolymers with a range of thermal and/or mechanical properties. For example, thermal analysis using differential scanning calorimetry (DSC) reveals that PLA-PGC18 polymers containing 10, 20, 30, or 40 mol% PGC18 monomer gradually become more crystalline with increased PGC mol%. The thermal properties of PCL-PGC18 and PLA-PGC18 copolymers are summarized in Table 2.
The poly(glycerol-monostearate)-based copolymers have lower surface energy than their corresponding PCL or PLGA counterparts, as determined using contact angle measurements on smooth casted films (Figure 2A). While PCL possesses an advancing water contact angle of 84°, the advancing contact angle for PCL-PGC18 (80:20) is ~120°. Likewise, PLGA possesses an advancing contact angle of 71°, while PLA-PGC18 (90:10) and PLA-PGC18 (60:40) exhibit advancing contact angles of 99° and 105°, respectively. Blending PCL or PLGA with their corresponding copolymer dopants results in advancing contact angle values between those obtained for pure polymers and copolymers, and affords a facile means to tune hydrophobicity (Figure 2B). In this case, both copolymer dopant concentration (i.e., 10% or 30% wt/wt) and copolymer composition (i.e., PLA-PGC18 (90:10) or PLA-PGC18 (60:40) species) affect hydrophobicity, with greater PGC18 content yielding higher contact angles.
Doping the synthesized copolymers into a solution of PCL or PLGA and subsequently electrospinning the blends achieves fibrous meshes with tunable hydrophobicity. Figure 3A illustrates how doping in 30% PCL-PGC18 or PLA-PGC18 transitions meshes from hydrophobic to superhydrophobic. Superhydrophobicity is defined as an apparent water contact angle ≥ 150° with a low contact angle hysteresis—defined as the difference between advancing and receding water contact angle measurements. The increased surface roughness of electrospun meshes also increases the apparent water contact angle of these materials in comparison to smooth films. Wettability is tuned by varying the concentration of copolymer dopant. For example, electrospun pure PCL meshes with ~7 µm diameter fibers possess an apparent contact angle of 123°, while meshes doped with 10, 30, and 50% (wt/wt) PCL-PGC18 exhibit apparent contact angles of 143°, 150°, and 160° at comparable fiber diameters, respectively (Figure 3B). Wettability is also controlled by the choice of copolymer dopant species. In this case, 6.5-7.5-µm fiber PLGA meshes doped with 30% PLA-PGC18 (90:10) or 30% PLA-PGC18 (60:40) exhibit apparent contact angles of 133° or 154°, respectively (Figure 3C). Altering (i.e., reducing) the fiber size also enhances hydrophobicity independent of dopant selection and/or concentration. This dependence of apparent contact angle on fiber diameter is shown for both PCL and PLGA in Figure 3D. Similar to electrospinning, electrosprayed PCL and doped-PCL coatings also display contact angles that increase with doping percentage, and even higher contact angles than those obtained by electrospinning are achieved with this technique (Figure 3E). By probing the mesh surface with different liquids (which possess different surface tensions) and reporting the contact angle, a critical surface tension value at which the mesh rapidly wets is determined. Figure 3F is a modified Zisman curve illustrating the critical surface tension studies for PLGA meshes doped with 30% PLA-PGC18 (60:40) and PCL meshes doped with 30% PCL-PGC18.
SEM imaging reveals that the meshes are the result of entangled microfibers. This technique is also useful for determining fiber or particle size, homogeneity, and interconnectivity. Figure 4A shows PCL + 30% PCL-PGC18 meshes with fiber diameters of 1-2 µm and 4-5 µm, while Figure 4B shows PLGA + 10% PLA-PGC18 meshes varying in fiber size from ~3 µm to ~7 µm. Electrosprayed coatings of PCL and PCL + 50% PCL-PGC18 are presented in Figure 4C, while electrosprayed coatings of PCL + 30% PCL-PGC18 of varying particle size are presented in Figure 4D.
Superhydrophobic PCL- and PLGA-based meshes are non-cytotoxic to NIH/3T3 fibroblasts (Figure 5A) and are well-tolerated in C57BL/6 mice, with modest fibrous encapsulation. Compared to non-porous films (not shown), meshes display a greater degree of cellular infiltration (i.e., macrophages) after 4 weeks’ implantation (Figure 5B-E)27. While the cytocompatibility/biocompatibility of superhydrophobic meshes is similar to non-superhydrophobic meshes, the in vitro performance of superhydrophobic meshes can be superior in drug delivery applications. Due to their slow wetting, superhydrophobic meshes are capable of sustaining drug release for significantly longer durations than non-superhydrophobic meshes, since drug release cannot occur without water contact. The in vitro drug release efficacy studies demonstrating this principle are described elsewhere12,13.
