Chapter 7: Designing and Machining
The shape of the living body is formed and maintained by self-healing and by
regeneration, on the base of proliferation of cells in vivo.

In this chapter, we learn thebasic designing and machining including the design of the artificial organs to be applied
to the living body.

7.1 Designing
7.1.1 Specifications
In organism, information is retained as a gene in the nucleotide sequence of
deoxyribonucleic acid (DNA) in the nucleus of the cell.

Cells, tissues and organs areformed with proteins synthesized according to the sequence information of the base.
The organism adapts to repetitive selection by the surrounding circumstances.
Cells form a tissue as a group of cells with repeating division.
proliferation is controlled by various factors.

A cell starts division, stops division, ordies in the interaction with the surrounding cells.

For example, a cell stops division,

when the cell is surrounded by the neighboring cells.
the division number exceeds a certain value.
organization of cells changes.

Division andA cell makes apoptosis, when

When the control changes, theCancer might occur in the similar process.

The behavior of the cell depends on the several factors: the cycle of cell mitosis, thenumber of division, the number of neighboring cells (coordination number) (Fig. 7.1)
[45].

The relation between factors can be discussed by simulation of formation of thecolony of cells.

Fig. 7.1: Simulation of cell colony.
© Shigehiro Hashimoto 2013, Published by Corona Publishing Co., Ltd. Tokyo, Japan

The design of the machine, on the other hand, is expressed by the specification.
Functionality and materials are described in the specification.
pump to send the liquid”.
the pressure head.

Let us see the case of “aThe energy source is selected according to the flow rate and

The material is selected according to the type of liquid (cf.

corrosive liquid) and the environmental conditions (cf. temperature).

The diameter ofthe connecting line is adjusted to the predetermined size.
The conventional products are available for designing machines.

Japanese

Industrial Standards (JIS), and International Standards by International
Organization for Standardization (ISO) are used for the reference.

For example,

standardized screws of size, shape and strength are used as the element of the machine.
There are various types in the pump (Fig. 7.2).

The piston bellows type of pumpcontrols the flow rate by the stroke volume and the beats (Fig. 7.2 (a)).

In thecentrifugal type of pump, the shape of the impeller is selected in conjunction with therotational speed of the impeller (Fig. 7.2 (b)).

The screw-type of pump controls theflow rate by the rotational speed of the screw (Fig. 7.2 (c), Fig. 6.16 and (b)).

Theroller pump (see 6.2.3) controls the flow rate by the peripheral speed and the diameterof the tube.

In Fig. 7.2, tubes of the inner diameter of 15 mm are connected at the inlet

and the outlet.

Fig. 7.2: Types of artificial heart.

© Shigehiro Hashimoto 2013, Published by Corona Publishing Co., Ltd. Tokyo, Japan

The artificial heart pumps the blood. Pumps are classified into two types: thepositive displacement types (piston bellows-type, screw-type, etc.) and the turbo
types (centrifugal type, etc.).

The cyclic variation of the rotational speed of theimpeller (or the screw) in the turbo type can generate pulsatile flow.

The density of theblood is close to that of the water. The viscosity of the blood is several times higher
than that of the water.
corrosive liquids.

Since the blood includes electrolyte, the blood is classified in

The thrombus formation and the destruction of blood cells should

be inhibited.
The washout effect may inhibit the growth of clot at the wall shear rate higher than
500 s－1 [25].

In the pulsatile flow, the clot growth in the stagnation area may be

inhibited by keeping the period shorter than 2 seconds, while the wall shear rate is lower
than 100 s－1 [29].

The erythrocytes destruction decreases at the shear rate periodicallybelow 300 s－1 [15] (see Fig. 4.42).
The machine might be used not only for the application limited to the initial design,
but also for the application beyond the initial strength limit. To keep the margin of thestrength, the design should include several times of the multiplied coefficient called “thesafety factor”.

