Physico-chemical properties and application of chitin and chitosan. Chitin is the “untwisted star” of polysaccharides. The main component of the exoskeleton

Capsule-type exoskeleton concept for emergency rescue operations

Zeltser A. G.1, Vereikin A. A.1, *, Goykhman A. V.1, Savchenko A. G.1, Zhukov A. A.1, Demchenko M. A.1

UDC: 21.865.8, 623.445.1, 623.445.2

1 Russia, MSTU im. N.E. Bauman

Introduction

The currently existing models of exoskeletons are a frame-type structure that has a minimum of connections with the human body. Thus, the exoskeleton of the lower extremities BLEEX is secured with straps to the feet, legs and back of the human operator, and it is rigidly attached only to the feet.

A fundamentally new concept of the exoskeleton actuator (AM) is proposed, which is based on the idea that in addition to increasing the physical capabilities of a person, the AM should also provide protection for his body, which is quite justified in the non-deterministic conditions of emergency rescue operations. The task has been set to ensure the creation of a universal design of the IM, which will allow, if necessary, to create a line of exoskeletons, which will include a version intended for combat operations. In this case, the power frame is replaced by an armored frame.

1. Determining the relative position of joints

IN As a preliminary stage in the synthesis of the tree-like kinematic diagram of the exoskeleton MI, active and passive degrees of mobility were outlined. By active we mean controlled degrees of mobility, and by passive we mean uncontrolled degrees. A preliminary diagram of the placement of the MI joints was obtained (Fig. 1) and the ranges of variation of the generalized coordinates in the joints were selected, which need to be clarified in the future, based on previous works and anthropometric data (including those proposed by the ergonomic design module of the CATIA software package). Preliminary dimensions of the exoskeleton and location have also been determined

nodes relative to each other. At this stage, the frame design was not worked out.

Rice. 1. Preliminary layout of the joints of the MI exoskeleton

2. Development of the general concept of the actuator

When studying the relative position of the main components, problems were identified that accompany the chosen capsule design, associated with the rigid connection of the structure’s movements to human movements. Thus, for the degree of mobility of the femoral link of the exoskeleton, an adduction-abduction type movement (change in roll), implemented through a cylindrical hinge based on a standard bearing assembly, leads to penetration of the MI link into the human body, which is completely unacceptable. In modern models of exoskeletons, problems of this kind are solved:

 removing the MI link from the human body in a direction perpendicular to the sagittal plane;

 assigning a range of change in the generalized joint coordinate that is significantly less than the permissible one determined from anthropometric parameters;

 strong separation in space of the axes of rotation of the joints, ensuring a change in the position of the hip in roll and pitch.

The previously accepted concept does not allow solving problems using the above methods. A solution has been proposed, which consists in the use of hinges with virtual

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mi axes of rotation coinciding with the axes of rotation of the corresponding human joints. Schematic diagrams of units corresponding to the accepted concept have been developed. Let's take a closer look at the back and hip of the MI exoskeleton.

2.1 Degrees of back mobility

The human back has high mobility, but the concept underlying modern exoskeletons does not allow its mobility to be fully realized. MI significantly limits the movements of the human operator corresponding to changes in the yaw position of the back.

Placing a simple cylindrical hinge behind the back does not solve the problem (Fig. 2). The spine in this case is the axis of rotation, therefore, when placing a rotation pair outside the body, we get a second axis that does not coincide with the first, which can lead to damage to the operator’s spine and body.

Rice. 2. Kinematic diagram of the back of the exoskeleton actuator

The way out of this situation is to use an articulation with a virtual axis of rotation that coincides with the axis of rotation of the human back, which is the spine. In Fig. Figure 3 shows the schematic structure of the spinal unit, which is a rolling guide curved along a certain radius corresponding to the distance to the virtual axis of rotation (item 1).

