Fabrication of Biocompatible Polycaprolactone–Hydroxyapatite Composite Filaments for the FDM 3D Printing of Bone Scaffolds

Process Development for Fabricating 3D-Printed Polycaprolactone-Infiltrated Hydroxyapatite Bone Graft Granules: Effects of Infiltrated Solution Concentration and Agitating Liquid

Bone grafts are commonly used in orthopedic and dental surgeries to facilitate bone repair and regeneration. A new type of bone graft, polycaprolactone-infiltrated three dimensionally printed hydroxyapatite (3DP HA/PCL), was previously developed by infiltrating polycaprolactone (PCL) into preformed three-dimensional-printed hydroxyapatite (3DP HA) that was fabricated using binder jetting technology combined with a low-temperature phase transformation process. However, when producing small granules, which are often used for bone grafting, issues of granule agglomeration emerged, complicating the application of this method. This study aimed to develop a fabrication process for 3DP HA/PCL bone graft granules using solution infiltration and liquid agitation. The effects of varying PCL solution concentrations (40% and 50% w/w) and different agitating liquids (deionized water or DI, N-Methyl-2-Pyrrolidone or NMP, and an NMP-DI mixture) on the properties of the resulting composites were investigated. XRD and FTIR analysis confirmed the coexistence of HA and PCL within the composites. The final PCL content was comparable across all conditions. The contact angles of 3DP HA/PCL were 26.3 and 69.8 degree for 40% and 50% PCL solution, respectively, when using DI, but were zero when using NMP and NMP-DI. The highest compression load resistance and diametral tensile strength were achieved using the 50% PCL solution with DI or the NMP-DI mixture. DI resulted in a dense PCL coating, while NMP and the NMP-DI mixture produced a porous and irregular surface morphology. All samples exhibited a porous internal microstructure due to PCL infiltration into the initial pores of the 3D-printed HA. Biocompatibility tests showed that all samples supported the proliferation of MC3T3-E1 cells, with the greatest OD values observed for the 50% PCL solution with DI or the NMP-DI mixture at each cultured period. Considering the microstructural, mechanical, and biological properties, the 50% PCL solution with the NMP-DI mixture demonstrated overall desirable properties.

Challenges to Improve Extrusion-Based Additive Manufacturing Process of Thermoplastics toward Sustainable Development

This review aims to present the different approaches to lessen the environmental impact of the extrusion-based additive manufacturing (MEX) process of thermoplastic-based resins and protect the ecosystem. The benefits and drawbacks of each alternative, including the use of biomaterials or recycled materials as feedstock, energy efficiency, and polluting emissions reduction, have been examined. First, the technological option of using a pellet-fed printer was compared to a filament-fed printer. Then, common biopolymers utilized in MEX applications are discussed, along with methods for improving the mechanical properties of associated printed products. The introduction of natural fillers in thermoplastic resins and the use of biocomposite filaments have been proposed to improve the specific performance of printed items, highlighting the numerous challenges related to their extrusion. Various polymers and fillers derived from recycling are presented as feeding raw materials for printers to reduce waste accumulation, showing the inferior qualities of the resulting goods when compared to printed products made from virgin materials. Finally, the energy consumption and emissions released into the atmosphere during the printing process are discussed, with the potential for both aspects to be controlled through material selection and operating conditions.

A comprehensive bench-to-bed look into the application of gamma-sterilized 3D-printed polycaprolactone/hydroxyapatite implants for craniomaxillofacial defects, an in vitro, in vivo, and clinical study

This study investigates the safety and efficacy of 3D-printed polycaprolactone/hydroxyapatite (PCL/HA) scaffolds for patient-specific cranioplasty surgeries, employing liquid deposition modeling (LDM) technology. This research is pioneering as it explores the impact of gamma radiation on PCL/HA scaffolds and utilizes printing ink with the highest content of HA known in the composite. The mechanical, morphological, and macromolecular stability of the gamma-sterilized scaffolds were verified before implantation. Subsequent research involving animal subjects was conducted to explore the effects of sterilized implants. Eventually, three clinical cases were selected for the implantation studies as part of a phase 1 non-randomized open-label clinical trial. It was shown that a 25 kGy gamma-ray dose for sterilizing the printed implants did not alter the required geometrical precision of the printed implants. The implants exhibited well-distributed HA and strength comparable to cancellous bone. Gamma radiation reduced hydrophobicity and water uptake capacity without inducing pyrogenic or inflammatory responses. Personalized PCL/HA substitutes successfully treated various craniomaxillofacial defects, including trauma-induced facial asymmetry and congenital deformities. HA nanoparticles in the ink stimulated significant osteoconductive responses within three months of implantation. Moreover, the results revealed that while larger implants may exhibit a slower bone formation response in comparison to smaller implants, they generally had an acceptable rate and volume of bone formation. This clinical trial suggests the application of a sterilized PCL/HA composite for craniomaxillofacial surgery is safe and could be considered as a substitute for autologous bone.

