A novel two-step sintering for nano-hydroxyapatite scaffolds for bone tissue engineering

Bioactivity, hemocompatibility, and inflammatory response of calcium incorporated sulfonated polyether ether ketone on mouse-derived bone marrow cells

Natural and synthetic polymeric materials, particularly soft and hard tissue replacements, are paramount in medicine. We prepared calcium-incorporated sulfonated polyether-ether ketone (SPEEK) polymer membranes for bone applications. The bioactivity was higher after 21 days of immersion in simulated body fluid (SBF) due to calcium concentration in the membrane. We present a new biomaterial healing system composed of calcium and sulfonated polyether ether ketone (Ca-SPEEK) that can function as a successful biomaterial without causing inflammation when tested on bone marrow cells. The Ca-SPEEK exhibited 13 ± 0.5% clot with low fibrin mesh formation compared to 21 ± 0.5% in SPEEK. In addition, the Ca-SPEEK showed higher protein adsorption than SPEEK membranes. As an inflammatory response, IL-1 and TNF-α in the case of Ca-SPEEK were lower than those for SPEEK. We found an early regulation of IL-10 in the case of Ca-SPEEK at 6 h, which may be attributed to the down-regulation of the inflammatory markers IL-1 and TNF-α. These results evidence the innovative bioactivity of Ca-SPEEK with low inflammatory response, opening venues for bone applications.

Fabrication of Novel 3-D Nanocomposites of HAp-TiC-h-BN-ZrO2: Enhanced Mechanical Performances and In Vivo Toxicity Study for Biomedical Applications

Due to excellent biocompatibility, bioactivities, and osteoconductivity, hydroxyapatite (HAp) is considered as one of the most suitable biomaterials for numerous biomedical applications. Herein, HAp was fabricated using a bottom-up approach, i.e., a wet chemical method, and its composites with TiC, h-BN, and ZrO2 were fabricated by a solid-state reaction method with enhanced mechanical and biological performances. Structural, surface morphology, and mechanical behavior of the fabricated composites were characterized using various characterization techniques. Furthermore, transmission electron microscopy study revealed a randomly oriented rod-like morphology, with the length and width of these nanorods ranging from 78 to 122 and from 9 to 13 nm. Moreover, the mechanical characterizations of the composite HZBT4 (80HAp-10TiC-5h-BN-5ZrO2) reveal a very high compressive strength (246 MPa), which is comparable to that of the steel (250 MPa), fracture toughness (14.78 MPa m1/2), and Young's modulus (1.02 GPa). In order to check the biocompatibility of the composites, numerous biological tests were also performed on different body organs of healthy adult Sprague-Dawley rats. This study suggests that the composite HZBT4 could not reveal any significant influence on the hematological, serum biochemical, and histopathological parameters. Hence, the fabricated composite can be used for several biological applications, such as bone implants, bone grafting, and bone regeneration.

Bioengineered cartilaginous grafts for repairing segmental mandibular defects

Reconstructing critical-sized craniofacial bone defects is a global healthcare challenge. Current methods, like autologous bone transplantation, face limitations. Bone tissue engineering offers an alternative to autologous bone, with traditional approaches focusing on stimulating osteogenesis via the intramembranous ossification (IMO) pathway. However, IMO falls short in addressing larger defects, particularly in clinical scenarios where there is insufficient vascularisation. This review explores redirecting bone regeneration through endochondral ossification (ECO), a process observed in long bone healing stimulated by hypoxic conditions. Despite its promise, gaps exist in applying ECO to bone tissue engineering experiments, requiring the elucidation of key aspects such as cell sources, biomaterials and priming protocols. This review discusses various scaffold biomaterials and cellular sources for chondrogenesis and hypertrophic chondrocyte priming, mirroring the ECO pathway. The review highlights challenges in current endochondral priming and proposes alternative approaches. Emphasis is on segmental mandibular defect repair, offering insights for future research and clinical application. This concise review aims to advance bone tissue engineering by addressing critical gaps in ECO strategies.

Enzymatically-mineralized double-network hydrogels with ultrahigh mechanical strength, toughness, and stiffness

Background: Synthetic hydrogels are commonly mechanically weak which limits the scope of their applications. Methods: In this study, we synthesized an organic-inorganic hybrid hydrogel with ultrahigh strength, stiffness, and toughness via enzyme-induced mineralization of calcium phosphate in a double network of bacterial cellulose nanofibers and alginate-Ca²⁺. Results: Cellulose nanofibers formed the first rigid network via hydrogen binding and templated the deposition of calcium phosphate, while alginate-Ca²⁺ formed the second energy-dissipating network via ionic interaction. The two networks created a brick-mortar-like structure, in which the "tortuous fracture path" mechanism by breaking the interlaced calcium phosphate-coated bacterial cellulose nanofibers and the hysteresis by unzipping the ionic alginate-Ca²⁺ network made a great contribution to the mechanical properties of the hydrogels. Conclusion: The optimized hydrogel exhibited ultrahigh fracture stress of 48 MPa, Young's modulus of 1329 MPa, and fracture energy of 3013 J/m², which are barely possessed by the reported synthetic hydrogels. Finally, the hydrogel represented potential use in subchondral bone defect repair in an ex vivo model.

Evaluation of the mechanical properties of hydroxyapatite-silica aerogel/epoxy nanocomposites: Optimizing by response surface approach

This study attempted to investigate the effects of adding hydroxyapatite and silica aerogel nanoparticles on the density, tensile, Izod impact, and morphological properties of epoxy using the Response Surface Methodology (RSM). RSM relied on Box-Behnken Design (BBD) was used to design the mechanical tests. The concurrent effects of two parameters including hydroxyapatite content and silica aerogels content on the mechanical properties have been evaluated. Finally, by using the equations obtained from regression for each of the responses, their optimal states were obtained using both the desirability approach and the Multi-Objective Particle Swarm Optimization (MOPSO) method. The results from tensile, and Izod impact tests indicated the combination of hydroxyapatite and silica aerogel nanoparticles led to an improvement in the tensile properties and energy absorption of epoxy matrix. The findings related to density test demonstrated that with addition of silica aerogel to the hydroxyapatite/epoxy nanocomposites, density of these samples was decreased. The maximum tensile strength of 86.9 MPa was obtained with hydroxyapatite content of 2.38 wt% and silica aerogels content of 4 wt%. Also, the maximum impact strength of 18.14 kJ/m2 was obtained with hydroxyapatite content of 1.11 wt% and silica aerogels content of 3.51 wt%. The field emission scanning electron microscope images showed the homogeneous distribution of combined hydroxyapatite and silica aerogel nanoparticles in epoxy matrix, except in 5 wt% of hydroxyapatite nanoparticles.

