High Hydration Levels Research Articles

Poly(methyl acrylate‐co‐hydroxyethyl acrylate) hydrogel implant material of strength and softness

The physiochemical properties of a hydrogel used as a scleral buckling implant for retinal detachment surgery are described. The new material was prepared by simultaneous polymerization and crosslinking of 2-hydroxyethyl acrylate with methyl acrylate and ethylene diacrylate, in the presence of an inert diluent, ethylene glycol. At equilibrium swelling, the hydrogen absorbed 17% water and had a durometer hardness (DH) of 15 (Shore Durometer A-2). A unique property of this material was its swelling hysteresis; when the gel swollen in 70% ethanol was placed in water, it retained a high level of hydration (75% water) and softness (DH 8), and most of its elasticity and strength as well. Then the swelling decreased very slowly so that the implant reached its ultimate size at equilibrium swelling in ca. 1 year. This property is especially useful in the scleral buckling procedure, in which a soft implant indents the sclera over the detached retina until reattachment is achieved. In addition to this advantage, this hydrogel is more elastic and stronger than available hydrogels of similar softness.

Unibase/glycol as an electrolyte medium for recording the electrodermal duct filling response.

ABSTRACTTwo experiments with 12 subjects each compared electrodermal recordings taken simultaneously with four different electrolyte media. These were polyethylene glycol, Unibase/glycol, Unibase, and hydrated agar (i.e., a site recorded with agar electrolyte which had been attached to the skin long enough to attain a high degree of hydration). The primary purpose was to compare the electrolyte containing a mixture of Unibase/glycol with the other electrolytes. The glycol and the hydrated agar were assumed to reflect low and high levels of epidermal hydration, respectively. These comparisons were made for monophasic negative SPRs and slow recovery SCRs (and their associated prestimulus levels), which are believed to reflect the endosomatic and exosomatic manifestations of the epidermal duct filling response.Unibase/glycol was quite similar to glycol alone with the exception of the prestimulus SPL associated with negative SPRs. Taken in conjunction with previous findings, the results suggest that for most aspects of electrodermal activity Unibase/glycol is a convenient electrolyte medium for use when minimal hydration is required. It is argued on theoretical grounds that minimal hydration is preferable for skin potential recordings.

A convenient, non-hydrating electrolyte medium for the measurement of electrodermal activity.

ABSTRACTTwo experiments with 12 subjects each compared electrodermal recordings taken simultaneously with four different electrolyte media. These were polyethylene glycol, Unibase/glycol, Unibase, and hydrated agar (i.e., a site recorded with agar electrolyte after presoaking it with water). The primary purpose was to compare the electrolyte containing a mixture of Unibase/glycol with the other electrolytes. The glycol and the hydrated agar were assumed to reflect low and high levels of epidermal hydration, respectively, while Unibase provided a comparison with Unibase alone. These comparisons were made for positive SPRs and rapid recovery SCRs (and their associated prestimulus levels), which are believed to reflect the endosomatic and exosomatic manifestations of the epidermal membrane response.Unibase/glycol was quite similar to glycol alone; thus it offers a more convenient electrolyte for use when minimal hydration is required. The results were interpreted as indicating that Unibase/glycol is preferable for skin potential recordings, while Unibase is to be preferred for skin conductance recordings.

Electrolyte medium effects on measurements of palmar skin potential.

ABSTRACTTwo experiments with 12 subjects each compared skin potential recordings taken simultaneously with four different electrolytes. These were polyethylene glycol, hydrated agar (at a site presoaked with water), fresh agar (i.e., not presoaked), and Unibase. The glycol controlled epidermal hydration at a minimal level, while presoaking produced a high level of hydration at the hydrated agar site. Fresh agar and Unibase represented normal recording conditions for these two electrolytes which have been recommended as “standard” for electrodermal measurements. This design permitted a comparison of two standard electrolytes with each other and with recordings from hydrated and unhydrated sites. These comparisons were made for both monophasic negative SPRs and positive SPRs and the prestimulus levels associated with each.The results replicated previous studies in showing a large effect of epidermal hydration on skin potential measurements. Recordings with agar and Unibase did not differ significantly. The effects of hydration were interpreted in terms of a reduction in the resistance of the stratum corneum and of alterations in the functioning of the dermal and epidermal membranes as a result of blockage of the sweat gland pore. In the light of this interpretation, it was suggested that both agar and Unibase substantially alter the functioning of the sweat glands under some conditions, and neither may be entirely suitable for skin potential measurements.