Laboratory scientists are familiar with the multi-step, semi-manual methods for biological cell harvesting from biological filter plates and the tedious and laborious effort involved in so doing. Recognizing the need for an automated biological cell harvesting apparatus to facilitate this procedure, applicants have developed the novel apparatus described hereinafter.
Very significantly, applicants discovered that an existing microplate washer, Model No. SLT 96PW available from Tecan USA, Inc. of Research Triangle Park, N.C., could be modified to achieve an entirely unintended function as an automated cell harvesting apparatus.
As known to those skilled in the art, the SLT 96PW microplate washer is a programmable microplate washer which utilizes an internal microprocessor control to wash/aspirate 96 well microplates. The MILLIPORE brand 96 well microplate is a well known brand of microplate, although other pharmaceutical support companies also distribute 96 well microplates.
In its original form, the SLT 96PW microplate washer apparatus comprises a fluid pump connected to a fluid dispensing head, a vacuum switch to initiate aspiration, a fixed tray for receiving a microplate to be washed, and a microcontroller for controlling the fluid dispensing and aspirating sequence achieved by 96 pairs of dispense/aspirate tubes provided in the dispensing head.
The microcontroller of the SLT 96PW microplate washer provides flexibility to the apparatus by allowing for programmable variations in the soak and aspirate times as well as in the volume and speed of fluid dispensing. The wash process in the SLT 96PW includes the following programmable parameters: the amount of fluid to dispense; the soak time; the aspirate time; and the number of times the cycle should be repeated for a microplate. As an option, the SLT 96PW includes a RS232 serial interface port that allows the apparatus to communicate synchronously with a personal computer or robot. In this mode, commands can be issued to the apparatus that specify the wash program to run, and the SLT 96PW can send response signals to these commands with a variety of codes indicating the status of the apparatus.
The fluid dispensing head of the SLT 96PW rides on a vertical track and has 96 pairs of stainless steel tubes depending downwardly from the bottom surface thereof. Each pair of stainless steel tubes includes a relatively shorter tube to dispense fluid and a relatively longer tube to aspirate the well in which the pair of tubes is positioned. The vertical track and a precision electric stepper motor allow the fluid dispensing head to be optimally vertically positioned for introducing/removing microplates and dispensing and removing fluid from the microplates. The 96 pairs of stainless steel tubes depending from the fluid dispensing head correspond to each of the 96 wells in sample microplates. Within each pair of stainless steel tubes, as noted hereinabove, one tube is used exclusively to dispense fluid from a common manifold, and the other tube is used exclusively to remove the fluid from the well by suction (aspiration). Once the fluid is removed from the 96 wells of the microplate, it is collected as waste in a remote container.
The SLT 96PW uses a double-diaphragm electric pump driven by a stepper motor with an optical shaft encoder for delivery of fluid. In the dispense mode, the pump can deliver between 25 and 300 microliters (ml) of liquid in 25 microliter (ml) increments. In the wash mode, the fluid pump can be programmed to deliver between 50 and 3000 microliters (ml) of liquid in 50 microliter (ml) increments, and the rate at which the fluid is dispensed can also be programmed into the apparatus.
The SLT 96PW has a manual, horizontally slidable tray for positioning microplates beneath the fluid dispensing head and a conventional LCD display to facilitate manual operation of the apparatus.
As would be appreciated by one skilled in the art of biological cell harvesting, the SLT 96PW as provided by the manufacturer was not intended for use as a cell harvester and cannot do so due to certain inherent features. For example, the fluid dispensing head has a tendency to remove biological cells intended for harvesting when fluid is removed from the wells of a filter plate placed therein. Also, the apparatus does not have any capability to collect the fluid from the individual wells of a filter plate in distinct containers which is desirable in many laboratory studies.
The stainless steel fluid dispensing tubes direct the flow of liquid directly down into the wells of a filter plate in such a manner that the fluid streams have a tendency to stir up biological cells that may have settled at the bottom of the wells. Also, in order for the original SLT 96PW to aspirate or remove liquid from the wells of a filter plate, the relatively long aspiration tubes must be immersed in the fluid. This dipping of the aspiration tubes into the fluid in the wells creates an opportunity for cross-contamination and, even more significantly, since there is no mechanism to separate the cells from the liquid, the cells themselves can be removed along with the liquid.
Finally, in some studies it is beneficial to collect the fluid from each of the filter plate wells in corresponding distinct containers, and the SLT 96PW with its common aspiration manifold has no means of collecting fluid from each well in a distinct container. Thus, these and other limitations which would be well known to one skilled in the art of cell harvesting would normally not lead one to attempt to use the SLT 96PW microplate washer as an apparatus for biological cell harvesting, a tedious procedure presently requiring the use of several devices and incorporating a number of manual steps.
Therefore, applicants' apparatus for automated biological cell harvesting is believed to fill a long-felt need for an automated apparatus for biological cell harvesting which obviates the need for the multiple step, semi-manual procedure presently utilized in the art. The simple-to-use and highly reliable automated biological cell harvesting apparatus described and claimed hereinafter meets these and other long-felt needs in the art for such an apparatus.