Advances in Filament Structure of 3D Bioprinted Biodegradable Bone Repair Scaffolds

Techniques and applications in 3D bioprinting with chitosan bio-inks for drug delivery: A review

Three-dimensional bioprinting leverages computer-aided design to construct tissues and organs with specialized bioinks. A notable biomaterial for this purpose is chitosan, a natural polysaccharide sourced from crustacean exoskeletons. Chitosan's biocompatibility, biodegradability, non-toxicity, and ability to promote cell adhesion and proliferation make it an excellent component for bioinks. Initially, the rheological properties of chitosan presented challenges for its use in bioprinting. Enhancements in its printability and stability were achieved by integrating it with other natural or synthetic polymers, facilitating its successful application in bioprinting. Chitosan-based bioinks are particularly promising for controlled drug delivery. Incorporating pharmaceuticals directly into the bioink enables the printed structures to serve as localized, sustained-release systems. This approach offers multiple advantages, including precise drug delivery to targeted disease sites, increased therapeutic efficiency, and reduced systemic side effects. Moreover, bioprinting allows for the customization of drug delivery mechanisms to meet individual patient requirements. Although there have been considerable advancements, the use of chitosan-based bioinks in drug delivery is still an emerging field. This review highlights chitosan's essential role in both systemic and localized drug delivery, underscoring its significance and discussing ongoing trends in its application for pharmaceutical purposes.

Research on Dual-Phase Composite Forming Process and Platform Construction of Radial Gradient Long Bone Scaffold

The structure and composition of natural bone show gradient changes. Most bone scaffolds prepared by bone tissue engineering with single materials and structures present difficulties in meeting the needs of bone defect repair. Based on the structure and composition of natural long bones, this study proposed a new bone scaffold preparation technology, the dual-phase composite forming process. Based on the composite use of multiple biomaterials, a bionic natural long bone structure bone scaffold model with bone scaffold pore structure gradient and material concentration gradient changes along the radial direction was designed. Different from the traditional method of using multiple nozzles to achieve material concentration gradient in the scaffold, the dual-phase composite forming process in this study achieved continuous 3D printing preparation of bone scaffolds with gradual material concentration gradient by controlling the speed of extruding materials from two feed barrels into a closed mixing chamber with one nozzle. Through morphological characterization and mechanical property analysis, the results showed that BS-G (radial gradient long bone scaffolds prepared by the dual-phase composite forming process) had obvious pore structure gradient changes and material concentration gradient changes, while BS-T (radial gradient long bone scaffolds prepared by printing three concentrations of material in separate regions) had a discontinuous gradient with obvious boundaries between the parts. The compressive strength of BS-G was 1.00 ± 0.19 MPa, which was higher than the compressive strength of BS-T, and the compressive strength of BS-G also met the needs of bone defect repair. The results of in vitro cell culture tests showed that BS-G had no cytotoxicity. In a Sprague-Dawley rat experimental model, blood tests and key organ sections showed no significant difference between the experimental group and the control group. The prepared BS-G was verified to have good biocompatibility and lays a foundation for the subsequent study of the bone repair effect of radial gradient long bone scaffolds in large animals.

Optimizing Filament-Based TCP Scaffold Design for Osteoconduction and Bone Augmentation: Insights from In Vivo Rabbit Models

