Numerical study on load-bearing capabilities of beam-like lattice structures with three different unit cells

The design and analysis of lattice structures manufactured using Additive Manufacturing (AM) technique is a new approach to create lightweight high-strength components. However, it is difficult for engineers to choose the proper unit cell for a certain function structure and loading case. In this paper, three beam-like lattice structures with triangular prism, square prism and hexagonal prism were designed, manufactured by SLM process using AlSi10Mg and tested. The mechanical performances of lattice structures with equal relative density, equal base area and height, and equal length for all unit cells were conducted by Finite Element Analysis (FEA). It was found that effective Young’s modulus is proportional to relative density, but with different affecting levels. When the lattice structures are designed with the same relative density or the same side lengths, the effective Young’s modulus of lattice structure with triangular prism exhibits the maximum value for both cases. When the lattice structures are designed with the same base areas for all unit cells, the effective Young’s modulus of lattice structures with square prism presents the maximum. FEA results also show that the maximum stress of lattice structures with triangular prisms in each comparison is at the lowest level and the stiffness-to-mass ratio remains at the maximum value, showing the overwhelming advantages in terms of mechanical strength. The excellent agreements between numerical results and experimental tests reveal the validity of FEA methods applied. The results in this work provide an explicit guideline to fabricate beam-like lattice structures with the best tensile and bending capabilities

Selective laser melting–enabled electrospinning: Introducing complexity within electrospun membranes

Additive manufacturing technologies enable the creation of very precise and well-defined structures that can mimic hierarchical features of natural tissues. In this article, we describe the development of a manufacturing technology platform to produce innovative biodegradable membranes that are enhanced with controlled microenvironments produced via a combination of selective laser melting techniques and conventional electrospinning. This work underpins the manufacture of a new generation of biomaterial devices that have significant potential for use as both basic research tools and components of therapeutic implants. The membranes were successfully manufactured and a total of three microenvironment designs (niches) were chosen for thorough characterisation. Scanning electron microscopy analysis demonstrated differences in fibre diameters within different areas of the niche structures as well as differences in fibre density. We also showed the potential of using the microfabricated membranes for supporting mesenchymal stromal cell culture and proliferation. We demonstrated that mesenchymal stromal cells grow and populate the membranes penetrating within the niche-like structures. These findings demonstrate the creation of a very versatile tool that can be used in a variety of tissue regeneration applications including bone healing

A primer of statistical methods for correlating parameters and properties of electrospun poly(l -lactide) scaffolds for tissue engineering-PART 1: Design of experiments

Tissue engineering scaffolds produced by electrospinning are of enormous interest, but still lack a true understanding about the fundamental connection between the outstanding functional properties, the architecture, the mechanical properties, and the process parameters. Fragmentary results from several parametric studies only render some partial insights that are hard to compare and generally miss the role of parameters interactions. To bridge this gap, this article (Part-1 of 2) features a case study on poly-l-lactide scaffolds to demonstrate how statistical methods such as design of experiments can quantitatively identify the correlations existing between key scaffold properties and control parameters, in a systematic, consistent, and comprehensive manner disentangling main effects from interactions. The morphological properties (i.e., fiber distribution and porosity) and mechanical properties (Young's modulus) are "charted" as a function of molecular weight (MW) and other electrospinning process parameters (the Xs), considering the single effect as well as interactions between Xs. For the first time, the major role of the MW emerges clearly in controlling all scaffold properties. The correlation between mechanical and morphological properties is also addressed. © 2014 Wiley Periodicals, Inc

A primer of statistical methods for correlating parameters and properties of electrospun poly(l -lactide) scaffolds for tissue engineering-PART 2: Regression

This two-articles series presents an in-depth discussion of electrospun poly-l-lactide scaffolds for tissue engineering by means of statistical methodologies that can be used, in general, to gain a quantitative and systematic insight about effects and interactions between a handful of key scaffold properties (Ys) and a set of process parameters (Xs) in electrospinning. While Part-1 dealt with the DOE methods to unveil the interactions between Xs in determining the morphomechanical properties (ref. Y1-4), this Part-2 article continues and refocuses the discussion on the interdependence of scaffold properties investigated by standard regression methods. The discussion first explores the connection between mechanical properties (Y4) and morphological descriptors of the scaffolds (Y1-3) in 32 types of scaffolds, finding that the mean fiber diameter (Y1) plays a predominant role which is nonetheless and crucially modulated by the molecular weight (MW) of PLLA. The second part examines the biological performance (Y5) (i.e. the cell proliferation of seeded bone marrow-derived mesenchymal stromal cells) on a random subset of eight scaffolds vs. the mechanomorphological properties (Y1-4). In this case, the featured regression analysis on such an incomplete set was not conclusive, though, indirectly suggesting in quantitative terms that cell proliferation could not fully be explained as a function of considered mechanomorphological properties (Y1-4), but in the early stage seeding, and that a randomization effects occurs over time such that the differences in initial cell proliferation performance (at day 1) is smeared over time. The findings may be the cornerstone of a novel route to accrue sufficient understanding and establish design rules for scaffold biofunctional vs. architecture, mechanical properties, and process parameters. © 2014 Wiley Periodicals, Inc

