The study, “Three-Dimension-Printed Porous Poly(Propylene Fumarate) Scaffolds with Delayed rhMBP-2 Release for Anterior Cruciate Ligament Graft Fixation,” was published in the peer-reviewed journal Tissue Engineering, Part A, the flagship journal published 24 times each year. Tissue Engineering is the official journal of TERMIS, the Tissue Engineering & Regenerative Medicine International Society. The paper is available to read, for free, on the Tissue Engineering website until March 27; co-authors include Mahrokh Dadsetan, PhD; Sanjeev Kakar, MD; Maurits G.L. Olthof, MD; Joshua Alan Parry, MD; Kristen L. Shogren; Andre Van Wijnen, PhD; and Michael Yaszemski, MD, PhD, all with the Mayo Clinic’s Department of Orthopaedic Surgery, Tissue Engineering and Biomaterials Laboratory.
In the paper, the researchers compared four different release approaches, and how they reduced the initial rhBMP-2 burst release and extended it over time. Furthermore, they demonstrated how strong their porous, bioabsorbable scaffold was, using a rabbit ACL reconstruction model. The paper’s abstract explains that most ACL ruptures are reconstructed using bioabsorbable implants, but that the implants frequently suffer complication due to incomplete bone filling. The bone regeneration could potentially be enhanced through 3D printed scaffolds and tissue engineering techniques, so the researchers first designed a strong 3D poly(propylene fumarate) (PPF) porous scaffold, and then determined the rhBMP-2 release kinetics.
The abstract continues: “To determine the degree of scaffold porosity that maintained suitable pullout strength, tapered scaffolds were fabricated with increasing porosity (0%, 20%, 35%, and 44%) and pullout testing was performed in a cadaveric rabbit ACL reconstruction model. Scaffolds were coated with carbonate hydroxyapatite (synthetic bone mineral [SBM]), and radiolabeled rhBMP-2 was delivered in four different experimental groups as follows: Poly(lactic-co–glycolic acid) microspheres only, microspheres and collage (50:50), collagen only, and saline solution only. rhBMP-2 release was measured at day 1, 2, 4, 8, 16, and 32. The microsphere delivery groups had a smaller burst release and released a smaller percentage of rhBMP-2 over the 32 days than the collagen and saline only groups. In conclusion, a porous bioabsorbable scaffold with suitable strength for a rabbit ACL reconstruction was developed. Combining a synthetic bone mineral coating with microspheres had an additive effect, decreasing the initial burst release and cumulative release of rhBMP-2. Future studies need to evaluate this scaffold’s fixation strength and bone filing capabilities in vivo compared to traditional bioabsorbable implants.”
The porous wedge scaffolds, measuring 3mm in diameter and 10mm in length, were designed using SOLIDWORKS, and were printed using the Viper si2 SLA 3D printer from 3D Systems. The implants had an acetone bath, and then were washed “extensively” with ethanol to get rid of any excess resin. Finally, the implants were post-cured in a 3D Systems UV oven for an hour. Testing ultimately determined that the 20% porous 3D printed PPF bioabsorbable scaffold maintained the proper amount of pullout strength in the ex vivo rabbit ACL graft fixation. However, the researchers say that further testing is necessary, to compare this scaffold’s subsequent in vivo bone filling and fixation strength.
Tissue Engineering co-editor-in-chief Peter C. Johnson, MD, Principal, MedSurgPI, and President and CEO, Scintellix, said about the study, “This work is a good example of the fusion of technologies – controlled release drug delivery and 3D printing.”
The research was funded by a grant, from the DePuy Synthes Joint Reconstruction and the Orthopaedic Research Education Foundation (OREF). Discuss in the Mayo Clinic forum at 3DPB.com.