In ‘Differential thermal analysis of the antibacterial effect of PLA-based materials planned for 3D printing,’ authors P. Maroti, B. Kocsis, A. Ferencz, M. Nyitrai, and D. Lorinczy explore the opportunities biomedical applications offer to research and medicine, along with the importance of evaluating materials used in creating devices.

In this study, researchers are specifically concerned with contamination risk and the purported antibacterial properties of PLA, along with PLA-HDT, a PLA-Ag nanocomposite, with DTA/TG. PLA and its derivatives have been attractive to researchers over time because of its natural plant-based origins and biodegradability. The researchers point out the need for sterilization in bioprinting practices, and especially for patients about to receive implants, with the most popular methods as follows:

• Steam sterilization (at high pressure and * 130 C)
• Dry sterilization (close to 200 C)
• Sterilization with radioactive sources
• Gas sterilization (mainly in ethylene oxide)

As research progressed, the team tested the antimicrobial properties of the materials, using the following:

• Micrococcus luteus–Sarcina lutea ATCC 9341 – commonly found in human skin flora
• Bacillus subtilis ATCC 6633 – bioassay organism for detecting antimicrobial agents
• Staphylococcus aureus ATCC 25923
• Escherichia coli ATCC 25922
• Pseudomonas aeruginosa ATCC 15442

“The surfaces of media were continuously inoculated with test bacteria; the test disks containing presumably antimicrobial materials were placed on the inoculated surface of the media,” explained the authors. “After 24 h incubation at 37 C in a thermostat, the disks were removed and discarded.”

The disks remained clear of bacterial colonies—even for weeks, although they did note that in a few cases ‘contaminated colonies’ were found, most likely due to faulty removal of the test with forceps, which caused the bacteria to be shifted into the initial sample area.

Ultimately, this type of evaluation is critical in bioprinting and the use of devices. The authors point out that ‘indiscriminate use of antifungal agents’ has led to an increase in microorganisms tolerant to drugs used today; in fact, they report that other researchers recently detected an antibacterial and antioxidant activity of a PLA nano-silver composite.

Results of this research also showed that the PLA-Ag composite would be the best choice for 3D printed products used in surgeries due to superior thermal parameters, although they also recommend PLA-HDT as having the potential for biomedical applications too.

“The bacterial test result was very surprising for us because the usual halo (‘paraselene’) around the printed sample did not appear,” stated the authors.

PLA-based sample disks in different bacterium milieu: Symbols are: bacterial beds BS, Bacillus subtilis; SA, Staphylococcus aureus; EC, Escherichia coli; PS, Pseudomonas aeruginosa; SL, Sarcina lutea. Printed samples: 1—PLA “Model” (20% CaCO3), 2—PLA, 3—PLA-Ag, 4—PLA “Gypsum” (50% CaCO3), 5—PLA-HDT. Photographs were made 5 days after the removal of disks (row a, except of PLA), 8 days of removal (row b) and at 11th day (row c).

PLA samples in SL—Sarcina lutea bed. Upper left PLA-Ag, upper right PLA-HDT and bottom PLA disks: a in 5 days, b after 10 days, c after 15 days and d after 19 days of removing the plastic disks. The two neighbor Petri-disks differ from each other only in the percentage of print completeness

The researchers continue to stress the importance of sterilization but realize now that high temperatures should not be used for disinfection. They also recommend HDT-PLA and PLAAg as ‘promising materials’ for composites in heat-based sterilization.

 “The results showed that these composites, based on their thermal characteristics, can be suitable for 3D print biomedical devices such as orthoses, casts, medical models and also surgical guides; therefore, their further examination should be important, regarding mechanical characteristics and their possible antibacterial effect,” concluded the researchers.

Bioprinting is achieved today with many different materials, from chitosan-gelatin hydrogels to nanofiber coated tubular scaffolds and more. Find out more PLA and other variations in creating biomedical devices here. What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

Heating and (spontaneous) cooling curves (inserts) for PLA base fiber: a with 10 °C min−1 and b with 40 °C min−1 heating rate. Solid lines: DTA average curves, dashed lines TG curves. Here and in all further figure too, the endotherm process is downward.

The melting (fusion) and cooling curves of PLA-HDT. In the case of 40 °C min−1 heating rate, there was no crystallization in the spontaneous cooling phase.