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Deposition of Patterned CaCO3 Films Using Binary Surfactant Systems

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Title:
Deposition of Patterned CaCO3 Films Using Binary Surfactant Systems
Creator:
Gutierrez, Javier
Gower, Laurie ( Mentor )
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Gainesville, Fla.
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University of Florida
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English

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University of Florida
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Deposition of Patterned CaCO3 Films Using Binary Surfactant Systems

Javier Gutierrez


ABSTRACT


This research studies a particulate system for drug detoxification. The specific particulate system of interest

consists of a core-shell particle coated with a porous calcium carbonate layer. This particulate system will work

by acting as a "micro-sponge" that will absorb the overdosed drug. Then, through degradation, the particle

will release the drug back into the body at non-toxic rates.



To facilitate research on the calcium carbonate layer, the research will be conducted on flat films instead of

on spherical particles. This flat surface consists of a monolayer of a binary surfactant system, upon which the

mineral film is deposited. The porosity of the calcium carbonate film will be patterned through the binary

system. Porosity will be achieved through phase segregation of surfactants.



INTRODUCTION


Electric In the United States alone, over 300,000 patients are annually admitted into the emergency room due

to drug overdose complications.1 Currently there is no effective on-site treatment of this condition.

Existing treatments - emeresis, stomach pumping, charcoal absorption - are all painful to the patient and require

a visit to the hospital.2 However, particle systems that can be injected into the body are being developed for

toxicity reversal applications. Systems currently being researched include smart microemulsions, silica core-

shell particles, nanotubules, and calcium carbonate core-shell particles.1 This last system - the CaCO3 system -

is the system of interest for this research. Each particle consists of a calcium carbonate shell and an oil

emulsion core. This system has numerous benefits. A calcium carbonate shell provides a built in filter for the

system, and CaCO3 itself is cheap, abundant, and biocompatible. This innovative idea is based on the principle

of surfactant self-assembly.



Surfactants, or amphiphiles, are molecules with both hydrophilic and hydrophobic regions. They normally have

a polar, water soluble head, and a non-polar, water insoluble tail.3 The phase segregation of amphiphiles is not

a thermodynamic phase transition. It is, rather, a change in conformation of the amphiphile. The driving force

for phase segregation of amphiphiles is the hydrophobic effect. This effect compels the amphiphile into






a conformation where the hydrophobic region is separated from the solution.4


The two drugs of interest in these investigations are amitriptyline and amiodarone. Amitriptyline is a

potent antidepressant, and amiodarone is prescribed as an antiarrhythmic agent. These were selected as study

drugs because they are among the most commonly overdosed drugs in the United States, with amitriptyline being

the leading method of suicide. The particles have an oil emulsion core because these drugs are lipophilic. This

will ensure that when the particles are introduced into the body, they will absorb the drug, since the drug will

prefer to be in an oily medium than in the bloodstream.



METHODS


The CaCO3 shell was initially investigated using flat films before advancing to spherical particles. Film porosity in

this research was achieved through phase segregation of amphiphiles. A binary surfactant system was used as

shown in Figures 1 and 2. The film surfactants had an ionic head, whereas the pore surfactant did not. The

film surfactants used were stearic acid and arachidic acid. These surfactants were negatively charged due to the

facile deprotonation of the carboxyl group. The pore surfactant used was cholesterol, which was neutral.

The cholesterol's alcohol functional group is not easily deprotonated - thus the net zero charge. The two

techniques used to deposit film on the surfactant monolayer were the CO2 Escape Technique and the

Peristaltic Pumping Technique. Film was characterized using Polarized Light Microscopy (PLM).






Stearatc (Cis)
--. ICholesterol

Arachidatc (Cmo) I


Figures 1 and 2. 1 - Charged Film Surfactants. 2 - Uncharged Pore Surfactant



Inputs The calcium carbonate film is proposed to deposit on the monolayer via a Polymer-Induced Liquid

Precursor process. This film is expected to begin as amorphous in nature, but with time, it should transform to

a crystalline structure.5 Figure 3 portrays the steps taken to attain patterned film formation. An aqueous
subphase, in this case a CaCO3 solution, is poured into a petri dish. Then, the binary surfactant system is spread

on the solution's surface. Finally, the film forms under the charged film surfactant.





CaCO3 son srfactant system film fo ---tion

CaC03 sol'n surfactant system film formation






Figure 3. Mechanics of film deposition in petri dishes.


CO2 Escape Technique


In the CO2 Escape Technique, 1 g CaCO3 was dissolved in 400 mL of deionized water. Then the solution was

stirred and bubbled with CO2 for five to six hours. The CaCO3 solution was then filtered via a buchner funnel

to remove any remaining CaCO3 powder. In each petri dish, 4 mL of the CaCO3 solution were mixed with

variable concentrations of Poly(a,p-dL-aspartic) acid, the polymer having a molecular weight of 8600 g/mol and

a solution concentration of 1 mg/mL. Finally, 4 pL of the surfactant system were spread on the solution's surface

with a microsyringe. The film was then allowed to deposit for several hours, observed with PLM and collected.



