Multiscale Mechanical Characterization of Polyether-2-ketone (PEKK) for Biomedical Application

Polyether-ether-2-ketone (PEKK) is a high-performance thermoplastic polymer used in various fields, from aerospace to medical applications, due to its exceptional mechanical and thermal properties. Nonetheless, the mechanical behavior of 3D-printed PEKK still deserves to be more thoroughly investigated, especially in view of its production by 3D printing, where mechanical properties measured at different scales are likely to be correlated to one another and to all play a major role in determining biomechanical properties, which include mechanical strength on one side and osteointegration ability on the other side. This work explores the mechanical behavior of 3D-printed PEKK through a multiscale approach, having performed both nanoindentation tests and standard tensile and compression tests, where a detailed view of strain distribution was achieved through Digital Image Correlation (DIC) techniques. Furthermore, for specimens tested up to failure, their fractured surfaces were analyzed through Scanning Electron Microscopy (SEM) to clearly outline fracture modes. Additionally, the internal structure of 3D-printed PEKK was explored through Computed Tomography (CT) imaging, providing a three-dimensional view of the internal structure and the presence of voids and other imperfections. Finally, surface morphology was analyzed through confocal microscopy. The multiscale approach adopted in the present work offers information about the global and local behavior of the PEKK, also assessing its material properties down to the nanoscale. Due to its novelty as a polymeric material, no previous studies have approached a multiscale analysis of 3D-printed PEKK. The findings of this study contribute to a comprehensive understanding of 3D-printed PEKK along with criteria for process optimization in order to customize its properties to meet specific application requirements. This research not only advances the knowledge of PEKK as a 3D-printing material but also provides insights into the multifaceted nature of multiscale material characterization.

Form Factors as Potential Imaging Biomarkers to Differentiate Benign vs. Malignant Lung Lesions on CT Scans

Indeterminate lung nodules detected on CT scans are common findings in clinical practice. Their correct assessment is critical, as early diagnosis of malignancy is crucial to maximise the treatment outcome. In this work, we evaluated the role of form factors as imaging biomarkers to differentiate benign vs. malignant lung lesions on CT scans. We tested a total of three conventional imaging features, six form factors, and two shape features for significant differences between benign and malignant lung lesions on CT scans. The study population consisted of 192 lung nodules from two independent datasets, containing 109 (38 benign, 71 malignant) and 83 (42 benign, 41 malignant) lung lesions, respectively. The standard of reference was either histological evaluation or stability on radiological followup. The statistical significance was determined via the Mann-Whitney U nonparametric test, and the ability of the form factors to discriminate a benign vs. a malignant lesion was assessed through multivariate prediction models based on Support Vector Machines. The univariate analysis returned four form factors (Angelidakis compactness and flatness, Kong flatness, and maximum projection sphericity) that were significantly different between the benign and malignant group in both datasets. In particular, we found that the benign lesions were on average flatter than the malignant ones; conversely, the malignant ones were on average more compact (isotropic) than the benign ones. The multivariate prediction models showed that adding form factors to conventional imaging features improved the prediction accuracy by up to 14.5 pp. We conclude that form factors evaluated on lung nodules on CT scans can improve the differential diagnosis between benign and malignant lesions.

Ex vivo biomechanical evaluation of polyester and polyblend suture techniques to perform equine laryngoplasty

OBJECTIVE

To validate the use of a polyblend tape suture in equine laryngoplasty (PL).

STUDY DESIGN

Experimental study.

ANIMALS

Thirty-two cadaveric larynges.

METHODS

Each larynx was randomly assigned to 1 of 4 groups: PL with polyblend tape suture (TigerTape), without (TT) or with a cannula (TTC) in the muscular process of the arytenoid cartilage, and PL with polyester suture (Ethibond), without (EB) or with a cannula (EBC). Construct stiffness, total migration, creep, and drift values were measured after 3000 cycles. The specimens were then loaded to failure to assess their residual properties: load at failure, total energy, displacement, and 2 stiffness coefficients.

