Fused Deposition Modeling 3D Printing: Test Platforms for Evaluating Post-Fabrication Chemical Modifications and In-Vitro Biological Properties.

3D printing is attracting considerable interest for its capacity to produce prototypes and small production runs rapidly. Fused deposit modeling (FDM) was used to produce polyvalent test plates for investigation of the physical, chemical, and in-vitro biological properties of printed materials. The polyvalent test plates (PVTPs) are poly-lactic acid cylinders, 14 mm in diameter and 3 mm in height. The polymer ester backbone was surface modified by a series of ramified and linear oligoamines to increase its hydrophilicity and introduce a positive charge. The chemical modification was verified by FT-IR spectroscopy, showing the introduction of amide and amine functions, and contact angle measurements confirmed increased hydrophilicity. Morphology studies (SEM, optical microscopy) indicated that the modification of PVTP possessed a planar morphology with small pits. Positron annihilation lifetime spectroscopy demonstrated that the polymeric free volume decreased on modification. An MTT-based prolonged cytotoxicity test using Caco-2 cells showed that the PVTPs are non-toxic at the cellular level. The presence of surface oligoamines on the PVTPs reduced biofilm formation by Candida albicans SC5314 significantly. The results demonstrate that 3D printed objects may be modified at their surface by a simple amidation reaction, resulting in a reduced propensity for biofilm colonization and cellular toxicity.

Elucidating the mechanism of the considerable mechanical stiffening of DNA induced by the couple Zn2+/Calix[4]arene-1,3-O-diphosphorous acid.

The couple Calix[4]arene-1,3-O-diphosphorous acid (C4diP) and zinc ions (Zn2+) acts as a synergistic DNA binder. Silicon NanoTweezer (SNT) measurements show an increase in the mechanical stiffness of DNA bundles by a factor of >150, at Zn2+ to C4diP ratios above 8, as compared to Zinc alone whereas C4diP alone decreases the stiffness of DNA. Electroanalytical measurements using 3D printed devices demonstrate a progression of events in the assembly of C4diP on DNA promoted by zinc ions. A mechanism at the molecular level can be deduced in which C4diP initially coordinates to DNA by phosphate-phosphate hydrogen bonds or in the presence of Zn2+ by Zn2+ bridging coordination of the phosphate groups. Then, at high ratios of Zn2+ to C4diP, interdigitated dimerization of C4diP is followed by cross coordination of DNA strands through Zn2+/C4diP inter-strand interaction. The sum of these interactions leads to strong stiffening of the DNA bundles and increased inter-strand binding.

Chemical growth and photochromism of silver nanoparticles into a mesoporous titania template.

Elaboration of mesoporous titanium oxide film supporting silver nanoparticles is described. Mesoporous titanium oxide films are characterized by TEM analysis. Titania films are infiltrated with a silver salt solution and chemical reduction treatments are performed using either a NaBH(4) or a formaldehyde solution. Infiltrated films are then characterized by TEM, SEM, AFM, UV-visible spectroscopy, X-ray diffraction, and Rutherford Backscattering Spectrometry (RBS). The utilization of a mesoporous titania substrate allows to control the nanoparticle size and the interparticle distance. RBS experiments provide the evidence that NaBH(4) treatment induces a strong accumulation of silver nanoparticles in the subsurface of the layer, while formaldehyde treatment induces the formation of silver nanoparticles embedded into almost the whole depth of the titania film. Large silver nanocrystals are also formed at the film surface whatever the reducer used. A broad visible absorption band related to the surface plasmon resonance (SPR) is obtained in both cases and is strongly red-shifted compared to the SPR obtained for silver nanoparticles inside a silica matrix. Moreover, irradiation with visible light causes the photooxidation of silver nanoparticles by titania and a complete discoloration of the material. The photooxidation is related to a drastic decrease in the silver nanoparticle size and is found to be reversible, particularly in the case of the material obtained by the formaldehyde reduction.