biomimetically in medical implants to imitate the mechanical
behavior of the original tissue (e.g., bone [13]), it is also important
to reduce the risk of implant failure. The mismatch of mechanical
properties between the prosthesis and the surrounding tissue has
been identified as a major cause of loosening of orthopedic implants
because the density of the host bone reduces [14, 15]—known as
stress shielding. When the bone loss is significant, fracture can easily
occur.
Conventional manufacturing techniques have been applied to
the fabrication of lattice structures in the past. For example, fiber
bonding, membrane lamination, molding, solvent casting, phase
separation, and foaming have been used in the context
[16, 17]. However, these techniques do not allow control of the
scaffold architecture—i.e., possible tailoring of structural parameters such as pore size and pore network; and they are time and
cost demanding [18]. The advent of additive manufacturing has
enabled the precise manufacture of lattice structures, thanks to the
possibility of controlling the spatial deposition of material. Such a
method allows an accurate control of pore size and structure, while
being cost-efficient. The popularity of additive manufacturing has
further increased given the possibility of manufacturing complex
shapes.
Scaffolds with functionally graded porosity are commonly manufactured using additive manufacturing techniques. One possible
way to obtain scaffolds with variable stiffness is to engineer the
spacing of the lattice structure: smaller pore size is used where
higher stiffness is required [19]. However, this strategy does not
work on woodpile lattices, as the bending stiffness of such lattices is
independent of the spacing across the bending direction. Here we
propose a solution that involves the deposition of filaments with
continuously variable cross section. Currently available technologies allow printing filaments with variable stiffness by using variable
cross-section nozzles [20]. However, this solution requires specific
hardware modifications. Here we present a manufacturing solution
to fabricate structured materials with variable stiffness via the control of a process parameter. This technique allows a continuous
variation of the stiffness by controlling the diameter of the extruded
filaments point to point without requiring a hardware modification.
2 Materials
Fused deposition modelling is an affordable method used to manufacture biomedical scaffolds. Several 3D printers are currently
available on the market. Here we make use of the Ultimaker 2 commercial machine [21].
32
Alessandra Bonfanti et al.
behavior of the original tissue (e.g., bone [13]), it is also important
to reduce the risk of implant failure. The mismatch of mechanical
properties between the prosthesis and the surrounding tissue has
been identified as a major cause of loosening of orthopedic implants
because the density of the host bone reduces [14, 15]—known as
stress shielding. When the bone loss is significant, fracture can easily
occur.
Conventional manufacturing techniques have been applied to
the fabrication of lattice structures in the past. For example, fiber
bonding, membrane lamination, molding, solvent casting, phase
separation, and foaming have been used in the context
[16, 17]. However, these techniques do not allow control of the
scaffold architecture—i.e., possible tailoring of structural parameters such as pore size and pore network; and they are time and
cost demanding [18]. The advent of additive manufacturing has
enabled the precise manufacture of lattice structures, thanks to the
possibility of controlling the spatial deposition of material. Such a
method allows an accurate control of pore size and structure, while
being cost-efficient. The popularity of additive manufacturing has
further increased given the possibility of manufacturing complex
shapes.
Scaffolds with functionally graded porosity are commonly manufactured using additive manufacturing techniques. One possible
way to obtain scaffolds with variable stiffness is to engineer the
spacing of the lattice structure: smaller pore size is used where
higher stiffness is required [19]. However, this strategy does not
work on woodpile lattices, as the bending stiffness of such lattices is
independent of the spacing across the bending direction. Here we
propose a solution that involves the deposition of filaments with
continuously variable cross section. Currently available technologies allow printing filaments with variable stiffness by using variable
cross-section nozzles [20]. However, this solution requires specific
hardware modifications. Here we present a manufacturing solution
to fabricate structured materials with variable stiffness via the control of a process parameter. This technique allows a continuous
variation of the stiffness by controlling the diameter of the extruded
filaments point to point without requiring a hardware modification.
2 Materials
Fused deposition modelling is an affordable method used to manufacture biomedical scaffolds. Several 3D printers are currently
available on the market. Here we make use of the Ultimaker 2 commercial machine [21].
32
Alessandra Bonfanti et al.