Multi-source Harvesting Systems for Electric Energy Generation on Smart Hip Prostheses - Biomedical Engineering Systems and Technologies - page 60

improve joint function [3]. The ordinary methodology to improve prostheses' function
has been based on the research of new designs, new materials, new fixation techniques
and new surgical techniques [4-6]. Although the everlasting life span is an essential
requirement for the next healthcare bio-systems generations, the 20-year revision rate
of current orthopaedic prostheses is still higher than 20%. Demographic changes and
scientific breakthroughs are the main reasons ascribed to the increase in the number
of primary and revision joint replacements [3], as well as the strong demand for joint
replacements and revisions predicted for the coming years [7]. After the first revision
procedure, the risk of failure increases even more [8]. Furthermore, the increase in the
number of inpatients less than 65 years due to joint disorders [9] is also being con-
sidered an important reason that supports the hypothesis of developing a new method-
ology to design prostheses with the ability to control their own life span. Current hip
prostheses are passive implants because they are not smart enough to promote maximal
bone-implant interaction. They match their design methodology with a design “not to
know” and “not to act against”.
Instrumented prostheses have been developed since the 60's of the 20th century [10].
Their methodological basis is to perform in-vivo measurement and data storage func-
tions to optimize passive implants, surgical procedures, preclinical testing and physio-
therapy programs [11, 12]. They have been used to validate models of the physiological
environment and customize physiotherapy programs [13, 14]. Contact forces and mo-
ments in the joint, temperature distribution along the implant, articular motions, mis-
alignments and detection of hip loosening [15-22] are the main quantities which have
been collected by instrumented implants. Telemetric platforms for orthopaedic implants
are being optimized to minimize electric energy consumption [22, 23]. Also, activation
circuits to wake up deep sleep electronics have already been developed to instrument
hip prostheses [24].
Several causes of implant failures were already identified [25]. Loosening, infection,
instability, heterotopic ossification or fractures not only can conduct to pain and inabil-
ity to walk, to self-care and to perform activities of daily living, but also can cause
cardiovascular, pulmonary, renal, arterial, nerve or infectious complications, or even
malignancy. More than 80% of the non-success surgical procedures are due to loosen-
ing of the prosthetic stem and cup [26]. Methods for hip loosening detection in hip im-
plants, as well as to identify the regions impaired by this progressive failure throughout
the implant's life span, are currently being proposed [19, 26]. Efficient power manage-
ment circuits were designed to energize telemetric system of smart hip implants [27].
Even though the number of methods and configurations to transduce energy from the
surrounding environment into electric energy is increasing [28-32], few research efforts
have been conducted to provide electric power supply for instrumented hip prosthesis.
Vibration-based energy harvesting is being considered the most appropriate method to
generate electric energy to supply the active elements of instrumented prostheses [27].
In order to enable loosening detection, an electromagnetic power transducer was re-
cently proposed by Morais et al. [27] to harvest electrical energy from the human gait
to supply smart hip prostheses. However, it was designed only with a single generator,
which decreases the reliability of the electric power generation because it is not a re-
dundant structure for power supplying. No studies have been reported about methods to
ensure high reliability of the electric energy generation on instrumented prostheses.