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Materials Science in Additive Manufacturing Additive manufacturing of 316L-Cu alloys

movement. In addition, implant materials must be Additive manufacturing (AM) is a manufacturing
biocompatible, resistant to corrosion, and not introduce method with ever-expanding popularity due to its
toxicity to the body. While materials such as titanium or various advantages over traditional production methods.
cobalt-chromium alloys are some of the many options Among other benefits, AM enables the production
available, 316L stainless steel (SS) is commonly used of intricate designs, easily customizable parts, and
in implants and fracture management devices due to small batch production. These properties make AM
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its high strength, excellent corrosion resistance, and an ideal method for producing biomedical devices.
good biocompatibility while remaining relatively low AM enables varying part sizes and geometry, allowing
cost. These properties are crucial for a material that will implants to be custom-fit to a patient. The process also
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be subjected to fluctuating loads while exposed to the makes producing custom and small numbers of parts
biological environment of the human body. However, financially accessible because it does not rely on fixed
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316L does not possess inherent antibacterial properties. tooling. In addition, the AM process is well-suited for
Patients are often required to take antibiotic medication producing custom alloy compositions due to its particle
to address concerns of post-surgery infection, but this form feedstock. Within the family of AM processes,
provides only temporary protection. Moreover, bacterial laser-directed energy deposition (L-DED) is well-fitted
strains can become antibiotic-resistant, rendering the for biomedical device manufacturing due to its higher
patient vulnerable to infection. As a result, there is a need material deposition rate over other methods and precise
for an alloy with similar mechanical properties to 316L control over alloy composition in small volumes. 19,20
while incorporating antibacterial features. DED can also produce functionally graded materials for
optimized performance, such as hard surfaces for wear
Copper (Cu) has long been recognized for its antibacterial resistance and tough cores for load-bearing capacity.
properties, as it can disrupt bacterial cell membranes and Therefore, AM and DED are attractive processes for
inhibit the growth of various pathogens. 7-12 Due to its producing metallic biomedical devices. While previous
antibacterial effect, Cu is used in critical surfaces found in work has explored the mechanical and antibacterial
drinking water distribution and hospital applications. Yet, properties of 316L-Cu, there is limited insight into this
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its antibacterial effect is joined with concerns of toxicity. alloy produced by AM.
Other antibacterial metals, like Ag, have also been studied
for toxicity when used for implant applications. Increased This research aims to test the mechanical and
Ag levels can be found in bodily fluids, though most effects antibacterial properties of 316L, 316L-3Cu (SS-3Cu),
are seen in local tissue surrounding the implant site. and 316L-5Cu (SS-5Cu) for implants and fracture
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Therefore, toxicity may depend on the alloy’s dose and the management devices. It is hypothesized that adding Cu
implant site’s sensitivity. Similarly, Cu toxicity may depend into a 316L matrix will provide inherent antibacterial
on several factors. A Cu ion concentration of 46 μg/mL is properties and similar mechanical performance to
highly toxic to fibroblasts in mice, while 2 mg/L may reach 316L when produced through laser DED. Mechanical
harmful levels in humans. 15,16 properties were evaluated by compressive loading and
hardness measurements, along with microstructure
While the exact method of Cu contact killing is still characterization. Antibacterial performance was
not fully understood, this has not withheld the element measured with 316L as the control against Staphylococcus
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from being used as an antibacterial material. Even aureus and Pseudomonas aeruginosa to measure the effect
though toxicity may not be boiled down to a simple of Cu addition against two common implant-related
alloying percentage, previous work has suggested Cu bacterial strains. 1,3
loadings up to 3% to be non-toxic while still providing
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an antibacterial effect. In contrast, separate studies 2. Materials and methods
suggested that a 316L-5Cu composition has a lower
tensile strength than 316L, but a 316L-3.5Cu alloy has 2.1. Sample preparation
improved hardness over 316L after undergoing an The raw materials used in this study consisted of 316L SS
aging treatment. 7,17 316L-Cu alloys have the potential powder (Höganäs, Sweden) with particle sizes ranging
to significantly improve the function of biomedical from 20 to 55 μm and Cu powder (GKN Hoeganaes,
implants by becoming intrinsically resistant to bacterial Cinnaminson, NJ, USA) with particle sizes ranging
colonization. However, a challenge lies in achieving from 15 to 53 μm. Although the L-DED system used
the right balance of Cu to enhance antibacterial effects in this study supports a larger powder size distribution,
without compromising the alloy’s mechanical integrity this particle size range was chosen to balance several
or resulting in toxicity to the body. properties. Finer particles were found to reduce powder

Volume 4 Issue 1 (2025) 2 doi: 10.36922/msam.7357