# Infrared Nanosecond Laser Texturing of Cu-Doped Bioresorbable Calcium Phosphate Glasses
## 1 Introduction  
Glass-based materials are gaining a steadily growing importance in our daily lives. The combined optical and dielectric properties of glasses made it possible to envisage many advanced applications apart from their traditional uses. These include a variety of applications in diverse fields such as biophotonics, microfluidics, smart-materials, and non-linear optics, to name a few [1; 2; 3]. Glass materials exhibit, for instance, an inherent advantage for microfluidics owing to their rigidity and inertness to bio-chemicals, and their reduced absorption, unlike, e.g., soft Polydimethylsiloxane (PDMS) [4]. Another recent development of interest for glass materials is in bio-compatible glasses. Bioactive glasses have attracted great interest for their properties, particularly compared to polymers and metals [5]. Indeed, silica-based bioactive glasses are commonly used for dental and orthopedic applications. Despite various advantages associated with silica-based bioactive glasses, they are facing certain limiting factors for applications in the biomedical field. The high crystallization tendency of silicate bioactive glasses limits their use in the fabrication of porous scaffolds [6] and makes it difficult to draw them into fibers [7; 8]. They were also found to have very slow biodegradability, which is highly undesirable in certain medical applications [9; 10]. As an alternative, phosphate glasses have received increased interest lately due to their more reliable and controlled dissolution combined with superior thermal stability that enables them to be drawn into fibers or sintered into scaffolds [11; 12; 13; 14]. This fact represents an added value in biological applications where the possibility of higher metal ions doping concentration, in comparison to silicate glasses, can provide phosphate glasses with special functional properties [15; 16]. Copper has been officially recognized as a metallic antimicrobial agent by the Environmental Protection Agency in 2008 [17]. Cu-doped materialsprovide promising perspectives and there has been a strong research interest for their use in bioceramics, bioc composites, biometallic materials, and bioactive glasses [18]. By combining all the previous features, Cu-doped phosphate glasses can be regarded as an ideal platform to be used in biomedical applications, in particular for implantable devices or bioscaffolds that are able to reduce bacterial growth and promote specific cell cultures. The wettability and surface texture of a bioactive glass play a significant role in protein adsorption or bacterial adhesion onto its surface [19]. In this regard, patternable surface texturing can enable scaffolding by allowing the selective growth of a specific strain of cells to grow, e.g., organoids, while reducing the potentially harmful growth of bacteria [20,21]. Various surface texturing techniques such as chemical etching, sandblasting, lithography, and electrochemical treatments are used to modify bioactive materials surfaces to achieve the desired functionality [22, 23, 24]. Another technique used to obtain such functional surfaces is based on sol-gel bioglasses. Indeed, they possess micro/nano-pores that increase the surface area, resulting in better interaction with the biological environment. However, sol-gel-based glasses show a much lower mechanical strength than the glasses synthesized through the melt-quenching technique, a fact that hinders their usability [25]. Compared to the above-mentioned techniques, laser micromachining represents a spatially selective and non-contact texturing method to process bulk glasses, introducing the desired surface functional features while preserving their bulk properties. Ultrafast lasers, i.e., femto- and pico-seconds, provide the unique advantage of allowing three-dimensional (3D) modification in glass structures with high precision. Material modification and interaction with these laser systems have raised an always-growing research interest in recent years [26,27].