Research aim
Custom made prostheses are nowadays the gold standard for the reconstruction of skull bones after trauma or tumors, since the bony deficiency substitution needs that both functional and aesthetic requirements must be fulfilled at the same time. The simultaneous satisfaction of both requirements depends on different factors: the functional compatibility is strongly related to the adopted material and process, whereas the aesthetical suitability depends on the reconstruction technique implemented to define the prosthesis geometry. Surgical techniques still contemplate the usage of autologous bone from the patient; it is then modelled when necessary in the operating theater. Nevertheless, using this methodology the patient is subjected to a double surgery (harvesting+implant) with a consequent disablement at the harvesting site; surgery duration is significant, since in the same operation, harvesting, modeling and implant of the bone have to be performed. At the same time, no actual assessment of the mechanical reliability of the device is possible. On the contrary, for huge skull defects, custom made prostheses are preferred although some difficulties are still present: starting from CT scans, the missing part is reconstructed and the prosthesis is manufactured in metal (Ti alloy), polymeric material (polymethylmetacrilate-PMMA) or ceramic (hydroxyapatite-HA). Also in these cases the procedure is not fully optimized as metallic prostheses, obtained using time consuming machining techniques, are often not suited to clinical requirements while PMMA and HA prostheses not always present adequate mechanical performances.
At the same time, from a technological point of view, the scientific literature presents some preliminary studies on innovative techniques applied to manufacture customer oriented prostheses; the main drawback is that these studies are focused on technological feasibility aspects and on the process reliability, while the problems related to the clinical perspectives or to the patient side are completely neglected.
More in detail, some of the cited studies are particularly focalized on those problems that typically exist during the preliminary steps, before the prosthesis implant; on the contrary, these studies completely neglect the primary problems related to clinical aspects, which affect the final part of the therapeutic procedure (i.e. implant biocompatibility, anchorage method, surface integrity). The above specified aspects have been not well analyzed yet; for this reason further efforts are still necessary to fully assess the suitability of the proposed procedures or to highlight new ones which could represent the breakthrough for problems related to the reconstruction of maxillo-facial or cranial defects.
Thus, the main goal of the present RP is to develop, using a multidisciplinary approach, a ready to use, easy to be implemented, procedure that allows to:
- overcome problems in prosthesis manufacturing due to morphological complexities (intricate shapes which present problems for the machining operations);
- improve the quality of the components related to both geometry (dimensional accuracy) and performance (mechanical characteristics and thickness uniformity);
- strongly decrease prosthesis manufacturing time as to have a maximum delivery time of 48 hours;
- enhance prosthesis performances in terms of both anchoring efficacy (to be optimized) and biocompatibility issues (manufacturing process can eventually affect biocompatibility of the Ti alloy).
Below a possible clinical application is presented: once the manufacturing process for a Ti custom made prosthesis will be available, such a procedure will be an output of the present RP.
The procedure starts from the patient CT scan (step 1), in order to precisely reconstruct the virtual model of the anatomic district (step 2) and, from the latter, the CAD geometry of the prosthesis through mirroring technique(step 3) is obtained. The procedure ends with the prosthesis manufacturing (step 4) and implant on the patient (step 5).
The technology for prosthesis manufacturing (SPF or SPIF) has to be chosen evaluating both geometrical characteristics and urgency of having the manufactured component.
As a matter of fact, SPIF guarantees a faster process set up leading to shorter waiting times for the patient, hence probably becoming the most suitable technology in those cases in which an open wound involves an infection risk. On the contrary, due to absence of dies, SPIF is not efficient when very intricate geometries are needed (zigomatic, maxilla or mandibular bone reconstruction): in this case SPF using purposely made ceramic disposable dies might be the right choice.
From an industrial point of view, SPIF and SPF technologies can be transferred to the manufacturing of high quality/ highperformance prostheses thanks to the validation of such technological processes trough experimental tests.
From an economic point of view, the introduction of innovative manufacturing techniques based on the paradigm of flexibility of the production process, will reduce the standard cost even of a single production lot (custom made prosthesis). Lastly, from a clinical point of view, the above described procedure will allow the decrease of the infection risk and the improvement of the patient recovery (due to time reduction of both surgical and post-surgical period).
An innovative approach like that investigated in the present RP allows to test and to improve new surgical techniques or to apply existing ones to different anatomic districts. In fact, due both to reduction of the time required for prosthesis production and to higher part accuracy, less invasive surgeries will be possible to replace missing bony parts, which are difficult to reproduce with the conventional methods.
The multidisciplinary approach, that characterizes the RP, requires a full integration among all the branches of knowledge involved in the study; in this way the limits of the actual state of the art will be overcome. In particular, the success of the proposed RP will promote the knowledge exchange and the skill improvement among both the different research groups and the single researchers involved in the network. The researchers expertise will be as a consequence enhanced by the introduction of innovative techniques in the bioengineering field, which are used up to now only for basic research in manufacturing applications. In this way, the base of knowledge from an industrial point of view will result strongly improved. Similarly, the introduction of these innovative techniques in the bioengineering domain will enrich the set of procedures and solutions that nowadays can be used for clinical applications.
Finally, from a clinic point of view, the definition of a new “customer oriented” procedure will allow a significant improvement in social terms increasing the quality of the clinical treatment for patients affected by serious pathologies.
The RP aim will be also supported by experimental activities; at the end of the 3-year research period will be thus available a wide base of knowledge for future developments in other research applications. More deeply, during the RP, experimental investigations will be executed to study the use of innovative alloys and techniques to the bioengineering sector. Such results will be subsequently extended to other clinical and productive contexts: in fact material characterization will be executed in order to define both the rheological behaviour (in plastic and superplastic conditions) and the performances of the formed parts.
In addition to the mechanical features and process optimization, cytotoxicity analyses will be executed to evaluate the effect of the implemented processes on the alloy biocompatibility; by doing that the correct integration with the host organism and the absence of negative effects on the patient health will be considered. In the same way, the design of customized prostheses will be optimized by means of FE numerical analyses; actually, even if this tool is poorly used in bioengineering applications, it results essential to minimize the operating risks and to ensure the good implant result.