Which 3D Printed Structure Is Most Cell Friendly?

The design revolution otherwise known as additive manufacturing has opened up an entire new way of thinking about implant/tissue interface. 3D printing technologies allows manufacturers to fine-tune an implant’s mechanical and physical properties in order to increase the functionality of each implant—whether to make an implant more infection resistant or, in this case, more cell and tissue friendly.

A team of researchers led by Carmen Torres-Sanchez, Ph.D. of The Wolfson School of Mechanical, Electrical and Manufacturing Engineering at Loughborough University in the UK took a systematic look at the impact of 3D printed design topology on biological and mechanical performance.

The research team compared different scaffold designs: triply periodic minimal surface (TPMS), a trabecular-like structure, and a lattice structure (a control scaffold).

Dr. Torres-Sanchez told OTW, “Although we are all different in terms of anatomy and physiological needs …in the ways we age, exercise, and live, medicine/technology that feeds into medical devices has largely been a one-size-fits-all approach. My 82-year-old neighbor has a very different lifestyle different from my 57-year-old neighbor who bikes 10 miles a day. If both individuals are in an accident and need an orthopedic device, they will need different products. With personalized medicine we have improved chances of producing long lasting orthopedic devices that allow cells to move in and create a mineral material that makes up our bone and carries no risk for infection.”

Dr. Torres-Sanchez and her team of researchers found that the cells are sensitive to topology—the way in which structures are arranged in a design—and that this can be used to facilitate faster tissue healing.

“Looking at the above image, the lattice square on the far right is the structure typically used in orthopedic surgery because it is simple to manufacture and easy to obtain. We looked at two types of topology: one that is generated mathematically and it has a repetitive pattern and another that was trabecular-like and generated through a geometrical algorithm to give randomness. Unlike with the mathematical one, here we tried to mimic nature and replicate what the trabecular structure does. When they were both tested against the traditional cubic lattice, we saw that by changing the topology, we could increase the mechanical performance to the point where it was much closer to what bone is actually like.”

Happy cells, happy bone?

Looking at the biological behavior of the cells within the structure, says Dr. Torres-Sanchez, there are two things that need to occur in order for cells to be “happy.”

“First, the cells must penetrate the bone to a sufficient degree. Second, once they are settled into their new ‘home,’ the cells need to proliferate and differentiate in that microarchitecture. It is then that we are able to measure maturation rate, this is, their ability to create bone. Cells do seem to be particularly ‘happy’ within a trabecular structure, but we don’t quite know why.”

“Do they actually remember the structure as ‘home’ because the trabecular-like structure is similar to bone? I believe this is the case. They do seem to have certain preferences, as in our previous study we showed that cells do not like sharp corners but prefer those that are rounded.”

“This technology will allow us to make people who are in need of orthopedic devices more comfortable and let them recover and go back to their normal lives sooner. The effects of trauma or disease are widespread, and there are mental health and societal-level issues that need to be dealt with. All of this means that we should use what is at hand, i.e., 3D printing—to address these problems.”

“It’s so easy,” said Dr. Torres-Sanchez. “You can have the manufacturing right next door to the operating theatre…you can 3D print the device and a few hours later someone can walk it over to the surgeon to implant into the patient. One of the current problems trauma surgeons have is that by the time they scan the patient and send the image for manufacturing, their wound and the surrounding bone have grown, so the implant shape is obsolete. So if we can shorten the time from design to manufacturing and implantation, then terrific!”