Three-dimensional (3D) printing is a new fabrication method for tissue engineering. The significant advantage of this new scaffold fabrication method is that it can precisely control scaffold architectures, which are printed from computer-assisted software. However, a scaffold is only a small biomimic unit of integral bone tissue. It not only needs three-dimensional biocompatible structures, but it should also mimic extracellular matrix (ECM) properties, such as providing a template for cell attachment, and stimulate bone tissue formation in vitro . In order to achieve the second target, we introduce cold atmospheric plasma (CAP) to modify scaffold surface roughness and chemical composition . Cold atmospheric plasma is an ionized gas, which was helium in this study. The composition of cold plasma includes various electrons, positive/negative ions, radicals, excited molecules, energetic photons, and ultraviolet (UV) wavelengths. Based on those compositions, plasma treatment has been developed for the effective surface modification of tissue engineering scaffold surfaces . In studying CAP treated 3D printing scaffolds, we showed that CAP surface modification can change topography. The treatment also alters the chemistry of the surface, which can significantly influence stem attachment and differentiation.
Poly lactic acid (PLA) (Natureworks, LLC, MN) was fabricated by a 3D Makerbot printer (Makerbot, NY). After it was printed, scaffolds were directly treated for further surface modification by cold atmospheric plasma (CAP) for 1, 3, and 5 minutes. The contact angles of deionized water on control and surface modified PLA scaffolds were measured in the static mode using a Tame-hart mode 300 contract angle goniometer. Average surface roughness values were obtained by atomic force microscopy (AFM) using a Parks Systems NX-10 microscope and XEI software.
RESULTS AND DISSCUSSIONS
Under the optimized cold plasma condition, the contact angle dramatically dropped after cold plasma treated, which indicated that cold plasma treated PLA scaffolds were more hydrophilic than untreated PLA scaffolds. The contact angle on untreated PLA scaffolds treated for 1, 3 and 5 min was 70±2°, 50±2°41±2°, 24±2°, respectively. The effects of CAP treatment on the topography of the PLA scaffolds can be summarized as the roughness was controlled by exposure time. The roughness (Rq) values for the untreated scaffold and CAP scaffolds treated for 1, 3, and 5 min were 1.168 nm, 10.45 nm, 22.87 nm, and 27.60 nm, respectively. After CAP treatment, the surface had much more roughness even when exposed for 1 min. This means the nanometric roughness had a maximum 300 % increase, which is consistent with SEM results. Both hydrophilicity and nanoscale roughness changes represented a very efficient plasma treatment. Those surface changes also played a very important role in cell attachment and bone formation which will also be presented.
In this study, CAP treatment is introduced as a new technology for altering scaffold surface chemistry and nanoscale topography. Contact angle and AFM results demonstrated that 3D printed PLA scaffolds after CAP treated were more hydrophilic with more roughness. The above surface property modification led to an enhancement in cell attachment and bone formation. Those promising results suggest that CAP surface modification may have potential applications in bone tissue engineering.
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This study was supported by the Northeastern University. Dr. Hilal Yazici is supported by TÜBİTAK (The Scientific and Technological Research Council of Turkey) – BİDEB (Programme Number: 2219).