Currently, the growing need for highly customized implants has become one of the key aspects to increase the life expectancy and reduce time and costs for prolonged hospitalizations due to premature failures of implanted prostheses. According to the literature, several technological solutions are considered suitable to achieve the necessary geometrical complexity, from the conventional subtractive approaches to the more innovative additive solutions. In the case of cranial prostheses, which must guarantee a very good fitting of the region surrounding the implant in order to minimize micromotions and reduce infections, the need of a product characterized by high geometrical complexity combined with both strength and limited weight, has pushed the research towards the adoption of manufacturing processes able to improve the product’s quality but being fast and flexible enough. The attention has been thus focused in this paper on sheet metal forming processes and, namely on the Single Point Incremental Forming (SPIF) and the Superplastic Forming (SPF). In particular, the complete procedure to design and produce titanium cranial prostheses for in vivo tests is described: starting from Digital Imaging and COmmunications in Medicine (DICOM) images of the ovine animal, the design was conducted and the production process simulated to evaluate the process parameters and the production set up. The forming characteristics of the prostheses were finally evaluated in terms of thickness distributions and part’s geometry. The effectiveness of the proposed methodology has been finally assessed through the implantation of the manufactured prostheses in sheep.

Main problems related to the adoption of magnesium alloys for temporary orthopedic prostheses manufacturing are (i) the need of an efficient production process and (ii) the high corrosion rate compared with the bone healing time. In this work, the single-point incremental forming (SPIF) process, an effective and flexible solution for manufacturing very small batches even composed by one piece, was investigated. Tests were conducted on AZ31B-H24 sheets and were aimed at understanding the effect of temperature on the mechanical characteristics (microstructure, hardness, and roughness) of the sheet after the above-mentioned forming process and their correlation with both the corrosion rate and the cytocompatibility. In addition, after the forming process, samples processed by SPIF were coated by electrospun polycaprolactone (PCL) to reduce the corrosion rate and to further improve the cytocompatibility. Grain refinement was achieved thanks to the combined effect of temperature and strain rate during forming and finer grain size resulted to improve the magnesium corrosion resistance. In simulated body fluids, the electrospun PCL-coated samples exhibited a slower pH increase compared with uncoated samples. No indirect cytotoxic effects were detected in vitro for MC3T3-E1 cells for both coated and uncoated samples. However, cells colonization was observed only on electrospun PCL-coated samples, suggesting the importance of the polymeric coating in promoting the adhesion and survival of seeded MC3T3-E1 cells on the implant surface.

An Mg-based alloy device manufactured via a superplastic forming process (Mg-AZ31+SPF) and coated using a hydrothermal method (Mg AZ31+SPF+HT) was investigated as a method to increase mechanical and osteointegration capability. The cell viability and osteointegrative properties of alloy-derived Mg AZ31+SPF and Mg AZ31+SPF+HT extracts were investigated regarding their effect on human mesenchymal stem cells (hMSCs) (maintained in basal (BM) and osteogenic medium (OM)) after 7 and 14 days of treatment. The viability was analyzed through metabolic activity and double-strand DNA quantification, while the osteoinductive effects were evaluated through qRT-PCR, osteoimage, and BioPlex investigations. Finally, a preliminary liquid mass spectrometry analysis was conducted on the secretome of hMSCs. Biocompatibility analysis revealed no toxic effect on cells’ viability or proliferation during the experimental period. A modulation effect was observed on the osteoblast pre-commitment genes of hMSCs treated with Mg-AZ31+SPF+HT in OM, which was supported by mineralization nodule analysis. A preliminary mass spectrometry investigation highlighted the modulation of protein clusters involved in extracellular exosomes, Hippo, and the lipid metabolism process. In conclusion, our results revealed that the Mg AZ31+SPF+HT extracts can modulate the canonical and non-canonical osteogenic process in vitro, suggesting their possible application in bone tissue engineering.

Sheet hydroforming (SHF) is a widely used metal forming process in aerospace and automotive industries due to its ability to produce complex shapes with near-net accuracy. SHF process parameters are usually optimized focusing on outputs such as shape accuracy and thickness distribution. However, in response to the increasing regulatory focus on energy efficiency and sustainability, integrating environmental performance into SHF optimization has become crucial. This study focuses on identifying proper environmental indicators, determined by means of life cycle assessment (LCA) and on analyzing them to assess their influence on the determination of the SHF workability window. SHF tests were conducted in different working conditions by varying the forming temperature and the oil pressure rate. For each test, thickness distribution and shape accuracy were considered as outputs for evaluating the manufacturing performance, whereas LCA models were used to assess the potential for the related direct and indirect environmental impact. Then, the most appropriate environmental outputs to be integrated into the process evaluation framework were determined.

The reshaping of End-of-Life (EoL) components by means of the sheet metal forming process has been considered largely attractive, even from the social and economic point of view. At the same time, EoL parts can often be characterized by non-uniform thicknesses or alternation of work-hardened/undeformed zones as the result of the manufacturing process. Such heterogeneity can hinder a proper reshaping of the EoL part, and residual marks on the reformed blanks can still be present at the end of the reshaping step. In a previous analysis, the authors evaluated the effectiveness of reshaping a blank with a deep-drawn feature by means of the Sheet Hydroforming (SHF) process: it was demonstrated that residual marks were still present if the deep-drawn feature was located in a region not enough strained during the reshaping step. Starting from this condition and adopting a numerical approach, additional investigations were carried out, changing the profile of the load applied by the blank holder and the maximum oil pressure. Numerical results were collected in terms of overall strain severity and residual height of the residual marks from the deep-drawn feature at the end of the reshaping step. Data were then fitted by accurate Response Surfaces trained by means of interpolant Radial Basis Functions and anisotropic Kriging algorithms, subsequently used to carry out a virtual optimization managed by multi-objective evolutionary algorithms (MOGA-II and NSGA-II). Optimization results, subsequently validated via experimental trials, provided the optimal working conditions to achieve a remarkable reduction of the marks from the deep-drawn feature without the occurrence of rupture.