The osteoimmunomodulatory property of a barrier collagen membrane and its manipulation via coating nanometer-sized bioactive glass to improve guided bone regeneration

Engineering a microparticle-loaded rough membrane for guided bone regeneration modulating osteoblast response without inducing inflammation

Guided bone regeneration (GBR) is a widely used procedure that prevents the fast in-growth of soft tissues into bone defect. Among the different types of membranes, the use of collagen membranes is the gold standard. However, these membranes are implanted in tissue location where a severe acute inflammation will occur and can be negatively affected. The aim of this study was to develop a collagen-based membrane for GBR that incorporated alginate-hydroxyapatite microparticles. Membranes were manufactured using collagen type I and gelatin and alginate-hydroxyapatite microparticles. Membranes were assessed in terms of topography by scanning electron microscopy and confocal microscopy; stability by swelling after an overnight incubation in saline and enzymatic degradation against collagenase and mechanical properties by tensile tests. Furthermore, the biological response was assessed with SaOs-2 cells and THP-1 macrophages to determine alkaline phosphatase activity and inflammatory cytokine release. Our results showed that the incorporation of different percentages of these microparticles could induce changes in the surface topography. When the biological response was analyzed, either membranes were not cytotoxic to THP-1 macrophages or to SaOs-2 cells and they did not induce the release of pro-inflammatory cytokines. However, the different surface topographies did not induce changes in the macrophage morphology and the release of pro- and anti-inflammatory cytokines, suggesting that the effect of surface roughness on macrophage behavior could be dependent on other factors such as substrate stiffness and composition. Collagen-gelatin membranes with embedded alginate-hydroxyapatite microparticles increased ALP activity, suggesting a positive effect of them on bone regeneration, remaining unaffected the release of pro- and anti-inflammatory cytokines.

Collagen-hydroxyapatite based scaffolds for bone trauma and regeneration: recent trends and future perspectives

Regenerative therapy, a key area of tissue engineering, holds promise for restoring damaged organs, especially in bone regeneration. Bone healing is natural to the body but becomes complex under stress and disease. Large bone deformities pose significant challenges in tissue engineering. Among various methods, scaffolds are attractive as they provide structural support and essential nutrients for cell adhesion and growth. Collagen and hydroxyapatite (HA) are widely used due to their biocompatibility and biodegradability. Collagen and nano-scale HA enhance cell adhesion and development. Thus, nano HA/collagen scaffolds offer potential solutions for bone regeneration. This review focuses on the use and production of nano-sized HA/collagen composites in bone regeneration.

Effects of bone surface topography and chemistry on macrophage polarization

Surface structure plays a crucial role in determining cell behavior on biomaterials, influencing cell adhesion, proliferation, differentiation, as well as immune cells and macrophage polarization. While grooves and ridges stimulate M2 polarization and pits and bumps promote M1 polarization, these structures do not accurately mimic the real bone surface. Consequently, the impact of mimicking bone surface topography on macrophage polarization remains unknown. Understanding the synergistic sequential roles of M1 and M2 macrophages in osteoimmunomodulation is crucial for effective bone tissue engineering. Thus, exploring the impact of bone surface microstructure mimicking biomaterials on macrophage polarization is critical. In this study, we aimed to sequentially activate M1 and M2 macrophages using Poly-L-Lactic acid (PLA) membranes with bone surface topographical features mimicked through the soft lithography technique. To mimic the bone surface topography, a bovine femur was used as a model surface, and the membranes were further modified with collagen type-I and hydroxyapatite to mimic the bone surface microenvironment. To determine the effect of these biomaterials on macrophage polarization, we conducted experimental analysis that contained estimating cytokine release profiles and characterizing cell morphology. Our results demonstrated the potential of the hydroxyapatite-deposited bone surface-mimicked PLA membranes to trigger sequential and synergistic M1 and M2 macrophage polarizations, suggesting their ability to achieve osteoimmunomodulatory macrophage polarization for bone tissue engineering applications. Although further experimental studies are required to completely investigate the osteoimmunomodulatory effects of these biomaterials, our results provide valuable insights into the potential advantages of biomaterials that mimic the complex microenvironment of bone surfaces.

