Encapsulation and Permeability Characteristics of Plasma Polymerized Hollow Particles
August 16th, 2012
We have used plasma enhanced chemical vapor deposition to deposit thin films ranging from a few nm to several 100 nm on nano-sized particles of various materials. We subsequently etch the core material to produce hollow nanoshells whose permeability is controlled by the thickness of the shell. We characterize the permeability of these coatings to small solutes and demonstrate that these barriers can provide sustained release of the core material over several days.
The overall goal of this experiment is to coat nanoparticles, nano powders or drug particles with a plasma polymer in order to control the release of the core material. Begin with the preparation of silicon nanoparticles or calcium chloride nano powders for deposition breaking any agglomerations. Then place the particles in a plasma reactor and coat the nanoparticles by plasma polymerization of isopropanol using plasma enhanced chemical vapor deposition.
Next, to determine the permeability of the deposited, shell dissolve the core materials in a proper solvent while monitoring concentration results obtained show the permeability of the core material based on measurements of the ionic conductivity in a suspension of coated particles in water. The idea for this method came from the film deposition literature. A lot of work has been done on plasma deposition of thin films and flat substrates, but not on particles.
So by adapting the coating method to particles, we open up possibilities for new nanomaterials. Visual demonstration of this method is critical as various steps are difficult to learn because they involve working in a low pressure plasma environment. Anam Shavan is a grad student from my laboratory, and she will now demonstrate this procedure.
First, wash the dry silica particles with pure ethanol. Leave the sample under a fume hood to evaporate the moisture. Next, sift the particles through a series of metallic meshes.
In order to break any remaining agglomerations, transfer the particles together with a small magnetic stir bar to the plasma zone of the tubular reactor. Now place one O-ring at the end of the glass tube, another at the end of the pipe connected to the pump and seal the glass reactor. Install the stainless steel clamping around the F flanges and hand tighten the screw around the clamp.
Fill the liquid nitrogen trap. When the surfers of the trap is cold. Add isopropanol in the bubbler and connect to the plasma reactor.
Next, place a rubber O-ring around the metal pipe and tighten the nut to seal the pipe to bubble a connection. Place the bubbler in a 34 degrees Celsius water bath. Turn on the Argonne gas flow controller and enter a set point of six SCCM with the pump on.
Gradually open the gate valve that connects the glass tube to the pump. Perform this a step carefully, because sudden increase in the pressure may cause the particles to be blown away by the flow. When the pressure reaches 200 milli to leave the gate valve fully open, place a magnetic stir under the glass tube and set the speed at 100 RPM.
Next, connect the aluminum ring around the tubular glass reactor to the radio frequency generator and connect the stainless steel clamp to the ground. Turn on the matching network. Next, switch on the AC line and the RF power generator.
Set the power at 30 watts for the entire process. After a specific duration of time, turn off the matching network RF generator, and the AC power respectively. Close the check valve and then turn off the argon flow controller.
Disconnect the bubbler from the valve and gradually increase the reactor pressure to atmospheric. Now open the clamp and using a metallic spatula, transfer the particles from the tube into a plastic dish. Hydrofluoric acid is a very corrosive acid.
An exposure of that to eye and skin may cause permanent damage. So wear goggles, face shield and wear lab coat. Place the sample under a fume hood for the entire process of adding hydrofluoric acid.
First, dilute 10 milliliters of hydrofluoric acid with 10 milliliters deionized water. Then add the acid solution to the coated particles. Place on a magnetic stir for 24 hours to dissolve the core.
After one day, dilute the sample with 50 milliliters of deionized water and centrifuge. Discard the top liquid layer into a plastic container and transfer the bottom particle layer to a plastic Petri dish. Wash the particles with ethanol and air dry transfer hollow particles into a vial with cap, and store the sample in a desiccate.
Fill the glass bottle of constant output atomizer with one millimolar potassium chloride, and install the bottle cap. Connect the compressed air hose to a membrane dryer, which is connected to the gas inlet of the atomizer. Then attach a filter to the outlet hose in order to collect the potassium chloride nanoparticles.
