Fabrication of novel bioactive hydroxyapatite-chitosan-silica hybrid scaffolds: Combined the sol-gel method with 3D plotting technique

Application of Hydroxyapatite Composites in Bone Tissue Engineering: A Review

The treatment of bone defects is complicated by clinical conditions, such as trauma, tumor resection, and infection, which result in defects and impair the bone's regenerative capacity. Hydroxyapatite (HAp), the primary inorganic component of bone, possesses good biocompatibility and osteoconductivity. However, it has poor mechanical properties, a slow degradation rate, and limited functionality, necessitating combination with other materials to broaden its application scope. This paper summarizes the importance and properties of HAp composites and provides a categorized review of current research on HAp composites in bone tissue engineering. These composite scaffolds not only offer excellent mechanical support for cell growth and tissue regeneration but also facilitate new bone formation and vascularization. Additionally, the challenges faced by HAp composites, such as material property optimization and improvement of preparation techniques, are discussed. The paper also summarizes the applications of HAp composites in bone defect repair, dental implants, spinal fusion, and other fields.

Achievements in 3D printing of silica-based materials for bone tissue engineering

Silica-based materials have been commonly studied in the field of bone tissue regeneration, due to their high bioactivity and osteogenic properties. There are two main strategies to obtain silica-based materials, a melt-quenching process using high temperatures, or a sol-gel reaction which can be carried out at mild conditions. Both techniques allow the preparation of calcium silicates and bioactive glasses, but pure silica can only be prepared through the sol-gel method. Furthermore, current clinical treatments require personalized scaffolds and these materials can be combined with the use of 3D printing techniques to obtain patient-specific scaffolds in a fast and precise fabrication process. This review focuses on the different silica-based 3D printable materials available nowadays as well as their physical, chemical and biological properties. Using high temperature, composites can be developed using Fused Deposition Modelling (FDM), while pure silica scaffolds can be prepared through Selective Laser Sintering (SLS) using silica particles. Moreover, silica particles can be 3D printed when combining polymeric binders and SLS, Stereolitography (SLA) or Direct Ink Writing (DIW); however, binder has to be removed at high temperatures after 3D printing. Alternatively, 3D printable silica materials can be obtained at mild temperatures through DIW or SLA, in this case only allowing the printing of composites or hybrids so far, with different proportions of silica. The properties of the resultant materials as well as the main advantages and disadvantages of the printing approaches are summarized in this review, together with the future perspectives in the field of silica 3D printed scaffolds.

Progress in chitin/chitosan and their derivatives for biomedical applications: Where we stand

Chitin and its deacetylated form, chitosan, have demonstrated remarkable versatility in the realm of biomaterials. Their exceptional biocompatibility, antibacterial properties, pro- and anticoagulant characteristics, robust antioxidant capacity, and anti-inflammatory potential make them highly sought-after in various applications. This review delves into the mechanisms underlying chitin/chitosan's biological activity and provides a comprehensive overview of their derivatives in fields such as tissue engineering, hemostasis, wound healing, drug delivery, and hemoperfusion. However, despite the wealth of studies on chitin/chitosan, there exists a notable trend of homogeneity in research, which could hinder the comprehensive development of these biomaterials. This review, taking a clinician's perspective, identifies current research gaps and medical challenges yet to be addressed, aiming to pave the way for a more sustainable future in chitin/chitosan research and application.

3D chitosan/hydroxyapatite scaffolds containing mesoporous SiO2-HA particles: A new step to healing bone defects

Biocompatible scaffolds with high mechanical strengths that contain biodegradable components could boost bone regeneration compared with nondegradable bone repair materials. In this study, porous chitosan (CS)/hydroxyapatite (HA) scaffolds containing mesoporous SiO2-HA particles were fabricated through the freeze-drying process. According to field emission scanning electron microscopy (FESEM) results, combining mesoporous SiO2-HA particles in CS/HA scaffolds led to a uniform porous structure. It decreased pore sizes from 320 ± 1.1 μm to 145 ± 1.4 μm. Moreover, the compressive strength value of this scaffold was 25 ± 1.2 MPa. The in-vitro approaches exhibited good sarcoma osteogenic cell line (SAOS-2) adhesion, spreading, and proliferation, indicating that the scaffolds provided a suitable environment for cell cultivation. Also, in-vivo analyses in implanted defect sites of rats proved that the CS/HA/mesoporous SiO2-HA scaffolds could promote bone regeneration via enhancing osteoconduction and meliorating the expression of osteogenesis gene to 19.31 (about 5-fold higher compared to the control group) by exposing them to the bone-like precursors. Further, this scaffold's new bone formation percentage was equal to 90 % after 21 days post-surgery. Therefore, incorporating mesoporous SiO2-HA particles into CS/HA scaffolds can suggest a new future tissue engineering and regeneration strategy.