RESULTS

After cyclic testing, the total migration and creep were lower in TTC (6.36 ± 1.20 mm; 1.35 ± 0.38 mm/s) than in EB (11.12 ± 4.20 mm; 3.39 ± 2.68 mm/s) and in the TT constructs (11.26 ± 1.49 mm; 3.20 ± 0.54 mm/s); however, no difference was found with EBC (9.19 ± 3.18 mm; 2.14 ± 0.99). A correlation was found between total migration and creep (R = .85). The TTC constructs failed at higher loads (129.51 ± 33.84 N) than EB (93.16 ± 18.21 N) and EBC (81.72 ± 13.26 N) whereas the EB and EBC constructs were less stiff than TT and TTC (P < .001).

CONCLUSION

Biomechanical properties were generally superior for the TTC constructs tested under cyclical loading. The TT and TTC constructs failed at a higher load than EB and EBC constructs. The cannula in TTC and EBC reduced the failure at the muscular process.

CLINICAL SIGNIFICANCE

These results provide evidence to support the in vivo evaluation of the polyblend tape suture with or without a cannula in the muscular process for laryngoplasty in horses.

Colour and Texture Descriptors for Visual Recognition: A Historical Overview

Colour and texture are two perceptual stimuli that determine, to a great extent, the appearance of objects, materials and scenes. The ability to process texture and colour is a fundamental skill in humans as well as in animals; therefore, reproducing such capacity in artificial (‘intelligent’) systems has attracted considerable research attention since the early 70s. Whereas the main approach to the problem was essentially theory-driven (‘hand-crafted’) up to not long ago, in recent years the focus has moved towards data-driven solutions (deep learning). In this overview we retrace the key ideas and methods that have accompanied the evolution of colour and texture analysis over the last five decades, from the ‘early years’ to convolutional networks. Specifically, we review geometric, differential, statistical and rank-based approaches. Advantages and disadvantages of traditional methods vs. deep learning are also critically discussed, including a perspective on which traditional methods have already been subsumed by deep learning or would be feasible to integrate in a data-driven approach.

Mechanical Behavior of Elastic Self-Locking Nails for Intramedullary Fracture Fixation: A Numerical Analysis of Innovative Nail Designs

Intramedullary nails constitute a viable alternative to extramedullary fixation devices; their use is growing in recent years, especially with reference to self-locking nails. Different designs are available, and it is not trivial to foresee the respective in vivo performances and to provide clinical indications in relation to the type of bone and fracture. In this work a numerical methodology was set up and validated in order to compare the mechanical behavior of two new nailing device concepts with one already used in clinic. In detail, three different nails were studied: (1) the Marchetti-Vicenzi's nail (MV₁), (2) a revised concept of this device (MV₂), and (3) a new Terzini-Putame's nail (TP) concept. Firstly, the mechanical behavior of the MV₁ device was assessed through experimental loading tests employing a 3D-printed component aimed at reproducing the bone geometry inside which the device is implanted. In the next step, the respective numerical model was created, based on a multibody approach including flexible parts, and this model was validated against the previously obtained experimental results. Finally, numerical models of the MV₂ and TP concepts were implemented and compared with the MV₁ nail, focusing the attention on the response of all devices to compression, tension, bending, and torsion. A stability index (SI) was defined to quantify the mechanical stability provided to the nail-bone assembly by the elastic self-locking mechanism for the various loading conditions. In addition, results in terms of nail-bone assembly stiffness, computed from force/moment vs. displacement/rotation curves, were presented and discussed. Findings revealed that numerical models were able to provide good estimates of load vs. displacement curves. The TP nail concept proved to be able to generate a significantly higher SI (27 N for MV₁ vs. 380 N for TP) and a greater stiffening action (up to a stiffness difference for bending load that ranges from 370 Nmm/° for MV₁ to 1,532 Nmm/° for TP) than the other two devices which showed similar performances. On the whole, a demonstration was given of information which can be obtained from numerical simulations of expandable fixation devices.

