Zinc in calcium phosphate mediates bone induction: in vitro and in vivo model

Tailoring of bioactive glass and glass-ceramics properties for in vitro and in vivo response optimization: a review

Bioactive glasses are inorganic biocompatible materials that can find applications in many biomedical fields. The main application is bone and dental tissue engineering. However, some applications in contact with soft tissues are emerging. It is well known that both bulk (such as composition) and surface properties (such as morphology and wettability) of an implanted material influence the response of cells in contact with the implant. This review aims to elucidate and compare the main strategies that are employed to modulate cell behavior in contact with bioactive glasses. The first part of this review is focused on the doping of bioactive glasses with ions and drugs, which can be incorporated into the bioceramic to impart several therapeutic properties, such as osteogenic, proangiogenic, or/and antibacterial ones. The second part of this review is devoted to the chemical functionalization of bioactive glasses using drugs, extra-cellular matrix proteins, vitamins, and polyphenols. In the third and final part, the physical modifications of the surfaces of bioactive glasses are reviewed. Both top-down (removing materials from the surface, for example using laser treatment and etching strategies) and bottom-up (depositing materials on the surface, for example through the deposition of coatings) strategies are discussed.

Peek@ZIF-8(CEL) as a Novel Bone Implant for Large Defect Repair and Enhanced Bone Healing via a Long-Term Stable Bioactive Releaser

The repair of large bone defects poses a significant challenge in orthopedics. Polyetheretherketone (PEEK) is a promising bone substitute, while it suffers a lack of bioactivity. Although several studies have been performed to further improve the bioactivities of PEEK by various surface modifications, PEEK offering long-term, multifaceted biofunctionalities remains still desired. In this study, we introduced metal-organic frameworks (MOFs), specifically ZIF-8 loaded with celecoxib (ZIF-8(CEL)), onto the PEEK surface through dopamine adhesion. The resulting PEEK@ZIF-8(CEL) aims to achieve long-term stable release of Zn ions and CEL for enhanced bone integration. Material characterization and biological experiments confirmed the successful integration of ZIF-8(CEL) onto PEEK and its positive biomedical effects, including creating a positive bone immunological environment and promoting bone growth. This study demonstrates the potential of PEEK@ZIF-8(CEL) as a novel repair material for large bone defects, offering a promising alternative in orthopedic applications.

Nano-ZnO-modified hydroxyapatite whiskers with enhanced osteoinductivity for bone defect repair

Hydroxyapatite (HA) whisker (HAw) represents a distinct form of HA characterized by its high aspect ratio, offering significant potential for enhancing the mechanical properties of bone tissue engineering scaffolds. However, the limited osteoinductivity of HAw hampers its widespread application. In this investigation, we observed HAw-punctured osteoblast membranes and infiltrated the cell body, resulting in mechanical damage to cells that adversely impacted osteoblast proliferation and differentiation. To address this challenge, we developed nano-zinc oxide particle-modified HAw (nano-ZnO/HAw). Acting as a reinforcing and toughening agent, nano-ZnO/HAw augmented the compressive strength and ductility of the matrix materials. At the same time, the surface modification with nano-ZnO particles improved osteoblast differentiation by reducing the mechanical damage from HAw to cells and releasing zinc ion, the two aspects collectively promoted the osteoinductivity of HAw. Encouragingly, the osteoinductive potential of 5% nano-ZnO/HAw and 10% nano-ZnO/HAw was validated in relevant rat models, demonstrating the efficacy of this approach in promoting new bone formation in vivo. Our findings underscore the role of nano-ZnO particle surface modification in enhancing the osteoinductivity of HAw from a physical standpoint, offering valuable insights into the development of bone substitutes with favorable osteoinductive properties while simultaneously bolstering matrix material strength and toughness.

Bioactive ceramic-based materials: beneficial properties and potential applications in dental repair and regeneration

Bioactive ceramics, primarily consisting of bioactive glasses, glass-ceramics, calcium orthophosphate ceramics, calcium silicate ceramics and calcium carbonate ceramics, have received great attention in the past decades given their biocompatible nature and excellent bioactivity in stimulating cell proliferation, differentiation and tissue regeneration. Recent studies have tried to combine bioactive ceramics with bioactive ions, polymers, bioactive proteins and other chemicals to improve their mechanical and biological properties, thus rendering them more valid in tissue engineering scaffolds. This review presents the beneficial properties and potential applications of bioactive ceramic-based materials in dentistry, particularly in the repair and regeneration of dental hard tissue, pulp-dentin complex, periodontal tissue and bone tissue. Moreover, greater insights into the mechanisms of bioactive ceramics and the development of ceramic-based materials are provided.

The Role of Zinc in Bone Tissue Health and Regeneration-a Review

Zinc is a micronutrient of key importance for human health. An increasing number of studies indicate that zinc plays a significant role in bone tissue's normal development and maintaining homeostasis. Zinc is not only a component of bone tissue but is also involved in the synthesis of the collagen matrix, mineralization, and bone turnover. It has been demonstrated that zinc can stimulate runt-related transcription factor 2 (Runx2) and promote the differentiation of osteoblasts. On the other hand, zinc has been found to inhibit osteoclast-like cell formation and to decrease bone resorption by stimulating osteoclasts' apoptosis. Moreover, zinc regulates the RANKL/RANK/OPG pathway, thereby facilitating bone remodeling. To date, not all mechanisms of Zn activity on bone tissue are well understood and documented. The review aimed to present the current state of research on the role of zinc in bone tissue, its beneficial properties, and its effects on bone regeneration. Since calcium phosphates as bone substitute materials are increasingly enriched in zinc ions, the paper included an overview of research on the potential role of such materials in bone filling and regeneration.

Ultra-Short Laser-Assisted Micro-Structure Formations on Mg/Zn Double-Doped Calcium Phosphate Ceramics for Enhanced Antimicrobial Activity

Bacterial infection is one of the most common and harmful medical issues following the implantation of materials and devices in the body leading to antibiotic resistance of diverse bacterial strains. In this work, a novel approach is presented combining adopted laser-based patterning method in addition to doping (Mg and Zn) metal ions to prepare calcium phosphate ceramic substrate, applicable in medicine, with enhanced surface antimicrobial characteristics. The preparation of tablets containing Mg (8.44 mol%) and Zn (2.63 mol%) β-tricalcium phosphate involved biomimetic precipitation of amorphous calcium phosphate in media of simulated body fluid enriched with Mg2+ and Zn2+ ions as well as the presence of valine as an organic additive, followed by step-wise calcination up to 1000 °C. The results from laser processing showed formation of deeper patterns with increased surface roughness (from 4.9 µm to 9.4 µm) as laser power and velocity increase, keeping constant the hatch sizes of 50 µm. The textured surfaces consist of peaks and valleys arrangement that change the morphology of Escherichia coli cells and decrease of cell viability. Our study reveals the possibilities of the application of ultra-short laser radiation as a potential alternative therapy for controlling the antimicrobial effect of the ceramic surface.

Proteomics as a tool to study the osteoimmunomodulatory role of metallic ions in a sol-gel coating

The success of bone implants depends on the osteoimmunomodulatory (OIM) activity of the biomaterials in the interactions with the periimplantary tissues. Many in vitro tests have been conducted to evaluate the osteoimmunology effects of biomaterials. However, results of these tests have often been inconclusive. This study examines the properties of newly developed sol-gel coatings doped with two metal ions associated with bone regeneration, Ca and Zn. The study uses both proteomic methods and traditional in vitro assays. The results demonstrate that proteomics is an effective tool to scrutinize the OIM properties of the materials. Moreover, sol-gel coatings offer excellent base materials to evaluate the effects of metal ions on these properties. The obtained data highlight the highly tunable nature of sol-gel materials; studying the materials with different doping levels supplies valuable information on the interactions between the immune and bone-forming processes.

