Copper-based biomaterials for bone and cartilage tissue engineering

Copper metabolism in osteoarthritis and its relation to oxidative stress and ferroptosis in chondrocytes

Ferroptosis, an iron-ion-dependent process of lipid peroxidation, damages the plasma membrane, leading to non-programmed cell death. Osteoarthritis (OA), a prevalent chronic degenerative joint disease among middle-aged and older adults, is characterized by chondrocyte damage or loss. Emerging evidence indicates that chondrocyte ferroptosis plays a role in OA development. However, most research has concentrated on ferroptosis regulation involving typical iron ions, potentially neglecting the significance of elevated copper ions in both serum and joint fluid of patients with OA. This review aims to fill this gap by systematically examining the interplay between copper metabolism, oxidative stress, ferroptosis, and copper-associated cell death in OA. It will provide a comprehensive overview of copper ions' role in regulating ferroptosis and their dual role in OA. This approach seeks to offer new insights for further research, prevention, and treatment of OA.

Copper Toxicity in Animals: A Review

Copper is an essential trace element in animals and humans. However, excessive intake of copper can cause copper ions to accumulate in tissues and organs of animals, leading to copper toxicity. Copper ions induce apoptosis and autophagy through oxidative stress-mediated mitochondrial dysfunction. In addition, copper induces cell death by targeting lipoylated tricarboxylic acid (TCA) cycling proteins, termed cuproptosis. In recent years, copper cytotoxicity studies have attracted attention. In addition, the number of cases of copper toxicity in animals has been increasing over the past years due to environmental pollution and overdose from copper feed supplements. Therefore, a comprehensive understanding of copper toxicity and the metabolism of copper ions can aid in devising strategies for preventing copper toxicity. This review introduces the tissue and organ toxicity and cytotoxicity caused by copper toxicity and reviews the metabolism of copper ions in tissues, organs, and cells. The paper also reviews the clinical cases and animal experiments of copper toxicity in recent years. Finally, the preventive and curative measures for copper toxicity and the future challenges are also discussed. The general objective of this paper is to provide a reliable reference for copper toxicity prevention.

Enhanced osteogenic and bactericidal performance of premixed calcium phosphate cement with photocrosslinked alginate thin film

The increasing prevalence of implant-associated infections (IAI) in orthopedics remains a public health challenge. Calcium phosphates (CaPs) are critical biomaterials in dental treatments and bone regeneration. It is highly desirable to endow CaPs with antibacterial properties. To achieve this purpose, we developed a photocrosslinked methacrylated alginate co-calcium phosphate cement (PMA-co-PCPC) with antibacterial properties, using α-tricalcium phosphate (α-TCP) powders with 16% amorphous contents as solid phase, liquid phases containing CuCl2 and SrCl2 as an inhibitor, and CaCl2 as an activator to construct PCPC. When CaCl2 started to activate the hydration reaction, Sr2+ or Cu2+ ions were exchanged with Ca2+, and α-TCP dissolution was restarted and gradually hydrated to form calcium-deficient hydroxyapatite (CDHA). PMA was added to crosslink with Cu/Sr ions and form gel-layer-wrapped hydrated CDHA. This study explored the binding mechanism of PMA and PCPC and the ion release rule of Ca2+ → Sr2+/Cu2+, optimized the construction of several antibacterial PMA-co-PCPC materials, and analyzed the physical, chemical, and biological properties. Because of the combined effect of Cu and Sr ions, the scaffold exhibited a potential antibacterial activity, promoting bone formation and vascular regeneration. This work provides a basis for designing antibacterial calcium phosphate biomaterials with controllable treatment, which is an important characteristic for preventing IAI of biomaterials.

Progress in copper-based materials for wound healing

Chronic wounds have become the leading cause of death, particularly among diabetic patients. Chronic wounds affect ~6.5 million patients each year, according to statistics, and wound care and management incur significant financial costs. The rising prevalence of chronic wounds, combined with the limitations of current treatments, necessitates the development of new and innovative approaches to accelerate wound healing. Copper has been extensively studied for its antibacterial and anti-inflammatory activities. Copper in its nanoparticle form could have better biological properties and many applications in health care.

Сopper nanoparticles supported on charcoal and betacellulin - Two novel stimulators of ovarian granulosa cell functions and their functional interrelationships

The present experiments are aimed to examine the effect of copper nanoparticles supported on charcoal (CuNPs/C), growth factor betacellulin (BTC) and their interrelationships in the control of ovarian cell functions. Porcine ovarian granulosa cells were cultured in the presence of CuNPs/C (0, 1, 10 or 100 ng/ml), BTC (100 ng/ml) and the combination of both, CuNPs/C + BTC. Markers of cell proliferation (BrDU incorporation), of the S-phase (PCNA) and G-phase (cyclin B1) of the cell cycle, markers of extrinsic (nuclear DNA fragmentation) and cytoplasmic/mitochondrial apoptosis (bax and caspase 3), and the release of progesterone and estradiol were assessed by BrDU test, TUNEL, quantitative immunocytochemistry and ELISA. Both CuNPs/C and BTC, when added alone, increased the expression of all the markers of cell proliferation, reduced the expression of all apoptosis markers and stimulated progesterone and estradiol release. Moreover, BTC was able to promote the CuNPs/C action on the accumulation of PCNA, cyclin B1, bax and estradiol output. These observations demonstrate the stimulatory action of both CuNPs/C and BTC on ovarian cell functions, as well as the ability of BTC to promote the action of CuNPs/C on ovarian cell functions.

Pro-angiogenic and antibacterial copper containing nanoparticles in PLGA/amorphous calcium phosphate bone nanocomposites

Large bone defects after trauma demand for adequate bone substitutes. Bone void fillers should be antibacterial and pro-angiogenic. One viable option is the use of composite materials like the combination of PLGA and amorphous calcium phosphate (aCaP). Copper stimulates angiogenesis and has antibacterial qualities. Either copper oxide (CuO) nanoparticles (NPs) were therefore added to PLGA/aCaP/CuO in different concentrations (1, 5 and 10 w/w %) or copper-doped tricalcium phosphate NPs (TCP with 2% of copper) were electrospun into PLGA/CuTCP nanocomposites. Bi-layered nanocomposites of PLGA/aCaP with different copper NPs (CuO or TCP) and a second layer of pristine PLGA were fabricated. Two clinical bacterial isolates (Staphylococcus aureus and Staphylococcus epidermidis) were used to assess antibacterial properties of the copper-containing materials. For angiogenesis, the chorioallantoic membrane (CAM) assay of the chicken embryo was performed. The higher the CuO content, the higher were the antibacterial properties, with 10 % CuO reducing bacterial adhesion most effectively. Vessel and cell densities were highest in the 5 % CuO containing scaffolds, while tissue integration was more pronounced at lower CuO content. The PLGA/aCaP/CuO (1 % CuO) behaved similar like PLGA/CuTCP in all angiogenic and antibacterial readouts, based on the same copper fraction. We conclude that CuO NPs or CuTCP NPs are useful components to increase angiogenic properties of nanocomposites and at the same time exhibiting antibacterial characteristics.

