Recent development in multizonal scaffolds for osteochondral regeneration

Osteochondral (OC) repair is an extremely challenging topic due to the complex biphasic structure and poor intrinsic regenerative capability of natural osteochondral tissue. In contrast to the current surgical approaches which yield only short-term relief of symptoms, tissue engineering strategy has been shown more promising outcomes in treating OC defects since its emergence in the 1990s. In particular, the use of multizonal scaffolds (MZSs) that mimic the gradient transitions, from cartilage surface to the subchondral bone with either continuous or discontinuous compositions, structures, and properties of natural OC tissue, has been gaining momentum in recent years. Scrutinizing the latest developments in the field, this review offers a comprehensive summary of recent advances, current hurdles, and future perspectives of OC repair, particularly the use of MZSs including bilayered, trilayered, multilayered, and gradient scaffolds, by bringing together onerous demands of architecture designs, material selections, manufacturing techniques as well as the choices of growth factors and cells, each of which possesses its unique challenges and opportunities.

The potential of eggshell hydroxyapatite, collagen, and EGCG (HAp-Col-EGCG) scaffold as a pulp regeneration material

Background

Hydrogel scaffold is a biomaterial that can facilitate cells in forming a tissue structure. It can promote cell adhesion, migration, and proliferation. Further research to find a new scaffold from natural resources is challenging, so this study aimed to characterize a hydrogel composite scaffold, which has the potential to be used as a regenerative material.

Methods

The formulation of HAp-Col-EGCG was mixed with different ratios of 1%, 2%, and 4% hydroxyapatite. We analyzed its injectability, pH, and gelation time. Scanning electron microscopy (SEM), energy X-ray Spectroscopy (EDX), and Fourier-transform infrared spectroscopy (FTIR) were used to evaluate the surface morphologies, element composition, and chemical properties of HAp-Col-EGCG.

Results

The results showed that the injectability test was almost 90 % in all groups. There was no significant difference in the median value of the pH at 0, 20, and 60 min in all groups, but there was a significant difference at 40 min. The average gelation times in all groups were not significant. SEM-EDX showed a microporous scaffold, with the HAp particles well distributed in the collagen pores at a ratio of 1.9, 2.29, and 1.89 Ca/P. The FTIR results showed intermolecular bonds in the HAp-Col-EGCG scaffold. The X-ray diffraction analysis showed that collagen and EGCG did not affect the crystal structure and size of HAp. Cytotoxicity test showed more dental pulp cell viability at the 4 % HAp concentration at 514.35 ± 15.45.

Conclusion

This study indicates that hydrogel scaffold from eggshell hydroxyapatite, collagen, and EGCG has a high potential for pulp regenerative therapy.

3D Bioprinted Scaffolds for Bone Tissue Engineering: State-Of-The-Art and Emerging Technologies

Treating large bone defects, known as critical-sized defects (CSDs), is challenging because they are not spontaneously healed by the patient’s body. Due to the limitations associated with conventional bone grafts, bone tissue engineering (BTE), based on three-dimensional (3D) bioprinted scaffolds, has emerged as a promising approach for bone reconstitution and treatment. Bioprinting technology allows for incorporation of living cells and/or growth factors into scaffolds aiming to mimic the structure and properties of the native bone. To date, a wide range of biomaterials (either natural or synthetic polymers), as well as various cells and growth factors, have been explored for use in scaffold bioprinting. However, a key challenge that remains is the fabrication of scaffolds that meet structure, mechanical, and osteoconductive requirements of native bone and support vascularization. In this review, we briefly present the latest developments and discoveries of CSD treatment by means of bioprinted scaffolds, with a focus on the biomaterials, cells, and growth factors for formulating bioinks and their bioprinting techniques. Promising state-of-the-art pathways or strategies recently developed for bioprinting bone scaffolds are highlighted, including the incorporation of bioactive ceramics to create composite scaffolds, the use of advanced bioprinting technologies (e.g., core/shell bioprinting) to form hybrid scaffolds or systems, as well as the rigorous design of scaffolds by taking into account of the influence of such parameters as scaffold pore geometry and porosity. We also review in-vitro assays and in-vivo models to track bone regeneration, followed by a discussion of current limitations associated with 3D bioprinting technologies for BTE. We conclude this review with emerging approaches in this field, including the development of gradient scaffolds, four-dimensional (4D) printing technology via smart materials, organoids, and cell aggregates/spheroids along with future avenues for related BTE.