Multi-scale characterization of the spatio-temporal interplay between elemental composition, mineral deposition and remodelling in bone fracture healing

Bone mineralization involves a complex orchestration of physico-chemical responses from the organism. Despite extensive studies, the detailed mechanisms of mineralization remain to be elucidated. This study aims to characterize bone mineralization using an in-vivo long bone fracture healing model in the rat. The spatio-temporal distribution of relevant elements was correlated to the deposition and maturation of hydroxyapatite and the presence of matrix remodeling compounds (MMP-13). Multi-scale measurements indicated that (i) zinc is required for both the initial mineral deposition and resorption processes during mature mineral remodeling; (ii) Zinc and MMP-13 show similar spatio-temporal trends during early mineralization; (iii) Iron acts locally and in coordination with zinc during mineralization, thus indicating novel evidence of the time-events and inter-play between the elements. These findings improve the understanding of bone mineralization by explaining the link between the different constituents of this process throughout the healing time. STATEMENT OF SIGNIFICANCE: Bone mineralization involves a complex orchestration of physico-chemical responses from the organism, the detailed mechanisms of which remain to be elucidated. This study presents a highly novel multi-scale multi-modal investigation of bone mineralization using bone fracture healing as a model system. We present original characterization of tissue mineralization, where we relate the spatio-temporal distribution of important trace elements to a key matrix remodeling compound (MMP-13), the initial deposition and maturation of hydroxyapatite and further remodeling processes. This is the first time that mineralization has been probed down to the nanometric level, and where key mineralization components have been investigated to achieve a comprehensive and mechanistic understanding of the underlying mineralization processes during bone healing.

The Role of Trace Elements and Minerals in Osteoporosis: A Review of Epidemiological and Laboratory Findings

The objective of the present study was to review recent epidemiological and clinical data on the association between selected minerals and trace elements and osteoporosis, as well as to discuss the molecular mechanisms underlying these associations. We have performed a search in the PubMed-Medline and Google Scholar databases using the MeSH terms "osteoporosis", "osteogenesis", "osteoblast", "osteoclast", and "osteocyte" in association with the names of particular trace elements and minerals through 21 March 2023. The data demonstrate that physiological and nutritional levels of trace elements and minerals promote osteogenic differentiation through the up-regulation of BMP-2 and Wnt/β-catenin signaling, as well as other pathways. miRNA and epigenetic effects were also involved in the regulation of the osteogenic effects of trace minerals. The antiresorptive effect of trace elements and minerals was associated with the inhibition of osteoclastogenesis. At the same time, the effect of trace elements and minerals on bone health appeared to be dose-dependent with low doses promoting an osteogenic effect, whereas high doses exerted opposite effects which promoted bone resorption and impaired bone formation. Concomitant with the results of the laboratory studies, several clinical trials and epidemiological studies demonstrated that supplementation with Zn, Mg, F, and Sr may improve bone quality, thus inducing antiosteoporotic effects.

Immunomodulatory zinc-based materials for tissue regeneration

Zinc(Zn)-based materials have contributed greatly to the rapid advancements in tissue engineering. The qualities they possess that make them so beneficial include their excellent biodegradability, biocompatibility, anti-bacterial activity, among and several others. Biomedical materials that act as a foreign body, will inevitably cause host immune response when introduced to the human body. As the osteoimmunology develops, the immunomodulatory characteristics of biomaterials have become an appealing concept to improve implant-tissue interaction and tissue restoration. Recently, Zn-based materials have also displayed immunomodulatory functions, especially macrophage polarization states. It can promote the transformation of M1 macrophages into M2 macrophages to enhance the tissue regeneration and reconstruction. This review covers mainly Zn-based materials and their characteristics, including metallic Zn alloys and Zn ceramics. We highlight the current advancements in the type of immune responses, as well as the mechanisms, that are induced by Zn-based biomaterials, most importantly the regulation of innate immunity and the mechanism of promoting tissue regeneration. To this end, we discuss their applications in biomedicine, and conclude with an outlook on future research challenges.

Bioprocess inspired formation of calcite mesocrystals by cation-mediated particle attachment mechanism

Calcite mesocrystals were proposed, and have been widely reported, to form in the presence of polymer additives via oriented assembly of nanoparticles. However, the formation mechanism and the role of polymer additives remain elusive. Here, inspired by the biomineralization process of sea urchin spine comprising magnesium calcite mesocrystals, we show that calcite mesocrystals could also be obtained via attachment of amorphous calcium carbonate (ACC) nanoparticles in the presence of inorganic zinc ions. Moreover, we demonstrate that zinc ions can induce the formation of temporarily stabilized amorphous nanoparticles of less than 20 nm at a significantly lower calcium carbonate concentration as compared to pure solution, which is energetically beneficial for the attachment and occlusion during calcite growth. The cation-mediated particle attachment crystallization significantly improves our understanding of mesocrystal formation mechanisms in biomineralization and offers new opportunities to bioprocess inspired inorganic ions regulated materials fabrication.

The addition of zinc ions to polymer-ceramic composites accelerated osteogenic differentiation of human mesenchymal stromal cells

Critical-sized bone defects, caused by congenital disorders or trauma, are defects that will not heal spontaneously and require surgical intervention. Recent advances in biomaterial design for the treatment of such defects focus on improving their osteoinductive properties. Here, we propose a bioactive composite with high ceramic content composed of poly(ethyleneoxide terephthalate)/poly(butylene terephthalate) (1000PEOT70PBT30, PolyActive, PA) and 50 % beta-tricalcium phosphate (β-TCP) with the addition of zinc in a form of a coating on the TCP particles. Due to its essential role in bone homeostasis, we hypothesised that the addition of zinc to the polymer-ceramic composite will further enhance its osteogenic properties. β-TCP particles were immersed in a zinc solution with a concentration of 15 or 45 mM. The addition of zinc did not alter the β-TCP composition or the release of calcium or phosphate ions. 3D porous 1000PEOT70PBT30 - β-TCP scaffolds were additively manufactured by "3D fibre deposition" and their ability to support the osteogenic differentiation was assessed by culturing clinically relevant human mesenchymal stromal cells (hMSCs) on the scaffolds for 3, 7, 14 and 28 days. The expression of osteogenic gene markers was increased in the presence of both zinc concentrations. Remarkably, upregulation of osteocalcin (OCN), a late osteogenic marker, was observed after three days of culture. Furthermore, enhanced extracellular matrix (ECM) production and mineralization was observed. These findings support the existing evidence on the osteogenic properties of zinc and further demonstrate that the incorporation of zinc into a polymer-ceramic composite could be a promising strategy in the field of regeneration of critical-sized bone defects.

Additively manufactured pure zinc porous scaffolds for critical-sized bone defects of rabbit femur

Additive manufacturing has received attention for the fabrication of medical implants that have customized and complicated structures. Biodegradable Zn metals are revolutionary materials for orthopedic implants. In this study, pure Zn porous scaffolds with diamond structures were fabricated using customized laser powder bed fusion (L-PBF) technology. First, the mechanical properties, corrosion behavior, and biocompatibility of the pure Zn porous scaffolds were characterized in vitro. The scaffolds were then implanted into the rabbit femur critical-size bone defect model for 24 weeks. The results showed that the pure Zn porous scaffolds had compressive strength and rigidity comparable to those of cancellous bone, as well as relatively suitable degradation rates for bone regeneration. A benign host response was observed using hematoxylin and eosin (HE) staining of the heart, liver, spleen, lungs, and kidneys. Moreover, the pure Zn porous scaffold showed good biocompatibility and osteogenic promotion ability in vivo. This study showed that pure Zn porous scaffolds with customized structures fabricated using L-PBF represent a promising biodegradable solution for treating large bone defects.

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L-PBF used to fabricate pure Zn porous scaffolds for bone implants.

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Degradation rates and mechanical strength suitable for bone implants.

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Pure Zn porous scaffolds showed good in vitro cytocompatibility with MC3T3-E1 cells.

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Pure Zn porous scaffolds have potential for large bone defect applications with osteogenic ability.