Advancement in "Garbage In Biomaterials Out (GIBO)" concept to develop biomaterials from agricultural waste for tissue engineering and biomedical applications

Presently on a global scale, one of the major concerns is to find effective strategies to manage the agricultural waste to protect the environment. One strategy that has been drawing attention among the researchers is the development of biocompatible materials from agricultural waste. This strategy implies successful conversion of agricultural waste products (e.g.: cellulose, eggshell etc.) into building blocks for biomaterial development. Some of these wastes contain even bioactive compounds having biomedical applications. The replacement and augmentation of human tissue with biomaterials as alternative to traditional method not only bypasses immune-rejection, donor scarcity, and maintenance; but also provides long term solution to damaged or malfunctioning organs. Biomaterials development as one of the key challenges in tissue engineering approach, resourced from natural origin imparts better biocompatibility due to closely mimicking composition with cellular microenvironment. The "Garbage In, Biomaterials Out (GIBO)" concept, not only recycles the agricultural wastes, but also adds to biomaterial raw products for further product development in tissue regeneration. This paper reviews the conversion of garbage agricultural by-products to the biocompatible materials for various biomedical applications.

Graphical abstract

The agro-waste biomass processed, purified, modified, and further utilized for the fabrication of biomaterials-based support system for tissue engineering applications to grow living body parts in vitro or in vivo.

Calcium Orthophosphate (CaPO4)-Based Bioceramics: Preparation, Properties, and Applications

Various types of materials have been traditionally used to restore damaged bones. In the late 1960s, a strong interest was raised in studying ceramics as potential bone grafts due to their biomechanical properties. A short time later, such synthetic biomaterials were called bioceramics. Bioceramics can be prepared from diverse inorganic substances, but this review is limited to calcium orthophosphate (CaPO4)-based formulations only, due to its chemical similarity to mammalian bones and teeth. During the past 50 years, there have been a number of important achievements in this field. Namely, after the initial development of bioceramics that was just tolerated in the physiological environment, an emphasis was shifted towards the formulations able to form direct chemical bonds with the adjacent bones. Afterwards, by the structural and compositional controls, it became possible to choose whether the CaPO4-based implants would remain biologically stable once incorporated into the skeletal structure or whether they would be resorbed over time. At the turn of the millennium, a new concept of regenerative bioceramics was developed, and such formulations became an integrated part of the tissue engineering approach. Now, CaPO4-based scaffolds are designed to induce bone formation and vascularization. These scaffolds are usually porous and harbor various biomolecules and/or cells. Therefore, current biomedical applications of CaPO4-based bioceramics include artificial bone grafts, bone augmentations, maxillofacial reconstruction, spinal fusion, and periodontal disease repairs, as well as bone fillers after tumor surgery. Prospective future applications comprise drug delivery and tissue engineering purposes because CaPO4 appear to be promising carriers of growth factors, bioactive peptides, and various types of cells.

Gelatin-based electrospun and lyophilized scaffolds with nano scale feature for bone tissue engineering application: review

The rebuilding of the normal functioning of the damaged human body bone tissue is one of the main objectives of bone tissue engineering (BTE). Fabricated scaffolds are mostly treated as artificial supports and as materials for regeneration of neo bone tissues and must closely biomimetic the native extracellular matrix of bone. The materials used for developing scaffolds should be biodegradable, nontoxic, and biocompatible. For the resurrection of bone disorder, specifically natural and synthetic polymers such as chitosan, PCL, gelatin, PGA, PLA, PLGA, etc. meet the requirements for serving their functions as artificial bone substitute materials. Gelatin is one of the potential candidates which could be blended with other polymers or composites to improve its physicochemical, mechanical, and biological performances as a bone graft. Scaffolds are produced by several methods including electrospinning, self-assembly, freeze-drying, phase separation, fiber drawing, template synthesis, etc. Among them, freeze-drying and electrospinning are among the popular, simplest, versatile, and cost-effective techniques. The design and preparation of freeze-dried and electrospun scaffolds are of intense research over the last two decades. Freeze-dried and electrospun scaffolds offer a distinctive architecture at the micro to nano range with desired porosity and pore interconnectivity for selective movement of small biomolecules and play its role as an appropriate matrix very similar to the natural bone extracellular matrix. This review focuses on the properties and functionalization of gelatin-based polymer and its composite in the form of bone scaffolds fabricated primarily using lyophilization and electrospinning technique and their applications in BTE.

Physical, chemical, and biological investigations of composites for biomedical applications

In this article, the interplay between structural, electrical, and surface properties in determining the collective behavior of(hydroxyapatite, HAP) and(strontium titanate, ST) composites was reported. The monoliths HAP and ST were synthesized using sol‐gel and solid‐state reaction, respectively, and were mixed in different atomic concentrations (20, 40, 60, and 80 at.%) to prepare a series of composites. The prepared composites were then subjected to x‐ray diffraction (XRD) and Raman analysis for probing the microstructural aspects. The analysis revealed no evidence of a phase that the reaction between the two monoliths might form. The crystallite sizes were in the range of 27.2–37.3 nm, and it increased with the content of ST in the composites. The Raman analysis revealed the presence of rutilethat was later found to be the link in the display of bone‐like apatite nucleation ability in the monolith ST and its composites. The FESEM analysis revealed that the grain sizes were 64–144 nm between the monoliths and were found to follow a similar trend to the crystallite size. The dielectric constantvaried with temperature ranging from 5 to 35 (1 MHz) at 310 K for all the specimens. The dependence ofon the grain size of the composites followed a nearly exponential relation. The bone‐like apatite forming ability of the composites was studied by incubating the specimens in simulated body fluid (SBF). Additionally, the cytocompatibility (MG63 cell lines) and protein adsorption (bovine serum albumin [BSA]) of the selected specimens were also studied to comprehensively understand the delicate relationship between the electrical and biological properties. The protein adsorption was primarily related to the surface charge, and its dependence was found to be linear. Additionally, theof the composites was ≤35, which compliments the protein adsorption behavior of the specimens. The amount of adsorbed protein for all the specimens considered in this study was in the range of 3–32μ g/ml. Furthermore, the specimens exhibited excellent cell viability of more than 90%. Based on the physical and biological investigations, 20H‐80S was established as the best specimen that blends the characteristic feature of both the monoliths. Finally, the TEM and STEM mapping of the best specimen, projecting the suitability of 20H‐80S in the design of electrically active scaffolds and possibly bioelectrets for biomedical applications, was also studied.

