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Fabrication of titanium based biphasic scaffold using selective laser melting and collagen immersion

manufacturing technique that fuses metal powders to In this paper, SLM is used to fabricate cpTi and Ti-
form functionally parts directly. It uses laser power Ta metallic porous structures using a unit cell design
source to fabricated parts based on computer aided that has been proven to be suitable for fabrication us-
design (CAD) files [15, 18-23] . There are many new re- ing SLM. CpTi is used as a benchmark material for
search opportunities that emerges due to the capability this method of forming biphasic scaffolds as the me-
of SLM in producing parts with complex geometry. chanical properties of these two materials have been
One of such areas includes the fabrication of metallic evaluated previously [33] . The novel biphasic scaffolds
porous structures with controlled porosity and varying constructs formed using the metallic porous structures
designs [12, 14, 16, 24-26] . The interest in this field has also and type 1 collagen is studied for the first time to in-
fueled focus on the use of biocompatible materials in vestigate the interface between these materials and
SLM. Among them, titanium alloys are of special in- type 1 collagen.
terest due to their excellent properties. Many studies
done on SLM produced titanium alloys such as 2. Experimental details
Ti6Al4V [13, 15, 27-30] and Ti6Al7Nb [16, 31, 32] . The studies 2.1 Scaffolds design
have proven their superior properties for biomedical
applications. Titanium-tantalum (TiTa) formation by Design concept of the scaffolds mimics the nature,
SLM has recently been studied [33] and it has the po- which involved a porous cpTi or TiTa scaffold base to
tential to outperform Ti6Al4V and commercially pure mimics the osseous bone structure’s mechanical stre-
titanium (cpTi) due to its higher strength to modulus ngth and a type 1 collagen phase as the cartilage phase.
ratio and better biocompatibility [34, 35] . The titanium scaffolds are designed using cubic unit
Despite the advantages titanium alloys provide, a cells of 1 mm × 1 mm × 1 mm, as shown in Figure 1.
single phase scaffold alone cannot meet the complex The unit cell is designed such that the fabricated
functional demands of bone and cartilage tissues as scaffolds have a porosity of 80.3% with square struts
these have wide differences in their chemical, struc- of 0.285 mm and square pore size of 0.715 mm. The
tural and mechanical properties [36] . Biphasic scaffolds fully infiltrated collagen matrix provides micro-en-
provide the solution by allowing the composition ra- vironment for cells attachment, migration, prolifera-
tio between the two phases to be tailored and altered tion and nutrient transportation. In future study, cells
to cater to individuals and for specific applications. can be encapsulated directly into collagen matrix.
Such biphasic scaffolds have a rigid osseous phase to
integrate with the native bone and a porous chondral 2.2 Biphasic scaffolds formation
phase to allow the seeding and proliferation of cells [37] .
Zhao et al. [38] prepared porous PLGA/titanium biph- All the scaffolds were fabricated using a SLM 250HL
asic scaffold and evaluated the mechanical properties, machine (SLM Solutions Group AG, Germany). The
microstructure and interface. The analysis showed that SLM machine uses a fiber laser with Gaussian beam
the scaffold has good overall integrity and stable in- profile and maximum power of 400 W. The laser has
terface. Nover et al. [39] recently fabricated an osteo- spot size of 80 μm. To prevent oxidation and degrada-
chondral grafts that consists of bone-like porous tita- tion of materials, all processing occurred in an argon
nium and a chondrocyte-seeded hydrogel. The porous environment with less than 0.05% oxygen [18] . The de-
titanium is made using SLM with cpTi, and together tailed characteristics of cpTi and TiTa powders
with the hydrogel, it is able to support robust cartilage have been described previously [33] . In this work, iden-
growth. As one of the essential component of ECM, tical processing parameters are used for TiTa and cpTi,
type 1 collagen has been widely used as tissue scaf- and is shown in Table 1.
fold material [40] . It is biocompatible and provides fa- For the hydrogel portion, 2 mg/ml collagen were
vorable cellular micro-environment to induce chon- prepared according to the manufacturer’s instruction.
drogenesis of mesenchymal stem cells (MSCs) in vivo. Briefly, the required volume of collagen was neutra-
For example, collagen-glycosaminoglycan phosph- lized with 1 M NaOH in PBS. The biphasic scaffolds
ate biphasic scaffold were evaluated in caprine femor- were prepared by immersing the scaffolds in de-
al condyle and lateral trochlear sulcus osteochondral gassed collagen solution while shaking gently. Excess
defects model. After 26 weeks of implantation, both collagen solution was removed before gelling at 37 °C.
scaffolds provide indications of structural repair [41] . A summary of the process is shown in Figure 2.

66 International Journal of Bioprinting (2017)–Volume 3, Issue 1