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Influence of elastomeric matrix and particle volume fraction on the mechanical response of magneto-active polymers

Magneto-active polymers (MAPs) are revolutionising the fields of material science and solid mechanics as well as having an important presence in the bioengineering community. These composites consist of a polymeric matrix (i.e., elastomer) filled with magnetic particles (i.e., iron particles). When bonded together, these two phases form a continuum solid that, under the application of an external magnetic field, mechanically reacts leading to changes in shape and volume or/and alterations in its rheological properties. Such a magneto-mechanical response is determined by the material properties of the polymeric matrix and magnetic particles. In this work, we present the mechanical characterisation of MAPs constituted by PDMS filled with carbonyl iron powder (CIP) particles. To this end, sixteen different combinations of elastomeric base/crosslinker mixing ratio (from 5:1 to 20:1) and particles' volume fraction (from 0% to 30%) are tested under tensile loading. These results are analysed and provide the bases for the formulation of a nonlinear constitutive model that accounts for these dependencies. The modelling approach is extended to incorporate magneto-mechanical effects. Finally, the complete model is used to provide theoretical guidance for magneto-active systems, highlighting potential applications in epithelial wound healing stimulation.DGG, DV and MAM acknowledge support from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 947723,project: 4D-BIOMAP). The authors acknowledge support from Programa de Apoyo a la Realización de Proyectos Interdisciplinares deI+D para Jóvenes Investigadores de la Universidad Carlos III de Madrid and Comunidad de Madrid, Spain (project: BIOMASKIN). DGG acknowledges support from the Talent Attraction grant (CM 2018 -2018-T2/IND-9992) from the Comunidad de Madrid and MAM acknowledges support from the Ministerio de Ciencia, Innovacion y Universidades, Spain (FPU19/03874)

Effect of Fibrin Concentration on the In Vitro Production of Dermo-Epidermal Equivalents

This article belongs to the Special Issue Advanced Biomaterials for Wound Healing 2021.Human plasma-derived bilayered skin substitutes were successfully used by our group to produce human-based in vitro skin models for toxicity, cosmetic, and pharmaceutical testing. However, mechanical weakness, which causes the plasma-derived fibrin matrices to contract significantly, led us to attempt to improve their stability. In this work, we studied whether an increase in fibrin concentration from 1.2 to 2.4 mg/mL (which is the useful fibrinogen concentration range that can be obtained from plasma) improves the matrix and, hence, the performance of the in vitro skin cultures. The results show that this increase in fibrin concentration indeed affected the mechanical properties by doubling the elastic moduli and the maximum load. A structural analysis indicated a decreased porosity for the 2.4 mg/mL hydrogels, which can help explain this mechanical behavior. The contraction was clearly reduced for the 2.4 mg/mL matrices, which also allowed for the growth and proliferation of primary fibroblasts and keratinocytes, although at a somewhat reduced rate compared to the 1.2 mg/mL gels. Finally, both concentrations of fibrin gave rise to organotypic skin cultures with a fully differentiated epidermis, although their lifespans were longer (25–35%) in cultures with more concentrated matrices, which improves their usefulness. These systems will allow the generation of much better in vitro skin models for the testing of drugs, cosmetics and chemicals, or even to “personalized” skin for the diagnosis or determination of the most effective treatment possible.This research was funded by Programa de Actividades de I+D entre Grupos de Investigación de la Comunidad de Madrid, S2018/BAA-4480, Biopieltec-CM; by Programa Estatal de I+D+i Orientada a los Retos de la Sociedad, RTI2018-101627-B-I00; by Programa de Apoyo a la Realización de Proyectos Interdisciplinares de I+D para Jóvenes Investigadores de la Universidad Carlos III de Madrid (project: BIOMASKIN); and by Cátedra Fundación Ramón Areces

A new microfluidic method enabling the generation of multi-layered tissues-on-chips using skin cells as a proof of concept

