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International Journal of Bioprinting OLS design for distal femur osseointegration

necrosis in the surrounding bone. This necrosis weakens Currently, metal three-dimensional (3D) printing
6-7
the mechanical bond between PMMA and the bone, using Ti6Al4V as a material through selective laser melting
resulting in early loosening known as aseptic loosening. (SLM) has become a commonly adopted technique for
8
Furthermore, owing to its smooth surface and structure, fabricating complex metal implants, 26,27 and numerous
PMMA lacks osteoconductive properties, thereby studies have demonstrated its applicability. 16,21,24,28
impeding favorable osseointegration. Related studies have Accordingly, in this study, metal 3D printing was employed
8
indicated that loosening of the interface between PMMA to fabricate implants with complex lattice structures.
and bone constitutes a prevalent cause for re-operation Designing lattice-optimized implants for the target
in distal femoral defects, leading to complications such anatomical region currently represents a prevailing trend
as fractures (14%) and nonunions (12%). Therefore, it in lattice development. Scholars have designed lattice
9
becomes evident that PMMA is not an optimal option for variations in types and sizes tailored for distinct regions,
reconstructing large bone defects in the distal femur. including craniofacial, dental implants, hip, tibial,
30
29
24
4,20
Implants featuring lattice structure that conforms to and spinal implants. 31-33 This optimization aims to align
the profile of the bone defect have emerged as a potential the lattice with the biomechanical conditions of the target
alternative for reconstructing large bone defects. In area, fostering the growth of surrounding bone. The design
3,10
the case of solid metal implants, the material properties of this study critically incorporated considerations related
of metals can lead to stress-shielding effects due to a to mechanical, structural, and cell growth aspects. This
mismatch with the bone’s elastic modulus (for instance, study aimed to integrate finite element analysis, parameter
Ti6Al4V has an elastic modulus of 110–120 GPa, while optimization, biomechanical test, in vitro biological
cortical bone ranges from 10 to 40 GPa). 11-13 However, test, and animal experiment to develop a lattice design
designing the lattice structure and modifying its alignment specifically tailored for distal femur defect reconstruction
allow for variation in the elastic modulus of the lattice to implants, with the primary objective of refining the
significantly improve the mechanical compatibility between lattice structures within the implant for improved overall
the implant and the bone. 13,14 This approach effectively performance. Through the design of cuboctahedron
circumvents the stress-shielding effect and enhances the lattice variations, incorporating different arrangements
implant’s osteoconductive properties, facilitating bone and lattice pillar diameters, and utilizing finite element
15
ingrowth into the implant. Moreover, the loading applied analysis to explore material properties under various
16
to the bone plays a critical role in stimulating bone growth parameters, we sought to identify an optimal lattice. This
within the implant. Several studies have demonstrated lattice was intended to generate an appropriate bone strain
16
that applying an appropriate load to the bone through the (4000 μ) at the bone interface, ultimately improving the
lattice on the implant, which generates strains near but not osseointegration effect of the implant. The bone interface
exceeding 4000 μ, effectively stimulates bone growth into strain behavior around the implant was verified using the
the implant and enhances osseointegration. 17,18 biomechanical test, and in vitro biological tests were used
to assess whether the optimal lattice structure (OLS) was
In the past decade, various lattice structures had been
extensively studied. 16,19-21 One notable lattice structure conducive to cell growth and proliferation. Additionally,
animal experiments were employed to simulate in vivo
is the cuboctahedron lattice, which is recognized for its responses of the implant, providing a comprehensive
simple appearance. The internal space within the lattice evaluation of the biological activity of the lattice and
22
facilitates efficient nutrient transportation and waste confirming its utility in assessing osseointegration ability.
removal, and the multi-corner design of the lattice structure
makes it conducive for the attachment and clustered 2. Materials and methods
growth of osteoblasts. 15,23 Although the cuboctahedron
lattice demonstrates favorable conditions for osteoblast 2.1. Cuboctahedron lattice-parametric design of
differentiation and growth, further investigation is unit lattice
warranted to evaluate its applicability for distal femur A cuboctahedron lattice is a polyhedral structure
reconstruction. Specifically, it is crucial to determine composed of eight triangular faces and six square faces,
22
whether the cuboctahedron lattice structure can mitigate featuring a total of 12 vertices and 24 edges. This lattice
the stress-shielding effect and enhance osteoconductivity. structure possesses a unit volume of 2 × 2 × 2 mm³. The
Finite element method (FEM) can be employed to analyze lattice alignment angle and the lattice pillar diameter are
the stress fields within the metallic implant and strain fields two primary structural parameters of the cuboctahedron
in the soft evolving tissue. This analysis assists in designing lattice. The lattice alignment angle was classified into two
24
the structural parameters of the cuboctahedron lattice to categories: 0° and 45°. The lattice pillars were designed with
align with the mechanical conditions of the distal femur. 25 a circular cross-section, and the diameter parameter was

Volume 10 Issue 2 (2024) 545 doi: 10.36922/ijb.2590