The carbomer we produce is a white loose powder with strong hygroscopicity. Therefore, it must be placed in a plastic bag in a dry place during storage. When we use carbomer, we usually make a gel and add it to daily chemicals or medical raw materials. What are the factors that affect the properties of carbomer gel? Including the pH value and ionic strength of the medium, the nature of the drug, and the presence of other excipients.
Factors affecting the properties of carbomer gel
The effect of pH
As the carbomer polymer has a large number of free carboxyl groups, its pKa value is usually small. When the pH of the medium is less than 4, the carboxyl groups hardly dissociate, and when the pH>4, the carboxyl groups begin to dissociate, the polymer swells, and the viscosity increases. , When the pH value is 8, the dissociation is almost complete and the viscosity is the largest. When carbomer is used as a carrier for basic drugs, after the drug is dissolved, the pH of the medium increases, the degree of carbomer dissociation increases, the gel layer thickens, and the drug release rate decreases, so as to achieve the control of drug release purpose. The pH value of the medium also affects the adhesion of the carbomer gel. When the pH value is lower than its pKa, the gel has a stronger bonding ability and increased adhesion. At the same time, the ionic strength of the medium can change the sensitivity of the carbomer gel to pH. When the ionic strength is high, the carbomer is easier to release protons, and its pKa value decreases, so it can dissociate and dissolve at a lower pH. rise.
Influence of ionic strength
In some drug delivery systems, the influence of the drug on the pH and ionic strength of the medium around the gel is not negligible, because the pH of the drug will also affect the properties of the gel, and the effect of acidic drugs is more obvious. The main drug is 2 In the case of 5-dihydroxybenzoic acid, the thickness of the gel layer is about twice the thickness of the gel layer formed by salicylic acid as the main drug, which proves that acidic drugs will increase the adhesion of the gel.
Influence of other excipients
In carbomer gel, if polyvinylpyrrolidone and polyoxyethylene are used as excipients at the same time, it may reduce the mucosal adhesion ability of carbomer gel. This decrease is also related to the concentration and molecular weight of coexisting excipients, and the concentration of excipients is high. (5%), can significantly reduce the adhesion of carbomer gel, when its concentration is reduced to 0.5%, the effect is small. Generally, the pH of the medium cannot change this property of polyvinylpyrrolidone and polyoxyethylene. Magnesium stearate can also reduce the adhesion of carbomer gel because of its hydrophobicity.