The wetting of the electrospun meshes can be followed non-destructively over time using microcomputed tomography and the commercially-available iodinated contrast agent Ioxaglate. The mesh is placed in an aqueous solution containing the contrast agent and imaged over time. As shown in Figure 6A the pure PCL mesh rapidly wets as water infiltrates the bulk material in the first day. In contrast, the meshes doped with 30% PCL-PGC18 remain non-wetted for >75 days, with air remaining within the bulk structure (Figure 6B). These results illustrate the importance of superhydrophobic bulk materials for non-wetting applications.
Lastly, the mechanical properties of electrospun meshes are determined from tensile testing. Table 3 shows representative mechanical data for PCL, PLGA, and their respective doped meshes (fiber size = 7 µm for all meshes) obtained from their stress-strain curves. As the percentage of doping increases, the elastic moduli (E) and ultimate tensile strengths of meshes tend to decrease.
Figure 1. Monomer/polymer synthesis, characterization, and subsequent processing into films, electrospun meshes, and electrosprayed coatings. (A) Purified monomer is a white crystalline solid at room temperature; (B) corresponding 1H NMR spectra for monomer; (C) photograph of purified polymers PLA-PGC18 (left) and PCL-PGC18 (right); (D) photograph of PCL doped with 30% (wt/wt) PCL-PGC18 and processed into a (from left to right): film, electrospun mesh, and electrosprayed coating.
Figure 2. Advancing and receding water contact angles on polymer/copolymer films. (A) Advancing and receding water contact angle measurements for undoped PCL and PLGA smooth films compared to those for pure PCL-PGC18 and pure PLA-PGC18 smooth films; (B) advancing and receding contact angle measurements for doped PCL and PLGA films. Please click here to view a larger version of this figure.
Figure 3. The processes of electrospinning and electrospraying generate rough surfaces that further enhance the hydrophobicity of PCL and PLGA. (A) Contact angle for electrospun PCL and PCL meshes doped with 30% PCL-PGC18 (80:20) meshes (fiber diameter ≈ 2.5 µm); PLGA meshes and PLGA meshes doped with 30% PLA-PGC18 (60:40) meshes (fiber diameter ≈ 6.5 µm), with both systems showing a transition from hydrophobic to superhydrophobic; (B) contact angles for PCL meshes as a function of increasing dopant copolymer concentration; (C) contact angles for PLGA meshes of ~6.5 µm diameter as a function of copolymer composition; (D) wettability as a function of fiber diameter for PCL (600 nm and 2.5 µm) and PLGA-based meshes (2.5 and 6.5 µm); (E) contact angles for electrosprayed PCL-based coatings as a function of copolymer doping concentration; (F) modified Zisman curves showing critical surface tension studies for PLGA meshes doped with 30% PLA-PGC18 (60:40) (circles with dashed connecting line) and PCL meshes doped with 30% PCL-PGC18 (squares with solid connecting line). Please click here to view a larger version of this figure.
Figure 4. SEM imaging of electrospun meshes and electrosprayed coatings reveals fiber/particle size and morphology. (A) Small-diameter PCL + 30% PCL-PGC18 fibers (1-2 µm) and corresponding large-diameter microfiber (4-5 µm) mesh (left and right, respectively), scale bar = 10 µm; (B) small-diameter PLGA + 10% PLA-PGC18 (90:10) (2.5-3.5 µm) microfiber and large diameter (6.5-7.5 µm) microfiber meshes (left and right, respectively; scale bar = 10 µm); (C) electrosprayed particles consisting of pure PCL (left), PCL + 50% PCL-PGC18 (right), scale bar = 20 µm; (D) electrosprayed PCL + 30% PCL-PGC18 particles of small (left) and large (right) radii (scale bar = 2 µm). Please click here to view a larger version of this figure.
Figure 5. In vitro and in vivo cell viability/biocompatibility of electrospun superhydrophobic meshes. (A) In vitro cell assay of NIH/3T3 fibroblast viability upon 24-hr incubation with PCL, PLGA, and doped meshes; (B and C) histological (H&E) specimens of in vivo foreign body response to superhydrophobic PLGA + 30 wt% PLA-PGC18 (60:40) electrospun meshes after 4 weeks’ subcutaneous implantation in C57BL/6 mice at 10X (B) and 40X (C) magnification; (D and E) response to implanted pure PLGA electrospun meshes at 10X (D) and 40X (E) magnification. Please click here to view a larger version of this figure.
