JOURNAL OF MATERIALS SCIENCE 34 (1 9 9 9 ) 3587 – 3590 SiO 2 Entrapment of animal cells Part I Mechanical features of sol-gel SiO 2 coatings V. M. SGLAVO, G. CARTURAN Dipartimento di Ingegneria dei Materiali, Universit ` a di Trento, I-38050 Trento, Italy E-mail: sglavo@ing.unitn.it R. DAL MONTE R.d.C. Scientifica, I-36077 Altavilla V.na, VI, Italy M. MURACA Istituto di Medicina Interna, Universit ` a di Padova, I-35100 Padova, Italy Natural silk fibers show valuable changes in elastic modulus, E , and failure stress, σ f , upon treatment with an air flux of gaseous Si-alkoxides bearing a thin sol-gel layer of SiO 2 on the fiber surface. These mechanical features are studied here as a function of the composition of gaseous flux and reaction time. Owing to the different behavior between original and treated fibers submitted to loading-unloading cycles, the maximum increase in E (about 50%) and σ f (about 30%) are discussed in terms of intermolecular surface interactions of -O-Si-O- bridging groups and protein macromolecules. As an extension of this system, composed of a thin sol-gel SiO 2 layer (0.05–0.1 µm) on protein surfaces, the mechanical improvement of collagen + cell deposits upon deposition of sol-gel SiO 2 is suggested. C  1999 Kluwer Academic Publishers 1. Introduction Some of the diverse arrays of sol-gel SiO 2 span the incorporation of functional organic molecules and bio- active species, including dyes [1], enzymes [2–4] and even cells [5–8]. As for living cell entrapment, two in- dependent approaches have been proposed: (1) integra- tion of cells even during SiO 2 sol-gel processing [5, 6] adjusted to fulfil restrictions concerning handling of liv- ing systems, and (2) build-up of a sol-gel SiO 2 coating, directly on the cell surface [7, 8] by exploitation of basic chemical reactivity of the silicon-alkoxide precursors. This second method, called Biosil [9, 10], is illustrated in Scheme 1. Living cells are left to adhere to fibers of scaffold- ing materials with selected mechanical properties and textured to avoid mass-transfer limitations, were they are invested by an air flux of silicon-alkoxide precur- sors. The silica layer originates from reaction of sur- face hydroxides and alkoxides; sol-gel thickness may be controlled by the time of treatment and by the con- centration of alkoxide in the air flux, which removes excess reagent and volatile toxic by-products. In addition to specific applications in vegetable cell production of secondary metabolites [7] and pancre- atic islet entrapment [8] this method appears to be an alternative or valuable addition to reported tech- niques in the design of hybrid bio-artificial liver [11]. A large variety of bio-reactors, containing viable hepato- cytes has been proposed [12]. Bio-reactors design based on multi-plated matrix-overlaid hepatocytes, provides an attractive organo-typical approach [13], mimiking the situation in vivo. Limitations of these systems are poor matrix resistance to shear stress exerted by pa- tient plasma flowing through the system and the lack of immuno-isolation. These shortcomings could be circumvented by improvement of incapsulation tech- nology. Preliminary results obtained with the Biosil method indicate that deposition of a 0.1–0.2 µm sil- ica layer on the surface of collagen-entrapped hepa- tocytes can be achieved with preservation of cell via- bility and functionality. Collectively, these features are quite promising for the purpose at hand: indeed, experi- ments have been carried out with the aim of ascertaining whether the method of Scheme 1 may be exploited for bio-artificial liver, neglecting the definition of specific features implied in the extension of the sol-gel tech- nique to complex biological systems. Current interest in this subject spurred us to orga- nize explorative work in order to investigate: (i) the nature of the composite sol-gel SiO 2 + collagen and inherent mechanical features, (ii) the barrier effect vs. macromolecule transport across the collagen + SiO 2 composite, and (iii) the metabolism of entrapped hep- atocytes for typical hepatic functions. In this first work we report the results regarding point (i). Collagen layers, promoting the mosaic-like struc- ture of hepatocytes, features a thickness of few hun- dreds of microns; they are gels composed of a protein network immobilizing the solvent, the solid mass be- ing about 0.1% in volume. Owing to this feature, the chemical, physical and mechanical characterization of 0022–2461 C  1999 Kluwer Academic Publishers 3587