Page 154 - IJB-9-5

International Journal of Bioprinting Guide about the effects of sterilization on 3D-printed materials for medicine

1. Introduction contact with the patient. For example, an anatomical model
for surgical planning and training is classified as Class I; a
Additive manufacturing (AM) and three-dimensional (3D) cutting guide or a positioning guide (that will be in short
printing technologies are revolutionizing manufacturing contact with the patient’s mucosa/body) is classified as
industries by enabling the development of devices and Class IIa, the same as a patient-specific tracheotomy tube.
products at the point of demand in a unique way. There An implantable plate will be a Class IIb, and a functional
are seven categories of AM technologies according to ISO/ implant, such as a knee implant, is classified as Class III.
[1]
ASTM 52900 : (i) vat photopolymerization (VP), which
includes stereolithography (SLA), digital light processing Although the first 3D printing or AM materials tested
(DLP), and volumetric 3D printing (3DVP); (ii) material and validated for medical use have appeared in recent
extrusion (ME), which includes fused filament fabrication years, most of the existing materials are not designed
(FFF) or fused deposition modeling (FDM) and direct and validated to follow the hospital standards and MDR
ink writing (DIW); (iii) material jetting (MJ); (iv) binder compliance, nor are their mechanical properties analyzed
jetting (BJ); (v) powder bed fusion (PBF), which includes for the main sterilization processes used in hospital settings,
selective laser sintering (SLS) and selective laser melting taking into account their indications of use [9,16-19] . Thus, it
(SLM); (vi) directed energy deposition (DED); and is important to understand the effects of these chemical
(vii) sheet lamination. and pressure processes and how the mechanical properties
This revolution has been accelerated due to the of 3D-printed parts are affected. All surgical instruments
COVID-19 pandemic and the supply shortages in the are cleaned and sterilized before they are used. In some
medical field [2-6] , further popularizing the manufacturing applications, certain sets of materials containing surgical
of patient-specific point-of-care medical device. AM and aid tools and implants are cleaned and sterilized several
[20]
3D printing in healthcare refer mainly to technologies times per day . The effect of sterilization on mechanical
focused on generating 3D physical objects to produce behavior and dimensional changes and distortion of
personalized medical devices (from anatomical models to 3D-printed parts is key to understanding its potential
[21]
personalized splints, advanced medicines, or implants) . applications and is the underlying cause of failures .
[7]
The generation of personalized tools for surgical planning Sterilization process can be performed by two different
and medical training models have become the main types of known processes : (i) thermal sterilization by
[22]
applications of 3D printing technologies . In most cases, dry heat or steam, also known as moist heat sterilization
[8]
the process is based on acquired images from a human or autoclave; (ii) low-temperature sterilization, such as
body, typically taken from both computed tomography chemical (with ethylene oxide or hydrogen peroxide) or
(CT) and magnetic resonance imaging (MRI). An identical radiation (ionizing or ultraviolet [UV] radiation). Most
copy, obtained either from volume rendering (VR) or 3D common sterilization methods available in hospitals are
computer-aided design (CAD) models, of the clinical case steam heat sterilization (also known as autoclave [AU]),
is an advantage for customizing the surgical approach [2,4,9] . gas plasma (also known as hydrogen peroxide [HPO]
In this process, customized surgical tools and implants can autoclave), and ethylene oxide . Other sterilization
[23]
be designed and produced [10-14] . These tools printed with techniques have significant disadvantages for their use in
AM technologies are being rapidly adopted, but most of hospitals. For instance, thermal sterilization by dry heat
the materials used for printing the tools were originally is at this moment banned from hospitals of the European
designed for applications in other (nonmedical) industries. Union due to the inactivity on prions . Then, radiation
[24]
In medical applications, functional products are subject sterilization, which is mainly used in the food industry as
to application-specific mechanical loads, pressure, erosion well as in the medical device industry, is not suitable for
[24]
and stress, and are exposed to chemicals and environmental hospitals . Ethylene oxide should be avoided for several
factors limited to specific working and storage conditions. reasons: (i) it changes the polymer structures; (ii) it causes
Additionally, the materials and manufacturing processes molecular weight loss; and (iii) it generates toxicity on the
and the design of parts depend not only on their indication surface of the sample, for example, in polylactic acid (PLA)
[25]
of use and the time of usage, but also on the performance or polyethylene terephthalate glycol (PETG) . Unlike
needed and the physical and chemical conditions they will the HPO low-temperature sterilization, no toxic residues
work in. Since May 2017, depending on their indication remain on the items that have been sterilized. Additionally,
of use and risk, AM medical applications are classified by this technique is not only effective and safe but also does not
[24]
the European Union as Medical Devices regulated under require any aeration time compared to ethylene oxide .
the Medical Device Regulation (MDR) . Thus, each The materials that have been studied so far include:
[15]
application is classified according to its risk and time in (i) PLA [24,26] , acrylonitrile butadiene styrene (ABS) [27-30] or

Volume 9 Issue 5 (2023) 146 https://doi.org/10.18063/ijb.756