Grupos Investigadores

Miembros del Grupo

López de Arancibia, Aitziber
Alaña Olivares
López Barberena

Líneas de Investigación

  • Análisis de Estructuras Metálicas
  • Estabilidad de Estructuras con Alta Sensibilidad a las Imperfecciones
  • Optimización topológica
  • Uniones para Estructuras Reticulares

Palabras Clave

  • Aplicaciones Biomecánicas
  • Caracterización Experimental
  • Estabilidad Estructural
  • Estructuras Lattice
  • Estructuras Monocapa
  • Fabricación Aditiva
  • Modelización Matemática y Simulación
  • Optimización topológica
  • Pandeo de Láminas
  • Uniones Semi-rígidas

Publicaciones Científicas desde 2018

  • Autores: Ruiz de Galarreta Moriones, Sergio (Autor de correspondencia); Jeffers, J. R. T.; Ghouse, S.
    ISSN: 0264-1275 Vol.189 2020 págs. 108546
    Cellular materials are gaining interest thanks to developments in additive manufacturing. Whilst Finite Element Analysis (FEA) is commonly used to obtain the mechanical behaviour of these structures, different modelling and simulation methodologies are followed in literature. Consequently, there is not a dear procedure to accurately evaluate the mechanical properties of porous structures. This study presents a method to perform FEA of lattice structures with accurate results. All inputs required to simulate compression testing of lattices in FEA were investigated, these included the modelling type, element size, number of unit cells required, boundary conditions and the material model. The effect of these variables on the modulus and yield strength of a lattice structure was studied. Lattices with two unit cell structures, varying unit cell sizes and relative densities were additively manufactured in stainless steel, compression tested and compared to FE simulations. The material model for the FE simulations was obtained from tensile testing individual micro-struts of varying diameters. FE simulation results were in good agreement with the experimental results with an average error for the modulus and yield strength of -10% and 17% respectively. The methodology presented should provide a foundation to accelerate development and adoption of these structures. (C) 2020 The Authors. Published by Elsevier Ltd.
  • Autores: Borghi, A. (Autor de correspondencia); Rodríguez Florez, Naiara; Ruggiero, F.; et al.
    ISSN: 1617-7959 Vol.19 N° 4 2020 págs. 1319-1329
    Sagittal craniosynostosis consists of premature fusion (ossification) of the sagittal suture during infancy, resulting in head deformity and brain growth restriction. Spring-assisted cranioplasty (SAC) entails skull incisions to free the fused suture and insertion of two springs (metallic distractors) to promote cranial reshaping. Although safe and effective, SAC outcomes remain uncertain. We aimed hereby to obtain and validate a skull material model for SAC outcome prediction. Computed tomography data relative to 18 patients were processed to simulate surgical cuts and spring location. A rescaling model for age matching was created using retrospective data and validated. Design of experiments was used to assess the effect of different material property parameters on the model output. Subsequent material optimization¿using retrospective clinical spring measurements¿was performed for nine patients. A population-derived material model was obtained and applied to the whole population. Results showed that bone Young¿s modulus and relaxation modulus had the largest effect on the model predictions: the use of the population-derived material model had a negligible effect on improving the prediction of on-table opening while significantly improved the prediction of spring kinematics at follow-up. The model was validated using on-table 3D scans for nine patients: the predicted head shape approximated within 2 mm the 3D scan model in 80% of the surface points, in 8 out of 9 patients.
  • Autores: Alaña Olivares, Markel (Autor de correspondencia); López de Arancibia, Aitziber; Pradera Mallabiabarrena, Ainara; et al.
    ISSN: 1751-6161 Vol.98 2019 págs. 357 - 368
    As result of the advances made in additive manufacturing in recent years, the design of porous materials with controlled mechanical properties has gained importance due to their capability to offer case-specific solutions in multiple applications. In terms of biomaterials, the use of lattice structures provides a considerable variety of mechanical and geometric properties that can enhance osseointegration and reduce stress shielding. In this paper, the elastic response of a modified face-centered cubic (FCC) unit cell was studied, and analytical expressions for macroscopic effective Young's moduli, shear moduli and Poisson's ratios were obtained, thus providing the necessary parameters for the homogenization of the unit cell. The analytical expressions of the homogenization parameters open the possibility for implementation in other research fields, such as topology optimization. Timoshenko beam theory was used to model the struts of the modified FCC unit cell and a finite element analysis using shear flexible beam elements was performed to assess the accuracy of the analytical expressions. In addition to modelling the bending of the beams, axial and torsional displacements were also considered for a more detailed analysis. It can be concluded that the expressions obtained represent the elastic behavior of the modified FCC unit cell with high accuracy.
