Table of Contents
Team Activities for Detailed Design Phase
During the detailed design phase, the team
- Analyzed testing related to the properties and cell compatibility of PDMS
- Investigated unexpected stiffening of PDMS in the incubator
- Chose the best options for mechanical strain application
- 3-D printed a pilot mold and use that mold to cast the first PDMS cell culture chamber
- Created plans for building and testing in the MSD II phase
Progress ReportTeam MYSCLE'S Progress Report can be viewed here.
Design UpdatesDuring this phase a new cell line, 3T3 fibroblasts, was proposed to be used with our cell straining device. After continued testing, design, and research, it was found that the 3T3 cell line proved to be more advantageous for our use when compared to the originally chosen SHOX2 cell line. A Pugh analysis comparing the two cell lines was completed to finalize our decision to change cell lines.
Strain application mechanisms were researched throughout this phase. The three main approaches were Rack-and-Pinion, Piston, and Adjustable Stroke designs. A Pugh analysis was completed to decide which design would best fit the project's parameters. In the end, the Rack-and-Pinion design appeared to best suit our criteria.
CAD ModelsCELL CHAMBER MOLD:
During this phase, the original mold design was 3D printed and tested. Attempting to mold a PDMS chamber (see Figure 8 for PDMS molded chamber), design flaws were identified and discussed for the second iteration of the mold design. A few of the major problems encountered during the molding process were no visibility of the PDMS solution within the mold and failure to open mold post curing. The mold was redesigned to include viewing "windows" and eliminate the lip on the lid. CAD models for both the original and updated mold designs are found below. Figure 7 illustrates both of the 3D mold prints in a side-by-side comparison.
ACTUATING SYSTEM ASSEMBLY:
The CAD model below illustrates the full assembly of the cell straining device. The device utilizes a hole and peg cell chamber, along with a purchasable actuator that mechanically strains the cell chamber.
Bill of Material (BOM)
Test Plan UpdatesWhile planning for MSDII, the need for PDMS Heat Curing Testing and Cellular Response to Strain Testing became evident. Test plans 10 and 11 were created to account for these parameters. Table 1 shows the revised list of Test Plans.
TABLE 1:Updated Test Plan List (click link to view test plan outline)
|Test Plan #||Engineering Requirement||Title||Purpose|
|1||2,3,4||Environmental Conditions||To ensure that the incubator is maintaining proper temperature, humidity, and CO2 levels.|
|2||1,5,6,18||Cell Growth/Viability||Monitor pH level with media color indicator. Confirm sterile environment with cell proliferation counts and cell attachment.|
|3||15, 16||Autoclave Testing||Determine if selected materials for mechanical strain applicator can withstand autoclave conditions.|
|4||3||Material Testing||Tensile Testing using ASTM standard D638.|
|5||5,9,13,14||Ease of Use||Assembly/Disassembly, Protocol, Intuitive Software, etc.|
|6||10,14,19,20||Chamber Design Test||Ensure chamber growth surface area is sufficient for cell growth and viewable with a microscope. Chamber height compatible with a microscope.|
|7||9||Software and Device Motion Testing||Verify that software performance is acceptable and it is producing desired outputs.|
|8||22||Cost||Determine whether project development costs are fully funded by allocated MSD funds.|
|9||23,24||Longevity Testing||Determine whether the device will withstand multiple uses (equal to five years with ten uses per year).|
|10||11||Heat Cure Testing||Determine whether different heat cure conditions affect the material properties of PDMS.|
|11||11||Cellular Response to Strain||Determine the effects of different strain % and frequency of strain on the cell culture formation.|
During this phase, material testing (Test Plan 4) was completed for 3 different ratios of PDMS (8:1, 10:1, and 12:1). Complications with the Instron machine led to inconclusive results for 8:1 and 12:1 ratios. However, results obtained from 10:1 ratio appear to meet our desired material properties. In addition, literature research has shown that 10:1 ratio appears to be the gold standard used in several laboratories. Summarized results of elastic moduli for 10:1 ratio PDMS are illustrated below in Figure 11.