A versatile method for combining different biopolymers in a core/shell fashion by 3D plotting to achieve mechanically robust constructs

[Research progress on chitosan composite scaffolds in bone tissue engineering]

Bone tissue engineering is a scientific field devoted to the development of materials that can repair or replace human bone tissue with biological and engineering methods. The stent, which provides structural support and adhesion sites for cell and tissue growth, is one of the key elements in tissue engineering. The scaffold may comprise metal, polymer, and ceramic biomaterial. The polymer scaffold is widely used due to its biocompatibility, biodegradability, and mechanical stability. Chitosan, as a natural polymer, is derived from chitin and has played a particularly important role in bone tissue engineering over the past two decades. In recent years, chitosan composites and their application in bone tissue engineering have received considerable attention due to their small foreign body reaction, excellent antibacterial properties, plasticity, suitability for inward cell growth, and bone conduction. This review will discuss the biocompatibility and osteogenesis research in vivo and in vitro of several common chitosan composites in bone tissue engineering.

Bioprinting of mineralized constructs utilizing multichannel plotting of a self-setting calcium phosphate cement and a cell-laden bioink

Due to their characteristic resemblance of the mineral component of bone, calcium phosphates are widely accepted as optimal bone substitute materials. Recent research focused on the development of pasty calcium phosphate cement (CPC) formulations, which can be fabricated into various shapes by low-temperature extrusion-based additive manufacturing, namely 3D plotting. While it could be demonstrated that sensitive substances like growth factors can be integrated in such printed CPC scaffolds without impairment of their biological activity live cells cannot be suspended in CPC as they may not be functional when enclosed in a solid and stiff matrix. In contrast, 3D bioprinting of soft cell-laden hydrogels (bioinks) enables the fabrication of constructs with spatially defined cell distribution, which has the potential to overcome problems of conventional cell seeding techniques-but such objects lack mechanical stability. Herein, we combine 3D plotting of CPC and bioprinting of a cell-laden bioink for the first time. As model bioink, an alginate-methylcellulose blend (alg/mc) was used, previously developed by us. Firstly, a fabrication regime was established, enabling optimal setting of CPC and cell survival inside the bioink. As the cells are exposed to the chemical changes of CPC precursors during setting, we studied the compatibility of the complex system of CPC and cell-laden alg/mc for a combined extrusion process and characterized the cellular behavior of encapsulated human mesenchymal stroma cells within the bioink at the interface and in direct vicinity to the CPC. Furthermore, biphasic scaffolds were mechanically characterized and a model for osteochondral tissue grafts is proposed. The manuscript discusses possible impacts of the CPC setting reaction on cells within the bioink and illustrates the advantages of CPC in bioprinting as alternative to the commonly used thermoplasts for bone tissue engineering.

3D bioprinting of functional tissue models for personalized drug screening and in vitro disease modeling

3D bioprinting is emerging as a promising technology for fabricating complex tissue constructs with tailored biological components and mechanical properties. Recent advances have enabled scientists to precisely position materials and cells to build functional tissue models for in vitro drug screening and disease modeling. This review presents state-of-the-art 3D bioprinting techniques and discusses the choice of cell source and biomaterials for building functional tissue models that can be used for personalized drug screening and disease modeling. In particular, we focus on 3D-bioprinted liver models, cardiac tissues, vascularized constructs, and cancer models for their promising applications in medical research, drug discovery, toxicology, and other pre-clinical studies.

3D neural tissue models: From spheroids to bioprinting

Three-dimensional (3D) in vitro neural tissue models provide a better recapitulation of in vivo cell-cell and cell-extracellular matrix interactions than conventional two-dimensional (2D) cultures. Therefore, the former is believed to have great potential for both mechanistic and translational studies. In this paper, we review the recent developments in 3D in vitro neural tissue models, with a particular focus on the emerging bioprinted tissue structures. We draw on specific examples to describe the merits and limitations of each model, in terms of different applications. Bioprinting offers a revolutionary approach for constructing repeatable and controllable 3D in vitro neural tissues with diverse cell types, complex microscale features and tissue level responses. Further advances in bioprinting research would likely consolidate existing models and generate complex neural tissue structures bearing higher fidelity, which is ultimately useful for probing disease-specific mechanisms, facilitating development of novel therapeutics and promoting neural regeneration.