High-performance bilayer composites for the replacement of osteochondral defects

Two novel bilayer constructs for the repair of osteochondral defects were developed from nanofibers and ceramic particles embedded into PVA matrices, exhibiting multiple promising properties similar to those of corresponding natural tissues.

Microstructural, electrical and biological activity in [Formula: see text] ceramic composites designed for tissue engineering applications

The article investigates electrically active ceramic composite of [Formula: see text] (HAP) and [Formula: see text] (BST) for biomedical applications. The study is a systematic blend of the materials science aspect of composites with a special focus on the dielectric and biological properties and their relationships. The article emphasized primarily extracting the dielectric constant ([Formula: see text] of the specimens (that lay in the range of 3-65) and related them to microstructural properties like the grain size and at.% of BST. A broad outlook on the importance of [Formula: see text] in determining the suitability of bioceramics for clinical applications is presented. Bioactivity analysis of the specimens led to probing the surface charges (that were negative), and it was found crucial to the growth of dense apatite layers. Furthermore, the cytocompatibility of the specimens displayed cell viability above 100% for Day 1, which increased substantially for Day 3. To reveal other biological properties of the composites, protein adsorption studies using bovine serum albumin (BSA) and fetal bovine serum (FBS) was carried out. Electrostatic interactions govern the adsorption, and the mathematical dependence on surface charges is linear. The protein adsorption is also linearly correlated with the [Formula: see text], intrinsic to the biomaterials. We delve deeper into protein-biomaterials interactions by considering the evolution of the secondary structure of BSA adsorbed into the specimens. Based on the investigations, 20 at.% HAP-80 at.% BST (20H-80B) was established as a suitable composite comprising the desired features of HAP and BST. Such explorations of electrical and biological properties are interesting for modulating the behavior of bioceramic composites. The results project the suitability of 20H-80B for designing electrically active smart scaffolds for the proposed biomedical applications and are expected to incite further clinical trials.

Selective Laser Melting of Hydroxyapatite: Perspectives for 3D Printing of Bioresorbable Ceramic Implants

Hydroxyapatite, being the major mineral component of tooth enamel and natural bones, is a good candidate for bone tissue engineering applications. One of the promising approaches for manufacturing of three-dimensional objects is selective laser sintering/melting which enables the creation of a dense structure directly during 3D printing by adding material layer-by-layer. The effect of laser irradiation with a wavelength of 10.6 μm on the behavior of mechanochemically synthesized hydroxyapatite under different treatment conditions was studied for the first time in this work. It was shown that, in contrast to laser treatment, the congruent melting is impossible under conditions of a relatively slow rate of heating in a furnace. Depending on the mode of laser treatment, hydroxyapatite can be sintered or melted, or partially decomposed into the more resorbable calcium phosphates. It was found that the congruent selective laser melting of hydroxyapatite can be achieved by treating the dense powder layer with a 0.2 mm laser spot at a power of 4 W and at a scanning speed of 700 mm/s. Melting was shown to be accompanied by the crystallization of a dense monolayer of oxyhydroxyapatite while preserving the initial apatite crystal lattice. The thickness of the melted layer, the presence of micron-sized pores, and the phase composition can be controlled by varying the scanning speed and laser power. This set of parameters permits the use of selective laser melting technology for the production of oxyhydroxyapatite biodegradable implants with acceptable properties by 3D printing.

Construction of Inorganic Bulks through Coalescence of Particle Precursors

Bulk inorganic materials play important roles in human society, and their construction is commonly achieved by the coalescence of inorganic nano- or micro-sized particles. Understanding the coalescence process promotes the elimination of particle interfaces, leading to continuous bulk phases with improved functions. In this review, we mainly focus on the coalescence of ceramic and metal materials for bulk construction. The basic knowledge of coalescent mechanism on inorganic materials is briefly introduced. Then, the properties of the inorganic precursors, which determine the coalescent behaviors of inorganic phases, are discussed from the views of particle interface, size, crystallinity, and orientation. The relationships between fundamental discoveries and industrial applications are emphasized. Based upon the understandings, the applications of inorganic bulk materials produced by the coalescence of their particle precursors are further presented. In conclusion, the challenges of particle coalescence for bulk material construction are presented, and the connection between recent fundamental findings and industrial applications is highlighted, aiming to provide an insightful outlook for the future development of functional inorganic materials.

Recent Developments of Biomaterials for Additive Manufacturing of Bone Scaffolds

Recent years have witnessed surging demand for bone repair/regeneration implants due to the increasing number of bone defects caused by trauma, cancer, infection, and arthritis worldwide. In addition to bone autografts and allografts, biomaterial substitutes have been widely used in clinical practice. Personalized implants with precise and personalized control of shape, porosity, composition, surface chemistry, and mechanical properties will greatly facilitate the regeneration of bone tissue and satiate the clinical needs. Additive manufacturing (AM) techniques, also known as 3D printing, are drawing fast growing attention in the fabrication of implants or scaffolding materials due to their capability of manufacturing complex and irregularly shaped scaffolds in repairing bone defects in clinical practice. This review aims to provide a comprehensive overview of recent progress in the development of materials and techniques used in the additive manufacturing of bone scaffolds. In addition, clinical application, pre-clinical trials and future prospects of AM based bone implants are also summarized and discussed.

