Geometric Cuts by an Autonomous Laser Osteotome Increase Stability in Mandibular Reconstruction With Free Fibula Grafts: A Cadaver Study.

BACKGROUND: Nonunion and plate exposure represent a major complication after mandibular reconstruction with free fibula flaps. These drawbacks may be resolved by geometric osteotomies increasing intersegmental bone contact area and stability. PURPOSE: The aim of this study was to compare intersegmental bone contact and stability of geometric osteotomies to straight osteotomies in mandibular reconstructions with free fibula grafts performed by robot-guided erbium-doped yttrium aluminum garnet laser osteotomy. STUDY DESIGN, SETTING, SAMPLE: This cadaveric in-vitro study was performed on fresh frozen human skull and fibula specimens. Computed tomography (CT) scans of all specimens were performed for virtual planning of mandibular resections and three-segment fibula reconstructions. The virtual planning was implemented in a Cold Ablation Robot-guided Laser Osteotome. PREDICTOR/EXPOSURE/INDEPENDENT VARIABLE: For predictor variables, straight and geometric puzzle-shaped osteotomies were designed at resection of the mandible and corresponding fibula reconstruction. MAIN OUTCOME VARIABLES: The primary outcome variable was the stability of the reconstructed mandible investigated by shearing tests. Moreover, secondary outcome variables were the duration of the laser osteotomies, the contact surface area, and the accuracy of the reconstruction, both evaluated on postsurgical CT scans. COVARIATES: Covariables were not applicable. ANALYSES: Data were reported as mean values (± standard deviation) and were statistically analyzed using an independent-sample t-test at a significance level of α = 0.05. Root mean square deviation was tested for accuracy. RESULTS: Eight skulls and 16 fibula specimens were used for the study. One hundred twelve successful laser osteotomies (96 straight and 16 geometrical) could be performed. Geometric osteotomies increased stability (110.2 ± 36.2 N vs 37.9 ± 20.1 N, P < .001) compared to straight osteotomies. Geometric osteotomy of the fibula took longer than straight osteotomies (10.9 ± 5.1 min vs 5.9 ± 2.2 min, P = .028) but could provide larger contact surface (431.2 ± 148.5 mm2 vs 226.1 ± 50.8 mm2, P = .04). Heat map analysis revealed a mean deviation between preoperational planning and postreconstructive CT scan of -0.8 ± 2.4 mm and a root mean square deviation of 2.51 mm. CONCLUSION AND RELEVANCE: Mandibular resection and reconstruction by fibula grafts can be accurately performed by a Cold Ablation Robot-guided Laser Osteotome without need for cutting guides. Osteotomy planning with geometric cuts offers higher stability and an increased bone contact area, which may enhance healing of the reconstructed mandible.

Parameter optimization in a finite element mandibular fracture fixation model using the design of experiments approach.

Only a few mandibular bone finite element (FE) models have been validated in literature, making it difficult to assess the credibility of the models. In a comparative study between FE models and biomechanical experiments using a synthetic polyamide 12 (PA12) mandible model, we investigate how material properties and boundary conditions affect the FE model's accuracy using the design of experiments approach. Multiple FE parameters, such as contact definitions and the materials' elastic and plastic deformation characteristics, were systematically analyzed for an intact mandibular model and transferred to the fracture fixation model. In a second step, the contact definitions for the titanium screw and implant (S-I), implant and PA12 mandible (I-M), and interfragmentary (IF) PA12 segments were optimized. Comparing simulated deformations (from 0 to -5 mm) and reaction forces (from 10 to 1'415 N) with experimental results showed a strong sensitivity to FE mechanical properties and contact definitions. The results suggest that using the bonded definition for the screw-implant contact of the fracture plate is ineffective. The contact friction parameter set with the highest agreement was identified: titanium screw and implant µ = 0.2, implant and PA12 mandible µ = 0.2, interfragmentary PA12 mandible µ = 0.1. The simulated reaction force (RMSE = 26.60 N) and surface displacement data (RMSE = 0.19 mm) of the FE analysis showed a strong agreement with the experimental biomechanical data. The results were generated through parameter optimization which means that our findings need to be validated in the event of a new dataset with deviating anatomy. Conclusively, the predictive capability of the FE model can be improved by FE model calibration through experimental testing. Validated preoperative quasi-static FE analysis could allow engineers and surgeons to accurately estimate how the implant's choice and placement suit the patient's biomechanical needs.

Apical Medium Flow Influences the Morphology and Physiology of Human Proximal Tubular Cells in a Microphysiological System.

