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Gellin Like a...Hydrophylic Cross-Linked Polymer?

Grades: 9
Author: Nathan Smith
Source: Original - This material is based upon work supported by the National Science Foundation under Grant No. EEC- 1542358.


Abstract

Students will prepare several recipes of Xanthan Gum-Glycerol polyester polymers and determine through testing and data analysis which one will serve best as wound dressings or other specific applications.


Objectives

What should students know as a result of this lesson?

  • That polymers have many unique properties that can be tuned for specific purposes
  • What a hydrogel is and several examples of hydrogel-based materials
  • Basic characterization techniques and vocabulary that help compare material properties
  • How to formulate hydrogel using 2 common food-safe ingredients

What should the students be able to do as a result of this lesson?

  • Formulate Xanthan-Glycerol hydrogels of varying ratios
  • Accurately record procedures and data in a lab notebook format
  • Communicate data based conclusions about hydrogel properties
  • Use and reflect on engineering and scientific principles by choosing and testing their own materials

Materials

  • Xanthan gum
  • Glycerol
  • A standard microwave (Low temperature oven can be used, but takes much longer)
  • Glass microscope slides or rectangular silicone candy molds
  • Larger heat safe glass containers like petri dishes or watch glasses
  • Acrylate hydrogel cubes, spheres, or spikes for initial observations

Procedures

Engagement

Pass out an unswelled hydrogel cube to partners in the classroom. Tell them to accurately describe the size and basic properties of the object as best they can. Then tell them that this is a hydrogel and explain what hydrogels are and list some of the many uses they have. Then have each group come and get a capped sample cup filled with water. This cup will contain a swelled hydrogel (swell for at least 2 hours), but will largely be invisible because its refraction index is similar to water. Tell them to gently feel in the water for an object. Each group can now try and characterize the swelled hydrogel.

Exploration

Scenario - A company has developed a medication for an illness that cannot survive normal injection or oral drug routes. You need to design a hydrogel that releases the medication over time in the form of an elastic patch that can remain on the skin or as a patch in a mucosal lining. You can provide a prompt from a fictional company to make this a more contextual project.

Explanation

Have students read the materials and methods from the paper these hydrogels are based on and produce a summary of the instructions with the class. Have each group mix a small sample (less than .2g) of xanthan with 1g of Glycerol and then put all the mixtures together in a single petri dish. Microwave the sample in 5-10s increments on 50% power until the hydrogel is a clear, tinged yellow-brown, solid sheet. Show the students the gel after cooling for a minute and use this to catalyze their own predictions. As a class you can summarize the protocol for creating the hydrogel so students have agreed upon the procedures.

Student groups of 2-3 now can predict what ratio's of Xanthan Gum to 1g Glycerol they would like to test to get a good idea of what sort of hydrogel will perform best. They should choose 3 different ratios to test and they should follow the procedure agreed upon. Samples will be mixed in small containers, poured onto a glass slide and microwaved in 5s intervals at 20-50% power (this % should be constant, determined by microwave available and teacher preparation). A running record style lab notebook will be kept. All procedures, problems, and observations should be written in the notebook.

The first 3 samples can be cut in half and characterized - 1 half for swelling behavior in 100mL water and 1 drop red food coloring. Another half can be used for stretch tests, tensile testing, conductivity, and general qualitative description. Templates for tensile instrons can be downloaded, and 3d-printed instron cookie cutters can also be created.

Once the first round of data is collected, students can share problems and successes and raw numbers. They will then create a larger sample according to an updated procedure of the formulation their data indicates will be most successful. A second round of testing will be completed and the class will put data into a single shared spreadsheet. After class data analysis they can complete a scientific paper based on their own and class data. A class period of research for background information on hydrogels may be necessary.

Elaboration

Students are assessed based on their final write-ups and a potential quiz covering background info on hydrogels


Prerequisites

Graphing, knowledge of the structure of scientific writing, and the scientific method/engineering design cycle


Best Teaching Practices

  • Hands on/Minds on Learning
  • Learning Cycle

Alignment with Standards

NGSS Standards:

  • HS-ETS1-3
  • HS-PS1-3

Ohio Standards:

  • Study of Matter: Properties of Matter
  • Study of Matter: Chemical Reactions
  • Forces and Motion: Types of Forces

Content Knowledge

Polymers, Crosslinking, Swelling Behavior, Elasticity, Opacity, Tension, Ester Bonds, Engineering Design Cycle


Safety

PPE (Goggles), Glassware, Applying forces to samples


Applications

Medicine (wound dressing, drug delivery, medication timed release, bio-compatibility), Electronics (Flexible materials, temporary degradable electrodes)


Assessment

The content and process of this Lesson could be used as an example of cross-linked polymer creation from common materials in 1-2 class periods, as a means to test many physical properties, and also as a long-term engineering project (5+ classes) to fit a specific community need, medicine being the most obvious connection.


Other Considerations

Grouping Suggestions:

  • 2-4 students in a group is appropriate. Logistics of using a single microwave for a class is the most difficult part. Signups can be employed, and each group should keep track of how long their sample was in the microwave. Multiple samples can be in the microwave at once, but intervals should be fairly short to ensure no excess steam or smoke from burning of hydrogel material builds up.

Pacing/Suggested Time:

  • 1-2 classes for testing a few properties of premade samples, 4-8 class periods depending on group size, final means of assessment, and materials available

Printable PDF Worksheets


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