Nature-inspired topographies on hydroxyapatite surfaces regulate stem cells behaviour

Surface topography is one of the key factors in regulating interactions between materials and cells. While topographies presented to cells in vivo are non-symmetrical and in complex shapes, current fabrication techniques are limited to replicate these complex geometries. In this study, we developed a microcasting technique and successfully produced imprinted hydroxyapatite (HAp) surfaces with nature-inspired (honeycomb, pillars, and isolated islands) topographies. The in vitro biological performance of the developed non-symmetrical topographies was evaluated using adipose-derived stem cells (ADSCs). We demonstrated that ADSCs cultured on all HAp surfaces, except honeycomb patterns, presented well-defined stress fibers and expressed focal adhesion protein (paxillin) molecules. Isolated islands topographies significantly promoted osteogenic differentiation of ADSCs with increased alkaline phosphatase activity and upregulation of key osteogenic markers, compared to the other topographies and the control unmodified (flat) HAp surface. In contrast, honeycomb topographies hampered the ability of the ADSCs to proliferate and differentiate to the osteogenic lineage. This work presents a facile technique to imprint nature-derived topographies on the surface of bioceramics which opens up opportunities for the development of bioresponsive interfaces in tissue engineering and regenerative medicine.

Study of Mechanical and Thermal Properties in Nano-Hydroxyapatite/Chitosan/Carboxymethyl Cellulose Nanocomposite-Based Scaffold for Bone Tissue Engineering: The Roles of Carboxymethyl Cellulose

Synthetic scaffolding for bone tissue engineering (BTE) has been widely utilized. The scaffold for BTE requires sufficient porosity as a template for bone cell development and growth so that it can be used in the treatment of bone defects and fractures. Nevertheless, the porosity significantly influences the compressive strength of the scaffold. Hence, controlling the porosity is a pivotal role to obtain a proper scaffold for practical BTE application. Herein, we fabricated the nanocomposite-based scaffold utilizing nano-hydroxyapatite (n-HA). The scaffold was prepared in combination with chitosan (Ch) and carboxymethyl cellulose (CMC). The ratios of n-HA, Ch, and CMC used were 40:60:0, 40:55:5, 40:50:10, 40:45:15, and 40:40:20, respectively. By controlling the Ch and CMC composition, we can tune the porosity of the nanocomposite. We found that the interpolation of the CMC prevails, as a crosslinker reinforces the nanocomposite. In addition, the binding to Ch enhanced the compressive strength of the scaffold. Thermal characteristics revealed the coefficient of thermal expansion decreases with increasing CMC content. The nanocomposite does not expand at 25–75 °C, which is suitable for human body temperature. Therefore, this nanocomposite-based scaffold is feasible for BTE application.

Effects of the Sintering Process on Nacre-Derived Hydroxyapatite Scaffolds for Bone Engineering

A hydroxyapatite scaffold is a suitable biomaterial for bone tissue engineering due to its chemical component which mimics native bone. Electronic states which present on the surface of hydroxyapatite have the potential to be used to promote the adsorption or transduction of biomolecules such as protein or DNA. This study aimed to compare the morphology and bioactivity of sinter and nonsinter marine-based hydroxyapatite scaffolds. Field emission scanning electron microscopy (FESEM) and micro-computed tomography (microCT) were used to characterize the morphology of both scaffolds. Scaffolds were co-cultured with 5 × 104/cm2 of MC3T3-E1 preosteoblast cells for 7, 14, and 21 days. FESEM was used to observe the cell morphology, and MTT and alkaline phosphatase (ALP) assays were conducted to determine the cell viability and differentiation capacity of cells on both scaffolds. Real-time polymerase chain reaction (rtPCR) was used to identify the expression of osteoblast markers. The sinter scaffold had a porous microstructure with the presence of interconnected pores as compared with the nonsinter scaffold. This sinter scaffold also significantly supported viability and differentiation of the MC3T3-E1 preosteoblast cells (p < 0.05). The marked expression of Col1α1 and osteocalcin (OCN) osteoblast markers were also observed after 14 days of incubation (p < 0.05). The sinter scaffold supported attachment, viability, and differentiation of preosteoblast cells. Hence, sinter hydroxyapatite scaffold from nacreous layer is a promising biomaterial for bone tissue engineering.

Three-Dimensional Extrusion Printing of Porous Scaffolds Using Storable Ceramic Inks

In this study, we describe the additive manufacturing of porous three-dimensionally (3D) printed ceramic scaffolds prepared with hydroxyapatite (HA), β-tricalcium phosphate (β-TCP), or the combination of both with an extrusion-based process. The scaffolds were printed using a novel ceramic-based ink with reproducible printability and storability properties. After sintering at 1200°C, the scaffolds were characterized in terms of structure, mechanical properties, and dissolution in aqueous medium. Microcomputed tomography and scanning electron microscopy analyses revealed that the structure of the scaffolds, and more specifically, pore size, porosity, and isotropic dimensions were not significantly affected by the sintering process, resulting in scaffolds that closely replicate the original dimensions of the 3D model design. The mechanical properties of the sintered scaffolds were in the range of human trabecular bone for all compositions. All ceramic bioinks showed consistent printability over a span of 14 days, demonstrating the short-term storability of the formulations. Finally, the mass loss did not vary among the evaluated compositions over a period of 28 days except in the case of β-TCP scaffolds, in which the structural integrity was significantly affected after 28 days of incubation in phosphate-buffered saline. In conclusion, this study demonstrates the development of storable ceramic inks for the 3D printing of scaffolds of HA, β-TCP, and mixtures thereof with high fidelity and low shrinkage following sintering that could potentially be used for bone tissue engineering in load-bearing applications.

Injection Molding of 3-3 Hydroxyapatite Composites

The manufacturing of ideal implants requires fabrication processes enabling an adjustment of the shape, porosity and pore sizes to the patient-specific defect. To meet these criteria novel porous hydroxyapatite (HAp) implants were manufactured by combining ceramic injection molding (CIM) with sacrificial templating. Varied amounts (Φ = 0–40 Vol%) of spherical pore formers with a size of 20 µm were added to a HAp-feedstock to generate well-defined porosities of 11.2–45.2 Vol% after thermal debinding and sintering. At pore former contents Φ ≥ 30 Vol% interconnected pore networks were formed. The investigated Young’s modulus and flexural strength decreased with increasing pore former content from 97.3 to 29.1 GPa and 69.0 to 13.0 MPa, agreeing well with a fitted power-law approach. Additionally, interpenetrating HAp/polymer composites were manufactured by infiltrating and afterwards curing of an urethane dimethacrylate-based (UDMA) monomer solution into the porous HAp ceramic preforms. The obtained stiffness (32–46 GPa) and Vickers hardness (1.2–2.1 GPa) of the HAp/UDMA composites were comparable to natural dentin, enamel and other polymer infiltrated ceramic network (PICN) materials. The combination of CIM and sacrificial templating facilitates a near-net shape manufacturing of complex shaped bone and dental implants, whose properties can be directly tailored by the amount, shape and size of the pore formers.

