3D printing of bone tissue engineering scaffolds

Recent advances on 3D-printed PCL-based composite scaffolds for bone tissue engineering

Population ageing and various diseases have increased the demand for bone grafts in recent decades. Bone tissue engineering (BTE) using a three-dimensional (3D) scaffold helps to create a suitable microenvironment for cell proliferation and regeneration of damaged tissues or organs. The 3D printing technique is a beneficial tool in BTE scaffold fabrication with appropriate features such as spatial control of microarchitecture and scaffold composition, high efficiency, and high precision. Various biomaterials could be used in BTE applications. PCL, as a thermoplastic and linear aliphatic polyester, is one of the most widely used polymers in bone scaffold fabrication. High biocompatibility, low cost, easy processing, non-carcinogenicity, low immunogenicity, and a slow degradation rate make this semi-crystalline polymer suitable for use in load-bearing bones. Combining PCL with other biomaterials, drugs, growth factors, and cells has improved its properties and helped heal bone lesions. The integration of PCL composites with the new 3D printing method has made it a promising approach for the effective treatment of bone injuries. The purpose of this review is give a comprehensive overview of the role of printed PCL composite scaffolds in bone repair and the path ahead to enter the clinic. This study will investigate the types of 3D printing methods for making PCL composites and the optimal compounds for making PCL composites to accelerate bone healing.

Advanced Binary Guanosine and Guanosine 5'-Monophosphate Cell-Laden Hydrogels for Soft Tissue Reconstruction by 3D Bioprinting

Soft tissue defects or pathologies frequently necessitate the use of biomaterials that provide the volume required for subsequent vascularization and tissue formation as autrografts are not always a feasible alternative. Supramolecular hydrogels represent promising candidates because of their 3D structure, which resembles the native extracellular matrix, and their capacity to entrap and sustain living cells. Guanosine-based hydrogels have emerged as prime candidates in recent years since the nucleoside self-assembles into well-ordered structures like G-quadruplexes by coordinating K⁺ ions and π-π stacking, ultimately forming an extensive nanofibrillar network. However, such compositions were frequently inappropriate for 3D printing due to material spreading and low shape stability over time. Thus, the present work aimed to develop a binary cell-laden hydrogel capable of ensuring cell survival while providing enough stability to ensure scaffold biointegration during soft tissue reconstruction. For that purpose, a binary hydrogel made of guanosine and guanosine 5'-monophosphate was optimized, rat mesenchymal stem cells were entrapped, and the composition was bioprinted. To further increase stability, the printed structure was coated with hyperbranched polyethylenimine. Scanning electron microscopic studies demonstrated an extensive nanofibrillar network, indicating excellent G-quadruplex formation, and rheological analysis confirmed good printing and thixotropic qualities. Additionally, diffusion tests using fluorescein isothiocyanate labeled-dextran (70, 500, and 2000 kDa) showed that nutrients of various molecular weights may diffuse through the hydrogel scaffold. Finally, cells were evenly distributed throughout the printed scaffold, cell survival was 85% after 21 days, and lipid droplet formation was observed after 7 days under adipogenic conditions, indicating successful differentiation and proper cell functioning. To conclude, such hydrogels may enable the 3D bioprinting of customized scaffolds perfectly matching the respective soft tissue defect, thereby potentially improving the outcome of the tissue reconstruction intervention.

Current advancements in bio-ink technology for cartilage and bone tissue engineering

In tissue engineering, the fate of a particular organ/tissue regeneration and repair mainly depends on three pillars - 3D architecture, cells used, and stimulus provided. 3D cell supportive structure development is one of the crucial pillars necessary for defining organ/tissue geometry and shape. In recent years, the advancements in 3D bio-printing (additive manufacturing) made it possible to develop very precise 3D architectures with the help of industrial software like Computer-Aided Design (CAD). The main requirement for the 3D printing process is the bio-ink, which can act as a source for cell support, proliferation, drug (growth factors, stimulators) delivery, and organ/tissue shape. The selection of the bio-ink depends upon the type of 3D tissue of interest. Printing tissues like bone and cartilage is always challenging because it is difficult to find printable biomaterial that can act as bio-ink and mimic the strength of the natural bone and cartilage tissues. This review describes different biomaterials used to develop bio-inks with different processing variables and cell-seeding densities for bone and cartilage 3D printing applications. The review also discusses the advantages, limitations, and cell bio-ink compatibility in each biomaterial section. The emphasis is given to bio-inks reported for 3D printing cartilage and bone and their applications in orthopedics and orthodontists. The critical/important performance and the architectural morphology requirements of desired bone and cartilage bio-inks were compiled in summary.

Challenges of Integrating New Technologies for Orthopedic Doctors to Face up to Difficulties during the Pandemic Era

In the field of orthopedics, competitive progress is growing faster because new technologies used to facilitate the work of physicians are continuously developing. Based on the issues generated in the pandemic era in this field, a research study was developed to identify the intention of orthopedic doctors to integrate new medical technologies. The survey was based on a questionnaire that was used for data collection. The quantitative study registered a sample of 145 orthopedic doctors. The data analysis was performed based on the IBM SPSS program. A multiple linear regression model was applied, which analyzed how the independent variables can influence the dependent variables. After analyzing the data, it was observed that the intention of orthopedic doctors to use new medical technologies is influenced by the advantages and disadvantages perceived by them, the perceived risks, the quality of the medical technologies, the experience of physicians in their use, and their receptivity to other digital tools. The obtained results are highly important both for hospital managers and authorities, illustrating the main factors that influence doctors to use emergent technologies in their clinical work.

Recent Advancements in Electrospun Chitin and Chitosan Nanofibers for Bone Tissue Engineering Applications

Treatment of large segmental bone loss caused by fractures, osteomyelitis, and non-union results in expenses of around USD 300,000 per case. Moreover, the worst-case scenario results in amputation in 10% to 14.5% of cases. Biomaterials, cells, and regulatory elements are employed in bone tissue engineering (BTE) to create biosynthetic bone grafts with effective functionalization that can aid in the restoration of such fractured bones, preventing amputation and alleviating expenses. Chitin (CT) and chitosan (CS) are two of the most prevalent natural biopolymers utilized in the fields of biomaterials and BTE. To offer the structural and biochemical cues for augmenting bone formation, CT and CS can be employed alone or in combination with other biomaterials in the form of nanofibers (NFs). When compared with several fabrication methods available to produce scaffolds, electrospinning is regarded as superior since it enables the development of nanostructured scaffolds utilizing biopolymers. Electrospun nanofibers (ENFs) offer unique characteristics, including morphological resemblance to the extracellular matrix, high surface-area-to-volume ratio, permeability, porosity, and stability. This review elaborates on the recent strategies employed utilizing CT and CS ENFs and their biocomposites in BTE. We also summarize their implementation in supporting and delivering an osteogenic response to treat critical bone defects and their perspectives on rejuvenation. The CT- and CS-based ENF composite biomaterials show promise as potential constructions for bone tissue creation.

In Situ Imaging and Anti-inflammation of 3D Printed Scaffolds Enabled by AIEgen

Three-dimensional (3D) printed bioactive scaffolds have been widely used in the field of bone tissue engineering. However, its in vivo visualization and bacterial inflammation are intractable issues during the surgery and treatment. Herein, we first synthesized an aggregation-induced emission-active luminogen (AIEgen) named 4BC with efficient reactive oxygen species (ROS) generation. Then, a series of 3D bioactive scaffolds loaded with 4BC were fabricated by a precipitation adsorption method, namely 4BC@scaffolds, which showed good in situ imaging performance for the implanted scaffolds by using simple UV light irradiation. Among them, the 4BC@TMP scaffold composed of trimagnesium phosphate (TMP) had excellent bactericidal ability for Escherichia coli and Staphylococcus aureus in vitro and resisted bacterial inflammation in vivo through photodynamic action. H&E and immunofluorescence staining were performed to further evaluate the inhibitory effect of bacterial inflammation in vivo. This work verified that AIEgen-based 3D scaffolds are promising bioactive frameworks for bioimaging and antibacterial applications.

