Lattice implants that generate homeostatic and remodeling strains in bone

Abstract

Bone remodeling is mediated by several factors including strain. An increase in strain between 1% and 10% compared to homeostasis can trigger bone formation. We aim to create an orthopedic implant using clinically established imaging and manufacturing methods that induces this strain control in human bone. Titanium scaffolds were manufactured with multiaxial apparent modulus tailored to the mechanical properties of bone defined from computed tomography scans of cadaver human tibiae. Five bone cubes were tested with corresponding titanium scaffolds by loading under compression, which is similar to the implanted tibia loading condition. Bone strain was precisely controlled by varying the scaffold modulus, from 0% to 15% bone strain increase. This strain increase is the magnitude reported to invoke bone's positive remodeling. Axial modulus was closely matched between titanium scaffolds and bone, ranging from 48-728 and 81-800 MPa, respectively, whereby scaffold axial modulus was within 2% of nominal target values. Fine control of multiaxial moduli resulted in transverse modulus that matched bone well; ranging from 42-648 and 47-585 MPa in scaffolds and bone respectively. The scaffold manufacturing material and method are already used in the orthopedic industry. This study has significant clinical implications as it enables the design of implants which positively harness bone's natural mechanoresponse and respect bone's mechanical anisotropy and heterogeneity.