Page 234 - IJB-10-6

International Journal of Bioprinting DIW of concave hydroxyapatite scaffolds

excellent shape fidelity. Unlike printed ceramic parts that saline (PBS), penicillin/streptomycin (Pen/Strep), HEPES,
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require sintering, self-setting inks avoid shrinkage 32,39,41–45 sodium pyruvate, Presto Blue kit, and mammalian protein
and produce biomimetic apatites with a composition extraction reagent (M-PER) were purchased from Thermo
closely resembling the mineral phase of natural bone. 46 Scientific-Gibco (USA). Lactate dehydrogenase (LDH)
Previous studies have demonstrated that CDHA-based and alkaline phosphatase (ALP, SensoLyte® pNPP) kits
ceramic printed parts have excellent biocompatibility and were purchased from Roche (Switzerland) and Anaspec
bioactivity, supporting bone ingrowth and functioning as (USA), respectively. Immunocytochemistry reagents,
bone scaffolds. 39,47 This has led to interest in incorporating TRIT-C conjugated phalloidin (Alexa Fluor 546), and
concavities into DIW CaP scaffolds. Various strategies 4′,6-diamidino-2-phenylindole (DAPI) were purchased
have been explored, including modifying the nozzle from Invitrogen (USA) and Merck (USA), respectively.
geometry to obtain concave channels 40,48,49 or altering the Paraformaldehyde was obtained from Aname-
ink formulation to introduce intra-strand porosity (e.g., by Instrumentación Científica (Spain). Glycine was purchased
incorporating sacrificial particles 38,50 or using emulsified from Serva (Spain).
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or foamed pastes ). However, the filament diameter often 2.2. Scaffold design
limits the size of the intra-strand pores, which can be Given the aforementioned advantages, slicer programs
insufficient. for 3D printing incorporate TPMS patterns, particularly

Hitherto, the potential of TPMS, while widely explored the G type. However, these 3D models are generated
in other 3D printing techniques, has not been exploited by intersecting 2D wavy lines with a defined porosity.
using DIW. In this study, we explore the use of TPMS This is different from generating the 3D model in a
models to create scaffolds with controlled concavities mathematical program (e.g., MATLAB), where unit cell
busing DIW, despite the challenge of filament convexity. numbers, dimensions, and/or volumetric fractions can
The combination of concave confined spaces with high be customized. This allows us to obtain sufficient and
permeable geometries and the enhanced bioactive and representative porosities for each geometry type when
osteogenic potential of reactive ceramics could produce slicing the coded geometry for DIW, taking into account
promising bone regenerative grafts. We used a self- the limitations of the printer.
setting α-TCP ink to create CDHA scaffolds with complex Three different types of TPMS scaffolds were coded
architectures. Three TPMS structures were selected as with MATLAB (MathWorks, USA), as in previous work.
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printing patterns for DIW: gyroid (G), diamond (D; also G, D, and S lattice structures with a defined number of cells
known as diamond Schwarz), and Schwarz (S; also called and volume fraction were generated by determining the
Schwarz primitive). Cylindrical scaffolds with different isosurface (U = 0) using the following TPMS equations :
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porosities were designed using a MATLAB code from
previous work, and their printability was evaluated. The K x) ( K y) + (
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resulting CDHA scaffolds were then evaluated for the U = cos ( x sin y cos K y) sin (I)
y
G
effects of pore architecture on physicochemical properties, ( Kz) + cos ( Kz)sin ( Kx) − C
blood permeability, mechanical behavior, and in vitro z z x G G
response of pre-osteoblastic (pre-OB) cells, compared
to the typical orthogonal printing pattern with the same U = sin ( K x) ( K y) sin ( K z) +
sin
total porosity. D x y z
y (
sin ( Kx)cos Ky) cos ( Kz) + coos
x
z
2. Materials and methods ( Kx) ( Ky) cos ( Kz) + cos (II)
sin
2.1. Materials x y z
y (
x (
(
Poloxamer 407 (Kolliphor® P 407), also known as Pluronic kx)cos Ky) sin Kz) − C D
z
F127, was purchased from BASF Pharmaceuticals
(Germany). Calcium phosphate dibasic (CaHPO4), U = cos ( K x) + ( K y) + cos ( K z) − C (III)
cos
calcium carbonate (CaCO3), Triton X-100, Alizarin red S x y z S
staining (AR-S), and cetyl pyridinium chloride powders
were obtained from Sigma-Aldrich (United States where the subscripts G, S and D refer to the type of
of America [USA]). Disposable 3D printer cartridge geometry; parameters K and C represent the structure’s
(3cc Optimum® Syringe Barrels) and 250 µm tapered periodicity and porosity, respectively. In each direction, K
dispensing tips (Gauge 22 SmoothFlow Tapered Tips) is defined as 2n , where n is the number of unit cells and L
from Nordson EFD (USA) were used for printing. McCoy’s L
5A media, fetal bovine serum (FBS), phosphate-buffered is the absolute size of the structure.
Volume 10 Issue 6 (2024) 226 doi: 10.36922/ijb.3805