Microfluidic-based tissues-on-chips (TOCs) have thus far been restricted to modelling simple epithelia as a single cell layer, but likely due to technical difficulties, no TOCs have been reported to include both an epithelial and a stromal component despite the biological importance of the stroma for the structure and function of human tissues. We present, for the first time, a novel approach to generate 3D multilayer tissue models in microfluidic platforms. As a proof of concept, we modelled skin, including a dermal and an epidermal compartment. To accomplish this, we developed a parallel flow method enabling the deposition of bilayer tissue in the upper chamber, which was subsequently maintained under dynamic nutrient flow conditions through the lower chamber, mimicking the function of a blood vessel. We also designed and built an inexpensive, easy-to-implement, versatile, and robust vinyl-based device that overcomes some of the drawbacks present in PDMS-based chips. Preliminary tests indicate that this biochip will allow the development and maintenance of multilayer tissues, which opens the possibility of better modelling of the complex cell–cell and cell–matrix interactions that exist in and between the epithelium and mesenchyme, allowing for better-grounded tissue modelling and drug screening.This work was supported by the "Programa de Actividades de I+D entre Grupos de Investigación de la Comunidad de Madrid" project S2018/BAA-4480, Biopieltec-CM and the Cátedra Fundación Ramón Areces

Tuning the cell and biological tissue environment through magneto-active materials

This review focuses on novel applications based on multifunctional materials to actuate biological processes. The first section of the work revisits the current knowledge on mechanically dependent biological processes across several scales from subcellular and cellular level to the cellcollective scale (continuum approaches). This analysis presents a wide variety of mechanically dependent biological processes on nervous system behaviour; bone development and healing; collective cell migration. In the second section, this review presents recent advances in smart materials suitable for use as cell substrates or scaffolds, with a special focus on magneto-active polymers (MAPs). Throughout the manuscript, both experimental and computational methodologies applied to the different treated topics are reviewed. Finally, the use of smart polymeric materials in bioengineering applications is discussed.This work has been supported by the Madrid Government (Comunidad de Madrid) under the Multiannual Agreement with UC3M in the line of "Fostering Young Doctors Research" (BIOMASKIN-CM-UC3M), and in the context of the V PRICIT (Regional Programme of Research and Technological Innovation, and support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 947723). DGG acknowledges support from the Talent Attraction grant (CM 2018-2018-T2/IND-9992) from the Comunidad de Madrid.Publicad

Technological advances in fibrin for tissue engineering

Fibrin is a promising natural polymer that is widely used for diverse applications, such as hemostatic glue, carrier for drug and cell delivery, and matrix for tissue engineering. Despite the significant advances in the use of fibrin for bioengineering and biomedical applications, some of its characteristics must be improved for suitability for general use. For example, fibrin hydrogels tend to shrink and degrade quickly after polymerization, particularly when they contain embedded cells. In addition, their poor mechanical properties and batch-to-batch variability affect their handling, long-term stability, standardization, and reliability. One of the most widely used approaches to improve their properties has been modification of the structure and composition of fibrin hydrogels. In this review, recent advances in composite fibrin scaffolds, chemically modified fibrin hydrogels, interpenetrated polymer network (IPN) hydrogels composed of fibrin and other synthetic or natural polymers are critically reviewed, focusing on their use for tissue engineering.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research was supported by Programa de Actividades de I + D entre Grupos de Investigación de la Comunidad de Madrid, S2018/BAA-4480, Biopieltec-CM, Programa Estatal de I + D + i Orientada a los Retos de la Sociedad, RTI2018-101627-B-I00, Proyectos de Generación de Conocimiento 2021, PID2021-126523OB-I00, Proyectos en colaboración público-privada 2021, CPP2021-008396, LOLICOMB Project, PID2020-116439GB-I00 and Cátedra Fundación Ramón Areces. Grant PID2021-126523OB-I00 funded by MCIN/AEI/10.13039/501100011033 and, as appropriate, by “ERDF A way of making Europe.” Grant CPP2021-008396 funded by MCIN/AEI/ 10.13039/501100011033 and by the European Union “NextGenerationEU/PRTR.”Publicad

Evaluation of different methodologies for primary human dermal fibroblast spheroid formation: automation through 3D bioprinting technology

