Boar semen controlled-delivery system: morphological investigation and in vitro fertilization test

Abstract

A technology for encapsulation of swine semen in barium alginate and protamine alginate has recently been proposed for the controlled release of the spermatozoa, thus reducing the number of instrumental inseminations required. Controlled-release capsules containing swine spermatozoa were prepared by adding saturated BaCl₂ solution to ejaculate and dropping the resulting suspension into a sodium alginate solution, leading to the formation of barium alginate capsules. A second type of capsule was obtained by cross-linking the barium alginate with protamine sulfate. Two types of membrane were thus obtained: barium alginate gel and a protamine cross-linked alginate membrane. Morphological (scanning electron microscopy and transmission electron microscopy), functional (motility, membrane integrity and in vitro fertilization test) and technological (capsule structure and weight) approaches were used to characterize the encapsulated spermatozoa and the controlled-delivery system. No differences in terms of morphological and functional characteristics (acrosome integrity and spermatozoa motility) between free and encapsulated semen were found. The technological process did not compromise in vitro fertilization potency of the spermatazoa, although seasonal variability was found. The capsule weight was related to either the pH of the semen or the season. This study represents the starting point for the development of further investigations into the storage and release kinetics of cells from the capsules and for the development of an in vivo fertilization protocol.