3D Printing Polymers with Supramolecular Functionality for Biological Applications

Supramolecular chemistry continues to experience widespread growth, as fine-tuned chemical structures lead to well-defined bulk materials. Previous literature described the roles of hydrogen bonding, ionic aggregation, guest/host interactions, and π-π stacking to tune mechanical, viscoelastic, and processing performance. The versatility of reversible interactions enables the more facile manufacturing of molded parts with tailored hierarchical structures such as tissue engineered scaffolds for biological applications. Recently, supramolecular polymers and additive manufacturing processes merged to provide parts with control of the molecular, macromolecular, and feature length scales. Additive manufacturing, or 3D printing, generates customizable constructs desirable for many applications, and the introduction of supramolecular interactions will potentially increase production speed, offer a tunable surface structure for controlling cell/scaffold interactions, and impart desired mechanical properties through reinforcing interlayer adhesion and introducing gradients or self-assembled structures. This review details the synthesis and characterization of supramolecular polymers suitable for additive manufacture and biomedical applications as well as the use of supramolecular polymers in additive manufacturing for drug delivery and complex tissue scaffold formation. The effect of supramolecular assembly and its dynamic behavior offers potential for controlling the anisotropy of the printed objects with exquisite geometrical control. The potential for supramolecular polymers to generate well-defined parts, hierarchical structures, and scaffolds with gradient properties/tuned surfaces provides an avenue for developing next-generation biomedical devices and tissue scaffolds.

Development of a clay based bioink for 3D cell printing for skeletal application

Three-dimensional printing of cell-laden hydrogels has evolved as a promising approach on the route to patient-specific or complex tissue-engineered constructs. However, it is still challenging to print structures with both, high shape fidelity and cell vitality. Herein, we used a synthetic nanosilicate clay, called Laponite, to build up scaffolds utilising the extrusion-based method 3D plotting. By blending with alginate and methylcellulose, a bioink was developed which allowed easy extrusion, achieving scaffolds with high printing fidelity. Following extrusion, approximately 70%-75% of printed immortalised human mesenchymal stem cells survived and cell viability was maintained over 21 days within the plotted constructs. Mechanical properties of scaffolds comprised of the composite bioink decreased over time when stored under cell culture conditions. Nevertheless, shape of the plotted constructs was preserved even over longer cultivation periods. Laponite is known for its favourable drug delivery properties. Two model proteins, bovine serum albumin and vascular endothelial growth factor were loaded into the bioink. We demonstrate that the release of both growth factors significantly changed to a more sustained profile by inclusion of Laponite in comparison to an alginate-methylcellulose blend in the absence of Laponite. In summary, addition of a synthetic clay, Laponite, improved printability, increased shape fidelity and was beneficial for controlled release of biologically active agents such as growth factors.

Handheld Co-Axial Bioprinting: Application to in situ surgical cartilage repair

Three-dimensional (3D) bioprinting is driving major innovations in the area of cartilage tissue engineering. Extrusion-based 3D bioprinting necessitates a phase change from a liquid bioink to a semi-solid crosslinked network achieved by a photo-initiated free radical polymerization reaction that is known to be cytotoxic. Therefore, the choice of the photocuring conditions has to be carefully addressed to generate a structure stiff enough to withstand the forces phisiologically applied on articular cartilage, while ensuring adequate cell survival for functional chondral repair. We recently developed a handheld 3D printer called "Biopen". To progress towards translating this freeform biofabrication tool into clinical practice, we aimed to define the ideal bioprinting conditions that would deliver a scaffold with high cell viability and structural stiffness relevant for chondral repair. To fulfill those criteria, free radical cytotoxicity was confined by a co-axial Core/Shell separation. This system allowed the generation of Core/Shell GelMa/HAMa bioscaffolds with stiffness of 200KPa, achieved after only 10 seconds of exposure to 700 mW/cm2 of 365 nm UV-A, containing >90% viable stem cells that retained proliferative capacity. Overall, the Core/Shell handheld 3D bioprinting strategy enabled rapid generation of high modulus bioscaffolds with high cell viability, with potential for in situ surgical cartilage engineering.