Die Angewandte Makromolekulare Chemie 169 (1989) 211 -216 (Nr. 2787)

a Department of Chemistry and the Polymer Research Center, University of Cincinnati, Cincinnati, Ohio 45221, U.S.A.

Department of Chemical and Nuclear Engineering, University of Cincinnati, Cincinnati, Ohio 45221, U.S.A.

Short Communication

An Investigation of the Controlled Release of Diacetylfluorescein (DAF) from Polymeric

Membranes

Ping Xua*, Shuhong Wanga, and David B. Greenbergb

(Received 9 June 1988)

SUMMARY: The release kinetics of diacetylfluorescein (DAF) from the polymeric membranes

has been studied. The polymeric membranes were made of polystyrene and polysul- fone materials in a monolithic form. This work employed a fluorescence spectro- photometer to monitor the release rates by the hydrolysis of DAF at 25°C. The investigation exhibited that the release rates follow a zero-order kinetic scheme. The effects of different loadings of DAF and acetone on the controlled release rates were also exploited.

ZUSAMMENFASSUNG: Die Kinetik der Freigabe von Diacetylfluorescin (DAF) aus Polymer-Membranen

wurde untersucht. Die Membranen wurden aus Polystyrol und Polysulfon in ,,mono- lithischer" Form hergestellt. Zur Ermittlung der Freigabegeschwindigkeit durch Hy- drolyse von DAF bei 25 OC wurde ein Fluoreszenz-Spektrophotometer benutzt. Die Untersuchung zeigte, da8 die Freigabe einer Nullter-Ordnung-Kinetik folgt. Die Ef- fekte verschiedener Beladung mit DAF und von Aceton auf die kontrollierte Freigabe wurden ebenfalls ausgewertet.

Introduction

During the past decade, controlled release technology as a new inter- disciplinary science has received increasing attention in the medical, pharma-

* Correspondence author.

0 1989 Hiithig & Wepf Verlag, Base1 0003-3146/89/%03.00 21 1

P. Xu, S. Wang, and D. B. Greenberg

ceutical, agricultural and environmental fields, among others. A variety of delivery systems such as physical and chemical systems has already been developed ' -4. Recently, the unique permeation characteristics of polymeric membranes have begun to be applied for controlled delivery of biologically active agents. It has been predicted that the major controlled release technology will be the polymeric membrane type. Therefore, developing polymeric membranes for controlled release technology is of importance in this area.

Diffusion-controlled membrane devices can be divided into two main categories: reservoir systems in which the active agent is totally encapsulated within a rate-controlling membrane, and monolithic systems in which the active agent is dispersed or dissolved in a rate-controlling matrix4. In this article, we will report various release behavior of diacetylfluorescein (DAF) from monolithic membranes made of polystyrene (PS) and polysulfone (PSF) resins in the phosphate buffer solution. These membranes with DAF have been used for the constant concentration of the substrate in the detec- tion and identification of microorganisms by means of the fluorescent tech- nique'.

Tab. I . Prepared membrane samples.

Membrane* sample

Polymeric material

Concentration of DAF (mg)

PS OOO PS 050 PS 100 PS 150 PS 200 PS 250 PS 300 PS 350 PSF OOO PSF 150 PSF 200 PSF 250 PSF 300

PS PS PS PS PS PS PS PS PSF PSF PSF PSF PSF

0 50.00

100.00 150.00 200.00 250.00 300.00 350.00

0 150.00 200.00 250.00 300.00

* Membrane thickness: 1.9 pm.

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Release of DAF from PorVmeric Membranes

Experimental

Materials

The polymers used, PS and PSF, were purchased from the Aldrich Chemical Company. DAF was provided by Sigma Chemical Company. All the chemical reagents (ACS certified) utilized in this study were obtained from Fisher Scientific.

Preparation of Membranes

500 mg of the polymer material ahead of time were dissolved in 9.0 ml of tetra- hydrofuran (THF). A suitable amount of DAF (see Tab. 1) was not added into the polymer solution with stirring until the polymer had been dissolved completely. Then the homogeneous DAF-polymer solution was cast by pouring the mixture onto a very clean glass plate at room temp. The membrane thickness was controlled by a knife edge. After approximately 60 min, the membrane was removed from the glass plate and dried to a constant weight in vacuum at room temp., and then cut into disks of 1.2 cm diameter by using a cork borer. Afterwards, they were stored in a desiccator.

