Page 252 - IJB-9-2

International Journal of Bioprinting Coronary and peripheral artery disease. State of the art.

of the printed construct after biomedical implantation . available stents. After implantation, the βCD-PCL-PTX
[64]
PLA is a SMP with non-irritant, biocompatibility and stent recovers its shape at 56.8°C, which can be achieved
biodegradability features. This material, in combination with a balloon containing hot water .
[71]
with PVA and FDM 3DP, has proven to be useful in the Carbonyl iron powder (CIP) is a pure form of iron used
production of stents with feasible mechanical properties in a wide variety of applications, from dietary supplement
and minimal invasive implantation . PLA proved to be to inductive electronic components. In our particular case,
[62]
a promising material for self-expandable stents, with a CIP has proven to be very useful for the reinforcement
diameter recovery ratio above 95% and length recovery of polymers thanks to its high physical strength .
[99]
ratio above 97%. One of the disadvantages of the system Together with the biocompatibility, antithrombotic effect
lies in the glass transition temperature of PLA (50-80ºC), and negligible toxicity of CIP [100-103] , CIP is an ingredient
which is 13-43°C above the human body temperature, thus with remarkable potential in the formulation of vascular
complicating the implantation procedure. Further studies prosthesis such as VS. CIP has been combined with PCL
regarding material properties and modification are needed in an attempt to improve the properties of the polymer .
[72]
to prove PLA as a stent material. The combination PCL-CIP was purely based on physical
Sulfated chitosan was used to modify the surface interactions (no chemical interactions were detected). The
of the PCL-printed stent by immobilization of 2-N, addition of 2% CIP improved the mechanical performance
6-O-sulfated chitosan, which gives rise to a so-called of PCL structures, including its flexibility. Moreover, the
“aminated stent” . The amination of PCL affected the hydrophobicity of PCL was reduced by the presence of CIP,
[36]
surface microstructure and the resultant interaction of with hydrophilic profile. This amount of CIP demonstrated
the stent with cells after implantation. In fact, despite in vitro that the PCL-CIP composite is adequate as
that both modified and unmodified PCL stents possessed stent ingredient. The structures were biocompatible,
adequate biocompatibility, the cellular proliferation was hemocompatible and non-thrombogenic. An indirect
enhanced after the surface modification. This result has correlation between the concentration of CIP and the
been explained by the roughness of the surface: “rough activation of platelets was reported (the higher the amount
[72]
surface of stents can highly improve endothelial cell of CIP, the lower the platelet activation) .
attachment and growth, while smooth surface contributes Shape memory alloys (SMA) can also be 3D-printed
to endothelial cell migration” . According to scanning by using PBF techniques. Different studies have revealed
[36]
electron microscopy images, the addition of sulfated that the use of 3DP (such as PBD or DED) for the
chitosan improved the superficial roughness, in agreement production of nitinol 3D structures (not specifically VS)
with the biocompatibility and cellular proliferation results. is very promising but requires the optimization of several
The surface modification did not influence the mechanical parameters [104-107] . No major studies have been devoted
properties, which is expectable since the amination is to the specific manufacturing of nitinol VS through 3DP.
performed after the 3DP process. The study of Lei et al. (2020) reported the use of nitinol
[68]
Among the SMP, PCL is one of the most currently as part of a personalized VS, but 3DP was solely used for
studied for 3DP of VS due to its high mechanical the fabrication of an aortic mold where nitinol wires were
properties and tunable transition temperature. PCL has subsequently placed (Figure 7).
been recently modified by the addition of cyclodextrin Table 4 gathers the most recent studies on the production
and acrylation . The acrylation enables the photo- of VS by 3DP methods and their main features. It is clear
[71]
polymerization of the final 3D construct and further that bioresorbable vascular stents (BRS) are currently in the
improves the final consistence and mechanical properties. spotlight due to their advantageous properties with respect
The lypophilic nature of both PTX and PCL implies their to permanent stents. The vast majority of materials recently
combination to be feasible and homogeneous. Nonetheless, used are synthetic polymers, which are more versatile and
an excessive hydrophobicity of the final system jeopardizes apt for 3DP techniques such as DED (FDM) and MEX,
the biocompatibility of the stent as well as the release and both of them are considered the most cost-effective 3DP
dissolution of PTX. The presence of β-cyclodextrin (βCD) techniques [108,109] . Moreover, polymers are in general
aims to improve the hydrophilicity of the resultant stent, pliable, they can be fabricated with different mechanical
therefore compensating the hydrophobic nature of PCL. properties, and some of them are biodegradable and
CDs are well known by their role as drug solubilizing biocompatible. Additionally, shape-memory polymers are
agent. PTX can bind well to the inner cavity of βCD to of great usefulness for the production of self-expandable
form easily soluble inclusion bodies. Sustained release devices. In fact, PCL is the most frequently used materials,
of PTX was reported for 15–20 days, revealing higher followed by PLA, in the printing of VS (Table 4) due to
performance with respect to other similar, commercially its biodegradability, biocompatibility, and shape memory

Volume 9 Issue 2 (2023) 244 https://doi.org/10.18063/ijb.v9i2.664