Analysis of Mechanical Properties of Dialysis Sets

Klara Fiedorova

, Martin Augustynek

, Frantisek Fojtik

and Milada Hlavackova

VSB Technical University of Ostrava, Faculty of Mechanical Engineering,

Department of Cybernetics and Biomedical Engineering, Ostrava, Czech Republic

VSB Technical University of Ostrava, Faculty of Mechanical Engineering,

Department of Applied Mechanics, Ostrava, Czech Republic

Keywords: Blood Dialysis Set, Haemodialysis, Mechanical Properties of PVC, Mechanical Tests.

Abstract: Dialysis sets are part of the dialysis circuit and are used every day. It is important to find out how the

dialysis sets behave under load and whether they retain their typical properties, which are the strength and

flexibility. Therefore, the mechanical properties of the dialysis sets are evaluated depending on the selected

physical parameters. For this reason, the sets are subject to temperature changes and changes in the pressure

of the peristaltic pump occlusion cylinders. To evaluate the mechanical properties of the dialysis sets, the

sets were subjected to stress tests and subsequent tests. The results were processed and analysed.

1 INTRODUCTION

Work deals with dialysis sets. Set are used during

blood dialysis. They ensure the transfer of blood

flowing from the patient's body to a blood-purifying

dialysis machine and to return the purified blood

back to the patient's body. The material from which

the dialysis sets are made is very important. Material

biocompatibility is an important component for the

success of hemodialysis. The set is not to produce

thrombogenic, inflammatory, immune or toxic

reactions. The dialysis sets must meet the criteria,

such as mechanical strength of material and optical

properties. Therefore it made of polyvinyl chloride.

Due to their chemical composition today they are

condemned. (Augustynek et al., 2014), (Neergaard

et al., 1971), (Liao et al., 2003) Therefore, the

products emerging from alternative materials. But

the use of PVC medical devices is still very

important, because some of the alternative materials

do not have the necessary properties. (Kostic et al.,

2017)

The result of the work should be an analysis of

the mechanical properties of dialysis sets. These

properties are dependent on physical parameters.

Mechanical properties mean the behaviour of

materials under the influence of external mechanical

forces. Sets are exposed to deformation by pressure

of occlusion cylinders and change in temperature of

saline. Dialysis sets must be strength, elasticity and

malleability to withstand stress tests. It is assumed

that under optimal conditions the dialysis sets meet

the standards. However, if the set goes through a

series of loads, measurements should demonstrate

the change of mechanical properties of dialysis sets.

This work focus on a group of AV dialysis sets,

which are most commonly used today. Because

dialysis sets are used during blood dialysis, their

properties may affect the quality of therapy.

Therefore, in this work, the sets undergo a load and

subsequent mechanical tests of physical properties.

By analyzing the obtained data we are able to

determine the limit of the mechanical load so as to

avoid a malfunction. (Brugger, 1999), (Beisser and

Oesterreich, 2018)

1.1 Properties of Dialysis Sets

Set should guarantee a safe path of blood from the

patient's body and return cleaned blood back. It

belongs to special medical supplies, which must

meet certain characteristics. In order to be able to

fulfil its function, set made from polyvinyl chloride.

To ensure the necessary features of the sets, PVC is

softened by the plasticizer during production. The

most commonly used plasticizer is di-ethylhexyl

phthalate (DEHP hereinafter). (Neergaard et al.,

1971), (Kostic et al., 2017)

Another reason for using PVC in making dialysis

sets is transparency and clarity. During the actual

228

Fiedorova, K., Augustynek, M., Fojtik, F. and Hlavackova, M.

Analysis of Mechanical Properties of Dialysis Sets.