Incorporating mesoporous SiO2-HA particles into chitosan/hydroxyapatite scaffolds: A comprehensive evaluation of bioactivity and biocompatibility

In this work, composite scaffolds with various composition ratios of chitosan (CS), hydroxyapatite (HA), and mesoporous SiO2 particles co-synthesized with hydroxyapatite (SiO2-HA) were fabricated via the freeze-drying method for bone tissue engineering applications. Morphological studies showed that adding mesoporous particles resulted in a structure with a more uniformly porous geometry, subsequently leading to reduced biodegradation rates and water absorption in the scaffolds. The bioactivity results showed the introduction of mesoporous particles notably enhanced the coverage of the scaffold surface with apatite films. Moreover, biocompatibility assessments using sarcoma osteogenic cell line (SAOS-2) highlighted mesoporous particles' positive impact on cell adhesion and growth. The fluorescence images showed spindle-shaped cells with a greater number and normal cell nuclei for the scaffolds containing mesoporous SiO2-HA particles. The MTT cytotoxicity results indicated that the scaffolds containing mesoporous particles showed approximately 25 % higher cell survival more than single chitosan-based ones. What is more, the mesoporous-containing scaffolds occurred to have the best alkaline phosphatase test (ALP) activity among all scaffolds. It is important to add that CS/HA/mesoporous SiO2-HA scaffolds including SAOS-2 cells showed no sign of either early or late apoptosis. These findings affirm the potential of CS/HA/mesoporous SiO2-HA scaffolds as promising implants for bone tissue engineering.

Chitosan scaffolds: Expanding horizons in biomedical applications

Chitosan, a natural polysaccharide from chitin, shows promise as a biomaterial for various biomedical applications due to its biocompatibility, biodegradability, antibacterial activity, and ease of modification. This review overviews "chitosan scaffolds" use in diverse biomedical applications. It emphasizes chitosan's structural and biological properties and explores fabrication methods like gelation, electrospinning, and 3D printing, which influence scaffold architecture and mechanical properties. The review focuses on chitosan scaffolds in tissue engineering and regenerative medicine, highlighting their role in bone, cartilage, skin, nerve, and vascular tissue regeneration, supporting cell adhesion, proliferation, and differentiation. Investigations into incorporating bioactive compounds, growth factors, and nanoparticles for improved therapeutic effects are discussed. The review also examines chitosan scaffolds in drug delivery systems, leveraging their prolonged release capabilities and ability to encapsulate medicines for targeted and controlled drug delivery. Moreover, it explores chitosan's antibacterial activity and potential for wound healing and infection management in biomedical contexts. Lastly, the review discusses challenges and future objectives, emphasizing the need for improved scaffold design, mechanical qualities, and understanding of interactions with host tissues. In summary, chitosan scaffolds hold significant potential in various biological applications, and this review underscores their promising role in advancing biomedical science.

3D and 4D printing hydroxyapatite-based scaffolds for bone tissue engineering and regeneration

The osseous tissue can be classified as a nanocomposite that encompasses a complex interweaving of organic and inorganic matrices. This intricate amalgamation consists of a collagen component and a mineral phase that are intricately arranged to form elaborate and perforated configurations. Hydroxyapatite, whether synthesized artificially or obtained from natural sources, has garnered considerable attention as a composite material in the field of bone tissue engineering due to its striking resemblance to bone in terms of structure and characteristics. Hydroxyapatite (HA) constitutes the predominant ceramic biomaterial for biomedical applications due to its ability to replicate the mineral composition of vertebrate bone. Nonetheless, it is noteworthy that the present biomimetic substance exhibits unfavorable mechanical characteristics, characterized by insufficient tensile and compressive strength, thus rendering it unsuitable for effective employment in the field of bone tissue engineering. Due to its beneficial attributes, hydroxyapatite (HA) is frequently employed in conjunction with various polymers and crosslinkers as composites to enhance mechanical properties and overall efficacy of implantable biomaterials engineered. The restoration of skeletal defects through the use of customized replacements is an effective way to replace damaged or lost bone structures. This method not only restores the bones' original functions but also reinstates their initial aesthetic appearance. The utilization of hydroxyapatite-polymer composites within 3D-printed grafts necessitates meticulous optimization of both mechanical and biological properties, in order to ensure their suitability for employment in medical devices. The utilization of 3D-printing technology represents an innovative approach in the manufacturing of HA-based scaffolds, which offers advantageous prospects for personalized bone regeneration. The expeditious prototyping method, with emphasis on the application of 3D printing, presents a viable approach in the development of bespoke prosthetic implants, grounded on healthcare data sets. 4D printing approach is an evolved form of 3D printing that utilizes programmable materials capable of altering the intended shape of printed structures, contingent upon single or dual stimulating factors. These factors include aspects such as pH level, temperature, humidity, crosslinking degree, and leaching factors.