Development of hybrid 3D printing approach for fabrication of high-strength hydroxyapatite bioscaffold using FDM and DLP techniques

This study develops a hybrid 3D printing approach that combines fused deposition modeling (FDM) and digital light processing (DLP) techniques for fabricating bioscaffolds, enabling rapid mass production. The FDM technique fabricates outer molds, while DLP prints struts for creating penetrating channels. By combining these components, hydroxyapatite (HA) bioscaffolds with different channel sizes (600, 800, and 1000μm) and designed porosities (10%, 12.5%, and 15%) are fabricated using the slurry casting method with centrifugal vacuum defoaming for significant densification. This innovative method produces high-strength bioscaffolds with an overall porosity of 32%-37%, featuring tightly bound HA grains and a layered surface structure, resulting in remarkable cell viability and adhesion, along with minimal degradation rates and superior calcium phosphate deposition. The HA scaffolds show hardness ranging from 1.43 to 1.87 GPa, with increasing compressive strength as the designed porosity and channel size decrease. Compared to human cancellous bone at a similar porosity range of 30%-40%, exhibiting compressive strengths of 13-70 MPa and moduli of 0.8-8 GPa, the HA scaffolds demonstrate robust strengths ranging from 40 to 73 MPa, paired with lower moduli of 0.7-1.23 GPa. These attributes make them well-suited for cancellous bone repair, effectively mitigating issues like stress shielding and bone atrophy.

Sacrificial biomaterials in 3D fabrication of scaffolds for tissue engineering applications

Three-dimensional (3D) printing technology has progressed exceedingly in the area of tissue engineering. Despite the tremendous potential of 3D printing, building scaffolds with complex 3D structure, especially with soft materials, still exist as a challenge due to the low mechanical strength of the materials. Recently, sacrificial materials have emerged as a possible solution to address this issue, as they could serve as temporary support or templates to fabricate scaffolds with intricate geometries, porous structures, and interconnected channels without deformation or collapse. Here, we outline the various types of scaffold biomaterials with sacrificial materials, their pros and cons, and mechanisms behind the sacrificial material removal, compare the manufacturing methods such as salt leaching, electrospinning, injection-molding, bioprinting with advantages and disadvantages, and discuss how sacrificial materials could be applied in tissue-specific applications to achieve desired structures. We finally conclude with future challenges and potential research directions.

Scaffold-mediated liver regeneration: A comprehensive exploration of current advances

The liver coordinates over 500 biochemical processes crucial for maintaining homeostasis, detoxification, and metabolism. Its specialized cells, arranged in hexagonal lobules, enable it to function as a highly efficient metabolic engine. However, diseases such as cirrhosis, fatty liver disease, and hepatitis present significant global health challenges. Traditional drug development is expensive and often ineffective at predicting human responses, driving interest in advanced in vitro liver models utilizing 3D bioprinting and microfluidics. These models strive to mimic the liver's complex microenvironment, improving drug screening and disease research. Despite its resilience, the liver is vulnerable to chronic illnesses, injuries, and cancers, leading to millions of deaths annually. Organ shortages hinder liver transplantation, highlighting the need for alternative treatments. Tissue engineering, employing polymer-based scaffolds and 3D bioprinting, shows promise. This review examines these innovative strategies, including liver organoids and liver tissue-on-chip technologies, to address the challenges of liver diseases.