DOI: 10.5220/0007555302280234

In Proceedings of the 12th International Joint Conference on Biomedical Engineering Systems and Technologies (BIOSTEC 2019), pages 228-234

ISBN: 978-989-758-353-7

blood dialysis is very important to check it by eye,

the nurse examines the blood. Thanks to these

characteristics nurse can see harm of dialysis tubing

or may capture a blood clot in the blood. (Di Landro

et al., 2005), (Latini et al., 2010)

Dialysis sets are important parts of the dialysis

device. There are two pressures on the dialysis set

during blood dialysis. The external pressure is

caused by the peristalsis pump. The effect of the

occlusion cylinders is to inject blood into the device

and further drive the circuit. Thus, a flow of a

certain value is created. Blood flowing through the

dialysis set produces internal pressure. During the

measurement, the temperature of the solution is

warmed to the temperature of the blood, ie it has a

temperature of 37℃. Therefore, the effect of the

temperature on the properties of the sets must be

considered. Optimum physical parameters under

which the dialysis is carried out, the temperature of

the solution through 37℃ and speed peristaltic pump

300 ml/min. (Rose et al., 2012), (Ronco and Levin,

2004), (Cihak and Augustynek, 2013), (Jeppsson

and Losell, 1994), (Brugger et al., 1997)

1.2 The Important Mechanical

Properties

The mechanical properties are evaluated in the work.

During testing, the sets undergo stress. The dialysis

set has to be characterized by basic features such as

strength, elasticity, toughness, malleability. We use

these properties in real use fatigue resistance.

Temperature plays a role in the material properties;

the influence of certain temperatures may cause a

change in the material structure. (Pelleg, 2013),

(Dowling, 2007)

The dialysis sets are produced from plasticized

polyvinyl chloride. Due to this fact, they are

characterized by strength, flexibility, elasticity, etc.

 Flexibility - elastic deformation before the

breach, evaluated using the modulus of

elasticity and stress.

 Strength - material resistance to deformation

and breach of external forces.

 Plasticity - the material retains permanent

deformation induced by external forces,

assessed using the relative size of the

permanent deformation prior to the breach.

 Toughness - resistant to high tension, this

feature is dependent on the strength and

plasticity. The measure of the work required

to deform a violation.

(Pelleg, 2013), (Dowling, 2007)

1.3 Standards Applied

The standard EN ISO 8638 Cardiovascular implants

and extracorporeal systems - Extracorporeal blood

circuit for haemodialyzer, haemodiafilter and

haemofilter deals with dialysis sets. The standard

lists the requirements for dialysis sets and tests that

test the dialysis sets. Tests are performed on the

testing machine, which will assess the ability of a

material to withstand the required stress. It records

the force which must be exerted in order to break the

material. Other values are modulus and elongation

of the material. (ČS EN ISO 6838, 2014)

1.4 Testing of Mechanical Properties

According to the standard above, dialysis sets are

subjected to a tensile test. This test is part of

mechanical static tests. The tensile strength is

performed on all materials because, thanks to the

measured values, we can further count the structural

elements and choose the appropriate material. The

tensile strength test indicates the force exerted,

variable elongation, elongation and material

constriction.

2 TESTING OF DIALYSIS SETS

Measurements were measured in were school lab

because the laboratory has a dialysis machine

Fresenius 4008 and other essential components that

are, dialysis sets Basic Line AV, dialyzers AV600S

and dialysate. Dialysis apparatus with dialyzer and

bag can be seen in Figure 1.

Figure 1: A – Bibag, B – Hemodialysis Fresenius 4008, C

– Dialysator AV 600S (Cihak and Augustynek, 2013).

Measurements are divided into several series. The

series differs in the used and set parameters. The

combination and the values of these parameters are

given in the following section. After the part of the

measurement has been completed, tensile tests are

carried out. The obtained data determine the

mechanical properties of the dialysis kits. The

assumed, that dialysis sets after a series of

Analysis of Mechanical Properties of Dialysis Sets

229

measurements when exposed to the highest pressure

and the highest temperature should have the greatest

degree of flexibility. Thus, there should be a greater

extension and the equation:



∙

∆

∙



∆

(1)

where  is force,  is the modulus of tensile

elasticity, 

∆

is tensile strength,  is original length,



∆

is elongation length. We can deduce that it will

increase the maximum force expended and the

modulus of elasticity decreases as the module

increases with stretching flexibility. (Pelleg, 2013),

(Beisser and Oesterreich, 2018), (Rose et al., 2012)

2.1 Determination of Possible Influence

of Changes of Physical Parameters

on Mechanical Properties of

Dialysis Sets

The tensile test is performed during the production

of the set. It is assumed that the sets will be used

under standard conditions. Such a set must have

certain features, such as flexibility, tightness,

plasticity, according to the standard. Therefore, the

aim of this work is to verify the effect of certain

physical parameters on the properties of the set.