Development of a Novel Marine-Derived Tricomposite Biomaterial for Bone Regeneration

Bone tissue engineering is a promising treatment for bone loss that requires a combination of porous scaffold and osteogenic cells. The aim of this study was to evaluate and develop a tricomposite, biomimetic scaffold consisting of marine-derived biomaterials, namely, chitosan and fucoidan with hydroxyapatite (HA). The effects of chitosan, fucoidan and HA individually and in combination on the proliferation and differentiation of human mesenchymal stem cells (MSCs) were investigated. According to the SEM results, the tricomposite scaffold had a uniform porous structure, which is a key requirement for cell migration, proliferation and vascularisation. The presence of HA and fucoidan in the chitosan tricomposite scaffold was confirmed using FTIR, which showed a slight decrease in porosity and an increase in the density of the tricomposite scaffold compared to other formulations. Fucoidan was found to inhibit cell proliferation at higher concentrations and at earlier time points when applied as a single treatment, but this effect was lost at later time points. Similar results were observed with HA alone. However, both HA and fucoidan increased MSC mineralisation as measured by calcium deposition. Differentiation was significantly enhanced in MSCs cultured on the tricomposite, with increased alkaline phosphatase activity on days 17 and 25. In conclusion, the tricomposite is biocompatible, promotes osteogenesis, and has the structural and compositional properties required of a scaffold for bone tissue engineering. This biomaterial could provide an effective treatment for small bone defects as an alternative to autografts or be the basis for cell attachment and differentiation in ex vivo bone tissue engineering.

Chitosan-Silica Hybrid Biomaterials for Bone Tissue Engineering: A Comparative Study of Xerogels and Aerogels

Chitosan (CS) is a natural biopolymer that shows promise as a biomaterial for bone-tissue regeneration. However, because of their limited ability to induce cell differentiation and high degradation rate, among other drawbacks associated with its use, the creation of CS-based biomaterials remains a problem in bone tissue engineering research. Here we aimed to reduce these disadvantages while retaining the benefits of potential CS biomaterial by combining it with silica to provide sufficient additional structural support for bone regeneration. In this work, CS-silica xerogel and aerogel hybrids with 8 wt.% CS content, designated SCS8X and SCS8A, respectively, were prepared by sol-gel method, either by direct solvent evaporation at the atmospheric pressure or by supercritical drying in CO₂, respectively. As reported in previous studies, it was confirmed that both types of mesoporous materials exhibited large surface areas (821 m²g^-1-858 m²g^-1) and outstanding bioactivity, as well as osteoconductive properties. In addition to silica and chitosan, the inclusion of 10 wt.% of tricalcium phosphate (TCP), designated SCS8T10X, was also considered, which stimulates a fast bioactive response of the xerogel surface. The results here obtained also demonstrate that xerogels induced earlier cell differentiation than the aerogels with identical composition. In conclusion, our study shows that the sol-gel synthesis of CS-silica xerogels and aerogels enhances not only their bioactive response, but also osteoconduction and cell differentiation properties. Therefore, these new biomaterials should provide adequate secretion of the osteoid for a fast bone regeneration.

Full physicochemical and biocompatibility characterization of a supercritical CO2 sterilized nano-hydroxyapatite/chitosan biodegradable scaffold for periodontal bone regeneration

Despite bone's innate self-renewal capability, some periodontal pathologic and traumatic defects' size inhibits full spontaneous regeneration. This current research characterized a 3D porous biodegradable nano-hydroxyapatite/chitosan (nHAp/CS, 70/30) scaffold for periodontal bone regeneration, which preparation method includes the final solvent extraction and sterilization through supercritical CO₂ (scCO₂). Micro-CT analysis revealed the fully interconnected porous microstructure of the nHAp/CS scaffold (total porosity 78 %, medium pore size 200 μm) which is critical for bone regeneration. Scanning electron microscopy (SEM) showed HAp crystals forming on the surface of the nHAp/CS scaffold after 21 days in simulated body fluid, demonstrating its bioactivity in vitro. The presence of nHAp in the scaffolds promoted a significantly lower biodegradation rate compared to a plain CS scaffold in PBS. Dynamic mechanical analysis confirmed their viscoelasticity, but the presence of nHAp significantly enhanced the storage modulus (42.34 ± 6.09 kPa at 10 Hz after 28 days in PBS), showing that it may support bone ingrowth at low-load bearing bone defects. Both scaffold types significantly inhibited the growth, attachment and colony formation abilities of S. aureus and E. coli, enhancing the relevance of chitosan in the grafts' composition for the naturally contaminated oral environment. At SEM and laser scanning confocal microscopy, MG63 cells showed normal morphology and could adhere and proliferate inside the biomaterials' porous structure, especially for the nHAp/CS scaffold, reaching higher proliferative rate at day 14. MG63 cells seeded within nHAp/CS scaffolds presented a higher expression of RUNX2, collagen A1 and Sp7 osteogenic genes compared to the CS samples. The in vivo subcutaneous implantation in mice of both scaffold types showed lower biodegradability with the preservation of the scaffolds porous structure that allowed the ingrowth of connective tissue until 5 weeks. Histology shows an intensive and progressive ingrowth of new vessels and collagen between the 3^rd and the 5^th week, especially for the nHAp/CS scaffold. So far, the scCO₂ method enabled the production of a cost-effective and environment-friendly ready-to-use nHAp/CS scaffold with microstructural, chemical, mechanical and biocompatibility features that make it a suitable bone graft alternative for defect sites in an adverse environment as in periodontitis and peri-implantitis.

