Water activity and glass transition temperatures of disaccharide based buffers for desiccation preservation of biologics by ProQuest


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									J. Biomedical Science and Engineering, 2009, 2, 594-605                                                                JBiSE
doi: 10.4236/jbise.2009.28086 Published Online December 2009 (http://www.SciRP.org/journal/jbise/).

Water activity and glass transition temperatures of disaccharide
based buffers for desiccation preservation of biologics
Justin Reis1, Ranjan Sitaula2, Sankha Bhowmick1,2,3
  Department of Mechanical Engineering, University of Massachusetts Dartmouth, Massachusetts, USA;
  Biomedical Engineering and Biotechnology Program, University of Massachusetts Dartmouth, Massachusetts, USA;
  285 Old Westport Road Room # Textile 210 N. Dartmouth, MA 02747, USA.
Email: sbhowmick@umassd.edu

Received 22 August 2009, revised 27 September 2009; accepted 28 September 2009.

ABSTRACT                                                           malian cells and gametes. While cryopreservation has a
                                                                   stringent requirement of storage in liquid nitrogen at a
Studying the thermophysical properties of disaccha-
                                                                   temperature in the vicinity of-196°C, desiccation pres-
ride based ternary solutions are gaining increasing
                                                                   ervation offers the ability to store cells at or near ambi-
importance because of their role as excepients in pres-
                                                                   ent conditions. At the same time it eliminates the usage
ervation protocols for biologics in general and mam-
                                                                   of toxic cryoprotectants such as glycerol and DMSO
malian cells in particular. Preservation strategies in-
                                                                   which require removal upon returning cells to ambient
volve not only cryopreservation, but novel approaches
                                                                   temperatures, severely affecting cell survival in the
like room temperature vitrification and lyophilization.
                                                                   process [1].
In this study we investigate the water activity and glass
                                                                      One of the hypotheses behind the mechanism of des-
transition temperature of citrate and tris buffers
                                                                   iccation preservation is the formation of glassy structure,
(widely used in the gamete preservation industry) with
                                                                   a highly viscous state that minimizes molecular mobility
trehalose or sucrose after partial desiccation. After
                                                                   of the matrix thereby suspending metabolic activities in
obtaining the water activity (aw) through equilibration
                                                                   the cells. Sugars, particularly disaccharides, have been
at different relative humidity environments, we
                                                                   effective in imparting cellular protection in the desic-
measured the glass transition temperature (Tg) of these
                                                                   cated state. A number of studies have demonstrated the
partially desiccated solutions using a differential
                                                                   ability of different sugars such as trehalose, sucrose,
scanning calorimetry (DSC). The experimental data
                                                                   raffinose and maltose to sustain a stable glassy state at
was used in conjunction with the Gordon-Taylor
                                                                   low moisture content [2,3,4,5,6,8]. Such sugars form
equation to obtain 3-D contours of Tg as a function of
                                                                   glasses at ambient temperature, thereby reducing mo-
water content and relative salt/sugar concentration.
                                                                   lecular mobility and allowing a prolonged stable storage
Results indicate that the glass transition behavior is a
                                                                   of biomaterials and cellular components [3,8,9,10,11].
strong function of the excepient combination. Overall,
                                                                      The survival of mammalian cells in vitro requires a
that trehalose solutions yielded larger values for Tg
                                                                   buffer or culture media generally consisting of various
than sucrose counterparts at low moisture contents in
                                                                   salt mixtures. In our study we chose to study ternary
combination with the same buffer. We also saw that
                                                                   sugar-salt-water solutions. The interactions of ternary
citrate solutions yielded larger glass transitions than
                                                                   solutions can often be extremely difficult to predict
their tris counterparts. Based on these results, a tre-
                                                                   without proper experimental studies of their thermo-
halose-citrate mixture can be picked as the preferred
                                                                   physics [6]. These interactions can produce results that
composition for storage applications. The 3-D contours
                                                                   may vary significantl
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