Interview with Paul Gatenholm, Biopolymer Technology

Biopolymers are the most important building blocks of all natural materials and living bodies on the earth. The majority of plants are made of cellulose, which acts as reinforcement; the cellulose is embedded in the matrix of hemicelluloses and cross-linked with lignin. The human body is composed of hard and soft tissues. Hard tissues, such as teeth and bones, are made up of collagen reinforced with oriented crystals of hydroxyapatite or structural proteins such as keratins. The soft tissues are made up of collagens and polysaccharides. Many animals, especially those living in water, use chitin as their main building block and control the hardness of the material by incorporating oriented crystals of calcium carbonate. The biological materials are superior to man-made synthetic materials with regard to the combination of mechanical properties, such as stiffness and impact strength and yet are very light in weight. They are also highly anisotropic and self-repairing.
Natural polymers were exploited by man long before recorded history. For thousands of years, natural materials such as wood, leaves, feathers, and bones, have been used for load-bearing purposes. During the past fifty years, natural materials have been replaced in many applications by synthetic polymers. Synthetic polymers, the main advantage of which is the attractive combination of low price and good processability, unfortunately have a negative environmental impact, contributing to waste accumulation and future shortage of non-renewable resources. Biopolymers are a better alternative as a source of raw materials due to their renewability and biodegradability. When they once again started to be used as materials, just a decade ago, the first generation of "new" biopolymeric materials was based on the direct transformation of starches and collagens into plastics. These biopolymeric materials performed rather poorly. Advances in molecular biology have created new opportunities to "grow" tailor-made biopolymers in plants and also produce them in microbial cells or be synthesised by isolated enzymes. There is, however, a lack of knowledge of the correlation between the molecular structure of biopolymers, which can today be altered in an almost unlimited way, and their material properties. Furthermore, there is a lack of technology for the controlled conversion of biomacromolecules into an hierarchical structure.

• Chemical and enzymatic modification of selected polysaccharides (xylans and amyloses) and characterisation of molecular structures and their correlation with their material properties
• Assembly and supramolecular organisation of tailor-made xylans and amyloses in films and coatings, microporous materials, fibres and biocomposites
• Chemical, physical, and enzymatic cross-linking during the formation of network biopolymers, biocoatings and bioadhesives
• Engineering of the surface and interfacial properties of biomacromolecular materials by phase separation and surface assembly

Polysaccharides - modification, characterisation and controlled assembly into films and coatings, microporous structures and biocomposites
Xylans and amyloses are among the most abundant biopolymers biosynthesised in the majority of plants. Yet, they are not utilised as materials. In collaboration with the Biobased Materials Center at Virginia Tech, USA we are isolating macromolecular xylans from various sources. We use both enzymes and wet chemistry to alter the molecular structure of xylans and evaluate the effect of their structure on material properties and ability to assemble with other polysaccharides, such as cellulose. Attempts are also made to prepare linear xylans and evaluate such polymers as raw materials for the manufacturing of fibres and oriented films. The assembly of tailor-made xylans onto surfaces of lignocellulosic can be used for the preparation of fibres with tailor-made surface properties.
Amylose is another important polysaccharide. The functional groups, providing crosslinking, self-assembly and controlled phase separation along with controlled interaction with other components, are attached to the main chain of amyloses by enzymatic and chemical means. Molecular modelling will be used to predict structure-property relationships.

Marine bioadhesives
Barnacles and mussels depend on their ability to attach to solid surfaces for survival. For this they have developed bioadhesives that stick to all kinds of wet surfaces. In fact, all adhesive events conducted by these marine organisms occur in the presence of water and ions. The understanding of "bioadhesive technology" developed by nature may serve both as a tool to interfere with the formation of bioadhesive bonding and as a source of inspiration for the development of new medical "glues", useful for joining tissue or promoting cell attachment in tissue engineering applications. The body fluids are in fact very similar in terms of ion strength to a marine environment.
In this programme, run in collaboration with the Center for Biotechnology at Tufts University, USA, the focus is on the isolation, separation and characterisation of this proteins present in the adhesive plaque formed by the barnacle on various substrates. The goal of the research is to generate sufficient quantities of the different proteins to enable suitable biophysical, biochemical and mechanical/thermal studies aimed at elucidating the curing mechanism of this bioadhesive.

Towards a sustainable society
We hope to be able to attract internationally recognised scientific experts to be associated with this research programme and become visiting scientists for varying periods of time. We are planning to develop a curriculum that will cover many of the topics studied by our PhD students. The programme, consisting of short courses, will also be offered to industry. A series of summer schools and training courses will be developed in collaboration with international scientists in this field. We anticipate that strong industrial collaboration and a partnership for Swedish and international companies will be offered. It is not unlikely that some innovations will result in the start-up of new companies. We believe that biomolecular materials developed in this programme will result in the transition of society into a more sustainable society. They will improve not only the environment but also the quality of life.