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Diamond-like carbon (DLC) films have been extensively applied as a solid lubricant and as a protective coating due to their attractive chemical, mechanical, and tribological properties. Furthermore, these properties of DLC coatings can be improved with the incorporation of nanoparticles of different materials, especially diamond nanoparticles (DNPs). Herein, the incorporation of chemical vapor deposition (CVD) DNPs was done from a deionized aqueous colloidal solution by using a controlled pulsed valve, which is an innovative aspect of this work. The CVD DNPs were pulverized into the plasma region and incorporated in the DLC films bulk with controllable size particle distribution and density. In addition, an enhanced process to obtain DNPs with suitable size distribution was established by using a high energy ball milling technique, centrifugation, and a special chemical cleaning process. The DLC films were deposited on a metallic substrate via a modified, pulsed DC plasma-enhanced chemical vapor deposition (PECVD) technique, with an additional cathode. X-ray diffractometry (XRD) and scanning electronic microscopy (SEM) techniques showed that an aqueous colloidal solution of high-purity DNPs with a mean diameter of 32 nm was obtained. Dynamic light scattering (DLS) results showed that it is possible to control particle size distribution by varying the milling and centrifugation time lengths. Therefore, a valuable result was that DLC films could be deposited with DNPs by using clean water without affecting deposition rate, the adhesion between the DLC films and substrates, the structural quality of the film, and keeping lower coefficient of friction.

Despite the potential antimicrobial activity of metallic nanoparticles, the increasing concerns about nanosafety have been holding back the use of these materials in therapeutics and biomedical devices. In the last years, several studies called attention to metallic nanoparticles toxicity. In the most part of in vitro studies performed with mammalian cells, metallic NPs reduced cell viability and induced genotoxicity and inflammatory responses. Bimetallic NPs have attracted great attention because they present distinct and even more advanced characteristics when compared to nanoparticles formed by a single metal. Recently, bimetallic NPs have emerged as an alternative to improve the antimicrobial activity of metallic nanoparticles, aiming at the broadening of the action spectrum and the reduction of the toxicity. However, the biocompatibility of bimetallic nanoparticles has been demonstrated only by in vitro studies. In the present work, the toxicity of AuPt nanoparticles was addressed both in vitro and in vivo. In addition, the antimicrobial activity of AuPt bimetallic nanoparticles has been evaluated in comparison with Au and Ag nanoparticles. The nanoparticles were characterized by ultraviolet-visible spectroscopy, dynamic light scattering, transmission electron microscopy, inductively coupled plasma optical emission spectroscopy, and X-ray diffraction. The antimicrobial activity was studied against Candida albicans, Pseudomonas aeruginosa, and Staphylococcus aureus. The toxicity of nanoparticles was evaluated in vitro by analyzing their toxicity against human fibroblast cells (HS68 cell line) and in vivo by embryonic toxicity test in zebrafish (Danio rerio). The results confirmed the intrinsic antimicrobial activity of the three types of nanoparticles but different toxicity. Bimetallic nanoparticles showed enhanced antimicrobial activity in comparison with Au nanoparticles but lower antimicrobial activity compared with Ag nanoparticles. However, AuPt nanoparticles showed great advantage over Ag nanoparticles due to the absence of cytotoxicity and lower toxicity in vivo.

The high hydrophilicity of cellulose nanocrystals (CNC) may result in poor dispersion in some matrices and solvents. So in this work, two different methodologies were used to reduce the hydrophilicity of CNC. In the first methodology, CNC were acetylated (CNC-Ac) in a mixture of acetic and hydrochloric acid, and in the second methodology, polyethylene glycol (PEG) was adsorbed onto CNC surface (CNC-PEG) under stirring in aqueous solution. CNC obtained by both methods were characterized by transmission electron microscopy (TEM), infrared spectroscopy (FTIR), X-ray diffraction (XRD), dynamic light scattering (DLS), zeta potential, and thermogravimetric analysis (TGA). Images of TEM showed that the intrinsic morphology of cellulose was preserved after both treatments. FTIR confirmed acetylation reaction by the presence of a new band at 1732 cm−1 (acetate groups) and the consumption of OH groups. XRD showed a reduction in the crystallinity index for both applied methodologies. DLS showed reduced stability in water for CNC-Ac and CNC-PEG. Values of zeta potential changed after acetylation, from − 45 mV (CNC) to − 1 mV (CNC-Ac), and after adsorption of PEG, to − 26.7 mV (CNC-PEG). TGA showed a reduction in the thermal stability after both treatments and a change in the main degradation behavior for CNC-PEG. MTT assays showed that both proposed functionalizations induce cell proliferation, being even more evident for acetylation because, in addition to viability increase with time, it increased with the sample concentration.