Electrospun 3D Scaffolds for Tissue Regeneration

Hierarchical and urchin-like chitosan/hydroxyapatite microspheres as drug-laden cell carriers

Biopolymer/hydroxyapatite (HAp) composites are one type of the most promising materials for a variety of biomedical applications. In this study, hierarchical and urchin-like chitosan/HAp nanowire (HU-CS/HAp NW) microspheres were for the first time synthesized by in situ hydrothermal treatment of chitosan/HAp (CS/HAp) microspheres in the acetic acid solution. The results indicate that HU-CS/HAp NW microspheres were spherical in morphology with a diameter of 100-300 μm. Their surface was mainly constructed by numerous HAp NWs with the diameter of 80-120 nm and showed a hierarchical and urchin-like nanofibrous architecture. It was found that the acidic hydrothermal treatment caused an in situ conversion of HAp NPs to HAp NWs. In vitro biocompatible evaluation indicates that HU-CS/HAp NW microspheres showed an enhanced cell attachment and proliferation due to the presence of hierarchical and urchin-like architecture. Furthermore, HU-CS/HAp NW microspheres showed a good adsorption capacity for tetracycline hydrochloride (model drug, one of the most representative antibiotics) with a higher adsorption capacity than CS/HAp microspheres and well maintained their antibacterial efficacy to inhibit the growth of bacteria: Escherichia coli and Staphylococcus aureus. Thus, the present HU-CS/HAp NW microspheres would be applicable as novel drug-laden cell carriers.

Multifunctional Scaffolds Based on Emulsion and Coaxial Electrospinning Incorporation of Hydroxyapatite for Bone Tissue Regeneration

Tissue engineering is nowadays a powerful tool to restore damaged tissues and recover their normal functionality. Advantages over other current methods are well established, although a continuous evolution is still necessary to improve the final performance and the range of applications. Trends are nowadays focused on the development of multifunctional scaffolds with hierarchical structures and the capability to render a sustained delivery of bioactive molecules under an appropriate stimulus. Nanocomposites incorporating hydroxyapatite nanoparticles (HAp NPs) have a predominant role in bone tissue regeneration due to their high capacity to enhance osteoinduction, osteoconduction, and osteointegration, as well as their encapsulation efficiency and protection capability of bioactive agents. Selection of appropriated polymeric matrices is fundamental and consequently great efforts have been invested to increase the range of properties of available materials through copolymerization, blending, or combining structures constituted by different materials. Scaffolds can be obtained from different processes that differ in characteristics, such as texture or porosity. Probably, electrospinning has the greater relevance, since the obtained nanofiber membranes have a great similarity with the extracellular matrix and, in addition, they can easily incorporate functional and bioactive compounds. Coaxial and emulsion electrospinning processes appear ideal to generate complex systems able to incorporate highly different agents. The present review is mainly focused on the recent works performed with Hap-loaded scaffolds having at least one structural layer composed of core/shell nanofibers.

Vascularization Strategies in 3D Cell Culture Models: From Scaffold-Free Models to 3D Bioprinting

The discrepancies between the findings in preclinical studies, and in vivo testing and clinical trials have resulted in the gradual decline in drug approval rates over the past decades. Conventional in vitro drug screening platforms employ two-dimensional (2D) cell culture models, which demonstrate inaccurate drug responses by failing to capture the three-dimensional (3D) tissue microenvironment in vivo. Recent advancements in the field of tissue engineering have made possible the creation of 3D cell culture systems that can accurately recapitulate the cell-cell and cell-extracellular matrix interactions, as well as replicate the intricate microarchitectures observed in native tissues. However, the lack of a perfusion system in 3D cell cultures hinders the establishment of the models as potential drug screening platforms. Over the years, multiple techniques have successfully demonstrated vascularization in 3D cell cultures, simulating in vivo-like drug interactions, proposing the use of 3D systems as drug screening platforms to eliminate the deviations between preclinical and in vivo testing. In this review, the basic principles of 3D cell culture systems are briefly introduced, and current research demonstrating the development of vascularization in 3D cell cultures is discussed, with a particular focus on the potential of these models as the future of drug screening platforms.