Enhanced osteogenesis and angiogenesis of biphasic calcium phosphate scaffold by synergistic effect of silk fibroin coating and zinc doping

Biphasic calcium phosphate (BCP) scaffold has been widely applied to bone regeneration because of its good biocompatibility and bone conduction property. However, the low mechanical strength and the lack of angiogenic and osteogenic induction properties have restricted its application in bone tissue regeneration. In this study, we combined zinc (Zn²⁺) doping and silk fibroin (SF) coating with expectation to enhance compressive strength, osteogenesis and angiogenesis of BCP scaffolds. The phase composition, morphology, porosity, compressive strength, in vitro degradation and cell behaviors were investigated systematically. Results showed that the scaffold coated with SF exhibited almost 3 times of compressive strength without compromising its porosity compared with the uncoated scaffold. Zn²⁺ doping and SF coating synergistically enhanced the alkaline phosphatase activity and osteogenesis-related genes expression of mouse bone mesenchymal stem cells (mBMSCs). Furthermore, SF coating notably improved the proliferation, cell viability and in vitro angiogenesis of human umbilical vein endothelial cells (HUVECs). This work provides a novel way to modify BCP scaffolds simultaneously with enhancing mechanical strength and biological properties.

Marine plankton exoskeletone-derived hydroxyapatite/polycaprolactone composite 3D scaffold for bone tissue engineering

3D porous scaffolds based on biodegradable polymers are one of the materials for bone tissue regeneration. In this study, a porous scaffold was prepared using a solvent casting/particulate leaching method that used polycaprolactone (PCL) and hydroxyapatite (OceanBone-HAp) extracted from a marine plankton exoskeleton to achieve excellent bone regeneration. In this study, the morphology and physicochemical properties of the PCL/OceanBone-HAp scaffolds were evaluated using scanning electron microscopy, X-ray diffraction, and porosity analysis. The results confirmed the porous structure of the scaffold and removal of the solvent and porogen particles. In vitro test results revealed superior cell adhesion, proliferation, and viability of PCL/OceanBone-HAp scaffolds compared to PCL scaffolds alone. The enhanced alkaline phosphatase activity and expression of bone morphogenetic protein 2, collagen type I α 1, osteocalcin, and bone sialoprotein in the PCL/OceanBone-HAp scaffolds were confirmed through ALP and real-time polymerase chain reaction assays. Moreover, in vivo experiments using a rabbit calvarial defect model showed that the PCL/OceanBone-HAp scaffold exhibited enhanced bone regeneration compared to the PCL scaffold. Therefore, the PCL/OceanBone-HAp scaffold is a promising scaffold for bone repair.

Lithium doped biphasic calcium phosphate: Structural analysis and osteo/odontogenic potential in vitro

Biphasic calcium phosphate (BCP) is generally considered a good synthetic bone graft material with osteoinductive potential. Lithium ions are trace elements that play a role in the bone-remodeling process. This study aimed to investigate the effects of lithium ions on the phase, crystal structure, and biological responses of lithium doped BCPs and to identify improvements in their osteogenic properties. Lithium-doped BCP powders with different doping levels (0, 5, 10, and 20 at%) were synthesized via the co-precipitation method. We found that the four types of lithium-doped BCP powders showed different phase compositions of hydroxyapatite and β-tricalcium phosphate. In addition, lithium ions favored entering the β-tricalcium phosphate structure at the Ca (4) sites and calcium vacancy sites [VCa(4)] up to 10 at%. This substitution improves the crystal stabilization by filling the vacancies with Ca2+ and Li+ in all Ca sites. However, when the concentration of Li ions was higher than 10 at%, lithium-induced crystal instability resulted in the burst release of lithium ions, and the osteogenic behavior of human dental pulp stem cells did not improve further. Although lithium ions regulate osteogenic properties, it is important to determine the optimal amount of lithium in BCPs. In this study, the most effective lithium doping level in BCP was approximately 10 at% to improve its biological properties and facilitate medical applications.

Nanomaterial integrated 3D printing for biomedical applications

3D printing technology, otherwise known as additive manufacturing, has provided a promising tool for manufacturing customized biomaterials for tissue engineering and regenerative medicine applications. A vast variety of biomaterials including metals, ceramics, polymers, and composites are currently being used as base materials in 3D printing. In recent years, nanomaterials have been incorporated into 3D printing polymers to fabricate innovative, versatile, multifunctional hybrid materials that can be used in many different applications within the biomedical field. This review focuses on recent advances in novel hybrid biomaterials composed of nanomaterials and 3D printing technologies for biomedical applications. Various nanomaterials including metal-based nanomaterials, metal-organic frameworks, upconversion nanoparticles, and lipid-based nanoparticles used for 3D printing are presented, with a summary of the mechanisms, functional properties, advantages, disadvantages, and applications in biomedical 3D printing. To finish, this review offers a perspective and discusses the challenges facing the further development of nanomaterials in biomedical 3D printing.

Sustained local ionic homeostatic imbalance caused by calcification modulates inflammation to trigger heterotopic ossification

Heterotopic ossification (HO) is a condition triggered by an injury leading to the formation of mature lamellar bone in extraskeletal soft tissues. Despite being a frequent complication of orthopedic and trauma surgery, brain and spinal injury, the etiology of HO is poorly understood. The aim of this study is to evaluate the hypothesis that a sustained local ionic homeostatic imbalance (SLIHI) created by mineral formation during tissue calcification modulates inflammation to trigger HO. This evaluation also considers the role SLIHI could play for the design of cell-free, drug-free osteoinductive bone graft substitutes. The evaluation contains five main sections. The first section defines relevant concepts in the context of HO and provides a summary of proposed causes of HO. The second section starts with a detailed analysis of the occurrence and involvement of calcification in HO. It is followed by an explanation of the causes of calcification and its consequences. This allows to speculate on the potential chemical modulators of inflammation and triggers of HO. The end of this second section is devoted to in vitro mineralization tests used to predict the ectopic potential of materials. The third section reviews the biological cascade of events occurring during pathological and material-induced HO, and attempts to propose a quantitative timeline of HO formation. The fourth section looks at potential ways to control HO formation, either acting on SLIHI or on inflammation. Chemical, physical, and drug-based approaches are considered. Finally, the evaluation finishes with a critical assessment of the definition of osteoinduction. STATEMENT OF SIGNIFICANCE: The ability to regenerate bone in a spatially controlled and reproducible manner is an essential prerequisite for the treatment of large bone defects. As such, understanding the mechanism leading to heterotopic ossification (HO), a condition triggered by an injury leading to the formation of mature lamellar bone in extraskeletal soft tissues, would be very useful. Unfortunately, the mechanism(s) behind HO is(are) poorly understood. The present study reviews the literature on HO and based on it, proposes that HO can be caused by a combination of inflammation and calcification. This mechanism helps to better understand current strategies to prevent and treat HO. It also shows new opportunities to improve the treatment of bone defects in orthopedic and dental procedures.

Mg-, Zn-, and Fe-Based Alloys With Antibacterial Properties as Orthopedic Implant Materials

Implant-associated infection (IAI) is one of the major challenges in orthopedic surgery. The development of implants with inherent antibacterial properties is an effective strategy to resolve this issue. In recent years, biodegradable alloy materials have received considerable attention because of their superior comprehensive performance in the field of orthopedic implants. Studies on biodegradable alloy orthopedic implants with antibacterial properties have gradually increased. This review summarizes the recent advances in biodegradable magnesium- (Mg-), iron- (Fe-), and zinc- (Zn-) based alloys with antibacterial properties as orthopedic implant materials. The antibacterial mechanisms of these alloy materials are also outlined, thus providing more basis and insights on the design and application of biodegradable alloys with antibacterial properties as orthopedic implants.

