Transcript Gelatin Diffusion Experiment

Gelatin Diffusion Experiment
Nanotechnology in Medicine
Neil S Forbes
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
• Green food dye contains tartrazine (FD&C yellow #5) and brilliant
blue FCF (FD&C blue #1), which have molecular formulae of
C16H9N4Na3O9S2 and C37H34N2Na2O9S3, and absorb yellow light at
427nm and blue light at 630nm
• Paints contain colored pigment particles that have much higher
molecular weights
Experiment Overview
• The diffusion of the dyes will be compared to the
diffusion of paint particles 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
Experimental Setup
• Dissolve gelatin at double
strength and heat to dissolve
• Lubricate the inside rim of the
smaller Petri with holes dilled in
the bottom
• Invert the small Petri dishes inside
each of the larger Petri dishes
and inject 10 ml of cooling gelatin
• Allow the gelatin to cool for about
20 minutes
Experimental Setup-2
• Dissolve food dye and tempera paint
in water so that the color is strong but
still translucent.
• Gently and very slowly pull up on the
small Petri dish that contains the
cooled gelatin. The gelatin will slip off
and remain attached to the bottom of
the larger Petri dish.
• Pour food dye and tempera paint
solutions into the region surrounding
the gelatin casts (be careful not to get
food coloring solution on the top)
• Set aside each Petri dish in a level
place that will not be disturbed for
several days.
Analysis
• Each day, at 8:30, 12:30, and 4:30 take digital photos or
make drawings of the gels
• Estimate the distance that the food dye and tempera
paint each have penetrated into the gelatin discs
• On the last day at the end of the experiment, pour out
the food dye and tempera paint solutions
• Use a ruler to measure the distance of penetration into
the gelatin discs
• The rate of diffusion is the penetration length divided by
the time
• Compare the diffusion rate of the different dyes.
• Image analysis will be explained at he end of the
experiment
Gelatin Diffusion System
A 2-3 mm thick cylinder of
gelatin, molded in a large Petri
dish
Dyes are added to the space
surrounding the gelatin mold
Food color vs.
tempera paint
Start
3 hours
8 hours
Diffusion is
first visible
Green Food Color
Dilute tempera paint
12 hours
24 hours
36 hours
48 hours
60 hours
72 hours
Final
Questions to consider
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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?
Results
• Diffusion is very slow (millimeters per
hour)
• The physical properties of a dye (or drug)
affect the diffusion rate
– Small molecule food coloring dyes diffuse
faster than colloidal suspensions of pigments
(tempera)
Implications
• Understanding the relation between
diffusion and convective delivery (through
the vasculature) is essential
• The properties of delivery systems should
be carefully tailored to enhance drug
penetration and retention