Biomaterials in bone and mineralized tissue engineering using 3D printing and bioprinting technologies

This review focuses on recently developed printable biomaterials for bone and mineralized tissue engineering. 3D printing or bioprinting is an advanced technology to design and fabricate complex functional 3D scaffolds, mimicking native tissue forin vivoapplications. We categorized the biomaterials into two main classes: 3D printing and bioprinting. Various biomaterials, including natural, synthetic biopolymers and their composites, have been studied. Biomaterial inks or bioinks used for bone and mineralized tissue regeneration include hydrogels loaded with minerals or bioceramics, cells, and growth factors. In 3D printing, the scaffold is created by acellular biomaterials (biomaterial inks), while in 3D bioprinting, cell-laden hydrogels (bioinks) are used. Two main classes of bioceramics, including bioactive and bioinert ceramics, are reviewed. Bioceramics incorporation provides osteoconductive properties and induces bone formation. Each biopolymer and mineral have its advantages and limitations. Each component of these composite biomaterials provides specific properties, and their combination can ameliorate the mechanical properties, bioactivity, or biological integration of the 3D printed scaffold. Present challenges and future approaches to address them are also discussed.

3D Printing and Bioprinting to Model Bone Cancer: The Role of Materials and Nanoscale Cues in Directing Cell Behavior

Bone cancer, both primary and metastatic, is characterized by a low survival rate. Currently, available models lack in mimicking the complexity of bone, of cancer, and of their microenvironment, leading to poor predictivity. Three-dimensional technologies can help address this need, by developing predictive models that can recapitulate the conditions for cancer development and progression. Among the existing tools to obtain suitable 3D models of bone cancer, 3D printing and bioprinting appear very promising, as they enable combining cells, biomolecules, and biomaterials into organized and complex structures that can reproduce the main characteristic of bone. The challenge is to recapitulate a bone-like microenvironment for analysis of stromal-cancer cell interactions and biological mechanics leading to tumor progression. In this review, existing approaches to obtain in vitro 3D-printed and -bioprinted bone models are discussed, with a focus on the role of biomaterials selection in determining the behavior of the models and its degree of customization. To obtain a reliable 3D bone model, the evaluation of different polymeric matrices and the inclusion of ceramic fillers is of paramount importance, as they help reproduce the behavior of both normal and cancer cells in the bone microenvironment. Open challenges and future perspectives are discussed to solve existing shortcomings and to pave the way for potential development strategies.

Pharmaceutical electrospinning and 3D printing scaffold design for bone regeneration

Bone regenerative engineering provides a great platform for bone tissue regeneration covering cells, growth factors and other dynamic forces for fabricating scaffolds. Diversified biomaterials and their fabrication methods have emerged for fabricating patient specific bioactive scaffolds with controlled microstructures for bridging complex bone defects. The goal of this review is to summarize the points of scaffold design as well as applications for bone regeneration based on both electrospinning and 3D bioprinting. It first briefly introduces biological characteristics of bone regeneration and summarizes the applications of different types of material and the considerations for bone regeneration including polymers, ceramics, metals and composites. We then discuss electrospinning nanofibrous scaffold applied for the bone regenerative engineering with various properties, components and structures. Meanwhile, diverse design in the 3D bioprinting scaffolds for osteogenesis especially in the role of drug and bioactive factors delivery are assembled. Finally, we discuss challenges and future prospects in the development of electrospinning and 3D bioprinting for osteogenesis and prominent strategies and directions in future.

