Cytotoxicity Study of UV-Laser-Irradiated PLLA Surfaces Subjected to Bio-Ceramisation: A New Way towards Implant Surface Modification.

In this research we subjected samples of poly(L-lactide) (PLLA) extruded film to ultraviolet (193 nm ArF excimer laser) radiation below the ablation threshold. The modified film was immersed in Simulated Body Fluid (SBF) at 37 °C for 1 day or 7 days to obtain a layer of apatite ceramic (CaP) coating on the modified PLLA surface. The samples were characterized by means of optical profilometry, which indicated an increase in average roughness (Ra) from 25 nm for the unmodified PLLA to over 580 nm for irradiated PLLA incubated in SBF for 1 day. At the same time, the water contact angle decreased from 78° for neat PLLA to 35° for irradiated PLLA incubated in SBF, which suggests its higher hydrophilicity. The obtained materials were investigated by means of cell response fibroblasts (3T3) and macrophage-like cells (RAW 264.7). Properties of the obtained composites were compared to the unmodified PLLA film as well as to the UV-laser irradiated PLLA. The activation of the PLLA surface by laser irradiation led to a distinct increase in cytotoxicity, while the treatment with SBF and the deposition of apatite ceramic had only a limited preventive effect on this harmful impact and depended on the cell type. Fibroblasts were found to have good tolerance for the irradiated and ceramic-covered PLLA, but macrophages seem to interact with the substrate leading to the release of cytotoxic products.

Classification of Copper Minerals by Handheld Laser-Induced Breakdown Spectroscopy and Nonnegative Tensor Factorisation.

Laser-induced breakdown spectroscopy (LIBS) analysers are becoming increasingly common for material classification purposes. However, to achieve good classification accuracy, mostly noncompact units are used based on their stability and reproducibility. In addition, computational algorithms that require significant hardware resources are commonly applied. For performing measurement campaigns in hard-to-access environments, such as mining sites, there is a need for compact, portable, or even handheld devices capable of reaching high measurement accuracy. The optics and hardware of small (i.e., handheld) devices are limited by space and power consumption and require a compromise of the achievable spectral quality. As long as the size of such a device is a major constraint, the software is the primary field for improvement. In this study, we propose a novel combination of handheld LIBS with non-negative tensor factorisation to investigate its classification capabilities of copper minerals. The proposed approach is based on the extraction of source spectra for each mineral (with the use of tensor methods) and their labelling based on the percentage contribution within the dataset. These latent spectra are then used in a regression model for validation purposes. The application of such an approach leads to an increase in the classification score by approximately 5% compared to that obtained using commonly used classifiers such as support vector machines, linear discriminant analysis, and the k-nearest neighbours algorithm.

Influence of Hydroxyapatite Surface Functionalization on Thermal and Biological Properties of Poly(l-Lactide)- and Poly(l-Lactide-co-Glycolide)-Based Composites.

Novel biocomposites of poly(L-lactide) (PLLA) and poly(l-lactide-co-glycolide) (PLLGA) with 10 wt.% of surface-modified hydroxyapatite particles, designed for applications in bone tissue engineering, are presented in this paper. The surface of hydroxyapatite (HAP) was modified with polyethylene glycol by using l-lysine as a linker molecule. The modification strategy fulfilled two important goals: improvement of the adhesion between the HAP surface and PLLA and PLLGA matrices, and enhancement of the osteological bioactivity of the composites. The surface modifications of HAP were confirmed by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), TGA, and elemental composition analysis. The influence of hydroxyapatite surface functionalization on the thermal and in vitro biological properties of PLLA- and PLLGA-based composites was investigated. Due to HAP modification with polyethylene glycol, the glass transition temperature of PLLA was reduced by about 24.5 °C, and melt and cold crystallization abilities were significantly improved. These achievements were scored based on respective shifting of onset of melt and cold crystallization temperatures and 1.6 times higher melt crystallization enthalpy compared with neat PLLA. The results showed that the surface-modified HAP particles were multifunctional and can act as nucleating agents, plasticizers, and bioactive moieties. Moreover, due to the presented surface modification of HAP, the crystallinity degree of PLLA and PLLGA and the polymorphic form of PLLA, the most important factors affecting mechanical properties and degradation behaviors, can be controlled.