There is a lack of physiologically relevant in vitro human kidney models for disease modelling and detecting drug-induced effects given the limited choice of cells and difficulty implementing quasi-physiological culture conditions. We investigated the influence of fluid shear stress on primary human renal proximal tubule epithelial cells (RPTECs) cultured in the micro-physiological Vitrofluid device. This system houses cells seeded on semipermeable membranes and can be connected to a regulable pump that enables controlled, unidirectional flow. After 7 days in culture, RPTECs maintained physiological characteristics such as barrier integrity, protein uptake ability, and expression of specific transporters (e.g., aquaporin-1). Exposure to constant apical side flow did not cause cytotoxicity, cell detachment, or intracellular reactive oxygen species accumulation. However, unidirectional flow profoundly affected cell morphology and led to primary cilia lengthening and alignment in the flow direction. The dynamic conditions also reduced cell proliferation, altered plasma membrane leakiness, increased cytokine secretion, and repressed histone deacetylase 6 and kidney injury molecule 1 expression. Cells under flow also remained susceptible to colistin-induced toxicity. Collectively, the results suggest that dynamic culture conditions in the Vitrofluid system promote a more differentiated phenotype in primary human RPTECs and represent an improved in vitro kidney model.

Quantitative Assessment of Point-of-Care 3D-Printed Patient-Specific Polyetheretherketone (PEEK) Cranial Implants.

Recent advancements in medical imaging, virtual surgical planning (VSP), and three-dimensional (3D) printing have potentially changed how today's craniomaxillofacial surgeons use patient information for customized treatments. Over the years, polyetheretherketone (PEEK) has emerged as the biomaterial of choice to reconstruct craniofacial defects. With advancements in additive manufacturing (AM) systems, prospects for the point-of-care (POC) 3D printing of PEEK patient-specific implants (PSIs) have emerged. Consequently, investigating the clinical reliability of POC-manufactured PEEK implants has become a necessary endeavor. Therefore, this paper aims to provide a quantitative assessment of POC-manufactured, 3D-printed PEEK PSIs for cranial reconstruction through characterization of the geometrical, morphological, and biomechanical aspects of the in-hospital 3D-printed PEEK cranial implants. The study results revealed that the printed customized cranial implants had high dimensional accuracy and repeatability, displaying clinically acceptable morphologic similarity concerning fit and contours continuity. From a biomechanical standpoint, it was noticed that the tested implants had variable peak load values with discrete fracture patterns and failed at a mean (SD) peak load of 798.38 ± 211.45 N. In conclusion, the results of this preclinical study are in line with cranial implant expectations; however, specific attributes have scope for further improvements.

Rapid carbon nanotubes suspension in organic solvents using organosilicon polymers.

A strategy for a simple dispersion of commercial multi-walled carbon nanotubes (MWCNTs) using two organosilicones, polycarbosilane SMP10 and polysilazane Ceraset PSZ20, in organic solvents such as cyclohexane, tetrahydrofuran (THF), m-xylene and chloroform is presented. In just a few minutes the combined action of sonication and the presence of Pt(0) catalyst is sufficient to obtain a homogeneous suspension, thanks to the rapid hydrosilylation reaction between SiH groups of the polymer and the CNT sidewall. The as-produced suspensions have a particle size distribution <1µm and remain unchanged after several months. A maximum of 0.47 and 0.50mg/ml was achieved, respectively, for Ceraset in THF and SMP10 in chloroform. Possible applications as polymeric and ceramic thin films or aerogels are presented.

Cytotoxicity evaluation of polymer-derived ceramics for pacemaker electrode applications.

Ceramics are known to be chemically stable, and the possibility to electrically dope polymer-derived ceramics makes it a material of interest for implantable electrode applications. We investigated cytotoxic characteristics of four polymer-derived ceramic candidates with either electrically conductive or insulating properties. Cytotoxicity was assessed by culturing C2C12 myoblast cells under two conditions: by exposing them to material extracts and by putting them directly in contact with material samples. Cell spreading was optically evaluated by comparing microscope observations immediately after the materials insertion and after 24 h culturing. Cell viability (MTT) and mortality (LDH) were quantified after 24-h incubation in contact with the materials. Comparison was made with biocompatible positive references (alumina, platinum, biocompatible stainless steel 1.4435), negative references (latex, stainless steel 1.4301) and controls (no material present in the culture wells). We found that the cytotoxic properties of tested ceramics are comparable to established reference materials. These ceramics, which are reported to be very stable, can be microstructured and electrically doped to a wide range of conductivity and are thus excellent candidates for implantable electrode applications including pacemakers.