Browsing by Author "Linder, Markus, Prof., Aalto University, Department of Biotechnology and Chemical Technology, Finland"

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Biochemical modification and functionalization of nanocellulose surface
(2015) Arola, Suvi
School of Chemical Technology | Doctoral dissertation (article-based)
Cellulose is an abundant biopolymer found in many different organisms ranging from microbes to plants and animals. The homopolymer, composed of repeating glucose units, forms mechanically strong nanosized fibrils and rods. In plants cellulose forms macroscopic fibers, which are incorporated in the cell walls. Recently, it has been shown that cellulose fibers can be disintegrated into the fibrils and rods by different chemical treatments. These materials are called nanocellulose. Nanocellulose is a promising material to replace fossil based materials because it is renewable, biodegradable and abundant. It holds great potential in many applications due to its superior mechanical properties and large surface area. For most applications modification of nanocellulose surface is needed due to its tendency to aggregate by hydrogen bonding to adjacent cellulose surfaces. In this thesis we took a biochemical approach on nanocellulose surface modification to achieve modified and functional materials. The advantages of this approach are that the reactions are done in mild aqueous ambient conditions and the amount of functionalities of biomolecules is broad. Four different approaches were chosen. First, genetically engineered cellulose binding proteins, were used to introduce amphiphilic nature to nanocellulose in order to create surface self-assembled nanocellulose films and to stabilize emulsions. This method was shown to be a good method for bringing new function to nanocellulose. (Publication I) Second, covalent coupling of enzymes directly onto modified nanocellulose surfaces provided a route for protein immobilization in bulk. Nanocellulose derivatives were shown to be well suited platforms for easy preparation of bioactive films. More over the film properties could be tuned depending on the properties of the derivative. (Publication II) Third, by modifying the nanocellulose surface with specific enzymes we could study the role of hemicellulose in nanocellulose fibril surface interactions. We showed that hemicellulose has an important role in nanofibrillated cellulose networks, yet its effects were different in aqueous and dry matrixes. (Publication III) Fourth, by modifying the specific function of cellulose binding protein via genetic engineering we showed how the binding properties can be altered and thus the functionalization properties can be tuned, and that the cellulose binding protein properties are substrate dependent. We also showed that nanocellulose as a model substrate in binding studies is a valuable tool for gaining new insight in protein binding behavior. (Publication IV) In conclusion, we showed that biochemical methods are feasible in nanocellulose modification and functionalization to study intrinsic properties of nanocellulose and cellulose binding proteins but also for creating new functional materials.
Bioinspired materials: Non-covalent modification of nanofibrillated cellulose and chitin via genetically engineered proteins and multilayered graphene
(2015) Malho, Jani-Markus
School of Science | Doctoral dissertation (article-based)
Biological nanocomposites such as nacre, bone and wood synergistically combine strength, stiffness and toughness with lightweight structure, whereas most man-made engineering materials with higher densities follow the rule-of-mixtures, according to which strength and toughness are mutually exclusive properties. Biomimetic approaches study and mimic nature’s concepts and material structures with the aim of developing high-performance bioinspired materials. Recent studies have shown that many of the properties of natural nanocomposites arise from their hierarchical structures from multiple length scales. Molecular level control and design are known to be crucial for the performance of the natural materials especially at the interfaces of the softer matrix and the harder reinforcing elements. In this work, examples of biopolymer matrices were studied from the mechanical perspective in order to understand how biological components, such as genetically engineered proteins and graphene flakes, could be used to design an organic matrix at the molecular level and to control its macroscopic material properties. The results indicated that the biopolymer networks can be functionalized non-covalently in aqueous and mild conditions directly via self-assembly in order to influence the mechanical properties. In Publications I and II, genetically engineered fusion proteins, incorporating hydrophobin - double cellulose binding domain or plain double cellulose binding domain, were used to tune the nanofibrillar cellulose network under conditions of controlled humidity. In Publication III, another genetically engineered fusion protein, chitin binding domain - aspein, was used to modify nanofibrillated chitin matrix through ionic interactions and biomimetic mineralization of calcium carbonate. In Publication IV, multilayered graphene flakes were exfoliated directly into native nanofibrillated cellulose networks in order to create nanocomposites with improved mechanical properties. Non-covalent modification of the colloidal biopolymer matrices is an efficient route to construct and study multifunctional nanocomposite materials by engineering the interfaces between the soft and hard phases. Importantly, genetically engineered proteins could pave the way towards new functional components for biomimetic structural nanocomposite materials while Nature’s materials continue to provide the constructing principles and inspiration for the development of biomimetic materials.