Calcium Phosphate Nanoparticles for Therapeutic Applications in Bone Regeneration

Bone injuries and diseases constitute a burden both socially and economically, as the consequences of a lack of effective treatments affect both the patients' quality of life and the costs on the health systems. This impended need has led the research community's efforts to establish efficacious bone tissue engineering solutions. There has been a recent focus on the use of biomaterial-based nanoparticles for the delivery of therapeutic factors. Among the biomaterials being considered to date, calcium phosphates have emerged as one of the most promising materials for bone repair applications due to their osteoconductivity, osteoinductivity and their ability to be resorbed in the body. Calcium phosphate nanoparticles have received particular attention as non-viral vectors for gene therapy, as factors such as plasmid DNAs, microRNAs (miRNA) and silencing RNA (siRNAs) can be easily incorporated on their surface. Calcium phosphate nanoparticles loaded with therapeutic factors have also been delivered to the site of bone injury using scaffolds and hydrogels. This review provides an extensive overview of the current state-of-the-art relating to the design and synthesis of calcium phosphate nanoparticles as carriers for therapeutic factors, the mechanisms of therapeutic factors' loading and release, and their application in bone tissue engineering.

Silver and gold doped hydroxyapatite nanocomposites for enhanced bone regeneration

We report the osteogenic potential of silver (Ag), gold (Au), or silver-gold doped hydroxyapatite nanoparticles (Ag-Au-HA) in zebrafish (ZF) jawbone regeneration (JBR) model. The hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂), Ag-HA, Au-HA, and Ag-Au-HA nanomaterials were synthesized by the co-precipitation procedure. The surface structures of Ag-HA, Au-HA, HA, and Ag-Au-HA were analysed by scanning electron microscopy, transmission-electron microscopy (TEM), x-ray diffraction, Fourier transform infrared (FTIR), UV-vis, energy dispersive x-ray spectroscopy (EDS), elemental mapping, and laser fluorescent spectroscopy. The TEM and EDS analysis confirmed that the Ag and Au are associated with the surface of HA nanoparticle. The chemical structure of HA, Ag-HA, Au-HA, and Ag-Au-HA nanoparticles was validated by FTIR and EDS analysis. We observed that Ag and Au are associated with HA nanoparticles by electrostatic, wander wall, and electrostatic and H-bonding interaction. The effect of Ag-HA, Au-HA, and Ag-Au-HA nanoparticles on bone regeneration was confirmed by ZF JBR model. The significant growth of ZF bone regeneration was observed in Ag-Au-HA nanoparticles as compared with HA, Ag-HA, and Au-HA nanoparticles. These results indicating a therapeutic potential of Ag-Au-HA compositions suggest these nanomaterials would be excellent for bone regeneration and fracture healing.

Three-dimensional printing with biomaterials in craniofacial and dental tissue engineering

With the development of technology, tissue engineering (TE) has been widely applied in the medical field. In recent years, due to its accuracy and the demands of solid freeform fabrication in TE, three-dimensional printing, also known as additive manufacturing (AM), has been applied for biological scaffold fabrication in craniofacial and dental regeneration. In this review, we have compared several types of AM techniques and summarized their advantages and limitations. The range of printable materials used in craniofacial and dental tissue includes all the biomaterials. Thus, basic and clinical studies were discussed in this review to present the application of AM techniques in craniofacial and dental tissue and their advances during these years, which might provide information for further AM studies in craniofacial and dental TE.

Past, Present, and Future of Regeneration Therapy in Oral and Periodontal Tissue: A Review

Chronic periodontitis is the most common disease which induces oral tissue destruction. The goal of periodontal treatment is to reduce inflammation and regenerate the defects. As the structure of periodontium is composed of four types of different tissue (cementum, alveolar bone periodontal ligament, and gingiva), the regeneration should allow different cell proliferation in the separated spaces. Guided tissue regeneration (GTR) and guided bone regeneration (GBR) were introduced to prevent epithelial growth into the alveolar bone space. In the past, non-absorbable membranes with basic functions such as space maintenance were used with bone graft materials. Due to several limitations of the non-absorbable membranes, membranes of the second and third generation equipped with controlled absorbability, and a functional layer releasing growth factors or antimicrobials were introduced. Moreover, tissue engineering using biomaterials enabled faster and more stable tissue regeneration. The scaffold with three-dimensional structures manufactured by computer-aided design and manufacturing (CAD/CAM) showed high biocompatibility, and promoted cell infiltration and revascularization. In the future, using the cell sheath, pre-vascularizing and bioprinting techniques will be applied to the membrane to mimic the original tissue itself. The aim of the review was not only to understand the past and the present trends of GTR and GBR, but also to be used as a guide for a proper future of regeneration therapy in the oral region.

Advances in additive manufacturing for bone tissue engineering scaffolds

This article reviews the current state of the art of additive manufacturing techniques for the production of bone tissue engineering (BTE) scaffolds. The most well-known of these techniques include: stereolithography, selective laser sintering, fused deposition modelling and three-dimensional printing. This review analyses in detail the basic physical principles and main applications of these techniques and presents a list of biomaterials for BTE applications, including commercial trademarks. It also describes and compares the main advantages and disadvantages and explains the highlights of each additive manufacturing technique and their evolution. Finally, is discusses both their capabilities and limitations and proposes potential strategies to improve this field.

Additive manufacturing of bone scaffolds

Additive manufacturing (AM) can obtain not only customized external shape but also porous internal structure for scaffolds, both of which are of great importance for repairing large segmental bone defects. The scaffold fabrication process generally involves scaffold design, AM, and post-treatments. Thus, this article firstly reviews the state-of-the-art of scaffold design, including computer-aided design, reverse modeling, topology optimization, and mathematical modeling. In addition, the current characteristics of several typical AM techniques, including selective laser sintering, fused deposition modeling (FDM), and electron beam melting (EBM), especially their advantages and limitations are presented. In particular, selective laser sintering is able to obtain scaffolds with nanoscale grains, due to its high heating rate and a short holding time. However, this character usually results in insufficient densification. FDM can fabricate scaffolds with a relative high accuracy of pore structure but with a relative low mechanical strength. EBM with a high beam-material coupling efficiency can process high melting point metals, but it exhibits a low-resolution and poor surface quality. Furthermore, the common post-treatments, with main focus on heat and surface treatments, which are applied to improve the comprehensive performance are also discussed. Finally, this review also discusses the future directions for AM scaffolds for bone tissue engineering.