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

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

Robocasting and Laser Micromachining of Sol-Gel Derived 3D Silica/Gelatin/β-TCP Scaffolds for Bone Tissue Regeneration

The design and synthesis of sol-gel silica-based hybrid materials and composites offer significant benefits to obtain innovative biomaterials with controlled porosity at the nanostructure level for applications in bone tissue engineering. In this work, the combination of robocasting with sol-gel ink of suitable viscosity prepared by mixing tetraethoxysilane (TEOS), gelatin and β-tricalcium phosphate (β-TCP) allowed for the manufacture of 3D scaffolds consisting of a 3D square mesh of interpenetrating rods, with macropore size of 354.0 ± 17.0 μm, without the use of chemical additives at room temperature. The silica/gelatin/β-TCP system underwent irreversible gelation, and the resulting gels were also used to fabricate different 3D structures by means of an alternative scaffolding method, involving high-resolution laser micromachining by laser ablation. By this way, 3D scaffolds made of 2 mm thick rectangular prisms presenting a parallel macropore system drilled through the whole thickness and consisting of laser micromachined holes of 350.8 ± 16.6-micrometer diameter, whose centers were spaced 1312.0 ± 23.0 μm, were created. Both sol-gel based 3D scaffold configurations combined compressive strength in the range of 2–3 MPa and the biocompatibility of the hybrid material. In addition, the observed Si, Ca and P biodegradation provided a suitable microenvironment with significant focal adhesion development, maturation and also enhanced in vitro cell growth. In conclusion, this work successfully confirmed the feasibility of both strategies for the fabrication of new sol-gel-based hybrid scaffolds with osteoconductive properties.

Incorporation of NGR1 promotes bone regeneration of injectable HA/nHAp hydrogels by anti-inflammation regulation via a MAPK/ERK signaling pathway

Suitable bone grafts are commonly required to achieve successful bone regeneration, wherein much effort has been spent to optimize their osteogenesis. Increasing evidence has demonstrated that reducing the levels of TNF-α can enhance bone regeneration at the injury site. Notoginsenoside R1 (NGR1) has been extensively studied in the field of anti-inflammation and regenerative medicine. Nanosized hydroxyapatite (nHAp) possesses excellent biocompatibility and osteoconductivity. In this study, we fabricated a thermoresponsive, injectable hyaluronic acid/nHAp (HA/nHAp) composite hydrogel incorporated with NGR1 to promote bone regeneration. Furthermore, NGR1-HA/nHAp hydrogel could enhance bone regeneration than those of HA and HA/nHAp hydrogels, profited by the underlying osteoblastic mechanism that NGR1 could facilitate activation of the MAPK/ERK signaling pathway and down-regulate the expression of TNF-α, ultimately upregulated expression of osteogenic genes. In summary, the NGR1-HA/nHAp composite hydrogel with controlled inflammation, and excellent osteogenic effect, will have great potential for use in bone regeneration applications.

Preparation of High Mechanical Strength Chitosan Nanofiber/NanoSiO2/PVA Composite Scaffolds for Bone Tissue Engineering Using Sol-Gel Method

The majority of chitosan-based bone tissue engineering (BTE) scaffolds have the problem of poor mechanical properties. However, modifying chitosan with conventional silane coupling agents to improve the mechanical properties of scaffolds will introduce additional complications, including cytotoxicity and poor biocompatibility. In this study, two types of organic−inorganic composite scaffolds (F-A-T0/T3/T5 and F-B-T5-P0/P0.5/P1.5/P2.5) were prepared using chitosan nanofibers (CSNF) prepared by the beating-homogenization method, combined with the sol−gel method, and further introduced polyvinyl alcohol (PVA). The F-A-T3 and F-B-T5-P1.5 exhibited interconnected pore and surface nanofibers structures, high porosity (>70%), outstanding swelling properties, and a controllable degradation rate. The Young’s modulus of TEOS: 5.0% (w/w), PVA: 1.5% (w/w) chitosan fiber scaffold is 8.53 ± 0.43 MPa in dry conditions, and 237.78 ± 8.86 kPa in wet conditions, which is four times that of F-A-T5 and twice that of F-B-T5-P0. Additionally, cell (MC3T3-E1) experiments confirmed that the two composite scaffolds had great cytocompatibility and were predicted to be used in the future in the field of BTE scaffolds.

(Bio)manufactured Solutions for Treatment of Bone Defects with Emphasis on US-FDA Regulatory Science Perspective

Bone defects, with second highest demand for surgeries around the globe, may lead to serious health issues and negatively influence patient lives. The advances in biomedical engineering and sciences have led to the development of several creative solutions for bone defect treatment. This review provides a brief summary of bone graft materials, an organized overview of top-down and bottom-up (bio)manufacturing approaches, plus a critical comparison between advantages and limitations of each method. We specifically discuss additive manufacturing techniques and their operation mechanisms in detail. Next, we review the hybrid methods and promising future directions for bone grafting, while giving a comprehensive US-FDA regulatory science perspective, biocompatibility concepts and assessments, and clinical considerations to translate a technology from a research laboratory to the market. The topics covered in this review could potentially fuel future research efforts in bone tissue engineering, and perhaps could also provide novel insights for other tissue engineering applications.

