Joey Dacula Mangadlao

Graphene nanocomposite for biomedical applications: fabrication, antimicrobial and cytotoxic investigations

Materials possessing excellent bacterial toxicity, while presenting low cytotoxicity to human cells, are strong candidates for biomaterials applications. In this study, we present the fabrication of a nanocomposite containing poly(N-vinylcarbazole) (PVK) and graphene (G) in solutions and thin films. Highly dispersed PVK-G (97-3 w/w%) solutions in various organic and aqueous solvents were prepared by solution mixing and sonication methods. The thermal properties and morphology of the new composite were analyzed using thermal gravimetry analysis (TGA) and atomic force microscopy (AFM), respectively. PVK-G films were immobilized onto indium tin oxide (ITO) substrates via electrodeposition. AFM was used to characterize the resulting topography of the nanocomposite thin films, while cyclic voltammetry and UV-vis were used to monitor their successful electrodeposition. The antimicrobial properties of the electrodeposited PVK-G films and solution-based PVK-G were investigated against Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis). Microbial growth after exposure to the nanocomposite, metabolic assay and live-dead assay of the bacterial solutions exposed to PVK-G presented fewer viable and active bacteria than those exposed to pure PVK or pure graphene solutions. The PVK-G film inhibited about 80% of biofilm surface coverage whereas the PVK- and G-modified surfaces allowed biofilm formation over almost the whole coated surface (i.e. > 80%). The biocompatibility of the prepared PVK-G solutions on NIH 3T3 cells was evaluated using the MTS cell proliferation assay. A 24 h exposure of the PVK-G nanocomposite to the NIH 3T3 cells presented ~80% cell survival.

3D Printing Biocompatible Polyurethane/Poly(lactic acid)/Graphene Oxide Nanocomposites: Anisotropic Properties

Blending thermoplastic polyurethane (TPU) with poly(lactic acid) (PLA) is a proven method to achieve a much more mechanically robust material, whereas the addition of graphene oxide (GO) is increasingly applied in polymer nanocomposites to tailor further their properties. On the other hand, additive manufacturing has high flexibility of structure design which can significantly expand the application of materials in many fields. This study demonstrates the fused deposition modeling (FDM) 3D printing of TPU/PLA/GO nanocomposites and its potential application as biocompatible materials. Nanocomposites are prepared by solvent-based mixing process and extruded into filaments for FDM printing. The addition of GO largely enhanced the mechanical property and thermal stability of the nanocomposites. Interestingly, we found that the mechanical response is highly dependent on printing orientation. Furthermore, the 3D printed nanocomposites exhibit good biocompatibility with NIH3T3 cells, indicating promise as biomaterials scaffold for tissue engineering applications.

Antimicrobial PVK:SWNT nanocomposite coated membrane for water purification: Performance and toxicity testing

This study demonstrated that coated nitrocellulose membranes with a nanocomposite containing 97% (wt%) of polyvinyl-N-carbazole (PVK) and 3% (wt%) of single-walled carbon nanotubes (SWNTs) (97:3 wt% ratio PVK:SWNT) achieve similar or improved removal of bacteria when compared with 100% SWNTs coated membranes. Membranes coated with the nanocomposite exhibited significant antimicrobial activity toward Gram-positive and Gram-negative bacteria (≈ 80-90%); and presented a virus removal efficiency of ≈ 2.5 logs. Bacterial cell membrane damage was considered a possible mechanism of cellular inactivation since higher efflux of intracellular material (Deoxyribonucleic acid, DNA) was quantified in the filtrate of PVK-SWNT and SWNT membranes than in the filtrate of control membranes. To evaluate possible application of these membrane filters for drinking water treatment, toxicity of PVK-SWNT was tested against fibroblast cells. The results demonstrated that PVK-SWNT was non toxic to fibroblast cells as opposed to pure SWNT (100%). These results suggest that it is possible to synthesize antimicrobial nitrocellulose membranes coated with SWNT based nanocomposites for drinking water treatment. Furthermore, membrane filters coated with the nanocomposite PVK-SWNT (97:3 wt% ratio PVK:SWNT) will produce more suitable coated membranes for drinking water than pure SWNTs coated membranes (100%), since the reduced load of SWNT in the nanocomposite will reduce the use of costly and toxic SWNT nanomaterial on the membranes.

Stimuli-Responsive Polymers and their Potential Applications in Oil-Gas Industry

Polymers with properties well-controlled by minor environmental variations have been widely utilized in nanoscience, nanotechnology, and nanomedicine. Herein, the classification of stimuli-responsive polymers will be discussed and related to some possible applications in the oil-gas industry. Current studies of stimuli-responsive polymers in the oil-gas production are mainly focused on enhanced oil recovery (EOR) processes. Still, their potential applications in various aspects of the oil-gas industry from upstream, midstream, and downstream processes are found to be promising.

