Biomechanical and microstructural characterisation of the porcine stomach wall: Location- and layer-dependent investigations Publication date: Available online 22 November 2019 Source: Acta Biomaterialia Author(s): Melanie Bauer, Enrique Morales-Orcajo, Lisa Klemm, Robert Seydewitz, Victoria Fiebach, Tobias Siebert, Markus Böl Abstract The mechanical properties of the stomach wall help to explain its function of storing, mixing, and emptying in health and disease. However, much remains unknown about its mechanical properties, especially regarding regional heterogeneities and wall microstructure. Consequently, the present study aimed to assess regional differences in the mechanical properties and microstructure of the stomach wall. In general, the stomach wall and the different tissue layers exhibited a nonlinear stress-stretch relationship. Regional differences were found in the mechanical response and the microstructure. The highest stresses of the entire stomach wall in longitudinal direction were found in the corpus (201.5 kPa), where food is ground followed by the antrum (73.1 kPa) and the fundus (26.6 kPa). In contrast, the maximum stresses in circumferential direction were 39.7 kPa, 26.2 kPa, and 15.7 kPa for the antrum, fundus, and corpus, respectively. Independent of the fibre orientation and with respect to the biaxial loading direction, partially clear anisotropic responses were detected in the intact wall and the muscular layer. In contrast, the innermost mucosal layer featured isotropic mechanical characteristics. Pronounced layers of circumferential and longitudinal muscle fibres were found in the fundus only, whereas corpus and antrum contained almost exclusively circumferential orientated muscle fibres. This specific stomach structure mirrors functional differences in the fundus as well as corpus and antrum. Within this study, the load transfer mechanisms, connected with these wavy layers but also in total with the stomach wall’s microstructure, are discussed. Graphical abstract

A Detailed Mechanical and Microstructural Analysis of Ovine Tricuspid Valve Leaflets Publication date: Available online 22 November 2019 Source: Acta Biomaterialia Author(s): William D. Meador, Mrudang Mathur, Gabriella P. Sugerman, Tomasz Jazwiec, Marcin Malinowski, Matthew R. Bersi, Tomasz A. Timek, Manuel K. Rausch Abstract The tricuspid valve ensures unidirectional blood flow from the right atrium to the right ventricle. The three tricuspid leaflets operate within a dynamic stress environment of shear, bending, tensile, and compressive forces, which is cyclically repeated nearly two billion times in a lifetime. Ostensibly, the microstructural and mechanical properties of the tricuspid leaflets have mechanobiologically evolved to optimally support their function under those forces. Yet, how the tricuspid leaflet microstructure determines its mechanical properties and whether this relationship differs between the three leaflets is unknown. Here we perform a microstructural and mechanical analysis in matched ovine tricuspid leaflet samples. We found that the microstructure and mechanical properties vary among the three tricuspid leaflets in sheep. Specifically, we found that tricuspid leaflet composition, collagen orientation, and valve cell nuclear morphology are spatially heterogeneous and vary across leaflet type. Furthermore, under biaxial tension the leaflets’ mechanical behaviors exhibited unequal degrees of mechanical anisotropy. Most importantly, we found that the septal leaflet was stiffer in the radial direction and not the circumferential direction as with the other two leaflets. The differences we observed in leaflet microstructure coincide with the varying biaxial mechanics among leaflets. Our results demonstrate the structure-function relationship for each leaflet in the tricuspid valve. We anticipate our results to be vital toward developing more accurate, leaflet-specific tricuspid valve computational models. Furthermore, our results may be clinically important, informing differential surgical treatments of the tricuspid valve leaflets. Finally, the identified structure-function relationships may provide insight into the homeostatic and remodeling potential of valvular cells in altered mechanical environments, such as in diseased or repaired tricuspid valves. Graphical abstract

