Osteo-immunomodulatory effects of macrophage-derived extracellular vesicles treated with biphasic calcium phosphate ceramics on bone regeneration.

Literature on osteoimmunology has demonstrated that macrophages have a great influence on biomaterial-induced bone formation. However, there are almost no reports clarifying the osteo-immunomodulatory capacity of macrophage-derived extracellular vesicles (EVs). This study comprehensively investigated the effects of EVs derived from macrophages treated with biphasic calcium phosphate (BCP) ceramics (BEVs) on vital events associated with BCP-induced bone formation such as immune response, angiogenesis, and osteogenesis. It was found that compared with EVs derived from macrophages alone (control, CEVs), BEVs preferentially promoted macrophage polarization towards a wound-healing M2 phenotype, enhanced migration, angiogenic differentiation, and tube formation of human umbilical vein endothelial cells, and induced osteogenic differentiation of mesenchymal stem cells. Analysis of 15 differentially expressed microRNAs (DEMs) related to immune, angiogenesis, and osteogenesis suggested that BEVs exhibited good immunomodulatory, pro-angiogenic, and pro-osteogenic abilities, which might be attributed to their specific miRNA cargos. These findings not only deepen our understanding of biomaterial-mediated osteoinduction, but also suggest that EVs derived from biomaterial-treated macrophages hold great promise as therapeutic agents with desired immunomodulatory capacity for bone regeneration.

A novel Chilean salmon fish backbone-based nanoHydroxyApatite functional biomaterial for potential use in bone tissue engineering.

Introduction: Given the ensuing increase in bone and periodontal diseases and defects, de novo bone repair and/or regeneration strategies are constantly undergoing-development alongside advances in orthopedic, oro-dental and cranio-maxillo-facial technologies and improvements in bio-/nano-materials. Indeed, there is a remarkably growing need for new oro-dental functional biomaterials that can help recreate soft and hard tissues and restore function and aesthetics of teeth/ dentition and surrounding tissues. In bone tissue engineering, HydroxyApatite minerals (HAp), the most stable CaP/Calcium Phosphate bioceramic and a widely-used material as a bone graft substitute, have been extensively studied for regenerative medicine and dentistry applications, including clinical use. Yet, limitations and challenges owing principally to its bio-mechanical strength, exist and therefore, research and innovation efforts continue to pursue enhancing its bio-effects, particularly at the nano-scale. Methods: Herein, we report on the physico-chemical properties of a novel nanoHydroxyApatite material obtained from the backbone of Salmon fish (patent-pending); an abundant and promising yet under-explored alternative HAp source. Briefly, our nanoS-HAp obtained via a modified and innovative alkaline hydrolysis-calcination process was characterized by X-ray diffraction, electron microscopy, spectroscopy, and a cell viability assay. Results and Discussion: When compared to control HAp (synthetic, human, bovine or porcine), our nanoS-HAp demonstrated attractive characteristics, a promising biomaterial candidate for use in bone tissue engineering, and beyond.

Osteogenic differentiation and proliferation of apical papilla stem cells using nanoparticles of Neo MTA and bioactive glass.

Objective: The aim of this study was to evaluate the osteogenic differentiation ability and proliferation of apical papilla stem cells using nanoparticles of Neo MTA and bioactive glass. Methods: Neo MTA and bioactive glass 45S5 nanoparticles were prepared and characterized using a transmission electron microscope and X-ray diffraction. Apical papilla stem cells were harvested from freshly-extracted fully-impacted wisdom teeth, cultured, and characterized using flow cytometric analysis. Tested nanomaterials were mixed and samples were classified into four equal groups as follows; Negative control group: SCAP with Dulbecco's modified eagle's medium, Positive control group: SCAP with inductive media, First experimental group: Neo MTA nanoparticles with SCAP, Second experimental group: Bioactive glass nanoparticles with SCAP. Osteoblastic differentiation was assessed using an alkaline phosphatase assay and RANKL expression using specific polyclonal antibodies by fluorescence microscope. The proliferation of SCAP was assessed using cell count and viability of Trypan Blue in addition to an MTT assay. Results: Isolated SCAP showed a non-hematopoietic origin. Neo MTA showed the highest ALP concentration followed by bioactive glass nanoparticles, and negative control. Bioactive glass nanoparticles showed the highest H score for RANKL protein expression followed by Neo MTA, and negative control. Bioactive glass nanoparticles showed the highest viable cell count. Conclusions: SCAP isolation is achievable from extracted fully impacted immature third molars. Both tested nanobiomaterials have the ability to induce osteogenic differentiation and proliferation of SCAP.

