A 3D-printed regenerative biomaterial called hyperelastic “bone” has been developed that is highly porous, supportive of cell growth, and fast to produce – factors which make it a promising bone graft material in humans.
A bone graft is a surgical procedure that involves the transplantation of bone tissue, and is most often used to repair complex fractures, fuse two bones together, regenerate bone lost to disease or injury, or heal bone around surgically implanted devices. Bone tissue used for grafts can come from the patient’s own body, a donor, or be man-made.
Synthetic and natural calcium phosphate (CaP)-based ceramic bone grafting materials are the most common biomaterial used for grafting because they have the ability to bond directly to living bone. Unfortunately, CaP-based ceramics are stiff, cannot be easily re-shaped or re-sized by surgeons, and are not ideal for minimally-invasive procedures. Even different formulations of this biomaterial (granules, putties, and cements) have their limitations as they can be washed away by blood, cause tissue damage because they require heat to harden, or are not porous enough to support bone tissue growth and vascularization.
As such, there is a need for a bone biomaterial that, in addition to supporting bone growth, is fast and easy to manufacture in the clinic, surgically-friendly, and cost-effective. A group of researchers from Northwestern University recently reported that they had developed a promising new 3D-printed biomaterial called hyperelastic “bone” (HB). It is made from the synthetic clinically-used materials hydroxyapatite and polycaprolactone or poly(lactic-co-glycolic acid), and can be rapidly 3D-printed at a rate of 275 cm3 per hour, which is approximately the same volume as an apple.
HB 3D-printer inks were easy to create and the researchers demonstrated that the inks could be printed into flexible sheets, complex structures, and a human-sized jaw bone. Tests of mechanical and physical properties reveal that HB is strong enough for non-direct load-bearing indications, can be compressed without becoming permanently deformed, and is 50% porous to facilitate cell and blood vessel growth.
In vitro experiments showed that bone-marrow-derived human mesenchymal stem cells, which are cells that have the ability to turn into many cells including bone, could attach, grow, and function in HB. In vivo studies in rodents using an orthopedic HB implantation and HB bone fusion model demonstrated that the material was not rejected by the host (biocompatible) and was actually superior to CaP-based ones in both biocompatibility and in supporting bone growth. The researchers were also successful in repairing part of a skull in a non-human primate by 3D-printing a large HB piece and trimming it to fit the defect site. After only four weeks, the HB promoted the growth of the primate’s existing bone tissue.
The “bone” developed in this study is technically and mechanically advantageous over current bone graft materials since it can be rapidly made with a 3D printer and supports greater tissue regeneration. These characteristics of HB, in turn, give it huge potential as a biomaterial for the repair of bone defects.
Written By: Fiona Wong, PhD