Preparation and characterization of PLA/PCL/HA composite scaffolds using indirect 3D printing for bone tissue engineering

Clinical translation of polycaprolactone-based tissue engineering scaffolds, fabricated via additive manufacturing: A review of their craniofacial applications

The craniofacial region is characterized by its intricate bony anatomy and exposure to heightened functional forces presenting a unique challenge for reconstruction. Additive manufacturing has revolutionized the creation of customized scaffolds with interconnected pores and biomimetic microarchitecture, offering precise adaptation to various craniofacial defects. Within this domain, medical-grade poly(ε-caprolactone) (PCL) has been extensively used for the fabrication of 3D printed scaffolds, specifically tailored for bone regeneration. Its adoption for load-bearing applications was driven mainly by its mechanical properties, adjustable biodegradation rates, and high biocompatibility. The present review aims to consolidating current insights into the clinical translation of PCL-based constructs designed for bone regeneration. It encompasses recent advances in enhancing the mechanical properties and augmenting biodegradation rates of PCL and PCL-based composite scaffolds. Moreover, it delves into various strategies improving cell proliferation and the osteogenic potential of PCL-based materials. These strategies provide insight into the refinement of scaffold microarchitecture, composition, and surface treatments or coatings, that include certain bioactive molecules such as growth factors, proteins, and ceramic nanoparticles. The review critically examines published data on the clinical applications of PCL scaffolds in both extraoral and intraoral craniofacial reconstructions. These applications include cranioplasty, nasal and orbital floor reconstruction, maxillofacial reconstruction, and intraoral bone regeneration. Patient demographics, surgical procedures, follow-up periods, complications and failures are thoroughly discussed. Although results from extraoral applications in the craniofacial region are encouraging, intraoral applications present a high frequency of complications and related failures. Moving forward, future studies should prioritize refining the clinical performance, particularly in the domain of intraoral applications, and providing comprehensive data on the long-term outcomes of PCL-based scaffolds in bone regeneration. Future perspective and limitations regarding the transition of such constructs from bench to bedside are also discussed.

Investigation of Degradation and Biocompatibility of Indirect 3D-Printed Bile Duct Stents

This study proposes a bile duct stent based on indirect 3D printing technology. Four ratio materials were synthesized from lactic acid (LA) and glycolide (GA) monomers by melt polymerization: PLA, PLGA (70:30), PLGA (50:50), and PLGA (30:70). The four kinds of material powders were preliminarily degraded, and the appearance was observed with an optical microscope (OM) and a camera. The weight and appearance of the four materials changed significantly after four weeks of degradation, which met the conditions for materials to be degraded within 4-6 weeks. Among them, PLGA (50:50) lost the most-the weight dropped to 13.4%. A stent with an outer diameter of 10 mm and an inner diameter of 8 mm was successfully manufactured by indirect 3D printing technology, demonstrating the potential of our research. Then, the degradation experiment was carried out on a cylindrical stent with a diameter of 6 mm and a height of 3 mm. The weight loss of the sample was less than that of the powder degradation, and the weight loss of PLGA (50:50) was the largest-the weight dropped to 79.6%. The nano-indenter system measured the mechanical properties of materials. Finally, human liver cancer cells Hep-3B were used to conduct in vitro cytotoxicity tests on the scaffolds to test the biocompatibility of the materials. A bile duct stent meeting commercial size requirements has been developed, instilling confidence in the potential of our research for future medical applications.

Design and development of 3D printed shape memory triphasic polymer-ceramic bioactive scaffolds for bone tissue engineering

Scaffolds for bone tissue engineering require considerable mechanical strength to repair damaged bone defects. In this study, we designed and developed mechanically competent composite shape memory triphasic bone scaffolds using fused filament fabrication (FFF) three dimensional (3D) printing. Wollastonite particles (WP) were incorporated into the poly lactic acid (PLA)/polycaprolactone (PCL) matrix as a reinforcing agent (up to 40 wt%) to harness osteoconductive and load-bearing properties from the 3D printed scaffolds. PCL as a minor phase (20 wt%) was added to enhance the toughening effect and induce the shape memory effect in the triphasic composite scaffolds. The 3D-printed composite scaffolds were studied for morphological, thermal, and mechanical properties, in vitro degradation, biocompatibility, and shape memory behaviour. The composite scaffold had interconnected pores of 550 μm, porosity of more than 50%, and appreciable compressive strength (∼50 MPa), which was over 90% greater than that of the pristine PLA scaffolds. The flexural strength was improved by 140% for 40 wt% of WP loading. The inclusion of WP did not affect the thermal property of the scaffolds; however, the inclusion of PCL reduced the thermal stability. An accelerated in vitro degradation was observed for WP incorporated composite scaffolds compared to pristine PLA scaffolds. The inclusion of WP improved the hydrophilic property of the scaffolds, and the result was significant for 40 wt% WP incorporated composite scaffolds having a water contact angle of 49.61°. The triphasic scaffold exhibited excellent shape recovery properties with a shape recovery ratio of ∼84%. These scaffolds were studied for their protein adsorption, cell proliferation, and bone mineralization potential. The incorporation of WP reduced the protein adsorption capacity of the composite scaffolds. The scaffold did not leach any toxic substance and demonstrated good cell viability, indicating its biocompatibility and growth-promoting behavior. The osteogenic potential of the WP incorporated scaffolds was observed in MC3T3-E1 cells, revealing early mineralization in pre-osteoblast cells cultured in different WP incorporated composite scaffolds. These results suggest that 3D-printed WP reinforced PLA/PCL composite bioactive scaffolds are promising for load bearing bone defect repair.

The polycaprolactone and silk fibroin nanofibers with Janus-structured sheaths for antibacterial and antioxidant by loading Taxifolin

Electrospinning is a widely recognized method for producing Janus or core-shell nanofibers. In this study, nanofibrous membranes were fabricated through co-axial electrospinning utilizing polycaprolactone (PCL) and silk fibroin (SF) as the Janus shell, and taxifolin (TAX) and SF as the core. The resulting nanofibers had diameters of 816 ± 161 nm and core diameters of 73 ± 5 nm. The morphology and properties of the PCL-SF@SF/TAX nanofibers were subsequently analyzed. The results demonstrated that the nanofibrous membranes achieved physical and chemical characteristics potential for tissue engineering and drug delivery. Specifically, the membranes exhibited a Young's modulus of 9.64 ± 0.29 MPa, a water contact angle of 79.1 ± 1.3°, and a weight loss of 17.3 ± 1.0 % over a period of 28 days. The incorporation of TAX endowed the membranes with antibacterial properties, effectively combating Escherichia coli and Staphylococcus aureus. Furthermore, the membranes demonstrated antioxidant capabilities, with a DPPH radical scavenging efficiency of 38.5 ± 5.6 % and a Trolox-equivalent antioxidant capacity of 0.24 ± 0.01 mM. The release of the antioxidant was sustained over 28 days, following first-order release kinetics. The nanofibrous membranes, referred to as PSST, exhibit promising potential for use as biomaterials, characterized by their antibacterial activity, antioxidant and cytocompatibility.

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.