Towards Polycaprolactone-Based Scaffolds for Alveolar Bone Tissue Engineering: A Biomimetic Approach in a 3D Printing Technique

The alveolar bone is a unique type of bone, and the goal of bone tissue engineering (BTE) is to develop methods to facilitate its regeneration. Currently, an emerging trend involves the fabrication of polycaprolactone (PCL)-based scaffolds using a three-dimensional (3D) printing technique to enhance an osteoconductive architecture. These scaffolds are further modified with hydroxyapatite (HA), type I collagen (CGI), or chitosan (CS) to impart high osteoinductive potential. In conjunction with cell therapy, these scaffolds may serve as an appealing alternative to bone autografts. This review discusses research gaps in the designing of 3D-printed PCL-based scaffolds from a biomimetic perspective. The article begins with a systematic analysis of biological mineralisation (biomineralisation) and ossification to optimise the scaffold's structural, mechanical, degradation, and surface properties. This scaffold-designing strategy lays the groundwork for developing a research pathway that spans fundamental principles such as molecular dynamics (MD) simulations and fabrication techniques. Ultimately, this paves the way for systematic in vitro and in vivo studies, leading to potential clinical applications.

Progress of Polymer-Based Dielectric Composites Prepared Using Fused Deposition Modeling 3D Printing

Polymer-based dielectric composites are of great importance in advanced electronic industries and energy storage because of their high dielectric constant, good processability, low weight, and low dielectric loss. FDM (Fused Deposition Modeling) is a greatly accessible additive manufacturing technology, which has a number of applications in the fabrication of RF components, but the unavoidable porosity in FDM 3D-printed materials, which affects the dielectric properties of the materials, and the difficulty of large-scale fabrication of composites by FDM limit its application scope. This study's main focus is on how the matrix, filler, interface, and FDM 3D printing parameters influence the electrical properties of FDM-printed polymer-based dielectric composites. This review article starts with the fundamental theory of dielectrics. It is followed by a summary of the factors influencing dielectric properties in recent research developments, as well as a projection for the future development of FDM-prepared polymer-based dielectric composites. Finally, improving the comprehensive performance of dielectric composites is an important direction for future development.

Evaluation of Physicochemical Properties of a Hydroxyapatite Polymer Nanocomposite for Use in Fused Filament Fabrication

Over the last decade, there has been an increasing interest in the use of bioceramics for biomedical purposes. Bioceramics, specifically those made of calcium phosphate, are commonly used in dental and orthopaedic applications. In this context, hydroxyapatite (HA) is considered a viable option for hard tissue engineering applications given its compositional similarity to bioapatite. However, owing to their poor mechanobiology and biodegradability, traditional HA-based composites have limited utilisation possibilities in bone, cartilage and dental applications. Therefore, the efficiency of nano HA (nHA) has been explored to address these limitations. nHA has shown excellent remineralising effects on initial enamel lesions and is widely used as an additive for improving existing dental materials. Furthermore, three-dimensional printing (3DP) or fused deposition modelling that can be used for creating dental and hard tissue scaffolds tailored to each patient's specific anatomy has attracted considerable interest. However, the materials used for producing hard tissue with 3DP are still limited. Therefore, the current study aimed to develop a hybrid polymer nanocomposite composed of nHA, nanoclay (NC) and polylactic acid (PLA) that was suitable for 3DP. The nHA polymer nanocomposites were extruded into filaments and their physiochemical properties were evaluated. The results showed that the addition of nHA and NC to the PLA matrix significantly increased the water absorption and contact angle. In addition, the hardness increased from 1.04 to 1.25 times with the incorporation of nHA. In sum, the nHA-NC-reinforced PLA could be used as 3DP filaments to generate bone and dental scaffolds, and further studies are needed on the biocompatibility of this material.

Combined Effects of HA Concentration and Unit Cell Geometry on the Biomechanical Behavior of PCL/HA Scaffold for Tissue Engineering Applications Produced by LPBF

This experimental study aims at filling the gap in the literature concerning the combined effects of hydroxyapatite (HA) concentration and elementary unit cell geometry on the biomechanical performances of additively manufactured polycaprolactone/hydroxyapatite (PCL/HA) scaffolds for tissue engineering applications. Scaffolds produced by laser powder bed fusion (LPBF) with diamond (DO) and rhombic dodecahedron (RD) elementary unit cells and HA concentrations of 5, 30 and 50 wt.% were subjected to structural, mechanical and biological characterization to investigate the biomechanical and degradative behavior from the perspective of bone tissue regeneration. Haralick's features describing surface pattern, correlation between micro- and macro-structural properties and human mesenchymal stem cell (hMSC) viability and proliferation have been considered. Experimental results showed that HA has negative influence on scaffold compaction under compression, while on the contrary it has a positive effect on hMSC adhesion. The unit cell geometry influences the mechanical response in the plastic regime and also has an effect on the cell proliferation. Finally, both HA concentration and elementary unit cell geometry affect the scaffold elastic deformation behavior as well as the amount of micro-porosity which, in turn, influences the scaffold degradation rate.

