Submicron foaming in gelatine by nanosecond and femtosecond pulsed laser irradiation S. Gaspard a , M. Oujja a , R. de Nalda a , C. Abrusci b , F. Catalina b , L. Ban ˜ares c , M. Castillejo a, * a Institute of Physical Chemistry Rocasolano, CSIC, Serrano 119, 28006 Madrid, Spain b Institute of Polymer Science and Technology, CSIC, Juan de la Cierva 3, 28006 Madrid, Spain c Department of Physical Chemistry, Faculty of Chemistry, Universidad Complutense de Madrid, 28040 Madrid, Spain Available online 30 January 2007 Abstract We compare the foaming characteristics induced by irradiation with single ns and fs laser pulses of UV, VIS and IR wavelengths on gelatines differing in gel strength (bloom values 75 and 225) and in crosslinking degree. We have observed that while laser irradiation with nanoseconds leads to the formation of a microfoam layer at 266 nm, and melting and crater formation at longer wavelengths (532 and 1064 nm), fs pulse irradiation leads to submicron foaming at all wavelengths studied (266, 400 and 800 nm). These results show the possibility of controlling the submicrometric foam structure in this biomaterial and can shed light into the working mechanisms of fs laser nanoprocessing in biomaterials, where increase of temperature, thermoelastic stress generation, and stress-induced bubble formation are mediated by the generated plasma. # 2007 Elsevier B.V. All rights reserved. PACS : 52.38.Mf laser ablation; 82.53.Ps femtosecond probing of biological molecules Keywords: Gelatine; Biopolymers; Femtosecond laser processing; Nanostructuring 1. Introduction Porous structures with high surface areas possess a wide range of applications [1]. Control of the pore size and shape in polymers and biopolymers is highly desirable in medical technology and biotechnology [2]. Using different fabrication techniques three-dimensional, microstructured constructs on polymeric supports can be developed for drug release and tissue engineering. Cell function, adhesion and proliferation are strongly influenced by the polymer physico-chemical proper- ties [3,4]. Laser microstructuring of polymers and biopolymers is an alternative method that conveys a series of advantages including high-resolution capability, low heat deposition in the substrate and high level of flexibility. Femtosecond (fs) lasers have been well established as a tool for subsurface machining of transparent materials and ultra- precise machining of solid-state materials [5]. Recently, fs ablation has been adapted as a biological tool to manipulate structures and chemistry on a microscopic scale [6–9]. Focusing fs laser pulses into biological media leads to optical breakdown and generation of a microplasma. Because of the nonlinear nature of plasma formation very fine and highly localized laser effects can be induced while minimizing thermal and mechanical damage to the surrounding material. For fs pulses, the pulse energy threshold for material modification is reduced by some orders of magnitude compared with ns or ps pulses [7–9]. Gelatine is a proteinaceous material derived from the parent protein structure of collagen. The gelatine manufacture is carried out by acid pre-treatment (Type-A) or alkali pre- treatment (Type-B) from bones in a reproducible way. Gelatine from successive extractions has different physical and chemical properties due to the hydrolytic degradation that takes place during the manufacturing process. After the pre-treatment, the first extract (with hot water) is obtained at the lowest temperature and exhibits higher bloom value or gel strength, which is the common parameter to measure the gelatine quality. Due to its interest for edible, pharmaceutical and photographic uses and for medical applications, this biomaterial has focussed much scientific interest [10]. www.elsevier.com/locate/apsusc Applied Surface Science 253 (2007) 6420–6424 * Corresponding author. Tel.: +34 91 5619400; fax: +34 91 5642431. E-mail address: marta.castillejo@iqfr.csic.es (M. Castillejo). 0169-4332/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2007.01.083