Review of Low-Cost 3D Bioprinters: State of the Market and Observed Future Trends

Three-dimensional (3D) bioprinting has become mainstream for precise and repeatable high-throughput fabrication of complex cell cultures and tissue constructs in drug testing and regenerative medicine, food products, dental and medical implants, biosensors, and so forth. Due to this tremendous growth in demand, an overwhelming amount of hardware manufacturers have recently flooded the market with different types of low-cost bioprinter models-a price segment that is most affordable to typical-sized laboratories. These machines range in sophistication, type of the underlying printing technology, and possible add-ons/features, which makes the selection process rather daunting (especially for a nonexpert customer). Yet, the review articles available in the literature mostly focus on the technical aspects of the printer technologies under development, as opposed to explaining the differences in what is already on the market. In contrast, this paper provides a snapshot of the fast-evolving low-cost bioprinter niche, as well as reputation profiles (relevant to delivery time, part quality, adherence to specifications, warranty, maintenance, etc.) of the companies selling these machines. Specifically, models spanning three dominant technologies-microextrusion, droplet-based/inkjet, and light-based/crosslinking-are reviewed. Additionally, representative examples of high-end competitors (including up-and-coming microfluidics-based bioprinters) are discussed to highlight their major differences and advantages relative to the low-cost models. Finally, forecasts are made based on the trends observed during this survey, as to the anticipated trickling down of the high-end technologies to the low-cost printers. Overall, this paper provides insight for guiding buyers on a limited budget toward making informed purchasing decisions in this fast-paced market.

Thermosensitive alginate-gelatin-nitrogen-doped carbon dots scaffolds as potential injectable hydrogels for cartilage tissue engineering applications

Hybrid injectable and biodegradable hydrogels based on oxidized alginate/gelatin and containing nitrogen-doped carbon dots (NCDs) as a reinforcement have been fabricated and crosslinked by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)/N-hydroxysuccinimide (NHS) as the chemical crosslinking agents in the hydrogel system. The idea of composite hydrogels relies on the assumption that they supply a microenvironment that is convenient for the exchange of nutrients via a porous structure and cell proliferation and have mechanical characteristics that approximately match natural tissue. The effect of the NCD content on the morphology structure, mechanical strength, swelling ratio, and biodegradation has been investigated. The results indicate that nanocomposite hydrogels containing a higher content of NCDs have smaller pore sizes and higher mechanical properties. The in vitro biodegradation and swelling behavior demonstrated that increasing the amount of NCDs up to 0.06% decreased the swelling ratio and weight loss of the hydrogels. The composite hydrogels are biocompatible, as verified by the MTT assay of MG-63 cells. The N-doped graphene quantum dots considerably affect degradation and interaction within the cells and hydrogels.

The low gelation time (120 s) and gelation temperature at body temperature (37 °C) make oxidized alginate/gelatin/NCDs hydrogels suitable as temperature-sensitive injectable hydrogels for cartilage tissue engineering.

Injectable hydrogels based on oxidized alginate-gelatin reinforced by carbon nitride quantum dots for tissue engineering

Stem cell treatment is promising in the various disorders treatment, but its effect is confined by the adverse conditions in the damaged tissues. The utilization of hydrogels has been suggested as a procedure to defeat this issue by developing the engraftment and survival of injected stem cells. Specifically, injectable hydrogels have drawn much attention due to their shape adaptability, ease of use, and the capability to reach body parts that are hard to access. In this study, the thermosensitive injectable hydrogels based on oxidized alginate, gelatin, and carbon nitride quantum dots (CNQDs) have been fabricated for tissue engineering. The mechanical characteristics of the nanocomposite hydrogels were investigated by rheology analysis. The results show that increasing the amount of CNQDs improve the mechanical strength of the nanocomposite hydrogels. The Cross-section morphology of freeze dried hydrogels comprising 0.25, 1.5, and 3.0% CNQDs indicate porous structure with interrelated pores. Besides, the result of in vitro degradation reveals that the hydrogels comprising CNQDs are more durable than the one without CNQDs. A reduction in the biodegradation and swelling ratio is perceived with the addition of CNQDs. The cell viability and attachment show that the nanocomposite hydrogels are biocompatible (>88%) with great cell adhesion to osteosarcoma cell line MG63 depending on the presence of CNQDs.

