Swelling and ketoprofen release characteristics of thermo- and pH-responsive copolymer gels

Thermogelling of double hydrophilic multiblock and triblock copolymers of N,N-dimethylacrylamide and N-isopropylacrylamide: chain architectural and Hofmeister effects

A series of thermoresponsive double hydrophilic (AB)(n) multiblock and ABA triblock copolymers of N,N-dimethylacrylamide (DMA) and N-isopropylacrylamide (NIPAM) with varying sequence lengths were synthesized via successive reversible addition-fragmentation chain transfer (RAFT) polymerizations by employing polytrithiocarbonate as the chain transfer agent. Previously, we reported that multiblock copolymers in dilute aqueous solutions can form either unimolecular or multimolecular micelles at elevated temperatures depending on the relative chain lengths of PDMA and PNIPAM sequences (Zhou et al. Langmuir 2007, 23, 13076-13084). In this follow-up work, we further explored and compared the chain architectural (multiblock vs triblock) and Hofmeister effects (addition of various sodium salts) on the gelation behavior of multiblock and ABA triblock copolymers at high concentrations and attempted to establish a correlation between the aggregation behavior and gelation properties of multiblock copolymers at low and high polymer concentrations, respectively. It was found that only m-PDMA(p)-PNIPAM(q) multiblock copolymers with PDMA and PNIPAM sequence lengths located within a specific range can form physical gels at elevated temperatures. Rheology measurements revealed that multiblock copolymers possess considerably lower critical gelation temperatures (CGT) and higher gel storage modulus, G'(gel), as compared to those of PNIPAM-b-PDMA-b-PNIPAM triblock copolymers possessing comparable sequence lengths. The addition of inorganic sodium salts can effectively facilitate thermogelling for multiblock and triblock copolymers, resulting in decreasing CGTs and critical gelation concentrations (CGCs) in the order of Hofmeister series with increasing hydration capabilities. The unique thermogelling behavior of aqueous multiblock copolymer solutions in the absence and presence of inorganic salts, as compared to that of ABA triblock copolymers, augurs well for their potential applications in various fields such as biomaterials and biomedicines.

Formulation of thermoresponsive and bioadhesive gel for treatment of oesophageal pain and inflammation

The aim of this study was the formulation and examination of a novel thermoresponsive and bioadhesive, in situ gelling drug delivery system, which can be used in the treatment of oesophageal pain and inflammation. A bioadhesive cellulose derivative (Metolose) 60SH) was used as a thermoresponsive material, because Metolose has thermal gelation properties at certain temperature. The thermal gelation temperature (T(2)) of Metolose 60SH 2 w/w% solution is above body temperature (65-66 degrees C), but by using different methods (Metolose 60SH concentration, auxiliary materials), it can be shifted near to body temperature. The pH alteration between pH=2-10 and the application of different alcohols did not influence the gelation temperature, but using water-soluble salts and changing the concentration of Metolose 60SH solution between 2 and 3 w/w% the thermal gelation point could be decreased. Different NSAIDs were used as model drugs and which had not influence on thermal gelation temperature, but difference in in vitro liberation and penetration can be observed. In vitro adhesion test pointed out that the condition of investigated membrane can change the adhesion. Morphological test of oesophageal tissue showed that investigated materials had no irritative or tissue-damaging effect on the oesophageal mucosa even after 12h.

Potential application of Metolose in a thermoresponsive transdermal therapeutic system

The purpose of the present study was to formulate a novel thermoresponsive membrane controlled therapeutic system from Metolose for possible transdermal application. Metolose gel shows thermal gelation property, which can be characterized by two (T(1), T(2)) temperatures. A sharp decrease of viscosity can be measured at T(1), but gelation can be observed at T(2). Different types of Metolose polymers were compared considering their thermoresponsive behaviour. Only thermal gelation was observed in the case of Metolose SM, while Metolose SH showed a sudden decrease of viscosity at T(1). Since this temperature is above the body temperature, so it should be shifted to the skin temperature in case of possible transdermal application. Modulation of thermoresponsibility was followed by rheological method, and the thermoresponsive drug release from Metolose gel was studied by static liberation test. Our results demonstrated that the effect of different salts (NaCl, NaHCO(3), KCl) of various concentrations in Metolose SH gel reduced T(1) to the skin temperature, which enabled enhanced drug release.

