PDF《Plenary Article》

8 h of in vitro incubation, and no motile spermatozoa were detectable after

24 h (Esbenshade and Nebel 1990). Swine spermatozoa need a di?erent approach in terms of procedure, with minimal sperm manipulation. An alternative biopolymer is represented by the family of alginates, unbranched polysaccharides extract from brown algae (e.g. Macrocystis spp., Laminaria spp.) Alginates are formed by the condensation of two acids: guluronic (G) and mannuronic acid (M). These are organized in brief homopolymers [or '

blocks'

, as C GGGGC (G-blocks), CMMMMC (M-blocks)] or hetero- polymers (-GMGMGMGM-). Guluronic acid units in G-blocks, given their molecular axial orientation, forms molecular '

pockets'

, which can be occupied by cross- linking divalentCtrivalent ions, such as Ca2+ , Sr2+ , Ba2+ , Al3+ , forming a three-dimensional network hydrogel. Hydrogel mechanical properties vary along with the G?M ratio (G-blocks yield harder gels) and the ion strength. The ?rst trials conducted by our research group on boar spermatozoa had considered the use of calcium alginate (CaAlg) in capsule preparation. The formation of a sperm-containing capsule has been reached with a single-step procedure to limit sperm overmanipulation. Brie?y, a saturated solution of bar- ium chloride is added to a sperm-rich fraction of an ejaculate until the desired concentration is reached (generally from

5 to

25 mM Ba++ . Such suspension is then added dropwise to a solution of sodium alginate under continuous stirring. Barium reacts immediately with alginate leading to the growth of a barium alginate membrane;

the inner Ba2+ ions di?use through the membrane, cross-linking at the interface and thickening Reprod Dom Anim

46 (Suppl. 2), 52C54 (2011);

doi: 10.1111/j.1439-0531.2011.01868.x ISSN 0936-6768 ?

2011 Blackwell Verlag GmbH the capsule wall. The process stops when all barium has di?used out of the semen droplet. The method gave well-formed capsules, but motility and spermatozoa speed were severely compromised (Torre et al. 2000). To avoid such problems, Ca2+ was substituted by Ba2+ : barium ion has the advantage to yield sti?er gels than Ca2+ ;

moreover, barium interferes with the calcium- triggered mechanisms of membrane hyperpolarization that parallels the sperm cell activation, limiting preco- cious capacitation and hyperactivation (Zhang and Gopalakrishnan 2005), with precocious sperm exhaus- tion. These hypotheses were con?rmed by a series of researches aiming to investigate the structure and functionality of barium alginate (BaAlg)-encapsulated spermatozoa: Vigo et al. (2002) report that BaAlg capsules maintain a high percentage of motile sperma- tozoa 1h........