3D printed scaffolds of biosilica and spongin from marine sponges: analysis of genotoxicity and cytotoxicity for bone tissue repair

Biosilica (BS) and spongin (SPG) from marine sponges are highlighted for their potential to promote bone regeneration. Moreover, 3D printing is introduced as a technology for producing bone grafts with optimized porous structures, allowing for better cell attachment, proliferation, and differentiation. Thus, this study aimed to characterize the BS and BS/SPG 3D printed scaffolds and to evaluate the biological effects in vitro. The scaffolds were printed using an ink containing 4 wt.% of sodium alginate. The physicochemical characteristics of BS and BS/SPG 3D printed scaffolds were analyzed by SEM, EDS, FTIR, porosity, evaluation of mass loss, and pH measurement. For in vitro analysis, the cellular viability of the MC3T3-E1 cell lineage was assessed using the AlamarBlue® assay and confocal microscopy, while genotoxicity and mineralization potential were evaluated through the micronucleus assay and Alizarin Red S, respectively. SEM analysis revealed spicules in BS, the fibrillar structure of SPG, and material degradation over the immersion period. FTIR indicated peaks corresponding to silicon oxide in BS samples and carbon oxide and amine in SPG samples. BS-SPG scaffolds exhibited higher porosity, while BS scaffolds displayed greater mass loss. pH measurements indicated a significant decrease induced by BS, which was mitigated by SPG over the experimental periods. In vitro studies demonstrated the biocompatibility and non-cytotoxicity of scaffold extracts. .Also, the scaffolds promoted cellular differentiation. The micronucleus test further confirmed the absence of genotoxicity. These findings suggest that 3D printed BS and BS/SPG scaffolds may possess desirable morphological and physicochemical properties, indicating in vitro biocompatibility.

Quantitative Evaluation of the Pore and Window Sizes of Tissue Engineering Scaffolds on Scanning Electron Microscope Images Using Deep Learning

The morphological characteristics of tissue engineering scaffolds, such as pore and window diameters, are crucial, as they directly impact cell-material interactions, attachment, spreading, infiltration of the cells, degradation rate and the mechanical properties of the scaffolds. Scanning electron microscopy (SEM) is one of the most commonly used techniques for characterizing the microarchitecture of tissue engineering scaffolds due to its advantages, such as being easily accessible and having a short examination time. However, SEM images provide qualitative data that need to be manually measured using software such as ImageJ to quantify the morphological features of the scaffolds. As it is not practical to measure each pore/window in the SEM images as it requires extensive time and effort, only the number of pores/windows is measured and assumed to represent the whole sample, which may cause user bias. Additionally, depending on the number of samples and groups, a study may require measuring thousands of samples and the human error rate may increase. To overcome such problems, in this study, a deep learning model (Pore D2) was developed to quantify the morphological features (such as the pore size and window size) of the open-porous scaffolds automatically for the first time. The developed algorithm was tested on emulsion-templated scaffolds fabricated under different fabrication conditions, such as changing mixing speed, temperature, and surfactant concentration, which resulted in scaffolds with various morphologies. Along with the developed model, blind manual measurements were taken, and the results showed that the developed tool is capable of quantifying pore and window sizes with a high accuracy. Quantifying the morphological features of scaffolds fabricated under different circumstances and controlling these features enable us to engineer tissue engineering scaffolds precisely for specific applications. Pore D2, an open-source software, is available for everyone at the following link: https://github.com/ilaydakaraca/PoreD2.

Bioinspired poly-dopamine/nano-hydroxyapatite: an upgrading biocompatible coat for 3D-printed polylactic acid scaffold for bone regeneration

Poly-lactic acid (PLA) has been proposed in dentistry for several regenerative procedures owing to its biocompatibility and biodegradability. However, the presence of methyl groups renders PLA hydrophobic, making the surface less ideal for cell attachment, and it does not promote tissue regeneration. Upgrading PLA with inductive biomaterial is a crucial step to increase the bioactivity of the PLA and allow cellular adhesion. Our purpose is to evaluate biocompatibility, bioactivity, cellular adhesion, and mechanical properties of 3D-printed PLA scaffold coated with poly-dopamine (PDA) and nano-hydroxyapatite (n-HA) versus PLA and PLA/n-HA scaffolds. The fused deposition modelling technique was used to print PLA, PLA with embedded n-HA particles, and PLA scaffold coated with PDA/n-HA by immersion. After matrices characterization for their chemical composition and surface properties, testing the compressive strength was pursued using a universal testing machine. The bioactivity of scaffolds was evaluated by monitoring the formation of calcium phosphate compounds after simulated body fluid immersion. The PLA/PDA/n-HA scaffold showed the highest compressive strength which was 29.11 ± 7.58 MPa with enhancing calcium phosphate crystals deposition with a specific calcium polyphosphate phase formed exclusively on PLA/PDA/n-HA. With cell viability assay, the PDA/n-HA-coated matrix was biocompatible with increase in the IC50, reaching ⁓ 176.8 at 72 without cytotoxic effect on the mesenchymal stem cells, promoting their adhesion and proliferation evaluated by confocal microscopy. The study explored the biocompatibility, bioactivity, and the cell adhesion ability of PDA/n-HA coat on a 3D-printed PLA scaffold that qualifies its use as a promising regenerative material.

Magnesium-oxide-enhanced bone regeneration: 3D-printing of gelatin-coated composite scaffolds with sustained Rosuvastatin release

Critical-size bone defects are one of the main challenges in bone tissue regeneration that determines the need to use angiogenic and osteogenic agents. Rosuvastatin (RSV) is a class of cholesterol-lowering drugs with osteogenic potential. Magnesium oxide (MgO) is an angiogenesis component affecting apatite formation. This study aims to evaluate 3D-printed Polycaprolactone/β-tricalcium phosphate/nano-hydroxyapatite/ MgO (PCL/β-TCP/nHA/MgO) scaffolds as a carrier for MgO and RSV in bone regeneration. For this purpose, PCL/β-TCP/nHA/MgO scaffolds were fabricated with a 3D-printing method and coated with gelatin and RSV. The biocompatibility and osteogenicity of scaffolds were examined with MTT, ALP, and Alizarin red staining. Finally, the scaffolds were implanted in a bone defect of rat's calvaria, and tissue regeneration was investigated after 3 months. Our results showed that the simultaneous presence of RSV and MgO improved biocompatibility, wettability, degradation rate, and ALP activity but decreased mechanical strength. PCL/β-TCP/nHA/MgO/gelatin-RSV scaffolds produced sustained release of MgO and RSV within 30 days. CT images showed that PCL/β-TCP/nHA/MgO/gelatin-RSV scaffolds filled approximately 86.83 + 4.9 % of the defects within 3 months and improved angiogenesis, woven bone, and osteogenic genes expression. These results indicate the potential of PCL/β-TCP/nHA/MgO/gelatin-RSV scaffolds as a promising tool for bone regeneration and clinical trials.

Biodegradable and 3D printable lysine functionalized polycaprolactone scaffolds for tissue engineering applications

Tissue engineering (TE) has sparked interest in creating scaffolds with customizable properties and functional bioactive sites. However, due to limitations in medical practices and manufacturing technologies, it is challenging to replicate complex porous frameworks with appropriate architectures and bioactivity in vitro. To address these challenges, herein, we present a green approach that involves the amino acid (l-lysine) initiated polymerization of ɛ-caprolactone (CL) to produce modified polycaprolactone (PCL) with favorable active sites for TE applications. Further, to better understand the effect of morphology and porosity on cell attachment and proliferation, scaffolds of different geometries with uniform and interconnected pores are designed and fabricated, and their properties are evaluated in comparison with commercial PCL. The scaffold morphology and complex internal micro-architecture are imaged by micro-computed tomography (micro-CT), revealing pore size in the range of ~300-900 μm and porosity ranging from 30 to 70 %, while based on the geometry of scaffolds the compressive strength varied from 143 ± 19 to 214 ± 10 MPa. Additionally, the degradation profiles of fabricated scaffolds are found to be influenced by both the chemical nature and product design, where Lys-PCL-based scaffolds with better porosity and lower crystallinity degraded faster than commercial PCL scaffolds. According to in vitro studies, Lys-PCL scaffolds have produced an environment that is better for cell adhesion and proliferation. Moreover, the scaffold design affects the way cells interact; Lys-PCL with zigzag geometry has demonstrated superior in vitro vitality (>90 %) and proliferation in comparison to other designs. This study emphasizes the importance of enhancing bioactivity while meeting morphology and porosity requirements in the design of scaffolds for tissue engineering applications.

