Modi®cation of collagen ®lms by ultraviolet irradiation Alina Sionkowska* Faculty of Chemistry, N. Copernicus University, 87-100 Torun Â, Poland Received 2 June 1999; accepted 11 August 1999 Abstract This work describes photochemical modi®cation of collagen ®lms, which are widely used in medical and consumer applications. Modi®cation of collagen ®lms by UV irradiation (254 nm) was investigated using dierential scanning calorimetry and scanning electron microscopy. It was found that the denaturation temperature of collagen decreased during irradiation and the surface of the ®lms was changed. Changes of denaturation temperature and surface of ®lms under UV irradiation point to the loss of water bonded to collagen. This is con®rmed by IR spectra. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: Collagen; Films; UV radiation; Thermal stability 1. Introduction Biopolymeric materials are intensively used in many ®elds and it is necessary to have a detailed description of material behaviour in order to select their proper use. One of the most important requirements of service life assessment is the characterisation of stability under envir- onmentally destructive conditions, e.g. light, temperature, humidity. Collagens are the major structural proteins of con- nective tissue such as skin, bone, cartilage, tendons and ligaments [1]. They constitute about one-third of the total body protein in mammals. There are dierent types of collagen. Each type has its own amino acid sequence, but all contain a signi®cant amount of triple- helical structure. Because of its biological properties and easy availability, type I collagen is widely used as a bio- material [2±5]. It is used in a variety of physical forms such as sponges, ®lms and membranes. Collagen pos- sesses characteristics as a biomaterial distinct from those of synthetic polymers. The most distinct is its mode of interaction with the body. The wide use of collagen in the ®elds of biomaterials is associated with natural proper- ties that include low immune response, low toxicity, the ability to promote cellular growth and attachment homeostasis and the ability of collagen solution to reconstitute in vitro into the micro®brillar structure found in natural tissues [6,7]. The immunochemical properties of collagen are now well established and treatments to reduce its antigenicity have been commonly used [8±10]. It is also known that cross-linking of collagen decreases the antigenicity of the collagen biomaterial [11,12]. In order to gain a satisfactory result from collagen used as a biomaterial, it becomes necessary to improve its physical, chemical and biological properties for some application. Physical modi®cation with ultraviolet irra- diation is useful for changing these properties. The transformation of biopolymer surface properties by UV treatments is more and more becoming a routine tool in obtaining materials for speci®c applications, because it allows modi®cation of the surface properties without changing the characteristics of the bulk of the material. However, precise control of the degree of transforma- tion is not easy, for there is still a lack of knowledge on the processes resulting from UV radiation attack. Knowledge of the conformational behaviour of collagen as a function of dose of UV radiation is important for both biomedical and consumer applications. In the ®eld of material science, it has increased interest in studying the harmful eects of UV irradiation on material stability. Collagen contains various components absorbing in the midultraviolet (300±320 nm) and near-ultraviolet (320±370 nm) ranges, besides aromatic amino acids (phenylalanine and tyrosine) absorbing in the far-ultra- violet (250±280 nm) range [13]. Physical modi®cation of collagen with UV irradiation was investigated widely [13±22]. These studies have demonstrated collagen cross-linking [14±17], destruction of tyrosyl and phenyl- alanyl residues [14,15], and conformational changes with chain degradation [16±20]. 0141-3910/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0141-3910(99)00176-7 Polymer Degradation and Stability 68 (2000) 147±151 * Tel.: +48-56-6214302; fax: +48-56-6542477.