Effect of Extruder Type in the Interface of PLA Layers in FDM Printers: Filament Extruder Versus Direct Pellet Extruder

FDM (Fused Deposition Modeling) is one of the most used and industrially applied additive manufacturing processes due to its fast prototyping and manufacturing, simplicity, and low cost of the equipment. However, the mechanical properties of the printed products have a large dependence on orientation and interface strength between layers which is mainly related to the thermal union obtained. This thermal union has a large dependence on the melting and cooling down process. Additionally, the materials used must be extruded in a continuous filament before their use, which limits the materials used. However, a pellet extruder could be used directly in the printing equipment, avoiding filament extrusion. In this work, specimens of PLA (Poly(lactic acid)) with different bead orientations have been produced via filament or pellet extrusion to compare the effect of the different melting processes in the manufacturing methodology. Pellet extruded specimens showed higher infill and mechanical properties. These results were related to better adhesion between layers due to the longer melting and cooling process. The result was confirmed using DSC and XRD techniques, where a higher crystallinity was observed. A bicomponent specimen (50% pellet-50% filament) was prepared and tested, showing higher mechanical results than expected, which was, again, due to the better thermal union obtained in the pellet extruder.

Promotion of In Vitro Osteogenic Activity by Melt Extrusion-Based PLLA/PCL/PHBV Scaffolds Enriched with Nano-Hydroxyapatite and Strontium Substituted Nano-Hydroxyapatite

Bone tissue engineering has emerged as a promising strategy to overcome the limitations of current treatments for bone-related disorders, but the trade-off between mechanical properties and bioactivity remains a concern for many polymeric materials. To address this need, novel polymeric blends of poly-L-lactic acid (PLLA), polycaprolactone (PCL) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) have been explored. Blend filaments comprising PLLA/PCL/PHBV at a ratio of 90/5/5 wt% have been prepared using twin-screw extrusion. The PLLA/PCL/PHBV blends were enriched with nano-hydroxyapatite (nano-HA) and strontium-substituted nano-HA (Sr-nano-HA) to produce composite filaments. Three-dimensional scaffolds were printed by fused deposition modelling from PLLA/PCL/PHBV blend and composite filaments and evaluated mechanically and biologically for their capacity to support bone formation in vitro. The composite scaffolds had a mean porosity of 40%, mean pores of 800 µm, and an average compressive modulus of 32 MPa. Polymer blend and enriched scaffolds supported cell attachment and proliferation. The alkaline phosphatase activity and calcium production were significantly higher in composite scaffolds compared to the blends. These findings demonstrate that thermoplastic polyesters (PLLA and PCL) can be combined with polymers produced via a bacterial route (PHBV) to produce polymer blends with excellent biocompatibility, providing additional options for polymer blend optimization. The enrichment of the blend with nano-HA and Sr-nano-HA powders enhanced the osteogenic potential in vitro.

Fabrication and Testing of Multi-Hierarchical Porous Scaffolds Designed for Bone Regeneration via Additive Manufacturing Processes

