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Biomedical subjects

R Petersson

Publications and source records attributed to R Petersson.

4 recordsLinked to original sources
PubMed1998

Rheological evaluation of Gelrite in situ gels for ophthalmic use.

One of the reasons for the relatively low bioavailability of conventional eye drops is their short precorneal contact times. In situ gels are promising ocular drug delivery systems since they are conveniently dropped into the eye as a liquid whereafter they undergo a transition into a gel. Due to their elastic properties hydrogels resist ocular drainage leading to longer contact times. In this paper the rheology of Gelrite in situ gels was studied. A complementary in vivo study for determining precorneal contact times in humans and in rabbits was performed. The elastic moduli of the gels increased with increasing concentration of electrolytes. At physiological concentration of the electrolytes, the elasticity of the gels was independent of Gelrite concentration. The human contact times increased up to 20 h with decreasing osmolality of the formulations. The results indicate that a high rate of the sol/gel transition results in long contact times.

Animals↗
PubMed1998

Rheological evaluation of poloxamer as an in situ gel for ophthalmic use.

The contact time of a vehicle on the cornea is of utmost importance for ocular drug delivery. In the present study rheological measurements were performed to study the gel and the sol-gel transition of an in situ gel, Poloxamer 407. The rheological measurements and a small in vivo study of ocular residence times in humans were used to evaluate poloxamer as an ocular vehicle. An increasing concentration of poloxamer resulted in a slightly increasing elasticity of the gels and a decreasing sol-gel transition temperature. The contact time increased with increasing concentration of poloxamer which could be explained and correlated with the rheology of poloxamer solutions/gels mixed with simulated tear fluid. The maximum contact time for the preparations studied was about 1 h. The poloxamer system did not seem to be promising as an ophthalmic in situ gel due to the strong concentration dependence of the sol-gel transition temperature combined with the dilution that occurs in the eye.

Gels↗
PubMed1984

Enterochromaffin cells in the rat gastrointestinal tract. Aspects of factors influencing quantification.

A quantitative study was made of the enterochromaffin (EC) cells, visualized with the Masson (slightly modified) and Falck-Hillarp techniques, in the rat gastrointestinal tract. Different factors influencing the quantification were analysed and the magnitude of methodological errors was estimated. The two histochemical techniques visualized the EC cells in different ways, influencing the quantification results. This means that a comparison of the quantitative results obtained by these techniques can only be made after correction by some factors. The frequency of EC cells is given as the number of cells both per mm3 mucosa (cellular density) and per segment of mucosa with a base of 1 mm2. The latter information takes into account both cellular density and mucosal thickness. The highest frequency of EC cells was found in the pyloric gland area of the stomach. On the border with the duodenum there was a marked decrease in this frequency and in the whole intestine the frequency was low, with only minor fluctuations of the mean values. The frequency was increased in the caecum, followed by a gradual decrease in the large intestine. The quantitative variation of the EC cells at the same gastrointestinal level was considerable, and was greater between animals than between serial sections within the same animal. The difference in EC cell frequency that was required to give significance was calculated. For quantitative studies the Masson method has some minor advantages over the Falck-Hillarp technique, as routine formalin-fixed deparaffinized sections can be used and no counterstaining is needed for the areal estimation.

Animals↗