Cell Instructive Behavior of Composite Scaffolds in a Co-Culture of Human Mesenchymal Stem Cells and Peripheral Blood Mononuclear Cells

The in vitro evaluation of 3D scaffolds for bone tissue engineering in mono-cultures is a common practice; however, it does not represent the native complex nature of bone tissue. Co-cultures of osteoblasts and osteoclasts, without the addition of stimulating agents for monitoring cellular cross-talk, remains a challenge. In this study, a growth factor-free co-culture of human bone marrow-derived mesenchymal stem cells (hBM-MSCs) and human peripheral blood mononuclear cells (hPBMCs) has been established and used for the evaluation of 3D-printed scaffolds for bone tissue engineering. The scaffolds were produced from PLLA/PCL/PHBV polymeric blends, with two composite materials produced through the addition of 2.5% w/v nanohydroxyapatite (nHA) or strontium-substituted nanohydroxyapatite (Sr-nHA). Cell morphology data showed that hPBMCs remained undifferentiated in co-culture, while no obvious differences were observed in the mono- and co-cultures of hBM-MSCs. A significantly increased alkaline phosphatase (ALP) activity and osteogenic gene expression was observed in co-culture on Sr-nHA-containing scaffolds. Tartrate-resistant acid phosphatase (TRAP) activity and osteoclastogenic gene expression displayed significantly suppressed levels in co-culture on Sr-nHA-containing scaffolds. Interestingly, mono-cultures of hPBMCs on Sr-nHA-containing scaffolds indicated a delay in osteoclasts formation, as evidenced from TRAP activity and gene expression, demonstrating that strontium acts as an osteoclastogenesis inhibitor. This co-culture study presents an effective 3D model to evaluate the regenerative capacity of scaffolds for bone tissue engineering, thus minimizing time-consuming and costly in vivo experiments.

A novel fluffy PLGA/HA composite scaffold for bone defect repair

Treatment of bone defects remains crucial challenge for successful bone healing, which arouses great interests in designing and fabricating ideal biomaterials. In this regard, the present study focuses on developing a novel fluffy scaffold of poly Lactide-co-glycolide (PLGA) composites with hydroxyapatite (HA) scaffold used in bone defect repair in rabbits. This fluffy PLGA/HA composite scaffold was fabricated by using multi-electro-spinning combined with biomineralization technology. In vitro analysis of human bone marrow mesenchymal stem cells (BMSCs) seeded onto fluffy PLGA/HA composite scaffold showed their ability to adhere, proliferate and cell viability. Transplant of fluffy PLGA/HA composite scaffold in a rabbit model showed a significant increase in mineralized tissue production compared to conventional and fluffy PLGA/HA composite scaffold. These findings are promising for fluffy PLGA/HA composite scaffolds used in bone defects.

Blend Electrospinning of Nigella sativa-Incorporating PCL/PLA/HA Fibers and Its Investigation for Bone Healing Applications

One of the well-known postoperative complications that requires a number of prophylactic and curative treatments is infection. The implications of postsurgical infections are further exacerbated by the emergence of antibiotic-resistant strains. Reduced effectiveness of synthetic antibiotics has led to an interest in plant-based substances. Extracts obtained from Nigella sativa have been shown to possess effective anti-infectious agents against bacteria frequently seen in bone infections. In this study, a fiber-based bone scaffold containing polycaprolactone, poly(lactic acid), and hydroxyapatite with N. sativa oil at varying concentrations was developed. Solvent electrospinning was used to fabricate the fibers with the specified composition. According to FE-SEM analysis, fibers with average diameters of 751 ± 82, 1000 ± 100, 1020 ± 90, and 1223 ± 112 nm were formed and successful integration of N. sativa oil into the fiber's structure was confirmed via FTIR. Staphylococcus aureus showed moderate susceptibility against the fibers with a maximum inhibition zone diameter of 11.5 ± 1.6 mm. MTT assay analysis exhibited concentration-dependent cell toxicity against fibroblast cells. In short, the antibacterial fibers synthesized in this study possessed antibacterial properties while also allowing moderate accommodation of CDD fibroblast cells at low oil concentrations, which can be a potential application for bone healing and mitigating postsurgical infections.

Advancements of 3D bioprinting in regenerative medicine: Exploring cell sources for organ fabrication

3D bioprinting has unlocked new possibilities for generating complex and functional tissues and organs. However, one of the greatest challenges lies in selecting the appropriate seed cells for constructing fully functional 3D artificial organs. Currently, there are no cell sources available that can fulfill all requirements of 3D bioprinting technologies, and each cell source possesses unique characteristics suitable for specific applications. In this review, we explore the impact of different 3D bioprinting technologies and bioink materials on seed cells, providing a comprehensive overview of the current landscape of cell sources that have been used or hold potential in 3D bioprinting. We also summarized key points to guide the selection of seed cells for 3D bioprinting. Moreover, we offer insights into the prospects of seed cell sources in 3D bioprinted organs, highlighting their potential to revolutionize the fields of tissue engineering and regenerative medicine.

Bone-Regeneration Therapy Using Biodegradable Scaffolds: Calcium Phosphate Bioceramics and Biodegradable Polymers

Calcium phosphate-based synthetic bone is broadly used for the clinical treatment of bone defects caused by trauma and bone tumors. Synthetic bone is easy to use; however, its effects depend on the size and location of the bone defect. Many alternative treatment options are available, such as joint arthroplasty, autologous bone grafting, and allogeneic bone grafting. Although various biodegradable polymers are also being developed as synthetic bone material in scaffolds for regenerative medicine, the clinical application of commercial synthetic bone products with comparable performance to that of calcium phosphate bioceramics have yet to be realized. This review discusses the status quo of bone-regeneration therapy using artificial bone composed of calcium phosphate bioceramics such as β-tricalcium phosphate (βTCP), carbonate apatite, and hydroxyapatite (HA), in addition to the recent use of calcium phosphate bioceramics, biodegradable polymers, and their composites. New research has introduced potential materials such as octacalcium phosphate (OCP), biologically derived polymers, and synthetic biodegradable polymers. The performance of artificial bone is intricately related to conditions such as the intrinsic material, degradability, composite materials, manufacturing method, structure, and signaling molecules such as growth factors and cells. The development of new scaffold materials may offer more efficient bone regeneration.