Data from cyclic tensile tests on sutured organs to evaluate creep behaviour, distraction, and residual thread strength

A number of applications in the surgical practice are based on tensile sutures aimed to keep soft tissues in place and compensate the exit of neuropathies, prolapses or general tissue relaxation. Long-term behaviour of these constructs need to be carefully examined in order to define tensile forces to be applied and to compare different suture anchors. Data here reported refer to equine laryngoplasties, where a suitable loading system has been designed in order to be able to test sutures in-sito, applying known forces ("On-site testing of sutured organs: an experimental set up to cyclically tighten sutures" (Pascoletti et al., 2020 [1])). The loading protocol was made of two steps: in the first step, 3000 loading cycles have been performed; in the following step, a tensile test up to rupture was performed. Cyclic load/displacement curves allow evaluating suture distraction, as a consequence of suture migration and/or soft tissues creep. Tensile curves allow evaluating the residual thread strength and its ultimate displacement. These data can provide a detailed insight of long-term suture behaviour and can be a reference to compare different threads and/or suture anchors.

Prosthetic Hip ROM from Multibody Software Simulation

The pre-operative planning of a hip arthroplasty entails the choice of the prosthetic hip model and of the position of both joint components with reference to bone. Assessing the impact of geometrical factors on the final hip range of motion (ROM) is not trivial, since it requires performing 3D evaluations. Nonetheless, it deserves to be studied since hip impingement and dislocation are still relevant complications in hip arthroplasty. This work pertains a numerical model for the assessment of the hip ROM in relation to cotyle position. External/internal rotation is considered as a benchmark, and multiple combinations of acetabular anteversion/inclination are considered. According to results, over two hundred different geometric configurations can be examined in few minutes, and the cotyle position can be so optimized with relevant benefits in term of hip ROM.

Multibody Models for the Analysis of a Fall From Height: Accident, Suicide, or Murder?

The final subject position is often the only evidence in the case of the fall of a human being from a given height. Foreseeing the body trajectory and the respective driving force may not be trivial due to the possibility of rotations and to an unknown initial position and momentum of the subject. This article illustrates how multibody models can be used for this aim, with specific reference to an actual case, where a worker fell into a stair well, prior to stair mounting, and he was found in an unexpected posture. The aim of the analysis was establishing if this worker was dead in that same place, if he had been pushed, and which was his initial position. A multibody model of the subject has been built ("numerical android"), given his stature and his known mass. Multiple simulations have been performed, following a design of experiments where various initial positions and velocity as well as pushing forces have been considered, while the objective function to be minimized was the deviation of the numerical android position from the actual worker position. At the end of the analysis, it was possible to point how a very limited set of conditions, all including the application of an external pushing force (or initial speed), could produce the given final posture with an error on the distance function equal to 0.39 m. The full analysis gives a demonstration of the potentiality of multibody models as a tool for the analysis of falls in forensic inquiries.

Numerical Simulation of an Intramedullary Elastic Nail: Expansion Phase and Load-Bearing Behavior

The Marchetti-Vicenzi's nail is an intramedullary device where six curved nails are kept straight by a closing ring in order to allow their insertion into the medullary canal of a long bone; in a following step, these nails stabilize the fracture due to the ring withdrawal and to the consequent elastic expansion of the nails. Pre-clinical testing of this sort of device is strongly advocated in order to be able to foresee their stability inside the medullary canal and to quantify their stiffening action on a broken bone. In this numerical work, an MB (Multi Body) model of the device has been developed, with the dual purpose of evaluating forces between the bone and the system components during its progressive opening and verifying the behavior of the stabilized bone when it undergoes external loading. Different solutions, for flexible body modeling (discretization with lumped parameters, “flexible body,” “FE Part”), have been analyzed and compared in terms of accuracy of results and required computational resources. Contact parameters have been identified and criteria to simplify geometries and therefore to reduce simulation times have been given. Results have allowed to demonstrate how a moderate lateral force is able to dislocate the fracture and how the final position of the retention nut can be optimized. On the whole, a tool for the pre-clinical testing of elastic intramedullary nails has been given.