(Hochman et al., 2015)

Work focuses on the influence of temperature

and pressure. The effect of temperature on the

mechanical properties of the set is derived from its

structure. PVC is made up of linear or slightly

branched chains. It is assumed that by varying the

temperature, the internal structure of the set will

expand or retract. At higher temperatures it will be

more flexible. On the contrary, the strength of the set

will fade. The effect of pressure on the mechanical

properties of the set will only affect the place of

direct action, not the length of the whole set. If the

pressure is increased, the material will weaken at the

point of application. This reduces the strength.

(Hochman et al., 2015)

2.2 Workflow Proposal

Since we cannot work with the biological material in

the laboratory, it is measured by with the

physiological solution heated to the temperature of

human blood, which is 37 ℃. Instead of connecting

to the vascular access use of circular bags, which

join dialysis sets. The saline which flows through the

circuit, it will drain back into the bag. The important

part is ripper for determining the mechanical

properties of dialysis sets, which we will evaluate.

Measurements must be carried out under steady

conditions (pressure, temperature, humidity).

Measurements on one set is always carried out only

once because dialysis sets are used for single use. In

the experimental measurement, two measuring

parameters are changed, namely the temperature of

the saline solution and the speed of the peristaltic

pump, thereby achieving a change in pressure.

Temperatures are used: 36.5ºC, 37ºC, and 37.5ºC

and speed of the peristaltic pump: 200 ml/min,

300 ml/min and 450 ml/min. Each combination of

measurement conditions shall be subjected to a four-

hour measurement.

Figure 2 shows a dialysis device. Part of a

dialysis machine belonging to the arterial part is

marked by the letters B, C and D. Part of dialysis

device marked with B is a peristaltic blood pump,

this section includes the insulin pump segment.

Under C is located the arterial blood pressure sensor

to which the set up via the transmitter. The heparin

pump is under D. The arterial part of the set also

includes the arterial chamber is located under the

letter E. The letters G, H, CH are the venous part of

the set. Point G shows the air sensor, here is placed

venous chamber. Below the H, there is a fuse in the

circuit that interrupts the blood flow in case of an

alarm. The pressure sensor can be found under the

letter CH. Letter A indicates the monitor. Under the

letter I, a physiological saline bag is found. Letter F

denotes a part, to which the inlet and outlet hoses are

attached, they are stored under the letter J. The

dialysis solution is made up of chemicals, which are

stored in parts marked K, L.

Figure 2: Dialysis machine.

2.3 Mechanical Test

Mechanical tests were carried out at VŠB-TUO at

the Faculty of Mechanical Engineering. It was tested

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on the device Testometric M500-50CT (see Figure

3). Those parts that were exposed to stress were

tested. In the case of experimental measurements, it

is peristaltic pump segment. Sets is characterized by

an inner diameter of 8 mm and an outside diameter

of 12 mm measured. The length of the test sample

was 6 cm. The sample was expanded at

100 mm/min. The samples were attached to the vice

of the instrument, each side being held at 0.5 cm.

The whole machine is controlled by software, where

the computer sets up the appropriate parameters

(length of the sample, the outer and inner diameter,

speed). After setting the appropriate parameters, the

machine starts.

After running a device the test material is

tensioned. The material to be tested should break

with a certain extension. The whole course of testing

is recorded in a graph of force versus extension.

Figure 3: Testing of dialysis kits.

3 DATA PROCESSING

Data obtained from material testing on mechanical

tests, calculations and measurements will be

processed and evaluated using tables and graphs.