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Rice. 3. Design diagram for the implementation of a joint that provides a change in the yaw of the operator’s back based on a cylindrical joint with a virtual axis of rotation

2.2 Degrees of hip mobility

The joint responsible for implementing the movement that ensures a change in the position of the human operator’s thigh in pitch, when the position of the person’s leg changes in roll, penetrates into the human body, thereby damaging it. The solution to this problem is the use of a cylindrical hinge with a virtual axis of rotation (items 1, 2 in Fig. 4).

Rice. 4. Design diagram of the implementation of the joint that provides a change in the yaw of the operator’s back

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3. Advantages and disadvantages of the proposed concept

The proposed general concept of the MI exoskeleton has a number of advantages:

 reduced dimensions due to the tight fit of the MI to the human operator’s body;

 With regard to basic human movements, it is possible to implement the principle of one movement of the operator - one movement of the exoskeleton, i.e. the change in the generalized coordinate in the articulation of the IM is adequate to the change in the generalized coordinate of the corresponding human joint. In modern versions of exoskeletons, a change in the generalized coordinates of one human joint corresponds to a certain set of changes in the generalized coordinates of the exoskeleton joints. However, it should be noted that this principle does not apply to all human movements, otherwise it would be necessary to greatly complicate the design of the MI and bring the number of degrees of mobility of the exoskeleton to the number of degrees of mobility of a person, which is not possible at this stage of technology development;

 some simplification of the control system due to the implementation of the principle of one movement of the operator - one movement of the exoskeleton;

 simplified mastery of IM human operator;

 improved ergonomics;

 the ability to modify the frame into an external load-bearing armored structure designed to protect against various shock loads;

 relatively lightweight design due to the fact that the armor and frame are a single whole;

 high structural rigidity.

 Among the disadvantages of the concept are:

 increase in degrees of mobility of the infarction;

 complication of the design of joints;

 increased energy consumption.

4. Developed actuator mechanism of the lower limb exoskeleton

The next stage after deciding on the use of virtual axes and developing the design diagrams of the IM joints is the development of a kinematic diagram taking into account the real and virtual axes of rotation. To obtain the exact geometric dimensions of the kinematic diagram of the exoskeleton MI, several solution methods were considered:

 full x-ray of the operator's body;

 assembly of a prototype of a kinematic model for its experimental refinement.

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Finally, the second method was chosen. At the same time, it was decided to combine the stages of developing the frame and assembling the experimental model. In Fig. Figure 5 shows a preliminary version of the capsular type MI exoskeleton of the lower extremities.

Advantages of the proposed design of the MI exoskeleton:

 simple and convenient arrangement of joints, including with a virtual axis of rotation;

 suitable for making an experimental model of the kinematic diagram of an IM in order to clarify the geometric dimensions and placement of degrees of mobility;

 removal from the actuator motors, which are currently considered pneumatic and hydraulic motors with translational movement of the output link, of all loads except the axial one, due to the movement of the output link along the guide;

 The executive motor is reliably protected from external mechanical influences by a casing, which is especially valuable when using pneumatic muscles as executive motors. This is achieved by introducing an additional lever connecting the output link of the actuator motor with the IM (Fig. 5);

 An increase in the service life of pneumatic muscles is achieved due to the fact that they do not bend during operation.

Rice. 5. Preliminary version of the exoskeleton actuator of the lower extremities of the capsule type

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5. Power plant

Modern exoskeletons can have sufficient autonomy only if the total power of the actuators is low, which affects, on the one hand, the load capacity and speed of movement in space, and the number of controlled degrees of mobility, on the other. Largely due to the last factor, the currently existing autonomous MIs are exoskeletons of the lower extremities only. The exoskeleton of the lower extremities BLEEX uses an internal combustion engine (ICE) as the main source of energy, generating hydraulic and electrical energy.

IN The possibility of using an internal combustion engine combined with a hydraulic or pneumatic supercharger is currently being explored. This should significantly reduce the weight and size characteristics of the power unit.