Clinical Assessment of Dental Implant Stability During Follow-Up: What Is Actually Measured, and Perspectives

The optimization of loading protocols following dental implant insertion requires setting up patient-specific protocols, customized according to the actual implant osseointegration, measured through quantitative, objective methods. Various devices for the assessment of implant stability as an indirect measure of implant osseointegration have been developed. They are analyzed here, introducing the respective physical models, outlining major advantages and critical aspects, and reporting their clinical performance. A careful discussion of underlying hypotheses is finally reported, as is a suggestion for further development of instrumentation and signal analysis.

Expression of periostin in human breast cancer

Background:

Periostin is a secreted adhesion protein, normally expressed in mesenchime-derived cells. Aberrant expression of the periostin gene in epithelial tumours seems to play a role in angiogenesis and metastases.

Aims:

To investigate periostin expression in a consecutive series of breast carcinomas and correlate it with established biological and prognostic factors.

Methods:

A consecutive series of 206 breast carcinomas was investigated by immunohistochemistry with a specific antiperiostin antibody. Immunohistochemical expression of oestrogen and progesterone receptors, Ki-67 (MIB-1), HER-2/neu, VEGF-A, VEGFR-1 and VEGFR-2 was analysed. Periostin expression was also investigated in MCF-7 and MDA-468 cell lines by immunohistochemistry, western blot and quantitative RT-PCR. Localisation of periostin was investigated in MCF-7 cells by the green fluorescent protein (GFP) approach.

Results:

Periostin was highly expressed in carcinoma cells, but not in normal breast tissues. The pattern of expression was mainly cytoplasmic. However, in 12% of cases a nuclear reactivity was observed. Nuclear periostin significantly correlated with tumour size, and with expression of oestrogen receptor, progesterone receptor, VEGF-A, VEGFR-1 and VEGFR-2. A nuclear localisation of periostin was also observed in MCF-7 and MDA-468 cell lines. In MCF-7 cells the nuclear localisation of periostin was also shown by transfection of a vector expressing a GFP-periostin chimeric protein.

Conclusions:

Results indicate that the aberrant gene expression of periostin in breast cancer cells is associated with an abnormal nuclear localisation of the protein. The nuclear localisation of periostin in breast cancer may induce significant biological effects.

Expression of periostin in human breast cancer: Biological and clinico-pathological correlations

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Background: Mesenchyme-specific genes are highly expressed by various types of human cancers. Recent lines of evidence suggest that periostin, a myoepithelial/basal gene, may play a role in the biology of breast cancer. Periostin is involved in metastatic process by taking part in mechanisms of adhesion and migration of epithelial cells. Furthermore, periostin seems to have a role in tumor angiogenesis through the up-regulation of vascular endothelial growth factor receptors in endothelial cells. We aimed at investigating the immunohistochemical expression of periostin in breast cancer and its correlation with established biological and prognostic factors. Methods: We performed immunohistochemical analysis of periostin in a consecutive series of 206 tumor samples from 200 patients with early breast carcinoma. To this aim, we used a specific antiperiostin antibody (Biovendor Laboratory Medicine, Inc., Palackeho 56, 612 00 Brno, Czech Republic). The intensity of immunoreactivity was scored as 0, 1, 2 or 3 denoting negative, weak, moderate and strong staining, respectively. Therefore, for statistical analysis, the periostin expression level for each case was putatively defined as positive if the predominant intensity was =1. We also analyzed immunohistochemical expression of Ki-67 (MIB-1), HER-2/neu, VEGF, VEGFR-1 and VEGFR- 2. Results: Periostin was found to be highly expressed by carcinoma cells, whereas it was absent in normal breast tissues. The pattern of expression was mainly cytoplasmic, although in some cases (11%) a nuclear reactivity was observed. A cytoplasmic expression was found in 108 out of 189 (57%) evaluable cases. Interestingly, a significant correlation was found between periostin expression and VEGF and VEGFR-1 (Spearman's rank test rho =0.37, p <0.0001 and rho=0.26, p=0.0005, respectively). Conclusions: These results strengthen the hypothesis of a relationship between periostin and vascular endothelial growth factor system. The role of periostin in angiogenesis and in other relevant molecular pathways in breast carcinoma deserves to be further investigated.

No significant financial relationships to disclose.