Design and properties of graded polyamide12/hydroxyapatite scaffolds based on primitive lattices using selective laser sintering

Scaffolds with favorable biological characteristics and controlled functional gradient architectures are preferable for the repair of damaged tissues in bone tissue engineering. In this study, the triply periodic minimal surfaces (TPMS) were introduced to design functional gradient porous scaffolds based on Primitive lattices which were then manufactured by selective laser sintering (SLS) using pure polyamide12 (PA12) material and PA12/hydroxyapatite (HA) composite material. The mechanical properties and permeability of the scaffolds were then evaluated by mechanical compression experiments and computational fluid dynamics (CFD) analysis. The radial-graded scaffold was found to have superior good mechanical properties and permeability and be favorable for the subsequent growth of bone tissue. Further, the optimal PA12/HA composition was determined by analyzing the effect of the addition of HA particles on the hydrophilicity and mechanical properties of the composite scaffold. Additionally, the cytotoxicity tests were performed to evaluate the effects of PA12/HA gradient scaffold on cell growth. The obtained results demonstrate that the radial gradient scaffold with 15% HA addition exhibits a feasible combination of comprehensive performance and biological activity, indicating a great application potential in the field of bone tissue engineering.

Additive Manufacturing of Biopolymers for Tissue Engineering and Regenerative Medicine: An Overview, Potential Applications, Advancements, and Trends

As a technique of producing fabric engineering scaffolds, three-dimensional (3D) printing has tremendous possibilities. 3D printing applications are restricted to a wide range of biomaterials in the field of regenerative medicine and tissue engineering. Due to their biocompatibility, bioactiveness, and biodegradability, biopolymers such as collagen, alginate, silk fibroin, chitosan, alginate, cellulose, and starch are used in a variety of fields, including the food, biomedical, regeneration, agriculture, packaging, and pharmaceutical industries. The benefits of producing 3D-printed scaffolds are many, including the capacity to produce complicated geometries, porosity, and multicell coculture and to take growth factors into account. In particular, the additional production of biopolymers offers new options to produce 3D structures and materials with specialised patterns and properties. In the realm of tissue engineering and regenerative medicine (TERM), important progress has been accomplished; now, several state-of-the-art techniques are used to produce porous scaffolds for organ or tissue regeneration to be suited for tissue technology. Natural biopolymeric materials are often better suited for designing and manufacturing healing equipment than temporary implants and tissue regeneration materials owing to its appropriate properties and biocompatibility. The review focuses on the additive manufacturing of biopolymers with significant changes, advancements, trends, and developments in regenerative medicine and tissue engineering with potential applications.

Fabrication and applications of bioactive chitosan-based organic-inorganic hybrid materials: A review

Organic-inorganic hybrid materials like bone, shells, and teeth can be found in nature, which are usually composed of biomacromolecules and nanoscale inorganic ingredients. Synergy of organic-inorganic components in hybrid materials render them outstanding and versatile performance. Chitosan is commonly used organic materials in bionic hybrid materials since its bioactive properties and could be controllable tailored by various means to meet complex conditions in different applications. Among these fabrication means, hybridization was favored for its convenience and efficiency. This review discusses three kinds of chitosan-based hybrid materials: hybridized with hydroxyapatite, calcium carbonate, and clay respectively, which are the representative of phosphate, carbonate, and hydrous aluminosilicates. Here, we reported the latest developments of the preparation methods, composition, structure and applications of these bioactive hybrid materials, especially in the biomedical field. Despite the great progress was made in bioactive organic-inorganic hybrid materials based on chitosan, some challenges and specific directions are still proposed for future development in this review.

Chitosan-based 3D-printed scaffolds for bone tissue engineering

Despite the spontaneous regenerative properties of autologous bone grafts, this technique remains dilatory and restricted to fractures and injuries. Conventional grafting strategies used to treat bone tissue damage have several limitations. This highlights the need for novel approaches to overcome the persisting challenges. Tissue-like constructs that can mimic natural bone structurally and functionally represent a promising strategy. Bone tissue engineering (BTE) is an approach used to develop bioengineered bone with subtle architecture. BTE utilizes biomaterials to accommodate cells and deliver signaling molecules required for bone rejuvenation. Among the various techniques available for scaffold creation, 3D-printing technology is considered to be a superior technique as it enables the design of functional scaffolds with well-defined customizable properties. Among the biomaterials obtained from natural, synthetic, or ceramic origins, naturally derived chitosan (CS) polymers are promising candidates for fabricating reliable tissue constructs. In this review, the physicochemical-biological properties and applications of CS-based 3D-printed scaffolds and their future perspectives in BTE are summarized.

Synthesis of an organic-inorganic hybrid with short organic molecular chains by sol-gel chemistry

An oligomer with short organic molecular chains was successfully synthesized with KH550 and KH560. This oligomer was combined with tetraethyl orthosilicate and calcium chloride to prepare an organic-inorganic hybrid biological material (OI-BM) by sol-gel chemistry. The hybrid was fully characterized by a series of instrumental characterizations including nuclear magnetic resonance spectrometry, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray energy spectroscopy and inductively coupled plasma spectrometry. OI-BM presented elastic deformation under compression. The elastic modulus and ultimate stress of OI-BM were 0.4 ± 0.1 GPa and 23.0 ± 4.0 MPa, respectively, lower than those of 45S5 bioactive glass (45S5-BG), whereas the strain at failure and modulus of toughness of OI-BM was about 4.5 times and 4 times higher. The hybrid is easy to form due to the improved mechanical property, suggesting excellent machining properties. The hybrid OI-BM produced hydroxyapatite in 1 h in simulated body fluid due to its excellent bioactivity. CCK-8 assay further demonstrated the desirable cytocompatibility of the hybrid. Thus, the hybrid can be a potential material for satisfying the mechanical property requirement of an implant.

