CORDIS - EU research results

Reverberating abrasive single use piezo electric driven device

Final Report Summary - RASPED (Reverberating abrasive single use piezo electric driven device)

The RASPED project featured the full title: 'A single use device for the implantation of hip prostheses that will reduce the stress generated within the femur during surgery preventing intra / post-operative femoral fractures consisting of a reverberating abrasive single use piezo electric drive device'.

The project was structured into the following Work packages (WPs):

WP 1: Characterisation of component concept
Task 1.1 - Bone shearing force test model specification
The task's objectives were:
- to create a series of test that will generate clinical and mechanical testing models data;
- to enable the development and subsequent manufacture of rasp drive mechanism.
Task 1.2 - Bone cutting movement test model specifications
The task's objectives were:
- to define the optimum cutting stroke and angle for the removal of bone tissue from both the cortical and intramedullary canal.
Task 1.3 - Drive mechanism characterisation
The task's objectives were:
- to analyse the amount of movement and forces required by the cutter and design an appropriate drive device that will for fill these requirements.

WP 2: Development and production of the rasp unit
The WP's technical objective was:
- to produce a series of prototype rasps and associated tooling.
Task 2.2 - Prototype rasp production
The task's objective was:
- to produce a series of prototype rasps and associated tooling.

WP 3: Drive mechanism development and prototype production
The WP's technical objectives:-
- to develop the process science for the production of the drive head that will carry the rasp device and any additional tooling that may be required during the operation.
Task 3.2 - Development and prototype production of the electronic amplitude generation unit
The tasks's objectives were:
- to develop and produce a unit for the generation of the required voltages and frequency's to drive the piezoelectric stacks contained within the drive mechanism.

WP 4: Mechanical validation and trials
The WP's technical objectives were:
- validation of the drive mechanism with respect to the movement and force generation;
- evaluation of the rasp will be performed to determine the optimum material removal rate has been achieved.

WP 5: Pre-clinical validation trials
The WP's technological objectives were:
- to determine the optimum process for the sterilisation of the rasp components.

WP 6 Exploitation and market stimulation
The WP's technological objectives were:
- to develop and establish exploitation mechanisms for the project results.

WP 7: Project management
The WP aimed:
- to ensure that all knowledge is created, managed and disseminated in a coordinated and coherent manner, along with all technical activities, legal aspects and other issues;
- to ensure that all aspects of the European Commission requirements for communication and reporting are met;
- to coordinate the overall legal, contractual, financial and administrative management of the consortium;
- to coordinate gender equality, ethical and science and society aspects of the project.

The initial samples of the rasp tool were designed with three different cutting faces. Testing was performed on the three cutting edges to determine the most efficiently cutting edge for the removal of both cortical and trabecular bone tissue. Development of the auxiliary tooling was performed and as a result of this work an acetabulum reamer was developed. Initially three cutting configuration concepts were designed; however following testing only two of the concepts gave acceptable material removal comparable with exciting devices.

Two configurations of the hand held Piezo driven device (PZT) have been designed and manufactured. One of these designs was discussed in the month 12 meeting and consisted of a mechanical amplification. The other was designed using in-line PZT stacks to generate a direct force through the rasp unit. This unit was tested with the associated monitoring and measuring electronics. The results of the PZT showed it to be incapable of providing enough force or stroke to generate sufficient cutting action.
- Using the data from work package (WP) 1 the optimum cutting stroke and angles have been determined and have been used in the manufacture of the rasp. Three different types of cutting teeth geometries have been designed to identify whether full length strait cut, small cusps or angled full length teeth work worked more efficiently.
- Ten rasp designs, having a variety of different geometries, have been produced. Testing has determined three out of the ten to be chosen for further trials.
- Work has been carried out on the displacement and force required by the cutter and a new Piezo driven device was designed and manufactured.
- An appreciation of bone material removal characteristics by the rasp was used to define the final design of driving devices. Further trials using the different configuration of cutting teeth were used to optimise the drive unit design.
- Work to determine insertion force and oscillatory displacement optima with respect to bone removal vs. instantaneously induced and residual stress in the proximal femur was performed.
- Testing using the optimum rasped design with the calculated optimum conditions for the drive unit were performed. The results of this testing showed that the drive unit was incapable of producing sufficient force or movement to allow for material removal. Therefore, it was decided to stop testing with the PZT and concentrate on an alternative device. The alternative device considered was that of the woodpecker a device used for initial testing during year 1.
- Methods of producing working prototype rasps without major tooling investment have been investigated and quotations were obtained.
- Since CAD models can be readily scaled, prototype rasps have been produced quickly and at low cost having sizes appropriate to the bovine femurs. These have provided more meaningful results.
- A variety of methods for volume manufacture of the rasps has been investigated. A further design change to the rasp was made to allow for ease of manufacture and thus allow it to be easily integrated into commercial manufacture.
- A number 316L stainless steel samples were supplied to for Cytotoxicity testing for biocompatibility. These were in two forms, the first being flat plates with a known surface area and weight the second samples were of the actual rasped units and acetabulum reamers. The results of this testing showed that the sample remained negative.
- Work has been done on the auxiliary tooling required for the rasp introduction in to the femur and for the formation of the acetabulum cup into the pelvic.