In situ and non-cytotoxic cross-linking strategy for 3D printable biomaterials

3D bioprinting allows the production of patient-specific tissue constructs with desired structural characteristics such as high resolution, controlled swelling degree, and controlled degradation behavior by mostly using hydrogels. Crosslinking of hydrogels is an essential parameter in bioprinting applications, which is beneficial for tuning structural specifications. In this study, gelatin-alginate-whey protein isolate based hydrogels have been used for 3D printing structures in a layer-by-layer fashion. These structures were cross-linked by the Amino Acid (monomer) Decorated and Light Underpinning Conjugation Approach (ANADOLUCA) method, which is a unique, non-invasive photosensitive cross-linking technique for protein-based mixtures. In that aim, hydrogel properties (e.g., printability, biocompatibility, rheologic and mechanical behavior) and cross-linking properties (e.g., swelling and degradation behavior) were studied. Results were compared with UV and ionic cross-linking techniques, which are the abundantly used techniques in such studies. The results showed that the ANADOLUCA method can be used for in situ cross-linking under mild conditions for the printing of bio-inks, and the proposed method can be used as an alternative for UV-based and chemical cross-linking techniques.

Crosslinking Strategies for 3D Bioprinting of Polymeric Hydrogels

Three-dimensional (3D) bioprinting has recently advanced as an important tool to produce viable constructs that can be used for regenerative purposes or as tissue models. To develop biomimetic and sustainable 3D constructs, several important processing aspects need to be considered, among which crosslinking is most important for achieving desirable biomechanical stability of printed structures, which is reflected in subsequent behavior and use of these constructs. In this work, crosslinking methods used in 3D bioprinting studies are reviewed, parameters that affect bioink chemistry are discussed, and the potential toward improving crosslinking outcomes and construct performance is highlighted. Furthermore, current challenges and future prospects are discussed. Due to the direct connection between crosslinking methods and properties of 3D bioprinted structures, this Review can provide a basis for developing necessary modifications to the design and manufacturing process of advanced tissue-like constructs in future.

Cell-cell interaction in a coculture system consisting of CRISPR/Cas9 mediated GFP knock-in HUVECs and MG-63 cells in alginate-GelMA based nanocomposites hydrogel as a 3D scaffold

The interaction between osteogenic and angiogenic cells through a coculturing system in biocompatible materials has been considered for successfully engineering vascularized bone tissue equivalents. In this study, we developed a hydrogel-blended scaffold consisted of gelatin methacryloyl (GelMA) and alginate enriched with hydroxyapatite nanoparticles (HAP) to model an in vitro prevascularized bone construct. The hydrogel-based scaffold revealed a higher mechanical stiffness than those of pure (GelMA), alginate, and (GelMA+ HAP) hydrogels. In the present study, we generated a green fluorescent protein (GFP) knock-in umbilical vein endothelial cells (HUVECs) cell line using the CRISPR/Cas9 technology. The GFP was inserted into the human-like ROSA locus of HUVECs genome. HUVECs expressing GFP were cocultured with OB-like cells (MG-63) within three-dimensionally (3D) fabricated hydrogel to investigate the response of cocultured osteoblasts and endothelial cells in a 3D structure. Cell viability under the 3D cocultured gel was higher than the 3D monocultured. Compared to the 3D monocultured condition, the cells were aligned and developed into the vessel-like structures. During 14 days of culture periods, the cells displayed actin protrusions by the formation of spike-like filopodia in the 3D cocultured model. Angiogenic and osteogenic-related genes such as CD31, vWF, and osteocalcin showed higher expression in the cocultured versus the monocultured. These results have collectively indicated that the 3D cocultured hydrogel facilitates interaction among cells, thereby having a greater effect on angiogenic and osteogenic properties in the absence of induction media.

Biomaterials Based on Marine Resources for 3D Bioprinting Applications

Three-dimensional (3D) bioprinting has become a flexible tool in regenerative medicine with potential for various applications. Further development of the new 3D bioprinting field lies in suitable bioink materials with satisfied printability, mechanical integrity, and biocompatibility. Natural polymers from marine resources have been attracting increasing attention in recent years, as they are biologically active and abundant when comparing to polymers from other resources. This review focuses on research and applications of marine biomaterials for 3D bioprinting. Special attention is paid to the mechanisms, material requirements, and applications of commonly used 3D bioprinting technologies based on marine-derived resources. Commonly used marine materials for 3D bioprinting including alginate, carrageenan, chitosan, hyaluronic acid, collagen, and gelatin are also discussed, especially in regards to their advantages and applications.