Construction of a PEGDA/chitosan hydrogel incorporating mineralized copper-doped mesoporous silica nanospheres for accelerated bone regeneration

Hydrogels, integrating diverse biocompatible materials, have emerged as promising candidates for bone repair applications. This study presents a double network hydrogel designed for bone tissue engineering, combining poly(ethylene glycol) diacrylate (PEGDA) and chitosan (CS) crosslinked through UV polymerization and ionic crosslinking. Concurrently, copper-doped mesoporous silica nanospheres (Cu-MSNs) were synthesized using a one-pot method. Cu-MSNs underwent additional modification through in-situ biomineralization, resulting in the formation of an apatite layer. Polydopamine was employed to facilitate the deposition of Calcium (Ca) and Phosphate (P) ions on the surface of Cu-MSNs (Cu-MSNs/PDA@CaP). Composite hydrogels were created by integrating varied concentrations of Cu-MSNs/PDA@CaP (25, 50, 100, 150, 200 μg/mL). Characterization unveiled distinctive interconnected porous structures within the composite hydrogel, showcasing a notable 169.6 % enhancement in compressive stress (elevating from 89.01 to 240.19 kPa) compared to pure PEGDA. In vitro biocompatibility experiments illustrated that the composite hydrogel maintained elevated cell viability (up to 106.6 %) and facilitated rapid cell proliferation over 7 days. The hydrogel demonstrated a substantial 57.58 % rise in ALP expression and a surprising 235.27 % increase in ARS staining. Moreover, it significantly enhanced the expression of crucial osteogenic genes, such as run-related transcription factors 2 (RUNX2), collagen 1a1 (Col1a1), and secreted phosphoprotein 1 (Spp1), establishing it as a promising scaffold for bone regeneration. This study shows how Cu-MSNs/PDA@CaP were successfully integrated into a double network hydrogel, resulting in a composite material with good biological responses. Due to its improved characteristics, this composite hydrogel holds the potential for advancing bone regeneration procedures.

Dual-Targeted Metal Ion Network Hydrogel Scaffold for Promoting the Integrated Repair of Tendon-Bone Interfaces

The tendon-bone interface has a complex gradient structure vital for stress transmission and pressure buffering during movement. However, injury to the gradient tissue, especially the tendon and cartilage components, often hinders the complete restoration of the original structure. Here, a metal ion network hydrogel scaffold, with the capability of targeting multitissue, was constructed through the photopolymerization of the LHERHLNNN peptide-modified zeolitic imidazolate framework-8 (LZIF-8) and the WYRGRL peptide-modified magnesium metal-organic framework (WMg-MOF) within the hydrogel scaffold, which could facilitate the directional migration of metal ions to form a dynamic gradient, thereby achieving integrated regeneration of gradient tissues. LZIF-8 selectively migrated to the tendon, releasing zinc ions to enhance collagen secretion and promoting tendon repair. Simultaneously, WMg-MOF migrated to cartilage, releasing magnesium ions to induce cell differentiation and facilitating cartilage regeneration. Infrared spectroscopy confirmed successful peptide modification of nano ZIF-8 and Mg-MOF. Fluorescence imaging validated that LZIF-8/WMg-MOF had a longer retention, indirectly confirming their successful targeting of the tendon-bone interface. In summary, this dual-targeted metal ion network hydrogel scaffold has the potential to facilitate synchronized multitissue regeneration at the compromised tendon-bone interface, offering favorable prospects for its application in the integrated reconstruction characterized by the gradient structure.

Fabrication of a Nanoscale Magnesium/Copper Metal-Organic Framework on Zn-Based Guided Bone Generation Membranes for Enhancing Osteogenesis, Angiogenesis, and Bacteriostasis Properties

Recently, zinc (Zn) and its alloys have demonstrated great potential as guided bone regeneration (GBR) membranes to treat the problems of insufficient alveolar bone volume and long-term osseointegration instability during dental implantology. However, bone regeneration is a complex process consisting of osteogenesis, angiogenesis, and antibacterial function. For now, the in vivo osteogenic performance and antibacterial activity of pure Zn are inadequate, and thus fabricating a platform to endow Zn membranes with multifunctions may be essential to address these issues. In this study, various bimetallic magnesium/copper metal-organic framework (Mg/Cu-MOF) coatings were fabricated and immobilized on pure Zn. The results indicated that the degradation rate and water stability of Mg/Cu-MOF coatings could be regulated by controlling the feeding ratio of Cu2+. As the coating and Zn substrate degraded, an alkaline microenvironment enriched with Zn2+, Mg2+, and Cu2+ was generated. It significantly improved calcium phosphate deposition, differentiation of osteoblasts, and vascularization of endothelial cells in the extracts. Among them, Mg/Cu1 showed the best comprehensive performance. The superior antibacterial activity of Mg/Cu1 was demonstrated in vitro and in vivo, which indicated significantly enhanced bacteriostatic activity against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli as compared to that of the bare sample. Bimetallic Mg/Cu-MOF coating could properly coordinate the multifunction on a Zn membrane and could be a promising platform for promoting its bone regeneration, which could pave the way for Zn-based materials to be used as barrier membranes in oral clinical trials.

A Multifunctional Scaffold for Bone Infection Treatment by Delivery of microRNA Therapeutics Combined With Antimicrobial Nanoparticles

Treating bone infections and ensuring bone repair is one of the greatest global challenges of modern orthopedics, made complex by antimicrobial resistance (AMR) risks due to long-term antibiotic treatment and debilitating large bone defects following infected tissue removal. An ideal multi-faceted solution would will eradicate bacterial infection without long-term antibiotic use, simultaneously stimulating osteogenesis and angiogenesis. Here, a multifunctional collagen-based scaffold that addresses these needs by leveraging the potential of antibiotic-free antimicrobial nanoparticles (copper-doped bioactive glass, CuBG) to combat infection without contributing to AMR in conjunction with microRNA-based gene therapy (utilizing an inhibitor of microRNA-138) to stimulate both osteogenesis and angiogenesis, is developed. CuBG scaffolds reduce the attachment of gram-positive bacteria by over 80%, showcasing antimicrobial functionality. The antagomiR-138 nanoparticles induce osteogenesis of human mesenchymal stem cells in vitro and heal a large load-bearing defect in a rat femur when delivered on the scaffold. Combining both promising technologies results in a multifunctional antagomiR-138-activated CuBG scaffold inducing hMSC-mediated osteogenesis and stimulating vasculogenesis in an in vivo chick chorioallantoic membrane model. Overall, this multifunctional scaffold catalyzes killing mechanisms in bacteria while inducing bone repair through osteogenic and angiogenic coupling, making this platform a promising multi-functional strategy for treating and repairing complex bone infections.

