TITLE
The Effects of Container Shape and Surface Tension on
Crystallization in the Microgravity Environment
FLIGHT DATE
April 9, 2013
PRINCIPAL INVESTIGATOR:
John Frost Ph.D., Overland High School, Cherry Creek School District, Aurora, CO
CO-INVESTIGATORS:
Abiy Alemayehu
Aldair Cid-Gonzalez
Janet Dominguez
Jacob Donohoue
Geffen Ferszt
Jennifer Nass-Fukai Ph.D.
Debra Gregg PE
Jericho Oviedo
Roberto Rodriguez
Cynthia Turcios
Ameen Sassi
GOAL:
The goal of this experiment is to determine if container shape and surface tension play a significant role on
crystallization in a microgravity environment.
OBJECTIVES:
The objective of this work is to determine if container shape and surface tension play a role on
crystallization in the microgravity environment. Understanding these effects on crystal growth is important
because of the pharmaceutical applications associated with biological crystal growth. An important step in
developing a new pharmaceutical drug is to develop a very thorough understanding of the active site the
proposed drug would act upon. While the molecular structure and function of many binding sites in the
human body are well understood, the exact 3-dimensional shape (often referred to as tertiary structure) of
many of these binding sites is not available. Computer simulations can provide a great deal of insight, but
the only way to truly understand the tertiary structure is to observe it through a process known as X-ray
diffraction. This process uses x-rays and a single crystal of the molecule in question to produce a
diffraction pattern which, through a complicated series of equations can be used to determine the exact 3dimensional structure of the molecule. Because this process relies on the diffraction pattern created by a
crystal, the purity and perfection of the crystal plays an important role in the quality of the structure
produced.
Crystal growth of biological molecules can be very challenging which has caused scientists to investigate
numerous ways to improve the process. One very successful improvement in the process of growing
biological crystals was to conduct the process in space. Because the microgravity environment removes
such complicating factors as density, convection, etc. which can cause imperfections in the crystal,
diffusion becomes the driving force in crystal growth. Diffusion is a relatively slow and very low energy
process which allows crystals to be grown in microgravity that are larger and which contain fewer
imperfections than those grown on earth. Growing biological crystals in space has proven to be so
successful that a number of different experimental packages developed solely for growing crystals in space
have been deployed on the Space Shuttle, as well as the Mir and International Space Stations. ISS has been
used extensively to grow some of the best examples of certain biological crystals ever produced, however
there may still be room to improve this process.
It is well known that surface tension is the dominant force acting upon liquids in a microgravity
environment and shape, which affects surface tension, therefore plays a large role on the position of the
liquid inside a container. Furthermore, it is also known that in the one-G environment, container shape
plays a role in the macro-scale growth of crystals. Flat containers (such as petri dishes) are known to
provide a higher potential for success when attempting to grow flat crystals, and round crystals containers
are known to be better for producing rounded crystals. However, this knowledge seems to be limited to the
results rather than a true understanding based upon documented experimentation. To the best of our
knowledge, no one has formally studied the effects of container shape and surface tension on the
crystallization process on earth, or in microgravity.
Using a series of differently shaped acrylic containers filled with a super saturated solution of sodium
acetate, we intend to study the effects of container shape on the crystallization process in the microgravity
environment. By initiating crystallization during the microgravity portions of the flight and comparing the
resulting crystals to those formed in identical containers grown in a 1-G environment we hope to formally
determine if container shape does indeed play a role in the formation of crystals.
METHODS AND MATERIALS:
2 Part Acrylic Christmas Ornaments, various shapes
Super Saturated Sodium Acetate Solution
Clear PVC Cement
Blunt-tip Push-Pins
26 Guage Blunt-tip Needles
Hot Glue
Cotton String
Foam Padding
NASA’s Green No-Residue Tape, various sizes
Glass Beakers – Various Sizes
Hot Plate
Glass Wool
Vernier Temperature Pro
1 mL polypropylene syringe
Vernier 3-Axis Accelerometer
Vernier Global Positioning System
Vernier Radiation Monitor
Drill
Scoopula
Water
Optical Microscope
Hook and Loop Fastener, Sticky Backed
PROCEDURE:
The acrylic containers were prepared by drilling a 0.125” hole through the side in such a way that provided
the best opportunity for all the air to be forced out of the container by the solution. The containers were
then cleaned by blowing any particles left from the drilling process out with air. The two halves were then
sealed using PVC cement, which chemically welded the halves together, and were allowed to dry as seen in
Figure 1. Next, we prepared a super saturated solution of sodium acetate by dissolving 147 g of anhydrous
sodium acetate in 100 mL of 100º C water. The still warm super saturated solution was then drawn up into
1 mL polypropylene syringes and injected into the acrylic containers. Hot glue was used to seal the filling
hole in the container and a blunted push-pin was tied with a length of string to each container. The prepared
containers were then allowed to cool and secured in a closed cell foam block which was attached to the
bottom of the glove box using hook and loop fasteners. During the flights, the containers were taken out of
the foam blocks and crystallization was initialized during the micro-gravity portion of the flight maneuver
by forcing the blunt-tipped pin through the hot glue seal. The control group containers were crystalized in
an identical fashion in the laboratory.