Enhancement of osteoblast activity on nanostructured NiTi/hydroxyapatite coatings on additive manufactured NiTi metal implants by nanosecond pulsed laser sintering

Background

The osteoinductive behaviors of nitinol (NiTi)-based metal implants for bone regeneration are largely dependent on their surface composition and topology. Continuous-mode laser sintering often results in complete melting of the materials and aggregation of particles, which lack control of heat transfer, as well as microstructural changes during sintering of the nanocomposite materials.

Methods

In the current study, in situ direct laser deposition was used to additively manufacture three-dimensional NiTi structures from Ni and Ti powders. The mechanical property of NiTi has been shown to be similar to bone. Nanosecond pulsed laser sintering process was then utilized to generate a nanoporous composite surface with NiTi alloy and hydroxyapatite (HA) by ultrafast laser heating and cooling of Ni, Ti, and HA nanoparticles mixtures precoated on the 3D NiTi substrates; HA was added in order to improve the biocompatibility of the alloy. We then studied the underlying mechanism in the formation of NiTi/HA nanocomposite, and the synergistic effect of the sintered HA component and the nanoporous topology of the composite coating. In addition, we examined the activity of bone-forming osteoblasts on the NiTi/HA surfaces. For this, osteoblast cell morphology and various biomarkers were examined to evaluate cellular activity and function.

Results

We found that the nanoscale porosity delivered by nanosecond pulsed laser sintering and the HA component positively contributed to osteoblast differentiation, as indicated by an increase in the expression of collagen and alkaline phosphatase, both of which are necessary for osteoblast mineralization. In addition, we observed topological complexities which appeared to boost the activity of osteoblasts, including an increase in actin cytoskeletal structures and adhesion structures.

Conclusion

These findings demonstrate that the pulsed laser sintering method is an effective tool to generate biocompatible coatings in complex alloy-composite material systems with desired composition and topology. Our findings also provide a better understanding of the osteoinductive behavior of the sintered nanocomposite coatings for use in orthopedic and bone regeneration applications.

Aromatic thermosetting copolyester bionanocomposites as reconfigurable bone substitute materials: Interfacial interactions between reinforcement particles and polymer network

Development of porous materials consisting of polymer host matrix enriched with bioactive ceramic particles that can initiate the reproduction of cellular organisms while maintaining in vivo mechanical reliability is a long-standing challenge for synthetic bone substitutes. We present hydroxyapatite (HA) reinforced aromatic thermosetting copolyester (ATSP) matrix bionanocomposite as a potential reconfigurable bone replacement material. The nanocomposite is fabricated by solid-state mixing a matching set of precursor oligomers with biocompatible pristine HA particles. During endothermic condensation polymerization reaction, the constituent oligomers form a mechanochemically robust crosslinked aromatic backbone while incorporating the HAs into a self-generated cellular structure. The morphological analysis demonstrates near-homogenous distributions of the pristine HAs within the matrix. The HAs behave as a crack-arrester which promotes a more deformation-tolerant formation with relatively enhanced material toughness. Chain relaxation dynamics of the nanocomposite matrix during glass transition is modified via HA-induced segmental immobilization. Chemical characterization of the polymer backbone composition reveals the presence of a hydrogen-advanced covalent interfacial coupling mechanism between the HAs and ATSP matrix. This report lays the groundwork for further studies on aromatic thermosetting copolyester matrix bionanocomposites which may find applications in various artificial bone needs.

Accelerated Bone Regeneration by Nitrogen-Doped Carbon Dots Functionalized with Hydroxyapatite Nanoparticles

We investigated the osteogenic potential of nitrogen-doped carbon dots (NCDs) conjugated with hydroxyapatite (HA) nanoparticles on the MC3T3-E1 osteoblast cell functions and in a zebrafish (ZF) jawbone regeneration (JBR) model. The NCDs-HA nanoparticles were fabricated by a hydrothermal cum co-precipitation technique. The surface structures of NCDs-HA nanoparticles were characterized by X-ray diffraction; Fourier transform infrared (FTIR), UV-vis, and laser fluorescence spectroscopies; and scanning electron microscopy, transmission electron microscopy (TEM), energy-dispersive spectrometry (EDS), and NMR analyses. The TEM data confirmed that the NCDs are well conjugated on the HA nanoparticle surfaces. The fluorescent spectroscopy results indicated that the NCDs-HA exhibited promising luminescent emission in vitro. Finally, we validated the chemical structure of NCDs-HA nanoparticles on the basis of FTIR, EDS, and ³¹P NMR analysis and observed that NCDs are bound with HA by electrostatic interaction and H-bonding. Cell proliferation assay, alkaline phosphatase, and Alizarin red staining were used to confirm the effect of NCDs-HA nanoparticles on MC3T3-E1 osteoblast proliferation, differentiation, and mineralization, respectively. Reverse transcriptase polymerase chain reaction was used to measure the expression of the osteogenic genes like runt-related transcription factor 2, alkaline phosphatase, and osteocalcin. ZF-JBR model was used to confirm the effect of NCDs-HA nanoparticles on bone regeneration. NCDs-HA nanoparticles demonstrated cell imaging ability, enhanced alkaline phosphatase activity, mineralization, and expression of the osteogenic genes in osteoblast cells, indicating possible theranostic function. Further, NCDs-HA nanoparticles significantly enhanced ZF bone regeneration and mineral density compared to HA nanoparticles, indicating a therapeutic potential of NCDs-HA nanoparticles in bone regeneration and fracture healing.

