Page 196 - IJB-10-4

International Journal of Bioprinting Horsetail-inspired lattice for bone use

undergoing aging, which further increases the risk for bone to realize simple nature-inspired designs with desirable
defects. These defects may result in bone loss and would performance required for respective applications.
1,2
require the substitution of bone mass through transplant or There have been many works conducted to broadly
grafting. Coupled with the limited supplies of grafts, there classify nature-inspired structures. It can be observed
21
has been increasing interest in bone tissue engineering that a common feature found in nature is tubular design
to produce synthetic substitutive scaffold that is able to appearing in cross-section. Such tubular design is often
mimic the performance of native organic bone material. 3,4 implemented in the tubes-in-tube configuration and
Fundamentally, the mechanical aspects of bone require it is demonstrated by examples such as horsetail plant,
to be porous for cell ingrowth and biomaterial transport, bamboo, and muscle tendons. Li et al. reported that such
as well as having mechanical performance similar to that of configuration is common in some mesocarps, which
host bone material (and not of the highest stiffness) to avoid are rich in vascular bundles that are of reticulation
stress shielding effects. When coupled with biomimetics distribution. Intuitively, the tubular designs would be
5
22
design consideration, the unit building block should, ideal for flow augmentation of the bone.
ideally, be able to demonstrate resilience to usage loading, The use of simple cubic Bravais lattices as building
and exhibit similar mechanical properties in all directions blocks for additive manufacturing design has been
to allow ease of design. Notably, while isotropy simplifies prevalent due to potential for high customizability. 23-25
design, the cortical bone also is transversely isotropic while The basic Bravais lattice family includes simple cubic
6
the trabecular bone is mostly isotropic; such characteristics (SC), body-centered cubic (BCC), and face-centered
provide strong impetus for an isotropic design or the ability cubic (FCC) structure. Interestingly, the BCC lattice has
to control the directionality when designing synthetic the smallest effective strut length of the basic lattices.
substitutive scaffolds. This functional aspect of mechanical Ferng et al. compared the effects of BCC and FCC lattice
performance has motivated studies into strategies for arrangements on flow and characteristics and observed
design and control of directionality or the attainment of that FCC lattice has higher flow velocity than the inlet,
isotropic characteristic. These performance requirements, due to the closed pack configuration of FCC lattice. The
7,8
26
which were difficult to achieve in the past, have been made greater difference with the inlet flow velocity, thus pressure
possible with advancement in additive manufacturing differential, indicates greater obstruction. While the study
processes. Additive manufacturing enabled the creation of performed by Ferng et al. focuses on the particles of Bravais
9
complex geometries at sub-millimeter-length scale that are lattices, it is intuitive that the volume occupied by the
challenging for conventional manufacturing techniques. 10 struts would affect packing efficiency when the lattices are
represented by connecting struts instead of the particles.
Mechanical performance tuning through substructure Therefore, there is an intrinsic motivation to apply BCC
control, which is made possible by additive manufacturing, lattice for flow obstruction minimization, which will be
has been widely studied. Lattice metamaterials constitute a important to bone scaffold-related applications. At present,
class of advance material that is realized with the availability studies on the effects of strut member modifications for
of additive manufacturing. Thus far, lattices based on the purpose of mechanical performance tuning remain
features, such as shells, struts, plates, or their hybrids, have scarce. Zhao et al. previously investigated the effect of
been proposed. One of the areas that have been studied the inner hollow strut size of the strut on the mechanical
for shell lattices is related to the mathematically controlled performance of a BCC lattice with prismatic struts, and
triply periodic minimal surfaces (TPMS). 11-15 There are reported that the elastic modulus increased by up to 14
also works related to the Boolean combinations of different times with the subtractive modification of the inner hollow
known strut or plate-based lattices to attain mechanical strut size. Additionally, BCC is also a bending-dominated
27
performance differentiation. 16-19 These methodologies lattice, which is expected to have lower elastic modulus
create complex structures, which may be computationally as compared with stretch-dominated lattice. The use of
heavy when applied. Nature, on the other hand, has BCC is therefore ideal for adjusting performance tuning
evolved over time through the process of nature selection. mechanism, which increases the elastic modulus.
The process has developed designs to fit the required Given the efficiency of naturally inspired cross-
performance in the most efficient way, through a multitude sectional structure and the ideal properties exhibited
of boundary conditions which we may not have priori by BCC lattices specific to bone scaffold application,
knowledge of. The designs may thus be geometrically it is our prime interest to evaluate effect of combining
20
non-rigid and be composed of random substructure that two-dimensional geometry and three-dimensional (3D)
is not of defined replications. It is intuitive that designers features in the context of mechanical performance tuning.
20
have a prime interest to leverage such natural evolution The performance of geometric adjustments on volumetric

Volume 10 Issue 4 (2024) 188 doi: 10.36922/ijb.2326