  • Autores: Rodríguez Florez, Naiara; Flórez Tapia, Ane Miren; Jeelani, N.U.O.; et al.
    ISSN: 1010-5182 Vol.47 N° 1 2019 págs. 170 - 178
    Purpose Late deformity/indentation is well-recognised following fronto-orbital remodelling (FOR) for metopic synostosis. We hypothesise that if damage to temporalis muscle were a contributor, the thickness of soft tissue and bone in the affected area would be reduced. Materials and methods Soft tissues and bone were separately segmented and reconstructed three-dimensionally from computed tomograms of 8 patients 1.5¿18 years post-FOR performed at 16 ± 2 months for metopic synostosis and from 8 age-matched controls. Soft tissue (taken as proxy for temporalis muscle) and bone thickness overall and in the indented areas were computed. Results Post-FOR, three-dimensional soft tissue thickness maps demonstrated temporalis extending upwards but falling short of the indented area. Overall skull thickness increased with age post-FOR (logarithmic fit R2 = 0.71) and for controls (R2 = 0.90). Although immediately post-FOR the future indented area had a thickness of 98% of control, it decreased linearly to 64% 16 years later (Pearson's r = 0.84). Conclusion These findings suggest that late post-FOR deformity/indentation is enhanced by limited upward extension (or retraction downwards) of temporalis muscle, while bone thickness in the affected area gradually decreases. This supports the hypothesis that aberrant re-attachment of the temporalis muscle makes a material contribution to late deformity following FOR for metopic synostosis.
  • Autores: Llavori, I. (Autor de correspondencia); Giner, E.; Zabala, A.; et al.
    ISSN: 0013-7944 Vol.214 2019 págs. 534 - 543
  • Autores: Mondal, A.; Rodríguez Florez, Naiara; O'Hara, J.; et al.
    ISSN: 0256-7040 Vol.35 N° 3 2019 págs. 501 - 507
    PURPOSE: Cranial lacunae (foci of attenuated calvarial bone) are CT equivalents of "copper beating" seen on plain skull radiographs in children with craniosynostosis. The qualitative presence of copper beating has not been found to be useful for the diagnosis of intracranial hypertension (IH) in these patients. 3D morphometric analysis (3DMA) allows a more systematic and quantitative assessment of calvarial attenuation. We used 3DMA to examine the relationship between cranial lacunae and IH in children with Crouzon and Apert syndromic craniosynostosis. METHODS: Patients were divided into IH and non-IH groups defined on an intention-to-treat basis. Pre-operative CT scans were converted into 3D skull models and processed to quantify lacunae as a percentage of calvarium surface area (LCP). This was done on individual bone and whole skull basis. RESULTS: Eighteen consecutive children with Crouzon's syndrome and 17 with Apert syndrome were identified. Median age at CT scan was 135 days (range 6-1778). Of the 35 children, 21 required surgery for IH at median age of 364 days (range 38-1710). Of these 21 children, 14 had lacunae with mean LCP of 3% (0-28%). Of the 14 non-IH children, 8 had lacunae with mean LCP of 2% (0-8%). LCP was not significantly different between IH and non-IH groups. Parietal bones were most likely to show lacunae (IH 14/21, non-IH 9/14), followed by occipital (IH 8/21, non-IH 3/14), and frontal (IH 6/21, non-IH 2/14).
  • Autores: Breakey, R.W.F.; Knoops, P.G.M.; Borghi, A.; et al.
    ISSN: 0032-1052 Vol.142 N° 5 2018 págs. 708E - 717E
    UND: When analyzing intracranial volume gain resulting from operative intervention in craniosynostosis, it is necessary to understand the underlying growth. The authors sought to create comprehensive intracranial volume and occipitofrontal circumference growth charts, as measured on unoperated craniosynostotic children, and aimed to investigate whether intracranial volume and occipitofrontal circumference could act as proxy measures for each other. METHODS: All preoperative Great Ormond Street Hospital patients with a diagnosis of Apert, Crouzon-Pfeiffer, or Saethre-Chotzen syndrome from the year 2004 onward were considered for this study. A control group of unaffected Great Ormond Street Hospital patients were also measured. Intracranial volume and occipitofrontal circumference were measured on the same scans. To study correlation between intracranial volume and occipitofrontal circumference, logarithmic fits were assessed. RESULTS: One hundred forty-seven craniosynostotic children with 221 preoperative scans were included (81 Apert, 81 Crouzon, 31 Pfeiffer, and 28 Saethre-Chotzen). The control group comprised 56 patients with 58 scans. Apert intracranial volume curves were significantly larger than those of other syndromes from 206 days onward; occipitofrontal circumference curves were not significantly different. The correlation coefficient between intracranial volume and occipitofrontal circumference was R = 0.87 for all syndromes combined and R = 0.91 for the control