A Systematic Comparison of Lipopolymers for siRNA Delivery to Multiple Breast Cancer Cell Lines: In vitro Studies Publication date: Available online 21 November 2019 Source: Acta Biomaterialia Author(s): Hamidreza Montazeri Aliabadi, Remant Bahadur K.C., Emira Bousoik, Ryley Hall, Ashley Barbarino, Bindu Thapa, Melissa Coyle, Parvin Mahdipoor, Hasan Uludağ ABSTRACT Small interfering RNA (siRNA) therapy is a promising approach for treatment of a wide range of cancers, including breast cancers that display variable phenotypic features. To explore the general utility of siRNA therapy to control aberrant expression of genes in breast cancer, we conducted a detailed analysis of siRNA delivery and silencing response in vitro in 6 separate breast cancer cell models (MDA-MB-231, MDA-MB-231-KRas-CRM, MCF-7, AU565, MDA-MB-435 and MDA-MB-468 cells). Using lipopolymers for siRNA complexation and delivery, we found a large variation in siRNA delivery efficiency depending on the specific lipopolymer used for siRNA complexation and delivery. Some lipopolymers were effective in all cell types used in this study, indicating the possibility of universal carriers for siRNA therapy. The delivery efficiency for effective lipopolymers was not correlated with dextran uptake in the cells tested, which indicated a receptor-mediated internalization for siRNA complexes with lipopolymers, unlike fluid-phase transfer associated with dextran uptake. Consistent with this, specific inhibitors involved in clathrin- and caveolin-mediated endocytosis significantly (>50%) reduced the internalization of siRNA complexes in all cell types. Using JAK2 and STAT3 silencing in MDA-MB-231 and MDA-MB-468 cells, a general correlation between the uptake and silencing efficiency at the mRNA level was evident, but it appeared that the choice of the target rather than the cell type was more critical for consistent silencing. We conclude that siRNA therapy with lipopolymers can be undertaken in multiple breast cancer cell phenotypes with similar efficiency, indicating the general applicability of non-viral RNAi in clinical management of molecularly heterogeneous breast cancers. Graphical abstract

Oligonucleotide-functionalized hydrogels for sustained release of small molecule (aptamer) therapeutics Publication date: Available online 21 November 2019 Source: Acta Biomaterialia Author(s): Nikunj K. Agrawal, Peter Allen, Young Hye Song, Rebecca A. Wachs, Yan Du, Andrew D. Ellington, Christine E. Schmidt Abstract Natural and synthetic hydrogels have been widely investigated as biomaterial scaffolds to promote tissue repair and regeneration. Nevertheless, the scaffold alone is often insufficient to drive new tissue growth, instead requiring continuous delivery of therapeutics, such as proteins or other biomolecules that work in concert with structural support provided by the scaffold. However, because of the high-water content, hydrogels tend to be permeable and cause rapid release of the encapsulated drug, which could lead to serious complications from local overdose and may result in the significant waste of encapsulated therapeutic(s). To this end, we designed an oligonucleotide-functionalized hydrogel that can provide sustained and controlled delivery of therapeutics for up to 4 weeks. To prove this concept, we successfully achieved sustained release (for over 28 days) of model anti-Nogo receptor (anti-NgR) RNA aptamer from oligonucleotide-functionalized hyaluronic acid-based hydrogel by changing the complementarity between the short antisense sequences and the aptamer. Furthermore, the released aptamer successfully blocked neuro-inhibitory effects of myelin-derived inhibitors and promoted neurite outgrowth from rat dorsal root ganglia in vitro. Because antisense sequences can be designed to bind to proteins, peptides, and aptamer, our oligonucleotide-functionalized hydrogel offers a promising therapeutic delivery system to obtain controlled release (both bolus and sustained) of various therapeutics for the treatment of complex diseases and injury models, such as spinal cord injury. Statement of Significance Producing a therapeutic effect often requires the administration of multiple injections with high dosages. This regimen causes discomfort to the patient and raises cost of treatment. Additionally, systemic delivery of therapeutics often results in adverse effects; therefore, local delivery at the site of injury is desirable. Therefore, in this study, we designed an oligonucleotide-functionalized biomaterial platform using ssDNA oligonucleotides (immobile species) as antisense sequences to increase residence time and fine-tune the release of anti-nogo receptor aptamer (mobile species) for spinal cord injury application. Because antisense sequences can be designed to bind proteins, peptides, and aptamer, our hydrogel offers a promising delivery system to obtain controlled release of various therapeutics for the treatment of complex diseases and injury models. Graphical abstract