IN In modern models of autonomous exoskeletons equipped with internal combustion engines, the engines are located behind the operator’s back in large backpacks, which reduces the mobility of the lumbar region, but, at the same time, allows the use of a larger engine, simultaneously providing back protection. It is possible to use the principle that is used on the Israeli army's Merkava tanks. The engine is located at the front, providing additional protection for the crew. To reduce the size of the suit, you can use an engine V-shaped configuration with a greatly increased camber angle. This configuration will literally allow the engine to lie flat on the chest or back, thereby significantly reducing the dimensions.

Conclusion

All highly developed countries of the world are working on projects of robotic exoskeletons equipped with powerful actuators, intended for use mainly in combat zones and emergency rescue operations. Developments in this direction are also underway in the Russian Federation, but at the moment the prospects for domestic developments seem very vague. Thus, there is an urgent need to conduct scientific research and implement technical projects in this area.

To date, the concept of the MI exoskeleton has been defined, and some design solutions have been worked out. A method is presented that allows one to calculate the dynamics of the MI taking into account the reactions of the supporting surface, and subsequently build a control system for the human-exoskeleton complex. The parallel design of two versions of the IM, which have a universal frame design, but differ in terms of actuators: hydraulic cylinders and pneumatic muscles, was chosen as priority directions for the development of this project. Currently, work is also underway on an experimental mock-up, which will allow us to evaluate the selected solutions.

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Table of contents of the topic "Arthropods. Chordata.":

Systematics and characteristic signs of arthropods summarized in the table. In terms of the number of species, the phylum Arthropoda is the most numerous among all others. More than three-quarters of the total number of all known species are representatives of this type.

For the share alone insects accounting for more than half of all known species. Arthropods have mastered all habitats on land and in water.

Basic plan arthropod body structure x was extremely successful, and through a process called adaptive radiation, one successfully evolved ancestral form gave rise to a variety of species that filled many different ecological niches.

Body plan in insects can be considered as an evolved structure of the segmented body of annelids. This example clearly shows how metameric segmentation can be used. Ancient arthropods had simple limbs along the entire length of their bodies, which probably performed a variety of functions, such as gas exchange, food acquisition, locomotion, and recognition of various signals. In modern arthropods, the tendency towards finer specialization compared to annelids has led to the appearance of more complex and more specialized limbs, with a more pronounced division of labor.

In the external structure, segmentation is still visible, but the number segments becomes less than .

Below we will look at other important features of arthropods. These, combined with the evolution of segmentation mentioned above, make it clear that they are thriving.

Exoskeleton. Cuticle.

Cuticle secreted by epidermal cells. IN cuticle composition includes chitin, a nitrogen-containing polysaccharide very similar to cellulose, which serves as the supporting material of plant cell walls. Chitin has high tensile strength (it is difficult to break when pulled at both ends). The binding of chitin with other chemical compounds can lead to changes in the properties of the exoskeleton. By adding mineral salts, for example (especially calcium salts), the exoskeleton can become harder, like that of crustaceans. Protein has the same effect. This creates the possibility of a wide variety of exoskeletons in terms of hardness, elasticity and rigidity. Cuticle flexibility plays an important role in joints.

Availability exoskeleton creates the following benefits:
1) it serves as a support, especially on land;
2) muscles are attached to the inner surface of the exoskeleton, in particular those involved in locomotion, including flight;
3) serves as protection against physical damage;
4) a waxy layer covering the cuticle, produced by a special gland in the epidermis, prevents drying out in terrestrial habitats;
5) the ability of insects to fly, as well as the ability of fleas and locusts to jump, depend on the presence of a very elastic protein in the exoskeleton;
6) the exoskeleton has low density, which is very important for flying animals;
7) the presence of a cuticle creates the possibility of the appearance of flexible joints between segments;
8) the exoskeleton can be modified to form hard jaws capable of biting, crushing, sucking or crushing food;
9) in some places the exoskeleton can be transparent, which ensures light penetration into the eyes and the possibility of camouflage in water.