Mechanical, Structural, and Biological Properties of Chitosan/Hydroxyapatite/Silica Composites for Bone Tissue Engineering

The aim of this work was to fabricate novel bioactive composites based on chitosan and non-organic silica, reinforced with calcium β-glycerophosphate (Ca-GP), sodium β-glycerophosphate pentahydrate (Na-GP), and hydroxyapatite powder (HAp) in a range of concentrations using the sol–gel method. The effect of HAp, Na-GP, and Ca-GP contents on the mechanical properties, i.e., Young’s modulus, compressive strength, and yield strain, of hybrid composites was analyzed. The microstructure of the materials obtained was visualized by SEM. Moreover, the molecular interactions according to FTIR analysis and biocompatibility of composites obtained were examined. The CS/Si/HAp/Ca-GP developed from all composites analyzed was characterized by the well-developed surface of pores of two sizes: large ones of 100 μm and many smaller pores below 10 µm, the behavior of which positively influenced cell proliferation and growth, as well as compressive strength in a range of 0.3 to 10 MPa, Young’s modulus from 5.2 to 100 MPa, and volumetric shrinkage below 60%. This proved to be a promising composite for applications in tissue engineering, e.g., filling small bone defects.

Three-Dimensional Printing of Hydroxyapatite Composites for Biomedical Application

Hydroxyapatite (HA) and HA-based nanocomposites have been recognized as ideal biomaterials in hard tissue engineering because of their compositional similarity to bioapatite. However, the traditional HA-based nanocomposites fabrication techniques still limit the utilization of HA in bone, cartilage, dental, applications, and other fields. In recent years, three-dimensional (3D) printing has been shown to provide a fast, precise, controllable, and scalable fabrication approach for the synthesis of HA-based scaffolds. This review therefore explores available 3D printing technologies for the preparation of porous HA-based nanocomposites. In the present review, different 3D printed HA-based scaffolds composited with natural polymers and/or synthetic polymers are discussed. Furthermore, the desired properties of HA-based composites via 3D printing such as porosity, mechanical properties, biodegradability, and antibacterial properties are extensively explored. Lastly, the applications and the next generation of HA-based nanocomposites for tissue engineering are discussed.

The effect of Allium cepa extract on the chitosan/PLGA scaffolds bioactivity

Allium cepa extracts (AC) allow the fabrication of a biomaterial that, together with chitosan and PLGA, could be osteoconductive and promote a better and faster regeneration of bone tissue, with biocompatibility and biomineralization properties. In this work, scaffolds were developed by the thermally induced phase separation (TIPS) technique. An in vitro bioactivity analysis was performed using simulated body fluid (SBF). Scanning electron microscopy (SEM), energy dispersion spectroscopy, and infrared spectroscopy were used for the scaffolds characterization. The results showed a structure with a pore size distribution between 50 and 100 μm, which allowed the uniform formation of biological apatite crystals on the surface of the scaffolds. The chitosan/policaprolactone/Allium cepa scaffold (ChPAC) showed the most promising results with a ratio of P/Ca between 1.6 and 1.7, a value very close to that of hydroxyapatite.

Chitosan-Hydroxyapatite Composite Layers Generated in Radio Frequency Magnetron Sputtering Discharge: From Plasma to Structural and Morphological Analysis of Layers

Chitosan-hydroxyapatite composite layers were deposited on Si substrates in radio frequency magnetron sputtering discharges. The plasma parameters calculated from the current-voltage radio frequency-compensated Langmuir probe characteristics indicate a huge difference between the electron temperature in the plasma and at the sample holder. These findings aid in the understanding of the coagulation pattern of hydroxyapatite-chitosan macromolecules on the substrate surface. An increase in the sizes of the spherical-shape grain-like structures formed on the coating surface with the plasma electron number density was observed. The link between the chemical composition of the chitosan-hydroxyapatite composite film and the species sputtered from the target or produced by excitation/ionization mechanisms in the plasma was determined on the basis of X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and residual gas mass spectrometry analysis.

Hydroxyl Groups Induce Bioactivity in Silica/Chitosan Aerogels Designed for Bone Tissue Engineering. In Vitro Model for the Assessment of Osteoblasts Behavior

Silica (SiO2)/chitosan (CS) composite aerogels are bioactive when they are submerged in simulated body fluid (SBF), causing the formation of bone-like hydroxyapatite (HAp) layer. Silica-based hybrid aerogels improve the elastic behavior, and the combined CS modifies the network entanglement as a crosslinking biopolymer. Tetraethoxysilane (TEOS)/CS is used as network precursors by employing a sol-gel method assisted with high power ultrasound (600 W). Upon gelation and aging, gels are dried in supercritical CO2 to obtain monoliths. Thermograms provide information about the condensation of the remaining hydroxyl groups (400-700 °C). This step permits the evaluation of the hydroxyl group's content of 2 to 5 OH nm-2. The formed Si-OH groups act as the inductor of apatite crystal nucleation in SBF. The N2 physisorption isotherms show a hysteresis loop of type H3, characteristic to good interconnected porosity, which facilitates both the bioactivity and the adhesion of osteoblasts cells. After two weeks of immersion in SBF, a layer of HAp microcrystals develops on the surface with a stoichiometric Ca/P molar ratio of 1.67 with spherulite morphology and uniform sizes of 6 μm. This fact asserts the bioactive behavior of these hybrid aerogels. Osteoblasts are cultured on the selected samples and immunolabeled for cytoskeletal and focal adhesion expression related to scaffold nanostructure and composition. The initial osteoconductive response observes points to a great potential of tissue engineering for the designed composite aerogels.