Prolongation will depend on selected physical

quantities (flow and temperature).

The following variables (shows in Table 1) are

used in the work.

Table 1: Overview of the variables.

Quantity: Unit:

Temperature of saline solution

[℃]

Speed peristaltic pump blood [ml/min]

Mechanical tests are extension [mm]

Maximum developed force [N]

Young's modulus [MPa]

Length is expressed [mm]

3.1 Dependence of Extension on

Temperature

The chart (Figure 4) shows the dependence of the

extension on the saline temperature. Three

temperatures were set for each used speed. On the X

axis the values of the saline temperature [℃] were

plotted, and an extension [mm] was recorded on the

Y axis. When the peristaltic pump speed was set at

200 ml/min, the largest extension from the 60 mm

sample was 367.071 mm, this sample was recorded

at 37℃. For 300 ml/min was the largest extension

414,57 mm (37℃) and for 450 ml/min it was

350,573 mm. We can see that prolonging varies with

temperature, which satisfies the assumption. It is

apparent from the graph that the least elongation has

200 ml/min samples and gradually increase with an

increasing flow. At a speed of pump 450 ml/min, the

extension does not change much. In this graph, we

can see that at the temperature of 37 °C, the test

sample is most prolonged.

Figure 4: The dependence of prolongation on temperature.

3.2 Dependence of Maximum Force on

Temperature

The graph (Figure 5) shows the dependence of

maximum force on the temperature of the saline.

Values were obtained by the same procedure as in

the previous chapter. On X axis, the saline

temperature [°C] is showed, and the maximum force

[N] is recorded at Y axis. From the values in the

graph it is evident that as the temperature of the

solution increased, the force that was needed to

break the test sample decreased. In the sample

obtained from the measurement at 200 ml/min, the

smallest applied force was 407.9 N at 37.5°C. For

300 ml/min is the smallest applied force 458.9 N at

36.5°C and for 450 ml/min is force 458,3 N at

37.5°C. The force applied to the test sample was the

smallest in the sample test at a pump speed of

200 ml / min. However, the maximum force applied

to the samples at a speed of the pump 450 ml/min is

less than the maximum force that was applied to the

samples measured at 300 ml/min. It can be seen in

this figure (Figure 5) that the samples measured at

37 ° C are the most stable.

Analysis of Mechanical Properties of Dialysis Sets

231

Figure 5: The dependence of the maximum forces on the

temperature.

3.3 Dependence of Modulus on

Temperature

The graph (Figure 6) shows the dependence of the

modulus on the temperature. The temperature of the

saline [°C] was plotted on the X axis and a modulus

of elasticity [MPa] was recorded on the Y axis.

Considering that the modulus of elasticity is the

greater the stronger the test material, in theory, in

our case, this modulus of elasticity should decrease.

Because sets that have been exposed to more stress

become more flexible. For samples generated at

200 ml/min, the maximum modulus of elasticity is

91.166 MPa at 37°C. For speed 300 ml/min, the

highest elasticity model was 54.7 MPa at 37°C. The

highest modulus for 450 ml/min is 53.773 MPa at

36.5°C. This chart (Figure 6) we confirm

assumption, namely the gradual decrease of the

modulus of elasticity with the increasing stress of

the set. Only the values listed on the sets measured

at 36.5°C, are different.

Flow rate 200 ml/min Flow rate 300 ml/min Flow rate 450 ml/min

Figure 6: The dependence of elastic modulus on

temperature.

3.4 Dependence of Extension on Flow

Rate

The graph (Figure 7) shows the dependence of the

elongation on the speed of the peristaltic pump. At

each temperature, each measured speed was used.

Flow rates [ml/min] were plotted on the X axis, the

elongation [mm] was plotted on the Y axis. The

increasing flow rate should result in prolongation of

the test specimens. Because the material becomes

more flexible. We can see, that for samples

measured at 36.5°C, the longest extension is

368.106 mm at 450 ml/min. The largest extension

for samples with a temperature of 37°C is

414.579 mm at a pump speed of 300 ml/min. The

largest extension for samples with a temperature of

37.5°C is 339.464 mm at a pump speed of

450ml/min. The graph shows that the sets exposed

to 37 ° C are out of the assumption.