PIECE 1

Chitin (C 8 H 13 NO 5) n (fr. chitine, from ancient Greek. χιτών: chiton - clothing, skin, shell) - a natural compound from the group of nitrogen-containing polysaccharides.

The main component of the exoskeleton (cuticle) of arthropods and a number of other invertebrates, it is part of the cell wall of fungi and bacteria.

In 1821, the Frenchman Henri Braconneau, director of the botanical garden in Nancy, discovered a substance in mushrooms that was insoluble in sulfuric acid. He called him fungin. Pure chitin is isolated for the first time from the outer shells of tarantulas. The term was proposed by the French scientist A. Odier, who studied the outer cover of insects, in 1823.

Chitin is one of the most common polysaccharides in nature; every year on Earth, about 10 gigatons of chitin are formed and decomposed in living organisms.

· Performs protective and supporting functions, ensuring cell rigidity - found in the cell walls of fungi.

· The main component of the exoskeleton of arthropods.

· Chitin is also formed in the bodies of many other animals - various worms, coelenterates, etc.

In all organisms that produce and use chitin, it is not found in pure form, but in combination with other polysaccharides, and is very often associated with proteins. Despite the fact that chitin is a substance very similar in structure, physicochemical properties and biological role to cellulose, chitin could not be found in organisms that form cellulose (plants, some bacteria).

Chitin is hard and translucent.

Chemistry of chitin

In their natural form, chitins from different organisms differ somewhat in composition and properties.

Chitin is insoluble in water and resistant to dilute acids, alkalis, alcohol and other organic solvents. Soluble in concentrated solutions of some salts (zinc chloride, lithium thiocyanate, calcium salts) and in ionic liquids.

When heated with concentrated solutions of mineral acids, it is destroyed (hydrolyzed).

Chitin is a nitrogen-containing polysaccharide (aminopolysaccharide).

Structural polysaccharides (cellulose, hemicellulose) in the cell walls of plants form extended chains, which, in turn, fit into strong fibers or plates and serve as a kind of framework in a living organism. The most common biopolymer in the world is a structural polysaccharide of plants - cellulose. Chitin is the second most abundant structural polysaccharide after cellulose.. In terms of its chemical structure, physicochemical properties and functions, chitin is close to cellulose. Chitin is an analogue of cellulose in the animal world.

In organisms living in nature, only chitin can be formed, and chitosan is a derivative of chitin. Chitosan is obtained from chitin by deacetylation with alkalis. Deacetylation is the reverse reaction to acetylation, i.e. substitution of a hydrogen atom for the acetyl group CH 3 CO.

Raw materials sources of chitin and chitosan

Chitin is a supporting component:

· cell tissue of most fungi and some algae;

· outer shell of arthropods(cuticle in insects, shell in crustaceans) and worms;

· some organs of mollusks.

PIECE 2

In the organisms of insects and crustaceans, cells of fungi and diatoms, chitin, in combination with minerals, proteins and melamines, forms the external skeleton and internal supporting structures.

Melanins determine the color of the integument and their derivatives (hair, feathers, scales) in vertebrates, the cuticle in insects, the peel of some fruits, etc.

Potential sources of chitin are diverse and widespread in nature. The total reproduction of chitin in the world's oceans is estimated at 2.3 billion tons per year, which can provide a global production potential of 150-200 thousand tons of chitin per year.

The most accessible and large-scale source of chitin for industrial development is the shells of commercial crustaceans. It is also possible to use the gladius (skeletal plate) of squid, sepion of cuttlefish, biomass of filamentous and higher fungi. Domesticated and breedable insects, due to their rapid reproduction, can provide significant chitin-containing biomass. These insects include silkworms, honey bees and house flies. In Russia, a widespread source of chitin-containing raw materials is Kamchatka crab and snow crab, the annual catch of which in the Far East amounts to up to 80 thousand tons, as well as angle-tail shrimp in the Barents Sea.

