## 4 Discussion  
In the last decade, femtosecond laser processing of biodegradable polymers for application in tissue engineering has been intensively studied by many research groups [54; 55; 56; 57; 58; 59; 60; 61]. However, things stand totally different regarding the treatment of bioceramics with ultra-short laser pulses for medical use, as the research is not as extensive [62; 63; 64; 65; 60; 61; 61; 60; 62; 63; 61; 64; 65]. The works of [PERSON], [PERSON], and [PERSON] [65; 66; 67; 68] clearly outline that \(\beta\)-TCP is one of the most investigated forms of calcium phosphates to be used in bone tissue regeneration. The group of [PERSON] et al. [69] describes bioreactor chambers filled with bioceramic granules of \(\beta\)-TCP and HA and implanted against the ribs in a large-animal model, leading to the generation of a mineralized tissue comparable to bone autografts, while [PERSON] et al. [70] evaluate the osteoconduction of this ceramic in the calvaria of rats. The ultra-fast laser surface modification method via a selection of different wavelengths and fluence modes of ceramic samples proposed in this paper is a novel approach for micropatterning of the \(\beta\)-TCP pellets' surface, as it produces a negligible amount of damage, due to the absence of thermal side effects [71; 72]. After precise tuning of laser parameters (N and F), gentle surface patterning of the \(\beta\)-TCP samples was achieved and cracks, material ejection, and transition to an \(\alpha\)-TCP form of the material were avoided. As a general tendency, from this first attempt of biological study, as well as the comparison of cellular spread on the polished \(\beta\)-TCP sample surface and laser-treated areas, it can be summarized that cellular expansion is more visible on the processed surfaces only in specific laser treatment regimes for both applied laser-patterning methods. It can be interpreted as a tendency that the adhesion points provided by the groove-like topography are favorable to the cell adhesion. The cells change their forms (Figures 10 and 12) in relation to diverse surface roughness; for example, we have an elongation of their form on the samples with lower roughness (1.3 \(\upmu\)m), which contributes to the elastic force, influencing the focal adhesions of cells. Furthermore, the cells tend to align on the grooves with increasing roughness parameters up to 1.5 \(\upmu\)m (Table 1), as demonstrated in Figure 9, owing to the contact-guidance alignment. However, on the surfaces with increased width and depth of the surface stripes, the cells do not have enhanced adhesion and proliferation rate, which could probably be attributed to the dimensions of the laser-created structures. This leads us to the conclusion that the size of the patterns is a precondition to the cell orientation. More specifically, the cells demonstrate enhanced sensitivity to micro-structures, whose range is approximately equal to the cellular dimensions. The group of [PERSON] [72] reported different morphologies and sizes of synthesized \(\beta\)-TCP powder such as nanoparticles, nanospheres, nanotubes, irregular shapes with agglomerations, and so on, after elaborate examination with FE-SEM, FTIR, EDX, TEM, surface area, and particle size analysis. Additional texturing of such bioceramic surfaces could significantly improve cell seeding, adhesion, and proliferation and enhance their application in bone tissue engineering [73; 74]. This statement is supported by the papers of _[PERSON]_ and _[PERSON]_, [75; 76], which report a high increase of MG63 population growth after fs laser micro-patterning, compared with that on smooth \(\beta\)-TCP substrates, as well as a tendency of cell elongation along the direction of the grooves in the case of linear patterned surfaces. This technique provides an interesting alternative to conventional surface treatments of calcium phosphates.