Bone implants or replacements are very scarce due to the low donor availability and the high rate of body rejection. For this reason, tissue engineering strategies have been developed as alternative solutions to this problem. This research sought to create a cellular scaffold with an intricate and complex network of interconnected pores and microchannels using salt leaching and additive manufacturing (3D printing) methods that mimic the hierarchical internal structure of the bone. A biocompatible hydrogel film (based on poly-ethylene glycol) was used to cover the surface of different polymeric scaffolds. This thin film was then exposed to various stimuli to spontaneously form wrinkled micropatterns, with the aim of increasing the contact area and the material’s biocompatibility. The main innovation of this study was to include these wrinkled micropatterns on the surface of the scaffold by taking advantage of thin polymer film surface instabilities. On the other hand, salt and nano-hydroxyapatite (nHA) particles were included in the polymeric matrix to create a modified filament for 3D printing. The printed part was leached to eliminate porogen particles, leaving homogenously distributed pores on the structure. The pores have a mean size of 26.4 ± 9.9 μm, resulting in a global scaffold porosity of ~42% (including pores and microchannels). The presence of nHA particles, which display a homogeneous distribution according to the FE-SEM and EDX results, have a slight influence on the mechanical resistance of the material, but incredibly, despite being a bioactive compound for bone cells, did not show a significant increase in cell viability on the scaffold surface. However, the synergistic effect between the presence of the hydrogel and the pores on the material does produce an increase in cell viability compared to the control sample and the bare PCL material.

Biomimetic, mussel-inspired surface modification of 3D-printed biodegradable polylactic acid scaffolds with nano-hydroxyapatite for bone tissue engineering

Polylactic acid (PLA) has been widely used as filaments for material extrusion additive manufacturing (AM) to develop patient-specific scaffolds in bone tissue engineering. Hydroxyapatite (HA), a major component of natural bone, has been extensively recognized as an osteoconductive biomolecule. Here, inspired by the mussel-adhesive phenomenon, in this study, polydopamine (PDA) coating was applied to the surface of 3D printed PLA scaffolds (PLA@PDA), acting as a versatile adhesive platform for immobilizing HA nanoparticles (nHA). Comprehensive analyses were performed to understand the physicochemical properties of the 3D-printed PLA scaffold functionalized with nHA and PDA for their potent clinical application as a bone regenerative substitute. Scanning electron microscopy (SEM) and element dispersive X-ray (EDX) confirmed a successful loading of nHA particles on the surface of PLA@PDA after 3 and 7 days of coating (PLA@PDA-HA3 and PLA@PDA-HA7), while the surface micromorphology and porosity remain unchanged after surface modification. The thermogravimetric analysis (TGA) showed that 7.7 % and 12.3% mass ratio of nHA were loaded on the PLA scaffold surface, respectively. The wettability test indicated that the hydrophilicity of nHA-coated scaffolds was greatly enhanced, while the mechanical properties remained uncompromised. The 3D laser scanning confocal microscope (3DLS) images revealed that the surface roughness was significantly increased, reaching Sa (arithmetic mean height) of 0.402 μm in PLA@PDA-HA7. Twenty-eight days of in-vitro degradation results showed that the introduction of nHA to the PLA surface enhances its degradation properties, as evidenced by the SEM images and weight loss test. Furthermore, a sustainable release of Ca²⁺ from PLA@PDA-HA3 and PLA@PDA-HA7 was recorded, during the degradation process. In contrast, the released hydroxyl group of nHA tends to neutralize the local acidic environments, which was more conducive to osteoblastic differentiation and extracellular mineralization. Taken together, this facile surface modification provides 3D printed PLA scaffolds with effective bone regenerative properties by depositing Ca²⁺ contents, improving surface hydrophilicity, and enhancing the in-vitro degradation rate.

Ascorbic Acid Enhances the Metabolic Activity, Growth and Collagen Production of Human Dermal Fibroblasts Growing in Three-dimensional (3D) Culture

Tissue engineering (TE) enables developing functional synthetic substitutes to be replaced with damaged tissues and organs instead of the use of auto or allografts. A wide range of biomaterials is currently in use as TE scaffolds. Among these materials, naturally-sourced ones are favourable due to being highly biocompatible and supporting cell growth and function whereas synthetic ones are advantageous because of the high tunability on mechanical and physical properties as well as being easy to process. Alongside the advantages of synthetic polymers, they mostly show hydrophobic behaviour that limits biomaterial-cell interaction and consequently the functioning of the developed TE constructs. In this study, we assessed the impact of L-Ascorbic acid 2-phosphate (AA2P) on improving the culture of human dermal fibroblasts (HDFs) growing on a three-dimensional (3D) scaffold made of polycaprolactone by emulsion templating technique. Our results demonstrated that AA2P enhances the metabolic activity, growth, and collagen production of HDFs when supplemented to their growth medium at 50 µg/mL concentration. It showed a great potential to be used as a growth medium supplement to circumvent the disadvantages of culturing human cells on a synthetic biomaterial that is not favoured in default. AA2P's potential to improve cell growth and collagen deposition may prove an effective way to culture human cells on 3D PCL PolyHIPE scaffolds for various TE applications.