Cellular Interaction of Bone Marrow Mesenchymal Stem Cells with Polymer and Hydrogel 3D Microscaffold Templates

Biomimicking biological niches of healthy tissues or tumors can be achieved by means of artificial microenvironments, where structural and mechanical properties are crucial parameters to promote tissue formation and recreate natural conditions. In this work, three-dimensional (3D) scaffolds based on woodpile structures were fabricated by two-photon polymerization (2PP) of different photosensitive polymers (IP-S and SZ2080) and hydrogels (PEGDA 700) using two different 2PP setups, a commercial one and a customized one. The structures' properties were tuned to study the effect of scaffold dimensions (gap size) and their mechanical properties on the adhesion and proliferation of bone marrow mesenchymal stem cells (BM-MSCs), which can serve as a model for leukemic diseases, among other hematological applications. The woodpile structures feature gap sizes of 25, 50, and 100 μm and a fixed beam diameter of 25 μm, to systematically study the optimal cell colonization that promotes healthy cell growth and potential tissue formation. The characterization of the scaffolds involved scanning electron microscopy and mechanical nanoindenting, while their suitability for supporting cell growth was evaluated with live/dead cell assays and multistaining 3D confocal imaging. In the mechanical assays of the hydrogel material, we observed two different stiffness ranges depending on the indentation depth. Larger gap woodpile structures coated with fibronectin were identified as the most promising scaffolds for 3D BM-MSC cellular models, showing higher proliferation rates. The results indicate that both the design and the employed materials are suitable for further assays, where retaining the BM-MSC stemness and original features is crucial, including studies focused on BM disorders such as leukemia and others. Moreover, the combination of 3D scaffold geometry and materials holds great potential for the investigation of cellular behaviors in a co-culture setting, for example, mesenchymal and hematopoietic stem cells, to be further applied in medical research and pharmacological studies.

Organ-On-A-Chip: A Survey of Technical Results and Problems

Organ-on-a-chip (OoC), also known as micro physiological systems or "tissue chips" have attracted substantial interest in recent years due to their numerous applications, especially in precision medicine, drug development and screening. Organ-on-a-chip devices can replicate key aspects of human physiology, providing insights into the studied organ function and disease pathophysiology. Moreover, these can accurately be used in drug discovery for personalized medicine. These devices present useful substitutes to traditional preclinical cell culture methods and can reduce the use of in vivo animal studies. In the last few years OoC design technology has seen dramatic advances, leading to a wide range of biomedical applications. These advances have also revealed not only new challenges but also new opportunities. There is a need for multidisciplinary knowledge from the biomedical and engineering fields to understand and realize OoCs. The present review provides a snapshot of this fast-evolving technology, discusses current applications and highlights advantages and disadvantages for biomedical approaches.

Collagen/Chitosan Functionalization of Complex 3D Structures Fabricated by Laser Direct Writing via Two-Photon Polymerization for Enhanced Osteogenesis

The fabrication of 3D microstructures is under continuous development for engineering bone substitutes. Collagen/chitosan (Col/CT) blends emerge as biomaterials that meet the mechanical and biological requirements associated with bone tissue. In this work, we optimize the osteogenic effect of 3D microstructures by their functionalization with Col/CT blends with different blending ratios. The structures were fabricated by laser direct writing via two-photons polymerization of IP-L780 photopolymer. They comprised of hexagonal and ellipsoidal units 80 µm in length, 40 µm in width and 14 µm height, separated by 20 µm pillars. Structures’ functionalization was achieved via dip coating in Col/CT blends with specific blending ratios. The osteogenic role of Col/CT functionalization of the 3D structures was confirmed by biological assays concerning the expression of alkaline phosphatase (ALP) and osteocalcin secretion as osteogenic markers and Alizarin Red (AR) as dye for mineral deposits in osteoblast-like cells seeded on the structures. The structures having ellipsoidal units showed the best results, but the trends were similar for both ellipsoidal and hexagonal units. The strongest osteogenic effect was obtained for Col/CT blending ratio of 20/80, as demonstrated by the highest ALP activity, osteocalcin secretion and AR staining intensity in the seeded cells compared to all the other samples.

Scaffolding Strategies for Tissue Engineering and Regenerative Medicine Applications

During the past two decades, tissue engineering and the regenerative medicine field have invested in the regeneration and reconstruction of pathologically altered tissues, such as cartilage, bone, skin, heart valves, nerves and tendons, and many others. The 3D structured scaffolds and hydrogels alone or combined with bioactive molecules or genes and cells are able to guide the development of functional engineered tissues, and provide mechanical support during in vivo implantation. Naturally derived and synthetic polymers, bioresorbable inorganic materials, and respective hybrids, and decellularized tissue have been considered as scaffolding biomaterials, owing to their boosted structural, mechanical, and biological properties. A diversity of biomaterials, current treatment strategies, and emergent technologies used for 3D scaffolds and hydrogel processing, and the tissue-specific considerations for scaffolding for Tissue engineering (TE) purposes are herein highlighted and discussed in depth. The newest procedures focusing on the 3D behavior and multi-cellular interactions of native tissues for further use for in vitro model processing are also outlined. Completed and ongoing preclinical research trials for TE applications using scaffolds and hydrogels, challenges, and future prospects of research in the regenerative medicine field are also presented.