Metal-based nanoparticles in antibacterial application in biomedical field: Current development and potential mechanisms

The rise in drug resistance in pathogenic bacteria greatly endangers public health in the post-antibiotic era, and drug-resistant bacteria currently pose a great challenge not only to the community but also to clinical procedures, including surgery, stent implantation, organ transplantation, and other medical procedures involving any open wound and compromised human immunity. Biofilm-associated drug failure, as well as rapid resistance to last-resort antibiotics, necessitates the search for novel treatments against bacterial infection. In recent years, the flourishing development of nanotechnology has provided new insights for exploiting promising alternative therapeutics for drug-resistant bacteria. Metallic agents have been applied in antibacterial usage for several centuries, and the functional modification of metal-based biomaterials using nanotechnology has now attracted great interest in the antibacterial field, not only for their intrinsic antibacterial nature but also for their ready on-demand functionalization and enhanced interaction with bacteria, rendering them with good potential in further translation. However, the possible toxicity of MNPs to the host cells and tissue still hinders its application, and current knowledge on their interaction with cellular pathways is not enough. This review will focus on recent advances in developing metallic nanoparticles (MNPs), including silver, gold, copper, and other metallic nanoparticles, for antibacterial applications, and their potential mechanisms of interaction with pathogenic bacteria as well as hosts.

In-vitro and in-vivo evaluation for the bio-natural Alginate/nano-Hydroxyapatite (Alg/n-HA) injectable hydrogel for critical size bone substitution

Currently, bio-natural injectable hydrogels are receiving a lot of attention due to their ability to control, adjust, and adapt to random bone defects, in addition, to their ability to mimic the composition of natural bones. From such a viewpoint, this study goal is to prepare and characterize the injectable hydrogels paste based on the natural alginate (Alg) derived from brown sea algae as a polysaccharide polymer, which coupled with nano biogenic-hydroxyapatite (n-HA) prepared from eggshells and enriched with valuable trace elements. The viscosity and mechanical properties of the paste were investigated. As well as the in-vitro study in terms of water absorption and biodegradability in the PBS, biocompatibility and the capability of the injectable Alginate/n-Hydroxyapatite (Alg/n-HA) to regenerate bone for the most suitable injectable form. The injectable hydrogel (BP -B sample) was chosen for the study as it had an appropriate setting time for injecting (13 mins), and suitable compressive strength reached 6.3 MPa. The in vivo study was also carried out including a post-surgery follow-up test of the newly formed bone (NB) in the defect area after 10 and 20 weeks using different techniques such as (SEM/EDX) and histological analysis, the density of the newly formed bone by Dual x-ray absorptiometry (DEXA), blood biochemistry and the radiology test. The results proved that the injectable hydrogels Alginate/n-Hydroxyapatite (Alg/n-HA) had an appreciated biodegradability and bioactivity, which allow the progress of angiogenesis, endochondral ossification, and osteogenesis throughout the defect area, which positively impacts the healing time and ensures the full restoration for the well-mature bone tissue that similar to the natural bone.

Bioactive elements manipulate bone regeneration

While bone tissue is known for its inherent regenerative abilities, various pathological conditions and trauma can disrupt its meticulously regulated processes of bone formation and resorption. Bone tissue engineering aims to replicate the extracellular matrix of bone tissue as well as the sophisticated biochemical mechanisms crucial for effective regeneration. Traditionally, the field has relied on external agents like growth factors and pharmaceuticals to modulate these processes. Although efficacious in certain scenarios, this strategy is compromised by limitations such as safety issues and the transient nature of the compound release and half-life. Conversely, bioactive elements such as zinc (Zn), magnesium (Mg) and silicon (Si), have garnered increasing interest for their therapeutic benefits, superior stability, and reduced biotic risks. Moreover, these elements are often incorporated into biomaterials that function as multifaceted bioactive components, facilitating bone regeneration via release on-demand. By elucidating the mechanistic roles and therapeutic efficacy of the bioactive elements, this review aims to establish bioactive elements as a robust and clinically viable strategy for advanced bone regeneration.

Harvest of functional mesenchymal stem cells derived from in vivo osteo-organoids

Bone marrow-derived mesenchymal stem cells (BM-MSCs) play a crucial role in stem cell therapy and are extensively used in regenerative medicine research. However, current methods for harvesting BM-MSCs present challenges, including a low yield of primary cells, long time of in vitro expansion, and diminished differentiation capability after passaging. Meanwhile mesenchymal stem cells (MSCs) recovered from cell banks also face issues like toxic effects of cryopreservation media. In this study, we provide a detailed protocol for the isolation and evaluation of MSCs derived from in vivo osteo-organoids, presenting an alternative to autologous MSCs. We used recombinant human bone morphogenetic protein 2-loaded gelatin sponge scaffolds to construct in vivo osteo-organoids, which were stable sources of MSCs with large quantity, high purity, and strong stemness. Compared with protocols using bone marrow, our protocol can obtain large numbers of high-purity MSCs in a shorter time (6 days vs. 12 days for obtaining passage 1 MSCs) while maintaining higher stemness. Notably, we found that the in vivo osteo-organoid-derived MSCs exhibited stronger anti-replicative senescence capacity during passage and amplification, compared to BM-MSCs. The use of osteo-organoid-derived MSCs addresses the conflict between the limitations of autologous cells and the risks associated with allogeneic sources in stem cell transplantation. Consequently, our protocol emerges as a superior alternative for both stem cell research and tissue engineering.

Copper-containing titanium alloys promote the coupling of osteogenesis and angiogenesis by releasing copper ions

Previous investigations have reported on the ability of copper (Cu)-bearing biomaterials to accelerate vascular formation and bone regeneration. However, few studies have explored the effects of Cu-bearing materials on the interactions between angiogenesis and osteogenesis. Therefore, in this study, we prepared Cu-containing alloys using selective laser melting (SLM) technology and investigated the impact of preosteoblasts seeded on Ti6Al4V-4.5Cu alloy on angiogenesis. Our results indicated that Ti6Al4V-4.5Cu alloys increased the expression of proangiogenic genes and proteins in preosteoblasts, which further stimulated vascular formation in endothelial cells. Besides, we discovered that the biological effects of the Ti6Al4V-4.5Cu alloy were partly attributed to the release of Cu ions. In short, our research demonstrated the ability of Ti6Al4V-4.5Cu alloys to promote the coupling of angiogenesis and osteogenesis by releasing Cu ions.