Mussel-inspired HA@TA-CS/SA biomimetic 3D printed scaffolds with antibacterial activity for bone repair

Bacterial infection is a major challenge that could threaten the patient's life in repairing bone defects with implant materials. Developing functional scaffolds with an intelligent antibacterial function that can be used for bone repair is very important. We constructed a drug delivery (HA@TA-CS/SA) scaffold with curcumin-loaded dendritic mesoporous organic silica nanoparticles (DMON@Cur) via 3D printing for antibacterial bone repair. Inspired by the adhesion mechanism of mussels, the HA@TA-CS/SA scaffold of hydroxyapatite (HA) and chitosan (CS) is bridged by tannic acid (TA), which in turn binds sodium alginate (SA) using electrostatic interactions. The results showed that the HA@TA-CS/SA composite scaffold had better mechanical properties compared with recent literature data, reaching 68.09 MPa. It displayed excellent degradation and mineralization capabilities with strong biocompatibility in vitro. Furthermore, the antibacterial test results indicated that the curcumin-loaded scaffold inhibited S.aureus and E.coli with 99.99% and 96.56% effectiveness, respectively. These findings show that 3D printed curcumin-loaded HA@TA-CS/SA scaffold has considerable promise for bone tissue engineering.

Extracellular vesicles: From bone development to regenerative orthopedics

Regenerative medicine aims to promote the replacement of tissues lost to damage or disease. While positive outcomes have been observed experimentally, challenges remain in their clinical translation. This has led to growing interest in applying extracellular vesicles (EVs) to augment or even replace existing approaches. Through the engineering of culture environments or direct/indirect manipulation of EVs themselves, multiple avenues have emerged to modulate EV production, targeting, and therapeutic potency. Drives to modulate release using material systems or functionalize implants for improved osseointegration have also led to outcomes that could have real-world impact. The purpose of this review is to highlight advantages in applying EVs for the treatment of skeletal defects, outlining the current state of the art in the field and emphasizing avenues for further investigation. Notably, the review identifies inconsistencies in EV nomenclature and outstanding challenges in defining a reproducible therapeutic dose. Challenges also remain in the scalable manufacture of a therapeutically potent and pure EV product, with a need to address scalable cell sources and optimal culture environments. Addressing these issues will be critical if we are to develop regenerative EV therapies that meet the demands of regulators and can be translated from bench to bedside.

Recent advances and future challenges of the starch-based bio-composites for engineering applications

Starch is regarded as one of the most promising sustainable materials due to its abundant yield and excellent biodegradability. From the perspective of practical engineering applications, this paper systematically describes the development of starch-based bio-composites in the past decade. Packaging properties, processing characteristics, and current challenges for the efficient processing of starch-based bio-composites are reviewed in industrial packaging. Green coatings, binders, adsorbents, flocculants, flame retardants, and emulsifiers are used as examples to illustrate the versatility of starch-based bio-composites in chemical agent applications. In addition, the work compares the application of starch-based bio-composites in conventional spinning with emerging spinning technologies and describes the challenges of electrostatic spinning for preparing nanoscale starch-based fibers. In terms of flexible electronics, the starch-based bio-composites are regard as a solid polymer electrolyte and easily modified porous material. Moreover, we describe the applications of the starch-based gels in tissue engineering, controlled drug release, and medical dressings. Finally, the theoretical input and technical guidance in the advanced sustainable engineering application of the starch-based bio-composites are provided in the work.

Application of photocrosslinkable hydrogels based on photolithography 3D bioprinting technology in bone tissue engineering

Bone tissue engineering (BTE) has been proven to be an effective method for the treatment of bone defects caused by different musculoskeletal disorders. Photocrosslinkable hydrogels (PCHs) with good biocompatibility and biodegradability can significantly promote the migration, proliferation and differentiation of cells and have been widely used in BTE. Moreover, photolithography 3D bioprinting technology can notably help PCHs-based scaffolds possess a biomimetic structure of natural bone, meeting the structural requirements of bone regeneration. Nanomaterials, cells, drugs and cytokines added into bioinks can enable different functionalization strategies for scaffolds to achieve the desired properties required for BTE. In this review, we demonstrate a brief introduction of the advantages of PCHs and photolithography-based 3D bioprinting technology and summarize their applications in BTE. Finally, the challenges and potential future approaches for bone defects are outlined.

Structural Mechanical Properties of 3D Printing Biomimetic Bone Replacement Materials

One of the primary challenges in developing bone substitutes is to create scaffolds with mechanical properties that closely mimic those of regenerated tissue. Scaffolds that mimic the structure of natural cancellous bone are believed to have better environmental adaptability. In this study, we used the porosity and thickness of pig cancellous bone as biomimetic design parameters, and porosity and structural shape as differential indicators, to design a biomimetic bone beam scaffold. The mechanical properties of the designed bone beam model were tested using the finite element method (FEM). PCL/β-TCP porous scaffolds were prepared using the FDM method, and their mechanical properties were tested. The FEM simulation results were compared and validated, and the effects of porosity and pore shape on the mechanical properties were analyzed. The results of this study indicate that the PCL/β-TCP scaffold, prepared using FDM 3D printing technology for cancellous bone tissue engineering, has excellent integrity and stability. Predicting the structural stability using FEM is effective. The triangle pore structure has the most stability in both simulations and tests, followed by the rectangle and honeycomb shapes, and the diamond structure has the worst stability. Therefore, adjusting the porosity and pore shape can change the mechanical properties of the composite scaffold to meet the mechanical requirements of customized tissue engineering.

Design and 3D Printing of Personalized Hybrid and Gradient Structures for Critical Size Bone Defects

Treating critical-size bone defects with autografts, allografts, or standardized implants is challenging since the healing of the defect area necessitates patient-specific grafts with mechanically and physiologically relevant structures. Three-dimensional (3D) printing using computer-aided design (CAD) is a promising approach for bone tissue engineering applications by producing constructs with customized designs and biomechanical compositions. In this study, we propose 3D printing of personalized and implantable hybrid active scaffolds with a unique architecture and biomaterial composition for critical-size bone defects. The proposed 3D hybrid construct was designed to have a gradient cell-laden poly(ethylene glycol) (PEG) hydrogel, which was surrounded by a porous polycaprolactone (PCL) cage structure to recapitulate the anatomical structure of the defective area. The optimized PCL cage design not only provides improved mechanical properties but also allows the diffusion of nutrients and medium through the scaffold. Three different designs including zigzag, zigzag/spiral, and zigzag/spiral with shifting the zigzag layers were evaluated to find an optimal architecture from a mechanical point of view and permeability that can provide the necessary mechanical strength and oxygen/nutrient diffusion, respectively. Mechanical properties were investigated experimentally and analytically using finite element analysis (FEA), and computational fluid dynamics (CFD) simulation was used to determine the permeability of the structures. A hybrid scaffold was fabricated via 3D printing of the PCL cage structure and a PEG-based bioink comprising a varying number of human bone marrow mesenchymal stem cells (hBMSCs). The gradient bioink was deposited inside the PCL cage through a microcapillary extrusion to generate a mineralized gradient structure. The zigzag/spiral design for the PCL cage was found to be mechanically strong with sufficient and optimum nutrient/gas axial and radial diffusion while the PEG-based hydrogel provided a biocompatible environment for hBMSC viability, differentiation, and mineralization. This study promises the production of personalized constructs for critical-size bone defects by printing different biomaterials and gradient cells with a hybrid design depending on the need for a donor site for implantation.

Copper-containing chitosan-based hydrogels enabled 3D-printed scaffolds to accelerate bone repair and eliminate MRSA-related infection

Bone defect combined with drug-resistant bacteria-related infection is a thorny challenge in clinic. Herein, 3D-printed polyhydroxyalkanoates/β-tricalcium phosphate (PHA/β-TCP, PT) scaffolds were prepared by fused deposition modeling. Then copper-containing carboxymethyl chitosan/alginate (CA/Cu) hydrogels were integrated with the scaffolds via a facile and low-cost chemical crosslinking method. The resultant PT/CA/Cu scaffolds could not only promote proliferation but also osteogenic differentiation of preosteoblasts in vitro. Moreover, PT/CA/Cu scaffolds exhibited a strong antibacterial activity towards a broad-spectrum of bacteria including methicillin-resistant Staphylococcus aureus (MRSA) through inducing the intercellular generation of reactive oxygen species. In vivo experiments further demonstrated that PT/CA/Cu scaffolds significantly accelerated bone repair of cranial defects and efficiently eliminated MRSA-related infection, showing potential for application in infected bone defect therapy.

