Appl Phys A (2009) 94: 719–729 DOI 10.1007/s00339-008-4950-z Modeling the dynamics of one laser pulse surface nanofoaming of biopolymers S. Lazare · R. Bonneau · S. Gaspard · M. Oujja · R. De Nalda · M. Castillejo · A. Sionkowska Received: 25 August 2008 / Accepted: 20 October 2008 / Published online: 15 November 2008 © Springer-Verlag 2008 Abstract Self standing films of biopolymers like gelatine, collagen, and chitosan irradiated with single nanosecond or femtosecond laser pulse easily yield on their surface, a nanofoam layer, formed by a cavitation and bubble growth mechanism. The laser foams have interesting properties that challenge the molecular features of the natural extracellular matrix and which make them good candidates for fabrication of artificial matrix (having nanoscopic fibers, large availabil- ity of cell adhesion sites, permeability to fluids due to the open cell structure). As part of the mechanistic study, the dynamics of the process has been measured in the nanosec- ond timescale by recording the optical transmission of the films at 632.8 nm during and after the foaming laser pulse. A rapid drop 100 → 0% taking place within the first 100 ns supports the cavitation mechanism as described by the pre- vious negative pressure wave model. As modeled a strong pressure rise (∼several thousands of bar) first takes place in the absorption volume due to pressure confinement and finite sound velocity, and then upon relaxation after some delay equal to the pressure transit time gives rise to a rar- efaction wave (negative pressure) in which nucleation and bubble growth are very fast. S. Lazare ( ) · R. Bonneau Institut des Sciences Moléculaires (ISM) UMR 5255, Université Bordeaux 1, 351 cours de la Libération, 33405 Talence, France e-mail: s.lazare@ism.u-bordeaux1.fr Fax: +33-540006645 S. Gaspard · M. Oujja · R. De Nalda · M. Castillejo Instituto de Química Física Rocasolano, CSIC, Serrano 119, 28006 Madrid, Spain A. Sionkowska Faculty of Chemistry, Nicolaus Copernicus University, Gagarin 7, 87-100 Toru´ n, Poland PACS 68.35.-p · 61.80.Ba · 78.47.+p 1 Introduction Detailed understanding of laser–matter interaction is the in- teresting source of new processes which are the future tech- nologies for industry, biomedicine, and research. In partic- ular, the field of laser ablation of biological tissue [1] is of prime importance and has been pursued for many years. In this framework we have discovered recently a new nanosec- ond (ns) or femtosecond (fs) laser induced foaming process on the surface of many bio-related polymers [2, 3] (Fig. 1). Among them collagen (Fig. 1a) is one of the most promis- ing for biomedical applications because of its natural role in the cellular matrix and its capability to be used without biocompatibility problems in cell culture and study, in tis- sue reconstruction and repair, etc. The laser-induced foam- ing of collagen easily yields an expanded nanocellular ma- terial with interesting properties which tend to rival the fea- tures of the natural extracellular matrix. In tissue cells live, adhere, and migrate in a fine network of mainly nanometric collagen fibers [4] which is ideally constructed by and for themselves [5]. The contact of the cells with the matrix is achieved by weak molecular interactions [6]. The so-called focal contacts are established between special integrin lig- ands and the matrix adhesion sites. The laser-induced foam- ing creates the properties that are necessary for cell life, i.e., the presence of nanoscopic fibers, increased availabil- ity of adhesion sites, and permeability to fluids due to the open cellular structure. For the development of these future applications it is necessary to investigate more deeply the foaming mechanisms. A particular objective is to gain some knowledge about the thermodynamic parameters (tempera- ture, pressure, degree of excitation, and ionization), gener-