The safety factor would become as small as possible to promote

downsizing.
In vivo, homeostasis is maintained by balance between antagonized actions in therange between thresholds.

Regeneration and self-repairing maintain the function of theentire system beyond the threshold. For example, when the blood vessel is broken,
the agent contained in blood or in the vessel walls (platelets and blood coagulation
factors) are activated to close the fracture surface, and to repair the vessel wall (see Fig.
6.18 (b)).

7.1.2 Draft
The contents of the design are expressed in the draft.
should be communicated by the drawings.

The intent of the design

In the drawings, three-dimensional designis projected onto a two dimensional plane.

© Shigehiro Hashimoto 2013, Published by Corona Publishing Co., Ltd. Tokyo, Japan

The third angle projection method is commonly used in the drawings.
of a front view, a plan view, and a side view.
aspects of the solid.
top.

It consists

The front view shows the representative

A plan view is placed above the front view, as viewed from theA side view is placed at the right side of the front view, as viewed from the right(Fig. 7.3).

Fig. 7.3: Third angle projection method.

The drawings are drawn with lines.

Each type of line has information (Fig. 7.4).

“Solid line” shows the outline. “Dashed line” shows the symmetry line.
introduces the dimension.

“Two-dot chain line” is used for hidden lines.

“Thin line”
Hatchingshows the cross section.

© Shigehiro Hashimoto 2013, Published by Corona Publishing Co., Ltd. Tokyo, Japan

Fig.7.4: Drawing.

The unit of mm is used for the dimension.

Several symbols are used in thedrawing: Φ for the diameter, R for the radius, ∠ for the angle, and ∟ or ⊥ for theright angle.
When the dimensional accuracy is required, the notation is used as follows.
range of dimension is displayed.
displayed with the number.

The

When there is a direction of the range, + or － is

When the dimension has engagement, the symbol of H isused with the corresponding dimension. For example, the surfaces are processed to fit
each other between the bearing and the shaft.
For the accuracy of the finished surface, ▽ symbol is used as ▽, ▽▽, or ▽▽▽.
The larger of the number of ▽ shows the smaller surface roughness (see 7.1.3).

For

fitting symbol, the combination of letters and numbers is used to show the relative
dimension, such as “H8 and h8” to the corresponding dimension.

7.1.3 Surface roughness
Minute irregularity of the surface is measured as "roughness." The roughness ismeasured by several methods: tracing the surface with a tip of the needle attached to thelever (Fig. 7.5), or using the reflection of light at the surface.

© Shigehiro Hashimoto 2013, Published by Corona Publishing Co., Ltd. Tokyo, Japan

Fig. 7.5: Measurement of roughness.

Most of the finished surface has unevenness at the order of micrometers.
unevenness of a large cycle is called "waviness".

The

The surface can be finished withsmaller roughness by polishing with the smaller diameter of the abrasive grains.
The roughness is displayed by several parameters: the arithmetic averageroughness Ra (Fig. 7.6), the maximum height Ry (between the peak and the valley)(Fig. 7.7), the ten-point average roughness Rz (Fig. 7.8), and the root mean squareroughness Rs.

Data of height at the surface are often displayed by the scale enlarged

against that of distance to emphasize the surface irregularities.

The unevenness along

the selected line segment on the surface is displayed in the two-dimensional way in Figs.
7.5-7.7.

© Shigehiro Hashimoto 2013, Published by Corona Publishing Co., Ltd. Tokyo, Japan

Fig. 7.6: Arithmetic average roughness: Ra.

Fig. 7.7: Maximum height: Ry.

The arithmetic average roughness Ra is calculated as the mean value of thedeviation from the averaged surface of the unevenness at the sampled line segment l.
1 𝑙
𝑅𝑎 = � |𝑦(𝑥)| 𝑑𝑑
𝑙 0

(7.1)

The ten-point average roughness Rz at the sampled line l is calculated as the averagevalue of the difference from the summit to the bottom.

The data of the height of thesummit and the depth of the valley from the mean plane are used.