Construction of Processable Ultrastiff Hydrogel for Periarticular Fracture Strutting and Healing

Development of bioactive bone and joint implants that offer superior mechanical properties to facilitate personalized surgical procedures remains challenging in the field of biomedical materials. As for the hydrogel, mechanical property and processability are major obstructions hampering its application as load-bearing scaffolds in orthopedics. Herein, we constructed implantable composite hydrogels with appealing processability and ultrahigh stiffness. Central to our design is the incorporation of a thixotropic composite network into an elastic polymer network via dynamic interactions to synthesize a percolation-structured double-network (DN) hydrogel with plasticity, followed by in situ strengthening and self-strengthening mechanisms for fostering the DN structure to the cojoined-network structure and subsequently mineralized-composite-network structure to harvest excellent stiffness. The ultrastiff hydrogel is shapeable and can reach a compressive modulus of 80-200 MPa together with a fracture energy of 6-10 MJ/m³, comparable to the mechanical performance of cancellous bone. Moreover, the hydrogel is cytocompatible, osteogenic, and showed almost no volume shrinkage within 28 days in simulated body fluid or culture medium. Such characteristics enabled the utility of a hydrogel in the reduction and stabilization of periarticular fracture treatment on a distal femoral AO/OTA B1 fracture rabbit model and successfully avoided the recollapse of the articular surface.

A flexible design framework to design graded porous bone scaffolds with adjustable anisotropic properties

Since the success of bone regenerative medicine depends on scaffold morphological and mechanical properties, numerous scaffolds designs have been proposed in the last decade, including graded structures that are suited to enhance tissue ingrowth. Most of these structures are based either on foams with a random pore definition, or on the periodic repetition of a unit cell (UC). These approaches are limited by the range of target porosities and obtained effective mechanical properties, and do not permit to easily generate a pore size gradient from the core to the periphery of the scaffold. In opposition, the objective of the present contribution is to propose a flexible design framework to generate various three-dimensional (3D) scaffolds structures including cylindrical graded scaffolds from the definition of a UC by making use of a non-periodic mapping. Conformal mappings are firstly used to generate graded circular cross-sections, while 3D structures are then obtained by stacking the cross-sections with or without a twist between different scaffold layers. The effective mechanical properties of different scaffold configurations are presented and compared using an energy-based efficient numerical method, pointing out the versatility of the design procedure to separately govern longitudinal and transverse anisotropic scaffold properties. Among these configurations, a helical structure exhibiting couplings between transverse and longitudinal properties is proposed and permits to extend the adaptability of the proposed framework. In order to investigate the capacity of common additive manufacturing techniques to fabricate the proposed structures, a subset of these configurations is elaborated using a standard SLA setup, and subjected to experimental mechanical testing. Despite observed geometric differences between the initial design and the actual obtained structures, the effective properties are satisfyingly predicted by the proposed computational method. Promising perspectives are offered concerning the design of self-fitting scaffolds with on-demand properties depending on the clinical application.

Optimization of guanosine-based hydrogels with boric acid derivatives for enhanced long-term stability and cell survival

Tissue defects can lead to serious health problems and often require grafts or transplants to repair damaged soft tissues. However, these procedures can be complex and may not always be feasible due to a lack of available tissue. Hydrogels have shown potential as a replacement for tissue grafts due to their ability to support cell survival and encapsulate biomolecules such as growth factors. In particular, guanosine-based hydrogels have been explored as a potential solution, but they often exhibit limited stability which hampers their use in the biofabrication of complex grafts. To address this issue, we explored the use of borate ester chemistry and more complex boric acid derivatives to improve the stability and properties of guanosine-based hydrogels. We hypothesized that the aromatic rings in these derivatives would enhance the stability and printability of the hydrogels through added π-π stack interactions. After optimization, 13 compositions containing either 2-naphthylboronic acid or boric acid were selected. Morphology studies shows a well-defined nanofibrilar structure with good printable properties (thixotropic behaviour, print fidelity and printability). Moreover, the pH of all tested hydrogels was within the range suitable for cell viability (7.4–8.3). Nevertheless, only the boric acid-based formulations were stable for at least 7 days. Thus, our results clearly demonstrated that the presence of additional aromatic rings did actually impair the hydrogel properties. We speculate that this is due to steric hindrance caused by adjacent groups, which disrupt the correct orientation of the aromatic groups required for effective π-π stack interactions of the guanosine building block. Despite this drawback, the developed guanosine-boric acid hydrogel exhibited good thixotropic properties and was able to support cell survival, proliferation, and migration. For instance, SaOS-2 cells planted on these printed structures readily migrated into the hydrogel and showed nearly 100% cell viability after 7 days. In conclusion, our findings highlight the potential of guanosine-boric acid hydrogels as tissue engineering scaffolds that can be readily enhanced with living cells and bioactive molecules. Thus, our work represents a significant advancement towards the development of functionalized guanosine-based hydrogels.

Conductive Polyaniline Particles Regulating In Vitro Hydrolytic Degradation and Erosion of Hydroxyapatite/Poly(lactide-co-glycolide) Porous Scaffolds for Bone Tissue Engineering

In addition to biocompatibility and bioactivity, scaffolds with superior bone tissue regenerative capacity should possess excellent functionality (e.g., electroactivity and conductivity) and biodegradability matching with the rate of bone reconstruction. However, current conductive scaffolds display a reduced biodegradability rate and weakened biocompatibility. In this study, injectable conductive porous scaffolds were fabricated, incorporating camphor sulfonic acid-doped polyaniline (PANI) into hydroxyapatite/poly(lactide-co-glycolide) (HA/PLGA) scaffolds, using solvent-casting/particulate-leaching methodology. These scaffolds demonstrated excellent electroactivity, conductivity, hydrophilicity, thermodynamic properties, antibacterial properties, and biocompatibility. Their degradation behavior was explored by regulating the PANI content. The results demonstrated that adding an appropriate content of PANI would increase the pore size, porosity, and water absorption of the conductive scaffold and promote the formation of filamentous fiber byproducts with acidic hydrolysates, which accelerated the degradation rate of the scaffold. Owing to π-π stacking and hydrogen bonding, the conductive scaffold with 10 wt % PANI efficiently retarded the decrease in the thermal and mechanical properties of the scaffolds during a 16 week degradation. Thus, better regulation of degradation behavior and correlation would allow conductive porous scaffolds, such as bone implants, to achieve better bone ingrowth and restoration.

Application of 3D Printing in Bone Grafts

The application of 3D printing in bone grafts is gaining in importance and is becoming more and more popular. The choice of the method has a direct impact on the preparation of the patient for surgery, the probability of rejection of the transplant, and many other complications. The aim of the article is to discuss methods of bone grafting and to compare these methods. This review of literature is based on a selective literature search of the PubMed and Web of Science databases from 2001 to 2022 using the search terms “bone graft”, “bone transplant”, and “3D printing”. In addition, we also reviewed non-medical literature related to materials used for 3D printing. There are several methods of bone grafting, such as a demineralized bone matrix, cancellous allograft, nonvascular cortical allograft, osteoarticular allograft, osteochondral allograft, vascularized allograft, and an autogenic transplant using a bone substitute. Currently, autogenous grafting, which involves removing the patient’s bone from an area of low aesthetic importance, is referred to as the gold standard. 3D printing enables using a variety of materials. 3D technology is being applied to bone tissue engineering much more often. It allows for the treatment of bone defects thanks to the creation of a porous scaffold with adequate mechanical strength and favorable macro- and microstructures. Bone tissue engineering is an innovative approach that can be used to repair multiple bone defects in the process of transplantation. In this process, biomaterials are a very important factor in supporting regenerative cells and the regeneration of tissue. We have years of research ahead of us; however, it is certain that 3D printing is the future of transplant medicine.