The role of integrin αvß3 in biphasic calcium phosphate ceramics mediated M2 Macrophage polarization and the resultant osteoinduction.

Calcium phosphate ceramics-based biomaterials were reported to have good biocompatibility and osteoinductivity and have been widely applied for bone defect repair and regeneration. However, the mechanism of their osteoinductivity is still unclear. In our study, we established an ectopic bone formation in vivo model and an in vitro macrophage cell co-culture system with calcium phosphate ceramics to investigate the effect of biphasic calcium phosphate on osteogenesis via regulating macrophage M1/M2 polarization. Our micro-CT data suggested that biphasic calcium phosphate had significant osteoinductivity, and the fluorescence co-localization detection found increased F4/80+/integrin αvß3+ macrophages surrounding the biphasic calcium phosphate scaffolds. Besides, our study also revealed that biphasic calcium phosphate promoted M2 polarization of macrophages via upregulating integrin αvß3 expression compared to tricalcium phosphate, and the increased M2 macrophages could subsequently augment the osteogenic differentiation of MSCs in a TGFß mediated manner. In conclusion, we demonstrated that macrophages subjected to biphasic calcium phosphate could polarize toward M2 phenotype via triggering integrin αvß3 and secrete TGFß to increase the osteogenesis of MSCs, which subsequently enhances bone regeneration.

Crosslinking chitosan with glucose via the modified Maillard reaction promotes the osteoinduction of mouse MC3T3-E1 pre-osteoblasts.

Bone defects are a common clinical issue, but therapeutic efficiency can be challenging in cases of more considerable traumas or elderly patients with degenerated physiological metabolism. To address this issue, a more suitable cell-biomaterial construct promoting bone regeneration has been extensively investigated, with the chitosan scaffold being considered a potential candidate. In this study, chitosan was crosslinked with different doses of glucose (CTS-10~50%Glc) using a modified Maillard reaction condition to develop a more appropriate cell-biomaterial construct. Mouse MC3T3-E1 pre-osteoblasts were seeded onto the scaffolds to examine their osteoinductive capability. The results showed that CTS-Glc scaffolds with higher glucose contents effectively improved the adhesion and survival of mouse MC3T3-E1 pre-osteoblasts and promoted their differentiation and mineralization. It was further demonstrated that the membrane integrin α5 subunit of pre-osteoblasts is the primary adhesion molecule that communicates with CTS-Glc scaffolds. After that, Akt signaling was activated, and then bone morphogenetic protein 4 was secreted to initiate the osteoinduction of pre-osteoblasts. The prepared CTS-Glc scaffold, with enhanced osteoinduction capability and detailed mechanism elucidations, offers a promising candidate material for advancing bone tissue engineering and clinical regenerative medicine. As a result, this study presents a potential tool for future clinical treatment of bone defects.

Evaluation of nanoscale versus hybrid micro/nano surface topographies for endosseous implants.

