Gel Diffusion Experiment

STEM ED/CHM Nanotechnology 2009

Background

   The delivery of nanoscale medicines to cells in the human body requires diffusion through tissues, organs and cell membranes This activity will explore the affect of particle size on diffusion rates Understanding molecular diffusion through human tissues is important for designing effective drug delivery systems

Introduction

    Measuring the diffusion of dyes in gelatin illustrates the transport of drugs in the extra-vascular space Gelatin is a biological polymeric material with similar properties to the connective extracellular matrix in tumor tissue Dyes are similar in molecular weight and transport properties to chemotherapeutics Their concentration can be easily determined simply by color intensity

Experiment Overview

   The diffusion of the dyes will be compared to demonstrate the effect of molecular weight on transport in tumors Gelatin will be formed into cylindrical shapes in Petri dishes and colored solutions will be added to the outer ring Over several days the distance that the dyes and particles penetrate into the gelatin cylinders will be measured

Set-up

 Collect materials – Petri Dishes – Food Dye – Syringes – Paper Cups – Gelatin – Crisco/Petroleum Jelly – Baking Pan  Prepare Gel Cast – Determine water needed for proper coverage in pan – Dissolve Gel into warm water (2Pks/Cup) – Microwave for 90 Sec.

– Pour into pan and let set.

Setup

 Gel Cast – Cut circles in pan w/metal cookie cutter – Remove excess – Move Gel Cast from pan and transfer to Petri Dish – Smooth side Down!

– Centered as best can  Adding Dye – Mix dyes in cups – Inject one color/dish – No dye on top of Cast – No seepage under cast – Do not move dishes after dye inserted

Collect Data and Observations

 Take Digital photos – Same time each day and at same interval  8:00 AM and again at 4:00 PM each day – From approximately same height and angle – Helps to have a good background under the Petri dish

Start 4 hours

Data Collection 3 Food Dyes

Diffusion is first visible

Questions to consider

 Are the results expected?  Which dyes penetrated better?

 Does that make sense?  Conversely, does fast diffusion mean greater or poorer retention?

 How could diffusion and retention be optimized?

 Is this the intuitive result?

Gel Diffusion Analysis

Nanotechnology Institute 2009

Image Analysis

Method 1: – Measure the dye penetration distance each day using a ruler – Use graph paper to plot distance vs. time – The rate is the slope of the line

Measurement by Hand

18 16 14 12 10 8 6 4 2 0 0 y = 0.2057x + 1.0715

20 40

Time

60 80

Image Analysis

 Group Pictures by Color in date/time order 6-1-0600 6-1-1800 6-2-0600 – Create a data table (paper or Excel) 6-2-1800

 Pick one color to start  Load the first morning shot – Windows Photo Gallery or other image program

 Using the magnifier expand the photo  With a MM ruler measure the gel cast  Next measure from the edge of the gel cast to the inner most edge of the diffusion

 The ratio of the diffusion measurement divided by the gel cast measurement multiplied by 60 equals the amount of diffusion  (15 mm/145 mm) x 60 mm = 6.207

Enter this number in the appropriate column of your data table  Repeat for all time periods and colors

 When finished your table might look something like this

 Use the graphing wizard to complete the project.