Additive manufacturing has emerged as a transformative tool in biomedical engineering, offering precise control over scaffold design for bone tissue engineering and regenerative medicine. While much attention has been focused on optimizing pore-based scaffold architectures, filament-based microarchitectures remain relatively understudied, despite the fact that the majority of 3D-printers generate filament-based structures. Here, we investigated the influence of filament characteristics on bone regeneration outcomes using a lithography-based additive manufacturing approach. Three distinct filament-based scaffolds (Fil050, Fil083, and Fil125) identical in macroporosity and transparency, crafted from tri-calcium phosphate (TCP) with varying filament thicknesses and distance, were evaluated in a rabbit model of bone augmentation and non-critical calvarial defect. Additionally, two scaffold types differing in filament directionality (Fil and FilG) were compared to elucidate optimal design parameters. Distance of bone ingrowth and percentage of regenerated area within scaffolds were measured by histomorphometric analysis. Our findings reveal filaments of 0.50 mm as the most effective filament-based scaffold, demonstrating superior bone ingrowth and bony regenerated area compared to larger size filament (i.e., 0.83 mm and 1.25 mm scaffolds). Optimized directionality of filaments can overcome the reduced performance of larger filaments. This study advances our understanding of microarchitecture's role in bone tissue engineering and holds significant implications for clinical practice, paving the way for the development of highly tailored, patient-specific bone substitutes with enhanced efficacy.

Fused Deposition Modeling 3D-Printed Scaffolds for Bone Tissue Engineering Applications: A Review

The emergence of bone tissue engineering as a trend in regenerative medicine is forcing scientists to create highly functional materials and scaffold construction techniques. Bone tissue engineering uses 3D bio-printed scaffolds that allow and stimulate the attachment and proliferation of osteoinductive cells on their surfaces. Bone grafting is necessary to expedite the patient's condition because the natural healing process of bones is slow. Fused deposition modeling (FDM) is therefore suggested as a technique for the production process due to its simplicity, ability to create intricate components and movable forms, and low running costs. 3D-printed scaffolds can repair bone defects in vivo and in vitro. For 3D printing, various materials including metals, polymers, and ceramics are often employed but polymeric biofilaments are promising candidates for replacing non-biodegradable materials due to their adaptability and environment friendliness. This review paper majorly focuses on the fused deposition modeling approach for the fabrication of 3D scaffolds. In addition, it also provides information on biofilaments used in FDM 3D printing, applications, and commercial aspects of scaffolds in bone tissue engineering.

Simvastatin-loaded 3D aerogel scaffolds promote bone regeneration

BACKGROUND

It is imperative to design a suitable material for bone regeneration that emulates the microstructure and compositional framework of natural bone while mitigating the shortcomings of current repair materials.

OBJECTIVE

The aim of the study is to synthesize a 3D aerogel scaffold composed of PLCL/gelatin electro-spun nanofiber loaded with Simvastatin and investigate its biocompatibility as well as its performance in cell proliferation and ossification differentiation.

METHODS

PLCL/gelatin nanofibers were fabricated in coaxial electrospinning with simvastatin added. Fibers were fragmented, pipetted into molds, frozen, and dried. The morphology of fibers and contact angles in 4 groups of PLCL, PLCL@S, 3D-PLCL, and 3D-PLCL@S was observed and compared. MC3T3-E1 cells were planted at the four materials to observe cell growth status, and ALP and ARS tests were conducted to compare the ossification of cells.

RESULTS

TEM scanning showed the coaxial fiber of the inner PLCL and outer gelatin. The mean diameter of the PLCL/gelatin fibers is 561 ± 95 nm and 631 ± 103 nm after the drug loading. SEM showed the fibers in the 3D-PLCL@S group were more curled and loose with more space interlaced. The contact angle in this group was 27.1°, the smallest one. Drug release test demonstrated that simvastatin concentration in the 3D-PLCL@S could remain at a relatively high level compared to the control group. The cell proliferation test showed that MC3T3-EI cells could embed into the scaffold deeply and exhibit higher viability in the 3D-PLCL@S group than other groups. The ossification tests of ALP and ARS also inferred that the 3D-PLCL@S scaffold could offer a better osteogenic differentiation matrix.

CONCLUSION

The PLCL/gelatin aerogel scaffold, when loaded with Simvastatin, demonstrates a more pronounced potential in enhancing osteoblast proliferation and osteogenic differentiation. We hypothesize that this scaffold could serve as a promising material for addressing bone defects.