We examined the effect of a nanoscale titanium surface topography (D) versus two hybrid micro/nanoscale topographies (B and OS) on adherent mesenchymal stem cells (MSCs) and bone marrow derived macrophages (BMMs) function in cell culture and in vivo. In the in vitro study, compared to OS and B surfaces, D surface induced earlier and greater cell spreading, and earlier and profound mRNA expression of RUNX2, Osterix and BMP2 in MSCs. D surface induced earlier and higher expression of RUNX2 and BMP2 and lower expression of inflammatory genes in implant adherent cells in vivo. Measurement of osteogenesis at implant surfaces showed greater bone-to-implant contact at D versus OS surfaces after 21 days. We explored the cell population on the D and OS implant surfaces 24 h after placement using single-cell RNA sequencing and identified distinct cell clusters including macrophages, neutrophils and B cells. D surface induced lower expression and earlier reduction of inflammatory genes expression in BMMs in vitro. BMMs on D, B and OS surfaces demonstrated a marked increase of BMP2 expression after 1 and 3 days, and this increase was significantly higher on D surface at day 3. Our data implicates a dynamic process that may be influenced by nanotopography at multiple stages of osseointegration including initial immunomodulation, recruitment of MSCs and later osteoblastic differentiation leading to bone matrix production and mineralization. The results suggest that a nanoscale topography (D) favorably modulates adherent macrophage polarization toward anti-inflammatory and regenerative phenotypes and promotes the osteoinductive phenotype of adherent mesenchymal stem cells. STATEMENT OF SIGNIFICANCE: Our manuscript contains original data developed to define effects of a novel nanotopography on the process of osseointegration at the cell and tissue level.  Few studies have compared the effects of a nanoscale surface versus the more typical hybrid micro/nano-scale surfaces used today. We have utilized single-cell RNA sequencing for the first time to identify earliest cell populations on implant surfaces in vivo. We provide data indicating that the nanoscale surface acts upon both osteoprogenitor and immune cell (macrophages) to alter the process of bone formation in a surface-specific manner. This work represents new observations regarding osseointegration and immunomodulation.

Fn-HMGB1 Adsorption Behavior Initiates Early Immune Recognition and Subsequent Osteoinduction of Biomaterials.

Implantable biomaterials are widely used in bone tissue engineering, but little is still known about how they initiate early immune recognition and the initial dynamics. Herein, the early immune recognition and subsequent osteoinduction of biphasic calcium phosphate (BCP) after implantation to the protein adsorption behavior is attributed. By liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis, the biomaterial-related molecular patterns (BAMPs) formed after BCP implantation are mapped, dominated by the highly expressed extracellular matrix protein fibronectin (Fn) and the high mobility group box 1 (HMGB1). Molecular dynamics simulations show that Fn has the ability to bind more readily to the BCP surface than HMGB1. The preferential binding of Fn provides a higher adsorption energy for HMGB1. Furthermore, multiple hydrogen bonding sites between HMGB1 and Fn are demonstrated using a molecular docking approach. Ultimately, the formation of BAMPs through HMGB1 antagonist glycyrrhizic acid (GA), resulting in impaired immune recognition of myeloid differentiation factor 88 (MYD88) mediated dendritic cells (DCs) and macrophages (Mφs), as well as failed osteoinduction processes is obstructed. This study introduces a mechanism for early immune recognition of implant materials based on protein adsorption, providing perspectives for future design and application of tissue engineering materials.

Functionalization of poly (lactic-co-glycolic acid) nano­calcium sulphate and fucoidan 3D scaffold using human bone marrow mesenchymal stromal cells for bone tissue engineering application.

This study aimed to functionalize a novel porous PLGA (Poly lactic-co-glycolic acid) composite scaffold in combination with nano­calcium sulphate (nCS) and/or fucoidan (FU) to induce osteogenic differentiation of human bone marrow stromal cells. The composite scaffolds (PLGA-nCS-FU, PLGA-nCS or PLGA-FU) were fabricated and subjected to characterization using Fourier-transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), Scanning electron microscopy (SEM) and Energy Dispersive X-Ray (EDX). The biocompatibility and osteogenic induction potential of scaffolds on seeded human bone marrow derived mesenchymal stromal cells (hBMSCs) were studied using cell attachment and alamar blue cell viability and alkaline phosphatase (ALP), osteocalcin and osteogenic gene expression, respectively. The composition of different groups was reflected in FTIR, XRD and EDX. The SEM micrographs revealed a difference in the surface of the scaffold before and after FU addition. The confocal imaging and SEM micrographs confirmed the attachment of cells onto all three composite scaffolds. However, the AB assay indicated a significant increase (p < 0.05) in cell viability/proliferation seeded on PLGA-nCS-FU on day 21 and 28 as compared with other combinations. A 2-fold significant increase (p < 0.05) in ALP and OC secretion of seeded hBMSCs onto PLGA-nCS-FU was observed when compared with other combinations. A significant increase in RUNX2, OPN, COL-I and ALP genes were observed in the cells seeded on PLGA-nCS-FU on day 14 and 28 as compared with day 0. In conclusion, the incorporation of both Fucoidan and Nano­calcium sulphate with PLGA showed a promising improvement in the osteogenic potential of hBMSCs. Therefore, PLGA-nCS-FU could be the ideal candidate for subsequent pre-clinical studies to develop a successful bone substitute to repair critical bone defects.