Optimizing the bio-degradability and biocompatibility of a biogenic collagen membrane through cross-linking and zinc-doped hydroxyapatite

Biogenic collagen membranes have been widely used as soft tissue barriers in guided bone regeneration (GBR) and guided tissue regeneration (GTR). Nevertheless, their clinical performance remains unsatisfactory because of their low mechanical strength and fast degradation rate in vivo. Although cross-linking with chemical agents is effective and reliable for prolonging the degradation time of collagen membranes, some adverse effects including potential cytotoxicity and undesirable tissue integration have been observed during this process. As a fundamental nutritional trace element, zinc plays an active role in promoting the growth of cells and regulating the degradation of the collagen matrix. Herein, a biogenic collagen membrane was cross-linked with glutaraldehyde-alendronate to prolong its degradation time. The physiochemical and biological properties were enhanced by the incorporation of zinc-doped nanohydroxyapatite (nZnHA), with the native structure of collagen preserved. Specifically, the cross-linking combined with the incorporation of 1% and 2% nZnHA seemed to endow the membrane with the most appropriate biocompatibility and tissue integration capability among the cross-linked membranes, as well as offering a degradation period of six weeks in a rat subcutaneous model. Thus, improving the clinical performance of biogenic collagen membranes by cross-linking together with the incorporation of nZnHA is a promising strategy for the improvement of biogenic collagen membranes. STATEMENT OF SIGNIFICANCE: The significance of this research includes.

The Role of Zinc in Bone Mesenchymal Stem Cell Differentiation

Zinc is an essential trace element for bone growth and bone homeostasis in the human body. Bone mesenchymal stem cells (BMSCs) are multipotent progenitors existing in the bone marrow stroma with the capability of differentiating along multiple lineage pathways. Zinc plays a paramount role in BMSCs, which can be spurred differentiating into osteoblasts, chondrocytes, or adipocytes, and modulates the formation and activity of osteoclasts. The expression of related genes also changed during the differentiation of various cell phenotypes. Based on the important role of zinc in BMSC differentiation, using zinc as a therapeutic approach for bone remodeling will be a promising method. This review explores the role of zinc ion in the differentiation of BMSCs into various cell phenotypes and outlines the existing research on their molecular mechanism.

Effect of ZnO-doped magnesium phosphate cements on osteogenic differentiation of mBMSCs in vitro

The insufficient osteogenesis of magnesium phosphate cements (MPCs) limits its further application. It is significant to develop a bioactive MPC with osteogenic properties. In this work, MPCs were reinforced by zinc oxide nanoparticles (ZnO-NPs). The composition, microstructure, setting time, compressive strength and degradation of ZnO-NPs/MPCs (ZNMPCs) were evaluated. The results showed that the setting times of MPCs were prolonged from 8.2 to 25.3 min (5.0ZNMPC). The exothermic temperatures were reduced from 45.8 ± 0.4℃ (MPCs) to 39.3 ± 0.5℃ (1.0ZNMPC). The compressive strength of ZNMPC composite cement with 1 wt. % ZnO-NPs (1.0ZNMPC) was the highest (42.9 MPa) among all the composite cements. Furthermore, the ZNMPCs were cultured with mouse bone marrow mesenchymal stem cells (mBMSCs). The results yielded that the ZNMPCs exhibited good cytocompatibility with enhanced differentiation, proliferation, and mineralization on mBMSCs, and it also pronouncedly elevated the expressions of genes and proteins involving osteogenesis. These findings suggested that ZNMPCs could drive the differentiation toward osteogenesis and mineralization of mBMSCs, providing a simple way to the MPC with enhanced osteogenesis for further orthopedic applications.

Enhanced osteogenesis and angiogenesis of calcium phosphate cement incorporated with zinc silicate by synergy effect of zinc and silicon ions

Calcium phosphate cement (CPC) with good injectability and osteoconductivity plays important roles in bone grafting application. Much attention has been paid to achieve multifunctionality through incorporating trace elements into CPC. Silicon and zinc can be used as additives to endow CPC with biological functions of osteogenesis, angiogenesis and anti-osteoclastogenesis. In this study, zinc and silicate ions were co-incorporated into CPC through mixing with submicron zinc silicate (Zn₂SiO₄, ZS) to obtain zinc silicate-modified CPCs (ZS/CPCs) with different contents. The results revealed that the addition of ZS increased the compressive strength, prolonged the setting time, and densified the structure of CPC. Low addition content of ZS facilitated the formation of surface apatite layer in the early mineralization stage. Incorporating ZS significantly induced osteogenesis of mouse bone marrow stromal cells (mBMSCs) and angiogenesis of human umbilical vein endothelial cells (HUVECs), and moreover, restricted osteoclastogenesis of Raw 264.7 in vitro. Silicate and zinc ions could be steadily released from ZS/CPCs into the culture medium. With the synergistic effect of silicate and zinc ions, ZS/CPCs provided an appropriate microenvironment for the immune cells to facilitate the osteogenesis of mBMSCs and angiogenesis of HUVECs further. Taken together, it can be concluded that incorporating ZS is an effective way to endow CPC with multifunctionality and better bone regeneration for bone defect repair.

Fabrication and characterization of biodegradable zinc matrix composites reinforced by uniformly dispersed beta-tricalcium phosphate via graphene oxide-assisted hetero-agglomeration

The development of biodegradable Zn matrix composites has been considered a promising approach to achieving enhanced mechanical properties, controllable degradation rate, good biocompatibility, and good osseointegration as orthopedic implants. However, scant literature regarding Zn matrix composites has been reported because of the great difficulty in dispersing the nano-sized bioactive reinforcements uniformly within the Zn matrix. In the present study, a novel and effective method were employed to obtain Zn matrix composites reinforced by uniformly dispersed beta-tricalcium phosphate (β-TCP) via graphene oxide (GO)-assisted hetero-agglomeration and subsequent spark plasma sintering process. A very low-content (0.04 vol%) few-layered GO was used as a coupling reagent to connect the Zn matrix and nano-sized TCP particles. In an appropriate polarity solvent, the negatively charged GO sheets could combine with both the positively charged Zn powder and TCP particles by electrostatic attraction and charge neutralization. Due to the nature of hetero-agglomeration, the flexible GO sheet could adhere to the large Zn powder and attracted a certain amount of TCP particles to form a Zn/GO/TCP sandwich structure by charge neutralization thereby forming a uniform dispersion of TCP particles within Zn matrix. After the spark plasma sintering (SPS) process, the TCP particles incorporated with very thin ZnO layers (thickness of a few dozen nanometers) formed a homogeneous and unique 3D network-like distribution in as-sintered TCP/Zn composites. A unique "snap pea"-like structure was confirmed at the grain boundary of α-Zn grains, which consisted of the TCP particles as "pea" and thin ZnO layer as "pod". Due to the uniform dispersion of bioactive TCP particles and unique structure of the TCP incorporating grain boundary, as-sintered 3TCP/Zn matrix composites possessed yield strength (YS) of 140.8 ± 7.7 MPa, failure strain of 36.0 ± 2.8%, the moderate degradation rate of 19.1 ± 3.3 μm·y^-1 and good cytocompatibility to MC3T3-E1 cells. Moreover, osteogenic differentiation activity evaluation revealed that the addition of TCP could significantly improve the expressions of the osteogenic differentiation-related gene (ALP) in MC3T3-E1 cells, thereby resulting in improved osteogenic capability. Therefore, biodegradable 3TCP/Zn matrix composites fabricated by GO-assisted hetero-agglomeration and subsequent SPS process could be a promising material as orthopedic implants.

Improved cytocompatibility and antibacterial properties of zinc-substituted brushite bone cement based on β-tricalcium phosphate

For bone replacement materials, osteoconductive, osteoinductive, and osteogenic properties are desired. The bacterial resistance and the need for new antibacterial strategies stand among the most challenging tasks of the modern medicine. In this work, brushite cements based on powders of Zinc (Zn) (1.4 wt%) substituted tricalcium phosphate (β-TCP) and non-substituted β-TCP were prepared and investigated. Their initial and final phase composition, time of setting, morphology, pH evolution, and compressive strength are reported. After soaking for 60 days in physiological solution, the cements transformed into a mixture of brushite and hydroxyapatite. Antibacterial activity of the cements against Enterococcus faecium, Escherichia coli, and Pseudomonas aeruginosa bacteria strains was attested. The absence of cytotoxicity of cements was proved for murine fibroblast NCTC L929 cells. Moreover, the cell viability on the β-TCP cement containing Zn²⁺ ions was 10% higher compared to the β-TCP cement without zinc. The developed cements are perspective for applications in orthopedics and traumatology.

