A Simple Method for Water Absorption Kinetics of Swellable Polymer Matrices


SY Patil1, US Patil1, HM Kadam2 and NR  Jadhav1*

1Bharati Vidyapeeth College of Pharmacy, Near Chitranagari, Kolhapur. Pin- 416013, Maharashtra , India.

2Bharati Vidyapeeth, Institute of Pharmacy, Erandwane, Pune, 411038. Maharashtra , India

*Corresponding Author E-mail: nrjadhav18@rediffmail.com


Purpose of the study was to develop a novel method for water absorption kinetics of swellable polymer matrices. Numerous findings have reported methods like use of optical microscopy (e.g., polarized microscopy, photomicrography, and optical imaging), spatula method, and nuclear magnetic resonance imaging. Due to their complexity and tedious nature, seldom are attempts made to study the kinetics of water absorption. Hence, we have developed the method using plastic sheets (perforated and nonperforated) to study water absorption kinetics. The method used 2 cm2 plastic sheets printed with black concentric circles of different diameters. Compacts were placed on these concentric circles on the plastic sheet and submerged in water placed in petri plate. At predefined time intervals the sheet and compact were taken out and weighed to determine weight of water absorbed (W). From W and time, the average velocity of water penetration front (U) and mass degree of swelling (Q) were calculated. It was observed that, the method gives entire water absorption kinetics up to the complete erosion of compacts without disturbing erosion front unlike other methods. The difference in the values of W, U and Q obtained from method using perforated plastic sheet non-perforated sheet were statistically insignificant at p<0.05. Initially for 1 hour, uptake of water was found to be rapid in all cases and maximum swelling attained was up to 5 hours followed by decline due to erosion of polymer chains from gelled layer of polymer compact. Because of simple set up, sensitivity, and less tedious nature, method seems to be promising.


KEY WORDS:   Novel method, swellable polymer matrices, water uptake.



In the advent of controlled drug delivery system, water swellable polymers have been of considerable interest to prolong the drug release. Specifically hydroxy propyl methyl cellulose (HPMC) has been widely used in design of extended release matrices. It shows good compression characteristics and has adequate swelling properties allowing rapid formation of gel layer, controlling drug release. To quantify the drug release from such swellable polymer matrices, a simple method has been needed 1-5.


The drug release from compressed swellable matrices is controlled by diffusion of the drug through the gel layer formed gradually around the polymer compact. Absorption of water by the polymer plays important role in the release of drug due to disentanglement of the polymeric chains 6-7 .To study water absorption kinetics of such polymers, different methods such as polarized microscopy, photomicrography, optical imaging, spatula method, and nuclear magnetic resonance imaging optical microscopy have been used 8-15.


Present method has been developed to overcome the drawbacks of existing methods. We have reported measurement of weight of water absorbed (W), mass degree of swelling (Q), average velocity of water penetration front (U) using the present method.



Methocel premium HPMC E-50LV was gifted by Colorcon Asia Ltd (Mumbai, India), Chlorpheniramine maleate (CPM) was supplied kindly by Supriya chemicals (Mumbai, India) and tartarazine as a coloring agent was purchased locally.



Preparation of compacts

Compacts of HPMC 50 cps and chlorpheniramine maleate (10 mg) weighing 600 mg were prepared by KBr press using 13 mm and 8 mm (250mg) flat faced punch and die set, at 2 tons pressure for 1 minute of dwell time. Total 6 compacts of 8 mm (Batch A) and 13 mm diameter (Batch B) each was prepared and subject to water absorption kinetic studies.


Water absorption kinetics

The compacts obtained were placed separately on plastic sheets (perforated and nonpeforated) having area 2 cm2, on which black concentric circles were drawn using computer-aided software. Concentric circles drawn had diameters of 13, 14, 16, 18, 20, 22, 24, 26mm for 13mm size compact, and 8, 9, 10, 12, 14, 16, 18, 20mm for 8 mm compact. 

The compact placed on each plastic sheet were separately submerged in petri plate containing 50 ml of water at 37±20C. At hourly intervals, plastic sheet along with compact was removed from petri plate, excess water was blotted with tissue paper and weighed for determination of water uptaken. Weight, thickness and diameter of compacts were determined for 13 hours.

The data obtained for weight of water absorbed was used to determine the mass degree of swelling (Q), rate of water absorption and average velocity of water penetration (U) using the formulae,



The plot of Q versus time (t) was obtained to study the swelling behavior of the compacts.



W, weight of water absorbed; t, time; ρw, density of water at 370C; 2A, area of tablet (area of tablet = π (DH+0.5D2, D, diameter, H, thickness) 16.



Water swellable polymeric matrices control the release of drug by formation of gel layer at the surface due to the swelling. It has been reported that, three distinct regions like swelling front, diffusion front and erosion front exist in swollen matirces. The process swelling decides the release of drug from the compact. And, hence, for the evaluation of such polymers, study of water absorption kinetics is important. Various methods have been reported for studying. Which inclues, optical methods etc15-21.


Figure 1: Computerized drawing of concentric circles drawn on plastic sheet.

Optical method reported for water absorption studies although gives precise idea regarding various fronts in the compacts of swellable matrices. Exact determination of water penetration front velocity, mass degree of swelling and weight of water absorbed has not been given in the literature. Routinely used spatula method for water uptake suffers from limitation of damage to the loosely bonded polymer chains at the erosion front, which if detached during weighing procedure may alter absorption kinetics and drug release mechanism 22-27. Hence  simple and novel method has been propsed using square plastic sheets. in one set of studies perforated plastic sheets were used, where as in another set nonperforated plastic sheet was used. The sheets were drawn with concentric circles on it as shown in Figure. 1. The swollen matrix placed on plastic sheet can be seen in the phorograph, as shown in figure 2.


Figure 2: A= Compact on perforated sheet, B= Compact on nonperforated sheet


To check and overcome obstacle posed by plastic sheet for penetration of solvent at lower surface, the use of perforated plastic sheet was made. Water absorption studies by both compacts (13mm and 8mm) rested on perforated and nonperforated sheets showed that, initial water uptake was quite higher for first one hour for all type of compacts followed by slow one up to 5 hrs. Later, uptake was found to be declined because of the erosion process as seen in figure. 3. The difference in amount of water absorbed by compacts rested on perforated and non perforated plastic sheet was statastical insignificant (P<0.05). Similar to the water absorption studies, findings on mass degree of swelling and average velocity of water penetration front has showed rapid increase in mass degree of swelling (Q) for first one hour followed by slow one and attaining maximum at 5th hour (Figure 4)


Average velocity of water penetration front was quite higher for one hour,which was followed by decline for both mass degree of swelling and average velocity of water penetration front (figure 5). The difference in values of Q and W obtained using  perforated and nonperforated sheets was statistically insignificant at (P<0.05). But, the difference in values of velocity of water penetration front was significant between compacts of 8 mm and 13 mm diameter.



Figure 3: Water absorbed (gm) Vs Time (hours)


Figure 4: Mass degree of swelling (Q) Vs Time (hours)


Figure 5: Avg. velocity of water penetration front (U) gm/sec Vs Time (hours)



The present method used for water absorption studies was found to be  simple, less tedious, inexpensive and non destructive unlike optical methods. It gives entire water absorption kinetics without damaging loosely bonded polymer network. Further exploration of method to check versatility, studies on rest of swellable polymers has been recommended.




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Received on 21.10.2008           Modified on 14.11.2008

Accepted on 23.12.2008          © RJPT All right reserved

Research J. Pharm. and Tech. 2(1): Jan.-Mar. 2009; Page 151-154