The symbiotic effect of osteoinductive extracellular vesicles and mineralized microenvironment on osteogenesis.

The increasing prevalence of bone-related diseases has raised concern about the need for an osteoinductive and mechanically stronger scaffold-based bone tissue engineering (BTE) alternative. A mineralized microenvironment, similar to the native bone microenvironment, is required in the scaffold to recruit and differentiate local mesenchymal stem cells at the bone defect site. Further, extracellular vesicles (EVs), pre-osteoblasts' secretome, contain osteoinductive cargo and have recently been exploited in bone regeneration. This work developed a cell-free and mechanically strong interpenetrating network-based scaffold for BTE by combining the action of osteoinductive EVs with a mineralized microenvironment. The MC3T3 (a pre-osteoblast cell line) is used as a source of EVs and as the target population. The optimal concentration of MC3T3-EVs was first determined to induce osteogenesis in target cells. The osteoinductive potential of the scaffold was estimated in vitro by osteogenesis-related markers like the alkaline phosphatase (ALP) enzyme and calcium content. The MC3T3-EVs cargo was also studied for osteoinductive signals such as ALP, calcium, and mRNA. The findings of this work indicated that MC3T3-EVs at a 90 µg/mL dose had significantly higher ALP activity than 0 µg/mL (1.47-fold), 10 µg/mL (1.41-fold), and 30 µg/mL (1.39-fold) EV-concentration on day 14. Further combination of the optimum dose of EVs with a mineralized microenvironment significantly enhanced ALP activity (1.5-fold) and mineralization (3.36-fold) as compared to the control group on day 7. EV cargo analysis revealed the presence of calcium, the ALP enzyme, and the mRNAs necessary for osteogenesis and angiogenesis. ALP activity was significantly boosted in the EV-containing target cells as early as day 1, and mineralization began on day 7 because MC3T3-EVs carry ALP enzymes and calcium as cargo. When osteoinductive EVs were combined with an osteoconductive mineralized microenvironment, osteogenesis was significantly enhanced in target cells at early time points. The interaction between osteoinductive EVs and the mineralized milieu facilitates the process of osteogenesis in the target cells and suggests a potential cell-free strategy for in vivo bone repair.

Comparative Osteogenesis of Three Clinical Bone Graft Materials: An In Vivo Study.

PURPOSE: To investigate bone regeneration among three different bone graft materials in a rat calvarum model. MATERIALS AND METHODS: A total of 24 rats had two 5-mm defects placed per calvarial. Rats were divided into four groups: bovine xenograft (XG), demineralized bone matrix (DBM), mineralized bone graft (MBG), and collagen membrane control (CC). Within each group, samples were collected at two time points: 4 weeks (T4) and 8 weeks (T8). Bone regeneration was assessed by microcomputed tomography (micro-CT) imaging and was analyzed using MATLAB software. Additionally, the fixed samples were subsequently demineralized for immunohistochemistry and histomorphometry. Slides were mounted and stained with hematoxylin and eosin (H&E) stain as well as bone morphogenetic protein 2 (BMP-2) and runt-related transcription factor 2 (RUNX2) markers. The numbers of positive cells/area were calculated for each group and analyzed. RESULTS: At 4 weeks, DBM showed low mineral density (7.7%) compared to the control (25.2%), but increased dramatically at 8 weeks (DBM, T8 = 27.6%; CC, T8 = 27.2%). Xenograft material showed an increase in mineral desnity between T4 and T8 (XG, T4 = 25.0%; XG, T8 = 32.3%). MBG remained consistent over the 8-week trial period (MBG, T4 = 30.4%; MBG, T8 = 30.4%). BMP-2 expression was present in cells adherent to all graft materials. RUNX2 expression was also observed in cells adherent to all graft materials, indicating that during the 4- to 8-week healing period, all materials supported osteogenesis. CONCLUSIONS: Compared to other materials, the DBM had high osteoinductive properties during the 4- to 8-week time period based on increased mineral content. All materials were associated with immunohistologic evidence of osteogenesis in the rat calvarial defect model.