In vivo characterization of 3D-printed polycaprolactone-hydroxyapatite scaffolds with Voronoi design to advance the concept of scaffold-guided bone regeneration

Three-dimensional (3D)-printed medical-grade polycaprolactone (mPCL) composite scaffolds have been the first to enable the concept of scaffold-guided bone regeneration (SGBR) from bench to bedside. However, advances in 3D printing technologies now promise next-generation scaffolds such as those with Voronoi tessellation. We hypothesized that the combination of a Voronoi design, applied for the first time to 3D-printed mPCL and ceramic fillers (here hydroxyapatite, HA), would allow slow degradation and high osteogenicity needed to regenerate bone tissue and enhance regenerative properties when mixed with xenograft material. We tested this hypothesis in vitro and in vivo using 3D-printed composite mPCL-HA scaffolds (wt 96%:4%) with the Voronoi design using an ISO 13485 certified additive manufacturing platform. The resulting scaffold porosity was 73% and minimal in vitro degradation (mass loss <1%) was observed over the period of 6 months. After loading the scaffolds with different types of fresh sheep xenograft and ectopic implantation in rats for 8 weeks, highly vascularized tissue without extensive fibrous encapsulation was found in all mPCL-HA Voronoi scaffolds and endochondral bone formation was observed, with no adverse host-tissue reactions. This study supports the use of mPCL-HA Voronoi scaffolds for further testing in future large preclinical animal studies prior to clinical trials to ultimately successfully advance the SGBR concept.

Functional anti-bone tumor biomaterial scaffold: construction and application

Bone tumors, including primary bone tumors and bone metastases, have been plagued by poor prognosis for decades. Although most tumor tissue is removed, clinicians are still confronted with the dilemma of eliminating residual cancer cells and regenerating defective bone tissue after surgery. Therefore, functional biomaterial scaffolds are considered to be the ideal candidates to bridge defective tissues and restrain cancer recurrence. Through functionalized structural modifications or coupled therapeutic agents, they provide sufficient mechanical strength and osteoinductive effects while eliminating cancer cells. Numerous novel approaches such as photodynamic, photothermal, drug-conjugated, and immune adjuvant-assisted therapies have exhibited remarkable efficacy against tumors while exhibiting low immunogenicity. This review summarizes the progress of research on biomaterial scaffolds based on different functionalization strategies in bone tumors. We also discuss the feasibility and advantages of the combined application of multiple functionalization strategies. Finally, potential obstacles to the clinical translation of anti-tumor bone bioscaffolds are highlighted. This review will provide valuable references for future advanced biomaterial scaffold design and clinical bone tumor therapy.

The Dual Effect of 3D-Printed Biological Scaffolds Composed of Diverse Biomaterials in the Treatment of Bone Tumors

Bone tumors, including primary bone tumors, invasive bone tumors, metastatic bone tumors, and others, are one of the most clinical difficulties in orthopedics. Once these tumors have grown and developed in the bone system, they will interact with osteocytes and other environmental cells in the bone system's microenvironment, leading to the eventual damage of the bone's physical structure. Surgical procedures for bone tumors may result in permanent defects. The dual-efficacy of tissue regeneration and tumor treatment has made biomaterial scaffolds frequently used in treating bone tumors. 3D printing technology, also known as additive manufacturing or rapid printing prototype, is the transformation of 3D computer models into physical models through deposition, curing, and material fusion of successive layers. Adjustable shape, porosity/pore size, and other mechanical properties are an advantage of 3D-printed objects, unlike natural and synthetic material with fixed qualities. Researchers have demonstrated the significant role of diverse 3D-printed biological scaffolds in the treatment for bone tumors and the regeneration of bone tissue, and that they enhanced various performance of the products. Based on the characteristics of bone tumors, this review synthesized the findings of current researchers on the application of various 3D-printed biological scaffolds including bioceramic scaffold, metal alloy scaffold and nano-scaffold, in bone tumors and discussed the advantages, disadvantages, and future application prospects of various types of 3D-printed biological scaffolds. Finally, the future development trend of 3D-printed biological scaffolds in bone tumor is summarized, providing a theoretical foundation and a larger outlook for the use of biological scaffolds in the treatment of patients with bone tumors.

