Activity: Gel Beads
Summary
This activity introduces concept of polymers and
gels, and relates this to engineering principles
used to design biomedical devices (such as an
artificial pancreas), bioreactors to produce high
value products (such as pharmaceuticals) and
filtration units to clean-up contaminated water
(such as in an aquifer or lake contaminated with
heavy metal wastes). Each of these are problems
that chemical, biological, and environmental engineers encounter regularly in the
working world, and each can have a significant impact on the lives of people
everywhere.
Engineering Connection
Engineers are using gel-beads for a myriad of applications including artificial
replacements and water clean-up. Biomedical engineers are using their
understanding of the human pancreas to create an artificial pancreas that could
be implanted into the body. Hundreds of thousands of gel beads would fit into a
semi-permeable membrane that would allow blood to circulate continuously
through the artificial pancreas. Gel beads are also able to “suck- up” a larger
number of toxic materials such as heavy metals and other pollutants.
Environmental engineers are using this “suck-up” property of the gel bead to
clean-up many types of wastewater streams.
Contents
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Learning Objectives
Materials
Introduction/Motivation
Vocabulary
Attachments
Procedure
Assessment
Extensions
Grade Level: K-12
Group Size: 1
Time Required: 30 minutes
Expendable Cost Per Group: US$ 0
Keywords: polymer, gel, crosslink
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Related Curriculum:
 Chemistry
Educational Standards:
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Oregon Science
 Identify basic tools used in engineering design. (K-1)
 Create structures using natural or designed materials and simple tools. (K1)
 Observe, measure, and record properties of objects and substances using
simple tools to gather data and extend the senses. (2)
 Use tools to construct a simple designed structure out of common objects
and materials. (2)
 Describe an engineering design that is used to solve a problem or address
a need. (2)
 Identify a problem that can be addressed through engineering design,
propose a potential solution, and design a prototype. (3)
 Describe how recent inventions have significantly changed the way people
live. (3)
 Based on observations and science principles, identify questions that can
be tested, design an experiment or investigation, and identify appropriate
tools. Collect and record multiple observations while conducting
investigations or experiments to test a scientific question or hypothesis. (45)
 Using science principles describe a solution to a need or problem given
criteria and constraints.(5)
 Explain that inventions may lead to other inventions and once an invention
exists, people may think of novel ways of using it. (4-5)
 Describe physical and chemical properties of matter and how they can be
measured. (6)
 Based on observation and scientific principals, propose questions or
hypotheses that can be examined through scientific investigation. Design
and conduct an investigation that uses appropriate tools and techniques to
collect relevant data. (6-8)
 Define a problem that addresses a need and identify science principals
that may be related to possible solutions. (6-8)
 Describe examples of how engineers have created inventions that address
human needs and aspirations. (6)
 Explain how new scientific knowledge can be used to develop new
technologies and how new technologies can be used to generate new
scientific knowledge. (7)
 Explain how scientific explanations and theories evolve as new information
becomes available. (8)
 Describe how different types and strengths of bonds affect the physical
and chemical properties of compounds. (9-12)
 Explain how chemical reactions result from the making and breaking of
bonds in a process that absorbs or releases energy. Explain how the rate
of a chemical reaction is affected by temperature, pressure, and
concentration. (9-12)
 Explain how energy and chemical elements pass through systems.
Describe how chemical elements are combined and recombined in
different ways as they cycle through the various levels of organization in
biological systems. (9-12)
 Explain how technological problems and advances create a demand for
new scientific knowledge and how new knowledge enables the creation of
new technologies. (9-12)
 Describe how new technologies enable new lines of scientific inquiry and
are largely responsible for changes in how people live and work. (9-12)
Learning Objectives
After this activity, students should be able to:
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List practical applications for gel bead properties
Describe polymers and the different between macro and micro molecules
Describe the unique characteristics of a gel
Materials List
Each student needs:
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A small cup filled halfway with 1 wt% calcium chloride solution
One or more small cups filled with 2 wt% sodium alginate solution in various
colors
One pipette
One small Ziploc bag
One small strainer
One bottle of Orbitz drink (not to drink)
Introduction/Motivation
A polymer is a long chain molecule with thousands of “repeat units” or mers
(hence the name polymer, meaning many units). In this lab the polymer is called
Sodium Alginate (Na-Alg) and it is extracted from brown seaweeds, the most
prominent of which is giant kelp (Macrocystis pyrifera) harvested from the
Pacific Ocean off the coast of California.. It is a product used in many foods as a
thickening agent and viscosifier (something used to modify the viscosity of a
liquid). We use a 2 wt% sodium alginate solution in water, which is similar in
consistency to a shake at McDonalds or Burger King. Think about that when you
get the “extra-thick” shake!