Figure 1. Acrylic Containers ready to be filled with super saturated solution of sodium acetate.
RESULTS:
A number of differences were observed, both between the different shapes, and between the experimental
and control groups. These differences are summarized below.
● Differences in amount of air bubbles
○ In the oval container, there were more and smaller bubbles in the experimental container
○
○
○
when compared with the control.
In both the experimental and the control group of the sphere container there were few if
any bubbles found.
In both the experimental and the control group of the cylinder container there were few
bubbles found. There was about the same amount of bubbles in both groups.
In both the experimental and the control group of the star container there were few
bubbles found. There was about the same amount of bubbles in both groups.
● Differences in thickness
○ In the oval container of the experimental group, there were thicker crystals and on the
○
○
○
control oval there were thinner crystals.
In the sphere container of the experimental group, there were thin crystals and in the
control group, the crystals were amorphous.
In the cylinder container of the experimental group, there were thin crystals while the
control group had thicker crystals.
In the star container of the experimental group, there were straw-like crystals. In the
control group of the star container, the crystals were amorphous.
● Differences in lengths
○ There were tall crystals found in the oval container of the experimental group and smaller
crystals were found in the oval control group.
○ In the sphere container of the experimental group, there were tall crystals and in the
control group, the crystals were amorphous.
○ In the cylinder container of the experimental group, there were tall straw like crystals and
in the controlled group there were thicker crystals.
○ In the star container of the experimental group, there were long crystals stretching from
the corner of the container the pointy tip of the container. In the control group of the star
container, there were small and thick crystals that were oriented at random.
● Differences in lengths between fractures
○ In the experimental part of the oval container, the crystals were fractured at the curve of
the oval and some fractured crystals at the edges of container.
○ In both experimental and control group, the crystals were fractured, some more
frequently and distinctly than others. Based on the curvature of most of the ornaments,
fractures occurred as the crystals grew, they bounced off the surfaces of the container at
an angle and kept growing.
○ In the experimental part of the cylinder container, there were very few fractured crystals
at the flat surface of the container and at the curvature of the cylinder, there were a lot of
fractured crystals and longer distance between fractures. In the control group of the
cylinder container, there were more fractures found in the same place but the length
between fractures was much smaller than the experimental containers.
○ In the experimental group of the star container, there were fractures along the curve and
the edge of the container. In the control group of the star container, there were fractures at
the same place but with smaller length between the fractures.
● Differences between orientations
○ The orientation of experimental group is similar with all the containers. They start from
the initial point with straw like crystals and grow in every direction until the crystals hit a
curve or the corner of the container. In the curved containers the crystal fractured and
formed smaller and smaller crystals. This went on all around the curve of all the
containers. For the star container of the experimental group, the crystals grew towards the
midpoint of the star.
A representative photograph of the experimental and control groups are shown below.
Figure 2. Representative images of the experimental (left) and control (right) group ovals.
Figure 3. Representative images of the experimental (left) and control (right) group spheres.
Figure 4. Representative images of the experimental (left) and control (right) group cylinders.
Figure 5. Representative images of the experimental (left) and control (right) group stars.
DISCUSSION:
The results obtained with this work confirm what has been known for some time, that the microgravity
environment affects the crystallization process in clearly observable ways. The effects of surface tension on
the crystallization process however are less clear. The complexity of the experiment introduced a number
of variables which we were unable to address this year but which may have had an effect on the results we
observed. These ranged from variability in the degree of super saturation in the crystallization solution to
the variability in the effects of the surface tension on the crystallization close to the inner surface of the
container compared to that in the bulk solution.