Review of alginate-based hydrogel bioprinting for application in tissue engineering

The dawn of 3D printing in medicine has given the field the hope of vitality in many patients fighting a multitude of diseases. Also entitled bioprinting, this appertains to its sequential printing of precursor ink, embodying cells and polymer/composite in a predetermined trajectory. The precursor ink, in addition to cells, is predominantly constituted of hydrogels due to its biodegradability and ability to mimic the body's anatomy and mechanical features, e.g. bones, etc. This review paper is devoted to explicating the bioprinting (3D/4D) of alginate hydrogels, which are extracts from brown algae, through extrusion additive manufacturing. Alginates are salt derivatives of alginic acid and constitute long chains of polysaccharides, which provides pliability and gelling adeptness to their structure. Alginate hydrogel (employed for extrusion) can be pristine or composite relying on the requisite properties (target application controlled or in vivo environment), e.g. alginate-natural (gelatin/agarose/collagen/hyaluronic acid/etc) and alginate-synthetic (polyethylene glycol (PEG)/pluronic F-127/etc). Extrusion additive manufacturing of alginate is preponderate among others with its uncomplicated processing, material efficiency (cut down on wastage), and outspread adaptability for viscosities (0.03-6 * 10⁴ Pa.s), but the procedure is limited by resolution (200 μm) in addition to accuracy. However, 3D-fabricated biostructures display rigidness (unvarying with conditions) i.e. lacks a smart response, which is reassured by accounting time feature as a noteworthy accessory to printing, interpreted as 4D bioprinting. This review propounds the specific processing itinerary for alginate (meanwhile traversing across its composites/blends with natural and synthetic consideration) in extrusion along with its pre-/during/post-processing parameters intrinsic to the process. Furthermore, propensity is also presented in its (alginate extrusion processing) application for tissue engineering, i.e. bones, cartilage (joints), brain (neural), ear, heart (cardiac), eyes (corneal), etc, due to a worldwide quandary over accessibility to natural organs for diverse types of diseases. Additionally, the review contemplates recently invented advance printing, i.e. 4D printing for biotic species, with its challenges and future opportunities.

Chemical insights into bioinks for 3D printing

Dedicated chemical strategies are required to form hydrogel networks from bioink components, allowing cell survival during 3D bioprinting processes.

Three-dimensional printing biotechnology for the regeneration of the tooth and tooth-supporting tissues

The tooth and its supporting tissues are organized with complex three-dimensional (3D) architecture, including the dental pulp with a blood supply and nerve tissues, complex multilayer periodontium, and highly aligned periodontal ligament (PDL). Mimicking such 3D complexity and the multicellular interactions naturally existing in dental structures represents great challenges in dental regeneration. Attempts to construct the complex system of the tooth and tooth-supporting apparatus (i.e., the PDL, alveolar bone, and cementum) have made certain progress owing to 3D printing biotechnology. Recent advances have enabled the 3D printing of biocompatible materials, seed cells, and supporting components into complex 3D functional living tissue. Furthermore, 3D bioprinting is driving major innovations in regenerative medicine, giving the field of regenerative dentistry a boost. The fabrication of scaffolds via 3D printing is already being performed extensively at the laboratory bench and in clinical trials; however, printing living cells and matrix materials together to produce tissue constructs by 3D bioprinting remains limited to the regeneration of dental pulp and the tooth germ. This review summarizes the application of scaffolds for cell seeding and biofabricated tissues via 3D printing and bioprinting, respectively, in the tooth and its supporting tissues. Additionally, the key advantages and prospects of 3D bioprinting in regenerative dentistry are highlighted, providing new ideas for dental regeneration.

Natural Polymers for Organ 3D Bioprinting

Three-dimensional (3D) bioprinting, known as a promising technology for bioartificial organ manufacturing, has provided unprecedented versatility to manipulate cells and other biomaterials with precise control their locations in space. Over the last decade, a number of 3D bioprinting technologies have been explored. Natural polymers have played a central role in supporting the cellular and biomolecular activities before, during and after the 3D bioprinting processes. These polymers have been widely used as effective cell-loading hydrogels for homogeneous/heterogeneous tissue/organ formation, hierarchical vascular/neural/lymphatic network construction, as well as multiple biological/biochemial/physiological/biomedical/pathological functionality realization. This review aims to cover recent progress in natural polymers for bioartificial organ 3D bioprinting. It is structured as introducing the important properties of 3D printable natural polymers, successful models of 3D tissue/organ construction and typical technologies for bioartificial organ 3D bioprinting.