Sonochemical synthesis of cellulose/hydroxyapatite nanocomposites and their application in protein adsorption

Hydroxyapatite (HA) is the main mineral constituent in the hard tissue of vertebrate, which is recognized as an important biomedical material owing to its excellent bioactivity and biocompatibility. Herein, we report a facile and green sonochemical route for the rapid synthesis of cellulose/HA nanocomposites in NaOH/urea aqueous solution. The in vitro behavior of the cellulose/HA nanocomposites was studied to evaluate the biological response of the nanocomposites following immersion in simulated body fluid for various periods (maximum of 28 days). The HA crystals formed on the surface of the nanocomposites were carbonate-containing apatite, which is similar to the naturally occurring calcium phosphate materials. The HA nanosheets (assembly of nanorods) were mineralized on the surface of the nanocomposites, and maximum mass of the nanocomposites was reached 1.82 times of initial mass after 28 days of soaking. Moreover, the as-prepared cellulose/HA nanocomposites have good cytocompatibility, and show a relatively high protein adsorption ability using hemoglobin as a model protein. These results indicate that the as-prepared cellulose/HA nanocomposites are promising for applications in various biomedical fields such as tissue engineering and protein/drug delivery.

Incorporation of Nanoalumina Improves Mechanical Properties and Osteogenesis of Hydroxyapatite Bioceramics

A handful of work focused on improving the intrinsic low mechanical properties of hydroxyapatite (HA) by various reinforcing agents. However, the big challenge regarding improving mechanical properties is maintaining bioactivity. To address this issue, we report fabrication of apatite-based composites by incorporation of alumina nanoparticles (n-Al₂O₃). Although numerous studies have used micron or submicron alumina for reinforcing hydroxyapatite, only few reports are available about the use of n-Al₂O₃. In this study, spark plasma sintering (SPS) method was utilized to develop HA-nAl₂O₃ dense bodies. Compared to the conventional sintering, decomposition of HA and formation of calcium aluminates phases are restricted using SPS. Moreover, n-Al₂O₃ acts as a bioactive agent while its conventional form is an inert bioceramics. The addition of n-Al₂O₃ resulted in 40% improvement in hardness along with a 110% increase in fracture toughness, while attaining nearly full dense bodies. The in vitro characterization of nanocomposite demonstrated improved bone-specific cell function markers as evidenced by cell attachment and proliferation, alkaline phosphatase activity, calcium and collagen detection and nitric oxide production. Specifically, gene expression analysis demonstrated that introduction of n-Al₂O₃ in HA matrix resulted in accelerated osteogenic differentiation of osteoblast and mesenchymal stem cells, as expression of Runx-2 and OSP showed 2.5 and 19.6 fold increase after 2 weeks (p < 0.05). Moreover, protein adsorption analysis showed enhanced adsorption of plasma proteins to HA-nAl₂O₃ sample compared to HA. These findings suggest that HA-nAl₂O₃ could be a prospective candidate for orthopedic applications due to its improved mechanical and osteogenic properties.

In vitro evaluation of a bone morphogenetic protein‑2 nanometer hydroxyapatite collagen scaffold for bone regeneration

Scaffold fabrication and biocompatibility are crucial for successful bone tissue engineering. Nanometer hydroxyapatite (nHAP) combined with collagen (COL) is frequently utilized as a suitable osseous scaffold material. Furthermore, growth factors, including bone morphogenetic protein‑2 (BMP‑2), are used to enhance the scaffold properties. The present study used blending and freeze‑drying methods to develop a BMP‑2‑nHAP‑COL scaffold. An ELISA was performed to determine the BMP‑2 release rate from the scaffold. Flow cytometry was used to identify rat bone marrow‑derived mesenchymal stem cells (BMSCs) prior to their combination with the scaffold. Scanning electron microscopy was used to observe the scaffold structure and BMSC morphology following seeding onto the scaffold. BMSCs were also used to assess the biological compatibility of the scaffold in vitro. BMP‑2‑nHAP‑COL and nHAP‑COL scaffolds were assessed alongside the appropriate control groups. Cells were counted to determine early cell adhesion. Cell Counting kit‑8 and alkaline phosphatase assays were used to detect cell proliferation and differentiation, respectively. Gross morphology confirmed that the BMP‑2‑nHAP‑COL scaffold microstructure conformed to the optimal characteristics of a bone tissue engineering scaffold. Furthermore, the BMP‑2‑nHAP‑COL scaffold exhibited no biological toxicity and was demonstrated to promote BMSC adhesion, proliferation and differentiation. The BMP‑2‑nHAP‑COL scaffold had good biocompatibility in vitro, and may therefore be modified further to construct an optimized scaffold for future bone tissue engineering.

Bone biomaterials and interactions with stem cells

Bone biomaterials play a vital role in bone repair by providing the necessary substrate for cell adhesion, proliferation, and differentiation and by modulating cell activity and function. In past decades, extensive efforts have been devoted to developing bone biomaterials with a focus on the following issues: (1) developing ideal biomaterials with a combination of suitable biological and mechanical properties; (2) constructing a cell microenvironment with pores ranging in size from nanoscale to submicro- and microscale; and (3) inducing the oriented differentiation of stem cells for artificial-to-biological transformation. Here we present a comprehensive review of the state of the art of bone biomaterials and their interactions with stem cells. Typical bone biomaterials that have been developed, including bioactive ceramics, biodegradable polymers, and biodegradable metals, are reviewed, with an emphasis on their characteristics and applications. The necessary porous structure of bone biomaterials for the cell microenvironment is discussed, along with the corresponding fabrication methods. Additionally, the promising seed stem cells for bone repair are summarized, and their interaction mechanisms with bone biomaterials are discussed in detail. Special attention has been paid to the signaling pathways involved in the focal adhesion and osteogenic differentiation of stem cells on bone biomaterials. Finally, achievements regarding bone biomaterials are summarized, and future research directions are proposed.

A simple way to achieve bioinspired hybrid wettability surface with micro/nanopatterns for efficient fog collection

Fog collection is receiving increasing attention for providing water in semi-arid deserts and inland areas. Inspired by the fog harvesting ability of the hydrophobic-hydrophilic surface of Namib desert beetles, we present a simple, low-cost method to prepare a hybrid superhydrophobic-hydrophilic surface. The surface contains micro/nanopatterns, and is prepared by incorporating femtosecond-laser fabricated polytetrafluoroethylene nanoparticles deposited on superhydrophobic copper mesh with a pristine hydrophilic copper sheet. The as-prepared surface exhibits enhanced fog collection efficiency compared with uniform (super)hydrophobic or (super)hydrophilic surfaces. This enhancement can be tuned by controlling the mesh number, inclination angle, and fabrication structure. Moreover, the surface shows excellent anti-corrosion ability after immersing in 1 M HCl, 1 M NaOH, and 10 wt% NaCl solutions for 2 hours. This work may provide insight into fabricating hybrid superhydrophobic-hydrophilic surfaces for efficient atmospheric water collection.