Enhanced osteogenic differentiation of stem cells by 3D printed PCL scaffolds coated with collagen and hydroxyapatite

Bone tissue engineering uses various methods and materials to find suitable scaffolds that regenerate lost bone due to disease or injury. Poly(ε-caprolactone) (PCL) can be used in 3D printing for producing biodegradable scaffolds by fused deposition modeling (FDM). However, the hydrophobic surfaces of PCL and its non-osteogenic nature reduces adhesion and cell bioactivity at the time of implantation. This work aims to enhance bone formation, osteogenic differentiation, and in vitro biocompatibility via PCL scaffolds modification with Hydroxyapatite (HA) and Collagen type I (COL). This study evaluated the osteosupportive capacity, biological behavior, and physicochemical properties of 3D-printed PCL, PCL/HA, PCL/COL, and PCL/HA/COL scaffolds. Biocompatibility and cells proliferation were investigated by seeding human adipose tissue-derived mesenchymal stem cells (hADSCs) onto the scaffolds, which were analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay, and 6-diamidino-2-phenylindole (DAPI) staining. In addition, the bone differentiation potential of the hADSCs was assessed using calcium deposition, alkaline phosphatase (ALP) activity, and bone-related protein and genes. Although all constructed scaffolds support hADSCs proliferation and differentiation, the results showed that scaffold coating with HA and COL can boost these capacities in a synergistic manner. According to the findings, the tricomponent 3D-printed scaffold can be considered as a promising choice for bone tissue regeneration and rebuilding.

Engineering biomaterials to 3D-print scaffolds for bone regeneration: practical and theoretical consideration

There are more than 2 million bone grafting procedures performed annually in the US alone. Despite significant efforts, the repair of large segmental bone defects is a substantial clinical challenge which requires bone substitute materials or a bone graft. The available biomaterials lack the adequate mechanical strength to withstand the static and dynamic loads while maintaining sufficient porosity to facilitate cell in-growth and vascularization during bone tissue regeneration. A wide range of advanced biomaterials are being currently designed to mimic the physical as well as the chemical composition of a bone by forming polymer blends, polymer-ceramic and polymer-degradable metal composites. Transforming these novel biomaterials into porous and load-bearing structures via three-dimensional printing (3DP) has emerged as a popular manufacturing technique to develop engineered bone grafts. 3DP has been adopted as a versatile tool to design and develop bone grafts that satisfy porosity and mechanical requirements while having the ability to form grafts of varied shapes and sizes to meet the physiological requirements. In addition to providing surfaces for cell attachment and eventual bone formation, these bone grafts also have to provide physical support during the repair process. Hence, the mechanical competence of the 3D-printed scaffold plays a key role in the success of the implant. In this review, we present various recent strategies that have been utilized to design and develop robust biomaterials that can be deployed for 3D-printing bone substitutes. The article also reviews some of the practical, theoretical and biological considerations adopted in the 3D-structure design and development for bone tissue engineering.

Regression Analysis of the Dielectric and Morphological Properties for Porous Nanohydroxyapatite/Starch Composites: A Correlative Study

This paper aims to investigate the dielectric properties, i.e., dielectric constant (ε′), dielectric loss factor (ε″), dielectric tangent loss (tan δ), electrical conductivity (σ), and penetration depth (Dp), of the porous nanohydroxyapatite/starch composites in the function of starch proportion, pore size, and porosity over a broad band frequency range of 5 MHz−12 GHz. The porous nanohydroxyapatite/starch composites were fabricated using different starch proportions ranging from 30 to 90 wt%. The results reveal that the dielectric properties and the microstructural features of the porous nanohydroxyapatite/starch composites can be enhanced by the increment in the starch proportion. Nevertheless, the composite with 80 wt% of starch proportion exhibit low dielectric properties (ε′, ε″, tan δ, and σ) and a high penetration depth because of its highly interconnected porous microstructures. The dielectric properties of the porous nanohydroxyapatite/starch composites are highly dependent on starch proportion, average pore size, and porosity. The regression models are developed to express the dielectric properties of the porous nanohydroxyapatite/starch composites (R2 > 0.96) in the function of starch proportion, pore size, and porosity from 1 to 11 GHz. This dielectric study can facilitate the assessment of bone scaffold design in bone tissue engineering applications.