A gel is formed when the polymer chains are tied together (crosslinked). Imagine
a 3-D spider web with water in all the empty space. Remember, the gel beads
are 98% water! A gel has qualities of both solid and a liquid. Jell-O is one gel
with which you are probably familiar, formed by heating the polymer gelatin to
denature it and then cooling it to reform as a tangled network with hydrogen
bonding. Sodium Alginate is chemically crosslinked using a calcium ion (see
Figure Crosslinking and Gelation). Both Jell-O and the gel beads made here are
in a special class of materials called hydrogels, which are used extensively in
the medical field for drug delivery, gel patches with medication embedded within
them to be released upon contact with a wound, dressings for burn victims,
artificial skin, etc.
The ORBITZ DRINK has not been produced since about 1996. Why? Because
very few people really enjoyed it (or bought it) in the US. It was a bigger hit
overseas. The liquid portion of the drink contains both xanthan gum and gellan
gum, two large polymer molecules (very similar to sodium alginate) that act
synergistically (together) to produce a “weak gel network”, which gives the liquid
a yield stress (like ketchup, paint, and many other liquids). This weak gel network
suspends the gel beads. It can be easily broken upon pouring, but it reforms
quickly when the drink is placed at rest. This weak network breaking and
reforming is what gives the Orbitz Drink its amazing properties to suspend the gel
beads at rest but let them move with the liquid when poured or shaken.
Vocabulary/Definitions:
Polymer: a long chain of repeating molecules. There are many common
polymers derived from algae, such a carrageen, xanthan gum, and gelann
gum.
Gel: a crosslink of polymer. A gel has qualities of both solid and a liquid.
Viscosity: the extent to which a fluid resists a tendency to flow
Elasticity: the property of a substance that makes it possible to change its length,
volume, or shape in direct response to a force and to recover its original form
upon the removal of a force
Crosslink: bonds that link one polymer to another (three-dimensional matrix)
Macromolecule: A very large molecule, such as a polymer or protein, consisting
of many smaller structural units linked together
Micro molecule: a molecule of relatively low molecular weight
Attachments
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Gel Bead/Orbitz Handouts
Procedure
Before the Activity
 Print copies of Gel Bead and Orbitz Handouts (attached) for each student
 Mix a 2 wt% sodium alginate solution in water and separate it into different
colors using food coloring
 Mix a 1 wt% calcium chloride solution in water
 Cut the tips off of ~20 small pipettes
 Pour ~50mL of the calcium chloride solution into each group’s cup
 Set out several communal containers of the colored sodium alginate solution
 Place 2-3 pipettes in each container of sodium alginate
With the Students
1. Give each group a bottle of Orbitz to look at and discuss the beads and the
reason they are suspended in the drink (Answer: they form a weak gel
network)
2. Explain that sodium alginate has similar properties and will form a gel when
placed in the calcium chloride
3. Have the students drop several droplets of the sodium alginate solution into
their container of calcium chloride (Note: Make sure students know not to
touch the edge of the pipette to the calcium chloride because it will get
clogged.)
4. After about 30 seconds, let the students take the droplets out of the calcium
chloride and feel that they are firm gel beads.
5. Allow the students to continue to make more gel bead for as long as time
allows.
6. Have each student pour their container of calcium chloride and gel beads
through a strainer and into a waste container, then pour the gel bead from
the strainer into a Ziploc bag to take home..
Assessment
Pre-Activity Assessment
Discussion Questions: Solicit, integrate and summarize student responses. Ask
the students:
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What do you think of when you think of a gel?
How are gels made?
Post-Activity Assessment
Informal discussion: How can this simple technology help engineers design
products for the future?
Activity Extensions
For older students, include this experiment:
1) Make gel beads as described above from the 2 wt% sodium alginate and
1wt% calcium chloride solutions supplied in lab. Use the different colors of
sodium alginate to help with your experiment as needed.
2) Develop a qualitative method to determine the % gelation vs. time – the
fraction of the bead that has formed a gel (or how much is still liquid) as a
function of time. Keep good notes on your experimental method so you can
describe it to someone later.
3) Sketch a plot of your experimental data of % gelation vs. time and try to
explain in general phenomenological terms (not detailed chemistry) what is going
on at the molecular level with both the calcium ion diffusing into the bead and the
bead crosslinking (forming a gel).
Owner
Dr. Skip Rochefort, Chemical Engineering Department, Oregon State University
Last modified: 8/7/09