Sustained zinc release in cooperation with CaP scaffold promoted bone regeneration via directing stem cell fate and triggering a pro-healing immune stimuli

Metal ions have been identified as important bone metabolism regulators and widely used in the field of bone tissue engineering, however their exact role during bone regeneration remains unclear. Herein, the aim of study was to comprehensively explore the interactions between osteoinductive and osteo-immunomodulatory properties of these metal ions. In particular, the osteoinductive role of zinc ions (Zn²⁺), as well as its interactions with local immune microenvironment during bone healing process, was investigated in this study using a sustained Zn²⁺ delivery system incorporating Zn²⁺ into β-tricalcium phosphate/poly(L-lactic acid) (TCP/PLLA) scaffolds. The presence of Zn²⁺ largely enhanced osteogenic differentiation of periosteum-derived progenitor cells (PDPCs), which was coincident with increased transition from M1 to M2 macrophages (M\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\varphi $$\end{document}φs). We further confirmed that induction of M2 polarization by Zn²⁺ was realized via PI3K/Akt/mTOR pathway, whereas marker molecules on this pathway were strictly regulated by the addition of Zn²⁺. Synergically, this favorable immunomodulatory effect of Zn²⁺ further improved the osteogenic differentiation of PDPCs induced by Zn²⁺ in vitro. Consistently, the spontaneous osteogenesis and pro-healing osteoimmunomodulation of the scaffolds were thoroughly identified in vivo using a rat air pouch model and a calvarial critical-size defect model. Taken together, Zn²⁺-releasing bioactive ceramics could be ideal scaffolds in bone tissue engineering due to their reciprocal interactions between osteoinductive and immunomodulatory characteristics. Clarification of this synergic role of Zn²⁺ during osteogenesis could pave the way to develop more sophisticated metal-ion based orthopedic therapeutic strategies.

The regulating effect of trace elements Si, Zn and Sr on mineralization of gelatin-hydroxyapatite electrospun fiber

Biomineralization approaches have been increasingly adopted to synthesizing advanced materials with superior properties. Nevertheless, the potential influence of inorganic trace elements on the mineralization process of collagen has been rarely reported, despite of the significant progress achieved on exploiting the critical roles of organic polymers in regulating the collagen mineralization. To this aim, the potential roles of Si, Zn and Sr in regulating the mineralization of gelatin-hydroxyapatite (HA) composite fibers have been examined in this study. The results indicated that the incorporation of trace elements not only promoted the biomineralization of gelatin, but also led to drastic change in the mineralization behavior. In particular, the gelatin-SiHA sample showed uniform mineralization predominantly inside the fibers, with nucleation and growth directions along the c-axis of the gelatin fibers. On the contrary, the gelatin-HA sample showed nucleation outside the fibers and spherical mineral crystals on top of fibers, typical structure for heterogeneous nucleation. As the mineralization process proceeded, the gelatin-ZnHA and gelatin-SrHA samples evolved into having similar structure as the gelatin-SiHA sample, despite of showing totally different mineralization behaviors at early time. Overall, the incorporation of trace elements seemed to lower the nucleation barriers, led to a more homogeneous mineralization mode within the fiber region and formation of mineralized structures closer to those in natural bone. Moreover, mineralized samples with trace elements demonstrated improved adhesion and cytoskeleton organization of osteoblastic cells. Such finding would provide important insight for understanding the mineralization process and the optimal design of advanced biological materials.

Biodegradable ZnLiCa ternary alloys for critical-sized bone defect regeneration at load-bearing sites: In vitro and in vivo studies

A novel biodegradable metal system, ZnLiCa ternary alloys, were systematically investigated both in vitro and in vivo. The ultimate tensile strength (UTS) of Zn0.8Li0.1Ca alloy reached 567.60 ± 9.56 MPa, which is comparable to pure Ti, one of the most common material used in orthopedics. The elongation of Zn0.8Li0.1Ca is 27.82 ± 18.35%, which is the highest among the ZnLiCa alloys. The in vitro degradation rate of Zn0.8Li0.1Ca alloy in simulated body fluid (SBF) showed significant acceleration than that of pure Zn. CCK-8 tests and hemocompatibility tests manifested that ZnLiCa alloys exhibit good biocompatibility. Real-time PCR showed that Zn0.8Li0.1Ca alloy successfully stimulated the expressions of osteogenesis-related genes (ALP, COL-1, OCN and Runx-2), especially the OCN. An in vivo implantation was conducted in the radius of New Zealand rabbits for 24 weeks, aiming to treat the bone defects. The Micro-CT and histological evaluations proved that the regeneration of bone defect was faster within the Zn0.8Li0.1Ca alloy scaffold than the pure Ti scaffold. Zn0.8Li0.1Ca alloy showed great potential to be applied in orthopedics, especially in the load-bearing sites.

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The first research work of ZnLiCa alloys to be used as biodegradable metals.

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The ultimate tensile strength (UTS) of Zn0.8Li0.1Ca alloy reached 567.60 ± 9.56 MPa, which is comparable to pure Ti, one of the most common material used in orthopedics.

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Porous scaffolds made of Zn0.8Li0.1Ca showed superior bone-defect-treating effects to pure Ti scaffolds in New Zealand rabbits.

The impact of Zn-doped synthetic polymer materials on bone regeneration: a systematic review

Introduction

To repair bone defects, a variety of bone substitution materials have been used, such as ceramics, metals, natural and synthetic polymers, and combinations thereof. In recent decades, a wide range of synthetic polymers have been used for bone regeneration. These polymers have the advantages of biocompatibility, biodegradability, good mechanical properties, low toxicity, and ease of processing. However, when used alone, they are unable to achieve ideal bone formation. Incorporating zinc (Zn) into synthetic polymers has been considered, as previous studies have shown that Zn²⁺ promotes stem cell osteogenesis and mineral deposition. The purpose of this systematic review was to provide an overview of the application and effectiveness of Zn in synthetic polymers for bone regeneration, whether used alone or in combination with other biomaterials. This study was performed according to the PRISMA guidelines.

Materials and methods

A search of the PubMed, Embase, and the Cochrane Library databases for articles published up to June 2020 revealed 153 relevant studies. After screening the titles, abstracts, and full texts, 13 articles were included in the review; 9 of these were in vitro, 3 were in vivo, and 1 included both in vitro and in vivo experiments.

Results

At low concentrations, Zn²⁺ promoted cell proliferation and osteogenic differentiation, while high-dose Zn²⁺ resulted in cytotoxicity and inhibition of osteogenic differentiation. Additionally, one study showed that Zn²⁺ reduced apatite formation in simulated body fluid. In all of the in vivo experiments, Zn-containing materials enhanced bone formation.

Conclusions

At appropriate concentrations, Zn-doped synthetic polymer materials are better able to promote bone regeneration than materials without Zn.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02195-y.

Hydroxyapatite Based Materials for Bone Tissue Engineering: A Brief and Comprehensive Introduction

Hydroxyapatite (HA) is widely used in bone tissue engineering for its bioactivity and biocompatibility, and a growing number of researchers are exploring ways to improve the physical properties and biological functions of hydroxyapatite. Up to now, HA has been used as inorganic building blocks for tissue engineering or as nanofillers to blend with polymers, furthermore, various methods such as ion doping or surface modification have been also reported to prepare functionalized HA. In this review, we try to give a brief and comprehensive introduction about HA-based materials, including ion-doped HA, HA/polymer composites and surface modified HA and their applications in bone tissue engineering. In addition, the prospective of HA is also discussed. This review may be helpful for researchers to get a general understanding about the development of hydroxyapatite based materials.