Electrically stimulated 3D bioprinting of gelatin-polypyrrole hydrogel with dynamic semi-IPN network induces osteogenesis via collective signaling and immunopolarization

In recent years, three-dimensional (3D) bioprinting of conductive hydrogels has made significant progress in the fabrication of high-resolution biomimetic structures with gradual complexity. However, the lack of an effective cross-linking strategy, ideal shear-thinning, appropriate yield strength, and higher print fidelity with excellent biofunctionality remains a challenge for developing cell-laden constructs, hindering the progress of extrusion-based 3D printing of conductive polymers. In this study, a highly stable and conductive bioink was developed based on polypyrrole-grafted gelatin methacryloyl (GelMA-PPy) with a triple cross-linking (thermo-photo-ionically) strategy for direct ink writing-based 3D printing applications. The triple-cross-linked hydrogel with dynamic semi-inner penetrating polymer network (semi-IPN) displayed excellent shear-thinning properties, with improved shape fidelity and structural stability during 3D printing. The as-fabricated hydrogel ink also exhibited "plug-like non-Newtonian" flow behavior with minimal disturbance. The bioprinted GelMA-PPy-Fe hydrogel showed higher cytocompatibility (93%) of human bone mesenchymal stem cells (hBMSCs) under microcurrent stimulation (250 mV/20 min/day). Moreover, the self-supporting and tunable mechanical properties of the GelMA-PPy bioink allowed 3D printing of high-resolution biological architectures. As a proof of concept, we printed a full-thickness rat bone model to demonstrate the structural stability. Transcriptomic analysis revealed that the 3D bioprinted hBMSCs highly expressed gene hallmarks for NOTCH/mitogen-activated protein kinase (MAPK)/SMAD signaling while down-regulating the Wnt/β-Catenin and epigenetic signaling pathways during osteogenic differentiation for up to 7 days. These results suggest that the developed GelMA-PPy bioink is highly stable and non-toxic to hBMSCs and can serve as a promising platform for bone tissue engineering applications.

Additively Manufactured MAX- and MXene-Composite Scaffolds for Bone Regeneration- Recent Advances and Future Perspectives

Human bones can suffer from various injuries, such as fractures, bone cancer, among others, which has initiated research activities towards bone replacement using advanced bio-materials. However, it is still challenging to design bio-scaffolds with bone-inducing agents to regenerate bone defects. In this regard, MAX-phases and MXenes (early transition metal carbides and/or nitrides) have gained notable attention due to their unique hydrophilicity, bio-compatibility, chemical stability, and photothermal properties. They can be used in bone tissue engineering as a suitable replacement or reinforcement for common bio-materials (polymers, bio-glasses, metals, or hydroxyapatite). To fabricate bio-scaffolds, additive manufacturing is prospective due to the possibility of controlling porosity and creating complex shapes with high resolution. Until now, no comprehensive article summarizing the existing state-of-the-art related to bone scaffolds reinforced by MAX-phases and MXenes fabricated by additive manufacturing has been published. Therefore, our article addresses the reasons for using bone scaffolds and the importance of choosing the most suitable material. We critically discuss the recent developments in bone tissue engineering and regenerative medicine using MAX-phases and MXenes with a particular emphasis on manufacturing, mechanical properties, and bio-compatibility. Finally, we discuss the existing challenges and bottlenecks of bio-scaffolds reinforced by MAX-phases and MXenes before deriving their future potential.

Effect of Pore Characteristics and Alkali Treatment on the Physicochemical and Biological Properties of a 3D-Printed Polycaprolactone Bone Scaffold

Polycaprolactone scaffolds were designed and 3D-printed with different pore shapes (cube and triangle) and sizes (500 and 700 μm) and modified with alkaline hydrolysis of different ratios (1, 3, and 5 M). In total, 16 designs were evaluated for their physical, mechanical, and biological properties. The present study mainly focused on the pore size, porosity, pore shapes, surface modification, biomineralization, mechanical properties, and biological characteristics that might influence bone ingrowth in 3D-printed biodegradable scaffolds. The results showed that the surface roughness in treated scaffolds increased compared to untreated polycaprolactone scaffolds (R _a = 2.3-10.5 nm and R _q = 17- 76 nm), but the structural integrity declined with an increase in the NaOH concentration especially in the scaffolds with small pores and a triangle shape. Overall, the treated polycaprolactone scaffolds particularly with the triangle shape and smaller pore size provided superior performance in mechanical strength similar to that of cancellous bone. Additionally, the in vitro study showed that cell viability increased in the polycaprolactone scaffolds with cubic pore shapes and small pore sizes, whereas mineralization was enhanced in the designs with larger pore sizes. Based on the results obtained, this study demonstrated that the 3D-printed modified polycaprolactone scaffolds exhibit a favorable mechanical property, biomineralization, and better biological properties; therefore, they can be applied in bone tissue engineering.

Dual antituberculosis drugs-loaded gelatin hydrogel bioimplant for treating spinal tuberculosis

Spinal tuberculosis (TB) represents around 1% of the recorded TB with a high mortality rate due to neurological complications and kyphosis. The current work aimed to develop a bioimplant scaffold to treat spinal TB disease. The scaffold is composed of a biocompatible semi-interpenetrating (semi-IPN) gelatin-based hydrogel incorporating mesoporous silica nanoparticles (MPS-NPs) loaded with rifampicin (RIF) and levofloxacin (LEV) to treat TB. The elastic modulus of the hydrogel was 7.18 ± 0.78 MPa. Minimum inhibitory concentrations (MIC) value against Mycobacterium bovis for LEV-loaded and RIF-loaded MPS-NPs were 6.50 and 1.33 µm/ml, respectively.Sequential release of drugs was observed after 15 days. Loading of the MPS-NPs in the hydrogel matrix governed the amount of released drugs by prolonging the period of release up to 60 days. WST-1 test confirmed the biocompatibility and safety of the developed vertebral hydrogel bioimplant. Histological and immunohistochemistry micrographs showed the progress in healing process with the bioimplant. Besides, loading of LEV and RIF in the implants declined the presence of the giant macrophages clusters as compared to control groups. All the obtained results support the potential use of the developed vertebral hydrogel bioimplant as a scaffold with good mechanical and biocompatible properties along with a good ability to eradicate the TB pathogen.

Polydopamine-coated 3D-printed β-tricalcium phosphate scaffolds to promote the adhesion and osteogenesis of BMSCs for bone-defect repair: mRNA transcriptomic sequencing analysis

Cellular bioactivity and tissue regeneration can be affected by coatings on tissue-engineered scaffolds. Using mussel-inspired polydopamine (PDA) is a convenient and effective approach to surface modification. Therefore, 3D-printed β-tricalcium phosphate (β-TCP) scaffolds were coated with PDA in this study. The effects of the scaffolds on the adhesion and osteogenic differentiation of seeded bone marrow mesenchymal stem cells (BMSCs) in vitro and on new-bone formation in vivo were investigated. The potential mechanisms and related differential genes were assessed using mRNA sequencing. It was seen that PDA coating increased the surface roughness of the 3D-printed β-TCP scaffolds. Furthermore, it prompted the adhesion and osteogenic differentiation of seeded BMSCs. mRNA sequencing analysis revealed that PDA coating might affect the osteogenic differentiation of BMSCs through the calcium signaling pathway, Wnt signaling pathway, TGF-beta signaling pathway, etc. Moreover, the expression of osteogenesis-related genes, such as R-spondin 1 and chemokine c-c-motif ligand 2, was increased. Finally, both the 3D-printed β-TCP scaffolds and PDA-coated scaffolds could significantly accelerate the formation of new bone in critical-size calvarial defects in rats compared with the control group; and the new bone formation was obviously higher in the PDA-coated scaffolds than in β-TCP scaffolds. In summary, 3D-printed β-TCP scaffolds with a PDA coating can improve the physicochemical characteristics and cellular bioactivity of the scaffold surface for bone regeneration. Potential differential genes were identified, which can be used as a foundation for further research.

