**2. The Electron-Beam Plasmachemical reactor and the treatment procedure**

286 Practical Applications in Biomedical Engineering

burning issue of the day.

treament control;

bioactivity;

treatment conditions;

The aims of the present study were as follows:

and antimicrobial activity, respectively.

The production of substances with novel biological and pharmacological properties on the

The products of the fibrinogen proteolytic degradation are known to inhibit the platelet aggregation [1]. Being the product of the intermediate stage of the fibrinogen-fibrin polymer conversion, fibrin-monomer strongly affects the platelet activity due to two very active sites in its molecule. These sites are formed by the proteolytic cleavage in sequence the N-temini of the fibrinogen Aα and Bβ chains and release of the fibrinopeptides A and B [2]. Low molecular weight products of the fibrin-monomer proteolytic degradation are considered to be promising compounds for the platelets inhibition. Unfortunately the industrial fibrinmonomer can not be degradated by proteolytic enzymes (such as trypsin, plasmin, thrombin, and etc.) due to its high polymerization tendency. Therefore, the alternative techniques for controllable modification of the fibrin-monomer structure should be found to produce

base of EBP-modified proteins and polysaccharides is considered as example.

peptides with the high antiaggregating activity and without polymerization tendency.

The natural renewable biopolymers chitin and, especially, chitosan are very promising for technological and industrial applications such as agriculture, food processing, cosmetics production and others [3, 4]. Chitosan, linear heterocopolymers of β-1,4-linked 2-amino-2 deoxy-D-glucopyranose and 2-acet-amido-2-deoxy-D-glucopyranose units, has many unique biological properties namely high biocompatibility with living tissues, biodegrability, ability to the complexation, and low toxicity. In medicine and pharmaceutics the water-soluble low molecular weight chitosans (less than 10 kDa) are usually required. These substances can be used as immune response-modulating or antibacterial agents, sorbents, radioprotectors, and for the production of microcapsules, thing films, and substrates for cell cultures [3, 4]. To produce the low molecular weight chitosans (LMWC) several techniques, including chemical, enzymatic, and radical treatment have been suggested [5]. Simple and rather low-cost chemical treatment is a conventional method, however toxic wastes and environment contamination are inherent in the chemical chitin and chitosan processing as well as in all techniques mentioned above. Besides, the chemical treatment is very time consuming and usually takes several hours. Thus, the development of the effective techniques for quick and environment friendly chitosan degradation is the

1. to experimentally prove the possibility of the EBP-stimulated hydrolysis of proteins and

2. to prove the controlablity of the EBP-treament and to develop the methods for the EBP-

3. to obtain the high yield of the low molecular weight products by optimizing the

4. to characterize both the structure products of the plasmachemical treatment and their

5. to obtain low molecular products of fibrin-monomer and chitosan with antiaggregating

polysaccharides as a result of the chitosans plasmachemical processing;

For the controllable biopolymers modification and low molecular mass substances production the special Electron Beam Plasmachemical Reactor (EBPR) was designed.

Figure 1 illustrates the design and operation of the EBPR. The focused continuous EB *3*  generated by the electron-beam gun 1 which is located in the high vacuum chamber *2* is injected into the working chamber *5* filled with the plasma-generating gas through the specially designed double-stage gas-dynamic injection window *4* [6]. Oxygen, nitrogen, noble gases, gaseous hydrocarbons and other atomic and molecular gases, water vapor, and vapors of some organic substances can be used for the EBP generation. The electrically heated evaporator *11* is placed inside the reaction chamber, as shown in figure 1, to add the vapor to the plasma-generating gas. Evidently, the pure vapor can be used for the EBP generation and, in this case, the reaction chamber is kept at given constant pressure by adjusting the heater power.

In passing through the gas the EB is scattered in elastic collisions and the energy of fast electrons gradually diminishes during various inelastic interactions with the medium (ionization, excitation, dissociation). As a result, the cloud *10* of the EBP is generated, all plasma parameters being functions of *x*, *y*, and *z* coordinates (*z* is the axis of the EB injection).

1 – electron beam; 2 – high vacuum chamber; 3 – EB; 4 – injection window; 5 – working chamber; 6 – mixing layer of the powder to be treated; 7 – piezoceramic plate; 8 – temperature sensor; 9 – glass container; 10 – EBP cloud; 11 – water evaporator; 12 – scanning system.

