**2. Tactile sensation and diabetic neuropathy**

detection of diabetic neuropathy (DPN) [1–3]. We consider the range of potential applications

We have conducted a number of studies on tactile sense-presentation technology that applies micro-vibrations using thin shape memory alloys (SMA) [1–11]. The SMA allows for a com-

Tactile-stimulus diagnostic techniques, such as the technique reported in this study, may be possible with other actuators such as small motors [12, 13], piezoelectric actuators [14], or pneumatic actuators [15]. However, each of these technologies requires large electromagnetic

Piezoelectric actuators need a driving voltage of the order of several tens of volts, and their inclusion of mechanical parts makes their application in portable devices difficult [14].

Our tactile-stimulus presentation technology that uses a thin SMA avoids the problems of size and power consumption. The present iteration of the device can be driven with a small

Quantitative diagnosis of DPN at present requires a machine costing at least several million yen and larger than 1 m on a side, such as nerve-conduction studies. Equipment for these tests, in addition to being cumbersome and expensive, requires skilled technicians for its operation. Some patients refuse a second examination because nerve conduction studies and electromyography studies can be quite painful. Many asymptomatic diabetes patients are left untreated because of the cost, difficulty, and pain caused by the current methods for quantitative diag-

In previous studies [1–3, 5–7], we have developed a range of simple, quantitative, and painless examination methods that use SMA, and the present study summarizes those studies and

A wide range of conditions contribute to hypoesthesia and/or peripheral nervous disorders, including the administration of anticancer drugs, DPN, vitamin deficiency, vasculitis, polyneuropathy, depression, alcohol dependence, infection, and uremia. However, the progress of the condition is generally slow, and most sufferers are initially unaware of its presence [16]. Peripheral neuropathy tests can be divided into two main types. The first is qualitative and includes the Achilles tendon reflex/vibration test. The second is nerve conduction studies (NCS), which involve complex and painful invasive examinations but provide quantified diagnoses. Both types require medical expertise and judgment and must be conducted by a healthcare professional. Patients have no access to their test results, making them less likely

Approximately, half of all patients with diabetes contract asymptomatic neuropathy [17]. As the causes of neuropathy are not limited to diabetes mellitus, it is assumed that there are many more asymptomatic neuropathy sufferers. Currently, patients are unable to perceive the condition themselves, and no simple quantification scale is available. Even patients whose condition is treatable may be unaware of its presence and therefore fail to seek treatment.

pact device that consumes little power and causes no pain to patients.

devices that require more power than that provided by a portable battery.

and the future potential of this technology.

nosis of the neurological effects of diabetes.

discusses future prospects.

to seek treatment.

battery [2, 3, 5–7].

110 Actuators

The sense of touch relies on four main tactile receptors in the skin: the Meissner's corpuscle, Merkel disc, Ruffini ending, and Pacinian corpuscle. As shown in **Figure 1**, Merkel discs are located in the epidermis and are approximately 10 μm in diameter. They are used to sense pressure and texture. Meissner's corpuscles are primarily located immediately below the epidermis and are between 30 and 140 μm in length and 40–60 μm in diameter. They are used to sense stroking and fluttering. Ruffini endings are also located in the dermis, have a length of approximately 0.5–2 mm, and are used for the sense stretching of the skin. Pacini corpuscles are located in the subcutis and are approximately 0.5–2 mm in length and 0.7 mm in diameter. Based on their response speed and size, the receptors are given four labels: fast adapting I and II (FA I and FA II) and slow adapting I and II (SA I and SA II).

The receptors are present at different densities in different regions of the human body. **Figure 2** [13] shows the innervation density in the hand, which is where most human tactile recognition takes place. Receptors are particularly dense in the fingers and especially in the tips. Human fingers are therefore sensitive to a range of stimuli. The response of the receptors is closely related to nervous system activity, and the tips of the fingers are therefore also densely supplied with capillary vessels. When a diabetic condition restricts the blood flow in the capillary

**Figure 1.** Tactile receptors of the skin [3].

While examining patients with multiple neuropathy-causing conditions, the underlying cause of any symptom is very difficult to distinguish, with any diagnostic method; thus, this chapter focuses on tactile anomalies and tactile reduction among the neurological abnormalities that

Quantitative Tactile Examination Using Shape Memory Alloy Actuators for the Early Detection…

http://dx.doi.org/10.5772/intechopen.75084

113

To confirm and diagnose the specific form of neuropathy that a patient has developed, an affected nerve must be biopsied from the patient, but this procedure is generally too invasive for the degree of suffering a patient is experiencing. Instead, clinicians administer a series of

