Page 12 - IJB-5-2

Application of additive manufacturing technology in orthopedic medical implant-Spinal surgery as an example
papers were then followed by a series of cadaveric studies Berretta et al. in the manufacturing of cranial implant .
[17]
describing the effectiveness of additively manufactured Both the mechanical performance, density variation,
plastic pedicle screw template [13,14] . In summary, the and dimensional accuracy of the implants were found
researchers found that by using the screw template the comparable to the design model and show the highest
intended insertion location and angle correlate. compressive strength resistance.
As a result, titanium was proposed as an alternative to Evidently, an additively manufactured porous
plastic models for surgical guides; however, it was also titanium structures have great potential for use as bone
found to have disadvantages such as cost and availability. substitute biomaterials. Titanium alloys have been used
In the study by Takemoto et al., additive manufactured for decades as a bioactive material , encouraging bony
[18]
[15]
titanium thoracic pedicle screw templates were assessed ingrowth onto exposed surfaces. For instance, titanium-
specifically looking at the landmarks used as contact tantalum (Ti-Ta) alloy can be fabricated using selective
points for the template, to ensure reproducibility and laser melting . Ti-Ta alloys are promising materials for
[19]
stability. This study showed a very high success rate for biomedical applications and surgical implants because
their templates, with failure defined as perforation of the it has high biocompatibility, corrosion resistance, and
pedicle wall by the screw, 98.4% of pedicle screws were good mechanical properties. Besides, electron beam
placed successfully for scoliosis patients and 100% for melting allows porous implants made from titanium
ligament ossification patients. The issue of cost was also alloys to be created with control over the shape and pore
addressed in this study stating that the production cost of structure. This technology has the potential to develop
10 templates in a singular patient amounted to $1000 for both patient-specific custom implants, as well as generic
titanium versus $200 for the plastic polyamide. bone substitute implants. Yang et al. examined a self-
[20]
The authors pointed out that even though the stabilizing artificial vertebral body created this way in an
non-metallic materials have approval from the US in vivo sheep model of the cervical spine. This study found
Pharmacopeia for use in the human body for 24 h when that these porous metal implants facilitated bony ingrowth
in contact with drills and surgical tools; the plastic would and resulted in very stable fixation in a load-bearing
likely produce debris, which would accumulate in the application – something that is not currently possible with
wound. The long-term effect of this residual material is other additively manufactured scaffold structures.
unknown, and in close proximity to the spinal cord, its Worldwide, a number of companies are already
safety is clearly questionable. The titanium templates also making additively manufactured customized surgical
have the advantage of higher strength and rigidity, being tools and templates to aid in spinal procedures, as
metallic. This ensures greater accuracy and reliability, well as custom spinal implants designed specifically
reduces the chance of warping and flexing, and eliminates for particular patients. Besides the customized spinal
the potential of the drill or screw cutting through the implants, the similar technologies were applied to other
material and/or producing debris as is the case for plastic recent orthopedic regenerative medicine treatment . A
[21]
guides. mandible that is coated with hydroxyapatite has been
additively manufactured . Furthermore, Mertens et al.
[22]
6. Additively Manufactured Custom constructed a titanium-made midfacial support and a
Implants graft fixture through additive manufacturing for patient
with midface defect . Customized cranial implants were
[23]
Recent advances and the increased availability of metal-
based additive manufacturing technologies such as designed and additively manufactured by Jardini et al. in
the surgical reconstruction of a large cranial defect .
[24]
direct or selective laser sintering (LS) and electron beam
melting have allowed for the development of customized 7. Surgeon Survey
spinal implants into current surgical practice.
Off the shelf, vertebral body and intervertebral disc Spinal surgeons attending the Annual Scientific Meeting
implants are already commonly used, but the ability to 3D of the Spine Society of Australia 2015 held in Canberra,
print both generic and custom metal implants has a number Australia, were asked to complete a short survey on
of potential advantages. For instance, intervertebral discs their knowledge and use of RP technology (additive
that can be printed to conform to the patient’s specific manufacturing) in their surgical practices and experience.
vertebral end plate geometry have performed well in 35 surgeons completed the survey, of which 81% (27)
cadaveric studies, achieving higher compressive failure were experienced, senior consultants. Although 80% of
loads, and better stiffness characteristics than flat implants respondents had heard of using additive manufacturing
produced in the same manner . On the other hand, for surgical planning, only 10 had ever used it. Of these
[16]
a high-temperature LS allows fabrication layering of 10, eight reported using it 0–2 times per year and two
complex structure such as high-performance biomaterial reported using it 3–5 times per year. Most users (7/10)
polymer, i.e., polyether ether ketone was applied by reported that it improved the surgical outcome, with the

8 International Journal of Bioprinting (2019)–Volume 5, Issue 2