  • Autores: Borghi, A.; Rodríguez Florez, Naiara; Rodgers, W.; et al.
    ISSN: 1350-4533 Vol.53 2018 págs. 58 - 65
    Implantation of spring-like distractors in the treatment of sagittal craniosynostosis is a novel technique that has proven functionally and aesthetically effective in correcting skull deformities: however, final shape outcomes remain moderately unpredictable due to an incomplete understanding of the skulldistractor interaction. The aim of this study was to create a patient specific computational model of spring assisted cranioplasty (SAC) that can help predict the individual overall final head shape. Pre-operative computed tomography images of a SAC patient were processed to extract a 3D model of the infant skull anatomy and simulate spring implantation. The distractors were modeled based on mechanical experimental data. Viscoelastic bone properties from the literature were tuned using the specific patient procedural information recorded during surgery and from x-ray measurements at follow-up. The model accurately captured spring expansion on-table (within 9% of the measured values), as well as at first and second follow-ups (within 8% of the measured values). Comparison between immediate, post-operative 3D head scanning and numerical results for this patient proved that the model could successfully predict the final overall head shape. This preliminary work showed the potential application of computational modeling to study. SAC, to support pre-operative planning and guide novel distractor design
  • Autores: Knoops, P.G.M. (Autor de correspondencia); Borghi, A.; Ruggiero, F.; et al.
    Revista: PLOS ONE
    ISSN: 1932-6203 Vol.13 N° 5 2018
    Repositioning of the maxilla in orthognathic surgery is carried out for functional and aesthetic purposes. Pre-surgical planning tools can predict 3D facial appearance by computing the response of the soft tissue to the changes to the underlying skeleton. The clinical use of commercial prediction software remains controversial, likely due to the deterministic nature of these computational predictions. A novel probabilistic finite element model (FEM) for the prediction of postoperative facial soft tissues is proposed in this paper. A probabilistic FEM was developed and validated on a cohort of eight patients who underwent maxillary repositioning and had pre- and postoperative cone beam computed tomography (CBCT) scans taken. Firstly, a variables correlation assessed various modelling parameters. Secondly, a design of experiments (DOE) provided a range of potential outcomes based on uniformly distributed input parameters, followed by an optimisation. Lastly, the second DOE iteration provided optimised predictions with a probability range. A range of 3D predictions was obtained using the probabilistic FEM and validated using reconstructed soft tissue surfaces from the postoperative CBCT data. The predictions in the nose and upper lip areas accurately include the true postoperative position, whereas the prediction under-estimates the position of the cheeks and lower lip.
  • Autores: Sharma, J.D.; O'Hara, J.; Borghi, A.; et al.
    ISSN: 1049-2275 Vol.29 N° 5 2018 págs. 1117 - 1122
    The Melbourne technique was described in 2008 as a novel method for complete correction of scaphocephaly. Since 2015, it has become our operation of choice for children with sagittal synostosis who are too old at presentation for minimally invasive techniques. Our modifications were 2-position (initially supine then prone) technique and undertaking a formal fronto-orbital remodeling to correct forehead contour. Retrospective chart review was used to record demographics, blood transfusion frequency and volumes, operating time, length of stay, clinical outcome, and complications. Eleven underwent modified Melbourne procedure between July 2015 and March 2017; 9 of 11 were male. All had a diagnosis of nonsyndromic sagittal synostosis. Mean age at surgery was 29 months. Mean surgical time was 6 hours. All patients required blood transfusion with a mean volume transfused of 29 mL/kg (range 13¿83 mL/kg). For those 5 patients where preoperative and postoperative measurements were available, there was an increase in mean cephalic index (CI) from 0.64 to 0.75. All postoperative patients had a CI of over 0.70. Three-dimensional shape analysis indicated head shape change addressing all phenotypic aspects of scaphocephaly. In the 5 patients in which analysis could be undertaken, the mean intracranial volume increased from 1481 cm3 preoperatively to 1671 cm3 postoperatively, a mean increase in intracranial volume of 14%.