Artificial Intelligence-Based 3D Printing Strategies for Bone Scaffold Fabrication and Its Application in Preclinical and Clinical Investigations

3D printing has become increasingly popular in the field of bone tissue engineering. However, the mechanical properties, biocompatibility, and porosity of the 3D printed bone scaffolds are major requirements for tissue regeneration and implantation as well. Designing the scaffold architecture in accordance with the need to create better mechanical and biological stimuli is necessary to achieve unique scaffold properties. To accomplish this, different 3D designing strategies can be utilized with the help of the scaffold design library and artificial intelligence (AI). The implementation of AI to assist the 3D printing process can enable it to predict, adapt, and control the parameters on its own, which lowers the risk of errors. This Review emphasizes 3D design and fabrication of bone scaffold using different materials and the use of AI-aided 3D printing strategies. Also, the adaption of AI to 3D printing helps to develop patient-specific scaffolds based on different requirements, thus providing feedback and adequate data for reproducibility, which can be improvised in the future. These printed scaffolds can also serve as an alternative to preclinical animal test models to cut costs and prevent immunological interference.

Effect of Therapeutic Radiation on Polycaprolactone/Hydroxyapatite Biomaterials in a Calvarial Model

Bone defects caused by cancer resection often require postoperative radiotherapy. Although various synthetic polymers have been introduced as graft materials, their biological behavior after radiation exposure remains unclear. Here, we investigated how polycaprolactone/hydroxyapatite (PCL/HA) implants respond to therapeutic radiation exposure (in terms of volume and bone regeneration). Four 8 mm diameter calvaria defects were surgically created on the parietal bone of 6 rabbits. PCL/HA implants made of porous, solid, and hybrid polymers were grafted by random placement in each defect. The fourth defect was left untreated. Four weeks after surgery, radiation exposure was conducted weekly for 6 weeks (total: 48 Gy). Micro-computed tomography and histologic analysis were performed at 3 and 6 months, and 6 months postradiation, respectively. The total augmented volumes of all implants showed no significant differences between 3- and 6-months postradiation computed tomography images. In histologic analysis, new bone areas were 0.45±0.11 mm2, 2.02±0.34 mm2, and 3.60±0.77 mm2 in solid, hybrid, and porous polymer grafts, respectively. Bone regeneration was limited to the periphery of the defect in the hybrid and porous polymer grafts, whereas new bone formed inside the porous implant. The total augmented volume of the defect was maintained without significant absorption even after radiation exposure. The PCL/HA implant maintained its structure despite radiation exposure. The porous PCL/HA implant demonstrated excellent bone regeneration, followed by the hybrid and solid implants. The PCL/HA implant is a promising candidate for bone defect reconstruction.

Entropically Toughened Robust Biodegradable Polymer Blends and Composites for Bone Tissue Engineering

Biodegradable polymers and composites are promising candidates for biomedical implants in tissue engineering. However, state-of-the-art composite scaffolds suffer from a strength-toughness dilemma due to poor interfacial adhesion and filler dispersion. In this work, we propose a facile and scalable strategy to fabricate strong and tough biocomposite scaffolds through interfacial toughening. The immiscible biopolymer matrix is compatible by the direct incorporation of a third polymer. Densely entangled polymer chains lead to massive crazes and global shear yields under tension. Weak chemical interaction and high-shear melt processing create nanoscale dispersion of nanofillers within the matrix. The resultant ternary blends and composites exhibit an 11-fold increase in toughness without compromising stiffness and strength. At 70% porosity, three-dimensional (3D)-printed composite scaffolds demonstrate high compressive properties comparable to those of cancellous bones. In vitro cell culture on the scaffolds demonstrates not only good cell viability but also effective osteogenic differentiation of human mesenchymal stem cells. Our findings present a widely applicable strategy to develop high-performance biocomposite materials for tissue regeneration.

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.

Nuciferine-loaded chitosan hydrogel-integrated 3D-printed polylactic acid scaffolds for bone tissue engineering: A combinatorial approach

Critical-sized bone defects resulting from severe trauma and open fractures cannot spontaneously heal and require surgical intervention. Limitations of traditional bone grafting include immune rejection and demand-over-supply issues leading to the development of novel tissue-engineered scaffolds. Nuciferine (NF), a plant-derived alkaloid, has excellent therapeutic properties, but its osteogenic potential is yet to be reported. Furthermore, the bioavailability of NF is obstructed due to its hydrophobicity, requiring an efficient drug delivery system, such as chitosan (CS) hydrogel. We designed and fabricated polylactic acid (PLA) scaffolds via 3D printing and integrated them with NF-containing CS hydrogel to obtain the porous biocomposite scaffolds (PLA/CS-NF). The fabricated scaffolds were subjected to in vitro physicochemical characterization, cytotoxicity assays, and osteogenic evaluation studies. Scanning electron microscopic studies revealed uniform pore size distribution on PLA/CS-NF scaffolds. An in vitro drug release study showed a sustained and prolonged release of NF. The cyto-friendly nature of NF in PLA/CS-NF scaffolds towards mouse mesenchymal stem cells (mMSCs) was observed. Also, cellular and molecular level studies signified the osteogenic potential of NF in PLA/CS-NF scaffolds on mMSCs. These results indicate that the PLA/CS-NF scaffolds could promote new bone formation and have potential applications in bone tissue engineering.

Synergistic coupling between 3D bioprinting and vascularization strategies

Three-dimensional (3D) bioprinting offers promising solutions to the complex challenge of vascularization in biofabrication, thereby enhancing the prospects for clinical translation of engineered tissues and organs. While existing reviews have touched upon 3D bioprinting in vascularized tissue contexts, the current review offers a more holistic perspective, encompassing recent technical advancements and spanning the entire multistage bioprinting process, with a particular emphasis on vascularization. The synergy between 3D bioprinting and vascularization strategies is crucial, as 3D bioprinting can enable the creation of personalized, tissue-specific vascular network while the vascularization enhances tissue viability and function. The review starts by providing a comprehensive overview of the entire bioprinting process, spanning from pre-bioprinting stages to post-printing processing, including perfusion and maturation. Next, recent advancements in vascularization strategies that can be seamlessly integrated with bioprinting are discussed. Further, tissue-specific examples illustrating how these vascularization approaches are customized for diverse anatomical tissues towards enhancing clinical relevance are discussed. Finally, the underexplored intraoperative bioprinting (IOB) was highlighted, which enables the direct reconstruction of tissues within defect sites, stressing on the possible synergy shaped by combining IOB with vascularization strategies for improved regeneration.

Theoretical and Experimental Investigation of 3D-Printed Polylactide Laminate Composites' Mechanical Properties

The purpose of this work is to theoretically and experimentally investigate the applicability of the Tsai-Hill failure criterion and classical laminate theory for predicting the strength and stiffness of 3D-printed polylactide laminate composites with various raster angles in mechanical tests for uniaxial tension and compression. According to the results of tensile and compression tests, the stiffness matrix components of the orthotropic individual lamina and strength were determined. The Poisson's ratio was determined using the digital image correlation method. It was found that the Tsai-Hill criterion is applicable for predicting the tensile strength and yield strength of laminate polymer composite materials manufactured via fused deposition modeling 3D printing. The calculated values of the elastic moduli for specimens with various raster angles correlate well with the values obtained experimentally. In tensile tests, the error for the laminate with a constant raster angle was 3.3%, for a composite laminate it was 4.4, in compression tests it was 11.9% and 9%, respectively.