Synergistic Fabrication of Dose-Response Chitosan/Dextran/β-Glycerophosphate Injectable Hydrogel as Cell Delivery Carrier for Cardiac Healing After Acute Myocardial Infarction

The human mesenchymal stem cells (hMSCs) therapy offering an encouraging the new methods to establish the conveying on the chitosan (C)/dextran (D)/β-glycerophosphate (β-GP) loaded with hMSCs to enhance the acute myocardial infarctions. The synthesized hMSCs-CD@β-GP system displayed the ratio of determination modules, size of the pore, absorbency, and the swellings ratio in the assortment of the 65 ka, 149 ± 39.8 µm, 92.2%, 42 ± 1.38, and 29 ± 1.9, respectively. The fabricated hMSCs-CD@β-GP was highly stable and physicochemical investigated and confirmed the suitability of the materials for cardiac regeneration applications. The in vitro examinations of the injectable hydrogels with hMSCs-CD@β-GP have recognized that the improved survival rate of the cells, increased the pro-inflammatory expressions factors, pro-angiogenic factors analysis confirmed the promising results of the ejection of fractions, fibrosis area, vessel density with decreased infractions size, with suggesting that the remarkable improvement of the heart regenerative function after myocardial infarctions. The new synergistic approach of the injectable hydrogels with hMSCs could able appropriate for the effective treatment of cardiac therapies after acute myocardial infarctions.

Robust and nanostructured chitosan-silica hybrids for bone repair application

In this study, chitosan-silica hybrids (CSHs) with superior mechanical strength and homogeneous dispersion of nano-sized silica particles were synthesized via a facile sol-gel method aiming for bone regeneration. The effects of varied acidic conditions of sol-gel reaction and inorganic/organic ratios on the performance of the hybrid were investigated. CSHs synthesized under weak acidic conditions (acetic acid, pH 4.0) showed a homogeneous nanostructure and robust strength (maximum compressive strength: 42.6 ± 3.3 MPa and 271 ± 31 MPa in wet and dry forms, respectively). However, those developed under the strong acidic condition (HCl, pH 4.0) and the strong acid condition plus lower pH (HCl, pH 2.8) tended to aggregate and exhibited inferior mechanical properties (compressive strength: 6.3 ± 0.3 MPa in wet form at pH 2.8). Under the latter conditions, the interactions between silica and chitosan were weak. Moreover, the mechanical properties of the CSHs could be tuned in a wide range by conveniently varying the inorganic/organic composition ratio between 50% and 70%. In vitro cytocompatibility study indicated that CSHs were non-cytotoxic. These results suggested that the weak acidic sol-gel process were essential for fabricating chitosan-silica hybrids with high mechanical strength, which had potential to be applied as a bone substitute.

Thyroxine-loaded chitosan/carboxymethyl cellulose/hydroxyapatite hydrogels enhance angiogenesis in in-ovo experiments

Angiogenesis is one of the most important processes in repair and regeneration of many tissues and organs. Blood vessel formation also play a major role in repair of dental tissue(s) after ailments like periodontitis. Here we report the preparation of chitosan/carboxymethyl cellulose/hydroxyapatite based hydrogels, loaded with variable concentrations of thyroxin i.e., 0.1 μg/ml, 0.5 μg/ml and 1 μg/ml. Scanning electron microcopy images (SEM) showed all hydrogels were found to be porous and solution absorption study exhibited high swelling potential in aqueous media. FTIR spectra confirmed that the used materials did not change their chemical identity in synthesized hydrogels. The synthesized hydrogels demonstrated good bending, folding, rolling and stretching abilities. The hydrogels were tested in chick chorioallantoic membrane (CAM) assay to investigate their angiogenic potential. Hydrogel containing 0.1 μg/ml of thyroxine showed maximum neovascularization. For cytotoxicity analyses, preosteoblast cells (MC3T3-E1) were seeded on these hydrogels and materials were found to be non-toxic. These hydrogels with pro-angiogenic activity possess great potential to be used for periodontal regeneration.

3D printing of a poly(vinyl alcohol)-based nano-composite hydrogel as an artificial cartilage replacement and the improvement mechanism of printing accuracy

A PVA-based composite hydrogel with a biomimetic gradient structure as an artificial cartilage replacement was constructed by an extrusion 3D printing technique.