The sum of the five

© Shigehiro Hashimoto 2013, Published by Corona Publishing Co., Ltd. Tokyo, Japanabsolute values of the height (from the maximum to the fifth) and five absolute valuesof the depth (from the maximum to the fifth) is divided by five.

𝑅𝑧 =|𝑦1 + 𝑦2 + 𝑦3 + 𝑦4 + 𝑦5 | + |𝑦6 + 𝑦7 + 𝑦8 + 𝑦9 + 𝑦10 |
5

(7.2)

Fig. 7.8: 10-point average roughness: Rz.

The mean square roughness (Rs) is the root of the average of the squares ofdeviations (y) from the mean surface.

1 𝑙
𝑅𝑠 = � � {𝑦(𝑥)}2 𝑑𝑑
𝑙 0

(7.3)

Relationship between the roughness of the surface and the wavelength of the lightdetermines the optical properties such as reflection and refraction.

The gap between

the summit and the valley less than the wavelength of visible light (approximately 1μm) makes a mirror.
The diameter of the human cells is the order of micrometers.

Unevenness of

micrometer order at the surface scaffold affects the behavior of the cell.

© Shigehiro Hashimoto 2013, Published by Corona Publishing Co., Ltd. Tokyo, Japan

7.2 Machining
7.2.1 Type of machining
Cells form tissues, organs, and an individual by mitosis, proliferation,differentiation, and orientation (see Fig. 4.33).

Living body is exposed to themagnetic, the electrical and the mechanical fields.

The behavior of the cells is

modified by the magnetic [32-34], electrical [35], and mechanical [14, 16, 27]
stimulations.
Magnetic, electric, and mechanical fields affect the orientation of the cell.

Whenelectrical pulses are applied on cells, the behavior of the cell changes (Fig. 7.9):
adhesion of cells to the scaffold is controlled, and subsequent differentiation andproliferation of cells are promoted by control of the density of cells [35].

The resultsof the research would be applied to the tissue technology in the field of regenerative
medicine.

Fig. 7.9: Cell culture with electric stimulation.

At the machine, each part is manufactured by the machining.
destruction of the material is applied in the machining.

Deformation and

The machining is categorized

into cutting, grinding, polishing, extrusion, melting, molding, welding, and pressurebonding.
The machine tool includes the drilling machine, the turning machine, the millingmachine, the planar, and NC (numerical controlled) machine tool.

© Shigehiro Hashimoto 2013, Published by Corona Publishing Co., Ltd. Tokyo, JapanAt the spinning, the melted material is squeezed from the die, and cooled.
solvent around the thread is vaporized, or the thread is coagulated in a solvent.

The
At theelectro spinning, the charged material is jetted to form thin threads by the high voltage.
The process is applied to make the scaffold of the cell culture.
At a surgical operation, a part of a living body is cut.

Because a rotary saw mightcatch the soft tissue around the bone, a reciprocating saw is applied to the cutting of thebone (Fig. 7.10). The idea comes from the difference in deformation of the workpiece.
The bone of the lesser compliance is selectively cut by the reciprocating saw.

Fig. 7.10: Saw-tooth.

It is not easy to define the machining position in vivo.
techniques such as MRI help positioning.

Tomographic imaging

The technology is applied to athree-dimensional display of the end position of the surgical tool, or to recognition of
the character of the tissue.

Several novel systems are introduced for the training andthe planning of surgery.
The image display during surgery is also implemented.

The online image helps toconfirm the position and to guide the direction during the surgery. The system shows
the operative field to multiple surgeons for the surgical training.
The image periodically fluctuates with the respiratory movement of the lung andwith the beating movement of the heart. The technique to compensate the position
synchronized with the periodic movement realizes the still image.