'Cookies on a tray': Superselective hierarchical microstructured poly(l-lactide) surface as a decoy for cells.

In this research we developed a micro-sized hierarchical structures on a poly(l-lactide) (PLLA) surface. The obtained structures consist of round-shaped protrusions with a diameter of ~20 µm, a height of ~3 µm, and the distance between them ~30 µm. We explored the effect of structuring PLLA to design a non-cytotoxic material with increased roughness to encourage cells to settle on the surface. The PLLA films were prepared using the casting melt extrusion technique and were modified using ultra-short pulse irradiation - a femtosecond laser operating at λ = 1030 nm. A hierarchical microstructure was obtained resembling 'cookies on a tray'. The cellular response of fibro- and osteoblasts cell lines was investigated. The conducted research has shown that the laser-modified surface is more conducive to cell adhesion and growth (compared to unmodified surface) to such an extent that allows the formation of highly-selectively patterns consisting of living cells. In contrast to eukaryotic cells, the pathogenic bacteria Staphylococcus aureus covered modified and unmodified structures in an even, non-preferential manner. In turn, adhesion pattern of eukaryotic fungus Saccharomyces boulardii resembled that of fibro- and osteoblast cells rather than that of Staphylococcus. The discovered effect can be used for fabrication of personalized and smart implants in regenerative medicine.

Controlling the 1 µm spontaneous emission in Er/Yb co-doped fiber amplifiers.

In this paper we present our experimental studies on controlling the amplified spontaneous emission (ASE) from Yb(3+) ions in Er/Yb co-doped fiber amplifiers. We propose a new method of controlling the Yb-ASE by stimulating a laser emission at 1064 nm in the amplifier, by providing a positive 1 µm signal feedback loop. The results are discussed and compared to a conventional amplifier setup without 1 µm ASE control and to an amplifier with auxiliary 1064 nm seeding. We have shown, that applying a 1064 nm signal loop in an Er/Yb amplifier can increase the output power at 1550 nm and provide stable operation without parasitic lasing at 1 µm.

Influence of Thermal Annealing on the Sinterability of Different Grades of Polylactide Microspheres Dedicated for Laser Sintering.

We present a comparison of the influence of the conditioning temperature of microspheres made of medical grade poly(L-lactide) (PLLA) and polylactide with 4 wt % of D-lactide content (PLA) on the thermal and structural properties. The microspheres were fabricated using the solid-in-oil-in-water method for applications in additive manufacturing. The microspheres were annealed below the glass transition temperature (Tg), above Tg but below the onset of cold crystallization, and at two temperatures selected from the range of cold crystallization corresponding to the crystallization of the α' and α form of poly(L-lactide), i.e., at 40, 70, 90, and 120 °C, in order to verify the influence of the conditioning temperature on the sinterability of the microspheres set as the sintering window (SW). Based on differential scanning calorimetry measurements, the SWs of the microspheres were evaluated with consideration of the existence of cold crystallization and reorganization of crystal polymorphs. The results indicated that the conditioning temperature influenced the availability and range of the SWs depending on the D-lactide presence. We postulate the need for an individual approach for polylactide powders in determining the SW as a temperature range free of any thermal events. We also characterized other core powder characteristics, such as the residual solvent content, morphology, particle size distribution, powder flowability, and thermal conductivity, as key properties for successful laser sintering. The microspheres were close to spheres, and the size of the microspheres was below 100 µm. The residual solvent content decreased with the increase of the annealing temperature. The thermal conductivities were 0.073 and 0.064 W/mK for PLA and PLLA microspheres, respectively, and this depended on the spherical shape of the microspheres. The wide angle X-ray diffraction (WAXD) studies proved that an increase in the conditioning temperature caused a slight increase in the crystallinity degree for PLLA microspheres and a clear increase in crystallization for the PLA microspheres.