Evaluation of Bone Repair Using a New Biphasic Synthetic Bioceramic (Plenum® Osshp) in Critical Calvaria Defect in Rats.

(1) Background: Biphasic bioceramics are synthetic bone substitutes that provide greater safety and better predictability in guided bone regeneration. This study aimed to evaluate the bone repair process using a new biphasic bioceramic of synthetic origin (Plenum® Osshp-70HA: 30ß-TCP) in critical calvarial defects. (2) Methods: seventy-four defects were created in rat calvaria and divided into two groups-Plenum® Osshp (PO), right side, and Straumann® BoneCeramic™ (BC), left side. Euthanasia was performed at 7, 15, 30, and 60 days after surgery. (3) Results: Lower gene expression was observed for runt-related transcription factor 2 (RUNX2) and vascular endothelial growth factor (VEGF) and higher expression for Integrin Binding Sialoprotein (IBSP). The results correlated with moderate immunolabeling for osteocalcin (OCN) and slight immunolabeling for osteopontin (OPN) in the PO group. Histometry showed a greater amount of biomaterial remaining in the PO group at 60 days. The microtomographic analysis showed a lower density of bone connectivity and a greater thickness of the trabeculae for the remnants of the PO group. (4) Conclusions: the Plenum® Osshp showed no differences compared to BoneCeramic™ and is therefore considered an effective option as a synthetic bone substitute in bone regeneration.

Fused Deposition Modeling Printed PLA/Nano ß-TCP Composite Bone Tissue Engineering Scaffolds for Promoting Osteogenic Induction Function.

Purpose: Large bone defects caused by congenital defects, infections, degenerative diseases, trauma, and tumors often require personalized shapes and rapid reconstruction of the bone tissue. Three-dimensional (3D)-printed bone tissue engineering scaffolds exhibit promising application potential. Fused deposition modeling (FDM) technology can flexibly select and prepare printed biomaterials and design and fabricate bionic microstructures to promote personalized large bone defect repair. FDM-3D printing technology was used to prepare polylactic acid (PLA)/nano ß-tricalcium phosphate (TCP) composite bone tissue engineering scaffolds in this study. The ability of the bone-tissue-engineered scaffold to repair bone defects was evaluated in vivo and in vitro. Methods: PLA/nano-TCP composite bone tissue engineering scaffolds were prepared using FDM-3D printing technology. The characterization data of the scaffolds were obtained using relevant detection methods. The physical and chemical properties, biocompatibility, and in vitro osteogenic capacity of the scaffolds were investigated, and their bone repair capacity was evaluated using an in vivo animal model of rabbit femur bone defects. Results: The FDM-printed PLA/nano ß-TCP composite scaffolds exhibited good personalized porosity and shape, and their osteogenic ability, biocompatibility, and bone repair ability in vivo were superior to those of pure PLA. The merits of biodegradable PLA and bioactive nano ß-TCP ceramics were combined to improve the overall biological performance of the composites. Conclusion: The FDM-printed PLA/nano-ß-TCP composite scaffold with a ratio of 7:3 exhibited good personalized porosity and shape, as well as good osteogenic ability, biocompatibility, and bone repair ability. This study provides a promising strategy for treating large bone defects.

Osteoinduction and osteoimmunology: Emerging concepts.

