During bone regeneration, the periosteum acts as a carrier for key regenerative cues, delivering osteochondroprogenitor cells and crucial growth factors to the injured bone. We developed a biocompatible, 3D polycaprolactone (PCL) melt electro-written membrane to act as a mimetic periosteum. Poly (ethyl acrylate) coating of the PCL membrane allowed functionalization, mediated by fibronectin and low dose recombinant human BMP-2 (rhBMP-2) (10-25 mu g/ml), resulting in efficient, sustained osteoinduction in vitro. In vivo, rhBMP-2 functionalized mimetic periosteum demonstrated regenerative potential in the treatment of rat critical-size femoral defects with highly efficient healing and functional recovery (80%-93%). Mimetic periosteum has also proven to be efficient for cell delivery, as observed through the migration of transplanted periosteum-derived mesenchymal cells to the bone defect and their survival. Ultimately, mimetic periosteum demonstrated its ability to deliver key stem cells and morphogens to an injured site, exposing a therapeutic and translational potential in vivo when combined with unprecedentedly low rhBMP-2 doses.

Mechanical environment plays a crucial role in regulating bone regeneration in bone defects. Assessing the mechanobiological behavior of patient-specific orthopedic scaffolds in-silico could help guide optimal scaffold designs, as well as intra- and post-operative strategies to enhance bone regeneration and improve implant longevity. Additively manufactured porous scaffolds, and specifically triply periodic minimal surfaces (TPMS), have shown promising structural properties to act as bone substitutes, yet their ability to induce mechanobiologially-driven bone regeneration has not been elucidated. The aim of this study is to i) explore the bone regeneration potential of TPMS scaffolds made of different stiffness biocompatible materials, to ii) analyze the influence of pre-seeding the scaffolds and increasing the post-operative resting period, and to iii) assess the influence of patient-specific parameters, such as age and mechanosensitivity, on outcomes. To perform this study, an in silico model of a goat tibia is used. The bone ingrowth within the scaffold pores was simulated with a mechano-driven model of bone regeneration. Results showed that the scaffold's architectural properties affect cellular diffusion and strain distribution, resulting in variations in the regenerated bone volume and distribution. The softer material improved the bone ingrowth. An initial resting period improved the bone ingrowth but not enough to reach the scaffold's core. However, this was achieved with the implantation of a pre-seeded scaffold. Physiological parameters like age and health of the patient also influence the bone regeneration outcome, though to a lesser extent than the scaffold design. This analysis demonstrates the importance of the scaffold's geometry and its material, and highlights the potential of using mechanobiological patient-specific models in the design process for bone substitutes.

A hybrid approach combining the laser powder bed fusion (LPBF) process and post-processing operations through 5-axis milling was employed to manufacture a Ti6Al4V aerospace component. From the design step, the requirements and needs in all the stages of the Hybrid Additive Manufacturing process were taken into account. A numerical simulation of distortions promoted by residual stresses during the additive process was employed to consider material allowance. The status of the as-built and post-processed component was analysed through scanning and CMM inspection and roughness measurements. The 3D scanned model of the as-built LPBF-ed component was used to understand the distortion behaviour of the component and compared to the numerical simulation. Finally, 5-axis milling operations were conducted in some critical surfaces in order to improve surface quality and dimensional accuracy of the as-built com-ponent. The inspection of the as-built and post-processed component showed the improvement achieved through the proposed hybrid approach. The work aims to provide the baselines needed to enable the metal Hybrid Additive Manufacturing of components with complex geometries where mandatory precision is required by integrating high accuracy machining operations as post-processing technique.(c) 2022 The Author(s). This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/).

Additively manufactured lattice structures enable the design of tissue scaffolds with tailored mechanical properties, which can be implemented in porous biomaterials. The adaptation of bone to physiological loads results in anisotropic bone tissue properties which are optimized for site-specific loads; therefore, some bone sites are stiffer and stronger along the principal load direction compared to other orientations. In this work, a semi-analytical model was developed for the design of transversely isotropic lattice structures that can mimic the anisotropy characteristics of different types of bone tissue. Several design possibilities were explored, and a particular unit cell, which was best suited for additive manufacturing was further analyzed. The design of the unit cell was parameterized and in-silico analysis was performed via Finite Element Analysis. The structures were manufactured additively in metal and tested under compressive loads in different orientations. Finite element analysis showed good correlation with the semi-analytical model, especially for elastic constants with low relative densities. The anisotropy measured experimentally showed a variable accuracy, highlighting the deviations from designs to additively manufactured parts. Overall, the proposed model enables to exploit the anisotropy of lattice structures to design lighter scaffolds with higher porosity and increased permeability by aligning the scaffold with the principal direction of the load.

Steel cylindrical shell structures such as silos and tanks are very sensitive to geometric imperfections and prone to a plastic instability failure known as elephant's foot (EF) buckling. This type of buckling arises under axial compression. The aim of this paper is to explore the plastic collapse response in conical shells with low semi-vertex angle values under compression. In a first step, the initial geometric imperfection shapes that dictate which plastic mechanisms arise were identified using finite element (FE) models. In a second step, a parametric study reported two plastic collapse mechanisms and showed that the elephant's foot plastic collapse mechanism is the most likely to appear in compressed conical shells with low d/t values, followed by the Yoshimura collapse mechanism, more common with larger d/t values. Finally, a practical model in which the parameters have been adjusted from numerical models has been derived for the elephant's foot plastic mechanism. This model provides the load-deformation behaviour of compressed conical shells at the post-collapse region. The load vs. end-shortening curves provided by the model have been validated through comparison with curves given by the FE models. The good agreement between the results proves the efficiency of the practical model to predict the collapse response of conical shells.

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.

Laser powder bed fusion (L-PBF) allows the production of metal lattice cellular structures with tailored mechanical properties. In order to generate the specific structural behavior it is of utmost importance to understand the response of the unit cells when different load conditions are considered. In this article the mechanical response of diamond based cellular structures has been investigated focusing on the impact of geometrical inaccuracy generated by the manufacturing process on the elastic anisotropy of the mentioned unit cell. The ii-CT analysis of the structures shows that the manufacturing deviations occur in certain orientations that depend highly on the building direction and proximity to nodes. The measured imperfection types were implemented in a finite element model in order to predict their single and combined effects in the elastic directional response. The results indicate that the L-PBF process can induce a significant change of elastic anisotropy in the diamond unit cells, including a substantial variation of the optimal orientation for minimal compliance. Methods are presented to calculate this anisotropy such that it can be taken into account when designing and using such lattice structures in real-life applications with multi-axial load conditions. (c) 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).