Open versus closed systems for vitrification of human oocytes and embryos

Abstract

Vitrification is now the dominant approach for cryopreservation of human oocytes and embryos; however, serious disagreement persists, particularly about biosafety issues. Techniques are categorized as either 'open' or 'closed' according to occurrence of direct contact between the medium and liquid nitrogen during cryopreservation. Advocates of closed systems emphasize the potential danger of disease transmission mediated through liquid nitrogen, and praise the safety of their approach; those who use the open systems refer to the lack of evidence of disease transmission and regard their systems as more consistent and efficient. The purpose of this review is to clarify whether open and closed systems are really open and closed; if closed systems are safe and free of any danger of contamination; if closed systems are equally efficient as open ones for cryopreservation of human embryos and oocytes by considering overall outcome; and finally, if ethical and legal concerns are sound when risks and benefits are considered in a broader sense. On the basis of these answers, implementation of rational measures to lower the theoretical danger of disease transmission are proposed while maintaining the achievements in cryopreservation that have contributed substantially to the advancement in assisted reproduction techniques during the past decade.

Applications and optimization of cryopreservation technologies to cellular therapeutics

“…Much has been learned about the biophysics underpinning vitrification [49], and Figure 3 depicts the important biophysical characteristics. The technology has recently become widely applied in reproductive cryo-banking for infertility treatment [50]. However [51] for a review), but these have yet to be applied to deliverable cell therapies.…”

Vitrification: the pioneering past to current trends and perspectives of cryopreserving human embryos, gametes and reproductive tissue

“…By 2010, the benefits of vitrified embryos and oocytes, having virtually no change from their fresh state, were gaining worldwide acceptance. 34,35 The diversity of issues surrounding the pros and cons of both open and closed device systems has been recently discussed by Vajta et al, 36 and is briefly mentioned in the following paragraphs. Historically, most clinical users of vitrification systems were misled that the ultrarapid cooling rates attained by the direct exposure of open devices to LN 2 were necessary to achieve high survival rates with embryos and oocytes.…”

“…In turn, one must warm more rapidly to combat the injurious effect of recrystallization. 43 Indeed, vitrification is a highly complex process, 36 whereby a reciprocal interaction exists between the cooling rate required to achieve vitrification of a solution and the concentration of CPA(s)/solutes. 48 53,54 The key component to optimizing post-warming survival, independent of device used, is to insure that the warming rate is greater than the cooling rate; of which the need for speed is inversely correlated with the concentration of the CPA used.…”

Closed vitrification of human oocytes and blastocysts: outcomes from a series of clinical cases

“…Although this risk may be theoretical in ART with no reports of contamination, there are concerns that the risk may increase for oocytes in longterm storage for fertility preservation, which is now common practice. Procedures have been developed to reduce the potential risk [10][11][12][13] and a number of closed vitrification tools developed [14], but there has been a reluctance to use closed systems due to the impact of slower cooling rates on survival.…”

“…Although it might depend on the tool, all closed vitrification systems achieved slower cooling rates than open systems [14]. In addition, some carriers are also associated with slower warming rates which may be more critical for survival [15,16].…”