The contrivanceassists the vision of the operator.
© Shigehiro Hashimoto 2013, Published by Corona Publishing Co., Ltd. Tokyo, Japan

7.2.2 Finishing and biological reaction
A virgin surface is formed in the material at cutting by the blade.

The chip side of

the blade is called “rake face”. The finished surface side of the blade is called "flank"(Fig. 7.11). Friction between the rake face and the chips affects the cutting force.
Friction phenomena at the flank affect the finish of the machined surface.

Thelubrication by cutting fluids reduces the cutting force, and improves the finish of thesurface by stabilizing the cutting conditions.

Some lubrications use the chemical

reaction at the virgin surface of the cutting.

The cutting fluid also has the cooling

effect.

Fig.7.11: Cutting.

In polishing, the unevenness of the surface is grinded by the mechanism of abrasivewear.
The machining method is selected according to the finishing accuracy.

Structuralchanges in the vicinity of the material surface at the machining change the mechanicalproperties near the surface.
hardening”.
material.

The plastic deformation at the surface causes “work"Quenching", and "annealing" are applied to change the property of the

Because the surface property of the material is easily varied by machining,temperature should be controlled during the machining.
In the processing using a mold, the mold release agent is applied to remove theproduct from the mold.

At the processing of material to be implanted in vivo, it isnecessary to pay attention to reaction of the living body with the residual release agents© Shigehiro Hashimoto 2013, Published by Corona Publishing Co., Ltd. Tokyo, Japanbesides the original material.
The material of synthetic polymer includes monomer.

The synthetic polymer has

the distribution of molecular weight, because of variations at the degree ofpolymerization. The component of the small molecular weight (the small dimensions)can dissolved from the bulk material, and has higher reactivity with living body (Fig.
7.12).

Through dissolution in the physiological fluid, the component may show the

toxicity and may cause inflammatory reactions.

Fig. 7.12: Synthetic polymer in organ.

7.2.3 Assembly
Every part is not formed before assembly in vivo.

Every adjacent part is formed

relatively each other. Several portions incorporate complementarity-redundantvariations, which allow modification adapted to the circumstances.

While maintaining

the diversity, the organism adapts to the surrounding environment.
The damaged vessel wall is clogged and repaired in vivo by several steps: adsorptionof platelets, and clot formation.

Elements for repair are contained in the vessel walland in the blood (see Fig. 6.18).

Does the fluid supply network system containelements for the repair in the system itself?

The blood clotting process also plays rollat the adhesive function between tissues.
The materials of the machine are connected by several ways: chemical reaction,
crimping at high pressure, and welding at high temperature.

At the prosthetic valve,rupture of the weld between the strut and the valve seat had occurred.

Without

welding, the durability was improved by cutting from one piece of material.
© Shigehiro Hashimoto 2013, Published by Corona Publishing Co., Ltd. Tokyo, Japan

Fine droplets of the ink are arranged in the ink jet printer.

The principle may be

applied for the alignment of cells in three dimensions.
A photocurable resin is hardened in a liquid.

Through the process, the solid can beformed along the trajectory of the optical path.

The technique is called

photolithography, and is applied to a micro machining [48, 49] (Fig. 7.13).

The

technique is suitable to form a model of a micro capillary, which has an internal
diameter of 5 μm (Fig. 7.14).

The technique can be applied to build complex

structures in three dimensions by stacking the layers.
In conventional surgical operations, threads have been used for the suture, and thestitches have been removed after fixation of the tissue.

When the biodegradable thread

is applied, the stitches need not to be removed after operation.

Fig. 7.13: Photolithography.

© Shigehiro Hashimoto 2013, Published by Corona Publishing Co., Ltd. Tokyo, Japan

Fig. 7.14: Micro channel.

Questions

Q 7.1: Create a specification of a pump for the left ventricle of human adult.

Q 7.2: Draw cross section of the connector including symmetry axis shown in Fig. 7.15.

Q 7.3: List representative value of surface roughness, and explain each definition ofroughness.

Fig. 7.15: Connector.
© Shigehiro Hashimoto 2013, Published by Corona Publishing Co., Ltd. Tokyo, Japan