Biomedical Engineering Reference
In-Depth Information
configuration of the osmotic pressure-driven drug delivery system is known as push-pull
systems [150]. A piece of hydrogel is loaded in a chamber surrounded by a semipermeable
membrane. When water is driven into the chamber, the hydrogel swells and pushes the
drug out of the chamber. Multicompartment of osmotic pressure-driven system can be fab-
ricated to deliver different types of drugs simultaneously. To generate a large osmotic pres-
sure gradient across the membrane, osmotically active ingredients, that is, sodium and
potassium chloride [151], and sucrose are added into the compartment. Cellulose acetate
is widely used to prepare semipermeable membrane, and water-soluble polymers such as
PEG are commonly used as a leachable component to form the orifices for the drug to be
released [152]. A similar concept was adopted by Pan et al. [153]. In their system, a coating
made of Eudragit L100 protects the system from acidic environment of the stomach, and
it dissolves in the small intestine. A semipermeable membrane is made from cellulose
acetate and chitosan. In the small intestine, although water is allowed to enter the core
through the semipermeable membrane, there are no orifices for the drug to be released.
The chitosan in the semipermeable membrane is eventually degraded by the microflora in
the colon; hence, the semipermeable membrane becomes porous and allows the drug to be
released driven by osmotic pressure.
Summary
Drug release rate control by coating technology can be a target at different control
mechanisms, namely, diffusion, erosion, and osmotic pressure. Understanding of those
mechanisms is critical to choose suitable materials and coating techniques for the
purpose of release rate control. For diffusion-controlled coatings, diffusivity and partition
coefficients are two key parameters, which can be affected by some common factors, such
as cross-linking density, hydrophilicity, and specific binding; however, partition-specific
control method (drug immobilization in the coating) is available as well. The ability to
control diffusivity and partition coefficients separately is beneficial to a more precise
release rate control. In the erosion and osmotic pressure coatings, diffusion plays a critical
role in determining the final release rate as well because it affects the degradation rate and
osmotic pressure.
References
[1] L. Shang, S. Zhang, S.S. Venkatraman, and H. Du, Physiological insights of pharmacokinetics
and host response for drug delivery system design,
Biomaterials and Engineering
(ISBN 0-87849-
480-4), edited by W. Ahmed, N. Ali, A. Öchsner, Trans Tech Publications, Switzerland, 419-472
(chapter 11), 2007
[2] T. Yoshida,
H. Tasaki,
A. Maeda,
M. Katsuma,
K. Sako,
and T. Uchida
,
Optimization of salting-
out taste-masking system for micro-beads containing drugs with high solubility,
Chemical and
Pharmaceutical Bulletin
56 (11) (2008) 1579-1584
[3] M. Cerea, W. Zheng, C.R. Young, and J.W. McGinity, A novel powder coating process for
attaining taste masking and moisture protective films applied to tablets,
International Journal of
Pharmaceutics
279 (2004) 127-139