Advances in materials-based therapeutic strategies against osteoporosis

Osteoporosis is caused by the disruption in homeostasis between bone formation and bone resorption. Conventional management of osteoporosis involves systematic drug administration and hormonal therapy. These treatment strategies have limited curative efficacy and multiple adverse effects. Biomaterials-based therapeutic strategies have recently emerged as promising alternatives for the treatment of osteoporosis. The present review summarizes the current status of biomaterials designed for managing osteoporosis. The advantages of biomaterials-based strategies over conventional systematic drug treatment are presented. Different anti-osteoporotic delivery systems are concisely addressed. These materials include injectable hydrogels and nanoparticles, as well as anti-osteoporotic bone tissue engineering materials. Fabrication techniques such as 3D printing, electrostatic spinning and artificial intelligence are appraised in the context of how the use of these adjunctive techniques may improve treatment efficacy. The limitations of existing biomaterials are critically analyzed, together with deliberation of the future directions in biomaterials-based therapies. The latter include discussion on the use of combination strategies to enhance therapeutic efficacy in the osteoporosis niche.

Bioactive Composite Methacrylated Gellan Gum for 3D-Printed Bone Tissue-Engineered Scaffolds

Gellan gum (GG) was chemically modified with methacrylic moieties to produce a photocrosslinkable biomaterial ink, hereinafter called methacrylated GG (GGMA), with improved physico-chemical properties, mechanical behavior and stability under physiological conditions. Afterwards, GGMA was functionalized by incorporating two different bioactive compounds, a naturally derived eumelanin extracted from the black soldier fly (BSF-Eumel), or hydroxyapatite nanoparticles (HAp), synthesized by the sol-gel method. Different ink formulations based on GGMA (2 and 4% (w/v)), BSF-Eumel, at a selected concentration (0.3125 mg/mL), or HAp (10 and 30% w_HAp/w_GGMA) were developed and processed by three-dimensional (3D) printing. All the functionalized GGMA-based ink formulations allowed obtaining 3D-printed GGMA-based scaffolds with a well-organized structure. For both bioactive signals, the scaffolds with the highest GGMA concentration (4% (w/v)) and the highest percentage of infill (45%) showed the best performances in terms of morphological and mechanical properties. Indeed, these scaffolds showed a good structural integrity over 28 days. Given the presence of negatively charged groups along the eumelanin backbone, scaffolds consisting of GGMA/BSF-Eumel demonstrated a higher stability. From a mechanical point of view, GGMA/BSF-Eumel scaffolds exhibited values of storage modulus similar to those of GGMA ones, while the inclusion of HAp at 30% (w_HAp/w_GGMA) led to a storage modulus of 32.5 kPa, 3.5-fold greater than neat GGMA. In vitro studies proved the capability of the bioactivated 3D-printed scaffolds to support 7F2 osteoblast cell growth and differentiation. BSF-Eumel and HAp triggered a different time-dependent physiological response in the osteoblasts. Specifically, while the ink with BSF-Eumel acted as a stimulus towards cell proliferation, reaching the highest value at 14 days, a higher expression of alkaline phosphatase activity was detected for scaffolds consisting of GGMA and HAp. The overall findings demonstrated the possible use of these biomaterial inks for 3D-printed bone tissue-engineered scaffolds.

Chitosan Based Materials in Cosmetic Applications: A Review

This review provides a report on the properties and recent advances in the application of chitosan and chitosan-based materials in cosmetics. Chitosan is a polysaccharide that can be obtained from chitin via the deacetylation process. Chitin most commonly is extracted from cell walls in fungi and the exoskeletons of arthropods, such as crustaceans and insects. Chitosan has attracted significant academic interest, as well as the attention of the cosmetic industry, due to its interesting properties, which include being a natural humectant and moisturizer for the skin and a rheology modifier. This review paper covers the structure of chitosan, the sources of chitosan used in the cosmetic industry, and the role played by this polysaccharide in cosmetics. Future aspects regarding applications of chitosan-based materials in cosmetics are also mentioned.

Additive manufacturing and performance of bioceramic scaffolds with different hollow strut geometries

Additively manufactured hollow-strut bioceramic scaffolds present a promising strategy towards enhanced performance in patient-tailored bone tissue engineering. The channels in such scaffolds offer pathways for nutrient and cell transport and facilitate effective osseointegration and vascularization. In this study, we report an approach for the slurry based additive manufacturing of modified diopside bioceramics that enables the production of hollow-strut scaffolds with diverse cross-sectional forms, distinguished by different configurations of channel and strut geometries. The prepared scaffolds exhibit levels of porosity and mechanical strength that are well suited for osteoporotic bone repair. Mechanical characterization in orthogonal orientations revealed that a square outer cross-section for hollow struts in woodpile scaffolds gives rise to levels of compressive strength that are higher than those of conventional solid cylindrical strut scaffolds despite a significantly lower density. Finite element analysis confirms that this improved strength arises from lower stress concentration in such geometries. It was shown that hollow struts in bioceramic scaffolds dramatically increase cell attachment and proliferation, potentially promoting new bone tissue formation within the scaffold channel. This work provides an easily controlled method for the extrusion-based 3D printing of hollow strut scaffolds. We show here how the production of hollow struts with controllable geometry can serve to enhance both the functional and mechanical performance of porous structures, with particular relevance for bone tissue engineering scaffolds.

3D bioprinting of dECM/Gel/QCS/nHAp hybrid scaffolds laden with mesenchymal stem cell-derived exosomes to improve angiogenesis and osteogenesis

Craniofacial bone regeneration is a coupled process of angiogenesis and osteogenesis, which, associated with infection, still remains a challenge in bone defects after trauma or tumor resection. 3D tissue engineering scaffolds with multifunctional-therapeutic properties can offer many advantages for the angiogenesis and osteogenesis of infected bone defects. Hence, in the present study, a microchannel networks-enriched 3D hybrid scaffold composed of decellularized extracellular matrix (dECM), gelatin (Gel), quaterinized chitosan (QCS) and nano-hydroxyapatite (nHAp) (dGQH) was fabricated by an extrusion 3D bioprinting technology. And enlightened by the characteristics of natural bone microstructure and the demands of vascularized bone regeneration, the exosomes (Exos) isolated from human adipose derived stem cells as angiogenic and osteogenic factors were then co-loaded into the desired dGQH₂₀hybrid scaffold based on an electrostatic interaction. The results of the hybrid scaffolds performance characterization showed that these hybrid scaffolds exhibited an interconnected pore structure and appropriate degradability (>61% after 8 weeks of treatment), and the dGQH₂₀hybrid scaffold displayed the highest porosity (83.93 ± 7.38%) and mechanical properties (tensile modulus: 62.68 ± 10.29 MPa, compressive modulus: 16.22 ± 3.61 MPa) among the dGQH hybrid scaffolds. Moreover, the dGQH₂₀hybrid scaffold presented good antibacterial activities (against 94.90 ± 2.44% ofEscherichia coliand 95.41 ± 2.65% ofStaphylococcus aureus, respectively) as well as excellent hemocompatibility and biocompatibility. Furthermore, the results of applying the Exos to the dGQH₂₀hybrid scaffold showed that the Exo promoted the cell attachment and proliferation on the scaffold, and also showed a significant increase in osteogenesis and vascularity regeneration in the dGQH@Exo scaffoldsin vitroandin vivo. Overall, this novel dECM/Gel/QCS/nHAp hybrid scaffold laden with Exo has a considerable potential application in reservation of craniofacial bone defects.

Biological Scaffolds Assembled with Magnetic Nanoparticles for Bone Tissue Engineering: A Review

Superparamagnetic iron oxide nanoparticles (SPION) are widely used in bone tissue engineering because of their unique physical and chemical properties and their excellent biocompatibility. Under the action of a magnetic field, SPIONs loaded in a biological scaffold can effectively promote osteoblast proliferation, differentiation, angiogenesis, and so on. SPIONs have very broad application prospects in bone repair, bone reconstruction, bone regeneration, and other fields. In this paper, several methods for forming biological scaffolds via the biological assembly of SPIONs are reviewed, and the specific applications of these biological scaffolds in bone tissue engineering are discussed.