Strontium-Substituted Nanohydroxyapatite-Incorporated Poly(lactic acid) Composites for Orthopedic Applications: Bioactive, Machinable, and High-Strength Properties

Traditional metal-alloy bone fixation devices provide structural support for bone repair but have limitations in actively promoting bone healing and often require additional surgeries for implant removal. In this study, we focused on addressing these challenges by fabricating biodegradable composites using poly(lactic acid) (PLA) and strontium-substituted nanohydroxyapatite (SrHAP) via melt compounding and injection molding. Various percentages of SrHAP (5, 10, 20, and 30% w/w) were incorporated into the PLA matrix. We systematically investigated the structural, morphological, thermal, mechanical, rheological, and dynamic mechanical properties of the prepared composites. Notably, the tensile modulus, a critical parameter for orthopedic implants, significantly improved from 2.77 GPa in pristine PLA to 3.73 GPa in the composite containing 10% w/w SrHAP. The incorporation of SrHAP (10% w/w) into the PLA matrix led to an increased storage modulus, indicating a uniform dispersion of SrHAP within the PLA and good compatibility between the polymer and nanoparticles. Moreover, we successfully fabricated screws using PLA composites with 10% (w/w) SrHAP, demonstrating their formability at room temperature and radiopacity when observed under X-ray microtomography (micro-CT). Furthermore, the water contact angle decreased from 93 ± 2° for pristine PLA to 75 ± 3° for the composite containing SrHAP, indicating better surface wettability. To assess the biological behavior of the composites, we conducted in vitro cell-material tests, which confirmed their osteoconductive and osteoinductive properties. These findings highlight the potential of our developed PLA/SrHAP10 (10% w/w) composites as machinable implant materials for orthopedic applications. In conclusion, our study presents the fabrication and comprehensive characterization of biodegradable composites comprising PLA and strontium-substituted nanohydroxyapatite (SrHAP). These composites exhibit improved mechanical properties, formability, and radiopacity while also demonstrating desirable biological behavior. Our results suggest that these PLA/SrHAP10 composites hold promise as machinable implant materials for orthopedic applications.

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.

Histomorphometric evaluation, SEM, and synchrotron analysis of the biological response of biodegradable and ceramic hydroxyapatite-based grafts: from the synthesis to the bed application

This study aimed to analyze the physicochemical and histological properties of nanostructured hydroxyapatite and alginate composites produced at different temperatures with and without sintering and implanted in rabbit tibiae. Hydroxyapatite-alginate (HA) microspheres (425-600 µm) produced at 90 and 5 °C without (HA90 and HA5) or with sintering at 1000 °C (HA90S and HA5S) were characterized and applied to evaluate thein vitrodegradation; also were implanted in bone defects on rabbit's tibiae (n= 12). The animals were randomly divided into five groups (blood clot, HA90S, HA5S, HA90, and HA5) and euthanized after 7 and 28 d. X-ray diffraction and Fourier-transform infrared analysis of the non-sintered biomaterials showed a lower crystallinity than sintered materials, being more degradablein vitroandin vivo. However, the sinterization of HA5 led to the apatite phase's decomposition into tricalcium phosphate. Histomorphometric analysis showed the highest (p< 0.01) bone density in the blood clot group, similar bone levels among HA90S, HA90, and HA5, and significantly less bone in the HA5S. HA90 and HA5 groups presented higher degradation and homogeneous distribution of the new bone formation onto the surface of biomaterial fragments, compared to HA90S, presenting bone only around intact microspheres (p< 0.01). The elemental distribution (scanning electron microscope and energy dispersive spectroscopy andμXRF-SR analysis) of Ca, P, and Zn in the newly formed bone is similar to the cortical bone, indicating bone maturity at 28 d. The synthesized biomaterials are biocompatible and osteoconductive. The heat treatment directly influenced the material's behavior, where non-sintered HA90 and HA5 showed higher degradation, allowing a better distribution of the new bone onto the surface of the biomaterial fragments compared to HA90S presenting the same level of new bone, but only on the surface of the intact microspheres, potentially reducing the bone-biomaterial interface.

Electrospun Poly(L-Lactic Acid)/Gelatin Hybrid Polymer as a Barrier to Periodontal Tissue Regeneration

Poly(L-lactic acid) (PLLA) and PLLA/gelatin polymers were prepared via electrospinning to evaluate the effect of PLLA and gelatin content on the mechanical properties, water uptake capacity (WUC), water contact angle (WCA), degradation rate, cytotoxicity and cell proliferation of membranes. As the PLLA concentration increased from 1 wt% to 3 wt%, the tensile strength increased from 5.8 MPa to 9.1 MPa but decreased to 7.0 MPa with 4 wt% PLLA doping. The WUC decreased rapidly from 594% to 236% as the PLLA content increased from 1 to 4 wt% due to the increased hydrophobicity of PLLA. As the gelatin content was increased to 3 wt% PLLA, the strength, WUC and WCA of the PLLA/gelatin membrane changed from 9.1 ± 0.9 MPa to 13.3 ± 2.3 MPa, from 329% to 1248% and from 127 ± 1.2° to 0°, respectively, with increasing gelatin content from 0 to 40 wt%. However, the failure strain decreased from 3.0 to 0.5. The biodegradability of the PLLA/gelatin blend increased from 3 to 38% as the gelatin content increased to 40 wt%. The viability of L-929 and MG-63 cells in the PLLA/gelatin blend was over 95%, and the excellent cell proliferation and mechanical properties suggested that the tunable PLLA/gelatin barrier membrane was well suited for absorbable periodontal tissue regeneration.

Advances in additive manufacturing of polycaprolactone based scaffolds for bone regeneration

Critical sized bone defects are difficult to manage and currently available clinical/surgical strategies for treatment are not completely successful. Polycaprolactone (PCL) which is a biodegradable and biocompatible thermoplastic can be 3D printed using medical images into patient specific bone implants. The excellent mechanical properties and low immunogenicity of PCL makes it an ideal biomaterial candidate for 3D printing of bone implants. Though PCL suffers from the limitation of being bio-inert. Here we describe the use of PCL as a biomaterial for 3D printing for bone regeneration, and advances made in the field. The specific focus is on the different 3D printing techniques used for this purpose and various modification that can enhance bone regeneration following the development pathways. We further describe the effect of various scaffold characteristics on bone regeneration both in vitro and the translational assessment of these 3D printed PCL scaffolds in animal studies. The generated knowledge will help understand cell-material interactions of 3D printed PCL scaffolds, to further improve scaffold chemistry and design that can replicate bone developmental processes and can be translated clinically.

Printing tissue-engineered scaffolds made of polycaprolactone and nano-hydroxyapatite with mechanical properties appropriate for trabecular bone substitutes

BACKGROUND

Bone tissue engineering, based on three-dimensional (3D) printing technology, has emerged as a promising approach to treat bone defects using scaffolds. The objective of this study was to investigate the influence of porosity and internal structure on the mechanical properties of scaffolds.

METHODS

We fabricated composite scaffolds (which aimed to replicate trabecular bone) from polycaprolactone (PCL) reinforced with 30% (wt.) nano-hydroxyapatite (nHAp) by extrusion printing. Scaffolds with various porosities were designed and fabricated with and without an interlayer offset, termed as staggered and lattice structure, respectively. Mechanical compressive testing was performed to determine scaffold elastic modulus and yield strength. Linear regression was used to evaluate mechanical properties as a function of scaffold porosity.

RESULTS

Different relationships between mechanical properties and porosities were noted for the staggered and lattice structures. For elastic moduli, the two relationships intersected (porosity = 55%) such that the lattice structure exhibited higher moduli with porosity values greater than the intersection point; vice versa for the staggered structure. The lattice structure exhibited higher yield strength at all porosities. Mechanical testing results also indicated elastic moduli and yield strength properties comparable to trabecular bone (elastic moduli: 14-165 MPa; yield strength: 0.9-10 MPa).

