Chapter 1
Introduction into Nano- and Biomaterials

Translated materials from the original work of Ryzhonkov, D.I., Levina, V.V., Dzidziguri, E.L. were used in this chapter.

Thomas Edison, inventor (1847-1931)

1.1 Definition of Nano- and Biomaterials

Nano (from Greek, nannos), meaning dwarf, is one billionth of or 10-9 part of a thing, for example, 1 nm = 10-9 m. Nanomaterials consist of nanostructured materials and nanoparticles, which can be defined as nano-sized complexes of interrelated atoms and/or molecules. Nanotechnology is defined as the knowledge and management of processes on a scale from 1 to 100 nm and application of object properties on a nanometer scale. Significant works in nanotechnology started in 1980. Definition for the term nanotechnology was given for the first time by Norio Taniguchi, a professor of Tokyo University, in 1974 in his paper Basic concepts of Nanotechnology, which mentioned "Nanotechnology mainly consists of the processing of separation, consolidation, and deformation of materials by one atom or one molecule."

Biomaterials can be defined as "materials intended to interface with biological systems to evaluate, treat, or replace any tissue, organ or function of the body" [1] or "any synthetic material which is used to replace part of a living system or to function in intimate contact with the living tissue [2]."

1.2 History of Nano- and Biomaterials Application

Nanomaterials and biomaterials are important because of their primal and initial applications, which date back to ancient times and the Middle Ages, when glassblowers insensibly used nanotechnology. They added gold chloride (AuCl3) to melted glass to change its color to ruby. Thousands of years BC, people knew and used natural fabrics such as cotton, silk and flax, and wool [3]. The Romans had the Lycurgus Cup during the fourth century AD (Anno Domino), which comprises silver and gold nanoparticles at a ratio of roughly 7 : 3, with a diameter size of 70 nm, as disclosed by modern analytic methods. The cup demonstrates a unique color display because of the presence of these metal nanoparticles. It appears green when observed in reflected light, for instance, in daylight, but turns red when light is propagated through it, which is now in the British museum. Historical applications of biomaterials include the use of linen threads by ancient Egyptians to close wounds. Europeans used a fiber made from catgut to close the wounds during the Middle Ages 4000 years ago. Inca surgeons repaired cranial fractures with gold plates in neurosurgery. Mayans used sea shells to create an artificial teeth. In the nineteenth and early twentieth centuries, a number of physicians began to explore the way in which the body reacted to implanted materials. After World War II, observations began to demonstrate the tolerance of the human body to some metals in vivo. Physician Harold Ridley who worked with World War II aviators had noticed that pieces of shattered cockpit canopies inadvertently embedded in the eyes of pilots were well tolerated; thus, he made the 1st formal assessment of "biocompatibility." Later he created implantable intraocular lenses from polymethylmetacrylate [1].

1.3 Methods for Preparing of Nanomaterials

Recently, a huge number of methods for nanomaterial preparation were developed, which led to a variety of nanomaterial properties and expanded the ranges of nanomaterial classes with the creation of a new and unique materials. The formation of high-dispersive structures might happen during phase changes, chemical interactions, recrystallization, amorphization, high mechanical stress, and biological synthesis. Improvement of primary methods for nanomaterials syntheses defined the main requirements such as:

• Method should provide control of composition and properties for obtaining of nanomaterials.
• Method should provide permanent stability of nanomaterials, principal protection of particle surfaces against oxidation and sintering during synthesis.
• Method should be highly productive and economical.
• Method should allow acquisition of nanomaterials with definite sizes or grains.

Basically, preparation of nanomaterials can be divided into up-bottom and bottom-up processes, which are based on crushing and integration, respectively. These processes are essential for nanomaterials syntheses, especially of mechanical, physical, chemical, and biological methods. Mechanical dispersion methods are based on the interaction between pressure, curve, vibration, friction, and cavitation processes. Physical methods for nanomaterial syntheses are based on physical transformations: evaporation, condensation, sublimation, hardening, thermocycling, and so on. Chemical methods are based on chemical dispersion process, chemical reaction, electrolysis, reduction, and thermal decomposition. Biological methods for nanomaterials syntheses are based on the use of biochemical processes in the protein-containing body.