Biomimetic Anti-inflammatory Nano-Capsule served as cytokines blocker and M2 polarization inducer for bone tissue repair Publication date: Available online 21 November 2019 Source: Acta Biomaterialia Author(s): Chengcheng Yin, Qin Zhao, Wu Li, Zifan Zhao, Jinyang Wang, Tian Deng, Peng Zhang, Kailun Shen, Zubing Li, Yufeng Zhang Abstract Controlling of pro-inflammation induced by pro-inflammatory cytokines and anti-inflammatory response induced by M2 macrophages is important for osteogenesis in the process of bone tissue repair. Thus, we fabricated biomimetic anti-inflammatory nano-capsule (BANC) that can block cytokines and promote M2 macrophage polarization, presenting a positive role for bone tissue repair. The BANC is a biomimic nanosystem, coated with lipopolysaccharide-treated macrophage cell membranes with cytokine receptors enveloping gold nanocage (AuNC) as “cytokine blocker”, and loaded with resolvin D1 inside into AuNC as “M2 polarization inducer” whose controlled-release could be triggered under near-infrared laser irradiation in sequence, and these chronological events were consistent with the healing process of bone tissue repair. Moreover, in vivo application of femoral bone defects revealed that the BANC composite boron-containing mesoporous bioactive glass scaffolds improved the final effects of bone tissue repair through preventing inflammatory response, promoting M2 polarization in sequence in accord with the in vitro investigation. Hence, cytokine neutralization and M2 macrophage polarization enables the BANC to enhance the bone tissue repair as a biomimetic anti-inflammation effector. Therefore, this study provides potential therapeutic strategies for trauma-mediated or inflammation-related bone defects based on a biomimetic nanomaterial with weakened pro-inflammatory and enhanced anti-inflammatory effects. Statement of Significance Cell membrane-mimic nanomaterials have been popular for blocking natural cell responses for some infection diseases, yet their role in biological process of bone repair is unknown. Here, we fabricated Biomimetic Anti-inflammatory Nano-Capsule (BANC), coated with cell membrane with cytokines receptors on the surface which could neutralize the pro-inflammatory cytokine receptor to block activated pro-inflammation, loaded with Resolvin D1 inside which could be controllably released by NIR irradiation to promote M2 macrophage polarization for the following bone formation during the process of bone repair. Administration of BANC as cytokines blocker and M2 polarization inducer to enhance the bone regeneration, thus presenting a promising potential for the treatment of bone repair and regeneration. Graphical abstract

Targeting Strategies for SuperParamagnetic Iron Oxide Nanoparticles in Cancer Therapy Publication date: Available online 20 November 2019 Source: Acta Biomaterialia Author(s): Defu Zhi, Ting Yang, Jian Yang, Shuang Fu, Shubiao Zhang Abstract Among various nanoparticles, superparamagnetic iron oxide nanoparticles (SPIONs) have been increasingly studied for their excellent superparamagnetism, magnetic heating properties, and enhanced magnetic resonance imaging (MRI). The conjugation of SPIONs with drugs to obtain delivery nanosystems has several advantages including magnetic targeted functionalization, in vivo imaging, magnetic thermotherapy, and combined delivery of anticancer agents. To further increase the targeting efficiency of drugs through a delivery nanosystem based on SPIONs, additional targeting moieties including transferrin, antibodies, aptamers, hyaluronic acid, folate, and targeting peptides are coated onto the surface of SPIONs. Therefore, this review summarizes the latest progresses in the conjugation of targeting molecules and drug delivery nanosystems based on SPIONs, especially focusing on their performances to develop efficient targeted drug delivery systems for tumor therapy. Graphical Abstract