Cell spheroids have recently emerged as an effective tool to recapitulate native microenvironments of living organisms in an in vitro scenario, increasing the reliability of the results obtained and broadening their applications in regenerative medicine, cancer research, disease modeling and drug screening. In this study the generation of spheroids containing primary human dermal fibroblasts was approached using the two-widely employed methods: hanging-drop and U-shape low adhesion plate (LA-plate). Moreover, extrusion-based three-dimensional (3D) bioprinting was introduced to achieve a standardized and scalable production of cell spheroids, decreasing considerably the possibilities of human error. This was ensured when U-shape LA-plates were used, showing an 85% formation efficiency, increasing up to a 98% when it was automatized using the 3D bioprinting technologies. However, sedimentation effect within the cartridge led to a reduction of 20% in size of the spheroid during the printing process. Hyaluronic acid (HA) was chosen as viscosity enhancer to supplement the bioink and overcome cell sedimentation within the cartridge due to the high viability values exhibited by the cells -around 80%- at the used conditions. Finally, (ANCOVA) of spheroid size over time for different printing conditions stand out HA 0.4% (w/v) 60 kDa as the viscosity-improved bioink that exhibit the highest cell viability and spheroid formation percentages. Besides, not only did it ensure cell spheroid homogeneity over time, reducing cell sedimentation effects, but also wider spheroid diameters over time with less variability, outperforming significantly manual loading.We kindly thank Daniel García for their guidance with the rheological experiments. This work was supported by Programa de Actividades de I + D entre Grupos de Investigación de la Comunidad de Madrid, S2018/ BAA-4480, Biopieltec-CM, Programa Estatal de I + D + i Orientada a los Retos de la Sociedad, RTI2018-101627-B-I00 and Cátedra Fundación Ramón Areces. The experimental techniques used during this study were performed in the CleanRooms of Bioengineering, Universidad Carlos III de Madrid, Madrid, Spain

3D bioprinting of functional human skin: production and in vivo analysis

Significant progress has been made over the past 25 years in the development of in vitro-engineered substitutes that mimic human skin, either to be used as grafts for the replacement of lost skin, or for the establishment of in vitro human skin models. In this sense, laboratory-grown skin substitutes containing dermal and epidermal components offer a promising approach to skin engineering. In particular, a human plasma-based bilayered skin generated by our group, has been applied successfully to treat burns as well as traumatic and surgical wounds in a large number of patients in Spain. There are some aspects requiring improvements in the production process of this skin; for example, the relatively long time (three weeks) needed to produce the surface required to cover an extensive burn or a large wound, and the necessity to automatize and standardize a process currently performed manually.This work was partially supported by grant DPI2014-61887-EXP from the Spanish Ministerio de Economía y Competitividad

Magneto-mechanical system to reproduce and quantify complex strain patterns in biological materials

Biological cells and tissues are continuously subjected to mechanical stress and strain cues from their surrounding substrate. How these forces modulate cell and tissue behavior is a major question in mechanobiology. To conduct studies under controlled varying physiological strain scenarios, a new virtually-assisted experimental system is proposed allowing for non-invasive and real-time control of complex deformation modes within the substrates. This approach is based on the use of extremely soft magneto-active polymers, which mimic the stiffness of biological materials. Thus, the system enables the untethered control of biological substrates providing reversible mechanical changes and controlling heterogeneous patterns. Motivated on a deep magneto-mechanical characterization across scales, a multi-physics and multi-scale in silico framework was developed to guide the experimental stimulation setup. The versatility and viability of the system have been demonstrated through its ability to reproduce complex mechanical scenarios simulating local strain patterns in brain tissue during a head impact, and its capability to transmit physiologically relevant mechanical forces to dermal fibroblasts. The proposed framework opens the way to understanding the mechanobiological processes that occur during complex and dynamic deformation states, e.g., in traumatic brain injury, pathological skin scarring or fibrotic heart remodeling during myocardial infarction.The authors thank Denis Wirtz (Johns Hopkins University) and Jean-Christophe Olivo-Marin (Institute Pasteur) for relevant discussion. The authors acknowledge support from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Program (Grant agreement No. 947723, project: 4D-BIOMAP), and from Programa de Apoyo a la Realizacion de Proyectos Interdiscisplinares de I+D para Jovenes Investigadores de la Universidad Carlos III de Madrid and Comunidad de Madrid (project: BIOMASKIN). MAMM and CGC acknowledges support from the Ministerio de Ciencia, Innovacion y Universidades, Spain (FPU19/03874 and FPU20/01459) and DGG acknowledges support from the Talent Attraction grant (CM 2018 - 2018-T2/IND-9992) from the Comunidad de Madrid

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