Laser Texturing as a Way of Influencing the Micromechanical and Biological Properties of the Poly(L-Lactide) Surface.

Laser-based technologies are extensively used for polymer surface patterning and/or texturing. Different micro- and nanostructures can be obtained thanks to a wide range of laser types and beam parameters. Cell behavior on various types of materials is an extensively investigated phenomenon in biomedical applications. Polymer topography such as height, diameter, and spacing of the patterning will cause different cell responses, which can also vary depending on the utilized cell types. Structurization can highly improve the biological performance of the material without any need for chemical modification. The aim of the study was to evaluate the effect of CO2 laser irradiation of poly(L-lactide) (PLLA) thin films on the surface microhardness, roughness, wettability, and cytocompatibility. The conducted testing showed that CO2 laser texturing of PLLA provides the ability to adjust the structural and physical properties of the PLLA surface to the requirements of the cells despite significant changes in the mechanical properties of the laser-treated surface polymer.

Laser-modified PLGA for implants: in vitro degradation and mechanical properties.

PURPOSE: Irradiations by CO2 laser poly(lactic-co-glycolic acid) surface lead to alterations of physicochemical properties of a copolymer. Effects of PLGA irradiations are results of photochemical and photothermal processes leading to polymer degradation. The scale of the degradation depends on the inducted surface modification. Hence the main goal of presented studies was to define the influence of CO2 laser irradiation with different process parameters, inducing three cases of surface modification, on mechanical properties and topography of PLGA during degradation in the aqueous environment. METHODS: Hydrolytic degradation were performed in distilled (demineralized) water. Mechanical properties were conducted in accordance with the PN-EN ISO 527-3:1998 standard. pH of incubating solution, specimens' topography, mass and geometrical dimensions were controlled during process. RESULTS: During the hydrolytic degradation, gradual changes in failure mode were observed from ductile failure characteristic for untreated PLGA to brittle failure of incubated PLGA regardless of the case of triggered modification. Tensile strength decreased with degradation time regardless of the case of surface modification with insignificant fluctuation in means Young's moduli. pH for each case decreased and topography od specimens become smoother with incubation time. CONCLUSIONS: PLGA surface modification by CO2 laser below the ablation threshold (P1) and at the ablation threshold (P2) leaded to surface functionalization, however, irradiation above the ablation threshold (P3) caused marked degradation of PLGA and accelerated specimens disintegration during incubation in the aquatic environment.

Diverse nature of femtosecond laser ablation of poly(L-lactide) and the influence of filamentation on the polymer crystallization behaviour.

Over the past few years we have witnessed growing interest in ultrafast laser micromachining of bioresorbable polymers for fabrication of medical implants and surface modification. In this paper we show that surface structuring of poly(L-lactide) with 300 fs laser pulses at 515 and 1030 nm wavelength leads to formation of defects inside the polymer as a result of laser beam filamentation. Filament-induced channels have diameter around 1 µm and length of hundreds of micrometers. SEM images of microchannels cross-sections are presented. The influence of wavelength and pulse spacing on bulk modification extent was investigated and parameters limiting filamentation were determined. We show that filamentation can be used for controlling properties of PLLA. The presence of filament-induced modifications such as empty microchannels and pressure wave-induced stress lead to increased ability of polymer to crystallize at lower temperature. Crystallization behaviour and crystal morphology after laser treatment was investigated in details using different analytical techniques such as WAXD, DSC and FTIR/ATR. Hydrolytic degradation experiment was performed. Presented method can be applied for controllable, spatially distributed modification of polymer crystallinity, crystalline phase structure and hydrolytic degradation profile.