Temperature 36,5 °C Temperature 37 °C Temperature 37,5 °C

Figure 7: Dependence of elongation on flow rate.

3.5 Dependence of the Maximum Force

on Flow Rate

The graph (Figure 8) shows the dependence of the

maximum applied force on the flow rate. The flow

velocity values [ml/min] were plotted on the X axis,

and a maximum force [N] was recorded on the Y

axis. Higher blood pump speeds should result in a

weakening of the material. We can see, that for

samples measured at 36.5°C, the maximum force is

479.6 N at 450 ml/min. The maximum force for

samples with a temperature of 37°C is 501.1 N at a

pump speed of 300 ml/min. The maximum force for

samples with a temperature of 37.5°C is 483.2 N at a

pump speed of 300 ml/min. We can see that the

effect of flow does not have such an effect on the

maximum force used, because the measured values

are quite similar. The data of samples measured at

37°C and 300 ml/min are again different.

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Temperature 36,5 °C Temperature 37 °C Temperature 37,5 °C

Figure 8: The dependence of the maximum forces on the

flow rate.

3.6 Dependence of Modulus on Flow

Rate

In the graph (Figure 9) we can see the evaluation of

the dependence of the modulus on the flow rate. The

flow velocity values [ml/min] were plotted on the X

axis and the modulus of elasticity [MPa] on the Y

axis. For samples generated at 36.5°C, the maximum

modulus of elasticity is 53.773 MPa at 450 ml/min.

Samples measured at 37°C and 37.5°C using a

different flow rate meet the theory that the elastic

modulus decreases with increasing effort. The values

of all measured samples shows (Figure 9) that the

values for the samples exposed at 37°C, again stands

out. We can see that the model flexibility is

diminished with increasing temperature.

Figure 9: Dependence of the elastic modulus on the flow

rate.

4 DISCUSSION

All combinations of temperatures and flows were

tested, one by one. A part of the dialysis sets that

was exposed to peristaltic pumps was tested.

Considering the assumptions set, the samples

obtained at temperature 37°C do not meet the

requirements. But the remaining samples confirm

the assumptions. These fluctuations can be justified

by the fact that hemodialysis is normally used at

37°C and this temperature influences the production

of sets.

The elongation of the sample and the applied

force applied to the specimen increases with the

load, ie the flow temperature and the flow rate. In

addition, the elastic modulus of test samples which

were subjected to increased strain gradually

decreases. Expansion between 200 - 400 mm was

recorded, with increasing expansion increasing the

maximum applied force, which was measured in the

range of 400 - 500 N. The range of 40 to 100 MPa

include modulus of elasticity.

Said modulus could not be verified by

calculation, as Hook's law applies only to a small

linear part that cannot be deducted from the chart.

Beyond this, there is a large deformation of the

material.

5 CONCLUSION

From the analysis of the experimental measurements

it is possible to confirm the assumptions that the

change of the physical parameters (temperature of

the physiological solution and the flow) affects the

properties of the dialysis sets. Changing the

mechanical properties of dialysis sets is not so

significant as to affect the safety of the use of sets.

The sets proved to be a very solid and durable

material on mechanical tests. Situations that may

occur in health care facilities under the supervision

of professional staff will not expose a set of

conditions to fatal failure of the material.

ACKNOWLEDGEMENTS

The work and the contributions were supported by

the project SV4508811/2101Biomedical

Engineering Systems XIV'. This study was also

supported by the research project The Czech Science

Foundation (GACR) 2017 No. 17- 03037S

Investment evaluation of medical device

development run at the Faculty of Informatics and

Management, University of Hradec Kralove, Czech

Republic. This study was supported by the research

project The Czech Science Foundation (TACR)

ETA No. TL01000302 Medical devices

development as an effective investment for public

and private entities.

Analysis of Mechanical Properties of Dialysis Sets

233

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