It is known that crustacean shells are quite expensive raw materials, and despite the fact that more than 15 methods for obtaining chitin from them have been developed, the question was raised about obtaining chitin and chitosan from other sources, among which small crustaceans and insects were considered.

Due to the widespread use of beekeeping in our country, it is possible to obtain chitinous raw materials (dead bees) on a significant scale. As of 2004, there were 3.29 million bee colonies in the Russian Federation in all categories of farms. The strength of a bee colony (the mass of worker bees in a bee colony, measured in kg) is on average 3.5-4 kg. In summer, during the period of active honey collection and in spring after wintering, the bee colony is renewed by almost 60-80%. Thus, the annual raw material base of dead bees can range from 6 to 10 thousand tons, this makes it possible to consider dead bees as a new promising source of insect chitosan along with traditional types of raw materials.

Chitin, which is part of the shell of crustaceans, forms a fibrous structure. In crustaceans, immediately after molting, the shell is soft, elastic, consisting only of a chitin-protein complex, but over time it becomes stronger due to mineralization of the structure mainly with calcium carbonate. Thus, the shell of crustaceans is built from three main elements - chitin, which plays the role of a frame, a mineral part, which gives the shell the necessary strength, and proteins, which make it a living tissue. The shell also contains lipids, melanins and other pigments.

The advantage of dead bees is the minimal content of minerals, since the cuticle of insects is practically not mineralized. In this regard, there is no need to carry out a complex demineralization procedure.

Physico-chemical properties and application of chitin and chitosan

Chitin and its deacetylated derivative chitosan have attracted the attention of a wide range of researchers and practitioners due to their complex of chemical, physicochemical and biological properties and an unlimited reproducible raw material base. The polysaccharide nature of these polymers determines their affinity for living organisms, and the presence of reactive functional groups (hydroxyl groups, amino group) provides the possibility of various chemical modifications that make it possible to enhance their inherent properties or add new ones in accordance with the requirements.

Interest in chitin and chitosan is associated with their unique physiological and environmental properties such as biocompatibility, biodegradation (complete decomposition under the influence of natural microorganisms), physiological activity in the absence of toxicity, the ability to selectively bind heavy metals and organic compounds, the ability to form fibers and films, and etc.

PIECE 3

The process of producing chitin involves removing mineral salts, proteins, lipids, and pigments from the raw material; therefore, the quality of chitin and chitosan depends largely on the method and degree of removal of these substances, as well as on the conditions of the deacetylation reaction. The requirements for the properties of chitin and chitosan are determined by the areas of their practical use, which are very diverse. In Russia, as in other countries, there is no single standard, but There is a division into chitin and chitosan for technical, industrial, food and medical purposes.

directions for their use of chitin and chitosan:

· nuclear industry: for localization of radioactivity and concentration of radioactive waste;

· medicine: as suture materials, wound and burn healing dressings. As part of ointments, various medicinal preparations, such as enterosorbent;

· agriculture: for the production of fertilizers, protection of seed material and crops;

· textile industry: for sizing and anti-shrink or water-repellent treatment of fabrics;

· paper and photographic industry: for the production of high-quality and special grades of paper, as well as for improving the properties of photographic materials;

· in the food industry serves as a preservative, juice and wine clarifier, dietary fiber, emulsifier;

· as a food additive shows unique results as an enterosorbent;

· in perfumery and cosmetics it is part of moisturizing creams, lotions, gels, hair sprays, shampoos;

· When purifying water, it serves as a sorbent and flocculant.

Chitin is insoluble in water, solutions of organic acids, alkalis, alcohols and other organic solvents. It is soluble in concentrated solutions of hydrochloric, sulfuric and formic acids, as well as in some saline solutions when heated, but when dissolved it depolymerizes noticeably. In a mixture of dimethylacetamide, N-methyl-2-pyrrolidone and lithium chloride, chitin dissolves without destroying the polymer structure. Low solubility makes it difficult to process and use chitin.

