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

Imaging Machine (FeinFocus 160.25, United States) tion of collagen into the scaffolds was also evident
at 70 kV and 20 µA with resolution of approximately where the type 1 collagen acts as coating over the
15 µm. Three-dimensional renderings and projection metal phase of the scaffolds. With type 1 collagen
planes were made using VGStudio Max software coating, the metallic scaffolds can have enhanced bi-
(Volume Graphics GmbH, Germany). ological response.
2.3.3 Mechanical characterization The resulting compression elastic constant and
yield strength of the as-fabricated lattice structures are
To obtain the compressive properties, the SLM fabri- shown in Table 2. The gradient of the straight-line
cated lattice cubic samples of designed dimensions of portion of the stress-strain curve is established to de-
10 mm × 1 0 mm × 1 0 mm was tested with 3 repli- fine the elastic constant and the yield strength is taken
cates, by using Instron Static Tester Series 5569 (In- as the stress at plastic compressive strain of 0.2%. The
stron, United States) using test conditions recom- standard deviation in the elastic constant and yield
mended by ISO 13314-2011. The tester is equipped strength may be due to the laser power fluctuations
with a 50 kN load cell. The compression tests were during SLM resulting in varying amount of powder
carried out at room temperature (25 °C). The loading adhesion on the struts. This in turn affects the com-
speed was set at 0.6 mm/min for all samples so as to pressive properties of the lattice structures.
maintain a constant strain rate. This is to minimize the The resulting elastic constants of both TiTa and
effects of different strain rates in titanium [42-44] . cpTi scaffolds are comparable to that of human bones
The compression tests were carried out until the which have wide range of elastic constants, for exam-
samples were fully deformed axially or when the ma- ple, from 1.0 to 25.0 GPa [45, 46] . This shows that with
ximum load of 50 kN was reached, whichever came careful design, TiTa and cpTi can serve as load bear-
first. The stress-strain curves, yield strengths and elas- ing implants while avoiding the adverse “stress shiel-
tic constants in compression of the as-fabricated sam- ding” effect [47] .
ples were then obtained from the compression tests.
The biphasic scaffolds formed are advantageous for
3. Results and Discussion several reasons. Firstly, they can be designed to fit
patient specifically using medical imaging such as
The fabrication of titanium based scaffolds using SLM X-ray. Secondly, they can be designed to cater to spe-
has the potential to be a technique for the repair and cific properties required in different bone regions.
regeneration of bone via tissue engineering. A skeletal Thirdly, the biphasic components can function sepa-
reconstruction scaffolds must have the mechanical rately, the hydrogel component can regulate cell dif-
properties that can support in vivo loads, promote tis- ferentiation and growth, while promoting bone rege-
sue in-growth and be biocompatible. neration and vasculature. The SLM produced scaffold
Micro-CT technique was used to visualize nonde- component can act as structural reinforcement and
structively the infiltration of type 1 collagen in to the provide the mechanical strength required during the
scaffolds, as shown in Figure 3A and Figure 3B. healing process.
The actual porosity of the cpTi and TiTa scaffolds are
59.86 ± 0.59% and 59.79 ± 0.68%, respectively. In Table 2. Compressive properties of S LM produced TiTa and
order to further study the interface between the type 1 commercially pure titanium samples (n = 5).
collagen and commercial pure titanium or TiTa, SEM Elastic Fonstant Yield Vtrength Strength to Hlastic
was used. Continuous interface was found to ex- Material (GPa) (MPa) Fonstant Uatio
−2
ist between the type 1 collagen and metal scaffolds. As TiTa 4.57 ± 0.09 151.93 ± 8.47 3.32 × 10
shown in Figure 3, the type 1 collagen infiltrated the cpTi 4.29 ± 0.15 121.20 ± 3.67 2.83 × 10
−2
pores of the metal scaffolds without any significant
impedance. 4. Conclusion
From the SEM images (Figure 3C and Figure 3D),
it can be observed that the surface of commercially Biphasic scaffolds provide bone-like mechanical prop-
pure titanium and TiTa scaffolds were rough due to the erties while having the potential to support cartilage
SLM powder fusion process which can results in growth. The SLM technique offers control over the
powder adhesions on the scaffolds [14] . The top colla- micro-scale complex design of the bone phase which
gen layer was between 200 µm and 500 µm. Infiltra- can be fabricated using biocompatible metals. In this
68 International Journal of Bioprinting (2017)–Volume 3, Issue 1