Hierarchical fibrillar scaffolds obtained by non-conventional layer-by-layer electrostatic self-assembly

3D Bioprinting in Tissue Engineering for Medical Applications: The Classic and the Hybrid

Three-dimensional (3D) printing, as one of the most popular recent additive manufacturing processes, has shown strong potential for the fabrication of biostructures in the field of tissue engineering, most notably for bones, orthopedic tissues, and associated organs. Desirable biological, structural, and mechanical properties can be achieved for 3D-printed constructs with a proper selection of biomaterials and compatible bioprinting methods, possibly even while combining additive and conventional manufacturing (AM and CM) procedures. However, challenges remain in the need for improved printing resolution (especially at the nanometer level), speed, and biomaterial compatibilities, and a broader range of suitable 3D-printed materials. This review provides an overview of recent advances in the development of 3D bioprinting techniques, particularly new hybrid 3D bioprinting technologies for combining the strengths of both AM and CM, along with a comprehensive set of material selection principles, promising medical applications, and limitations and future prospects.

Biomimetic Layer-by-Layer Self-Assembly of Nanofilms, Nanocoatings, and 3D Scaffolds for Tissue Engineering

Achieving surface design and control of biomaterial scaffolds with nanometer- or micrometer-scaled functional films is critical to mimic the unique features of native extracellular matrices, which has significant technological implications for tissue engineering including cell-seeded scaffolds, microbioreactors, cell assembly, tissue regeneration, etc. Compared with other techniques available for surface design, layer-by-layer (LbL) self-assembly technology has attracted extensive attention because of its integrated features of simplicity, versatility, and nanoscale control. Here we present a brief overview of current state-of-the-art research related to the LbL self-assembly technique and its assembled biomaterials as scaffolds for tissue engineering. An overview of the LbL self-assembly technique, with a focus on issues associated with distinct routes and driving forces of self-assembly, is described briefly. Then, we highlight the controllable fabrication, properties, and applications of LbL self-assembly biomaterials in the forms of multilayer nanofilms, scaffold nanocoatings, and three-dimensional scaffolds to systematically demonstrate advances in LbL self-assembly in the field of tissue engineering. LbL self-assembly not only provides advances for molecular deposition but also opens avenues for the design and development of innovative biomaterials for tissue engineering.

Chain conformation of poly(acrylic acid)-graft-poly(ethylene oxide)-graft-dodecyl in solution: an anomalous counter-ions condensation

A dielectric spectroscopy study on a polyelectrolyte in aqueous solutions, which contains hydrophobic groups in part of the side chains poly(acrylic acid)-graft-poly(ethylene oxide)-graft-dodecyl (PAA-g-PEO-g-dodecyl) is reported. A refined double layer polarization model was proposed to analyze the double dielectric relaxations in the dielectric spectra. Various electrical and structural parameters of the copolymers were obtained. Besides the crossover concentration, another turning point around 4 mg mL^-1 was identified through the analysis of all the dielectrical parameters including dielectric increment, relaxation time and correlation length. According to the scaling relationship between the correlation length and concentration, a necklace-like structure was predicted. In addition, 4 mg mL^-1 was proven to be the transition point between string-controlling with bead-controlling structure of the chains. In addition, the fraction of effective charges on the chains was illustrated by Ito's counter-ions fluctuation theory, as well as its linear dependence relationship with the zeta potential. Meanwhile, the counter-ions condensation behavior was consistent with the avalanche-like trend, which was predicted by theory for a hydrophobic polyelectrolyte with a necklace conformation. The results demonstrated that the electrostatic interactions were the main driving force of the necklace-like structure with pendant globules when the string-controlling structure was below 4 mg mL^-1. While hydrophobic interactions are the main driving force of the structure of bead-controlling above 4 mg mL^-1.