Figure 6. Contrast-enhanced microcomputed tomography (µCT) characterization of the bulk wetting of superhydrophobic meshes. The iodinated CT contrast agent Ioxaglate (80 mgI/ml) in water serves as a non-invasive marker of water infiltrating (A) non-superhydrophobic PCL meshes and (B) superhydrophobic PCL + 30% PCL-PGC18 meshes. Color map indicates non-wetted mesh as red and transitioning from yellow to green to blue/purple as wetting progresses. Please click here to view a larger version of this figure.
Electrospun Synthetic Polymers: | Reference(s): |
Poly(lactide-co-glycolide) | 27,36,43,48-52 |
Polyglycolide | 52,53 |
Poly(lactide-co-caprolactone) | 54-57 |
Polycaprolactone | 13,58-66 |
Polylactide | 52,67 |
Poly(vinyl alcohol) | 68-71 |
Poly(ethylene glycol)/block copolymers | 72,73 |
Poly(ester urethane)s | 74-78 |
Poly(trimethylene carbonate) | 79 |
Poly(dimethyl siloxane) | 80,81 |
Poly(ethylene-co-vinyl acetate) | 82 |
Polyvinylpyrrolidone | 83 |
Polyamide(s) | 84-86 |
Polyhydroxybutryate | 87,88 |
Polyphosphazene(s) | 89,90 |
Poly(propylene carbonate) | 91-93 |
Polyethyleneimine | 94,95 |
Poly(γ-glutamic acid) | 96 |
Silicate | 97,98 |
Table 1: Examples of synthetic biomedical polymers that have been electrospun for biomedical applications, with accompanying references.
Copolymer | Conversion (%) | Lactidea | Glycerola | Mn (g/mol)b | Mw/Mn | Tg (°C)c | Tm (°C) | Tc (°C) | ∆Hf (J/g) |
PLA-PGC18 (90:10) | 92 | 89 | 11 | 12,512 | 1.5 | 28 | – | – | – |
PLA-PGC18 (80:20) | 96 | 78 | 23 | 10,979 | 1.5 | 17 | 33 | 11 | 3 |
PLA-PGC18 (70:30) | 90 | 66 | 34 | 17,305 | 1.5 | * | 40 | 17 | 23 |
PLA-PGC18 (60:40) | 86 | 54 | 47 | 13,226 | 1.6 | * | 43 | 27 | 32 |
PCL-PGC18 (80:20) | 99 | (caprolactone) 81 | 19 | 21,100 | 1.7 | -53 | 31 | 19 | 55 |
Table 2: Characterization of synthesized copolymers. aMole %; bAs determined by size-exclusion chromatography (THF, 1.0 mL/min); Mn = number average molecular weight, Mw/Mn = dispersity. cTg = glass transition temperature; Tm= melting temperature; Tc = crystallization temperature; ΔHf = heat of fusion. d No Tg was observed for these semicrystalline polymers over the temperature range from -75 °C to 225 °C.
Mesh Composition | Elastic Modulus (E) (MPa) | Ultimate Tensile Strength (MPa) |
PCLa | 15.3 | 1.5 |
+ 10% PCL-PGC18 | 10.8 | 1.5 |
+ 30% PCL-PGC18 | 3.5 | 0.8 |
PLGAb | 84.9 | 2.6 |
+ 10% PLA-PGC18 (60:40) | 40.3 | 0.8 |
+ 30% PLA-PGC18 (60:40) | 10.1 | 0.3 |
Table 3: Representative tensile properties of electrospun meshes. aFiber size for PCL and PCL-based meshes ≈ 7 µm. bFiber size for PLGA and PLGA-based meshes ≈ 7 µm.
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 polymer weight percent, and fabrication conditions, the wettability of the resulting electrospun/electrosprayed materials is controlled. The materials fabricated in this work are from non-toxic and biocompatible polymers, and possess a meta-stable air barrier in the presence of water.
The critical steps in this protocol involve 1) synthesizing copolymers using ring-opening polymerization, 2) electrospinning or electrospraying these copolymers with a corresponding biomedical polymer such as PCL or PLGA; and 3) characterizing their morphology, non-wetting behavior/hydrophobicity, mechanical properties, and in vitro/in vivo biocompatibility. If difficulties with polymer synthesis, modification, and/or electrospinning are encountered, the following techniques will help identify and troubleshoot these issues.