CONCLUSIONS

Taken together, this study demonstrates that scaffolds printed from PCL/30% (wt.) nHAp with lattice and staggered structure offer promise for treating trabecular bone defects. This study identified the effect of porosity and internal structure on scaffold mechanical properties and provided suggestions for developing scaffolds with mechanical properties for substituting trabecular bone.

Engineered biomimetic micro/nano-materials for tissue regeneration

The incidence of tissue and organ damage caused by various diseases is increasing worldwide. Tissue engineering is a promising strategy of tackling this problem because of its potential to regenerate or replace damaged tissues and organs. The biochemical and biophysical cues of biomaterials can stimulate and induce biological activities such as cell adhesion, proliferation and differentiation, and ultimately achieve tissue repair and regeneration. Micro/nano materials are a special type of biomaterial that can mimic the microstructure of tissues on a microscopic scale due to its precise construction, further providing scaffolds with specific three-dimensional structures to guide the activities of cells. The study and application of biomimetic micro/nano-materials have greatly promoted the development of tissue engineering. This review aims to provide an overview of the different types of micro/nanomaterials, their preparation methods and their application in tissue regeneration.

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.

Mechanical, biocompatibility and antibacterial studies of gelatin/polyvinyl alcohol/silkfibre polymeric scaffold for bone tissue engineering

The current study focuses on the incorporation of natural polymers (gelatin, silk fibre) and synthetic (polyvinyl alcohol) polymer towards the fabrication of a novel composite for bone tissue engineering. The Electrospinning method was used to fabricate the novel gelatin/polyvinyl alcohol/silk fibre scaffold. XRD, FTIR and SEM-EDAX analysis was performed to characterize the composite. The characterized composite was investigated for its physical properties (porosity and mechanical studies) and biological studies (antimicrobial activity, hemocompatibility, bioactivity). The fabricated composite showed high porosity and the highest tensile strength of 34 MPa, with elongation at a break of 35.82 for the composite. The antimicrobial activity of the composite was studied and the zone of inhibition was measured around 51 ± 0.54 for E. coli, 48 ± 0.48 for S. aureus and 50 ± 0.26 for C. albicans. The hemolytic % was noted around 1.36 for the composite and the bioactivity assay revealed the formation of apatite on composite surfaces.

A Review of the Application of Natural and Synthetic Scaffolds in Bone Regeneration

The management of bone defects is complicated by the presence of clinical conditions, such as critical-sized defects created by high-energy trauma, tumour resection, infection, and skeletal abnormalities, whereby the bone regeneration capacity is compromised. A bone scaffold is a three-dimensional structure matrix serving as a template to be implanted into the defects to promote vascularisation, growth factor recruitment, osteogenesis, osteoconduction, and mechanical support. This review aims to summarise the types and applications of natural and synthetic scaffolds currently adopted in bone tissue engineering. The merits and caveats of natural and synthetic scaffolds will be discussed. A naturally derived bone scaffold offers a microenvironment closer to in vivo conditions after decellularisation and demineralisation, exhibiting excellent bioactivity, biocompatibility, and osteogenic properties. Meanwhile, an artificially produced bone scaffold allows for scalability and consistency with minimal risk of disease transmission. The combination of different materials to form scaffolds, along with bone cell seeding, biochemical cue incorporation, and bioactive molecule functionalisation, can provide additional or improved scaffold properties, allowing for a faster bone repair rate in bone injuries. This is the direction for future research in the field of bone growth and repair.

Nature-Inspired Heat and Moisture Exchanger Filters Composed of Gelatin and Chitosan for the Design of Eco-Sustainable "Artificial Noses"

For long-term mechanical ventilation, during anesthesia or intensive care, it is crucial to preserve a minimum level of humidity to avoid damage to the respiratory epithelium. Heat and moisture exchange filters (HME), also called "artificial noses," are passive systems that contribute to delivering inspired gases at about the same conditions of healthy respiration, i.e., 32 °C and relative humidity higher than 90%. Current HME devices suffer from limitations linked either to performance and filtration efficiency to their inadequate antibacterial efficiency, sterilization methods, and durability. Furthermore, in times of global warming and diminishing petroleum oil reserves, replacing the employing of synthetic materials with biomass biodegradable raw materials has considerable economic and environmental value. In the present study, a generation of eco-sustainable, bioinspired, and biodegradable HME devices are designed and developed through a green-chemistry process based on raw materials deriving from food waste and taking inspiration from the functioning, structure, and chemistry of our respiratory system. In particular, different blends are obtained by mixing aqueous solutions of gelatin and chitosan in various polymer ratios and concentrations and then by cross-linking them with different low amounts of genipin, a natural chemical cross-linker. Finally, the blends, post-gelation, are freeze-dried to obtain three-dimensional (3D) highly porous aerogels reproducing both the highly exposed surface area of the upper respiratory ways and the chemical composition of the mucus secretion covering the nasal mucosae. Results are comparable with accepted standards for HME devices and suitable bacteriostatic potential, thus validating these bioinspired materials as promising candidates to be used as an eco-sustainable generation of HME devices.

Polydopamine-assisted tranilast immobilization on a PLA chamber to enhance fat flaps regeneration by reducing tissue fibrosis

Tissue engineering chambers (TECs) have been shown to be useful in regenerating adipose tissue. However, tissue fibrosis caused by the chambers compromises the final volume of the newly formed adipose tissue. Surface modifications can compensate for the lack of biocompatibility of an implant. Tranilast (Tra) is an antifibrotic drug used to treat fibrotic pathologies, including keloids and scleroderma. In this study, a polydopamine-assisted tranilast coating (pDA + Tra) was prepared on a polylactic acid (PLA) chamber to minimize tissue fibrosis and achieve a large volume of fat flap regeneration. The in vitro results showed that, in contrast to a PLA chamber, roughness increased, and the fibroblast adhesion and smooth muscle antibody-positive immunoreactivity decreased in the PLA + pDA + Tra chamber. In addition, pedicled adipose tissue flaps were separated from the back of the rabbit and inserted into each chamber using the classic TEC procedure. After 16 weeks, the marked attenuation of fibrosis and promotion of fat regeneration was observed in the PLA + pDA + Tra chamber in contrast to the PLA chamber. Moreover, in contrast to the PLA chamber, Q-PCR results showed that fibrotic factor TGF-β was significantly reduced, associated with a remarkable increase in adipogenic differentiation transcription factors PPAR-γ and C/EBPα in the PLA + pDA + Tra chamber after 16 weeks (p < 0.05). Thus, PLA chambers loaded with pDA + Tra on the surface have good biocompatibility, and chemical anti-fibrosis reagents can synergistically reduce fibrosis formation while excellently promoting adipose tissue regeneration.

Recent advances in modified poly (lactic acid) as tissue engineering materials

As an emerging science, tissue engineering and regenerative medicine focus on developing materials to replace, restore or improve organs or tissues and enhancing the cellular capacity to proliferate, migrate and differentiate into different cell types and specific tissues. Renewable resources have been used to develop new materials, resulting in attempts to produce various environmentally friendly biomaterials. Poly (lactic acid) (PLA) is a biopolymer known to be biodegradable and it is produced from the fermentation of carbohydrates. PLA can be combined with other polymers to produce new biomaterials with suitable physicochemical properties for tissue engineering applications. Here, the advances in modified PLA as tissue engineering materials are discussed in light of its drawbacks, such as biological inertness, low cell adhesion, and low degradation rate, and the efforts conducted to address these challenges toward the design of new enhanced alternative biomaterials.

