Thermal Inkjet Dispense for Pharmaceutical Research

Lindsey Rucker, Hugh Hobbs, Ahson SaeedSchool of Chemical, Biological, and Environmental Engineering

Is Mixing Achievable?

HP applies their thermal inkjet printing technology to simplify the drug titration method. One HP consumable print head is loaded, which is capable of dispensing over a range of 15 pL to 1 µL. This leads to reduced labor costs and time requirements, and increased precision.

•Simplifies drug titration method•Leads to reduced labor costs•Reduction in time

HP Direct Titration Method

Improvements Over the Old Method

Solution

Traditional Method

Drug discovery involves a titration process in which the effects of different concentrations of potential drug compounds are analyzed. Current methods of analysis involve steps which are labor intensive, error prone and, more importantly time consuming.

Problem

Challenge: Why Mixing Is Necessary

•DMSO penetrating in single point•Cell death caused by high concentration at points of penetration.

No Jitter

Immediately after dispense

5 seconds

after dispens

e

1 minute after

dispense

Cell death

No Cell Death

Immediately after dispense

Jitter

Jittering Method“Jittering”: oscillation of the well plate using the stage to induce shear between the deposited fluid, and fluid already in well. The stage can oscillate in the front to back direction (FB) or dual axis (FBLR).

Quantitative MethodA significant change in counts is caused by the solution not being fully mixed. Once the fluorescence signal, or counts, reaches a steady level, the conclusion can be made that mixing has occurred. This has been determined to be the best method to quantify mixing using kinetic data.

Vessel Radius BondNumber

Theoretically Mix

Standard water cup

45 mm 270 Yes

96 well plate

3.5 mm 1.7 Yes

384 well plate

1.9 mm 0.5 No

r=fluid densityα = acceleration due to gravityL = radius of capillary tubeg= surface tension of the interface

2aLBo

Qualitative MethodBond Number: A ratio of the body forces to the surface tension forces. A bond number less than 1 indicates that the surface tension forces are dominating the body forces.

In essence thermal inkjet technology consists of a resister and a fluid reservoir. The resister is positioned directly under (above) the filling reservoir. The resistor rapidly heats the fluid forming a bubble which pushes a drop of ink out of the nozzle.

16 of the nozzles depicted at the left are present on the printer heat used in the instrument.

•Two jittering methods were tested for mixing results: Jitter- while- dispense (JWD) and Jitter- post- dispense (JPD).

•JPD has been determined to be the optimal mixing method for both large and small dispense volumes, based on the slopes in the data plotted above.

•Plot A displays results for 50 nL dispense volume, and plot B displays results for 200 nL dispense volumes.

Results

Proposal

•The team recommends to use JPD in the FBLR direction for larger dispense volumes. JPD is also the optimal mixing method for small volumes, however, stage direction requires further testing.•It is recommended to further investigate the jitter time and amplitude for both large and small dispense volumes.

Thermal Inkjet and Titration ToolThermal Inkjet Technology Hewlett Packard Titration Tool and Print Head

AcknowledgementsThe Engineering Team would like to thank:• Hewlett Packard

• Kenneth Ward•Heather Paris• Ken Duda • Michael J Day

• Philip H Harding 

HP Method

Traditional Method

A B