Also important important properties of chitosan are hygroscopicity, sorption properties, and swelling ability. Due to the fact that the chitosan molecule contains many hydroxyl, amine and other end groups, its hygroscopicity is very high (2-5 molecules per monomer unit, which is located in the amorphous regions of polymers). In this indicator, chitosan is second only to glycerin and superior to polyethylene glycol and calleriol (high-polymer alcohol from pear). Chitosan swells well and firmly holds the solvent in its structure, as well as substances dissolved and suspended in it. Therefore, in dissolved form, chitosan has much greater sorption properties than in undissolved form.

Chitosan can be biodegraded by chitinase and lysozyme. Chitinases- These are enzymes that catalyze the decomposition of chitin. Produced in the bodies of animals containing chitin. Lysozyme produced in the body of animals and humans. Lysozyme- an enzyme that destroys the bacterial cell wall, resulting in its dissolution. Creates an antibacterial barrier at points of contact with the external environment. Contained in saliva, tears, and nasal mucosa. Chitosan products, which completely decompose under the influence of natural microorganisms, do not pollute the environment.

Main component of the shell of insects, crustaceans and other arthropods

First letter "x"

Second letter "i"

Third letter "t"

The last letter of the letter is "n"

Answer for the question "The main component of the shell of insects, crustaceans and other arthropods", 5 letters:
chitin

Alternative crossword questions for the word chitin

Organic substance that makes up the outer hard covering of crustaceans, insects and other arthropods and which is found in the membranes of a number of fungi and some types of green algae

Outer hard cover of arthropods

Crayfish shell material

Organic matter that makes up the outer hard covering of crustaceans and insects

"Body armor" of beetle wings

Definition of the word chitin in dictionaries

Encyclopedic Dictionary, 1998 The meaning of the word in the dictionary Encyclopedic Dictionary, 1998
a polysaccharide formed by amino sugar residues of acetylglucosamine. The main component of the exoskeleton (cuticle) of insects, crustaceans and other arthropods. In mushrooms it replaces cellulose, with which it is similar in chemical and physical properties and biological...

Wikipedia Meaning of the word in the Wikipedia dictionary
Chitin is a natural compound from the group of nitrogen-containing polysaccharides. Chemical name: poly-N-acetyl-D-glucose-2-amine, a polymer of N-acetylglucosamine residues linked by β-(1→4)-glycosidic bonds. The main component of the exoskeleton (cuticle...

New explanatory dictionary of the Russian language, T. F. Efremova. The meaning of the word in the dictionary New explanatory dictionary of the Russian language, T. F. Efremova.
m. Organic substance that makes up the outer hard covering of crustaceans, insects and other arthropods and which is found in the membranes of a number of fungi and some types of green algae.

Great Soviet Encyclopedia The meaning of the word in the dictionary Great Soviet Encyclopedia
(French chitine, from Greek chiton ≈ clothing, skin, shell), a natural compound from the group of polysaccharides; the main component of the exoskeleton (cuticle) of arthropods and a number of other invertebrates; it is also part of the cell wall of fungi and bacteria....

Examples of the use of the word chitin in literature.

The beast lay nearby - shackled in a thick chitin, large-headed, with short thick breasts, more like horns, compound eyes.

The second chrysalid ran into the barrier wall of Vega and the Irish woman, even from him chitin there was none left, everything turned to greasy ashes.

The skin has turned into chitin, cuticle, on a tanned face, blue eyes seemed surprisingly bright and large.

During the transition to upright walking, evolution developed supporting structures in the body, and on the outside there was a combination of larval skin and pale chitin.

She clasped her right hand with her left, running her fingers along the beads chitin, which were her identification mark: Raen, Sept Sul, Met-maren, Contrin.