Ceramic Materials for Biomedical Applications: An Overview on Properties and Fabrication Processes

A growing interest in creating advanced biomaterials with specific physical and chemical properties is currently being observed. These high-standard materials must be capable to integrate into biological environments such as the oral cavity or other anatomical regions in the human body. Given these requirements, ceramic biomaterials offer a feasible solution in terms of mechanical strength, biological functionality, and biocompatibility. In this review, the fundamental physical, chemical, and mechanical properties of the main ceramic biomaterials and ceramic nanocomposites are drawn, along with some primary related applications in biomedical fields, such as orthopedics, dentistry, and regenerative medicine. Furthermore, an in-depth focus on bone-tissue engineering and biomimetic ceramic scaffold design and fabrication is presented.

A simple and fast method for screening production of polymer-ceramic filaments for bone implant printing using commercial fused deposition modelling 3D printers

3D printing is a promising technique for obtaining bone implants. However, 3D printed bone implants, especially those printed using fused deposition modelling, are still in the experimental phase despite decades of work. Research on new materials faces numerous limitations, such as reagents' cost and machines' high prices to produce filaments for 3D printing polymer-ceramic composites for fused deposition modelling. This paper presents a simple, low-cost, and fast method of obtaining polymer-ceramic filaments using apparatus consisting of parts available in a hardware store. The method's versatility for producing the filaments was demonstrated on two different biodegradable polymers - polylactic acid and polycaprolactone - and different concentrations of calcium phosphate - β-tricalcium phosphate - in the composite, up to 50 % by weight. For screening purposes, numerous scaffolds were 3D printed from the obtained filaments on a commercial 3D printer. Structural, mechanical, and biological tests show that the 3D printed scaffolds are suitable for bone implants, as their structure, mechanical, and non-cytotoxic properties are evident. Moreover, the proposed method of composite forming is a simplification of the processes of manufacturing and researching 3D printed materials with potential applications in the regeneration of bone tissue.

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.

Design and manufacture of 3D-cylindrical scaffolds based on PLA/TPU/n-HA with the help of dual salt leaching technique suggested for use in cancellous bone tissue engineering

A series of 3-D scaffolds based on polylactic acid (PLA) and thermoplastic polyurethane (TPU) as major phase and hydroxyapatite nanoparticles (n-HA) were prepared by using the dual leaching technique. Fourier-transform infrared spectroscopy analysis showed that almost the interactions between the constituent materials can be identified based on their functional groups. The results of thermogravimetric analysis were used to obtain the best time to prepare the samples without residual of any progen additives. The scanning electron macroscopy images clearly proved that the dual leaching technique is an effective method to prepare the appropriate morphology and also a very good dispersion and distribution for n-HA can be obtained. Dynamic contact angles showed that the presence of TPU in the PLA matrix has a positive effect on the hydrophilicity of the scaffolds. The bulk modulus (κ) values of S-PLA70TPU30H5 in dry and wet conditions were 321 and 212 Pa, respectively and the compressibility coefficient (β) of pure samples was higher than that of other scaffolds, while among the nanocomposite samples, the compressibility coefficient of S-PLA70TPU30H5 and S-PLA50TPU50H5 samples in dry and wet conditions was higher than that of other samples. Biological tests such as 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) tetrazolium reduction assay, cell adhesion, 4',6-diamidino-2-phenylindole (DAPI) analysis and alizarin red were also performed, and the results obtained for 3D scaffolds were good. In the DAPI analysis test, sample 3D-S-PLA70TPU30H5 showed good behavior, and also in the alizarin red test, the amount of minerals created in 3D-S-PLA50TPU50H5 was significant.

3D-Printed Polycaprolactone Implants Modified with Bioglass and Zn-Doped Bioglass

In this work, composite filaments in the form of sticks and 3D-printed scaffolds were investigated as a future component of an osteochondral implant. The first part of the work focused on the development of a filament modified with bioglass (BG) and Zn-doped BG obtained by injection molding. The main outcome was the manufacture of bioactive, strong, and flexible filament sticks of the required length, diameter, and properties. Then, sticks were used for scaffold production. We investigated the effect of bioglass addition on the samples mechanical and biological properties. The samples were analyzed by scanning electron microscopy, optical microscopy, infrared spectroscopy, and microtomography. The effect of bioglass addition on changes in the SBF mineralization process and cell morphology was evaluated. The presence of a spatial microstructure within the scaffolds affects their mechanical properties by reducing them. The tensile strength of the scaffolds compared to filaments was lower by 58-61%. In vitro mineralization experiments showed that apatite formed on scaffolds modified with BG after 7 days of immersion in SBF. Scaffold with Zn-doped BG showed a retarded apatite formation. Innovative 3D-printing filaments containing bioglasses have been successfully applied to print bioactive scaffolds with the surface suitable for cell attachment and proliferation.

Periodontal bone regeneration with a degradable thermoplastic HA/PLCL bone graft

Strategic bone grafts are required to regenerate periodontal bone defects owing to limited self-healing. Current bioceramic particle or deproteinized bovine bone (DBB) products are not able to ideally meet clinical requirements, such as insufficient operability and slow degradation rates. Herein, a strong-interacted bone graft was designed and synthesized by modifying hydroxyapatite (HA) with a lactide-caprolactone copolymer (PLCL) to improve component homogeneity and mechanical properties. The physical-chemical analysis indicated that HA particles were homogenously distributed in HA/PLCL bone grafts, possessed outstanding thermoplasticity, and facilitated clinic operability and initial mechanical support. The in vitro study suggested that HA/PLCL bone graft degraded in a spatiotemporal model. Micropores were formed on the non-porous surface at the beginning, and interconnected porous structures were gradually generated. Furthermore, HA/PLCL bone grafts exhibited excellent biocompatibility and osteogenic ability as revealed in vitro cell culture and in vivo animal experiments. When applied to rat periodontal bone defects, the HA/PLCL bone graft showed a non-inferior bone regeneration compared to the commercial DBB. This study proposes a potential bone graft for periodontal bone repair with thermoplastic, spatiotemporal degraded, and osteogenic characteristics.

Characterization of PLA/PCL/Nano-Hydroxyapatite (nHA) Biocomposites Prepared via Cold Isostatic Pressing

Hydroxyapatite has the closest chemical composition to human bone. Despite this, the use of nano-hydroxyapatite (nHA) to produce biocomposite scaffolds from a mixture of polylactic acid (PLA) and polycaprolactone (PCL) using cold isostatic pressing has not been studied intensively. In this study, biocomposites were created employing nHA as an osteoconductive filler and a polymeric blend of PLA and PCL as a polymer matrix for prospective usage in the medical field. Cold isostatic pressing and subsequent sintering were used to create composites with different nHA concentrations that ranged from 0 to 30 weight percent. Using physical and mechanical characterization techniques such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and density, porosity, tensile, and flexural standard tests, it was determined how the nHA concentrations affected the biocomposite's general properties. In this study, the presence of PLA, PCL, and nHA was well identified using FTIR, XRD, and SEM methods. The biocomposites with high nHA content showed intense bands for symmetric stretching and the asymmetric bending vibration of PO₄^3-. The incorporation of nHA into the polymeric blend matrix resulted in a rather irregular structure and the crystallization became more difficult. The addition of nHA improved the density and tensile and flexural strength of the PLA/PCL matrix (0% nHA). However, with increasing nHA content, the PLA/PCL/nHA biocomposites became more porous. In addition, the density, flexural strength, and tensile strength of the PLA/PCL/nHA biocomposites decreased with increasing nHA concentration. The PLA/PCL/nHA biocomposites with 10% nHA had the highest mechanical properties with a density of 1.39 g/cm³, a porosity of 1.93%, a flexural strength of 55.35 MPa, and a tensile strength of 30.68 MPa.