Transition metals in angiogenesis - A narrative review

The aim of this paper is to offer a narrative review of the literature regarding the influence of transition metals on angiogenesis, excluding lanthanides and actinides. To our knowledge there are not any reviews up to date offering such a summary, which inclined us to write this paper. Angiogenesis describes the process of blood vessel formation, which is an essential requirement for human growth and development. When the complex interplay between pro- and antiangiogenic mediators falls out of balance, angiogenesis can quickly become harmful. As it is so fundamental, both its inhibition and enhancement take part in various diseases, making it a target for therapeutic treatments. Current methods come with limitations, therefore, novel agents are constantly being researched, with metal agents offering promising results. Various transition metals have already been investigated in-depth, with studies indicating both pro- and antiangiogenic properties, respectively. The transition metals are being applied in various formulations, such as nanoparticles, complexes, or scaffold materials. Albeit the increasing attention this field is receiving, there remain many unanswered questions, mostly regarding the molecular mechanisms behind the observed effects. Notably, approximately half of all the transition metals have not yet been investigated regarding potential angiogenic effects. Considering the promising results which have already been established, it should be of great interest to begin investigating the remaining elements whilst also further analyzing the established effects.

Engineered biochemical cues of regenerative biomaterials to enhance endogenous stem/progenitor cells (ESPCs)-mediated articular cartilage repair

As a highly specialized shock-absorbing connective tissue, articular cartilage (AC) has very limited self-repair capacity after traumatic injuries, posing a heavy socioeconomic burden. Common clinical therapies for small- to medium-size focal AC defects are well-developed endogenous repair and cell-based strategies, including microfracture, mosaicplasty, autologous chondrocyte implantation (ACI), and matrix-induced ACI (MACI). However, these treatments frequently result in mechanically inferior fibrocartilage, low cost-effectiveness, donor site morbidity, and short-term durability. It prompts an urgent need for innovative approaches to pattern a pro-regenerative microenvironment and yield hyaline-like cartilage with similar biomechanical and biochemical properties as healthy native AC. Acellular regenerative biomaterials can create a favorable local environment for AC repair without causing relevant regulatory and scientific concerns from cell-based treatments. A deeper understanding of the mechanism of endogenous cartilage healing is furthering the (bio)design and application of these scaffolds. Currently, the utilization of regenerative biomaterials to magnify the repairing effect of joint-resident endogenous stem/progenitor cells (ESPCs) presents an evolving improvement for cartilage repair. This review starts by briefly summarizing the current understanding of endogenous AC repair and the vital roles of ESPCs and chemoattractants for cartilage regeneration. Then several intrinsic hurdles for regenerative biomaterials-based AC repair are discussed. The recent advances in novel (bio)design and application regarding regenerative biomaterials with favorable biochemical cues to provide an instructive extracellular microenvironment and to guide the ESPCs (e.g. adhesion, migration, proliferation, differentiation, matrix production, and remodeling) for cartilage repair are summarized. Finally, this review outlines the future directions of engineering the next-generation regenerative biomaterials toward ultimate clinical translation.

Electrospun Scaffolds Based on Poly(butyl cyanoacrylate) for Tendon Tissue Engineering

Tendon disorders are common medical conditions that could lead to significant disability, pain, healthcare costs, and a loss of productivity. Traditional approaches require long periods of treatment, and they largely fail due to the tissues weakening and the postoperative alterations of the normal joint mechanics. To overcome these limitations, innovative strategies for the treatment of these injuries need to be explored. The aim of the present work was the design of nano-fibrous scaffolds based on poly(butyl cyanoacrylate) (PBCA), a well-known biodegradable and biocompatible synthetic polymer, doped with copper oxide nanoparticles and caseinphosphopeptides (CPP), able to mimic the hierarchical structure of the tendon and to improve the tissue healing potential. These were developed as implants to be sutured to reconstruct the tendons and the ligaments during surgery. PBCA was synthetized, and then electrospun to produce aligned nanofibers. The obtained scaffolds were characterized for their structure and physico-chemical and mechanical properties, highlighting that CuO and CPP loading, and the aligned conformation determined an increase in the scaffold mechanical performance. Furthermore, the scaffolds loaded with CuO showed antioxidant and anti-inflammatory properties. Moreover, human tenocytes adhesion and proliferation to the scaffolds were assessed in vitro. Finally, the antibacterial activity of the scaffolds was evaluated using Escherichia coli and Staphylococcus aureus as representative of Gram-negative and Gram-positive bacteria, respectively, demonstrating that the CuO-doped scaffolds possessed a significant antimicrobial effect against E. coli. In conclusion, scaffolds based on PBCA and doped with CuO and CPP deserve particular attention as enhancers of the tendon tissue regeneration and able to avoid bacterial adhesion. Further investigation on the scaffold efficacy in vivo will assess their capability for enhancing the tendon ECM restoration in view of accelerating their translation to the clinic.

The role of copper chromite nanoparticles on physical and bio properties of scaffolds based on poly(glycerol-azelaic acid) for application in tissue engineering fields

Tissue engineering combines suitable cells, engineering methods, and proper biochemical factors to develop functional and biological tissues and repair damaged tissues. In this study, we focused on synthesizing and characterizing a nanocomposite scaffold based on glycerol and azelaic acid (Gl-Az) combined with copper chromite (CuCr₂O₄) nanoparticles in order to increase the osteogenic differentiation efficiency of human adipose-derived stem cells (hADSCs) on fabricated scaffolds. The degradability and hydrophobicity properties as well as mechanical and thermal behaviors of nanocomposite scaffolds were investigated. Next, the cell toxicity of glycerol, azelaic acid and CuCr₂O₄ nanoparticles was studied by MTT assay test and acridine orange staining. Finally, the osteogenic differentiation of hADSCs on Gl-Az-CuCr₂O₄ scaffolds was examined using alkaline phosphatase activity (ALP) and calcium content. The obtained results demonstrated that Gl-Az-1%CuCr₂O₄ not only showed appropriate mechanical strength, biocompatibility and degradability but also influenced the capability of hADSCs to differentiate into osteogenic lineages. The hADSCs culture in Gl-Az-1%CuCr₂O₄ showed a significant increase in ALP activity levels and calcium biomineralization after 14 days of osteogenic differentiation. In conclusion, the Gl-Az-1%CuCr₂O₄ nanocomposite could be used as a biocompatible and degradable scaffold to induce the bone differentiation of hADSCs and it could be a promising scaffold in bone regenerative medicine.

