3D Printable Ink Helps Induce Bone Regeneration

A new study describes a novel three-dimensional (3D) printable ink used to produce a synthetic, hyperelastic bone (HB) implant that rapidly induces bone regeneration and growth.

Developed by researchers at Northwestern University (NU, Chicago, IL, USA), the synthetic osteoregenerative HB, composed of 90% hydroxyapatite (HA) and 10% polycaprolactone, can be rapidly printed from extruded liquid inks at room temperatures. The resulting 3D-printed HB exhibits elastic mechanical properties, is highly absorbent, supported cell viability and proliferation, and induces osteogenic differentiation of bone marrow–derived human mesenchymal stem cells.

In a study to evaluate HB in vivo in a mouse subcutaneous implant model for material biocompatibility (at 7 and 35 days), in a rat posterolateral spinal fusion model for new bone formation (at eight weeks), and in a large, primate calvarial defect case study (at four weeks), HB did not elicit a negative immune response, became vascularized, quickly integrated with surrounding tissues, and rapidly ossified and supported new bone growth without the need for added biological factors.

One of the biggest advantages of the new material is that the end product can be customized to the patient. While in traditional bone transplant surgeries, autologous bone has to be shaped and molded to exactly fit the area where it is needed, with HB, the patient’s body can be scanned and digitized so that a personalized section of synthetic bone can be 3-D printed. Due to its distinct mechanical properties, the biomaterial can also be easily trimmed and cut to fit the size and shape needed during a procedure. The study was published on September 28, 2016, in Science Translational Medicine.

“We can incorporate antibiotics to reduce the possibility of infection after surgery; we also can combine the ink with different types of growth factors, if needed, to further enhance regeneration. It's really a multi-functional material,” said senior author Ramille Shah, PhD, of the departments of materials science & engineering and surgery. “You put stem cells on our scaffolds, they turn into bone cells and start to up-regulate their expression of bone specific genes. This is in the absence of any other osteo-inducing substances; it's just the interaction between the cells and the material itself.”

HA is a naturally occurring mineral form of calcium apatite. Up to 50% by volume and 70% by weight of human bone is a modified form of HA, and carbonated calcium-deficient HA is the main mineral of which dental enamel and dentin are composed. But in spite of its attractive biological properties, HA has drawbacks, such as low bioresorption rate in vivo, poor stimulating effect on the growth of new bone tissues, low crack resistance, and small fatigue durability in the physiological environment. The added polymer provides HA with elasticity because of the way its structure is designed and printed.

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