Controlled Release of Biomolecules from pH-sensitive Network Polymers Prepared by Radiation Polymerization

New pH-Sensitive Glycopolymers for Colon-Specific Drug Delivery

pH-sensitive hydrogels are suitable candidates for oral delivery of therapeutic peptides, proteins, and drugs, due to their ability to respond to environmental pH changes. New pH-sensitive glycopolymers have been developed by free-radical polymerization of methacrylic acid and 6-acryloyl-glucose-1, 2, 3, 4-tetraacetate, using 1, 6-hexandiol diacrylate and 1, 6-hexandiol propoxylate diacrylate as cross-linking agents. The hydrogels were characterized by differential scanning calorimetry and FTIR. Equilibrium swelling studies were carried out in enzyme-free simulated gastric and intestinal fluids (SGF and SIF, respectively). A model drug, olsalazine [3, 3'-azobis (6-hydroxy benzoic acid)] as an azo derivative of 5-aminosalicylic acid, was entrapped in these gels and the in vitro release profiles were established separately in both enzyme-free SGF and SIF. The drug-release profiles indicated that the amount of drug released depended on the degree of swelling. The hydrogels containing polar propoxylate groups were hydrolyzed rather easily.

The Relation Between Swelling Properties and Cross-Linking of Hydrogels Designed for Colon-Specific Drug Delivery

Copolymers of 2-hydroxyethyl methacrylate (HEMA) and methacrylic acid (MAA)-based hydrogels containing 5% and 10% of a cross-linking agent were studied as drug delivery systems. Terephthalic acid was covalently linked with HEMA, abbreviated as CA (cross-linking agent). Free radical cross-linking copolymerization of HEMA and methacrylic acid (MAA) in three different molar ratios, mixed with a particulate 3, 3-azobis (6-hydroxy benzoic acid) (ABHB) as an azo derivative of 5-aminosalicylic acid with the various ratios CA as cross-linking agent were carried out with using 2, 2, Azobisisobutyronitrile as initiator at the temperature range 60-70 degrees C. The compositions of the cross-linked three-dimensional polymers were determined by FTIR spectroscopy. Glass transition temperature of the network polymers was determined calorimetrically. The hydrolysis of drug-polymer conjugates was carried out in cellophane membrane dialysis bags containing an aqueous buffer solution (pH 7.4 and pH 1) at 37 degrees C. The drug-release profiles indicate that the amount of drug release depends on its degree of swelling and cross-linking.

Synthesis of Starch—Poly(Sodium Acrylate-co-Acrylamide) Superabsorbent Hydrogel with Salt and pH-Responsiveness Properties as a Drug Delivery System

The synthesis and swelling behavior of a superabsorbent hydrogel based on starch (St) and polyacrylonitrile (PAN) were investigated. The physical mixture of St and PAN was hydrolyzed with NaOH solution to yield St—poly(sodium acrylate-co-acrylamide) superabsorbent hydrogels. The nitrile groups of PAN were completely converted to a mixture of hydrophilic carboxamide and carboxylate groups during the basic hydrolysis followed by in situ crosslinking of the PAN chains by the starch alkoxide ions. A mechanism for hydrogel formation was proposed and the structure of the product was established using FTIR spectroscopy. The effect of reaction variables, such as, base concentration, hydrolysis time, and temperature were systematically optimized to achieve a hydrogel with swelling capacity as high as possible. The optimized swelling capacity in distilled water was found to be >500g/g. The absorbency of the hydrogels indicated that the swelling ratios decreased with ionic strength increases. The St—poly(sodium acrylate-co-acrylamide) hydrogel exhibited a pH-responsive swelling—deswelling behavior at pH's 2 and 8. This on—off switching behavior provides the hydrogel with the potential to control delivery of bioactive agents. Release profiles of ibuprofen (IBU), a poor watersoluble drug, from the hydrogels were studied under both simulated gastric and intestinal pH conditions. The release was much quicker at pH 7.4 than at pH 1.2. The swelling rates of the hydrogels with various particle sizes were investigated as well.

Polymer-based biodegradable drug delivery systems in pain management

Pain is an unpleasant sensory experience commonly produced by damage to bodily tissues and it is one of the most significant public health problems, because 21.5% of the world population is estimated to suffer from pain. It results in a total loss of more than 165 billion US dollars each year in the United States alone. Pain reflects a mixture of various pathophysiologic, psychologic, and genetic contributions. When undertreated, pain usually results in serious immune and metabolic upset. Therefore, it requires wide understanding and intensive effort for a better management. Currently, pain control is limited by the modest efficiency of the used drugs, the serious side effects of these drugs, and the inefficacy of conventional drug administration. By the introduction of the technology of biodegradable controlled-release devices into clinical practice, pain control not only benefits from these novel methods for a better delivery of various drugs, but the side effects of the drugs are reduced because use of the devices improves patient compliance. Biodegradable controlled-release devices are polymer-based devices that are designed to deliver drugs locally in a predesigned manner. Recently, there was a high interest in developing these devices for the delivery of different drugs used for pain control. This paper first highlights the dimensions and basics of the problem of pain. Then, it presents an overview of the biodegradable polymers that are used in drug delivery systems and summarizes the studies carried out on these systems in the field of pain management. We refer to our experience in developing a device for multimodal drug delivery, including the use of nanotechnology. Future perspectives are also presented.