Nucleoside-Based Cross-Linkers for Hydrogels with Tunable Properties

Herein, we report bioderived cross-linkers to create biopolymer-based hydrogels with tunable properties. Nucleosides (inosine and uridine) and ribose (pentose sugar lucking the nitrogenous base) were partially oxidized to yield inosine dialdehyde (IdA), uridine dialdehyde (UdA), and ribose dialdehyde (RdA). The dialdehydes were further used as cross-linkers with polysaccharide chitosan to form hydrogels. Depending on the cross-linker type and concentration, the hydrogels showed tunable rheological, mechanical, and liquid holding properties allowing the preparation of injectable, soft, and moldable hydrogels. Computational modeling and molecular dynamics simulations shed light on hydrogel formation and revealed that, in addition to covalent bonding, noncovalent interactions (π-π stacking, cation-π, and H-bonding) also significantly contributed to the cross-linking process. To demonstrate various application possibilities, the prepared hydrogels were used as a growth platform for plant cells, as injectable inks for layer-by-layer 3D printing applications, and as moldable hydrogels for soft lithography to replicate the microstructure of the plant. These findings suggest that the obtained tunable biocompatible hydrogels have the potential to be good candidates for various biotechnological applications.

Multiple Reprocessing of Conductive PLA 3D-Printing Filament: Rheology, Morphology, Thermal and Electrochemical Properties Assessment

Additive manufacturing technologies are gaining more and more attention, resulting in the development or modification of 3D printing techniques and dedicated materials. On the other hand, economic and ecological aspects force the industry to develop material recycling strategies. In this work, the multiple reprocessing of a commercially available PLA conductive composite with carbon black filler, dedicated to 3D printing, was investigated. The effects of extrusion temperature (190 °C and 200 °C) and reprocessing steps (1-5 steps) on the rheology, morphology, thermal and electrochemical properties of the conductive PLA 3D-printing filament were evaluated. The results showed deterioration of the thermal stability and material strength, as well as the influence of reprocessing on the melting point, which increases after initial melting. The electronic conduction mechanism of the composite depends on the percolation paths and it is also affected by the multiple processing. The reversibility of the [Fe(CN)₆]^3-/4- redox process diminishes with a higher degradation level of the conductive PLA. Importantly, the material fluidity was too high after the multiple reprocessing, which should be considered and suitably corrected during CB-PLA application as a 3D-printed electrode material.

Guided cortical and cancellous bone formation using a minimally invasive technique of BMSC- and BMP-2-laden visible light-cured carboxymethyl chitosan hydrogels

A cavity defect inside the bone is formed by deformed cancellous bone from the fixation of the cortical bone, and consequently, abnormal bone healing occurs. Therefore, repairing cancellous bone defects is a remarkable topic in orthopedic surgery. In this study, we prepared bone marrow-derived stem cell (BMSC)-laden and bone morphogenetic protein-2 (BMP-2)-laden visible light-cured carboxymethyl chitosan (CMCS) hydrogels for cortical and cancellous bone healing. Proton nuclear magnetic resonance (¹H NMR) analysis confirmed the methacrylation of CMCS (CMCSMA), resulting in 55 % of substitution. The higher concentration of CMCSMA hydrogel resulted in the lower swelling ratio, the larger viscosity, the slower degradation behavior, and the stronger compressive strength. The 5 w/v% hydrogel exhibited a controlled BMP-2 release for 14 days, while the 7 and 10 w/v% hydrogels displayed a controlled BMP-2 release for 28 days. Results of in vitro cytotoxicity and cell proliferation assays revealed the biocompatibility of the samples. In vivo animal tests demonstrated that BMSC- and BMP-2-laden 7 w/v% CMCSMA (CMCSMA+Cell+BMP-2) improved bone formation in the defected cortical and cancellous bones of the femur, as analyzed by micro-computed tomography (micro-CT) and histological evaluations. Consequently, we suggested that CMCSMA+Cell+BMP-2 can be a valuable scaffold for restoring cortical and cancellous bone defects.

Influence of Process Parameters on the Characteristics of Additively Manufactured Parts Made from Advanced Biopolymers

Over the past few decades, additive manufacturing (AM) has become a reliable tool for prototyping and low-volume production. In recent years, the market share of such products has increased rapidly as these manufacturing concepts allow for greater part complexity compared to conventional manufacturing technologies. Furthermore, as recyclability and biocompatibility have become more important in material selection, biopolymers have also become widely used in AM. This article provides an overview of AM with advanced biopolymers in fields from medicine to food packaging. Various AM technologies are presented, focusing on the biopolymers used, selected part fabrication strategies, and influential parameters of the technologies presented. It should be emphasized that inkjet bioprinting, stereolithography, selective laser sintering, fused deposition modeling, extrusion-based bioprinting, and scaffold-free printing are the most commonly used AM technologies for the production of parts from advanced biopolymers. Achievable part complexity will be discussed with emphasis on manufacturable features, layer thickness, production accuracy, materials applied, and part strength in correlation with key AM technologies and their parameters crucial for producing representative examples, anatomical models, specialized medical instruments, medical implants, time-dependent prosthetic features, etc. Future trends of advanced biopolymers focused on establishing target-time-dependent part properties through 4D additive manufacturing are also discussed.

Biomaterials Based on Organic Polymers and Layered Double Hydroxides Nanocomposites: Drug Delivery and Tissue Engineering

The development of biomaterials has a substantial role in pharmaceutical and medical strategies for the enhancement of life quality. This review work focused on versatile biomaterials based on nanocomposites comprising organic polymers and a class of layered inorganic nanoparticles, aiming for drug delivery (oral, transdermal, and ocular delivery) and tissue engineering (skin and bone therapies). Layered double hydroxides (LDHs) are 2D nanomaterials that can intercalate anionic bioactive species between the layers. The layers can hold metal cations that confer intrinsic biological activity to LDHs as well as biocompatibility. The intercalation of bioactive species between the layers allows the formation of drug delivery systems with elevated loading capacity and modified release profiles promoted by ion exchange and/or solubilization. The capacity of tissue integration, antigenicity, and stimulation of collagen formation, among other beneficial characteristics of LDH, have been observed by in vivo assays. The association between the properties of biocompatible polymers and LDH-drug nanohybrids produces multifunctional nanocomposites compatible with living matter. Such nanocomposites are stimuli-responsive, show appropriate mechanical properties, and can be prepared by creative methods that allow a fine-tuning of drug release. They are processed in the end form of films, beads, gels, monoliths etc., to reach orientated therapeutic applications. Several studies attest to the higher performance of polymer/LDH-drug nanocomposite compared to the LDH-drug hybrid or the free drug.

Regenerated silk fibroin loaded with natural additives: a sustainable approach towards health care

According to World Health Organization (WHO), on average, 0.5 Kg of hazardous waste is generated per bed every day in high-income countries. The adverse effects imposed by synthetic materials and chemicals on the environment and humankind have urged researchers to explore greener technologies and materials. Amidst of all the natural fibers, silk fibroin (SF), by virtue of its superior toughness (6 × 10⁴∼16 × 10⁴ J/kg), tensile strength (47.2-67.7 MPa), tunable biodegradability, excellent Young's modulus (1.9-3.9 GPa), presence of functional groups, ease of processing, and biocompatibility has garnered an enormous amount of scientific interests. The use of silk fibroin conjoint with purely natural materials can be an excellent solution for the adverse effects of chemical-based treatment techniques. Considering this noteworthiness, vigorous research is going on in silk-based biomaterials, and it is opening up new vistas of opportunities. This review enswathes the structural aspects of silk fibroin along with its potency to form composites with other natural materials, such as curcumin, keratin, alginate, hydroxyapatite, hyaluronic acid, and cellulose, that can replace the conventionally used synthetic materials, providing a sustainable pathway to biomedical engineering. It was observed that a large amount of polar functional moieties present on the silk fibroin surface enables them to compatibilize easily with the natural additives. The conjunction of silk with natural additives initiates synergistic interactions that mitigate the limitations offered by individual units as well as enhance the applicability of materials. Further the current status and challenges in the commercialization of silk-based biomedical devices are discussed.