Femtosecond laser induced robust periodic nanoripple structured mesh for highly efficient oil-water separation

Marine oil spills have induced severe water pollution and threatened sea ecosystems, which also result in a loss of energy resources. To deal with this problem, much work has been done for using superhydrophobic or superhydrophilic mesh for oil-water separation. Nevertheless, there are still great challenges in the rapid fabrication of extremely durable mesh with superwetting properties, particularly considering the highly efficient oil-water separation. In this study, we present a simple, efficient method to fabricate superhydrophilic and underwater superoleophobic stainless steel mesh surfaces with one-step femtosecond laser induced periodic nanoripple structures. The as-prepared mesh shows high separation efficiency, which is higher than 99% for various oil-water mixtures. More importantly, the wettability and the separation efficiency of the fabricated mesh show no obvious change after the abrasion tests and corrosion tests, indicating that the as-prepared samples possess robust stability. This study provides an efficient route for constructing durable and highly efficient separation mesh, which can be applied in the cleanup of large-scale oil spills in the near future.

From waste to high-value product: Jackfruit peel derived pectin/apatite bionanocomposites for bone healing applications

Public requirements encouraged by the current asset framework drive industry to expand its general effectiveness by enhancing existing procedures or finding new uses for waste. Thus, the aim of this study was the isolation, fabrication, and characterization of pectin derived from jackfruit (Artocarpus heterophyllus) peels and the generation of hybrid of pectin (P)/apatite (HA) (P/HA) bionanocomposites. In this process, the natural pectin polymer derived from the peel of jackfruits was used in different concentrations for the fabrication of HA bionanocomposites. Characterization of the isolated pectin and bionanocomposites samples was performed with ¹H NMR and ¹³C NMR, FTIR, XRD, SEM-EDX, and HR-TEM. Cytocompatibility, ALP, fibroblast stem cells, anti-inflammatory and cell adhesion testing of the fabricated bionanocomposites was showed good biocompatibility. Our results signify that the fabricated bionanocomposites might be applicable as bone graft materials.

Calcium Silicate Improved Bioactivity and Mechanical Properties of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Scaffolds

The poor bioactivity and mechanical properties have restricted its biomedical application, although poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) had good biocompatibility and biodegradability. In this study, calcium silicate (CS) was incorporated into PHBV for improving its bioactivity and mechanical properties, and the porous PHBV/CS composite scaffolds were fabricated via selective laser sintering (SLS). Simulated body fluid (SBF) immersion tests indicated the composite scaffolds had good apatite-forming ability, which could be mainly attributed to the electrostatic attraction of negatively charged silanol groups derived from CS degradation to positively charged calcium ions in SBF. Moreover, the compressive properties of the composite scaffolds increased at first, and then decreased with increasing the CS content, which was ascribed to the fact that CS of a proper content could homogeneously disperse in PHBV matrix, while excessive CS would form continuous phase. The compressive strength and modulus of composite scaffolds with optimal CS content of 10 wt % were 3.55 MPa and 36.54 MPa, respectively, which were increased by 41.43% and 28.61%, respectively, as compared with PHBV scaffolds. Additionally, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay indicated MG63 cells had a higher proliferation rate on PHBV/CS composite scaffolds than that on PHBV. Alkaline phosphatase (ALP) staining assay demonstrated the incorporation of CS significantly promoted osteogenic differentiation of MG63 cells on the scaffolds. These results suggest that the PHBV/CS composite scaffolds have the potential in serving as a substitute in bone tissue engineering.

Graphene oxide as an interface phase between polyetheretherketone and hydroxyapatite for tissue engineering scaffolds

The poor bonding strength between biopolymer and bioceramic has remained an unsolved issue. In this study, graphene oxide (GO) was introduced as an interface phase to improve the interfacial bonding between polyetheretherketone (PEEK) and hydroxyapatite (HAP) for tissue engineering scaffolds. On the one hand, the conjugated structure of GO could form strong π-π stacking interaction with the benzene rings in PEEK. On the other hand, GO with a negatively charge resulting from oxygen functional groups could adsorb the positively charged calcium atoms (C sites) of HAP. Consequently, the dispersibility and compatibility of HAP in the PEEK matrix increased with increasing GO content up to 1 wt%. At this time, the compressive strength and modulus of scaffolds increased by 79.45% and 42.07%, respectively. Furthermore, the PEEK-HAP with GO (PEEK-HAP/GO) scaffolds possessed the ability to induce formation of bone-like apatite. And they could support cellular adhesion, proliferation as well as osteogenic differentiation. More importantly, in vivo bone defect repair experiments showed that new bone formed throughout the scaffolds at 60 days after implantation. All these results suggested that the PEEK-HAP/GO scaffolds have a promising potential for bone tissue engineering application.

Sustained delivery of calcium and orthophosphate ions from amorphous calcium phosphate and poly(L-lactic acid)-based electrospinning nanofibrous scaffold

The purpose of this study is to investigate electrospinning poly(L-lactic acid) (PLLA) nanofibrous scaffold with different contents of amorphous calcium phosphate (ACP), which is suitable for using in bone regeneration through sustained release of calcium and orthophosphate ions. Three groups of nanofibrous scaffolds, ACP-free PLLA, ACP-5 wt%/PLLA and ACP-10 wt%/PLLA, are developed and characterized by scanning electron microscopy and gel permeation chromatography. Calcium and phosphate colorimetric assay kits are used to test ions released from scaffold during hydrolytic degradation. The results show ACP-5 wt%/PLLA and ACP-10 wt%/PLLA scaffolds have relatively high degradation rates than ACP-free PLLA group. The bioactivity evaluation further reveals that ACP-5 wt%/PLLA scaffold presents more biocompatible feature with pre-osteoblast cells and significant osteogenesis ability of calvarial bone defect. Due to the facile preparation method, sustained calcium and orthophosphate release behavior, and excellent osteogenesis capacity, the presented ACP/PLLA nanofibrous scaffold has potential applications in bone tissue engineering.