**Figure 1.** The design of the plasmachemical reactor and the treatment procedure

The electromagnetic scanning system *12*, which is placed inside the working chamber near the injection window is able to deflect the injected EB axis in *x* and *y* directions and, therefore, to control the spatial distribution of the plasma particles over the plasma bulk. The working chamber is preliminary evacuated to pressure 10-2 Torr and then filled with plasma generating media. The samples to be treated were inserted into the EBPR reaction zone as solid powders with characteristic particle size ~ 100 mcm and as thing films. The powder of the substance to be treated partially fills the glass container *9*. Thin plate *7* made of piezoelectric ceramics is placed on the container bottom. Being fed with AC-voltage the plate vibrates, throws up the powder particles and forms the mixing layer 6 of the treated material. The miniature thermo-sensor *8* is inserted into the container to monitor the material temperature *Ts* during the treatment. To prevent the thermal distraction of the biological material all samples were processed at *Ts*<50 C. In the case of proteins *Ts* was ~ 37 C. The temperature control was carried out by selecting the EB current *Ib* (1 < *Ib* < 100 mA).

Bio-Medical Applications of the Electron-Beam Plasma 289

1. The biomaterials should be processed at low temperatures (Ts <50 C) to prevent the

2. The effect of the biomaterials modification was found to crucially depend on the dose of the biomaterial irradiation by the EBP particles. Usually, the material properties, especially its bioactivity, change abruptly when the certain irradiation dose has been accumulated, but if the dose exceeds this threshold level the bioactivity doesn't increase

3. The direct bombardment by high energy electrons (*Eb* 100 keV and higher) is known to

It means that biomaterials should be processed by the EBP generated by the beams of the moderate *Eb* and that the plasma particles densities and the local power input must be

The controlling system of the EBPR is able to vary *Eb* (25 < *Eb* < 40 keV) and *Ib* (1 < *Ib* < 100 mA). The system supports various scanning modes of the EB injected into the reaction chamber (linear in *x* or *y* directions, circle or ellipse, rectangular raster, multi-triangle or saw-tooth), and both the amplitudes and frequencies of the scanning can be varied. The controlling system also supports the intermittent modes of the EB generation that enables to the biomaterials treatment in the decaying EBP. The pulse frequency can be tuned within the range 1-1000 Hz; the shortest and longest pauses between the EB pulses are 10-3 s and 1.0

The EBPR controlling system also includes the gas-feeding unit which has a feedback with the valves of the vacuum system. The gas-feeding system supplies one or two plasmagenerating gases to the reaction chamber from separate external vessels, thereby keeping the total pressure of the gas mixture (within the range 0,1 < *Pm* < 100 Torr) and partial pressures

**4. The tests of the EBPR and optimization of the biomaterial treatment** 


The computer simulation of the dusty EBP was carried out to preliminary estimate optimal parameters of the biomaterial treatment. The following processes were taken into account:

The local EB power input *Q*(*x*,*y*,*z*), densities of charged particles of the EBP in various zones of the plasma bulk (including the mixing layer), and the temperature of the dust particles

material destruction caused by overheating.

damage or destruct bio-molecules [9, 10].

uniform over the reaction bulk, predictable and controllable.

any more [8].

s respectively.

**procedure** 

of the mixture components constant.








Special software was developed to calculate irradiation doses as functions of the electron beam characteristics, gas pressure and chemical composition, treatment duration, and beam scanning parameters [7], see section "The control of EBP-modification process".

#### **3. The operation modes of the EBPR**

The reaction zone (item *6* in figure 1) of the EBPR is the plasma of an aerosol, as it is sometimes called "dusty plasma". In general, the operation parameters of the reactor responsible for the properties of the plasma of this kind are as follows.


In comparison with the plasma treatment of conventional powder materials (e.g. metals, ceramics, carbon, etc.) the biomaterials processing has at least three important peculiarities.


It means that biomaterials should be processed by the EBP generated by the beams of the moderate *Eb* and that the plasma particles densities and the local power input must be uniform over the reaction bulk, predictable and controllable.

The controlling system of the EBPR is able to vary *Eb* (25 < *Eb* < 40 keV) and *Ib* (1 < *Ib* < 100 mA). The system supports various scanning modes of the EB injected into the reaction chamber (linear in *x* or *y* directions, circle or ellipse, rectangular raster, multi-triangle or saw-tooth), and both the amplitudes and frequencies of the scanning can be varied. The controlling system also supports the intermittent modes of the EB generation that enables to the biomaterials treatment in the decaying EBP. The pulse frequency can be tuned within the range 1-1000 Hz; the shortest and longest pauses between the EB pulses are 10-3 s and 1.0 s respectively.

The EBPR controlling system also includes the gas-feeding unit which has a feedback with the valves of the vacuum system. The gas-feeding system supplies one or two plasmagenerating gases to the reaction chamber from separate external vessels, thereby keeping the total pressure of the gas mixture (within the range 0,1 < *Pm* < 100 Torr) and partial pressures of the mixture components constant.