Biological Roles and Delivery Strategies for Ions to Promote Osteogenic Induction

Bone is the most studied tissue in the field of tissue regeneration. Even though it has intrinsic capability to regenerate upon injury, several pathologies and injuries could hamper the highly orchestrated bone formation and resorption process. Bone tissue engineering seeks to mimic the extracellular matrix of the tissue and the different biochemical pathways that lead to successful regeneration. For many years, the use of extrinsic factors (i.e., growth factors and drugs) to modulate these biological processes have been the preferred choice in the field. Even though it has been successful in some instances, this approach presents several drawbacks, such as safety-concerns, short release profile and half-time life of the compounds. On the other hand, the use of inorganic ions has attracted significant attention due to their therapeutic effects, stability and lower biological risks. Biomaterials play a key role in such strategies where they serve as a substrate for the incorporation and release of the ions. In this review, the methodologies used to incorporate ions in biomaterials is presented, highlighting the osteogenic properties of such ions and the roles of biomaterials in controlling their release.

Bioinorganic supplementation of calcium phosphate-based bone substitutes to improve in vivo performance: a systematic review and meta-analysis of animal studies

Supplementation of CaP-based bone graft substitutes with bioinorganics such as strontium, zinc or silicon is an interesting approach to increase the biological performance in terms of bone regenerative potential of calcium phosphate (CaP)-based bone substitutes. However, the in vivo efficacy of this approach has not been systematically analyzed, yet. Consequently, we performed a systematic review using the available literature regarding the effect of bioinorganic supplementation in CaP-based biomaterials on new bone formation and material degradation in preclinical animal bone defect models and studied this effect quantitatively by performing a meta-analysis. Additional subgroup analyses were used to study the effect of different bioinorganics, animal model, or phase category of CaP-based biomaterial on bone formation or material degradation. Results show that bioinorganic supplementation increases new bone formation (standardized mean difference [SMD]: 1.43 SD, confidence interval [CI]: 1.13-1.73). Additional subgroup analysis showed that strontium, magnesium and silica significantly enhanced bone formation, while zinc did not have any effect. This effect of bioinorganic supplementation on new bone formation was stronger for DCPD or β-TCP and biphasic CaPs than for HA or α-TCP (p < 0.001). In general, material degradation was slightly hindered by bioinorganic supplementation (mean difference [MD]: 0.84%, CI: 0.01-1.66), with the exception of strontium that significantly enhanced degradation. Overall, bioinorganic supplementation represents an effective approach to enhance the biological performance of CaP-based bone substitutes.

β-tricalcium phosphate for bone substitution: Synthesis and properties

β-tricalcium phosphate (β-TCP) is one the most used and potent synthetic bone graft substitute. It is not only osteoconductive, but also osteoinductive. These properties, combined with its cell-mediated resorption, allow full bone defects regeneration. Its clinical outcome is sometimes considered to be "unpredictable", possibly due to a poor understanding of β-TCP physico-chemical properties: β-TCP crystallographic structure is not fully uncovered; recent results suggest that sintered β-TCP is coated with a Ca-rich alkaline phase; β-TCP apatite-forming ability and osteoinductivity may be enhanced by a hydrothermal treatment; β-TCP grain size and porosity are strongly modified by the presence of minute amounts of β-calcium pyrophosphate or hydroxyapatite impurities. The aim of the present article is to provide a critical, but still rather comprehensive review of the current state of knowledge on β-TCP, with a strong focus on its synthesis and physico-chemical properties, and their link to the in vivo response. STATEMENT OF SIGNIFICANCE: The present review documents the richness, breadth, and interest of the research devoted to β-tricalcium phosphate (β-TCP). β-TCP is synthetic, osteoconductive, osteoinductive, and its resorption is cell-mediated, thus making it one of the most potent bone graft substitutes. This comprehensive review reveals that there are a number of aspects, such as surface chemistry, crystallography, or stoichiometry deviations, that are still poorly understood. As such, β-TCP is still an exciting scientific playground despite a 50 year long history and > 200 yearly publications.

In vitro evaluation of novel titania-containing borate bioactive glass scaffolds

Titanium-containing borate bioactive glass scaffolds (0, 5, 15, and 20 mol %, identified as BRT0, BRT1, BRT3, and BRT4) with a microstructure similar to that of human trabecular bone were prepared and evaluated in vitro for potential bone loss applications in revision total knee arthroplasty (rTKA). Methyl thiazolyl tetrazolium (MTT) cell viability assays of scaffold ion release extracts revealed that BRT0 scaffolds (0 mol % titanium) inhibited cell proliferation and activity at day 14. At day 30, all scaffold extracts decreased cell proliferation and activity significantly. However, live/dead cell assay results demonstrated that degradation products from all the scaffolds had no inhibitory effect on cell viability. Significant bactericidal efficacies of BRT3 extracts against Escherishia coli (Gram-negative) and BRT1 extracts against Staphylococcus aureus and Staphylococcus epidermidis (both Gram-positive bacteria) were demonstrated. Finally, evaluation of the cell/bioactive glass surface interactions showed well-spread cells on the surface of the BRT3 glass discs and BRT1 and BRT3 scaffolds, when compared to BRT0 and BRT4 scaffolds. The results indicate that by changing the Ti⁴⁺ :B³⁺ ratio, the ion release and consequently cell proliferation could be improved. in vitro results in this study demonstrate that BRT3 scaffolds could be a promising candidate for addressing bone loss in rTKAs; however, in vivo studies would be required to evaluate the effect of a dynamic environment on the cell and tissue response to the fabricated scaffolds.

Sapucaia nut: Morphophysiology, minerals content, methodological validation in image analysis, phenotypic and molecular diversity in Lecythis pisonis Cambess

Sapucaia or Lecythis pisonis Cambess. is an ornamental tree that produces edible, tasty, and nutritious nuts, and can be used for timber production. Sapucaia has potential as a functional food, owing to optimal nutritional and particularly Se levels. The present study sought to characterize the seeds of 21 sapucaia matrices from forest remnants of a neotropical hotspot (Atlantic Forest) and farms in two Brazilian states. Biometrics, germination, vigor, lignin content in the teguments, minerals content, and phenotypic and molecular diversity were analyzed. The seeds of matrices 16 and 21 were the most vigorous. Nuts from matrices 21 and 17 contained the highest amounts of Se. Matrices 5, 8, and 21 were the most phenotypically distant; whereas matrix 21 was the most genetically distant. Importantly, we validated a new non-destructive and efficient X-ray-based methodology for internal and densitometric analysis of sapucaia seeds, and demonstrated a high genetic divergence among matrices.

Zinc as a Therapeutic Agent in Bone Regeneration

Zinc is an essential mineral that is required for normal skeletal growth and bone homeostasis. Furthermore, zinc appears to be able to promote bone regeneration. However, the cellular and molecular pathways through which zinc promotes bone growth, homeostasis, and regeneration are poorly understood. Zinc can positively affect chondrocyte and osteoblast functions, while inhibiting osteoclast activity, consistent with a beneficial role for zinc in bone homeostasis and regeneration. Based on the effects of zinc on skeletal cell populations and the role of zinc in skeletal growth, therapeutic approaches using zinc to improve bone regeneration are being developed. This review focuses on the role of zinc in bone growth, homeostasis, and regeneration while providing an overview of the existing studies that use zinc as a bone regeneration therapeutic.

