For new skin, press 'print'

Brian Derby, Ph.D., head of the Inkjet Printing of Human Cells Project says, "When people grow cells for autografts, they only grow the keratinocytes of the epidermis. The greater challenge for tissue engineers is full-thickness skin, which has a more complicated cell structure and vascularization."

The process entails cultivating large populations of cells (from a small sample of a patient's own cells) into an external shape that will exactly fit a wound and with an internal structure that optimizes survival and proliferation. Prior research proved that this is possible by seeding a three-dimensional scaffold with cells and cultivating them in situ.

Even so, the technology is a long way from commercial viability. The next step is to progress from a single layer to a hundred or more layers, each different from the preceding one. The idea is to produce a temporary precursor structure that will regenerate into skin.

"A lot of the basic concepts are already there," Dr. Derby says.

"The main engineering problem is keeping the thicker layers alive. For five to 10 layers, you can bathe cells in nutrients, and they will thrive. For intermediate thicknesses, you need prevascularization. Greater thicknesses require artificial vascularization. Introducing porosity enables the body, abetted with angiogenesis, to vascularize itself."

Other issues include determining how to mitigate the scarring response and formulating an ideal concoction of nutrients and chemical factors to mix with cell lines.

"From a technical point of view, I don't see this as impossible," Dr. Derby says. "I think all the issues will be resolved in five to 10 years so we can begin animal testing and then clinical trials."

Methodology The research team obtained two types of human fibroblasts: Type 1 primary cells and HT1080 sarcoma cells. Prior to deposition, the cells were cultured using standard procedures, transferred to fresh media, centrifuged, agitated with a pipette and redispersed in a nutrient-rich fluid at desired concentrations.

Fibroblast cell suspensions were directly printed from a 30 micrometer diameter jet for 120 seconds at 13 kHz, and with piezoelectric excitation pulses of 30, 40, 50 and 60 volts, into growth media or directly onto a well plate.¹ During incubation, cells were monitored via a light microscope. (A control sample was pipetted into a well to ensure that any observed cell death was not caused by contamination or other external factors.) By 72 hours, the research team observed extensive cell attachment and proliferation. The cells continued to attach, spread and proliferate almost to confluency within 144 hours.

Conventional methods limit tissue growth to a few millimeters thick. However, with inkjet technology, says Dr. Derby, "We can place designated cells in any designated position in order to grow tissue, bones or organs."

1. It takes approximately 6,600 drops to print one cell. Printing for two minutes at 13 kHz results in the deposition of 243 cells.