Microarchitecture of titanium cylinders obtained by additive manufacturing does not influence osseointegration in the sheep

Abstract

Large bone defects are a challenge for orthopedic surgery. Natural (bone grafts) and synthetic biomaterials have been proposed but several problems arise such as biomechanical resistance or viral/bacterial safety. The use of metallic foams could be a solution to improve mechanical resistance and promote osseointegration of large porous metal devices. Titanium cylinders have been prepared by additive manufacturing (3D printing/rapid prototyping) with a geometric or trabecular microarchitecture. They were implanted in the femoral condyles of aged ewes; the animals were left in stabling for 90 and 270 days. A double calcein labeling was done before sacrifice; bones were analyzed by histomorphometry. Neither bone volume, bone/titanium interface nor mineralization rate were influenced by the cylinder’s microarchitecture; the morphometric parameters did not significantly increase over time. Bone anchoring occurred on the margins of the cylinders and some trabeculae extended in the core of the cylinders but the amount of bone inside the cylinders remained low. The rigid titanium cylinders preserved bone cells from strains in the core of the cylinders. Additive manufacturing is an interesting tool to prepare 3D metallic scaffolds, but microarchitecture does not seem as crucial as expected and anchoring seems limited to the first millimeters of the graft.

Effect of Pore Size of Porous-Structured Titanium Implants on Tendon Ingrowth

“…Many studies on porous materials have been conducted recently, mainly on osseointegration [ 28 , 40 ]. Porous materials provide a larger specific surface area and access for cells, oxygen, and nutrients to improve the biocompatibility of materials and promote tissue integration [ 22 ].…”

“…Therefore, a physiological porous structure may promote tendon fixation. Rony et al compared implants with trabecular microarchitecture and purely geometric microarchitecture and reported that the former did not show better osseointegration [ 40 ]. Therefore, it seems irresponsible to simply imitate the trabecular bone or tendon structure.…”

Recent advances in regenerative biomaterials

“…Ceramics, polymers and metals are all the candidate materials to support bone regeneration. Typically, ceramics stimulate mineralization via mimicking the inorganic portion of natural bone [ 223 , 224 ], polymers work as the bone ECM via mimicking crosslinking of collagen fibrils [ 225 , 226 ], and metals provide the mechanical support sometimes [ 227 ].…”

Correlation between Ca Release and Osteoconduction by 3D-Printed Hydroxyapatite-Based Templates

“…11,12 On the contrary, this concave micropore geometry exhibited no advantage over the orthogonal-patterned pores when tested on titanium (Ti) cylinders in vivo. 13 Other reports have disclosed no osteoconductive advantages of HA-based and β-TCP templates over plain polymers in vitro, or when implanted in calvarial defects in the rabbit, except when functionalized with BMPs. 14 Nevertheless, none of the aforementioned studies investigated whether the discrepancies in the amount of new bone regeneration might be attributable to variations in Ca release from the HA templates.…”