Design of a Cryogenic Tissue Pulverizer for Biochemical Analysis Preparation Sara Alford Team Leader Christine Koranda Communications Carla Maas BWIG Ryan Roth BSAC Biomedical Engineering Design 402 University of Wisconsin Madison May 7 2003 Advisor Paul Thompson Clients Jeff Ross and Charles Tessier Abstract The cryogenic tissue pulverizer processes surgically removed tissue by freezing and grinding the sample into a powder 10 m diameter particles To accomplish this task our design incorporates a pneumatic driven grinding head with a grinding chamber After careful consideration between motor and pneumatic driven designs a pneumatically grinding mechanism was chosen for the final design The pneumatic cylinder controlled by a timer circuit and solenoid delivers the power needed to grind the sample The sample is placed in a grinding chamber surrounded by a polystyrene insulated cooling chamber containing a dry ice and alcohol bath This ensures that the tissue will remain frozen throughout the grinding process A detachable grinding head attaches to the pneumatic cylinder and pulverizes the sample The contour of the grinding head and the curvature of the grinding chamber were matched in order to maximize tissue contact Our efforts this semester have been focused on building a working prototype It was tested using liver tissue samples and its performance compared to the existing method using a mortar and pestle Design Problem To design a device that comp letes the preparation process done manually to prep a tissue sample for biochemical analysis The device should freeze the tissue with liquid nitrogen and grind it to a powder The sample should be easily collected Overview of Project Work Work on this project began in BME 301 during the spring semester of 2002 Initial design mechanism for the grinding method and background research was focused on during that semester Three designs were initially considered The next semester fall 2002 focused on choosing a method to deliver the power needed to grind A motor driven and pneumatic driven design were explored thoroughly before choosing a pneumatically powered grinding mechanism Initial testing to determine the best mechanism of pounding and shape of the grinding head and bowl were undertaken Near the end of the semester the development of a prototype was started This last semester continued work on the prototype including the designing of a sample grinding chamber and cooling chamber An electrical timing circuit was made to control the pounding rate of the grinding head The prototype was working by mid semester and then tested with liver samples in the lab to rate its performance The project was displayed at the 2 engineering EXPO and was awarded an honorable mention as well as a K 12 Outreach Award A patent proposal was submitted but was not accepted by WARF Background Biological and Clinical Rationale When a tumor is removed from a patient during a surgical resection a pathologist analyzes it with microscopy The information about the tumor cells obtained through this method is often insufficient to determine precisely what kind of treatment is most effective for the patient A more accurate and informative analysis of the tissue is desired and therefore the tissue sample is sent to a molecular biology laboratory for profiling of DNA RNA and protein This information is important in determining a possible specific treatment that may inhibit or decrease tumor growth However before a profile can be completed the tissue sample must be preserved and prepared for the molecular testing The current preparation procedure involves freezing the sample with liquid nitrogen and using a mortar and pestle to grind up the sample to a fine powder This process is tedious and time consuming A molecular biologist may spend several hours per day solely grinding samples Our proposed device would replace the current manual preparation of tissue samples allowing the researcher to spend his her time on other tasks Ultimately this device would be placed in a clinical setting so that a physician or other health care staff could simply insert the fresh extracted sample and later remove the ground sample to be sent to a laboratory for testing Design Requirements and Constraints The final design must fulfill several client requirements Appendix A The device should freeze a tissue sample less than a gram in mass with liquid nitrogen and subsequently grind the sample to a powder the consistency of powdered sugar 10 m diameter After analysis the sample should be efficiently collected The device needs to have the capability to prepare 40 tissue samples per day with each sample processing time less than or comparable to the manual processing time of 15 minutes All parts in contact with the tissue sample should be removable or easily cleaned to avoid cross contamination of tissue samples Lastly the device should fit on a laboratory bench 3 Cryogenic System Design Considerations Due to the use of liquid nitrogen our group needs to be aware of its implications to the overall design In general a cryogenic storage device must be designed to withstand forces resulting from internal pressure the weight of contents and bending stresses All materials that come in contact with the sample must withstand the cold temperature of liquid nitrogen 196o C Most cryogenic devices are based on the concept of a dewar flask principle a double walled container with the inner space being well insulated In this design the inner vessel is constructed of a material compatible with the cryogenic fluid making material compatibility a major factor in designing a system Flynn 1997 Properties and behavior of materials included must be considered at low temperatures since they often vary significantly from room temperature These factors include thermal properties such as the ability to conduct heat as well as thermal expansivity a material s cyclic expansion and contraction due to a change in temperature from low to room temperature It also includes mechanical properties such as ductility and brittleness Materials exhibiting low temperature embrittlement should not be used in cryogenic systems When a material is subjected to a force of high enough stress level the elastic behavior of the material will no longer hold The material becomes brittle breaking without any more deformation or becomes ductile permanently deformed Both results lead to system failure and inadequate performance Material s brittleness