Femtosecond lasers allow for high-precision, high-quality ablation of biological tissues thanks to their capability of minimizing the thermal loads into the irradiated material. Nevertheless, reported ablation rates remain still too limited to enable their exploitation on a clinical level. This study demonstrates the possibility to upscale the process of fs laser ablation of bone tissue by employing industrially available fs laser sources. A comprehensive parametric study is presented in order to optimize the bone tissue ablation rate while maintaining the tissue health by avoiding excessive thermal loads. Three different absorption regimes are investigated by employing fs laser sources at 1030 nm, 515 nm and 343 nm. The main differences in the three different wavelength regimes are discussed by comparing the evolution of the ablation rate and the calcination degree of the laser ablated tissue. The maximum of the ablation rate is obtained in the visible regime of absorption where a maximum value of 0.66 mm3/s is obtained on a non-calcined tissue for the lowest laser repetition rate and the lowest spatial overlap between successive laser pulses. In this regime, the hemoglobin present in the fresh bone tissue is the main chromophore involved in the absorption process. To the best of our knowledge, this is the highest ablation rate obtained on porcine femur upon fs laser ablation.

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The laser patterning of implant materials for bone tissue engineering purposes has proven to be a promising technique for controlling cell properties such as adhesion or differentiation, resulting in enhanced osteointegration. However, the possibility of patterning the bone tissue side interface to generate microstructure effects has never been investigated. In the present study, three different laser-generated patterns were machined on the bone surface with the aim of identifying the best surface morphology compatible with osteogenic-related cell recolonization. The laser-patterned bone tissue was characterized by scanning electron microscopy and confocal microscopy in order to obtain a comprehensive picture of the bone surface morphology. The cortical bone patterning impact on cell compatibility and cytoskeleton rearrangement on the patterned surfaces was assessed using Stromal Cells from the Apical Papilla (SCAPs). The results indicated that laser machining had no detrimental effect on consecutively seeded cell metabolism. Orientation assays revealed that patterns with larger hatch distances were correlated with higher cell cytoskeletal conformation to the laser-machined patterns. To the best of our knowledge, this study is the first to consider and evaluate bone as a biological interface that can be engineered for improvement. Further investigations should focus on the in vivo implications of this direct patterning.

Femtosecond laser processing of bone tissue has shown great potential for osteotomy procedures where high precision cutting and the preservation of bone tissue functions are of primary importance. Nonetheless, the ablation rates related to this kind of process still remain too low for this technology to be exploitable in a real surgical procedure. Moreover, the strong dependence of the process outcomes from factors such as the processing environment, the type of pre-processing and post-processing treatment of the bone tissue, the species of the processed animal and the bone part itself, stall the full development and advancement of this technique. This study highlights the key role of the anatomical region (femur, tibia, etc.) and species (pig, chicken, etc.) of the investigated bone tissue samples to provide a solid reference on the impact of the choice of types of samples on laser ablation studies of bone tissue. Results show that it is essential to choose the best animal model for a specific case study, which depends to a large extent on the objectives of the research subject. There are no perfect animal models: the selection of one animal model is often associated with its similarity to the human model because the goal is the validation of experiments in clinical setting. However, most studies do not take these variabilities into account in their conclusions.