Enhanced osteoarthritis therapy by nanoengineered mesenchymal stem cells using biomimetic CuS nanoparticles loaded with plasmid DNA encoding TGF-β1

Mesenchymal stem cells (MSCs) therapy shows the potential benefits to relieve clinical symptoms of osteoarthritis (OA), but it is uncertain if it can repair articular cartilage lesions — the main pathology of OA. Here, we prepared biomimetic cupper sulfide@phosphatidylcholine (CuS@PC) nanoparticles (NPs) loaded with plasmid DNA (pDNA) encoding transforming growth factor-beta 1 (TGF-β1) to engineer MSCs for enhanced OA therapy via cartilage regeneration. We found that the NPs not only promoted cell proliferation and migration, but also presented a higher pDNA transfection efficiency relative to commercial transfection reagent lipofectamine 3000. The resultant CuS/TGF-β1@PC NP-engineered MSCs (termed CTP-MSCs) were better than pure MSCs in terms of chondrogenic gene expression, glycosaminoglycan deposition and type II collagen formation, favoring cartilage repair. Further, CTP-MSCs inhibited extracellular matrix degradation in interleukin-1β-induced chondrocytes. Consequently, intraarticular administration of CTP-MSCs significantly enhanced the repair of damaged cartilage, whereas pure MSCs exhibited very limited effects on cartilage regeneration in destabilization of the medial meniscus (DMM) surgical instability mice. Hence, this work provides a new strategy to overcome the limitation of current stem cell therapy in OA treatment through developing more effective nanoengineered MSCs.

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Biomimetic CuS nanoparticles (NPs) loaded with TGF-β1 pDNA are prepared for nanoengineering of MSCs.

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CuS/TGF-β1@PC NPs are more efficient than commercial transfection agent in terms of pDNA transfection.

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The NP-engineered CTP-MSCs exhibit enhanced migration, chondrogenesis and inhibition of ECM degradation.

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CTP-MSCs effectively treat osteoarthritis (OA) mice models via cartilage regeneration.

Preparation and characterizations of an injectable and biodegradable high-strength iron-bearing brushite cement for bone repair and vertebral augmentation applications

Brushite cements have good osteoconductive and resorbable properties, but the low mechanical strength and poor injectability limit their clinical applications in load-bearing conditions and minimally invasive surgery. In this study, an injectable brushite cement that contains monocalcium phosphate monohydrate (MCPM) and β-tricalcium phosphate (β-TCP) as its solid phase and ammonium ferric citrate (AFC) solution as the aqueous medium was designed to have high mechanical strength. The optimized formulation achieved a compressive strength of 62.8 ± 7.2 MPa, which is above the previously reported values of hand-mixing brushite cements. The incorporation of AFC prolonged the setting times and greatly enhanced the injectability and degradation properties of the cements. In vitro and in vivo experiments demonstrated that the brushite cements exhibited good biocompatibility and bone regeneration capacity. The novel brushite cement is promising for bone healing in load-bearing applications.

A bionic composite hydrogel with dual regulatory functions for the osteochondral repair

Due to the avascular nature of cartilage, it is difficult to heal and regenerate spontaneously after injury. At present, tissue engineering has become a promising strategy for repairing damaged cartilage, but the use of seed cells and growth factors is limited. In addition, the importance of mechanical compatibility of scaffold materials is often ignored. In this study, osteochondral scaffold was designed as a bilayer structure with a dense γ-Polyglutamic acid/carboxymethyl chitosan/bacterial cellulose (PGA/CMCS/BC) hydrogel cartilage layer and a porous nano HA-containing PGA/CMCS/BC hydrogel osteogenic layer. In addition, bioactive ions were introduced into the hydrogel scaffold to adjust the mechanical and swelling properties of the material to match the mechanical properties of natural articular cartilage. At the same time, based on the structural characteristics of bone and cartilage, magnesium and copper ions were introduced into the double-layer hydrogel scaffold, respectively, to prepare the cartilage layer and the bone layer, which endowed the material with excellent antibacterial properties and achieved the purpose of the integrated repair of bone and cartilage. The results showed that, after adding magnesium ions, the tensile breaking strength of material was increased from 0.66 MPa to 1.37 MPa，the corresponding compression modulus of the material (strain 0-12%) increased from 0.15 MPa to 0.58 MPa whilst the maximum mass swelling rate decreased from 155% to 75%. The results of in vivo experiments show that the group with bioactive ions had a much better effect on the repair of osteochondral defects, compared with group without bioactive ions, demonstrating such double ion regulation strategy is a very practical strategy for the treatment of osteochondral defects.

Relationship between Selected Micronutrient Concentrations, Total Antioxidant Status, Pain Severity, and the Image of 1H MR Spectroscopy in Degenerative Spine Disease: A Case-Control Study

Osteoarthritis of the spine is a common disease and constitutes a significant problem in highly developed countries. Due to the aging of the population, the number of patients with advanced degenerative changes continues to grow. Trace elements and antioxidant status may play an active role in the pathogenesis of osteoarthritis of the spine. The aim of this study was to assess the relationship between total antioxidant status (TAS), the concentration of selected elements (Zn, Cu, Se, Mn) in the serum, nutritional and environmental factors, the severity of pain, and images of degenerative changes in the spine demonstrated in proton magnetic resonance spectroscopy (¹H MRS). The study included 90 patients with degenerative spine disease and 40 healthy people. Serum Zn, Cu, Se, and Mn concentrations were determined by atomic absorption spectrometry. The Cu/Zn molar ratio was calculated. TAS was determined spectrophotometrically using a ready-made Randox kit. The severity of spine pain was assessed using the visual analogue scale VAS. In the ¹H MRS study, the fat/water ratio was determined in L1 and L5 vertebral bodies and in the L4/5 intervertebral disc. In patients with osteoarthritis of the spine, there was a reduced concentration of Zn and Cu in the serum (0.77 ± 0.22 mg/L, 1.1 ± 0.35 mg/L) compared to the control group (0.83 ± 0.13 mg/L, 1.25 ± 0.41 mg/L, respectively). In the study group, we also observed a significantly lower Cu concentration in smokers (1.07 ± 0.35 mg/L) compared to non-smokers (1.17 ± 0.34 mg/L). A relationship between the female sex and a decreased concentration of TAS in the serum, both in people with degenerative spine disease and in healthy people, has been demonstrated. In patients with serum TAS levels below the reference values, the fat/water ratio was higher in the L5 spine shaft, while in those with elevated Mn levels, the value was higher in the L4/L5 intervertebral disc, which indicates a greater degree of degeneration in both cases. Patients with normal serum Cu concentration experienced lower pain intensity assessed in the VAS scale. The study showed some abnormalities in serum trace element levels and TAS in patients with osteoarthritis of the spine.