The effect of trace elements on BMP-2, BMP-7 and STRO-1+ cells in hip replacement

To explore the correlation between the trace elements in the proximal femur and BMP-2, BMP-7 and STRO-1+ cells in hip replacement, and analyze the therapeutic effect of prosthesis loosening in clinic. Fifty-one patients undergone the first hip replacement in xxx hospital from August 2016 to August 2019 were selected as the study subjects, including 26 females and 25 males, aged 52-89 years. The bone marrow mesenchymal stem cells (BMSCs) were cultured in vitro for flow cytometry, and the string-1+ in BMSCs was detected and analyzed. After that, the expression of bone morphogenetic protein 2 (BMP-2) and bone morphogenetic protein 7 (BMP-7) in the cells were detected by enzyme-linked immunosorbent assay, the content of trace elements in the supernatant was detected by radioimmunoassay, and the collected data were analyzed statistically. In the analysis of the content of trace elements, it was found that the correlation between trace elements was dependent on the separation area, and all trace elements had no correlation with BMP2. Ca2⁺, Mg2⁺ were correlated with the level of BMP7 and Ca2⁺, VD3 was correlated with the percentage of STOR-1⁺ cells. Further analysis showed that the correlation between trace elements was dependent on bone mineral density (BMD) area, and there was a positive correlation between vitamin D3 (VD3), parathyroid hormone (PTH), zinc, and BMD in zone 7. To sum up, it is found that trace elements may be related to prosthesis loosening, which provides experimental basis for the treatment of prosthesis loosening later.

A pure zinc membrane with degradability and osteogenesis promotion for guided bone regeneration: In vitro and in vivo studies

Selection of an appropriate membrane material for guided bone regeneration (GBR) is still ongoing among resorbable and nonresorbable membranes with different characteristics. The major problem with nonresorbable membranes is the inevitable secondary surgery, while resorbable polymer membranes have limitations in providing sufficient mechanical support during the bone repair period due to premature loss of mechanical strength. Pure magnesium foil has been evaluated to explore its feasibility as a resorbable GBR membrane. It exhibited better mechanical properties, whereas poor formability and fast degradation rate were noted. In light of this, pure zinc membrane was developed as a pilot research in this paper. We designed three types of pure zinc membranes: pure Zn without pores, pure Zn with 300 µm diameter and 1000 µm diameter pores, and pure titanium without pores as a control. The mechanical property, in vitro immersion tests, and MC3T3-E1 cell viability assays were tested. Moreover, in vivo behaviors of three type zinc membranes were evaluated by using a rat calvarial critical-sized bone defect model. The experimental results indicated that pure Zn membrane with 300 µm pores showed the most favorable osteogenic capability, comparable to that of titanium membrane without pores. Therefore, considering appropriate degradation rate, adequate mechanical maintenance, and profitable osteogenic capacity, metallic pure zinc is believed to be a promising candidate for barrier membranes in GBR therapy for bone regeneration, and its mechanical property can be enhanced with further alloying. STATEMENT OF SIGNIFICANCE: Metallic element zinc plays a pivotal role in the growth and mineralization of bone tissues. As a pilot research, three type of guided bone regeneration (GBR) membranes were developed in the present work: pure Zn without pores, pure Zn with 300 µm-diameter and 1000 µm-diameter pores respectively. The mechanical property, in vitro immersion tests and MC3T3-E1 cell viability assays were tested, with pure titanium without pores as a control, thereafter the in vivo performance were evaluated by using a rat calvarial critical-sized bone defect model. It indicated that pure Zn membrane with 300 µm pores showed the most favorable osteogenic capability, comparable to that of titanium membrane control, and is believed to be a promising material candidate as barrier membrane in GBR therapy for bone regeneration.

Study on osteogenesis of zinc-loaded carbon nanotubes/chitosan composite biomaterials in rat skull defects

Chitosan with hydroxyapatite composition, a natural polymer, may be a biomaterial of importance for bone regeneration. Carbon nanotube, a nanoscale material, has been another focus for bone restoration. Zinc, an essential trace element, contributes to the development and growth of skeletal system. The purpose of the current research was to investigate the effects of Zinc-loaded Carbon Nanotubes/Chitosan composite biomaterials in the restoration of rat skull defects, and to verify the hypothesis that these zinc ions of appropriate concentration would strengthen the osteogenesis of rat defects. Four different groups of composite biomaterials were fabricated from no Zinc Carbon nanotubes/Chitosan (GN), 0.2% Zinc-Carbon nanotubes/Chitosan (GL), 1% Zinc-Carbon nanotubes/Chitosan (GM) and 2% Zinc-Carbon nanotubes/Chitosan (GH). After characterizations, these composite biomaterials were then transplanted into rat skull defects. The experimental animals were executed at 12 weeks after transplanted surgeries, and the rat skull defects were removed for related analyses. The results of characterizations suggested the Zinc-loaded composite biomaterials possessed good mechanical and osteoinductive properties. An important finding was that the optimal osteogenic effect appeared in rat skull defects transplanted with 1% Zinc-Carbon nanotubes/Chitosan. Overall, these composite biomaterials revealed satisfactory osteogenesis, nevertheless, there was a requirement to further perfect the zinc ion concentrations to achieve the better bone regeneration.

Repair of segmental rabbit radial defects with Cu/Zn co-doped calcium phosphate scaffolds incorporating GDF-5 carrier

Repair of segmental bone defects is a challenge in orthopaedics. A bone substitute is a potential solution for this challenge, and angiogenesis and osteogenesis are critical to the performance of scaffold materials. For enhancing angiogenesis and osteogenesis activities of implanted scaffolds, Cu/Zn co-doped calcium phosphate scaffolds carrying GDF-5-release microspheres were prepared and implanted into surgically created critical-sized rabbit radial defects. Radiological examination, histological analysis and biomechanical tests were used to evaluate the bone healing-union. Results showed that, with increasing Cu/Zn concentrations, new bone area, new blood vessel density, and bending failure load all increased significantly. Furthermore, Cu/Zn co-doped scaffolds incorporating GDF-5-release microspheres exhibited further increased angiogenesis and osteogenesis (vs. Cu/Zn co-doped alone), as well as a superior bending failure load. These show that, simultaneous incorporation of trace essential ions and GDF-5 combines pro-angiogenic and pro-osteogenic actions of these bioactive substances, potentially offering an effective approach to assist the healing of critical-sized bone defects.

Osteogenic potential of poly(ethylene glycol)-amorphous calcium phosphate composites on human mesenchymal stem cells

Synthetic hydrogel-amorphous calcium phosphate composites are promising candidates to substitute biologically sourced scaffolds for bone repair. While the hydrogel matrix serves as a template for stem cell colonisation, amorphous calcium phosphate s provide mechanical integrity with the potential to stimulate osteogenic differentiation. Here, we utilise composites of poly(ethylene glycol)-based hydrogels and differently stabilised amorphous calcium phosphate to investigate potential effects on attachment and osteogenic differentiation of human mesenchymal stem cells. We found that functionalisation with integrin binding motifs in the form of RGD tripeptide was necessary to allow adhesion of large numbers of cells in spread morphology. Slow dissolution of amorphous calcium phosphate mineral in the scaffolds over at least 21 days was observed, resulting in the release of calcium and zinc ions into the cell culture medium. While we qualitatively observed an increasingly mineralised extracellular matrix along with calcium deposition in the presence of amorphous calcium phosphate-loaded scaffolds, we did not observe significant changes in the expression of selected osteogenic markers.

3D printing of metal–organic framework incorporated porous scaffolds to promote osteogenic differentiation and bone regeneration

A nanoZIF-8 modified porous composite scaffold was fabricated via extrusion-based 3D printing technology, which could promote osteogenesis in vitro and accelerate bone regeneration in vivo.

Improving osteogenesis of calcium phosphate bone cement by incorporating with manganese doped β-tricalcium phosphate

Lack of osteogenic capacity limits the bone repair effect of calcium phosphate cement (CPC). In present work, bivalent manganese ion (Mn²⁺) doped β-tricalcium phosphate (Mn-TCP) was incorporated into CPC to enhance its osteogenic ability. The incorporation of Mn-TCP promoted the hydration reaction of CPC. The presence of Mn²⁺ made the hydration products finer. When adding 10 wt% Mn-TCP in CPC (Mn-CPC-1), the setting time of CPC was shortened, whereas the strength and injectability were not changed. Mouse Bone marrow mesenchymal stem cells (mBMSCs) on Mn-CPC-1 and CPC with 20 wt% Mn-TCP (Mn-CPC-2) presented better adhesion and spreading behaviors. Besides, Mn-CPC-1 promoted the gene levels of ALP, Col-I and OC while Mn-CPC-2 promoted the gene levels of Runx2 and OC. Cellular behaviors were related to two points: one was the increase of adsorption capacity of proteins (e.g. BSA) after changing the surface properties of bone cements; and the other was the biological role of Mn²⁺ released from CPC in osteogenesis. All the results indicated that CPC incorporated with 10 wt% Mn-TCP has good osteogenesis and proper physicochemical properties, which will be a prospective biomaterial applying in the area of bone regeneration.

