Molecular interactions in collagen and chitosan blends
Introduction
Collagen and chitin are amongst the most abundant polymers in life. They both have intrinsic properties that provide a strong but manipulable scaffolding structure in many multi-cellular organisms. Collagen and chitosan (CC) (a more soluble derivative of chitin) do not exist together as blends in nature, but the specific properties of each may be used to produce man made blends that confer unique structural and mechanical properties. The uses of relatively low cost, low pollution biomaterials with specific properties has great potential for the development of a new generation of prosthetic implants. One of the most promising features of chitosan is its excellent ability to be processed into porous structures for use in cell transplantation and tissue regeneration. A number of researchers have examined the tissue response to various chitosan-based implants [1], [2], [3]. In general, these materials have been found to evoke a minimal foreign reaction. In most cases, no major fibrous encapsulation has been observed [4], [5], [6]. Medical and pharmaceutical applications of chitosan include its use in bandages, sponges, membranes, artificial skin, contact lenses, control release drugs, bone disease treatment and surgical sutures [7], [8].
An important aspect of the properties of a blend is the miscibility of its components. Miscibility in polymer blends is assigned to specific interactions between polymeric components, which usually give rise to a negative free energy of mixing in spite of the high molecular weight of polymers. The most common interactions in the blends are: hydrogen bonding, ionic and dipole, π-electrons and charge-transfer complexes. Most polymer blends are immiscible with each other due to the absence of specific interactions, however mixtures of collagen with synthetic and natural polymers are of increasing interest to scientists and technologists [9], [10]. Blends of CC have been used for design of polymeric scaffolds for the in vitro culture of human epidermoid carcinoma cells [11], as membrane for controlled release [12], [13], [14], and as implant fibres [15], [16]. The influence of chitosan on physicochemical and biochemical properties of collagen has been studied previously [17], [18], [19], [20]. It has been shown that chitosan can modify the properties of collagen when the biological or mechanical properties are considered. Moreover, the formation of polyanion–polycation complexes between CC was observed [19]. From the foregoing, further physical and structural characterisation of the CC is required to develop novel biomaterial properties that allow a more extensive characterisation of the effect of miscibility at the molecular level. In the study presented here we have used a variety of complementary biophysical characterisation methods to produce a better insight into CC interactions.
Section snippets
Materials and methods
Collagen was obtained in our laboratory from tail tendons of young albino rats. Briefly, tendons were excised and washed in distilled water, and blended in a Waring blender in 0.5 m acetic acid, samples were then spun at 10,000 rpm in a Sorvall centrifuge and the soluble fraction decanted and lyophilised. Chitosan (360,000 molecular weight) was obtained from Fluka, Switzerland. Polymeric blends were prepared by mixing of suitable volumes of CC in 0.5 m acetic acid such that a series of 11
Results and discussion
The analytical techniques used to characterise the interactions of the CC blends are described below.
Discussion
Previous research by Taraval and Domard [17], [19] and Domard and Taraval [18] indicated that CC interactions are polyelectrolytic, and from interpretation of data postulated the presence of a polyanion/polycation complex and a competing collagen gelation process. They also proposed a physical separation of collagen microgels encapsulated by the complex, and that complexes contain denatured collagen. Their FTIR evidence also points to the presence of a novel hydrogen bonding in the CC
Conclusion
Our overall conclusion is that collagen chitosan blends are miscible and interact at the molecular level, new hydrogen bonding networks appear to alter the collagen helical character and therefore the overall physical parameters of the blend. Our explanation of the changes in viscosity is through a triphasic system where the CC blend contains a third ‘gelatin’ like phase. The presence of a collagen substrate without collagen helical characteristics may be beneficial for biomaterial design. By
Acknowledgments
Financial support from NATO GRANT 978595 the Scientific Research Committee (KBN, Poland, grant no. 3 P05A 06922) and the SHEFC JREI fund is gratefully acknowledged.
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Present address: Department of Optometry and Vision Sciences, University of Cardiff, Redwood Building, King Edward VII Avenue, Cathays Park, Cardiff, CF10 3NB Wales, UK.