Apparatus

The equipment and instrumentation for the determination process of the release rates of DAF is illustrated in Fig. I . The system is primarily composed of two parts: a fluorescence spectrophotometer (Perkin Elmer LS-5) and a signal processor (model 4402, EG & G Pncenton Applied Research). The cuvettes made of polystyrene were purchased from Markson.

-ling b f s m cwette

light

signal processor

Fig. 1. Fluorescence apparatus.

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P. Xu, S. Wang, and D. B. Greenberg

Procedure

The fluorescence spectrophotometer was turned on and allowed to warm up for at least 15 min. The excitation and emission gratings for DAF were then set to 465 nrn and 520 nm, respectively. A constant value of gain (15.0) was chosen. All aqueous solutions were tested with an excitation slit width of 15 nm and an emission slit width of 20 nm in order to provide maximum irradiation and detection.

Results and Discussion

In the study of the controlled release from membrane-controlled DAF, two kinds of working media were used: (a) 2.9 ml phosphate buffer plus 0.1 ml acetone; (b) 3.0 ml phosphate buffer'. Two preliminary studies were con- ducted to ascertain the response of the media and the unloaded membranes (PS 000 and PSF OOO). The results demonstrated that they did not fluoresce.

The hydrolysis reaction of membrane-controlled DAF release took place in a cuvette with stirring at 25 "C. The results of controlled release are given in Fig. 2. Clearly, the release rates of membrane-controlled DAF follow the

0 1.0 8.0 12.0 16.0 20.0 21.0 Time (h)

Fig. 2. Plot of the release rates of membrane controlled DAF versus time. o PS 050; 0 PSF 250; in medium (a).

zero-order kinetics in the period of 24 hours. The effects of different loadings of DAF on the release rates were observed, which are shown in Fig. 3 and 4. From Fig. 3, we see that the release rate of DAF increases with

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Release of DAFfrom Polymeric Membranes

0 0.1 0.2 0.3 0.1 0.5 0.6 0.7 0.8 Ratio of DAF to PS (weight ratio)

Fig. 3. Effect of different loadings on the release rates of DAF from PS membra- nes. o in medium (a); A in medium (b).

0 0.1 0.2 0.3 0.1 0.5 0.6 0.7 0.8 Ratio of DAF to PSF (weight ratio)

Fig. 4. Effect of different loadings on the release rates of DAF from PSF membra- nes. o in medium (a); A in medium (b).

the increase of DAF loading in PS membrane in medium (a), but is independent of the loading of DAF in medium (b). This may be because acetone can swell PS, thus the sizes of channels in the membranes become enlarged. Swelling of PS can, therefore, control the release of DAF from the

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P. Xu, S. Wang, and D. B. Greenberg

PS membranes. From Fig. 4, it is illustrated that the release rates of DAF in medium (a) are less than those of DAF in medium (b), and that the release rates are independent of the loading of DAF. This may be because acetone is a nonsolvent for PSF, which results in that the sizes of channels in the PSF membranes contract. This effect makes it more difficult for DAF to release from the PSF membranes since the change of channel size can affect the diffusion coefficient of DAF in the polymeric membranes.

It is gratefully acknowledged that this work was supported by a grant from the Membrane Technology Center of the University of Cincinnati. Ping Xu also wishes to acknowledge a URC Research Fellowship provided by the University Research Council of the University of Cincinnati.

A. F. Kydonieus, in Controlled Release Technologies: Methods, Theory, and Applications, Vol. I, A. F. Kydonieus (Ed.), CRC Press, Inc., Boca Raton, Florida, 1980, p. 1 F. Theeuwes, in: Directed Drug Delivery, R. T. Borchardt, A. J. Repta, V. J. Stella (Eds.), Humana Press, Clifton, New Jersey, 1985, p. 121 P. I. Lee, W. R. Good, in: Controlled-Release Technology, Pharmaceutical Applications, P. I. Lee, W. R. Good (Eds.), American Chemical Society, Wa- shington DC, 1987, p. 1 J. H. Richards, in: Polymer Permeability, J. Comyn (Ed.), Elsevier Applied Science Publishers, London and New York 1985, p. 217 P. Xu, D. B. Greenberg, Biotechnol. Bioeng., in press A. P. Snyder, T. T. Wang, D. B. Greenberg, Appl. Environ. Microbiol. 51 (1986) %9

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