Biomedical Engineering Reference
In-Depth Information
basal plane and/or pyramid. A hexagonal prism seen in isolation cannot be
distinguished from another differently oriented hexagonal prism. In contrast, a
hexagonal bipyramid is a closed form that can appear on the growth form by itself;
however, it can also appear in combination with the basal face and/or various prisms.
Visual inspections of the crystallite shape using the height-to-baseline ratio or the
apical angle can readily distinguished bipyramids from other differently oriented
bipyramids. For that reason, the broad range within which the experimentally
observed pyramidal facets differ is directly observable on the obtained images
reported in the literature.
Strom et al. [
44
] have noticed that the fish-type ice binding surface enhances
the growth rate along the [001] direction, which is part of the secondary prismatic
surfaces (
hk
0). Their face indices, as observed experimentally [
81
-
84
], vary from
(110) up to (410); (110) is the most frequently reported secondary prismatic form.
The identification of the (110) secondary prism in ice grown in the presence of
sculpin AFP is reported [
81
]. The sculpin AFP is responsible for the growth of
prismatic (2 -1 0) ice crystals, where (2 -1 0) is symmetrically identical to (110)
[
5
,
85
]. Combinations of secondary prisms with primary (and other secondary)
forms are not ruled out theoretically. Indeed, ice crystallites grown out of a
solution with AFGPs exhibit (
hk
0) surfaces [
86
], sometimes in combination with
the primary surface (100) [
87
]. It is easier to observe the difference of secondary
face orientations in the case of bipyramids. PBC in [010] is the most strongly
bonded PBC contained in the secondary pyramidal surfaces (
h
0
l
). A large variety
in secondary pyramidal shapes has been observed in terms of height-to-baseline
ratios or apical angles (cf. Fig.
2.20
). The experimentally observed variety of
secondary pyramidal surfaces activated by the fish-type ice binding surface [
84
]
ranges from (302) to higher than (401). Among others, (201) is the most common
secondary pyramid triggered by the wild-type sculpin AFP [
83
] and by the winter
flounder AFP type I[
88
,
89
]. However, no explanation has been given for the
specific occurrence of (201) [
83
]. In line with the theoretical formulation, none of
the pyramids produced by the fish-type ice binding surface, matches in shape the
primary pyramid (101) illustrated in Fig.
2.20
. As predicted, secondary pyramids
appear in combination with primary (and other secondary) forms; the bipyramidal
crystals depicted in the observations [
84
] are combined with the basal face (001) and
also some unidentified prismatic facets. The theoretically admissible occurrence of
combinations of secondary and primary surfaces can be verified in the experimental
images. For example, a combination of (201) and (001) is observed [
83
].
AFPs of the sculpin engage secondary prisms such as (2 -1 0), while AFPs of
the winter flounder later engage the secondary pyramid (201) even though both
families have closely related and largely hydrophobic ice binding surfaces [
83
].
The explanation provided in ref. [
83
] was that although both ice binding surfaces
were indeed hydrophobic, they differed in their structure properties, such as the
arrangement of their binding intervals. It is reported [
83
] that the wild type and
few sculpin AFP variants produce secondary pyramids with different degrees of
activity even though most sculpin AFPs produce prismatic ice crystals. In addition,
the origin of the explanation could be due to the ice binding surface structural
