In-Silico Prediction of Mechanical Behaviour of Uniform Gyroid Scaffolds Affected by Its Design Parameters for Bone Tissue Engineering Applications

Due to their excellent properties, triply periodic minimal surfaces (TPMS) have been applied to design scaffolds for bone tissue engineering applications. Predicting the mechanical response of bone scaffolds in different loading conditions is vital to designing scaffolds. The optimal mechanical properties can be achieved by tuning their geometrical parameters to mimic the mechanical properties of natural bone. In this study, we designed gyroid scaffolds of different user-specific pore and strut sizes using a combined TPMS and signed distance field (SDF) method to obtain varying architecture and porosities. The designed scaffolds were converted to various meshes such as surface, volume, and finite element (FE) volume meshes to create FE models with different boundary and loading conditions. The designed scaffolds under compressive loading were numerically evaluated using a finite element method (FEM) to predict and compare effective elastic moduli. The effective elastic moduli range from 0.05 GPa to 1.93 GPa was predicted for scaffolds of different architectures comparable to human trabecular bone. The results assert that the optimal mechanical properties of the scaffolds can be achieved by tuning their design and morphological parameters to match the mechanical properties of human bone

Epigenetic Upregulation of Endogenous VEGF-A Reduces Myocardial Infarct Size in Mice

<div><p>“Epigenetherapy” alters epigenetic status of the targeted chromatin and modifies expression of the endogenous therapeutic gene. In this study we used lentiviral <i>in vivo</i> delivery of small hairpin RNA (shRNA) into hearts in a murine infarction model. shRNA complementary to the promoter of vascular endothelial growth factor (VEGF-A) was able to upregulate endogenous VEGF-A expression. Histological and multiphoton microscope analysis confirmed the therapeutic effect in the transduced hearts. Magnetic resonance imaging (MRI) showed <i>in vivo</i> that the infarct size was significantly reduced in the treatment group 14 days after the epigenetherapy. Importantly, we show that promoter-targeted shRNA upregulates all isoforms of endogenous VEGF-A and that an intact hairpin structure is required for the shRNA activity. In conclusion, regulation of gene expression at the promoter level is a promising new treatment strategy for myocardial infarction and also potentially useful for the upregulation of other endogenous genes.</p></div

Analysis for mechanism of action for promoter targeted shRNAs.

<p>(a) RT-PCR analysis for different VEGF-A isoforms. The expression levels for different isoforms were studied using primers specific to each isoform. Total VEGF-A protein level was measured with ELISA. (b) Reversing DNA methylation with 5-Azacytidine treatment induces responses in MS1 cells but erases responses in C166 cells. Cells were treated with 1 µM 5-Azacytidine, transduced with different vectors on day 3 and samples were collected on day 8. qRT-PCR analysis of VEGF-A and B-actin mRNA levels in MS1 cells and C166 cells. (c) qChIP assay in MS1 cells using antibody against H3K27me3. (d) The VEGF-A gene promoter in C166 cells was also analyzed for basal DNA methylation levels without 5-Azacytidine treatment using MeDIP. Cells were transduced with different vectors using MOI 10, 10 days timepoint. (e) RT-PCR analysis of VEGF-A mRNA levels after C166 cells were transfected with siRNA oligos. Results are calculated in reference to housekeeping gene ACTB and control oligo. (f) CBP-CREB interaction inhibitor (7.5 µM) abolishes the upregulation of VEGF-A by LV-451 in C166 cells. For all results, mean ± SD shown.</p

ELISA assay of myocardial infarction samples and analysis for single-stranded vectors for a mechanistical view.

<p>(a) ELISA analysis of VEGF-A protein from transduced hearts, (b) ELISA assay from growth medium of C166 cells transduced with LV-451 and corresponding single stranded vectors using MOI 10, 7 days time point. (c) RT-PCR analysis of VEGF-A mRNA levels. C166 cells were transduced with LV-451 and corresponding single stranded vectors using MOI 10, 11 days time point. (d) qChIP assay of C166 cells using antibodies against H3K4me2. Cells were transduced with LV-451 and corresponding single stranded vectors using MOI 10, 11 days timepoint. All results are shown as mean ± SD.</p

Intracellular distribution of LV-451 expressed RNA and VEGF-A mRNA in transduced cells.

<p>C166 cells were subjected to RNA-FISH analysis with LV-451 or VEGF mRNA probes. (a) Confocal microscopy images of LV-451 transduced (MOI 10) cells 72 h post transduction. Distribution of LV-451 RNA (green) and VEGF-A mRNA (red) probe binding induced signals is shown. Nuclei were visualized with DAPI (grey). Scale bars, 5 µm. (b) Quantification of LV-451 RNA or VEGF-A mRNA RNA-FISH signal spots detected in LV-451 transduced (MOI 4, 40, 200) cells at 72 h post transduction and in nontransduced control cells. The amount of signal was calculated in the nucleus (white), the cytosol (grey) and whole cell (black). Error bars = SD. (c) Nucleus size in response to LV transduction. CTRL sample is nontransduced C166 cells and LV-451 is C166 cells transduced with LV-451 vector.</p

Multiphoton microscopy and histology analysis of myocardial infarction animals.

<p>(a) Multiphoton laser scanning microscopy (MPLSM) analysis of GFP expression in transduced mouse heart, (b) Immunohistological analysis of GFP expression in mouse heart, (c) antibody omitted control, (d and k) Massons Trichrome staining from mouse heart transduced with VEGF-A upregulating LV-451 and shRNA control, respectively, (e and l) insert from infarcted area of d and k, respectively, (h and o) insert from infarct borderzone (f, i, m, p) alpha-SMA staining of smooth muscle cells, arrows point to arteriols formed, (g, j, n, q) CD-31 staining of endothelial cells. Scale bars (a) 100 µm, (d and k) 2000 µm, (e, f, g, h, i, j, l, m, n, o, p, q) 200 µm.</p

MRI analysis of murine myocardial infarction.

<p>Infarct size in VEGF-A upregulated (shRNA) and in control (shRNA Control) groups measured using MRI (a), and representative examples of short axis cine images with outlined (red lines) infarcts in late diastole at days 4 and 14 in both shRNA and shRNA control animals (b).</p