Topographic Orientation of Scaffolds for Tissue Regeneration: Recent Advances in Biomaterial Design and Applications

Tissue engineering to develop alternatives for the maintenance, restoration, or enhancement of injured tissues and organs is gaining more and more attention. In tissue engineering, the scaffold used is one of the most critical elements. Its characteristics are expected to mimic the native extracellular matrix and its unique topographical structures. Recently, the topographies of scaffolds have received increasing attention, not least because different topographies, such as aligned and random, have different repair effects on various tissues. In this review, we have focused on various technologies (electrospinning, directional freeze-drying, magnetic freeze-casting, etching, and 3-D printing) to fabricate scaffolds with different topographic orientations, as well as discussed the physicochemical (mechanical properties, porosity, hydrophilicity, and degradation) and biological properties (morphology, distribution, adhesion, proliferation, and migration) of different topographies. Subsequently, we have compiled the effect of scaffold orientation on the regeneration of vessels, skin, neural tissue, bone, articular cartilage, ligaments, tendons, cardiac tissue, corneas, skeletal muscle, and smooth muscle. The compiled information in this review will facilitate the future development of optimal topographical scaffolds for the regeneration of certain tissues. In the majority of tissues, aligned scaffolds are more suitable than random scaffolds for tissue repair and regeneration. The underlying mechanism explaining the various effects of aligned and random orientation might be the differences in “contact guidance”, which stimulate certain biological responses in cells.

Nanomaterials in Bone Regeneration

Nanomaterials are promising in the development of innovative therapeutic options that include tissue and organ replacement, as well as bone repair and regeneration. The expansion of new nanoscaled biomaterials is based on progress in the field of nanotechnologies, material sciences, and biomedicine. In recent decades, nanomaterial systems have bridged the line between the synthetic and natural worlds, leading to the emergence of a new science called nanomaterial design for biological applications. Nanomaterials replicating bone properties and providing unique functions help in bone tissue engineering. This review article is focused on nanomaterials utilized in or being explored for the purpose of bone repair and regeneration. After a brief overview of bone biology, including a description of bone cells, matrix, and development, nanostructured materials and different types of nanoparticles are discussed in detail.

Functional role of inorganic trace elements in dentin apatite-Part II: Copper, manganese, silicon, and lithium

Trace elements are recognized as being essential in dentin and bone apatite. The effects of zinc, strontium, magnesium, and iron were discussed in part I. In part II, we evaluated the functional role of copper, manganese, silicon, and lithium on dentin apatite, with critical effects on morphology, crystallinity, and solubility. An electronic search was performed on the role of these trace elements in dentin apatite from January 2000 to January 2022. The recent aspects of the relationship between four different trace elements and their critical role in the structure and mechanics of dentin were assessed. These findings show that elements play a vital role in the human body, especially in the crystalline structure of dentin apatite. Copper presents immense benefits in dental restorative biomaterials because of its importance in enhancing odontogenesis. The biological role of manganese in dentin apatite is still largely unknown, but it has gained attention for many of its broad physiological functions such as modulating osteoblast proliferation, differentiation, and metabolism in bones. The functional role of silicon in dentin apatite is similarly lacking, but findings reveal its importance in mineralization and collagen formation, making it useful for the field of restorative dentistry. Likewise, lithium was found to have important roles in dentin mineralization as well as in the formation of dentin bridges and tissues. Therefore, there is growing importance in studying the aforementioned elements in the context of dentin apatite.

Cu2+ Release from Polylactic Acid Coating on Titanium Reduces Bone Implant-Related Infection

Implant-related infection (IRI) is a major problem in orthopedics. Copper (Cu) is an essential trace element with strong bactericidal activity and, thus, presents potential for reducing IRI. The present study explored a straightforward strategy for releasing Cu²⁺ from titanium (Ti) implants, and we conducted a preliminary study to assess the feasibility of this approach in clinical translation. Polylactic acid (PLA) coatings containing different concentrations of copper ions were prepared on Ti discs. The antibacterial activity and biocompatibility of the copper ion-incorporated Ti implants were evaluated using Staphylococcus aureus (S. aureus), bone marrow mesenchymal stem cells (BMSCs) and animal models. In vitro, the coatings produced burst release of Cu²⁺ in 12 h, and inhibited S. aureus growth in a dose-dependent manner. The coatings prepared from PLA solutions containing 0.5 or 1.0 mg/mL reduced the viability and osteogenic differentiation of BMSCs, but these effects were negated after the coatings were immersed in culture medium for 6 h. Four weeks after implantation, the Cu-free K-wires challenged with S. aureus had persistent infection and inferior fracture healing to the other three groups, while Cu-coated wires had no evidence of infection. Furthermore, the Cu-coated wires placed in rabbits without S. aureus challenge showed superior fracture healing to the other three groups. These results suggest that PLA coatings containing Cu²⁺ may be an effective design for reducing IRI without adversely affecting adjacent bone healing.

Production and Characterization of a Coconut Oil Incorporated Gelatin-Based Film and Its Potential Biomedical Application

The influence of coconut oil (CO) on a gelatin-based film was investigated when used as a potential wound dressing material. There is limited study on CO in protein-based wound dressing materials. Therefore, in this study a self-supporting, continuous and homogenous CO incorporated gelatin-based film was formulated and obtained by solution casting method. The influence of CO on physicochemical and thermal properties of gelatin-based film was also determined. Moreover, the effect CO in gelatin films on cell viability and cell migration was analysed with a preliminary cell culture study. Homogenous dispersion of 10% (w/w) CO was obtained in films when 3% (v/w) Tween 80, a surfactant, was incorporated to 20% (w/w) plasticized gelatin film forming solution. Effect of CO on gelatin-based film was observed via phase separation by SEM analysis. Water uptake of gelatin film with no CO, GE film; and 10% (w/w) CO incorporated GE film, GE-CO, were 320% and 210%, respectively, after 3 hours in water. FTIR analysis showed triglyceride component of CO and increased hydrogen bonding between NH groups of gelatin in GE-CO films. DSC results suggested a more ordered structure of GE-CO film due to an increase in melt-like transition temperature and melting enthalpy of GE-CO film. CO content also increased cell viability, assessed by XTT Assay since cell viability was approximately 100% when L929 cell culture was incubated with GE-CO of 5-100 μg/mL. Moreover, GE-CO samples within 5-25 μg/mL concentration range, increased proliferation of L929 cells since cell viability was significantly higher than the 100% viable cell culture control (P < 0.05) which is also an indication of efficient healing. However, GE decreased viability of L929 cells significantly at 100-10 μg/mL concentration range (P < 0.05) and were toxic at concentrations of 100, 75 and 50 μg/mL which decreased ∿50% of the viability of the cells. Scratch Assay to assess in vitro wound healing showed cell migration towards scratch after 24 h as an indication of wound healing only in GE-CO samples. This study showed that, CO could efficiently be added to gelatin-based films for preparation of a primary wound dressing biomaterial which is also demonstrated to have a promising wound healing effect for minor wounds.