Pumping Technique


In the Pumping Technique, 2 mL of a CaCI solution were filtered into small petri dishes. Then, variable

concentrations of Poly(a,p-dL-aspartic) acid were added to each petri dish. Afterwards, 4 pL of the binary

surfactant system were spread onto the solution's surface with a microsyringe. Fisher Scientific Ultra-Slow

Peristaltic Pumps were used to pump 2 mL of (NH4)2CO3 into each petri dish over a time span of approximately

1 hour and 20 minutes. The film deposited was collected. PLM was used to observe the film both on solution and

once collected.



The binary surfactant systems used ranged from 100% film surfactants to 50% film surfactant/50% pore

surfactant. The polymer concentration ranged from 0 - 50 pg/mL.



RESULTS AND DISCUSSION


Poly(a,p-dL-aspartic) acid was added to the petri dishes in this experiment to inhibit crystal growth and to allow

a PILP process to take place. CO2 was bubbled through the aqueous subphase in the CO2 Escape Technique

to increase the solubility of CaCO3 in water.



At control with no polymer, no film formation took place (Figure 4A). This suggests that a PILP process induces

the deposition of film. As polymer concentration increased, less crystals formed since the polymer acts as an

inhibitor for crystal formation. As shown in Figure 4B, when only film surfactant was used, a continuous film

was formed. The single surfactant systems of 100% Arachidic and Stearic acids gave continuous, non-porous

film. The binary surfactant systems of film and pore surfactants created patterned, porous film with the pore

size decreasing as percentage of film surfactant increased (C,D). However, the pores formed as a network

of channels, not as individual circular holes. There was not any noticeable difference between films formed

using Stearic acid and those formed using Arachidic acid.


















A B












C D


Figure 4. Pictures of CaCO3 film formation. A. Both calcite and vaterite crystals from in a control

petri dish in the absence of polymer. B. At 100% film surfactant, a continuous, non-porous film forms

in solution. C. Film formed under 80% stearic acid: 20% cholesterol binary system and then collected

on microscope slide. D. Film formed under 80% arachidic acid: 20% cholesterol binary system and

then collected on microscope slide.



Both the Pumping and CO2 Escape techniques are acceptable methods for the formation of CaCO3 film.

However, when the film was collected and viewed under LPM, the CaCO3 film deposited by the Pumping

Technique was birefringent (Figure 5A), indicating crystallinity. This varied from the results obtained using the

CO2 Escape technique (Figure 5B). With the latter technique, the films were clear, indicating amorphous

material. Furthermore, film formation and crystallization occurred more rapidly using the Pumping technique.
















A B


Figure 5. Pictures of CaCO3 film collected from solution, 10X magnification. A. Formation of

100% arachidic acid film via the Pumping Technique. B. Formation of 100% arachidic acid film via

the CO2 Escape Technique.






Using a binary surfactant system, increasing the amount of film surfactant resulted in formation of film with

smaller pores. Accordingly, the best film for drug detoxification applications was formed with the 95% film

surfactant/ 5% pore surfactant. Furthermore, over 50% film surfactant was necessary to achieve reasonable film

and pore formation.



CONCLUSION


Both the CO2 Escape and Pumping Techniques are acceptable methods to form CaCO3 film. However, the

Pumping Technique is more suitable for this research. Using a binary surfactant system, increasing the amount of

film surfactant results in formation of film with smaller pores. Accordingly, the best film for drug

detoxification applications was formed with the 95% film surfactant/ 5% pore surfactant.


ACKNOWLEDGEMENTS


I would like to thank Dr. Laurie Gower for her extensive guidance in this research project. Her

consideration facilitated my learning in this research opportunity. Only through her advice and knowledge did

this research become reality. I would also like to thank Vishal Patel and Debra Lush, two graduate students whom

I worked with. They willingly offered needed aid which fomented my understanding of the research. Their

knowledge, experience, and friendship made this opportunity a memorable experience. Thanks as well to

Allison Kurz, Matthew Olszta, and the rest of the Gower group for their advice and aid.


REFERENCES


1. Moudgil, B.M., Seventh Year Annual Report. 2001: Engineering Research Center for Particle Science and

Technology, University of Florida.



2. Rumack, B.H., Poisoning: Prevention of absorption, in Poisoning and Overdose 1983, Aspen: Rockville. p. 13-18.



3. Walker, Peter ed. Chambers Dictionary of Science and Technology. Chambers: New York, NY. 1999.



4. Hamley, Ian W. Introduction to Soft Matter. Wiley: Chichester, England. 2000.



5. Gower LB, Odom DJ. "Deposition of calcium carbonate films by a polymer-induced liquid-precursor (PILP) process."

J. Crystal Growth 2000.












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