표적지향 약물 전달 시스템을 위한 Fe3O4를 캡슐화한 PCL 나노입자의 제조 및 특성

김경연, 박성배, 함승주, 김우식

연세대학교 공과대학 화학공학과

Characterization and Preparation of PCL encapsulated  Fe3O4 nanoparticle for targeted drug delivery system

Kyong-Yon Kim, Seong-Bae Park, Seungjoo Haam, and Woo-Sik Kim

Department of Chemical Engineering, College of Engineering,

Theories and Application of Chem. Eng., 2002, Vol. 8, No.1

화학공학의 이론과 응용 제 8권 제 1호 2002년

Yonsei University, Seoul 120-749, Korea

Introduction

Magnetic polymer particles have been of interest since they exhibit wide application in the fields of gene manipulation, immunoassay, cell isolation, enzyme immobilization, targeted delivery of drugs, DNA separation, and so on. (1)

Magnetic drug targeting should be safe and effective, i.e. particles capable of carrying the desired and releasing drug at a controlled rate. Since magnetic colloidal particles could in principle be a suitable vehicle their external-field responsiveness.

In general, magnetite is well-known materials, properly characterized in many aspects, of which toxicity has been demonstrated to be quite low (LD50 in rat: 400mg/kg). (2) Magnetic particles alone, however, are not most suitable as drug vehicles, because of limitations in controlling the amount of drug they carry and the rate at which they can release it. Unlike inorganic magnetic particles, biodegradable polymers can release previously absorbed drugs at a rate determined by their degradation. (3) In addition, nanoparticle encapsulation has been proven useful for reducing the toxicity of certain drugs. Nanoparticles, like other colloidal carriers extended for drug delivery, after intravenous administration, are normally retained mainly by the reticuloendothelial system. (4)

In the present work, nano-sized poly □-caprolactone (PCL) particles, widely used as biodegradable polymeric carrier containing magnetite were prepared employing emulsification-diffusion method. This study focused on the development of the encapsulation process utilizing ethyl acetate as a dispersed solvent. The key factors which affected the characteristics of magnetic PCL particles such as their morphology, size distribution was investigated. Finally magnetic hysteresis of magnetic PCL particles were investigated.

Theory

The emulsion-diffusion has been proposed to prepare nanoparticles from preformed polymers (5) This process involves the emulsification of a partially water-miscible solvent, containing the polymer, in an aqueous phase, containing a stabilizer.

The subsequent addition of water to system cause the solvent to diffuse into the external phase, resulting in the aggregation of polymer in nanoparticles.

Nanoparticles formation is believed to occur because rapid solvent diffusion produces region of local supersaturation near the interface, and nanoparticles are formed due to the ensuing interfacial phase transformation and polymer aggregation that occur in these interfacial domains. The process is highly efficient, reproducible and easy to scale up. Ethyl acetate was used as partially water-miscible solvents because of their widely recognized low toxicity, good solubilizing properties and low boiling points. Poly(vinyl alcohol) was selected as stabilizer agents for the emulsification and to stabilize the external dispersion. They facilitate the formation of the emulsion and prevent agglomeration and coalescence of the dispersed polymer particles during solvent evaporation.

Experimental

1. Preparation of PCL encapsulated magnetite nanoparticles

0.25g of PCL and 0.15g of magnetite were dissolved in 5ml of ethyl acetate. The organic phase was added into 10ml of aqueous phase containing stabilizer. After mutual saturation of organic and continuous phase, the mixture was emulsified for 10min with ultrasonic homogenizer at 50% power. In order to allow for diffusion of ethyl acetate into water, water was subsequently added to o/w emulsion solution under the moderate stirring. After reaction  sample was obtained through cleaning procedure that included serum replacement in a stirred filtration cell and three cycles of centrifugation at 12000rpm. The magnetic PCL nanoparticles were dried in a vacuum oven at 35℃ and stored in container. In order to interpret the influence of phase volume on the solvent miscibility with water, In experiments were performed with O:W phase volume ratio ranging from 1:1.5 to 1:4. The variation of the size and the morphology of the particles were investigated by SEM, TEM and DLS. Magnetic properties were also measured by IR, VSM (Vibrating sample magnetometry)

Result and Discussion

1. Morphology

Fig 1. SEM image of PCL particles with O:W phase ratio (A)1:1.5 (B)1:2 (C)1:3 (D)1:4

The morphology of nanospheres was observed using the SEM according to various phase ratio emulsion, As illustrated in Fig.1 (B), the use of the O:W phase ratio of 1:2 resulted in the fabrication of relatively small microspheres. Attractively, the further the increase of the W phase volume ratio, the bigger the formation of microsphers. Also, some microspheres displayed surface defects and irregularity in Fig.1 (C). This observation was in good agreement with the earlier reports that fast removal of solvents from polymeric droplet affected the surface morphology. (6) Therefore, the O:W phase ratio of 1:2 which was saturated the continuous phase was utilized to form optimally microspheres.

2. Size & Size distribution

Fig.2 (A) and (B) showed TEM pictures and size distribution profiles of the magnetite PCL particles. Our observations on particle characteristics showed moderately monodispersed nanoparticles of 150±10nm diameter, and spherical shape.

Theories and Application of Chem. Eng., 2002, Vol. 8, No. 1

(A)	(B)

Fig. 2(A) TEM image(Bar length :200nm), (B) Size distribution of the magnetic PCL particles

3. Chemical Structure

Fig. 3 shows the infrared spectra of the presence of active groups on magnetic PCL particles.

Fig 3. IR spectra of the PCL and Magnetic PCL particles

Strong peaks at 3557/cm(hydroxyl bond), 1726/cm(carbonyl bond), 2943/cm(carboxyl-hydro bond) was shown on the PCL particles. The most significant band of magnetic PCL particles (570/cm) was identified by comparison with magnetite(570/cm) (7)

4. Magnetic properties

A magnetic hysteresis loop of the magnetic PCL particles was given in Fig.4. This displays the magnetization of the sample at 25℃, as the magnetic field of the susceptometer cycles between +10000 and -10000Oe. Under magnetic filelds, the curves showed no hysteresis, also the remanence and coercitivity were zero. The curves indicated that magnetic PCL particles showed paramagnetic behavior.

Fig 4. Magnetic hysteresis loop of the Magnetic PCL particles

Conclusion

Proposed technique enabled preparation of nano-sized PCL encapsulated magnetite. The particles prepared in our study present some advantages. First, preparation of the particles was very simple. Second, the magnetic particles having suitable magnetic properties could easily and gently were separated by using a magnetic field. Third, magnetic PCL particles could be applicable in magnetically controlled drug targeting.

Reference

[1] Xiaoning An, J. Applied Polymer Science, 81, 1175-1181 (2001)

[2] A. Iannone, R. L. Margin, Magn. Reson. Med. 22, 435-442 (1991)

[3] J.L. Arias, V. Gallardo, J. Controlled Realease, 77, 309-321 (2001)

[4] Upasna Gaur, Tapas K. De, Int. J. of pharmaceutics, 202, 1-10 (2000)

[5] D. Quintanar-Guerrero, E. Allemann, H.Fessi, Int. J. Pharmaceutics, 188, 155-164 (1999)

[6] Honkee Sah, J. of Controlled Release, 47, 233-245 (1997)

[7] Vladimir S. Zaitsev, J. Colloid and Interface Science, 212, 49-57 (1999)