It is important to ensure the purity of the monomers and that they do not contain trace water, such as that from the atmosphere. The presence of water may prevent or terminate polymerization, result in low molecular weight polymers, or yield polymers with extremely broad molecular weight distributions. Always evacuate the contents of polymerization vessels and re-fill with dry nitrogen or argon, and perform all additions (monomers and catalysts) under dry, inert atmosphere. If polymerization appears incomplete or unsuccessful, it may be necessary to dry the reagents by distillation, or re-crystallize the monomers to improve purity. If de-benzylation of the resulting copolymer appears unsuccessful (as observed by subsequent 1H NMR analysis), it may be necessary to add more catalyst or use a different catalyst reagent. We specifically note here that unsuccessful deprotection has been observed with certain Pd/C catalysts, and it is best to use the one listed in the Table of Materials.
Several technical difficulties may be encountered during the electrospinning and electrospraying process. 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 (in this case, increase the collection distance), or if adjusting the voltage does not adequately solve a dragging droplet at the needle tip, reduce the collection distance. If fibers are not forming, it may be necessary to increase the viscosity of the solution by increasing the polymer concentration; the same is true if the fibers appear to have a bead-on-string morphology. If the difficulties remain, it may be necessary to switch to a different electrospinning solvent. For more troubleshooting, Leach and coworkers47 provide a comprehensive troubleshooting guide to electrospinning.
While electrospinning and electrospraying are useful techniques for fabricating biomedical materials, they do have limitations. First, these techniques rely on a grounded target to collect fibers or particles, so electrical conductivity is an important parameter to consider. It may be difficult to electrospin or electrospray materials that are particularly good electrical insulators, since the polymer jet may be more attracted to areas surrounding these substrates. One possible solution involves securing less-conductive materials to conductive copper tape. Additionally, while we have been successful in electrospinning meshes up to 1 mm thick, the fabrication of extremely thick meshes may be hindered due to the insulating nature of the polymer coating on the collector. At this point, meshes may increase in surface area without much increase in their overall thickness. Second, depending on the size of mesh desired, a substantial amount of material is required to achieve sufficient solution viscosity (which is required for electrospinning, as chain entanglements are necessary for fiber formation). Therefore, electrospinning may not be a suitable option for precious materials; electrospraying generally uses lower concentrations and thus is less demanding in terms of the required quantity of material. If the sample quantity is very limited, it may be possible to reduce material loss by omitting connector tubing (which otherwise adds to overall dead volume). Lastly, the determination of critical surface tension relies on the use of various probing liquids, which also possess different viscosities. As such, this method has a potential limitation in that viscosity is also a contributing factor to these results.
Superhydrophobic materials are an exciting class of biomaterials, which are finding increased use for a range of applications in drug delivery, tissue engineering, wound healing, and anti-fouling. Several techniques exist for enhancing surface roughness to materials for biomimetic and non-wetting applications, such as layer-by-layer assembly15, micropatterning/microtexturing102, electrospinning1,5,13, and electrospraying32. Of these approaches, electrospinning and electrospraying are particularly attractive methods due to their scalability and general compatibility with underlying substrates. In conclusion, this strategy combining polymer chemistry and process engineering is a versatile and general one that will enable other researchers to prepare, characterize, and study new biomaterials where wettability of the materials is a key design feature.
The authors have nothing to disclose.
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.