Gradually open the compressed air valve to the membrane dryer. Allow the particles to accumulating the filter for five hours. Close the compressed air valve.
Carefully remove the filter and collect the particles. Place the sample in a desiccate uniformly coat the potassium chloride particles by preparing the vacuum system and following the plasma deposition process As shown earlier. In a glass vial, add 10 milliliters of deionized water to the coated potassium chloride and mix on a magnetic stir.
Incubate the sample at 25 degrees Celsius. Insert the conductivity meter probe into the vial. Record the conductivity over 30 days.
This process can be applied to a variety of core materials, including oxides, salts, and metals. These images obtained by transmission electron microscopy, the radial uniformity of the films and measure their thickness coated particles range from 37 nanometers to 200 nanometers in diameter. The plasma polymerized cell is a permeable barrier as demonstrated by the fact that the core material can be removed by etching or dissolution after removal of the silica core is complete.
The radial uniformity and thickness of the films are quite high for the purposes of evaluating the permeability through these films. A potassium chloride core material allows monitoring of the dissolution of potassium chloride by measuring ionic conductivity of the solution. In this experiment, coated potassium chloride particles was suspended in water and the conductivity of the solution was followed for a period of 30 days.
The uncoated potassium chloride particles in the control sample dissolved within a very short time of approximately one minute. By contrast, coated potassium chloride shows a significantly slower release rate. The release profile of the coated particles is characterized by an initial burst that takes place within the first hour, followed by a much slower release that takes several days to complete depending on the thickness of the film.
After watching this video, you should have a good understanding of how to encapsulate nanoparticles in plasma pose coatings with well controlled thickness once mastered, this technique can be done in about an hour. If it's performed properly, remember to handle the reactor carefully to avoid pressure leaks that would prevent the plasma from operating properly after its development. We hope this technique will pave the way for researchers in the field of material science.
Further in vivo experiments can answer additional questions like, what is best coating material and thickness for efficient drug release?
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Overview
This study focuses on the coating of nanoparticles with plasma polymers to control the release of core materials. Using plasma enhanced chemical vapor deposition, thin films are deposited on nano-sized particles, which are then etched to create hollow nanoshells. The permeability of these coatings is characterized, demonstrating their potential for sustained release applications.
Key Study Components
Area of Science
- Nanotechnology
- Materials Science
- Drug Delivery Systems
Background
- Plasma polymerization is a technique used for coating surfaces.
- Thin films can be deposited on various substrates, including nanoparticles.
- Controlling permeability is crucial for drug release applications.
- Previous work has focused on flat substrates rather than particles.
Purpose of Study
- To develop a method for coating nanoparticles with plasma polymers.
- To control the release of core materials from these coatings.
- To characterize the permeability of the coatings to small solutes.
Methods Used
- Preparation of silicon nanoparticles or calcium chloride nano powders.
- Coating of nanoparticles using plasma enhanced chemical vapor deposition.
- Etching of core materials to produce hollow nanoshells.
- Measurement of ionic conductivity to assess permeability.
Main Results
- Successful deposition of thin films on nano-sized particles.
- Creation of hollow nanoshells with controlled permeability.
- Demonstration of sustained release of core materials over several days.
- Characterization of permeability based on ionic conductivity measurements.
Conclusions
- The method allows for precise control over the release of materials.
- Hollow nanoshells can be tailored for specific applications in drug delivery.
- This approach expands the application of plasma deposition techniques to nanoparticles.
Frequently Asked Questions
Chapters in this video
0:05
Title
1:37
Preparation of Silica Nanoparticles for Deposition
2:23
Preparation of the Vacuum System
2:47
Plasma Deposition Process
4:27
Preparation of Hollow Particles by Dissolution of Core Material
5:36
Characterization of Permeability (Rate of Core Release)
6:56
Results: Plasma Polymerized Hollow Particles
8:40
Conclusion
