'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.

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.

PGS/HAp Microporous Composite Scaffold Obtained in the TIPS-TCL-SL Method: An Innovation for Bone Tissue Engineering.

In this research, we synthesize and characterize poly(glycerol sebacate) pre-polymer (pPGS) (1H NMR, FTiR, GPC, and TGA). Nano-hydroxyapatite (HAp) is synthesized using the wet precipitation method. Next, the materials are used to prepare a PGS-based composite with a 25 wt.% addition of HAp. Microporous composites are formed by means of thermally induced phase separation (TIPS) followed by thermal cross-linking (TCL) and salt leaching (SL). The manufactured microporous materials (PGS and PGS/HAp) are then subjected to imaging by means of SEM and µCT for the porous structure characterization. DSC, TGA, and water contact angle measurements are used for further evaluation of the materials. To assess the cytocompatibility and biological potential of PGS-based composites, preosteoblasts and differentiated hFOB 1.19 osteoblasts are employed as in vitro models. Apart from the cytocompatibility, the scaffolds supported cell adhesion and were readily populated by the hFOB1.19 preosteoblasts. HAp-facilitated scaffolds displayed osteoconductive properties, supporting the terminal differentiation of osteoblasts as indicated by the production of alkaline phosphatase, osteocalcin and osteopontin. Notably, the PGS/HAp scaffolds induced the production of significant amounts of osteoclastogenic cytokines: IL-1ß, IL-6 and TNF-α, which induced scaffold remodeling and promoted the reconstruction of bone tissue. Initial biocompatibility tests showed no signs of adverse effects of PGS-based scaffolds toward adult BALB/c mice.

The Effect of Pore Size Distribution and l-Lysine Modified Apatite Whiskers (HAP) on Osteoblasts Response in PLLA/HAP Foam Scaffolds Obtained in the Thermally Induced Phase Separation Process.

In this research, we prepared foam scaffolds based on poly(l-lactide) (PLLA) and apatite whiskers (HAP) using thermally induced phase separation technique supported by the salt leaching process (TIPS-SL). Using sodium chloride having a size of (a) 150-315 µm, (b) 315-400 µm, and (c) 500-600 µm, three types of foams with different pore sizes have been obtained. Internal structure of the obtained materials has been investigated using SEM as well as µCT. The materials have been studied by means of porosity, density, and compression tests. As the most promising, the composite prepared with salt size of 500-600 µm was prepared also with the l-lysine modified apatite. The osteoblast hFOB 1.19 cell response for the scaffolds was also investigated by means of cell viability, proliferation, adhesion/penetration, and biomineralization. Direct contact cytotoxicity assay showed the cytocompatibility of the scaffolds. All types of foam scaffolds containing HAP whiskers, regardless the pore size or l-lysine modification induced significant stimulatory effect on the cal-cium deposits formation in osteoblasts. The PLLA/HAP scaffolds modified with l-lysine stimulated hFOB 1.19 osteoblasts proliferation. Compared to the scaffolds with smaller pores (150-315 µm and 315-400 µm), the PLLA/HAP foams with large pores (500-600 µm) promoted more effective ad-hesion of osteoblasts to the surface of the biomaterial.