Additively manufactured titanium scaffolds and osteointegration - meta-analyses and moderator-analyses of in vivo biomechanical testing

Abstract

Introduction Maximizing osteointegration potential of three-dimensionally-printed porous titanium (3DPPT) is an ongoing focus in biomaterial research. Many strategies are proposed and tested but there is no weighted comparison of results. Methods We systematically searched Pubmed and Embase to obtain two pools of 3DPPT studies that performed mechanical implant-removal testing in animal models and whose characteristics were sufficiently similar to compare the outcomes in meta-analyses (MAs). We expanded these MAs to multivariable meta-regressions (moderator analysis) to verify whether statistical models including reported scaffold features (e.g., “pore-size”, “porosity”, “type of unit cell”) or post-printing treatments (e.g., surface treatments, adding agents) could explain the observed differences in treatment effects (expressed as shear strength of bone-titanium interface). Results “Animal type” (species of animal in which the 3DPPT was implanted) and “type of post-treatment” (treatment performed after 3D printing) were moderators providing statistically significant models for differences in mechanical removal strength. An interaction model with covariables “pore-size” and “porosity” in a rabbit subgroup analysis (the most reported animal model) was also significant. Impact of other moderators (including “time” and “location of implant”) was not statistically significant. Discussion/conclusion Our findings suggest a stronger effect from porosity in a rat than in a sheep model. Additionally, adding a calcium-containing layer does not improve removal strength but the other post-treatments do. Our results provide overview and new insights, but little narrowing of existing value ranges. Consequent reporting of 3DPPT characteristics, standardized comparison, and expression of porosity in terms of surface roughness could help tackle these existing dilemmas. Graphical abstract

Complex geometry and integrated macro-porosity: Clinical applications of electron beam melting to fabricate bespoke bone-anchored implants

“…In clinical use, EBM-manufactured devices (both off-the-shelf and patient-specific implants) have noteworthy merits in comparison to those obtained by conventional manufacturing methods that produce solid structures. For example, reduced overall bulk minimises the stiffness mismatch between the implant and bone, and therefore stress shielding [12] , while the porous geometry allows for bone (and soft tissue) ingrowth, allowing for improved mechanical anchorage [144] . Patient-specific implants allow for a better fit of the prosthesis and potentially better function (such as extended range of motion) compared to off-the-shelf implants, as in the case of acetabular cups.…”

Aleaciones metálicas para aplicaciones ortopédicas: una revisión sobre su respuesta al estrés fisiológico y a los procesos de corrosión

“…La reducción prolongada de la tensión puede ocasionar que el hueso se debilite, en el reparto de la carga entre el hueso y el implante, la cantidad de tensión que soporta cada uno está relacionado con que tan rígido es [23], al ser el implante más rígido que el hueso este genera una "protección contra el estrés" [8] [9] , esta protección afecta la remodelación y cicatrización ósea haciendo que el hueso se vuelva poroso y débil [24], [25]. Como el hueso debajo de los implantes se adaptó a esa baja tensión, el hueso curado va a ser débil y por eso al retirar los implantes se pueden presentar refracturas, esto pasa más con el acero que con el titanio, ya que el titanio posee la biocompatibilidad y el comportamiento biomecánico adecuado, además, la alta resistencia a la fatiga y a la tracción y su bajo módulo elástico, lo convierten en un material menos propenso a generar esta protección [23][9] [26].…”

Evolution from Bioinert to Bioresorbable: In Vivo Comparative Study of Additively Manufactured Metal Bone Scaffolds

“…Consequently, research has delved into the potential of additively manufactured Ti scaffolds for bone regeneration applications. [12][13][14][15] The porous structure obtained through additive manufacturing techniques lowers the elastic moduli of Ti-based materials, and numerous clinical trials have showcased the successful use of these scaffolds in calvaria and tibia defects. [16][17][18][19] Despite these promising preclinical findings, Ti-based scaffolds possess non-biodegradable and bio-inert properties, causing their material, structure, and biomechanics to remain largely unaltered long after implantation.…”