A Review of 3D Printed Bone Implants

3D printing, that is, additive manufacturing, has solved many major problems in general manufacturing, such as three-dimensional tissue structure, microenvironment control difficulty, product production efficiency and repeatability, etc., improved the manufacturing speed and precision of personalized bone implants, and provided a lot of support for curing patients with bone injuries. The application of 3D printing technology in the medical field is gradually extensive, especially in orthopedics. The purpose of this review is to provide a report on the related achievements of bone implants based on 3D printing technology in recent years, including materials, molding methods, optimization of implant structure and performance, etc., in order to point out the existing shortcomings of 3D printing bone implants, promote the development of all aspects of bone implants, and make a prospect of 4D printing, hoping to provide some reference for the subsequent research of 3D printing bone implants.

Fabrication and Characterization of PCL/HA Filament as a 3D Printing Material Using Thermal Extrusion Technology for Bone Tissue Engineering

The most common three-dimensional (3D) printing method is material extrusion, where a pre-made filament is deposited layer-by-layer. In recent years, low-cost polycaprolactone (PCL) material has increasingly been used in 3D printing, exhibiting a sufficiently high quality for consideration in cranio-maxillofacial reconstructions. To increase osteoconductivity, prefabricated filaments for bone repair based on PCL can be supplemented with hydroxyapatite (HA). However, few reports on PCL/HA composite filaments for material extrusion applications have been documented. In this study, solvent-free fabrication for PCL/HA composite filaments (HA 0%, 5%, 10%, 15%, 20%, and 25% weight/weight PCL) was addressed, and parameters for scaffold fabrication in a desktop 3D printer were confirmed. Filaments and scaffold fabrication temperatures rose with increased HA content. The pore size and porosity of the six groups’ scaffolds were similar to each other, and all had highly interconnected structures. Six groups’ scaffolds were evaluated by measuring the compressive strength, elastic modulus, water contact angle, and morphology. A higher amount of HA increased surface roughness and hydrophilicity compared to PCL scaffolds. The increase in HA content improved the compressive strength and elastic modulus. The obtained data provide the basis for the biological evaluation and future clinical applications of PCL/HA material.

3D-Printed PCL Scaffolds Coated with Nanobioceramics Enhance Osteogenic Differentiation of Stem Cells

With advances in bone tissue engineering, various materials and methods have been explored to find a better scaffold that can help in improving bone growth and regeneration. Three-dimensional (3D) printing by fused deposition modeling can produce customized scaffolds from biodegradable polyesters such as polycaprolactone (PCL). Although the fabricated PCL scaffolds exhibited a lack of bioactivity and poor cell attachment on their surfaces, herein, using a simple postfabrication modification method with hydroxyapatite (HA) and bioglasses (BGs), we obtained better cell proliferation and attachment. Biological behavior and osteosupportive capacity of the 3D-printed scaffolds including PCL, PCL/HA, PCL/BG, and PCL/HA/BG were evaluated in this study, while human adipose tissue-derived mesenchymal stem cells (hADSCs) were cultured on the scaffolds. The cell morphology, attachment, and proliferation were investigated using scanning electron microscopy (SEM), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay, and 4',6-diamidino-2-phenylindole (DAPI) staining. In the next step, the ability of stem cells to differentiate into osteoblasts was evaluated by measuring alkaline phosphatase (ALP) activity, calcium deposition, and bone-related gene and protein expression. In the end, the expression levels of miR-20a, miR-125a, and their target genes were also investigated as positive and negative regulators in osteogenesis pathways. The results showed that the coated scaffolds with bioceramics present a more appropriate surface for cell adhesion and proliferation, as well as efficient potential in inducing osteoconduction and osteointegration compared to PCL alone and control. The PCL/HA/BG scaffold exhibited higher in vitro cell viability and bone formation compared to the other groups, which can be due to the synergistic effect of HA and BG. On the whole, this tricomponent 3D-printing scaffold has a promising prospect for bone tissue engineering applications.