Silicone oil | Sigma-Aldrich | 85409 | |
Cis-2-Phenyl-1,3-dioxan-5-ol | Sigma-Aldrich | 13468 | |
Benzyl bromide | Sigma-Aldrich | B17905 | Toxic, lacrymator/eye irritant, use in chemical fume hood |
Potassium hydroxide | Sigma-Aldrich | 221473 | Corrosive |
Rotary evaporator | Buchi | R-124 | |
High-vacuum pump | Welch | 8907 | |
Nitrogen, ultra high purity | Airgas | NI UHP300 | Compressed gas |
Tetrahydrofuran, stabilized with BHT | Pharmaco-Aaper | 346000 | Flammable. Dried through column of XXX |
Dichloromethane | Pharmaco-Aaper | 313000 | Flammable, toxic. |
Separatory funnel (1 L) | Fisher Scientific | 13-678-606 | |
Sodium sulfate | Sigma-Aldrich | 239313 | |
Ethanol, absolute | Pharmaco-Aaper | 111USP200 | Flammable, toxic. |
Buchner funnel | Fisher Scientific | FB-966-F | |
Methanol | Pharmaco-Aaper | 339000ACS | Flammable, toxic. |
Hydrochloric acid | Sigma-Aldrich | 320331 | Corrosive. Diluted to 2N in distilled water. |
Ethyl chloroformate, 97% | Sigma-Aldrich | 185892 | Toxic, flammable, harmful to environment |
Triethylamine (anhydrous) | Sigma-Aldrich | 471283 | Toxic, flammable, harmful to environment |
Diethyl ether | Pharmaco-Aaper | 373ANHACS | Highly flammable. Purified through XXX column. |
3,6-Dimethyl-1,4-dioxane-2,5-dione (D,L-lactide) | Sigma-Aldrich | 303143 | |
Tin (II) ethylhexanoate | Sigma-Aldrich | S3252 | Toxic. |
ε-caprolactone (97%) | Sigma-Aldrich | 704067 | |
Toluene, anhydrous | Sigma-Aldrich | 244511 | Flammable, toxic. |
Glass syringe | Hamilton Company | 1700-series | |
Deuterated chloroform | Cambridge Isotopes Laboratories, Inc. | DLM-29-10 | Toxic |
Nuclear magnetic resonance instrument | Varian | V400 | |
Palladium on carbon catalyst | Strem Chemicals, Inc. | 46-1707 | |
Hydrogenator unit | Parr | 3911 | |
Hydrogenator shaker vessel | Parr | 66CA | |
Hydrogen | Airgas | HY HP300 | Highly flammable. |
Diatomaceous earth | Sigma-Aldrich | 22140 | |
2H,2H,3H,3H-perflurononanoic acid | Oakwood Products, Inc. | 10519 | Toxic. |
Stearic acid | Sigma-Aldrich | S4751 | |
N,N’-dicyclohexylcarbodiimide | Sigma-Aldrich | D80002 | Toxic, irritant. |
4-(dimethylamino) pyridine | Sigma-Aldrich | 107700 | Toxic. |
Hexanes | Pharmaco-Aaper | 359000ACS | Toxic, flammable. |
Gel permeation chromatography (GPC) system | Rainin | ||
GPC column | Waters | WAT044228 | |
Differential scanning calorimeter | TA Instruments | Q100 | |
Chloroform | Pharmaco-Aaper | 309000ACS | Toxic. |
N,N-dimethylformamide | Sigma-Aldrich | 227056 | Toxic, flammable. |
Polycaprolactone, MW 70-90 kg/mol | Sigma-Aldrich | 440744 | |
Poly(lactide-co-glycolide), MW 136 kg/mol | Evonik Industries | LP-712 | |
10-mL glass syringe | Hamilton Company | 81620 | |
18 AWG blunt needle | BRICO Medical Supplies | BN1815 | |
Electrospinner enclosure box | Custom-built | N/A | Made of acrylic panels |
High voltage DC supply | Glassman High Voltage, Inc. | PS/EL30R01.5 | High voltages, electrocution hazard |
Linear (translating) stage | Servo Systems Co. | LPS-12-20-0.2 | Optional |
Programmable motor & power supply | Intelligent Motion Systems, Inc. | MDrive23 Plus | Optional |
24V DC motor & power supply | McMaster-Carr | 6331K32 | Optional |
Aluminum collector drum | Custom-built | Optional | |
Syringe pump | Fisher Scientific | 78-0100I | |
Inverted optical microscope | Olympus | IX70 | |
Scanning electron microscope | Carl Zeiss | Supra V55 | |
Conductive copper tape | 3M | 16072 | |
Aluminum SEM stubs | Electron Microscopy Sciences | 75200 | |
Contact angle goniometer | Kruss | DSA100 | |
Propylene glycol | Sigma-Aldrich | W294004 | Toxic. |
Ethylene glycol | Sigma-Aldrich | 324558 | Toxic. |
Ioxaglate | Guerbet | ||
Fetal bovine serum | American Type Culture Collection | 30-2020 | |
Micro-computed tomography instrument | Scanco | ||
Image analysis software (Analyze) | Mayo Clinic | ||
Tensile tester | Instron | 5848 | |
Micrometer | Multitoyo | 293-340 | |
Calipers | Fisher Scientific | 14-648-17 |