The relatively simple task of preparing a super saturated solution of sodium acetate proved to be much
more difficult when used in this application. A super saturated solution of sodium acetate is incredibly
unstable and nucleation can occur with the slightest disturbance. Furthermore, the process of filling the
containers was relatively slow and we now suspect that during the time that some containers were being
filled, evaporation of water from the hot solution caused a distribution in the extent of super saturation of
the solution from container to container. This posed a huge challenge as filled containers cooled and
oversaturated samples filled later in the process spontaneously crystallized. When this occurred we were
forced to dissolve the crystals, clean the containers, and try again. This introduced yet another variable as
some containers were out of necessity filled with a different batch of sodium acetate solution than the
containers which did not spontaneously crystallize.
Container shapes were chosen based on the known relationship between the geometry of an angle/edge and
the surface tension exercised on a liquid in contact with that surface edge. A star shape was chosen for its
acute angles, while an oval, sphere, and cylinder where chosen for their various degrees of curvature.
Obviously with the exception of the sphere, the angles present are variable and in some cases quite
different, the gentle curve of the circular portion of the cylinder compared to the 90 degree edge at the top
and bottom, for example. While we failed to account for this, future work will attempt to address this with
more specificity, perhaps by eliminating the oval and cylinders and replacing them with different sized
spheres and cubes.
As mentioned earlier, while the results of this year’s flight were inconclusive, they did provide hints and
insights into the effects of surface tension on crystallization and how we might best study it. Future work
will focus on limiting the number of confounding variables, reducing the size and number of parts, and
reducing the amount of time needed to conduct the experiment in preparation for incorporating this work
into a NanoRack to be flown on the ISS. We also intend to forge a relationship with a local university to
have our results analyzed using an X-ray diffraction instrument. This would be an extremely valuable
resource which would allow us to investigate the atomic scale results in addition to the macro-scale effects
of surface tension on crystallization. It would also make it easier to obtain numerical, rather than subjective
data. In addition, while we intend to continue using sodium acetate to investigate this relationship, we
eventually hope to utilize a molecule more closely related to the biological molecules which require these
types of advanced crystal growth techniques and which have the most significance to the development of
new pharmaceuticals.
CONCLUSION:
This work confirmed the substantial effects on crystallization that microgravity plays and confirmed the
suitability of our small molecule in the development of this work. The effects of container shape and
surface tension on crystallization were inconclusive due to a large number of confounding variables, only
some of which can be addressed on earth, but the results did yield hints that there is indeed a relationship.
Future work promises to reduce many of the confounding variables, decrease the size, and increase the
quantitative data obtained.
ACKNOWLEDGEMENTS:
We would like to thank the following individuals for their support:
The National Aeronautics and Space Administration
NASA Offices of Research Integration, Education, Reduced Gravity Education Flight Program and
Reduced Gravity
Overland High School and Cherry Creek School District
Thermo Fischer Scientific
The Rotary Club of Aurora-Fitzsimons
The American Chemical Society
The Nass-Fukai Family
Artistic Apparel
Kevin Brown
REFERENCES:
Lide, David R. CRC Handbook of Chemistry and Physics: A Ready-reference Book of Chemical
and Physical Data. Boca Raton, FL: CRC, 1994. Print.
Mark Milton Weislogel, PhD, 26 April 2013 “The Capillary Flow Experiments: Handheld Fluid
Experiments for International Space Station” National Aeronautics and Space Administration.
http://www.nasa.gov/mission_pages/station/research/experiments/978.html
Richard J. Staples, July 2010. “Growing and Mounting Crystals Your Instrument will Treasure".
Michigan State University Department of Chemistry and Chemical Biology.
http://www2.chemistry.msu.edu/facilities/crystallography/staples.html
Pasquale Di Palermo, July 2001. “Advanced Protein Crystallization Facility (APCF) Fact Sheet”.
European Space Agency, National Aeronautics and Space Administration.
www.nasa.gov/centers/marshall/news/background/facts/apcf.html
CONTACT INFORMATION:
John Frost PhD
Thermo Fisher Scientific, NMR Technology Group
5445 Conestoga Ct. Suite 202
Boulder, CO 80012
303-802-6305
John.Frost@ThermoFisher.com
Jennifer Nass-Fukai PhD
Overland High School, Cherry Creek School District
Science Department Head
720-727-3844
jnass-fukai@cherrycreekschools.org