Functionalised polyurethane scaffolds mimicking cardiac primitive cell niche microenvironment by additive manufacturing

Human cardiac fibroblasts (CFs) have been found to deposit in vitro a 2D “biomatrix” (BM) with similar composition to the natural cardiac extracellular matrix (ECM). The study of the behaviour of human cardiac primitive cells (CPCs) in contact with BM showed that laminin-1 (LN1) promotes the adhesion, viability, proliferation and differentiation of CPCs. Recently, a polyurethane (PU) with elastomeric-like properties was synthesised and scaffolds were prepared by melt-extrusion additive manufacturing (AM). In this work, PU scaffolds were surface functionalised with LN1 and BM with the aim to reproduce CPC-niche microenvironment. Gelatin (G) was also grafted as a control. METHODS: PU was synthesized from poly(ε-caprolactone) diol (Mn = 2000 Da), 1,4-budandiisocyanate and L-lysine ethyl ester dihydrochloride. Bi-layered scaffolds with 0°/90° lay-down pattern were prepared by additive-manufacturing technique. Functionalisation was performed by two steps: 1) acrylic acid grafting/polymerization following Argon Plasma treatment; 2) carbodiimide mediated grafting of LN1, G or solubilised BM (produced by in vitro culture of CFs, followed by decellularisation and further BM solubilisation in a pepsin solution). Physicochemical characterisation of the surface coating was performed by XPS, FTIR-ATR, colorimetric tests, static contact angle measurements and ELISA assay. In vitro cell tests were performed using CPCs. RESULTS: PU scaffolds showed a mean fibre diameter of 152±5 μm and mean spacing of 505±5 μm. FITR-ATR analysis of coated scaffolds showed higher intensity of the absorption bands at 3370 cm-1 (-OH and –NH stretching) and 1650 cm-1 (amide I). Contact angle decreased from 90° for PU to 60-70° for LN1, G and BM coated PU. XPS analysis confirmed the successful surface functionalisation. CPC proliferation on PU-LN1 scaffolds was higher than on PU scaffolds, increasing from 8.2 % on day 7 to 11.8% on day 14. LN1-functionalization also stimulated CPC differentiation into cardiomyocytes, smooth muscle cells and endothelial cells (RT-PCR analysis). Scaffolds were found to slowly degrade in vitro by hydrolytic mechanism, whereas using an enzyme (lipase) degradation occurred in 3 weeks. Subcutaneous implantation of scaffolds in mice showed their tissue compatibility, low inflammatory response and low degradation rate (they were stable after 1 month). DISCUSSION & CONCLUSIONS: PU scaffolds fabricated by AM and surface grafted with LN1 or BM were developed as 3D substrates mimicking CPC niche microenvironment. They could be used as cellularised patches for in vivo implantation in myocardial tissue engineering or as in vitro models of CPC niches to study CPC behaviour in both normal and pathological conditions

Computer-Aided Wet-Spinning

Computer-aided wet-spinning (CAWS) has emerged in the past few years as a hybrid fabrication technique coupling the advantages of additive manufacturing in controlling the external shape and macroporous structure of biomedical polymeric scaffold with those of wet-spinning in endowing the polymeric matrix with a spread microporosity. This book chapter is aimed at providing a detailed description of the experimental methods developed to fabricate by CAWS polymeric scaffolds with a predefined external shape and size as well as a controlled internal porous structure. The protocol for the preparation of poly(ε-caprolactone)-based scaffolds with a predefined pore size and geometry will be reported in detail as a reference example that can be followed and simply adapted to fabricate other kinds of scaffold, with a different porous structure or based on different biodegradable polymers, by applying the processing parameters reported in relevant tables included in the text

The effect of post-mastectomy radiation therapy on breast implants: Unveiling biomaterial alterations with potential implications on capsular contracture

Post-mastectomy breast reconstruction with expanders and implants is recognized as an integral part of breast cancer treatment. Its main complication is represented by capsular contracture, which leads to poor expansion, breast deformation, and pain, often requiring additional surgery. In such a scenario, the debate continues as to whether the second stage of breast reconstruction should be performed before or after post-mastectomy radiation therapy, in light of potential alterations induced by irradiation to silicone biomaterial. This work provides a novel, multi-technique approach to unveil the role of radiotherapy in biomaterial alterations, with potential involvement in capsular contracture. Following irradiation, implant shells underwent mechanical, chemical, and microstructural evaluation by means of tensile testing, Attenuated Total Reflectance Fourier Transform InfraRed spectroscopy (ATR/FTIR), Scanning Electron Microscopy (SEM), high resolution stylus profilometry, and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS). Our findings are consistent with radiation-induced modifications of silicone that, although not detectable at the microscale, can be evidenced by more sophisticated nanoscale surface analyses. In light of these results, biomaterial irradiation cannot be ruled out as one of the possible co-factors underlying capsular contracture