Comparison of Physicochemical, Mechanical, and (Micro-)Biological Properties of Sintered Scaffolds Based on Natural- and Synthetic Hydroxyapatite Supplemented with Selected Dopants

The specific combinations of materials and dopants presented in this work have not been previously described. The main goal of the presented work was to prepare and compare the different properties of newly developed composite materials manufactured by sintering. The synthetic- (SHAP) or natural- (NHAP) hydroxyapatite serves as a matrix and was doped with: (i) organic: multiwalled carbon nanotubes (MWCNT), fullerenes C60, (ii) inorganic: Cu nanowires. Research undertaken was aimed at seeking novel candidates for bone replacement biomaterials based on hydroxyapatite—the main inorganic component of bone, because bone reconstructive surgery is currently mostly carried out with the use of autografts; titanium or other non-hydroxyapatite -based materials. The physicomechanical properties of the developed biomaterials were tested by Scanning Electron Microscopy (SEM), Dielectric Spectroscopy (BSD), Nuclear Magnetic Resonance (NMR), and Differential Scanning Calorimetry (DSC), as well as microhardness using Vickers method. The results showed that despite obtaining porous sinters. The highest microhardness was achieved for composite materials based on NHAP. Based on NMR spectroscopy, residue organic substances could be observed in NHAP composites, probably due to the organic structures that make up the tooth. Microbiology investigations showed that the selected samples exhibit bacteriostatic properties against Gram-positive reference bacterial strain S. epidermidis (ATCC 12228); however, the property was much less pronounced against Gram-negative reference strain E. coli (ATCC 25922). Both NHAP and SHAP, as well as their doped derivates, displayed in good general compatibility, with the exception of Cu-nanowire doped derivates.

Inorganic Nanoparticles in Bone Healing Applications

Modern biomedicine aims to develop integrated solutions that use medical, biotechnological, materials science, and engineering concepts to create functional alternatives for the specific, selective, and accurate management of medical conditions. In the particular case of tissue engineering, designing a model that simulates all tissue qualities and fulfills all tissue requirements is a continuous challenge in the field of bone regeneration. The therapeutic protocols used for bone healing applications are limited by the hierarchical nature and extensive vascularization of osseous tissue, especially in large bone lesions. In this regard, nanotechnology paves the way for a new era in bone treatment, repair and regeneration, by enabling the fabrication of complex nanostructures that are similar to those found in the natural bone and which exhibit multifunctional bioactivity. This review aims to lay out the tremendous outcomes of using inorganic nanoparticles in bone healing applications, including bone repair and regeneration, and modern therapeutic strategies for bone-related pathologies.

Preparation and characterization of a novel drug-loaded Bi-layer scaffold for cartilage regeneration

The incidence of articular cartilage defects is increasing year by year. In order to repair the cartilage tissue at the defect, scaffolds with nanofiber structure and biocompatibility have become a research hotspot. In this study, we designed and fabricated a bi-layer scaffold prepared from an upper layer of drug-dispersed gelatin methacrylate (GELMA) hydrogel and a lower layer of a drug-encapsulated coaxial fiber scaffold prepared from silk fiber (SF) and polylactic acid (PLA). These bi-layer scaffolds have porosity (91.26 ± 3.94%) sufficient to support material exchange and pore size suitable for cell culture and infiltration, as well as mechanical properties (2.65 ± 0.31 MPa) that meet the requirements of cartilage tissue engineering. The coaxial fiber structure exhibited excellent drug release properties, maintaining drug release for 14 days in PBS. In vitro experiments indicated that the scaffolds were not toxic to cells and were amenable to chondrocyte migration. Notably, the growth of cells in a bi-layer scaffold presented two states. In the hydrogel layer, cells grow through interconnected pores and take on a connective tissue-like shape. In the coaxial fiber layer, cells grow on the surface of the coaxial fiber mats and appeared tablet-like. This is similar to the structure of the functional partitions of natural cartilage tissue. Together, the bi-layer scaffold can play a positive role in cartilage regeneration, which could be a potential therapeutic choice to solve the current problems of clinical cartilage repair.

Bipolar Metal Flexible Electrospun Fibrous Membrane Based on Metal-Organic Framework for Gradient Healing of Tendon-to-Bone Interface Regeneration

Metal ions play a significant role in tissue repair, with widely application in clinical treatment. However, the therapeutic effect of metal ions is always limited due to metabolization and narrow repair capability. Here, a bipolar metal flexible electrospun fibrous membrane based on a metal-organic framework (MOF), which is bioinspired by the gradient structure of the tendon-to-bone interface, with a combination of regulating osteoblasts differentiation and angiogenesis properties, is constructed successfully by a continuous electrospinning technique and matching the longitudinal space morphology for synchronous regeneration. Furthermore, the MOF, acting as carriers, can not only achieve the sustainable release of metal ions, but promote the osteogenesis and tenogenesis on the scaffold. The in vitro data show that this novel hierarchical structure can accelerate the tenogenesis, the biomineralization, and angiogenesis. Moreover, in the in vivo experiment, the flexible fibrous membrane can promote tendon and bone tissue repair, and fibrocartilage reconstruction, to realize the multiple tissue synchronous regeneration at the damaged tendon-to-bone interface. Altogether, this newly developed bipolar metal flexible electrospun fibrous membrane based on a MOF, as a new biomimetic flexible scaffold, has great potential in reconstruct the tissue damage, especially gradient tissue damage.

3D printed porous sulfonated polyetheretherketone scaffold for cartilage repair: Potential and limitation

Objective

The treatment of cartilage lesions has always been a difficult problem. Although cartilage tissue engineering provides alternative treatment options for cartilage lesions, biodegradable tissue engineering scaffolds have limitations.

Methods

In this study, we constructed a porous PEEK scaffold via 3D printing, surface-engineered with concentrated sulfuric acid for 15 s (SPK-15), 30 s (SPK-30), and 60 s (SPK-60). We systematically evaluated the physical and chemical characteristics and biofunctionalities of the scaffolds, and then evaluated the macrophage polarization modulating ability and anti-inflammatory effects of the sulfonated PEEK, and observed the cartilage-protective effect of SPK using a co-culture study. We further evaluated the repair effect of PEEK and SPK by implanting the prosthetic scaffold into a cartilage defect in a rabbit model.