In vitro measurement of the chemical changes occurring within β-tricalcium phosphate bone graft substitutes Publication date: Available online 20 November 2019 Source: Acta Biomaterialia Author(s): Yassine Maazouz, Iris Rentsch, Bin Lu, Bastien Le Gars Santoni, Nicola Doebelin, Marc Bohner Abstract Several mechanisms proposed to explain the osteoinductive potential of calcium phosphates involve surface mineralization (“bioactivity”) and mention the occurrence of concentration gradients between the inner and the outer part of the implanted material. Determining the evolution of the local chemical environment occurring inside the pores of an implanted bone graft substitute (BGS) is therefore highly relevant. A quantitative and fast method was developed to measure the chemical changes occurring within the pores of β-Tricalcium Phosphate (β-TCP) granules incubated in a simulated body fluid. A factorial design of experiment was used to test the effect of particle size, specific surface area, microporosity, and purity of the β-TCP granules. Large pH, calcium and phosphate concentration changes were observed inside the BGS and lasted for several days. The kinetics and magnitude of these changes (up to 2 pH units) largely depended on the processing and properties of the granules. Interestingly, processing parameters that increased the kinetics and magnitude of the local chemical changes are parameters considered to favor calcium phosphate osteoinduction, suggesting that the model might be useful to predict the osteoinductive potential of BGSs. Statement of significance Recent results suggest that in situ mineralization of biomaterials (polymers, ceramics, metals) might be key in their ability to trigger ectopic bone formation. This is the reason why the effect on in situ mineralization of various synthesis parameters of β-tricalcium phosphate granules was studied (size, microporosity, specific surface area, and Ca/P molar ratio). To the best of our knowledge, this is the first article devoted to the chemical changes occurring within the pores of a bone graft substitute. We believe that the manuscript will prove to be highly important in the design and mechanistic understanding of drug-free osteoinductive biomaterials. Graphical abstract

Interfacial toughening effect of suture structures Publication date: Available online 19 November 2019 Source: Acta Biomaterialia Author(s): Zengqian Liu, Zhefeng Zhang, Robert O. Ritchie Abstract Suture interfaces are one of the most common architectural designs in natural material-systems and are critical for ensuring multiple functionalities by providing flexibility while maintaining connectivity. Despite intensive studies on the mechanical role of suture structures, there is still a lack of understanding on the fracture mechanics of suture interfaces in terms of their interactions with impinging cracks. Here we reveal an interfacial toughening effect of suture structures by means of “excluding” cracks away from interfaces based on a dimensionless micro-mechanical model for single-leveled and hierarchical suture interfaces with triangular-shaped suture teeth. The effective stress-intensity driving forces for crack deflection along, versus penetration through, an interface at first impingement and on subsequent kinking are formulated and compared with the corresponding resistances. Quantitative criteria are established for discerning the cracking modes and fracture resistance of suture interfaces with their dependence on sutural tooth sharpness and interfacial toughness clarified. Additionally, the effects of structural hierarchy are elucidated through a consideration of hierarchical suture interfaces with fractal-like geometries. This study may offer guidance for designing bioinspired suture structures, especially for toughening materials where interfaces are a key weakness. Statement of significance Suture interfaces are one of the most common architectural material designs in biological systems, and are found in wide range of species including armadillo osteoderms, boxfish armor, pangolin scales and insect cuticles. They are designed to provide flexibility while maintaining connectivity. Despite many studies on the mechanical role of suture structures, there is still little understanding of their role in terms of interactions with impinging cracks. Here we reveal an interfacial toughening effect of suture structures by means of “excluding” cracks away from interface based on a dimensionless micro-mechanical model for single-leveled and hierarchical suture interfaces with triangular-shaped suture teeth. Quantitative criteria are established for discerning the cracking mode and fracture resistance of the interfaces with their dependences on sutural tooth sharpness and interfacial toughness clarified. Graphical abstract