The recognition and importance of immune cells during bone regeneration, including around bone biomaterials, has led to the development of an entire field termed "osteoimmunology," which focuses on the connection and interplay between the skeletal system and immune cells. Most studies have focused on the "osteogenic" capacity of various types of bone biomaterials, and much less focus has been placed on immune cells despite being the first cell type in contact with implantable devices. Thus, the amount of literature generated to date on this topic makes it challenging to extract needed information. This review article serves as a guide highlighting advancements made in the field of osteoimmunology emphasizing the role of the osteoimmunomodulatory properties of biomaterials and their impact on osteoinduction. First, the various immune cell types involved in bone biomaterial integration are discussed, including the prominent role of osteal macrophages (OsteoMacs) during bone regeneration. Thereafter, key biomaterial properties, including topography, wettability, surface charge, and adsorption of cytokines, growth factors, ions, and other bioactive molecules, are discussed in terms of their impact on immune responses. These findings highlight and recognize the importance of the immune system and osteoimmunology, leading to a shift in the traditional models used to understand and evaluate biomaterials for bone regeneration.

Synthesis, Characterization, and Bioactivity of Mesoporous Bioactive Glass Codoped with Zinc and Silver.

Due to the overconsumption of antimicrobials, antibiotic-resistant bacteria have become a critical health issue worldwide, especially methicillin-resistant S. aureus (MRSA) and vancomycin-resistant E. faecalis (VRE). Recently, many efforts have been made to load metals into bioactive glasses to enhance the multifunctionality of materials, such as antibacterial and osteoinductive functions. Zinc has been documented to stimulate the gene expression of various regulatory factors in bone cells. Meanwhile, previous studies have reported that silver and zinc could be a promising antibacterial combination with synergistic antimicrobial effects. Here, we sought to develop a biomaterial coreleasing zinc and silver, designated 80S-ZnAg, and to evaluate its antibacterial activity and biocompatibility. The textural analyses demonstrated different coreleasing patterns of zinc and silver for the materials. The chemical characterization revealed that the zinc in 80S-ZnAg could be the network modifier when its molar ratio was high, releasing more zinc; zinc could also be the network former when its molar ratio was low, showing an extremely low rate of release. However, the ICP results for 80S-Zn3Ag2 demonstrated up to 7.5 ppm of zinc and 67.6 ppm of silver. Among all the 80S-ZnAg materials, 80S-Zn3Ag2 demonstrated more marked antibacterial activity against MRSA and VRE than the others, with inhibition zones of 11.5 and 13.4 mm, respectively. The cytotoxicity assay exhibited nearly 90% cell viability at 20 mg/mL of 80-Zn3Ag2. Further clinical study is needed to develop an innovative biomaterial to address the issue of antibiotic resistance.

Camouflaged angiogenic BMP-2 functions exposed by pico-paracrine biohybrids.

The constant release of human bone morphogenetic protein 2 (rhBMP-2) in the picomolar range (Pico-Stat) from PDLLA-biohybrids led to the detection of intrinsic novel pro- and anti-angiogenic functions of this cytokine. As integrant part in this perspective of previous work, first evidence for the binding of rhBMP-2, as an inverse agonist, to allosteric angiogenic receptors in cocultures of human endothelial cells is reported.

Cell-Instructive Mineralized Microenvironment Regulates Osteogenesis: A Growing SYMBIOSIS of Cell Biology and Biomaterials Engineering in Bone Tissue Regeneration.

