X-Message-Number: 9345
Date: Tue, 24 Mar 1998 09:00:05 -0800 (PST)
From: Doug Skrecky <>
Subject: freeze drying without anhydroprotectant

Authors
  Curtil A.  Pegg DE.  Wilson A.
Institution
  Medical Cryobiology Unit, University of York, United Kingdom.
Title
  Freeze drying of cardiac valves in
  preparation for cellular repopulation.
Source
  Cryobiology.  34(1):13-22, 1997 Feb.
Abstract
  When freeze-dried cardiac valves have been implanted they
  remained acellular. This study is the initial step in the development of a
  method designed to repopulate the substance of the
  freeze-dried valve with fibroblasts and the lumenal surface
  with endothelial cells. In this scheme, the
  freeze-drying process performs three
  functions; it provides a porous matrix, it kills the donor cells, and it
  preserves the collagen structure and hence the mechanical strength of the
  valve. This paper describes the production of appropriate porosity in
  freeze-dried porcine pulmonary valve leaflets. We found that
  Tg' for this material is -83 degrees C, which made it impracticable to
  freeze-dry exclusively from the glassy state. Uncontrolled
  freeze-drying produced a variable structure
  with most of the pores considerably smaller than the desired size and a dense
  layer, apparently devoid of perforations, on the surface. Compacted layers
  also occurred within the substance of the leaflets. These appearances
  suggested that extensive collapse had occurred during the
  drying process. Variation of the cooling rate, the primary
  drying temperature, and the warming rate during secondary
  drying enabled us to identify the following conditions that
  provided satisfactory internal porosity: cooling at 5 degrees C/min, vacuum
  drying for 6 h at -20 degrees C, and secondary
  drying for 10 h during rewarming at 0.06-0.08 degrees C/min.
  The internal cavities measured 100-350 microns2 by ca. 400 microns2, which is
  adequate to provide access for the fibroblasts (cross-sectional area ca.
  150-200 microns2 when rounded but fusiform when attached. However, the
  internal porous structure rarely communicated with the surface and mechanical
  perforation was required to provide continuity between the surface and the
  internal sponge. The resulting method provides a basis for studies of cell
  colonization.

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