Corrosion resistance and antibacterial activity of zinc-loaded montmorillonite coatings on biodegradable magnesium alloy AZ31

A Zinc-loaded montmorillonite (Zn-MMT) coating was hydrothermally prepared using Zn²⁺ ion intercalated sodium montmorillonite (Na-MMT) upon magnesium (Mg) alloy AZ31 as bone repairing materials. Biodegradation rate of the Mg-based materials was studied via potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS) and hydrogen evolution tests. Results revealed that both Na-MMT and Zn-MMT coatings exhibited better corrosion resistance in Dulbecco's modified eagle medium (DMEM) + 10% calf serum (CS) than bare Mg alloy AZ31 counterparts. Hemolysis results demonstrated that hemocompatibility of the Na-MMT and Zn-MMT coatings were 5%, and lower than that of uncoated Mg alloy AZ31 pieces. In vitro MTT tests and live-dead stain of osteoblast cells (MC3T3-E1) indicated a significant improvement in cytocompatibility of both Na-MMT and Zn-MMT coatings. Antibacterial properties of two representative bacterial strains associated with device-related infection, i.e. Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), were employed to explore the antibacterial behavior of the coatings. The measured inhibitory zone and bacterial growth rate confirmed that Zn-MMT coatings exhibited higher suppression toward both E. coli and S. aureus than that of Na-MMT coatings. The investigation on antibacterial mechanism through scanning electron microscopy (SEM) and lactate dehydrogenase (LDH) release assay manifested that Zn-MMT coating led to severe breakage of bacterial membrane of E. coli and S. aureus, which resulted in a release of cytoplasmic materials from the bacterial cells. In addition, the good inhibition of Zn-MMT coatings against E. coli and S. aureus might be attributed to the slow but sustainable release of Zn²⁺ ions (up to 144 h) from the coatings into the culture media. This study provides a novel coating strategy for manufacturing biodegradable Mg alloys with good corrosion resistance, biocompatibility and antibacterial activity for future orthopedic applications. STATEMENT OF SIGNIFICANCE: The significance of the current work is to develop a corrosion-resistant and antibacterial Zn-MMT coating on magnesium alloy AZ31 through a hydrothermal method. The Zn-MMT coating on magnesium alloy AZ31 shows better corrosion resistance, biocompatibility and excellent antibacterial ability than magnesium alloy AZ31. This study provides a novel coating on Mg alloys for future orthopedic applications.

In vitro evaluation of the ZX11 magnesium alloy as potential bone plate: Degradability and mechanical integrity

Considering the excellent biocompatibility of magnesium (Mg) alloys and their better mechanical properties compared to polymer materials, a wrought MgZnCa alloy with low contents of Zn (0.7 wt%) and Ca (0.6 wt%) (ZX11) was developed by twin roll casting (TRC) technology as potential biodegradable bone plates. The degradability and cell response of the ZX11 alloy were evaluated in vitro, as well as the mechanical integrity according to tensile tests after immersion. The results revealed a slightly higher degradation rate for the rolled ZX11, in comparison to that of the annealed one. It was mainly caused by the deformation twins and residual strain stored in the rolled alloy, which also seemed to promote localized degradation, thereby leading to a relatively fast deterioration in mechanical properties, especially the fracture strain/elongation. In contrast, after the annealing treatment, the alloy showed relatively lower strength, yet a lower degradation rate and quite stable elongation during the initial weeks of immersion were observed. More importantly, the ZX11 alloy, regardless of the annealing treatment, showed good in vitro cytocomopatibility regarding human primary osteoblasts. The assessment indicates the rolled alloy as a good choice for implantation sites where relatively high mechanical strength is needed during the early implantation, while the annealed alloy is a potential candidate for the sites which demand stable mechanical integrity during service. STATEMENT OF SIGNIFICANCE: The development of magnesium alloys as bone implants demands low degradation rate to gain not only a slow hydrogen evolution, but also a stable mechanical integrity during service. The present study develops a micro-alloyed MgZnCa alloy via twin roll casting (TRC) technology. It exhibited limited cytotoxicity, fairly low degradation rate and comparable strength to the reported Mg-1Zn-5Ca alloy which has been used as bone screws in clinical trials, indicating the great potential application as biodegradable bone implants. Furthermore, it showed good mechanical integrity during immersion to support the defect healing. Our results can aid other researchers to evaluate the mechanical integrity of biodegradable materials and to pay more attention to the effect of degradation behaviour on mechanical integrity of materials.

Simonkolleite Coating on Poly(Amino Acids) to Improve Osteogenesis and Suppress Osteoclast Formation in Vitro

Zinc can enhance osteoblastic bone formation and stimulate osteogenic differentiation, suppress the differentiation of osteoclast precursor cells into osteoclasts, and inhibit pathogenic bacterial growth in a dose-dependent manner. In this study, simonkolleite, as a novel zinc resource, was coated on poly (amino acids) (PAA) via suspending PAA powder in different concentrations of zinc chloride (ZnCl₂) solution, and the simonkolleite-coated PAA (Zn–PAA) was characterized by SEM, XRD, FT-IR and XPS. Zinc ions were continuously released from the coating, and the release behavior was dependent on both the concentration of the ZnCl₂ immersing solution and the type of soak solutions (SBF, PBS and DMEM). The Zn–PAA was cultured with mouse bone marrow stem cells (BMSCs) through Transwell^TM plates, and the results indicated that the relative cell viability, alkaline phosphatase (ALP) activity and mineralization of BMSCs were significantly higher with Zn–PAA as compared to PAA. Moreover, the Zn–PAA was cultured with RAW264.7 cells, and the results suggested an inhibiting effect of Zn–PAA on the cell differentiation into osteoclasts. In addition, Zn–PAA exhibited an antibacterial activity against both S. aureus and E. coli. These findings suggest that simonkolleite coating with certain contents could promote osteogenesis, suppress osteoclast formation and inhibit bacteria, indicating a novel way of enhancing the functionality of synthetic bone graft material and identifying the underline principles for designing zinc-containing bone grafts.

S, Hegde A, ES SP, Johnson RP, Das SP, Vazirally S, Rekha PD. Effect of calcium glucoheptonate on proliferation and osteogenesis of osteoblast-like cells in vitro

Calcium is the key macromineral having a role in skeletal structure and function, muscle contraction, and neurotransmission. Bone remodeling is maintained through a constant balance between calcium resorption and deposition. Calcium deficiency is resolved through calcium supplementation, and among the supplements, water-soluble organic molecules attracted great pharmaceutical interest. Calcium glucoheptonate is a highly water-soluble organic calcium salt having clinical use; however, detailed investigations on its biological effects are limited. We assessed the effects of calcium glucoheptonate on cell viability and proliferation of osteoblast-like MG-63 cells. Calcium uptake and mineralization were evaluated using Alizarin red staining of osteoblast-like MG-63 cells treated with calcium glucoheptonate. Expression of osteogenic markers were monitored by western blotting, immunofluorescence, and qRT-PCR assays. Increased proliferation and calcium uptake were observed in the MG-63 cells treated with calcium glucoheptonate. The treatment also increased the expression of osteopontin and osteogenic genes such as collagen-1, secreted protein acidic and cysteine rich (SPARC), and osteocalcin. Calcium glucoheptonate treatment did not exert any cytotoxicity on colorectal and renal epithelial cells, indicating the safety of the treatment. This is the first report with evidence for its beneficial effect for pharmaceutical use in addressing calcium deficiency conditions.