Dual-Nozzle 3D Printed Nano-Hydroxyapatite Scaffold Loaded with Vancomycin Sustained-Release Microspheres for Enhancing Bone Regeneration

Background

Successful treatment of infectious bone defect remains a major challenge in the orthopaedic field. At present, the conventional treatment for infectious bone defects is surgical debridement and long-term systemic antibiotic use. It is necessary to develop a new strategy to achieve effective bone regeneration and local anti-infection for infectious bone defects.

Methods

Firstly, vancomycin / poly (lactic acid-glycolic acid) sustained release microspheres (VAN/PLGA-MS) were prepared. Then, through the dual-nozzle 3D printing technology, VAN/PLGA-MS was uniformly loaded into the pores of nano-hydroxyapatite (n-HA) and polylactic acid (PLA) scaffolds printed in a certain proportion, and a composite scaffold (VAN/MS-PLA/n-HA) was designed, which can not only promote bone repair but also resist local infection. Finally, the performance of the composite scaffold was evaluated by in vivo and in vitro biological evaluation.

Results

The in vitro release test of microspheres showed that the release of VAN/PLGA-MS was relatively stable from the second day, and the average daily release concentration was about 15.75 μg/mL, which was higher than the minimum concentration specified in the guidelines. The bacteriostatic test in vitro showed that VAN/PLGA-MS had obvious inhibitory effect on Staphylococcus aureus ATCC-29213. Biological evaluation of VAN/MS-PLA/n-HA scaffolds in vitro showed that it can promote the proliferation of adipose stem cells. In vivo biological evaluation showed that VAN/MS-PLA/n-HA scaffold could significantly promote bone regeneration.

Conclusion

Our research shows that VAN/MS-PLA/n-HA scaffolds have satisfying biomechanical properties, effectively inhibit the growth of Staphylococcus aureus, with good biocompatibility, and effectiveness on repairing bone defects. The VAN/MS-PLA/n-HA scaffold provide the clinic with an application prospect in bone tissue engineering.

3D-printed hydroxyapatite scaffolds for bone tissue engineering: A systematic review in experimental animal studies

The use of 3D-printed hydroxyapatite (HA) scaffolds for stimulating bone healing has been increasing over the years. Although all the promising effects of these scaffolds, there are still few studies and limited understanding of their interaction with bone tissue and their effects on the process of fracture healing. In this context, this study aimed to perform a systematic literature review examining the effects of different 3D-printed HA scaffolds in bone healing. The search was made according to the preferred reporting items for systematic reviews and meta-analysis (PRISMA) orientations and Medical Subject Headings (MeSH) descriptors "3D printing," "bone," "HA," "repair," and "in vivo." Thirty-six articles were retrieved from PubMed and Scopus databases. After eligibility analyses, 20 papers were included (covering the period of 2016 and 2021). Results demonstrated that all the studies included in this review showed positive outcomes, indicating the efficacy of scaffolds treated groups in the in vivo experiments for promoting bone healing in different animal models. In conclusion, 3D-printed HA scaffolds are excellent candidates as bone grafts due to their bioactivity and good bone interaction.

Silk Fibroin/Collagen/Hydroxyapatite Scaffolds Obtained by 3D Printing Technology and Loaded with Recombinant Human Erythropoietin in the Reconstruction of Alveolar Bone Defects

The fast osteogenesis of the large alveolar fossa and the maintenance of the height of the alveolar ridge after tooth extraction have always been a clinical challenge. Therefore, this work describes the creation of innovative silk fibroin/collagen/hydroxyapatite (SCH) biological scaffolds by 3D printing technology, which are loaded with recombinant human erythropoietin (rh-EPO) for the reconstruction of bone defects. Low-temperature 3D printing can maintain the biological activity of silk fibroin and collagen. The SCH scaffolds showed the ideal water absorption and porosity, being a sustained-release carrier of rh-EPO. The optimized scaffolds had ideal mechanical properties in vitro, and MC3T3-E1 cells could easily adhere and proliferate on it. In vivo experiments in rabbits demonstrated that the composite scaffolds gradually degraded and promoted the accumulation and proliferation of osteoblasts and the formation of collagen fibers, significantly promoting the reconstruction of mandibular defects. In this study, a novel composite biological scaffold was prepared using 3D printing technology, and the scaffold was innovatively combined with the multifunctional growth factor rh-EPO. This provides a new optimized composite material for the reconstruction of irregular mandible defects, and this biomaterial is promising for clinical reconstruction of alveolar bone defects.

Characterization of PLA/PCL/Green Mussel Shells Hydroxyapatite (HA) Biocomposites Prepared by Chemical Blending Methods

Recently, there has been an increase in the number of studies conducted on the process of developing hydroxyapatite (HA) to use in biocomposites. HA can be derived from natural sources such as bovine bone. The HA usage obtained from green mussel shells in biocomposites in this study will be explored. The research goal is to investigate the composition effect of biomaterials derived from polycaprolactone (PCL), polylactic acid (PLA), as well as HA obtained from green mussel shells with a chemical blending method on mechanical properties and degradation rate. First, 80 mL of chloroform solution was utilized to immerse 16 g of the PLA/PCL mixture with the ratios of 85:15 and 60:40 for 30 min. A magnetic stirrer was used to mix the solution for an additional 30 min at a temperature and speed of 50 °C and 300 rpm. Next, the hydroxyapatite (HA) was added in percentages of 5%, 10%, and 15%, as well as 20% of the PLA/PCL mixture's total weight. It was then stirred for 1 h at 100 rpm at 65 °C to produce a homogeneous mixture of HA and polymer. The biocomposite mixture was then added into a glass mold as per ASTM D790. Following this, biocomposite specimens were tested for their density, biodegradability, and three points of bending in determining the effect of HA and polymer composition on the degradation rate and mechanical properties. According to the findings of this study, increasing the HA and PLA composition yields a rise in the mechanical properties of the biocomposites. However, the biocomposite degradation rate is increasing.

Horizon of exosome-mediated bone tissue regeneration: The all-rounder role in biomaterial engineering

Bone injury repair has always been a tricky problem in clinic, the recent emergence of bone tissue engineering provides a new direction for the repair of bone injury. However, some bone tissue processes fail to achieve satisfactory results mainly due to insufficient vascularization or cellular immune rejection. Exosomes with the ability of vesicle-mediated intercellular signal transmission have gained worldwide attention and can achieve cell-free therapy. Exosomes are small vesicles that are secreted by cells, which contain genetic material, lipids, proteins and other substances. It has been found to play the function of material exchange between cells. It is widely used in bone tissue engineering to achieve cell-free therapy because it not only does not produce some immune rejection like cells, but also can play a cell-like function. Exosomes from different sources can bind to scaffolds in various ways and affect osteoblast, angioblast, and macrophage polarization in vivo to promote bone regeneration. This article reviews the recent research progress of exosome-loaded tissue engineering, focusing on the mechanism of exosomes from different sources and the application of exosome-loaded scaffolds in promoting bone regeneration. Finally, the existing deficiencies and challenges, future development directions and prospects are summarized.