Results

Compared to the PEEK, SPK-15 and SPK-60 scaffolds, SPK-30 has a good micro/nanostructure, appropriate biomechanical properties (compressive modulus, 43 ± 5 MPa; Shaw hardness, 20.6 ± 1.3 HD; close to native cartilage, 30 ± 8 MPa, 17.8 ± 0.8 HD), and superior biofunctionalities. Compared to PEEK, sulfonated PEEK can favor macrophage polarization to the M2 phenotype, which increases anti-inflammatory cytokine secretion. Furthermore, SPK can also prevent macrophage-induced cartilage degeneration. The in-vivo animal experiment demonstrates that SPK can favor new tissue ingrowth and integration, prevent peri-scaffold cartilage degeneration and patellar cartilage degeneration, inhibit inflammatory cytokine secretion, and promote cartilage function restoration.

Conclusion

The present study confirmed that the 3D printed porous sulfonated PEEK scaffold could promote cartilage functional repair, and suggests a new promising strategy for treating cartilage defects with a functional prosthesis that spontaneously inhibits nearby cartilage degeneration.

Translational potential of this article

In the present study, we propose a new cartilage repair strategy based on a porous, non-biodegradable polyetheretherketone (PEEK) scaffold, which may bring up a new treatment route for elderly patients with cartilage lesions in the future.

Copper and Copper/Zn Ratio in a Series of Children with Chronic Diseases: A Cross-Sectional Study

Copper is an essential micronutrient for humans. A cross-sectional and comparative study was done to assess serum Cu levels and serum copper/zinc (Cu/Zn) ratio and its association with nutritional indicators in a series of children and adolescents with chronic diseases. Anthropometric, biochemical, dietary, body composition, and bone densitometry assessments were carried out. Serum Cu and Zn were measured by atomic absorption spectrophotometry. Seventy-eight patients (55% women) participated. The mean serum Cu in the entire series and by nutritional status through body mass index (BMI) was normal. Serum Cu decreased significantly with age and was meaningfully higher in children than in adolescents. The risk of finding altered Cu levels in children and men was higher than in adolescents and women, respectively. Twenty-two per cent of patients had abnormal serum copper levels, 13 had hypercupremia, and four had hypocupremia. The Cu/Zn ratio was greater than 1.00 for 87% of the patients, which is an indicator of an inflammatory state. All patients with hypozincemia and hypocupremia had deficient Zn intake, but only 65% of the patients with hypercupremia had dietary Zn deficiency. Consequently, the Cu/Zn ratio could indicate an inflammatory state and a high risk of zinc deficiency in this specific child population.

Tuning the Properties of PNIPAm-Based Hydrogel Scaffolds for Cartilage Tissue Engineering

Poly(N-isopropylacrylamide) (PNIPAm) is a three-dimensional (3D) crosslinked polymer that can interact with human cells and play an important role in the development of tissue morphogenesis in both in vitro and in vivo conditions. PNIPAm-based scaffolds possess many desirable structural and physical properties required for tissue regeneration, but insufficient mechanical strength, biocompatibility, and biomimicry for tissue development remain obstacles for their application in tissue engineering. The structural integrity and physical properties of the hydrogels depend on the crosslinks formed between polymer chains during synthesis. A variety of design variables including crosslinker content, the combination of natural and synthetic polymers, and solvent type have been explored over the past decade to develop PNIPAm-based scaffolds with optimized properties suitable for tissue engineering applications. These design parameters have been implemented to provide hydrogel scaffolds with dynamic and spatially patterned cues that mimic the biological environment and guide the required cellular functions for cartilage tissue regeneration. The current advances on tuning the properties of PNIPAm-based scaffolds were searched for on Google Scholar, PubMed, and Web of Science. This review provides a comprehensive overview of the scaffolding properties of PNIPAm-based hydrogels and the effects of synthesis-solvent and crosslinking density on tuning these properties. Finally, the challenges and perspectives of considering these two design variables for developing PNIPAm-based scaffolds are outlined.

Effects of Extracellular Osteoanabolic Agents on the Endogenous Response of Osteoblastic Cells

The complex multidimensional skeletal organization can adapt its structure in accordance with external contexts, demonstrating excellent self-renewal capacity. Thus, optimal extracellular environmental properties are critical for bone regeneration and inextricably linked to the mechanical and biological states of bone. It is interesting to note that the microstructure of bone depends not only on genetic determinants (which control the bone remodeling loop through autocrine and paracrine signals) but also, more importantly, on the continuous response of cells to external mechanical cues. In particular, bone cells sense mechanical signals such as shear, tensile, loading and vibration, and once activated, they react by regulating bone anabolism. Although several specific surrounding conditions needed for osteoblast cells to specifically augment bone formation have been empirically discovered, most of the underlying biomechanical cellular processes underneath remain largely unknown. Nevertheless, exogenous stimuli of endogenous osteogenesis can be applied to promote the mineral apposition rate, bone formation, bone mass and bone strength, as well as expediting fracture repair and bone regeneration. The following review summarizes the latest studies related to the proliferation and differentiation of osteoblastic cells, enhanced by mechanical forces or supplemental signaling factors (such as trace metals, nutraceuticals, vitamins and exosomes), providing a thorough overview of the exogenous osteogenic agents which can be exploited to modulate and influence the mechanically induced anabolism of bone. Furthermore, this review aims to discuss the emerging role of extracellular stimuli in skeletal metabolism as well as their potential roles and provide new perspectives for the treatment of bone disorders.

New Concept and Apparatus for Cytocentrifugation and Cell Processing for Microscopy Analysis

Cytocentrifugation is a common technique for the capture of cells on microscopic slides. It usually requires a special cytocentrifuge or cytorotor and cassettes. In the study presented here, we tested the new concept of cytocentrifugation based on the threaded connection of the lid and the sample holder to ensure an adjustable flow of solutions through the filters and the collection of the filtered solutions in the reservoir during centrifugation. To test this concept, we developed a device for the preparation of cell samples on circular coverslips. The device was tested for the capture and sample processing of both eukaryotic and prokaryotic cells, cell nuclei, and mitochondria for microscopy analysis including image cytometry. Moreover, an efficient procedure was developed for capturing formaldehyde-fixed cells on non-treated coverslips without cell drying. The results showed that the tested arrangement enables the effective capture and processing of all of the tested samples and the developed device represents an inexpensive alternative to common cytocentrifuges, as only the paper filter is consumed during sample processing, and no special centrifuge, cytorotor, or cassette is necessary. As no additional system of solution removal is required during sample staining, the tested concept also facilitates the eventual automation of the staining procedure.