One of the objectives of bone tissue engineering is to produce scaffolds that are biocompatible, osteoinductive, and mechanically equivalent to the natural extracellular matrix of bone in terms of structure and function. Reconstructing the osteoconductive bone microenvironment into a scaffold can attract native mesenchymal stem cells and differentiate them into osteoblasts at the defect site. The symbiotic relationship between cell biology and biomaterial engineering could result in composite polymers containing the necessary signals to recreate tissue- and organ-specific differentiation. In the current work, drawing inspiration from the natural stem cell niche to govern stem cell fate, the cell-instructive hydrogel platforms were constructed by engineering the mineralized microenvironment. This work employed two different hydroxyapatite delivery strategies to create a mineralized microenvironment in an alginate-PEGDA interpenetrating network (IPN) hydrogel. The first approach involved coating of nano-hydroxyapatite (nHAp) on poly(lactide-co-glycolide) microspheres and then encapsulating the coated microspheres in an IPN hydrogel for a sustained release of nHAp, whereas the second approach involved directly loading nHAp into the IPN hydrogel. This study demonstrate that both direct encapsulation and a sustained release approach showed enhanced osteogenesis in target-encapsulated cells; however, direct loading of nHAp into the IPN hydrogel increased the mechanical strength and swelling ratio of the scaffold by 4.6-fold and 1.14-fold, respectively. In addition, the biochemical and molecular studies revealed improved osteoinductive and osteoconductive potential of encapsulated target cells. Being less expensive and simple to perform, this approach could be beneficial in clinical settings.

Dexamethasone release pattern via a three-dimensional system for effective bone regeneration.

For over a decade, dexamethasone (DEX) has been used for bone regenerative and anti-inflammatory purposes. It has also shown promise for inducing bone regeneration by using it as component of osteoinductive differentiation medium, particularly forin vitroculture models. Despite its osteoinductive properties, its use is limited due to its associated cytotoxicity, particularly when used at higher concentrations. DEX has adverse effects when taken orally; thus, it is best to use it in a targeted manner. Even when given locally, the pharmaceutical should be distributed in a controlled manner based on the needs of the wounded tissue. However, because drug activity is assessed in two-dimensional (2D) circumstances and the target tissue is a three-dimensional (3D) structure, assessing DEX activity and dosage in a 3D milieu is critical for bone tissue development. The current review examines the advantages of a 3D approach over traditional 2D culture methods and delivery devices for controlled DEX delivery, particularly for bone repair. Further, this review explores the latest advancement and challenges in biomaterial-based therapeutic delivery approaches for bone regeneration. This review also discusses possible future biomaterial-based strategies to study efficient DEX delivery.

Osteogenic Potential of Nano-Hydroxyapatite and Strontium-Substituted Nano-Hydroxyapatite.

Nanohydroxyapatite (nanoHA) is the major mineral component of bone. It is highly biocompatible, osteoconductive, and forms strong bonds with native bone, making it an excellent material for bone regeneration. However, enhanced mechanical properties and biological activity for nanoHA can be achieved through enrichment with strontium ions. Here, nanoHA and nanoHA with a substitution degree of 50 and 100% of calcium with strontium ions (Sr-nanoHA_50 and Sr-nanoHA_100, respectively) were produced via wet chemical precipitation using calcium, strontium, and phosphorous salts as starting materials. The materials were evaluated for their cytotoxicity and osteogenic potential in direct contact with MC3T3-E1 pre-osteoblastic cells. All three nanoHA-based materials were cytocompatible, featured needle-shaped nanocrystals, and had enhanced osteogenic activity in vitro. The Sr-nanoHA_100 indicated a significant increase in the alkaline phosphatase activity at day 14 compared to the control. All three compositions revealed significantly higher calcium and collagen production up to 21 days in culture compared to the control. Gene expression analysis exhibited, for all three nanoHA compositions, a significant upregulation of osteonectin and osteocalcin on day 14 and of osteopontin on day 7 compared to the control. The highest osteocalcin levels were found for both Sr-substituted compounds on day 14. These results demonstrate the great osteoinductive potential of the produced compounds, which can be exploited to treat bone disease.

Microalgae Applications to Bone Repairing Processes: A Review.

Research on regeneration and accelerated recovery processes of bone tissue has driven a growing interest in the scientific community. Implementing natural materials to reduce rejections due to biocompatibility issues is an important trend. Biofunctionalization processes have been proposed to promote osseointegration in implant materials, and those substances able to generate an adequate environment for cell proliferation are the object of several studies. Because of their high protein content and their anti-inflammatory, antibacterial, antimicrobial, and healing properties, microalgae represent a natural source of bioactive compounds, and are proposed as candidates for tissue regeneration applications. In this paper microalgae are reviewed as a source of biofunctionalized materials focused on orthopedic applications.