Fabricating Superhydrophobic Polymeric Materials for Biomedical Applications

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.