layer-by-layer assembly of collagen thin films- controlled thickness and biocompatibility

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Biomedical Microdevices 3:4, 301±306, 2001 # 2001 Kluwer Academic Publishers. Manufactured in The Netherlands. Layer-By-Layer Assembly of Collagen Thin Films: Controlled Thickness and Biocompatibility Gregory G.S. Grant, 1 Dmitry S. Koktysh, 1 BoGeon Yun, 2 Robert L. Matts, 2 and Nicholas A. Kotov 1 * 1 Department of Chemistry, Oklahoma State University, 107 PS I, Stillwater, OK 74078 2 Department of Biochemistry and Molecular Biology, Noble Research Center, Oklahoma State University, Stillwater, OK 74078 Abstract. The extracellular matrix molecular collagen is the one of the most widely utilized scaffolding materials in tissue engineering. However, obtaining uniform bioactive collagen ®lms in the nanoscale range and precisely controlling the physical and chemical properties of these biological ®lms is still a challenge for biomedical engineering. Layer-by-layer assembly, i.e., sequential adsorption of oppositely charged macromolecular species, is a powerful new ®lm preparation technique that can be applied to the design of versatile biomaterials, with well-controlled interfacial, mechanical and biological functions. To demonstrate the feasibility of biomaterial design by means of layer-by-layer assembly, type-I collagen thin ®lms were prepared by using this technique with poly(styrene) sulfonate as a partner polyelectrolyte. The gradual build-up of the collagen ®lms was con®rmed by UV-vis spectroscopy and ellipsometry, while their surface morphology was assessed by atomic force microscopy. The thickness of the collagen layers can be changed by increasing the number of bilayers adsorbed with an increment of 13 nm. It was found that the layer-by-layer assembled collagen scaffolds can support the attachment and growth of C2C12 myoblast cells and PC12 pheochromocytoma cells. Accurate thickness control and compatibility with nerve cell precursors indicate the utility of layer-by-layer assembled ®lms in neuro- prosthesis. Key Words. layer-by-layer assembly, thin ®lms, polyelectrolytes, collagen, biocompatibility Introduction The preparation of ultrathin polymer ®lms is of scienti®c and practical interest for various biomedical ®elds from tissue engineering to dialysis. Thin ®lm biomaterials in the form of coatings or membranes can be made from either naturally occurring, synthetic polymers or a combination of both (Angelova and Hunkeler, 1999). The composite ultrathin ®lms open the possibility of combining the biocompatibility of naturally occurring polymers with the versatility of the chemical and physical properties of synthetic polymers. Biodegradable natural polymers such as collagen are particularly attractive for such compositions. As a ®brous protein, collagen is the major component of mammalian connective tissue (Pachence, 1996). It is also involved in many important biological functions such as tissue regeneration and cell attachment (Hubbell, 1995; Pachence et al., 1987). Type-I collagen is the most abundant among the many types of collagen (Pachence, 1996). In relationship to its framework-forming function in living organisms, it has the ability to self-assemble into rigid gels and ®bers (Christiansen et al., 2000; Pins and Silver, 1995; Silver and Garg, 1997). Thin ®lms of type-I collagen can be easily prepared by non-speci®c adsorption from solution or spin-coating techniques but they display a high degree of roughness and poor strand alignment. Additionally, it is dif®cult to regulate ®lm thickness, particularly when nanometer scale precision is needed, for instance, in biomineralization studies. (Carrino et al., 1996; Falini et al., 1998; Nakamura and Caplan, 1994; Uemura et al., 1997) Layer-by-layer (LBL) adsorption of polyelectrolytes introduced by G. Decher in the beginning of the 1990s (Decher, 1997; Decher and Hong, 1991), allows for the deposition of homogeneous, robust ®lms with layer thickness and interlayer separation controlled on the nanometer scale. Other advantages of the assembly include the control of the surface structure, which, in turn, may be employed to govern the biological responses. Presently, we are at the onset of the study of the biological properties of the LBL ®lms and yet the importance of biomaterials made by LBL have been demonstrated (Elbert et al., 1999; Koktysh et al., 2000; Ngankam et al., 2000). In this paper, we describe the method of LBL deposition of collagen thin ®lms, which later can be combined with other colloids that can be LBL assembled to produce structurally and functionally versatile materials. *Corresponding author. 301

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Page 1: Layer-By-Layer Assembly of Collagen Thin Films- Controlled Thickness and Biocompatibility

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