Application of Hydrogels as Three-Dimensional Bioprinting Ink for Tissue Engineering

The use of three-dimensional bioprinting technology combined with the principle of tissue engineering is important for the construction of tissue or organ regeneration microenvironments. As a three-dimensional bioprinting ink, hydrogels need to be highly printable and provide a stiff and cell-friendly microenvironment. At present, hydrogels are used as bioprinting inks in tissue engineering. However, there is still a lack of summary of the latest 3D printing technology and the properties of hydrogel materials. In this paper, the materials commonly used as hydrogel bioinks; the advanced technologies including inkjet bioprinting, extrusion bioprinting, laser-assisted bioprinting, stereolithography bioprinting, suspension bioprinting, and digital 3D bioprinting technologies; printing characterization including printability and fidelity; biological properties, and the application fields of bioprinting hydrogels in bone tissue engineering, skin tissue engineering, cardiovascular tissue engineering are reviewed, and the current problems and future directions are prospected.

Manufacturing of scaffolds with interconnected internal open porosity and surface roughness

Manufacturing of three-dimensional scaffolds with multiple levels of porosity are an advantage in tissue regeneration approaches to influence cell behavior. Three-dimensional scaffolds with surface roughness and intra-filament open porosity were successfully fabricated by additive manufacturing combined with chemical foaming and porogen leaching without the need of toxic solvents. The decomposition of sodium citrate, a chemical blowing agent, generated pores within the scaffold filaments, which were interconnected and opened to the external environment by leaching of a water-soluble sacrificial phase, as confirmed by micro-CT and buoyancy measurements. The additional porosity did not result in lower elastic modulus, but in higher strain at maximum load, i.e. scaffold ductility. Human mesenchymal stromal cells cultured for 24 h adhered in greater numbers on these scaffolds when compared to plain additive-manufactured ones, irrespectively of the scaffold pre-treatment method. Additionally, they showed a more spread and random morphology, which is known to influence cell fate. Cells cultured for a longer period exhibited enhanced metabolic activity while secreting higher osteogenic markers after 7 days in culture. STATEMENT OF SIGNIFICANCE: Inspired by the function of hierarchical cellular structures in natural materials, this work elucidates the development of scaffolds with multiscale porosity by combining in-situ foaming and additive manufacturing, and successive porogen leaching. The resulting scaffolds displayed enhanced mechanical toughness and multiscale pore network interconnectivity, combined with early differentiation of adult mesenchymal stromal cells into the osteogenic lineage.

Fabrication and Bioactivity of Peptide-Conjugated Biomaterial Tissue Engineering Constructs

Tissue engineering combines materials engineering, cells and biochemical factors to improve, restore or replace various types of biological tissues. A nearly limitless combination of these strategies can be combined, providing a means to augment the function of a number of biological tissues such as skin tissue, neural tissue, bones, and cartilage. Compounds such as small molecule therapeutics, proteins, and even living cells have been incorporated into tissue engineering constructs to influence biological processes at the site of implantation. Peptides have been conjugated to tissue engineering constructs to circumvent limitations associated with conjugation of proteins or incorporation of cells. This review highlights various contemporary examples in which peptide conjugation is used to overcome the disadvantages associated with the inclusion of other bioactive compounds. This review covers several peptides that are commonly used in the literature as well as those that do not appear as frequently to provide a broad scope of the utility of the peptide conjugation technique for designing constructs capable of influencing the repair and regeneration of various bodily tissues. Additionally, a brief description of the construct fabrication techniques encountered in the covered examples and their advantages in various tissue engineering applications is provided.

Multifunctional 3D-printed bioceramic scaffolds: Recent strategies for osteosarcoma treatment

Osteosarcoma is the most prevalent bone malignant tumor in children and teenagers. The bone defect, recurrence, and metastasis after surgery severely affect the life quality of patients. Clinically, bone grafts are implanted. Primary bioceramic scaffolds show a monomodal osteogenesis function. With the advances in three-dimensional printing technology and materials science, while maintaining the osteogenesis ability, scaffolds become more patient-specific and obtain additional anti-tumor ability with functional agents being loaded. Anti-tumor therapies include photothermal, magnetothermal, old and novel chemo-, gas, and photodynamic therapy. These strategies kill tumors through novel mechanisms to treat refractory osteosarcoma due to drug resistance, and some have shown the potential to reverse drug resistance and inhibit metastasis. Therefore, multifunctional three-dimensional printed bioceramic scaffolds hold excellent promise for osteosarcoma treatments. To better understand, we review the background of osteosarcoma, primary 3D-printed bioceramic scaffolds, and different therapies and have a prospect for the future.

Biocompatible scaffolds constructed by chondroitin sulfate microspheres conjugated 3D-printed frameworks for bone repair

Most bone repair scaffolds are multi-connected channel structure, but the hollow structure is not conducive to the transmission of active factors, cells and so on. Here, microspheres were covalently integrated into 3D-printed frameworks to form composite scaffolds for bone repair. The frameworks composed of double bond modified gelatin (Gel-MA) and nano-hydroxyapatite (nHAP) provided strong support for related cells climbing and growth. Microspheres, which were made of Gel-MA and chondroitin sulfate A (CSA), were able to connect the frameworks like bridges, providing channels for cells migration. Additionally, CSA released from microspheres promoted the migration of osteoblasts and enhanced osteogenesis. The composite scaffolds could effectively repair mouse skull defect and improve MC3T3-E1 osteogenic differentiation. These observations confirm the bridging effect of microspheres rich in chondroitin sulfate and also determine that the composite scaffold can be as a promising candidate for enhanced bone repair.

Sericin/Nano-Hydroxyapatite Hydrogels Based on Graphene Oxide for Effective Bone Regeneration via Immunomodulation and Osteoinduction

Background

Immune responses and osteogenesis differentiation induced by implants are crucial for bone tissue regeneration. Consideration of only one of those properties is not sufficient. To investigate the synergistic actions, we designed alginate/graphene oxide/sericin/nanohydroxyapatite (Alg/GO/Ser/nHAP) nanocomposite hydrogels with both osteoimmunomodulatory and osteoinductive activities. This study aimed to explore the effect of hydrogel with osteoimmunomodulatory properties on promoting osteogenesis of bone marrow stem cells (BMSCs).

Methods

Alg/GO/Ser/nHAP nanocomposite hydrogel was fabricated and was characterized by SEM, FTIR, XRD, stress-strain, rheology, swelling and degradation. After the impact of sericin on M2 macrophage polarization was identified, the BMSCs viability and adhesion were evaluated by CCK8 assay, live/dead staining, cytoskeleton staining. The cell osteogenic differentiation was observed by ALP/ARS staining, immunofluorescence staining, RT-PCR, and Western blotting, respectively. Rat cranial defect model was used to assess osteoimmunomodulatory effects of scaffolds in vivo by micro‑computed tomographic, histological, and immunohistochemical analyses after 8 weeks of healing.

Results

In vitro experiments revealed that the hydrogel presented desirable mechanical strength, stability, porosity, and biocompatibility. Significantly, sericin and nHAP appeared to exert synergistic effects on bone regeneration. Sericin was observed to inhibit the immune response by inducing macrophage M2-type polarization to create a positive osteoimmune microenvironment, contributing to improving osseointegration at the bone-implant interface to promote osteogenesis. However, the osteogenic differentiation in rat BMSCs was further enhanced by combining nHAP and sericin in the nanocomposite hydrogel. Eventually, the hydrogel was implanted into the rat cranial defect model, assisting in the reduction of local inflammation and efficient bone regeneration.

Conclusion

The nanocomposite hydrogel stimulated bone formation by the synergistic effects of immunomodulation of macrophage polarization by sericin and direct osteogenic induction by nHAP, demonstrating that such a scaffold that modulates the osteoimmune microenvironment to promote osteogenesis is a promising approach for the development of bone tissue engineering implants in the future.