1.3.1 Mechanical Dispersion Methods for Nanomaterial Synthesis

Most mechanical dispersion methods involve mechanical milling, intensive plastic deformation, and mechanical interactions between various mediums.

Mechanical milling is determined by local mechanical interactions appearing in the strain field of the given material. Due to locality and impulsivity in the area of dispersing material, loads can be focused for a short time and cause formation of particle defects, stacking faults, deformations, and cracks. Finally, milling of materials will occur, as well as acceleration of mass transfer, mixing of components in material, and activation of chemical interactions between solid reagent compounds. Mechanical milling or grinding is conducted by using of various equipment such as vibration mills (Figure 1.1), ball mills, hygroscopic mills, attrition mills (Figure 1.2), vortex mills (Figure 1.3), and jet mills.

Figure 1.1 Scheme of vibration mill for nanomaterial preparation (reproduced with permission of BKL Publishers).

Figure 1.2 Scheme of attrition milling device for nanomaterial preparation (reproduced with permission of BKL Publishers).

Figure 1.3 Scheme of vortex mill device for nanomaterial preparation (reproduced with permission of BKL Publishers).

Grinding in vortex mills is primarily intended for ductile metal conversion into nanopowders. In these devices, collisions between the abrasive particles of grinding material will occur. Inside the working chamber of a jet, mill propellers rotate in opposite directions with a speed of 3000 rotations per minute (Figure 1.3). Depending on the nature of the grinding material, particles might be obtained in splintered, flaky, and rounded forms.

Another type of mill for nanomaterial preparation is the planetary centrifugal mill, which allows fast and fine crushing of hard milling materials. In hygroscopic mills, the grinding drum rotates horizontally and vertically at the same time.

Jet mills are designed for the effective production of nanopowders. They provide fine crushing of material by inserting compressed gas jet (air, nitrogen, etc.) or hot steam into working chamber from the nozzles, with sonic or ultrasonic velocity. Inside the working chamber, grinding materials undergo vortex motion and multiple collisions, resulting in their intensive abrasion. Jet mills are used for grinding of metals, ceramics, polymers, and their different combinations.

Also, the grinding of fragile and specially embrittled materials, for example, electrolytic sediments and spongy metals, can be conducted inside jet mills. An inert atmosphere can prevent the oxidation inside the working chamber of jet mills.

Moreover, for effective grinding, it is recommended that the grinding process be conducted in liquid organic mediums, such as hydrocarbons and oleic acid. Nanoparticles obtained by mechanical milling methods usually have various shapes, ranging from uniaxial to flaky or lamellar. As-obtained powder size depends on synthesis conditions and ranges from 1 to 100 nm.

Mechanochemical method is one of the means to grind materials and involves increase in the physical interaction between mixtures of various components, as well as mechanochemical reactions likely initiated or accelerated by mechanical interactions due to the deformation and destruction of the grinding material. Thus, in the solid phase, chemical reactions might occur in solutions and melts at high temperatures. The flow of mechanochemical reaction depends on the dispersity of initial substances, their characteristics, and conditions of grinding. The effect of deformation on material properties can be characterized by mechanical activation, referred to mechanical processes, during which reaction ability of solid material will increase.

1.3.2 Intensive Plastic Deformation Methods for Nanomaterial Synthesis

In order to form nanostructures in bulk materials, special mechanical schemes for deformation are applied. They allow significant distortions in samples at relatively low temperatures. Intensive plastic deformation methods include the following:

1. a. Torsion under high pressure
2. b. Equal-channel angular pressing
3. c. Comprehensive forging method
4. d....