A Wearable Insole System to Measure Plantar Pressure and Shear for People with Diabetes

Abstract

Pressure coupled with shear stresses are the critical external factors for diabetic foot ulceration assessment and prevention. To date, a wearable system capable of measuring in-shoe multi-directional stresses for out-of-lab analysis has been elusive. The lack of an insole system capable of measuring plantar pressure and shear hinders the development of an effective foot ulcer prevention solution that could be potentially used in a daily living environment. This study reports the development of a first-of-its-kind sensorised insole system and its evaluation in laboratory settings and on human participants, indicating its potential as a wearable technology to be used in real-world applications. Laboratory evaluation revealed that the linearity error and accuracy error of the sensorised insole system were up to 3% and 5%, respectively. When evaluated on a healthy participant, change in footwear resulted in approximately 20%, 75% and 82% change in pressure, medial–lateral and anterior–posterior shear stress, respectively. When evaluated on diabetic participants, no notable difference in peak plantar pressure, as a result of wearing the sensorised insole, was measured. The preliminary results showed that the performance of the sensorised insole system is comparable to previously reported research devices. The system has adequate sensitivity to assist footwear assessment relevant to foot ulcer prevention and is safe to use for people with diabetes. The reported insole system presents the potential to help assess diabetic foot ulceration risk in a daily living environment underpinned by wearable pressure and shear sensing technologies.

In-shoe plantar pressure measurement technologies for the diabetic foot: A systematic review

“…The evolution of developed equipment shows that the concept of an insole to assess plantar pressures is predominant [ [35] , [36] , [37] , [38] , [39] , [40] , [41] , [42] , [43] , [44] , [45] ]. While systems for measure plantar pressures are prevalent, it's noteworthy that some authors advocate for a hybrid model, simultaneously measuring shear forces in the horizontal plane along with vertical pressures on the shoe insole [ 35 , 36 , [46] , [47] , [48] , [49] , [50] , [51] , [52] ]. Shear results from friction of the foot with the insole itself, which may indicate potential overheating of the skin and an increased risk of injury [ 35 , 36 ].…”

“…This review identified several types of technology integrated into the proposed measurement systems, including resistive technology [ 44 , [53] , [54] , [55] , [56] , [57] , [58] , [59] , [60] , [61] , [62] , [63] , [64] , [65] ], piezoelectric [ 39 , 40 , 46 ], capacitive [ 41 , 52 , 66 ], inductive [ 49 , 51 ], fiber optics [ 38 , 50 , [67] , [68] , [69] , [70] , [71] , [72] ] and textile technology with piezoresistive features [ [73] , [74] , [75] ]. In Fig.…”

An exploratory in-situ dynamic mechanical analysis on the shearing stress–strain mechanism of human plantar soft tissue

“…The heel, the fifth, and the first metatarsal heads are tested at about 10%, 63%, and 72% of the foot length measured from the posterior-most point in the anterior–posterior direction, respectively, in reference to earlier research on foot morphology 24 and plantar pressure 25 . Based on the pressure distribution on the plantar 26 – 28 , the line M1-M2 is seen as perpendicular to the longitudinal direction, with both situated at the intersection of the 72% “meridian” and the axis of the first and second metatarsal bone. Similarly, M5 is situated at the intersection of the 63% "meridian" and the axis of the fifth metatarsal bone.…”

Triboelectric Insoles with Normal‐Shear Plantar Stress Perception

“…Plantar stress and its distribution allow numerous research, such as foot compositions and functions, [1][2][3] human biomechanics, [4] DOI: 10.1002/adfm.202313458 and body health, [5] calling for wearable awareness in the fields of footwear design, [6,7] athletic evaluation, [6,8] and disease diagnosis. [9][10][11][12] Similar to the normal stress in the vertical direction, the shear stress in the tangential direction that associates with friction has played a crucial role in human motion and tissue lesions, [3,13] demonstrating its significance in sports science (e.g., basketball [14] and soccer [15] ) and medical research (e.g., foot ulceration [16] and diabetes [17] ).…”

“…In contrast to traditional platform-type measurements in some fixed scenarios, [18,19] footwear systems (e.g., insoles, socks, and shoes) have exhibited considerable suitability in terms of the displacement distance, operational place, and duration, [10,11,20] thereby paving the way to flexibly measure plantar stress and applications such as motion monitoring and disease diagnosis. [21,22] In these footwear systems, the aforementioned normal and shear stress are measured based on different transduction principles, including optical, [23,24] capacitive, [7,25] magnetism, [26,27] and piezoresistance principles. [28] However, the constraints of the external power supply have impeded the portability and flexibility of insole systems in daily life.…”