Hybrid 3D Printed and Electrospun Multi-Scale Hierarchical Polycaprolactone Scaffolds to Induce Bone Differentiation

Complex scaffolds composed of micro- and nano-structures are a key target in tissue engineering and the combination of sequential 3D printing and electrospinning enables the fabrication of these multi-scale structures. In this work, dual 3D printed and electrospun polycaprolactone (PCL) scaffolds with multiple mesh layers were successfully prepared. The scaffold macro- and micro-porosity were assessed by optical and scanning electron microscopy, showing that electrospun fibers formed aligned meshes within the pores of the scaffold. Consequently, the hydrophilicity of the scaffold increased with time, enhancing cell adhesion and growth. Additionally, compression tests in back and forth cycles demonstrated a good shape recovery behavior of the scaffolds. Biological results indicated that hybrid PCL scaffolds are biocompatible and enable a correct cell culture over time. Moreover, MC3T3-E1 preosteoblast culture on the scaffolds promoted the mineralization, increased the alkaline phosphatase (ALP) activity and upregulated the expression of early and late osteogenic markers, namely ALP and osteopontin (OPN), respectively. These results demonstrate that the sequential combination of 3D printing and electrospinning provides a facile method of incorporating fibers within a 3D printed scaffold, becoming a promising approach towards multi-scale hierarchical scaffolds capable of guiding the osteogenic differentiation.

Research Progress of Shape Memory Polymer and 4D Printing in Biomedical Application

As a kind of smart material, shape memory polymer (SMP) shows great application potential in the biomedical field. Compared with traditional metal-based medical devices, SMP-based devices have the following characteristics: 1) The adaptive ability allows the biomedical device to better match the surrounding tissue after being implanted into the body by minimally invasive implantation; 2) it has better biocompatibility and adjustable biodegradability; 3) mechanical properties can be regulated in a large range to better match with the surrounding tissue. 4D printing technology is a comprehensive technology based on smart materials and 3D printing, which has great application value in the biomedical field. 4D printing technology breaks through the technical bottleneck of personalized customization and provides a new opportunity for the further development of the biomedical field. This paper summarizes the application of SMP and 4D printing technology in the field of bone tissue scaffolds, tracheal scaffolds, and drug release, etc. Moreover, this paper analyzes the existing problems and prospects, hoping to provide a preliminary discussion and useful reference for the application of SMP in biomedical engineering.

3D printed-electrospun PCL/hydroxyapatite/MWCNTs scaffolds for the repair of subchondral bone

Osteochondral defect caused by trauma or osteoarthritis exhibits a major challenge in clinical treatment with limited symptomatic effects at present. The regeneration and remodeling of subchondral bone play a positive effect on cartilage regeneration and further promotes the repair of osteochondral defects. Making use of the strengths of each preparation method, the combination of 3D printing and electrospinning is a promising method for designing and constructing multi-scale scaffolds that mimic the complexity and hierarchical structure of subchondral bone at the microscale and nanoscale, respectively. In this study, the 3D printed-electrospun poly(ɛ-caprolactone)/nano-hydroxyapatites/multi-walled carbon nanotubes (PCL/nHA/MWCNTs) scaffolds were successfully constructed by the combination of electrospinning and layer-by-layer 3D printing. The resulting dual-scale scaffold consisted of a dense layer of disordered nanospun fibers and a porous microscale 3D scaffold layer to support and promote the ingrowth of subchondral bone. Herein, the biomimetic PCL/nHA/MWCNTs scaffolds enhanced cell seeding efficiency and allowed for higher cell-cell interactions that supported the adhesion, proliferation, activity, morphology and subsequently improved the osteogenic differentiation of bone marrow mesenchymal stem cells in vitro. Together, this study elucidates that the construction of 3D printed-electrospun PCL/nHA/MWCNTs scaffolds provides an alternative strategy for the regeneration of subchondral bone and lays a foundation for subsequent in vivo studies.

Biomedical polymer scaffolds mimicking bone marrow niches to advance in vitro expansion of hematopoietic stem cells

Hematopoietic stem cell (HSC) transplantation provides an effective platform for the treatment of hematological disorders. However, the donor shortage of HSCs and immune responses severely restrict the clinical applications of HSCs. Compared to allogeneic transplantation, autogenous transplantation poses less risk to the immune system, but the problem associated with insufficient HSCs remains a substantial challenge. A significant strategy for obtaining sufficient HSCs is to promote the expansion of HSCs. In vivo, a bone marrow microenvironment supports the survival and hematopoiesis of HSCs. Therefore, it is crucial to establish a platform that mimics the features of a bone marrow microenvironment for the in vitro expansion of HSCs. Three-dimensional (3D) scaffolds have emerged as the most powerful tools to mimic cellular microenvironments for the growth and proliferation of stem cells. Biomedical polymers have been widely utilized as cell scaffolds due to their advantageous features including favorable biocompatibility, biodegradability, as well as adjustable physical and chemical properties. This review focuses on recent advances in the study of biomedical polymer scaffolds that mimic bone marrow microenvironments for the in vitro expansion of HSCs. Bone marrow transplantation and microenvironments are first introduced. Then, biomedical polymer scaffolds for the expansion of HSCs and future prospects are summarized and discussed.

3D bioprinting of in situ vascularized tissue engineered bone for repairing large segmental bone defects

Large bone defects remain an unsolved clinical challenge because of the lack of effective vascularization in newly formed bone tissue. 3D bioprinting is a fabrication technology with the potential to create vascularized bone grafts with biological activity for repairing bone defects. In this study, vascular endothelial cells laden with thermosensitive bio-ink were bioprinted in situ on the inner surfaces of interconnected tubular channels of bone mesenchymal stem cell-laden 3D-bioprinted scaffolds. Endothelial cells exhibited a more uniform distribution and greater seeding efficiency throughout the channels. In vitro, the in situ bioprinted endothelial cells can form a vascular network through proliferation and migration. The in situ vascularized tissue-engineered bone also resulted in a coupling effect between angiogenesis and osteogenesis. Moreover, RNA sequencing analysis revealed that the expression of genes related to osteogenesis and angiogenesis is upregulated in biological processes. The in vivo 3D-bioprinted in situ vascularized scaffolds exhibited excellent performance in promoting new bone formation in rat calvarial critical-sized defect models. Consequently, in situ vascularized tissue-engineered bones constructed using 3D bioprinting technology have a potential of being used as bone grafts for repairing large bone defects, with a possible clinical application in the future.

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3D bioprinting was used to fabricate in situ vascularized tissue engineered bone.

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In situ bioprinted endothelial cells exhibited uniform distribution and greater seeding efficiency.

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3D-bioprinted scaffold produced coupling between angiogenesis and osteogenesis.

Strategies to improve bioactive and antibacterial properties of polyetheretherketone (PEEK) for use as orthopedic implants

Polyetheretherketone (PEEK) has gradually become the mainstream material for preparing orthopedic implants due to its similar elastic modulus to human bone, high strength, excellent wear resistance, radiolucency, and biocompatibility. Since the 1990s, PEEK has increasingly been used in orthopedics. Yet, the widespread application of PEEK is limited by its bio-inertness, hydrophobicity, and susceptibility to microbial infections. Further enhancing the osteogenic properties of PEEK-based implants remains a difficult task. This article reviews some modification methods of PEEK in the last five years, including surface modification of PEEK or incorporating materials into the PEEK matrix. For surface modification, PEEK can be modified by chemical treatment, physical treatment, or surface coating with bioactive substances. For PEEK composite material, adding bioactive filler into PEEK through the melting blending method or 3D printing technology can increase the biological activity of PEEK. In addition, some modification methods such as sulfonation treatment of PEEK or grafting antibacterial substances on PEEK can enhance the antibacterial performance of PEEK. These strategies aim to improve the bioactive and antibacterial properties of the modified PEEK. The researchers believe that these modifications could provide valuable guidance on the future design of PEEK orthopedic implants.