Capturing instructive cues of tissue microenvironment by silica bioreplication Publication date: Available online 19 November 2019 Source: Acta Biomaterialia Author(s): Sze Wing Tang, Wai Yuen, Ishdeep Kaur, Stella W. Pang, Nicolas H. Voelcker, Yun Wah Lam Abstract Cells in tissues are enveloped by an instructive niche made of the extracellular matrix. These instructive niches contain three general types of information: topographical, biochemical and mechanical. While the combined effects of these three factors are widely studied, the functions of each individual one has not been systematically characterised, because it is impossible to alter a single factor in a tissue microenvironment without simultaneously affecting the other two. Silica BioReplication (SBR) is a process that convert biological samples into silica, faithfully preserving the original topography at the nano-scale. We explored the use of this technique to generate inorganic replicas of intact mammalian tissues, including tendon, cartilage, skeletal muscle and spinal cord. Scanning electron and atomic force microscopy showed that the resulting replicas accurately preserved the three-dimensional ultrastructure of each tissue, while all biochemical components were eradicated by calcination. Such properties allowed the uncoupling the topographical information of a tissue microenvironment from its biochemical and mechanical components. Here, we showed that human mesenchymal stem cells (MSC) cultured on the replicas of different tissues displayed vastly different morphology and focal adhesions, suggesting that the topography of the tissue microenvironment captured by SBR could profoundly affect MSC biology. MSC cultured on tendon replica elongated and expressed tenocytes marker, while MSC on the spinal cord replica developed into spheroids that resembled neurospheres, in morphology and in the expression of neurosphere markers, and could be further differentiated into neuron-like cells. This study reveals the significance of topographical cues in a cell niche, as tissue-specific topography was sufficient in initiating and directing differentiation of MSC, despite the absence of any biochemical signals. SBR is a convenient and versatile method for capturing this topographical information, facilitating the functional characterisation of cell niches. Graphical abstract

The use of bioactive matrices in regenerative therapies for traumatic brain injury Publication date: Available online 18 November 2019 Source: Acta Biomaterialia Author(s): Hui X. Tan, Mark P. Del Borgo, Marie-Isabel Aguilar, John S. Forsythe, Juliet M. Taylor, Peter J. Crack Abstract Functional deficits due to neuronal loss are a common theme across multiple neuropathologies, including traumatic brain injury (TBI). Apart from mitigating cell death, another approach to treating brain injuries involves re-establishing the neural circuitry at the lesion site by utilizing exogeneous and/or endogenous stem cells to achieve functional recovery. While there has been limited success, the emergence of new bioactive matrices that promote neural repair introduces new perspectives on the development of regenerative therapies for TBI. This review briefly discusses current development on cell-based therapies and the use of bioactive matrices, hydrogels in particular, when incorporated in regenerative therapies. Desirable characteristics of bioactive matrices that have been shown to augment neural repair in TBI models were identified and further discussed. Understanding the relative outcomes of newly developed biomaterials implanted in vivo can better guide the development of biomaterials as a therapeutic strategy, for biomaterial-based cellular therapies are still in their nascent stages. Nonetheless, the value of bioactive matrices as a treatment for acute brain injuries should be appreciated and further developed. Statement of significance Cell-based therapies have received attention as an alternative therapeutic strategy to improve clinical outcome post-traumatic brain injury but have achieved limited success. Whilst the incorporation of newly developed biomaterials in regenerative therapies has shown promise in augmenting neural repair, studies have revealed new hurdles which must be overcome to improve their therapeutic efficacy. This review discusses the recent development of cell-based therapies with a specific focus on the use of bioactive matrices in the form of hydrogels, to complement cell transplantation within the injured brain. Moreover, this review consolidates in vivo animal studies that demonstrate relative functional outcome upon the implantation of different biomaterials to highlight their desirable traits to guide their development for regenerative therapies in traumatic brain injury. Graphical Abstract