A trefoil knotted polymer produced through ring expansion

A synthetic strategy is reported for the production of a trefoil knotted polymer from a copper(I)-templated helical knot precursor through ring expansion. The expected changes in the properties of the knotted polymer compared to a linear analogue, for example, reduced hydrodynamic radius and lower intrinsic viscosity, together with an atomic force microscopy (AFM) image of individual molecular knots, confirmed the formation of the resulting trefoil knotted polymer. The strategies employed here could be utilized to enrich the variety of available polymers with new architectures.

High-Strength Stereolithographic 3D Printed Nanocomposites: Graphene Oxide Metastability

The weak thermomechanical properties of commercial 3D printing plastics have limited the technologys application mainly to rapid prototyping. In this report, we demonstrate a simple approach that takes advantage of the metastable, temperature-dependent structure of graphene oxide (GO) to enhance the mechanical properties of conventional 3D-printed resins produced by stereolithography (SLA). A commercially available SLA resin was reinforced with minimal amounts of GO nanofillers and thermally annealed at 50 and 100 °C for 12 h. Tensile tests revealed increasing strength and modulus at an annealing temperature of 100 °C, with the highest tensile strength increase recorded at 673.6% (for 1 wt % GO). Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) also showed increasing thermal stability with increasing annealing temperature. The drastic enhancement in mechanical properties, which is seen to this degree in 3D-printed samples reported in literature, is attributed to the metastable structure of GO, polymer-nanofiller cross-linking via acid-catalyzed esterification, and removal of intercalated water, thus improving filler-matrix interaction as evidenced by spectroscopy and microscopy analyses.

Electropolymerized and polymer grafted superhydrophobic, superoleophilic, and hemi-wicking coatings

A novel one step approach to fabricate superhydrophobic and superoleophilic electrodeposited coatings is reported. By performing additional surface-initiated atom transfer radical polymerization (SI-ATRP) from the coating, a further change in wettability of the substrates to a variety of liquids was observed.

Grafted Carbazole-Assisted Electrodeposition of Graphene Oxide

The electrodeposition of graphene oxide (GO) by covalently linked electroactive monomer, carbazole (Cbz) is first demonstrated herein. This is based on the electropolymerization and electrodeposition of covalently linked Cbz units when a potential is applied. During the electrochemical process, the Cbz groups electropolymerize and carry the GO nanosheets as it electrodeposits on the substrate. Moreover, the GO-Cbz sheets selectively deposit onto the conducting regions of the substrate, which demonstrates its promise for the fabrication of electropatterned graphene-based devices. In addition, GO-Cbz is a promising material for the fabrication of nanocomposite coatings for anticorrosion application. In as little as 1 wt % GO-Cbz loading, a protection efficiency as high as 95.4% was achieved.

Catenated PS-PMMA block copolymers via supramolecularly templated ATRP initiator approach.

A novel route to synthesize catenated macrocyclic PS-PMMA block copolymers is demonstrated via combination of supramolecular chemistry and controlled radical polymerization (CRP). Polymerization of styrene with bromopropionate ester initiator coupled with phenanthroline Cu(I) complex affords a four arm PS macroinitiator, which upon further chain extension by polymerization of MMA generates a four arm PS-PMMA block copolymer. Intramolecular coupling of PS-PMMA-Br arms via low temperature styrene-assisted atom transfer radical coupling (ATRC) leads to the formation of PS-PMMA catenand, which generates the metal-free catenated macrocyclic PS-PMMA block copolymer after removal of Cu metal. The interlocked structures of catenated block copolymers are confirmed by GPC, NMR, and AFM image analysis.

3D Printing of Photocurable Cellulose Nanocrystal Composite for Fabrication of Complex Architectures via Stereolithography

The advantages of 3D printing on cost, speed, accuracy, and flexibility have attracted several new applications in various industries especially in the field of medicine where customized solutions are highly demanded. Although this modern fabrication technique offers several benefits, it also poses critical challenges in materials development suitable for industry use. Proliferation of polymers in biomedical application has been severely limited by their inherently weak mechanical properties despite their other excellent attributes. Earlier works on 3D printing of polymers focus mainly on biocompatibility and cellular viability and lack a close attention to produce robust specimens. Prized for superior mechanical strength and inherent stiffness, cellulose nanocrystal (CNC) from abaca plant is incorporated to provide the necessary toughness for 3D printable biopolymer. Hence, this work demonstrates 3D printing of CNC-filled biomaterial with significant improvement in mechanical and surface properties. These findings may potentially pave the way for an alternative option in providing innovative and cost-effective patient-specific solutions to various fields in medical industry. To the best of our knowledge, this work presents the first successful demonstration of 3D printing of CNC nanocomposite hydrogel via stereolithography (SL) forming a complex architecture with enhanced material properties potentially suited for tissue engineering.