Biomineralization: From Material Tactics to Biological Strategy

Biomineralization is an important tactic by which biological organisms produce hierarchically structured minerals with marvellous functions. Biomineralization studies typically focus on the mediation function of organic matrices on inorganic minerals, which helps scientists to design and synthesize bioinspired functional materials. However, the presence of inorganic minerals may also alter the native behaviours of organic matrices and even biological organisms. This progress report discusses the latest achievements relating to biomineralization mechanisms, the manufacturing of biomimetic materials and relevant applications in biological and biomedical fields. In particular, biomineralized vaccines and algae with improved thermostability and photosynthesis, respectively, demonstrate that biomineralization is a strategy for organism evolution via the rational design of organism-material complexes. The successful modification of biological systems using materials is based on the regulatory effect of inorganic materials on organic organisms, which is another aspect of biomineralization control. Unlike previous studies, this study integrates materials and biological science to achieve a more comprehensive view of the mechanisms and applications of biomineralization.

Biomimetic Mineralized Hierarchical Graphene Oxide/Chitosan Scaffolds with Adsorbability for Immobilization of Nanoparticles for Biomedical Applications

Biomimetic calcium phosphate mineralized graphene oxide/chitosan (GO/CS) scaffolds with hierarchical structures were developed. First, GO/CS scaffolds with large micropores (∼300 μm) showed high mechanical strength due to the electrostatic interaction between the oxygen-containing functional groups of GO and the amine groups of CS. Second, octacalcuim phosphate (OCP) with porous structures (∼1 μm) was biomimetically mineralized on the surfaces of the GO/CS scaffolds (OCP-GO/CS). The hierarchical microporous structures of OCP-GO/CS scaffolds provide a suitable environment for cell adhesion and growth. The scaffolds have exceptional adsorbability of nanoparticles. Bone morphogenetic protein-2 (BMP-2)-encapsulated bovine serum albumin (BSA) nanoparticles and Ag nanoparticles (Ag-NPs) were adsorbed in the scaffolds for enhancement of osteoinductivity and antibacterial properties, respectively. Antibacterial tests showed that the scaffolds exhibited high antibacterial properties against both Escherichia coli and Staphylococcus epidermidis. In vitro and in vivo experiments revealed that the scaffolds have good biocompatibility, enhanced bone marrow stromal cells proliferation and differentiation, and induced bone tissue regeneration. Thus, the biomimetic OCP-GO/CS scaffolds with immobilized growth factors and antibacterial agents might be excellent candidates for bone tissue engineering.

Biosynthesis and Characterization of Cross-Linked Fmoc Peptide-Based Hydrogels for Drug Delivery Applications

Recently, scientific and technological interest in the synthesis of novel peptide-based hydrogel materials have grown dramatically. Applications of such materials mostly concern the biomedical field with examples covering sectors such as drug delivery, tissue engineering, and production of scaffolds for cell growth, thanks to their biocompatibility and biodegradability. In this work we synthesized Fmoc-Phe₃ based hydrogels of different chirality by using a biocatalytic approach. Moreover, we investigated the possibility of employing a crosslinker during the biosynthetic process and we studied and compared some chemico-physical features of both crosslinked and non-crosslinked hydrogels. In particular, we investigated the rheological properties of such materials, as well as their swelling ability, stability in aqueous medium, and their structure by SEM and AFM analysis. Crosslinked and non-crosslinked hydrogels could be formed by this procedure with comparable yields but distinct chemico-physical features. We entrapped dexamethasone within nanopolymeric particles based on PLGA coated or not with chitosan and we embedded these nanoparticles into the hydrogels. Dexamethasone release from such a nanopolymer/hydrogel system was controlled and sustained and dependent on genipin crosslinking degree. The possibility of efficiently coupling a drug delivery system to hydrogel materials seem particularly promising for tissue engineering applications, where the hydrogel could provide cells the necessary support for their growth, while nanoparticles could favor cell growth or differentiation by providing them the necessary bioactive molecules.