Our tactile test method stimulates the following four main tactile receptors in the skin: the Meissner's corpuscle, the Merkel disc, the Ruffini ending, and the Pacinian corpuscle. Though it may also stimulate other receptors, this device clearly provides a tactile stimulus that at least stimulates the haptic receptors. Precise diagnostic methods require the application of electric current to a patient's nervous system and measuring response. These tests are painful, while our haptic stimulator causes no pain at all. We have not performed biopsy studies to conclusively demonstrate to diagnoses pathologically confirmed with DPN. But we have shown that the device can quickly, inexpensively, and painlessly assess a patient's tactile

In this study, a tactile device was developed that presented present a range of tactile stimuli to the fingers of a subject and then measured the response from the driving parameters of the

To generate the physical stimuli, an SMA wire was employed. Within the typical operating temperature range, SMA has two phases, each with a different crystal structure and therefore different properties. The first is a high-temperature phase, called the Austenite phase, and the second a low-temperature phase, called the Martensite phase. When the temperature exceeds a critical threshold (70°C), the SMA alternates between the two phases, causing the crystal structure, and therefore the shape of the SMA, to change. SMA has been widely used in actuation and sensing applications and in the aerospace, automotive, and biomedical sectors.

When SMA is formed into a thin wire, its length originally 3 mm at a low-temperature phase will change at a known temperature. In the current study, the SMA wire (Toki Corp., BioMetal, BMF75) was used to create a compact actuator, the characteristics of which are shown in **Figure 3**. When the temperature of an SMA wire passes T1 (68°C), the wire begins to shrink up to 5% lengthwise at the temperature T2, reaching a minimum at T2 (73°C). As the

As the alloy has an electrical resistance of 0.6 ohms per 1 mm, its length can be controlled by supplying a pulse current. This instantaneously increases the temperature, shrinking the wire.

tests to collate a program similar to quantitative diagnosis and treatment program.

response with novel technology in some clinical studies [1–3].

**3.1. A compact SMA actuator to generate micro-vibrations**

temperature is reduced, the wire gradually returns to its initial length.

**3. Design of the measurement device**

could indicate DPN.

tactile actuators.

**Figure 2.** Innervation density of tactile receptors [18].

vessels or destroys them, sensitivity to tactile sensations is restricted. Most diabetes patients, even at an early stage of the disease, have reduced sensitivity to tactile sensations in the fingers and feet. The extent of the decline is a measure of the progress of the condition.

Diabetic neuropathy (DPN) is caused by the degradation of axons in peripheral nerves, which decrease nerve function in slow progression. The rate of degeneration depends on the ability of the patients to control their glycemic index; thus, it varies with each individual. Nerves are distributed throughout the body and vary in function. For that reason, neurological diagnostic methods vary depending on the parts and functions of the nerve distributed, thus making uniform standards difficult to formulate. For example, in the event of dysuria arising from DPN, the patient may consult a urologist. However, a patient who feels discomfort or numbness in the sole of the foot owing to DPN may consult an orthopedist, and both patients may not consult a diabetes specialist until their condition has degraded significantly. DPN presents a variety of symptoms that patients are likely to consult a range of specialists for the same underlying condition. Diagnosis of DPN is so complicated and time-consuming that even many diabetes specialists are not equipped for quantitative studies.

Neuropathy can also be caused by other diseases, but DPN is distinguished by a few symptoms.

DPN presents diffuse neuropathy, with bilateral symmetry. The nerve failure is focused on sensory functions, and DPN tends to progress from peripheral nerves inward.

While examining patients with multiple neuropathy-causing conditions, the underlying cause of any symptom is very difficult to distinguish, with any diagnostic method; thus, this chapter focuses on tactile anomalies and tactile reduction among the neurological abnormalities that could indicate DPN.

To confirm and diagnose the specific form of neuropathy that a patient has developed, an affected nerve must be biopsied from the patient, but this procedure is generally too invasive for the degree of suffering a patient is experiencing. Instead, clinicians administer a series of tests to collate a program similar to quantitative diagnosis and treatment program.

Our tactile test method stimulates the following four main tactile receptors in the skin: the Meissner's corpuscle, the Merkel disc, the Ruffini ending, and the Pacinian corpuscle. Though it may also stimulate other receptors, this device clearly provides a tactile stimulus that at least stimulates the haptic receptors. Precise diagnostic methods require the application of electric current to a patient's nervous system and measuring response. These tests are painful, while our haptic stimulator causes no pain at all. We have not performed biopsy studies to conclusively demonstrate to diagnoses pathologically confirmed with DPN. But we have shown that the device can quickly, inexpensively, and painlessly assess a patient's tactile response with novel technology in some clinical studies [1–3].

In this study, a tactile device was developed that presented present a range of tactile stimuli to the fingers of a subject and then measured the response from the driving parameters of the tactile actuators.