Final report of the safety assessment of methacrylic acid

Methacrylic Acid is an organic acid used at concentrations between 50 and 88 percent to pretreat the nail and maximize the adhesion between the nail and artificial nail extender. Methacrylic Acid is readily absorbed through mucous membranes of the lungs, the gastrointestinal tract, and the skin; and is distributed to all major tissues. Oral LD50 values for rats ranged from 277 to 2260 mg/kg; acute toxicity symptoms included severe gastric irritation, gasping, labored respiration, prostration and hematuria. In a short-term inhalation study, rats exposed to Methacrylic Acid at 1300 ppm showed nose and eye irritation and weight loss, while necropsy results and blood and urine tests were normal. Methacrylic Acid is an ocular toxicant in animals. Undiluted Methacrylic Acid is corrosive to the skin of rabbits and guinea pigs. Exposure as limited as 3 minutes can cause severe erythema and slight to moderate edema. Exposure from 15 minutes to 24 hours under occlusive patches can cause marked to severe discoloration, slight to severe subcutaneous hemorrhages, necrosis, ulcerations, severe erythema, edema and concave eschar. Methacrylic Acid was irritating and caused strong rubefaction and scab formation in a guinea pig maximization test at challenge concentrations from 10 to 100 percent. It was difficult to determine if the results were type IV hypersensitivity reactions or simple irritation. In three other studies, guinea pigs were not sensitized. Methacrylic Acid was not a reproductive/developmental toxicant in rats or mice. Methacrylic Acid was negative in Salmonella typhimurium mutagenicity tests using strains TA98, TA100, TA1535 and TA1537 both with and without metabolic activation, but was positive in a DNA-cell-binding assay. Case reports involving Methacrylic Acid often involve children. Effects from ingestion include drooling, gagging, and vomiting. Children exposed to Methacrylic Acid as a result of accidental spills caused first and second degree burns to the eyes, face, hands, arms, and chest. The Consumer Product Safety Commission has required child-resistant packaging for liquid household products containing more than 5 percent Methacrylic Acid (weight-to-volume) in a single package. Since Methacrylic Acid is an extremely corrosive chemical, a primary concern about its use as a cosmetic ingredient was the ability to limit exposure to the nail when pretreating the nail prior to application of an artificial nail extender. A videotape presentation demonstrated that a trained professional could use a small applicator brush to dab a limited volume of Methacrylic Acid only to the center of the nail, allowing the monomer liquid to diffuse down the nail without any exposure to the skin. There were no available data to demonstrate that an individual consumer could apply Methacrylic Acid and avoid inadvertent skin contact. In order to minimize any exposure to the acid, the Expert Panel concluded that nail primers containing Methacrylic Acid could be used safely by trained individuals instructed to ensure that there be no contact with the skin. The CIR Expert Panel recognized that there are no chronic inhalation toxicity data on Methacrylic Acid, but was concerned that inhalation of Methacrylic Acid could affect the respiratory tract. Since the inhalation exposure time is significantly increased in a commercial setting, the Panel was more concerned about the safety of the nail technician than the consumer. The Expert Panel concluded that the current NIOSH recommended exposure limit of 20 ppm would provide adequate protection.

Stimulus-responsive "smart" hydrogels as novel drug delivery systems

Recently, there has been a great deal of research activity in the development of stimulus-responsive polymeric hydrogels. These hydrogels are responsive to external or internal stimuli and the response can be observed through abrupt changes in the physical nature of the network. This property can be favorable in many drug delivery applications. The external stimuli can be temperature, pH, ionic strength, ultrasonic sound, electric current, etc. A majority of the literature related to the development of stimulus-responsive drug delivery systems deals with temperature-sensitive poly(N-isopropyl acrylamide) (pNIPAAm) and its various derivatives. However, acrylic-based pH-sensitive systems with weakly acidic/basic functional groups have also been widely studied. Quite recently, glucose-sensitive hydrogels that are responsive to glucose concentration have been developed to monitor the release of insulin. The present article provides a brief introduction and recent developments in the area of stimulus-responsive hydrogels, particularly those that respond to temperature and pH, and their applications in drug delivery.

Simultaneous optimization of percutaneous delivery and adhesion for ketoprofen poultice

Topical poultices of ketoprofen were prepared using deionized water, propylene glycol (X1), and glycerin (X2) as the vehicle in combination with hydrophilic matrix materials, including gelatin (X3) and sodium polyacrylate. A mixture design was utilized to evaluate the influence of these constituents (X1-X3) on the adhesion of the poultice and the percutaneous penetration of ketoprofen from poultices. The adhesion of the poultice was measured based on the L-Peel test method using a Tensile and Compression Testing Machine. Percutaneous delivery was conducted using nude mouse skin as the barrier. The poultice containing the highest weight fraction of gelatin demonstrated the highest value of peak stress, whereas the poultice containing 0% weight fraction of gelatin showed the smallest value among all formulations. This indicates that gelatin was the main factor determining the adhesion of the poultice. However, the interactive influence of propylene glycol with gelatin on the adhesion of the poultice cannot be ignored. On the contrary, the formulation having the maximal penetration rate was determined to be the vehicle with 0% weight fraction of gelatin and the highest percent weight fraction of glycerin. This indicates that the presence of glycerin in the poultice was able to increase the flux of ketoprofen to some extent. Quantification of individual's effect based on this mixture design resulted in a polynomial equation: Peak stress=0.033X1+0.016X2+0.12X3, flux=1.90X1+4.70X2-6.65X3. Finally, an optimized formulation with acceptable adhesion and a flux comparable to two commercial products was developed in this study.

Release behavior of ketoprofen from poly(acryloyl-L-proline methyl ester) gels having different crosslinked networks

In order to clarify the relationship between the crosslinked structure of thermo-responsive polymer and drug release profile, polymer gels based on acryloyl-L-proline methyl ester (A-ProOMe) were synthesized in a mixture of water and acetone by the following two methods: a simultaneously occurring process of radiation-induced polymerization and crosslinking without a crosslinker (self-bridging method), and radiation-induced polymerization in the presence of the crosslinker tetradecaethylene glycol dimethacrylate (crosslinker method). The pronounced gap in thermo-response between two A-ProOMe gels, with an apparent degree of crosslinking of 11 for 1-propanol, shows a different shrinking pattern in the initial stage of time. The gels, which were obtained with the self-bridging method and the crosslinker method, were kept constant at a swelling ratio of 17 in water at 0 degree C for all systems. However, those values fell to 0.5 and 4, respectively, at 10 min after the temperature was increased to 37 degrees C. The release mechanism of ketoprofen from two gel devices showed an anomalous (non-Fickian) transport, in which the release of ketoprofen with a low water-solubility could be directly related to the rapid release of water accompanying a gel shrinkage.