Biocompatible Glycine-Assisted Catalysis of the Sol-Gel Process: Development of Cell-Embedded Hydrogels

The sol-gel process can be used for hydrogel cross-linking, thus opening an attractive route for the design of biocompatible hydrogels under soft conditions. The sol-gel process can be catalysed at basic or acidic pH values, under neutral conditions with the addition of a nucleophile. Therefore, working around pH 7 unlocks the possibility of direct cell embedment and the preparation of bioinks. We aimed to propose a generic method for sol-gel 3D bioprinting, and first screened different nucleophilic catalysts using bis-silylated polyethylene glycol (PEG) as a model hydrogel. A synergistic effect of glycine and NaF, used in low concentrations to avoid any toxicity, was observed. Biocompatibility of the approach was demonstrated by embedding primary mouse mesenchymal stem cells. The measure of viscosity as a function of time showed the impact of reaction parameters, such as temperature, complexity of the medium, pH and cell addition, on the kinetics of the sol-gel process, and allowed prediction of the gelation time.

Scaffolding Strategies for Tissue Engineering and Regenerative Medicine Applications

During the past two decades, tissue engineering and the regenerative medicine field have invested in the regeneration and reconstruction of pathologically altered tissues, such as cartilage, bone, skin, heart valves, nerves and tendons, and many others. The 3D structured scaffolds and hydrogels alone or combined with bioactive molecules or genes and cells are able to guide the development of functional engineered tissues, and provide mechanical support during in vivo implantation. Naturally derived and synthetic polymers, bioresorbable inorganic materials, and respective hybrids, and decellularized tissue have been considered as scaffolding biomaterials, owing to their boosted structural, mechanical, and biological properties. A diversity of biomaterials, current treatment strategies, and emergent technologies used for 3D scaffolds and hydrogel processing, and the tissue-specific considerations for scaffolding for Tissue engineering (TE) purposes are herein highlighted and discussed in depth. The newest procedures focusing on the 3D behavior and multi-cellular interactions of native tissues for further use for in vitro model processing are also outlined. Completed and ongoing preclinical research trials for TE applications using scaffolds and hydrogels, challenges, and future prospects of research in the regenerative medicine field are also presented.

Current Trends in Fabrication of Biomaterials for Bone and Cartilage Regeneration: Materials Modifications and Biophysical Stimulations

The aim of engineering of biomaterials is to fabricate implantable biocompatible scaffold that would accelerate regeneration of the tissue and ideally protect the wound against biodevice-related infections, which may cause prolonged inflammation and biomaterial failure. To obtain antimicrobial and highly biocompatible scaffolds promoting cell adhesion and growth, materials scientists are still searching for novel modifications of biomaterials. This review presents current trends in the field of engineering of biomaterials concerning application of various modifications and biophysical stimulation of scaffolds to obtain implants allowing for fast regeneration process of bone and cartilage as well as providing long-lasting antimicrobial protection at the site of injury. The article describes metal ion and plasma modifications of biomaterials as well as post-surgery external stimulations of implants with ultrasound and magnetic field, providing accelerated regeneration process. Finally, the review summarizes recent findings concerning the use of piezoelectric biomaterials in regenerative medicine.

The summary of the most important cell-biomaterial interactions that need to be considered during in vitro biocompatibility testing of bone scaffolds for tissue engineering applications

Tissue engineered products (TEPs), which mean biomaterials containing either cells or growth factors or both cells and growth factors, may be used as an alternative to the autografts taken directly from the bone of the patients. Nevertheless, the use of TEPs needs much more understanding of biointeractions between biomaterials and eukaryotic cells. Despite the possibility of the use of in vitro cellular models for initial evaluation of the host response to the implanted biomaterial, it is observed that most researchers use cell cultures only for the evaluation of cytotoxicity and cell proliferation on the biomaterial surface, and then they proceed to animal models and in vivo testing of bone implants without fully utilizing the scientific potential of in vitro models. In this review, the most important biointeractions between eukaryotic cells and biomaterials were discussed, indicating molecular mechanisms of cell adhesion, proliferation, and biomaterial-induced activation of immune cells. The article also describes types of cellular models which are commonly used for biomaterial testing and highlights the possibilities and drawbacks of in vitro tests for biocompatibility evaluation of novel scaffolds. Finally, the review summarizes recent findings concerning the use of adult mesenchymal stem cells for TEP generation and compares the potential of bone marrow- and adipose tissue-derived stem cells in regenerative medicine applications.

Preparation and Enrichment Properties of Magnetic Dodecyl Chitosan/Silica Composite for Emerging Bisphenol Contaminants

Magnetic dodecyl chitosan/silica composite was synthesized and characterized for the enrichment of emerging bisphenol contaminants. The result demonstrated that bispehnol A, bisphenol AF, bisphenol F, and bisphenol S can be efficiently extracted via the resulting composite from aqueous solution. The adsorption rate of four investigated bisphenols on the resulting composite was achieved in the range of 87⁻99% within 15 min. Bispehnol A was taken as a representative adsorbate to investigate the adsorption studies in detail. The hydrophobic interaction was proposed as the principal mechanism for the adsorption of BPs. The satisfactory reusability of the resulting composite can be quickly achieved by magnetic separation technologies. Magnetic dodecyl chitosan/silica composite has a potential to be applied as a type of efficient and easily recyclable sorbent for the removal of trace organic pollutants from aqueous sample.