Osteoconductivity of bone substitutes with filament-based microarchitectures: Influence of directionality, filament dimension, and distance

63Additive manufacturing can be applied to produce personalized bone substitutes. At present, the major three-dimensional (3D) printing methodology relies on filament extrusion. In bioprinting, the extruded filament consists mainly of hydrogels, in which growth factors and cells are embedded. In this study, we used a lithography-based 3D printing methodology to mimic filament-based microarchitectures by varying the filament dimension and the distance between the filaments. In the first set of scaffolds, all filaments were aligned toward bone ingrowth direction. In a second set of scaffolds, which were derived from the identical microarchitecture but tilted by 90°, only 50% of the filaments were in line with the bone ingrowth direction. Testing of all tricalcium phosphate-based constructs for osteoconduction and bone regeneration was performed in a rabbit calvarial defect model. The results revealed that if all filaments are in line with the direction of bone ingrowth, filament size and distance (0.40-1.25 mm) had no significant influence on defect bridging. However, with 50% of filaments aligned, osteoconductivity declined significantly with an increase in filament dimension and distance. Therefore, for filament-based 3D- or bio-printed bone substitutes, the distance between the filaments should be 0.40 to 0.50 mm irrespective of the direction of bone ingrowth or up to 0.83 mm if perfectly aligned to it.

Study on properties of 3D-printed GelMA hydrogel scaffolds with different nHA contents

Biological 3D printing is a reliable technology for 3D printing bone repair scaffolds with simple operation, high efficiency, and relatively low cost. Gelatin methacryloyl (GelMA) hydrogels have attracted much attention due to their good biocompatibility, but the poor mechanical properties limit their application in bone reconstruction engineering. In this study, nano-hydroxyapatite (nHA) particles were added to GelMA hydrogels, and the performances of composite hydrogel scaffolds with different nHA contents were investigated in terms of rheological properties, light transmission properties, surface morphology, mechanical properties, and biocompatibility. The experimental results showed that the incorporation of nHA particles could effectively improve the printability and mechanical properties of the scaffolds, the scaffold fibers had better resistance to deformation, improved degradation rate, and biological experiments confirmed that nHA particles had no significant cytotoxicity. However, the addition of HA particles also reduced the light transmission properties of the slurry, and when its content exceeds a certain value, the hydrogel scaffolds show incomplete curing and eventually affect their test performance. The results can offer guidance and reference for the selection of ink and function for 3D printing bone repair scaffold.

Biological Response to Bioinspired Microporous 3D-Printed Scaffolds for Bone Tissue Engineering

The scaffold is a key element in the field of tissue engineering, especially when large defects or substitutions of pathological tissues or organs need to be clinically addressed. The expected outcome is strongly dependent on the cell–scaffold interaction and the integration with the surrounding biological tissue. Indeed, mimicking the natural extracellular matrix (ECM) of the tissue to be healed represents a further optimization that can limit a possible morphological mismatch between the scaffold and the tissue itself. For this aim, and referring to bone tissue engineering, polylactic acid (PLA) scaffolds were 3D printed with a microstructure inspired by the trabecular architecture and biologically evaluated by means of human osteosarcoma SAOS-2 cells. The cells were seeded on two types of scaffolds differing for the designed pore size (i.e., 400 and 600 µm), showing the same growth exponential trend found in the control and no significant alterations in the actin distribution. The microporous structure of the two tested samples enhanced the protein adsorption capability and mRNA expression of markers related to protein synthesis, proliferation, and osteoblast differentiation. Our findings demonstrate that 3D-printed scaffolds support the adhesion, growth, and differentiation of osteoblast-like cells and the microporous architecture, mimicking the natural bone hierarchical structure, and favoring greater bioactivity. These bioinspired scaffolds represent an interesting new tool for bone tissue engineering and regenerative medicine applications.