Stem cells are cells that have not yet specialized into particular types of cells, e.g. blood cells, stomach cells, etc. Stem cells have captured the interest of the medical community because they have a unique ability to replicate themselves through cell division and differentiate into various specialized cell types. This attribute gives them tremendous potential in the emergent medical field of regenerative medicine, specifically for repairing damaged or destroyed tissue. Adult stem cells have been isolated from adipose (fatty) tissue, bone marrow, blood, and other tissues in the body. Unfortunately, many therapies require a greater number of stem cells than can be collected from the patient or a donor’s tissue. Therefore, cells that are isolated from tissue need to be cultured to reach a quantity of cells suitable for therapy.

To generate these cells more rapidly than current practices, MPR has designed a high-yield chamber for the cells derived from adipose (fatty) tissue. Adipose tissue is collected from the abdomen via liposuction. The extracted tissue is then digested by an enzyme (collagenase) to isolate endothelial and adult stem cells. The high-yield chamber was designed to multiply the population of these cells. For this purpose, the MPR high-yield chamber is a major improvement over existing culture chambers in that it is smaller and more efficient, while simpler and less expensive to operate.

Full Image CFD Model Results, Slot and Port Inlets. The computational results show that the slot (top) design is more favorable and provides more even distribution of the growth media than the port (bottom) design.

Cell growth is promoted by giving cells a suitable substrate and providing nutrition with growth media (liquid containing oxygen and nutrients). Cell growth is deficient when growth conditions are unfavorable, i.e. temperature is not carefully controlled, media becomes locally depleted, media flow creates excessive shear on cells, etc. MPR designed the high-yield biochamber to achieve favorable growth conditions on all of the growth surfaces in the chamber volume.

MPR designed high-yield chambers in three sizes, providing growth surface areas of 0.1 m², 0.5 m², or 2.5 m² (roughly 10 ft² to 250 ft²). Key design objectives of each chamber were to:

• Provide uniform flow of media over all growth surfaces,
  
  
• Ensure that oxygen is delivered to all areas of the growth surfaces,
  
  
• Obtain good cell adhesion to the growth surface,
  
  
• Limit shear due to media flow at the growth surface,
  
  
• Minimize the volume of costly growth media required, and
  
  
• Minimize the footprint of the chamber.

MPR developed a vertical plate chamber design to satisfy these requirements, where surface area is enhanced by providing multiple, vertical growth surfaces within a single, flooded chamber. For efficient use of space and media, adherent cells are grown on both sides of the plates. The growth surfaces are individually removable to allow inspection or harvesting during the culture process. Within the chamber, a perforated plate and slot inlet evenly distribute flow throughout the entire volume of the chamber, thereby ensuring that uniform flow is delivered to all growth surfaces. This design eliminates the need for multiple channels or chambers with individual distribution systems or ports, as in other cell culture devices. Growth media enters through the top of the chamber, flows through each channel created by adjacent parallel plates, and exits at the bottom of the chamber.

Development of the parallel plate high-yield chamber design required careful attention to the growth chamber configuration. Specifically, key factors included:

• Inlet geometry,
  
  
• Inlet position,
  
  
• Outlet position relative to inlet position,
  
  
• Chamber height and width,
  
  
• Growth plate spacing,
  
  
• Growth plate orientation with respect to the inlet, and
  
  
• Inlet and outlet fluid plenum heights.

Fluid and oxygen mass transport calculations were used to initially scope the system dimensions. To ensure uniform media flow throughout the chamber, several fluid distribution options were identified, including the addition of perforated plates, baffles, screens/meshes, or packing materials. To evaluate specific dimensions and to determine whether fluid distribution components would be necessary, a computational fluid dynamics (CFD) model was developed, and analyses were performed for proposed configuration (see Figure 1). The results of the CFD analyses suggested that, through the used of a slot-shaped inlet, uniform flow could be achieved without addition of fluid distributors. CFD results for the slot-shaped inlet configuration were more favorable than for a port inlet configuration.

Based on these CFD results, a test chamber was constructed out of machined plastic parts (see Figure 2). The design of the test chamber allowed testing of the chamber with or without fluid distributors and with a variety of inlet positions. Dye was added to the fluid at the inlet after steady state flow was achieved in each configuration, allowing observation of fluid distribution within the chamber. Fluid jetting from inlet ports was observed, causing preferential flow to some plate channels. Slot-shaped inlets mitigated this effect but resulted in dead spots near the inlets. This effect was mitigated by use of a perforated plate between the slot inlet and the growth plates, and by increasing the slot depth.

The optimized test chamber was sent to a site specified by our client for growth testing. MPR provided polystyrene growth plates that were specially treated on their surfaces to facilitate cell adhesion. The results of the growth tests were positive, showing an even distribution of cells growing on the growth plates throughout the chamber. This result demonstrated that growth media was successfully distributed to all areas of the chamber.

Assembled Test Chamber. Iterative prototyping resulted in this final design for the high-yield chamber.

Based on the success of fluid and growth testing, the geometric parameters from the test chamber were used to develop a commercial prototype design. The prototype was designed in CAD, with consideration for fabrication by injection molding.

The development of the high-yield biochamber demonstrates the effectiveness of an iterative development approach. Each step of the development process incrementally provides the needed information and data until finally a well-justified commercial prototype is reached. Instead of a commercial prototype that is strictly conceptual, design parameters have been selected based on calculations, modeling, and testing results. This approach increases confidence that the commercial high-yield chamber will perform as intended.

For further information on this article, a copy of the latest MPR Profile or our engineering services, contact Larry Cundy.