Methodology for performing biomechanical push-out tests for evaluating the osseointegration of calvarial defect repair in small animal models

Abstract

Push-out tests are frequently used to evaluate the bone-implant interfacial strength of orthopedic implants, particularly dental and craniomaxillofacial applications. There currently is no standard method for performing push-out tests on calvarial models, leading to a variety of inconsistent approaches. In this study, fixtures and methods were developed to perform push-out tests in accordance with the following design objectives: (i) the system rigidly fixes the explanted calvarial sample, (ii) it minimizes lateral bending, (iii) it positions the defect accurately, and (iv) it permits verification of the coaxial alignment of the defect with the push-out rod. The fixture and method was first validated by completing push-out experiments on 30 explanted murine cranial caps and two explanted leporine cranial caps, all induced with bilateral sub-critical defects (5.0 mm and 8.0 mm nominal diameter for the murine and leporine models, respectively). Defects were treated with an autograft (i.e., excised tissue flap), a shape memory polymer (SMP) scaffold, or a PEEK implant. Additional validation was performed on 24 murine cranial caps induced with a single, unilateral critically-sized defect (8.0 mm nominal diameter) and treated with an autograft or a SMP scaffold. A novel fixture was developed for performing push-out mechanical tests to characterize the strength of a bone-implant interface in calvarial defect repair. The fixture uses a 3D printed vertical clamp with mating alignment component to fix the sample in place without inducing lateral bending and verify coaxial alignment of push-out rod with the defect. The fixture can be scaled to different calvarial defect geometries as validated with 5.0 mm bilateral and 8.0 mm single diameter murine calvarial defect model and 8.0 mm bilateral leporine calvarial defect model.

Trends in bioactivity: inducing and detecting mineralization of regenerative polymeric scaffolds

“…226,227 Push-out tests are also frequently employed to give insight into scaffold osteointegration with surrounding tissues, and efforts continue to be made to refine best practices. 228 Microscopic biomechanical analyses are also utilized to give insight into nanoscale mechanical properties. 222 Nanoindentation can be utilized to measure enhanced local hardness imparted by mineralized bone tissue.…”

High-Throughput Bioprinting of Spheroids for Scalable Tissue Fabrication

“…Unconfined compression tests were conducted using an Instron 5966 mechanical testing system (Instron, Norwood, MA,) with a 10 kN load cell, using a modified fixture as per a previous report 25 52 . For the setup, the explants were aligned on a plate with a central hole matching the defects, ensuring an unobstructed path for the probe.…”

The Current Status, Prospects, and Challenges of Shape Memory Polymers Application in Bone Tissue Engineering

“…The mechanical push-out bar was vertically aligned with the bone defect in cranial defect models of rats and New Zealand rabbits, respectively. It resulted in the development of a push-out test to assess the strength between the implants and the edge of the bone defect [ 70 ]. Michaela and colleagues [ 71 ] then affirmed the role of PCL-DA SMP scaffold for bone repair in non-critical zone size cranial defects in 6-month-old New Zealand rabbits.…”