Antibacterial Properties & Cytocompatibility of EPL in 3D Printed Composite Scaffolds

Chinese researchers continue to study 3D printing materials and structures, releasing their findings in the recently published ‘Study on antibacterial properties and cytocompatibility of EPL coated 3D printed PCL/HA composite scaffolds.’

The study of biocompatible materials and scaffolds suitable for sustaining cells is of enormous interest to researchers around the world as they hope to move forward in tissue engineering—and of course eventually reaching the ultimate goal of 3D printing human organs and one day eliminating waiting lists for transplants. Today, bioprinting has offered strides in creating innovative microenvironments, seeding cells like human dermal fibroblasts, and even fabricating heart tissue in space.

Bone regeneration continues to be an area of challenge overall, but progress is being made with tissue engineering.

“Bone tissue engineering provides a new route for the therapy of bone defects. The scaffolds for bone tissue engineering must have pores interconnected in three dimensions, with highly regular pore formation and structure. The porous structure provides space for cell migration, adhesion, and the ingrowth of new bone tissue. Scaffolds for bone tissue engineering should have reasonable strength and bioactivity, without causing any adverse effects,” explained the researchers.

SEM images: PCL scaffold at 300 μm (a), PCL scaffold at 5 μm (b), PCL/HA scaffold at 300 μm (c), PCL/HA scaffold at 5 μm (d), EPL/PCL/HA scaffold at 300 μm (e), EPL/PCL/HA scaffold at 5 μm (f).

In attempting to create an aseptic environment, the researchers used ε-poly-L-lysine (EPL), an antimicrobic cationic polypeptide for modifying the surfaces of polycaprolactone/hydroxyapatite (PCL/HA) scaffolds. EPL, offering a “wide antimicrobial spectrum,” is already popular for use in food applications, as well as electronics, agriculture, and more; to date, it has not been used with 3D printed PCL/HA scaffolds.

“Microorganisms such as bacteria and fungi do not easily develop resistance to this polypeptide,” stated the researchers.

The mission in this study was to use FDM 3D printing to fabricate scaffolds and then analyze the properties of the ε-poly-lysine/polycaprolactone/hydroxyapatite. The team also examined both biocompatibility and osteoconductivity of the scaffolds.

Antibacterial activity was examined with the ‘zone of inhibition test,’ using the following:

• aureus(Gram-positive bacteria)
• coli(Gram-negative bacteria)
• mutans(oral facultative anaerobic bacteria)

Upon magnifying the scaffolds, the researchers noted that pore sizes were ‘within range’ for suitable bone regeneration—leading to the conclusion that the scaffolds would be able to support the ‘formation and growth of bone.’ Further examination showed that EPL was present in scaffolds and its chemical properties did not change. EPL was found to offer great potential and versatility for improving the scaffolds in the initial stages of bone formation.

Antimicrobial effect of scaffolds on S. aureus (A), E. coli (B) and S. mutans (C); bacteria cultures after 24 hours: PCL scaffolds (Aa, Ba and Ca), PCL/HA scaffolds (Ab, Bb and Cb), EPL/PCL/HA scaffolds (Ac, Bc and Cc); subsequent culture for 3 days: PCL scaffolds (Ad, Bd and Cd), PCL/HA scaffolds (Ae, Be and Ce), EPL/PCL/HA scaffolds (Af, Bf and Cf).

“The created scaffolds were found to be cytocompatible as well as capable of osteogenic differentiation and antimicrobial activity in vitro, which is beneficial not only to bone regeneration, but to reduce or prevent the incidence of the infective complications in reparative bone formation,” concluded the researchers. “Further investigations are needed to determine if the present scaffolds can support functional tissue regeneration in vivo.”

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(A) Stress strain curves of PCL and PCL/HA scaffolds. (B) Compressive modulus of PCL and PCL/HA scaffolds. The data were represented as mean ± standard deviation (SD; n = 5; *p < 0.05).