Hierarchical scaffolds enhance osteogenic differentiation of human Wharton's jelly derived stem cells

Hierarchical structures, constituted by polymeric nano and microfibers, have been considered promising scaffolds for tissue engineering strategies, mainly because they mimic, in some way, the complexity and nanoscale detail observed in real organs. The chondrogenic potential of these scaffolds has been previously demonstrated, but their osteogenic potential is not yet corroborated. In order to assess if a hierarchical structure, with nanoscale details incorporated, is an improved scaffold for bone tissue regeneration, we evaluate cell adhesion, proliferation, and osteogenic differentiation of human Wharton's jelly derived stem cells (hWJSCs), seeded into hierarchical fibrous scaffolds. Biological data corroborates that hierarchical fibrous scaffolds show an enhanced cell entrapment when compared to rapid prototyped scaffolds without nanofibers. Furthermore, upregulation of bone specific genes and calcium phosphate deposition confirms the successful osteogenic differentiation of hWJSCs on these scaffolds. These results support our hypothesis that a scaffold with hierarchical structure, in conjugation with hWJSCs, represents a possible feasible strategy for bone tissue engineering applications.

Combined additive manufacturing approaches in tissue engineering

Advances introduced by additive manufacturing (AM) have significantly improved the control over the microarchitecture of scaffolds for tissue engineering. This has led to the flourishing of research works addressing the optimization of AM scaffolds microarchitecture to optimally trade-off between conflicting requirements (e.g. mechanical stiffness and porosity level). A fascinating trend concerns the integration of AM with other scaffold fabrication methods (i.e. "combined" AM), leading to hybrid architectures with complementary structural features. Although this innovative approach is still at its beginning, significant results have been achieved in terms of improved biological response to the scaffold, especially targeting the regeneration of complex tissues. This review paper reports the state of the art in the field of combined AM, posing the accent on recent trends, challenges, and future perspectives.

Towards the design of 3D multiscale instructive tissue engineering constructs: Current approaches and trends

The design of 3D constructs with adequate properties to instruct and guide cells both in vitro and in vivo is one of the major focuses of tissue engineering. Successful tissue regeneration depends on the favorable crosstalk between the supporting structure, the cells and the host tissue so that a balanced matrix production and degradation are achieved. Herein, the major occurring events and players in normal and regenerative tissue are overviewed. These have been inspiring the selection or synthesis of instructive cues to include into the 3D constructs. We further highlight the importance of a multiscale perception of the range of features that can be included on the biomimetic structures. Lastly, we focus on the current and developing tissue-engineering approaches for the preparation of such 3D constructs: top-down, bottom-up and integrative. Bottom-up and integrative approaches present a higher potential for the design of tissue engineering devices with multiscale features and higher biochemical control than top-down strategies, and are the main focus of this review.

Electrostatically driven self-assembly of CdTe nanoparticles with organic chromophores probed via Ham effect

The polarity difference between nanoparticle's surface and medium is utilized for studying electrostatically driven self-assembly; moreover, diminishing the repulsive forces via charge neutralization fosters the self-organization of QDs into 2D sheets.

Evolving marine biomimetics for regenerative dentistry

New products that help make human tissue and organ regeneration more effective are in high demand and include materials, structures and substrates that drive cell-to-tissue transformations, orchestrate anatomical assembly and tissue integration with biology. Marine organisms are exemplary bioresources that have extensive possibilities in supporting and facilitating development of human tissue substitutes. Such organisms represent a deep and diverse reserve of materials, substrates and structures that can facilitate tissue reconstruction within lab-based cultures. The reason is that they possess sophisticated structures, architectures and biomaterial designs that are still difficult to replicate using synthetic processes, so far. These products offer tantalizing pre-made options that are versatile, adaptable and have many functions for current tissue engineers seeking fresh solutions to the deficiencies in existing dental biomaterials, which lack the intrinsic elements of biofunctioning, structural and mechanical design to regenerate anatomically correct dental tissues both in the culture dish and in vivo.