Biomaterials 21 (2000) 1509}1517
Physical}mechanical, moisture absorption and bioadhesive properties
of hydroxypropylcellulose hot-melt extruded "lms
Michael A. Repka*, James W. McGinity
College of Pharmacy, University of Texas at Austin, Austin, TX 78712, USA
Received 12 November 1999; accepted 31 January 2000
Abstract
The objective of this study was to investigate the moisture absorption, physical}mechanical and bioadhesive properties of hot-melt
extruded hydroxypropylcellulose (HPC) "lms containing polymer additives. These additives included polyethylene glycol (PEG) 5%,
polycarbophil 5%, carbomer 5%, Eudragit E-100 5%, and sodium starch glycolate (SSG) 5%. Relative humidity (RH) and
temperature parameters of the "lms studied included 253C at 0, 50, 80 and 100% RH, and 403C at 0 and 100% RH, stored for 2 weeks.
Tensile strength and percent elongation were determined on an Instron according to the ASTM standards. The bioadhesive
properties of the HPC/PEG 3350 5% "lm and the polycarbophil 5% containing "lms, with and without PEG, were investigated
in vivo on the human epidermis. Although all "lms studied exhibited an increase in percent water content as the percent RH increased,
the SSG containing "lm exhibited an almost three-fold increase in percent water content compared to that of the HPC/PEG "lm. The
temperature storage condition of 403C/100% RH (versus 253C/100% RH) increased the percent water content of the SSG containing
"lm. Percent elongation was highest for "lms containing polycarbophil 5% (without PEG). In addition, the HPC "lm containing
polycarbophil 5% exhibited a greater force of adhesion and elongation at adhesive failure in vivo, and a lower modulus of adhesion
when compared to the HPC/PEG "lm. A novel approach to determine bioadhesion of "lms to the human epidermis is
presented. 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Hot-melt; Extruded "lms; Hydroxypropylcellulose; Polycarbophil; Carbomer; Sodium starch gylcolate; Polyacrylate; Physical}mechanical
properties; Bioadhesion; In vivo; Novel
1. Introduction
Thin "lms for transdermal/transmucosal (TD/TM)
drug delivery devices and wound care applications are
frequently produced utilizing cast "lms from aqueous or
solvent-based systems. Aitken-Nichol et al. discussed nu-
merous disadvantages accompanying these techniques
which included environmental concerns, long processing
times and high costs [1]. Gutierrez-Rocca and McGinity
demonstrated that stable mechanical properties for acryl-
ic cast "lms may not be attained for up to 60 d, which
ultimately a!ects the rate of release of drugs incorporated
into the "lms [2]. Hjartstam et al. reported that alter-
ations in cellulose "lm structure in#uenced both drug
transport and the mechanical properties [3]. In addition,
moisture permeability and moisture uptake of TD/TM
"lms may in#uence the drug release rate as well as the
* Corresponding author. Tel.: 512-471-4841; fax: 512-471-2746.
E-mail address: m.repka@mail.utexas.edu (M.A. Repka).
adhesion of "lms to the epidermis or mucosa. It has been
shown that the type and level of plasticizer, temperature,
and relative humidity, all a!ect drug release, moisture
uptake, and mechanical properties of "lms formed from
aqueous dispersions [4}9].
Gutierrez-Rocca and McGinity reported that plas-
ticizers would increase the workability, #exibility, and
distensibility of a polymer [2,10]. Plasticizers modify the
physical}mechanical properties, by lowering the melt vis-
cosity, glass transition temperature and elastic modulus
of a polymeric "lm [2,4]. These physical}mechanical
alterations also play an important role in adhesive prop-
erties of "lms to solid substrates [11]. Gutierrez-Rocca
et al. demonstrated that the mechanical properties for
"lms prepared from aqueous latex dispersion Eudragit
L 30D containing varying amounts of triethyl citrate,
exhibited a reduction in elasticity and an increase in
tensile strength at 233C/50% RH with increasing time. It
was concluded that the transitional change in mechanical
behavior was due to residual moisture in the "lm, since
both water and the plasticizer will have a synergistic
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