Artur M. Pinto

Graphene-based materials biocompatibility: A review

Graphene-based materials (GBMs) have broad potential applications in biomedical engineering and biotechnology. However, existing studies regarding biological effects of GBMs often present contradictory or inconclusive results. This work presents a review of published data in order to provide a critical overview of the state of the art. Firstly, the distinct physical-chemical nature of the GBMs available is clarified, as well as the production methods involved. The review then discusses the available in vitro (with bacterial and mammalian cells) and in vivo studies concerning evaluation of GBMs biocompatibility, as well as existing hemocompatibility studies. The biocompatibility issues concerning composite materials that incorporate GBMs are addressed in a separate section, since encapsulation in a polymer matrix modifies biological interactions. The most pertinent questions that should be addressed in future works are also emphasized.

Biocompatibility of poly(lactic acid) with incorporated graphene-based materials

The incorporation of graphene-based materials has been shown to improve mechanical properties of poly(lactic acid) (PLA). In this work, PLA films and composite PLA films incorporating two graphene-based materials - graphene oxide (GO) and graphene nanoplatelets (GNP) - were prepared and characterized regarding not only biocompatibility, but also surface topography, chemistry and wettability. The presence of both fillers changed the films surface topography, increasing the roughness, and modified the wettability - the polar component of surface free energy increased 59% with GO and decreased 56% with GNP. Mouse embryo fibroblasts incubated with both fillers exceeded the IC(50) in both cases with a concentration of 10 μg mL(-1). No variations in cell proliferation at the surface of the composite films were observed, except for those containing GO after 24 h incubation, which presented higher cell proliferation than pristine PLA films. Platelet adhesion to PLA and PLA/GNP films was lower in the presence of plasma proteins than when no proteins were present. Furthermore, incorporation of GNP into PLA reduced platelet activation in the presence of plasma proteins. The results indicated that low concentrations of GO and GNP may be incorporated safely in PLA to improve aspects relevant for biomedical applications, such as mechanical properties.

Poly(lactic acid) Composites Containing Carbon-Based Nanomaterials: A Review

Poly(lactic acid) (PLA) is a green alternative to petrochemical commodity plastics, used in packaging, agricultural products, disposable materials, textiles, and automotive composites. It is also approved by regulatory authorities for several biomedical applications. However, for some uses it is required that some of its properties be improved, namely in terms of thermo-mechanical and electrical performance. The incorporation of nanofillers is a common approach to attain this goal. The outstanding properties of carbon-based nanomaterials (CBN) have caused a surge in research works dealing with PLA/CBN composites. The available information is compiled and reviewed, focusing on PLA/CNT (carbon nanotubes) and PLA/GBM (graphene-based materials) composites. The production methods, and the effects of CBN loading on PLA properties, namely mechanical, thermal, electrical, and biological, are discussed.

Polymer surface adsorption as a strategy to improve the biocompatibility of graphene nanoplatelets.

The biointeractions of graphene-based materials depend on their physico-chemical properties. These properties can be manipulated by polymer adsorption. Graphene nanoplatelets (GNP-C) were modified with PVA, HEC, PEG, PVP, chondroitin, glucosamine, and hyaluronic acid. These materials were characterized by SEM, DLS, XPS, Raman spectroscopy, and TGA. Surface adsorption was confirmed for all polymers. Biocompatibility evaluation showed that all of these materials induced low haemolysis (<1.7%) at concentrations up to 500μgmL(-1). GNP-C-PVA and GNP-C-HEC presented the lowest haemolysis percentages and were therefore more thoroughly studied. The morphology of HFF-1 cells was investigated by microscopy (optical, fluorescence, TEM) in order to evaluate interactions with GNP materials. Small GNP-C nanoplatelets were observed to enter cells independently of the surface treatment. For pristine GNP-C at a concentration of 50μgmL(-1), ROS production increased 4.4-fold. This effect is lower for GNP-C-PVA (3.3-fold) and higher for GNP-C-HEC (5.1-fold). Resazurin assays showed that GNP-C caused toxicity in HFF-1 cells at concentrations above 20μgmL(-1) at 24h, which decreased at 48 and 72h. PVA surface adsorption rendered GNP-C non-toxic at concentrations up to 50μgmL(-1). LIVE/DEAD assays showed that at 20 and 50μgmL(-1) cell death is significantly lower for GNP-C-PVA compared to pristine GNP-C. Modification of nanoplatelets with HEC resulted in no benefit in terms of biocompatibility, whereas PVA considerably improved the biocompatibility.

Viscoplastic model analysis about the influence of graphene reinforcement in poly (lactic acid) time-dependent mechanical behaviour

Biodegradable polymers can be applied to produce automobile parts, following ecological recommendations and eco-design philosophies. In some applications, a constant or dynamic load applied to the part can further reduce its life cycle due to creep or fatigue cumulative damage. Hence, the reinforcement of these polymers with graphene may enhance the mechanical properties and change the time-dependent mechanical behaviour. In this work, experimental results are presented and discussed, that enable the comparison between pure polylactic acid (PLA) and PLA reinforced with 2 wt.% of graphene nanoplatelets (GNP). Monotonic tensile tests under different strain rates and loading-unloading cycles are used to access and compare the time-dependent mechanical behaviour of both materials. Furthermore, the material parameters of a time-dependent constitutive model, that combines hyperelastic springs and viscoplastic dashpots, were calibrated based on these experimental test results. The differences between material model parameters enable to verify the thixotropic influence of graphene.