A chitosan-coated PCL/nano-hydroxyapatite aerogel integrated with a nanofiber membrane for providing antibacterial activity and guiding bone regeneration

A guided bone regeneration (GBR) membrane can act as a barrier to prevent the invasion and interference from foreign soft tissues, promoting infiltration and proliferation of osteoblasts in the bone defect area. Herein, a composite scaffold with dual functions of osteogenesis and antibacterial effects was prepared for GBR. A polycaprolactone (PCL)/nano-hydroxyapatite (n-HA) aerogel produced by electrospinning and freeze-drying techniques was fabricated as the loose layer of the scaffold, while a PCL nanofiber membrane was used as the dense layer. Chitosan (CS) solution served as a middle layer to provide mechanical support and antibacterial effects between the two layers. Morphological results showed that the loose layer had a porous structure with n-HA successfully dispersed in the aerogels, while the dense layer possessed a sufficiently dense structure. In vitro antibacterial experiments illustrated that the CS solution in the middle layer stabilized the scaffold structure and endowed the scaffold with good antibacterial properties. The cytocompatibility results indicated that both fibroblasts and osteoblasts exhibited superior cell activity on the dense and loose layers, respectively. In particular, the dense layer made of nanofibers could work as a barrier layer to inhibit the infiltration of fibroblasts into the loose layer. In vitro osteogenesis analysis suggested that the PCL/n-HA aerogel could enhance the bone induction ability of bone mesenchymal stem cells, which was confirmed by the increased expression of the alkaline phosphatase activity. The loose structure facilitated the infiltration and migration of bone mesenchymal stem cells for better osteogenesis. In summary, such a composite scaffold exhibited excellent osteogenic and antibacterial properties as well as the barrier effect, thus holding promising potential for use as GBR materials.

Electrical aligned polyurethane nerve guidance conduit modulates macrophage polarization and facilitates immunoregulatory peripheral nerve regeneration

Biomaterials can modulate the local immune microenvironments to promote peripheral nerve regeneration. Inspired by the spatial orderly distribution and endogenous electric field of nerve fibers, we aimed to investigate the synergistic effects of electrical and topological cues on immune microenvironments of peripheral nerve regeneration. Nerve guidance conduits (NGCs) with aligned electrospun nanofibers were fabricated using a polyurethane copolymer containing a conductive aniline trimer and degradable L-lysine (PUAT). In vitro experiments showed that the aligned PUAT (A-PUAT) membranes promoted the recruitment of macrophages and induced their polarization towards the pro-healing M2 phenotype, which subsequently facilitated the migration and myelination of Schwann cells. Furthermore, NGCs fabricated from A-PUAT increased the proportion of pro-healing macrophages and improved peripheral nerve regeneration in a rat model of sciatic nerve injury. In conclusion, this study demonstrated the potential application of NGCs in peripheral nerve regeneration from an immunomodulatory perspective and revealed A-PUAT as a clinically-actionable strategy for peripheral nerve injury.

Macrophages in guided bone regeneration: potential roles and future directions

Guided bone regeneration (GBR) is one of the most widely used and thoroughly documented alveolar bone augmentation surgeries. However, implanting GBR membranes inevitably triggers an immune response, which can lead to inflammation and failure of bone augmentation. It has been shown that GBR membranes may significantly improve in vivo outcomes as potent immunomodulators, rather than solely serving as traditional barriers. Macrophages play crucial roles in immune responses and participate in the entire process of bone injury repair. The significant diversity and high plasticity of macrophages complicate our understanding of the immunomodulatory mechanisms underlying GBR. This review provides a comprehensive summary of recent findings on the potential role of macrophages in GBR for bone defects in situ. Specifically, macrophages can promote osteogenesis or fibrous tissue formation in bone defects and degradation or fibrous encapsulation of membranes. Moreover, GBR membranes can influence the recruitment and polarization of macrophages. Therefore, immunomodulating GBR membranes are primarily developed by improving macrophage recruitment and aggregation as well as regulating macrophage polarization. However, certain challenges remain to be addressed in the future. For example, developing more rational and sophisticated sequential delivery systems for macrophage activation reagents; addressing the interference of bone graft materials and dental implants; and understanding the correlations among membrane degradation, macrophage responses, and bone regeneration.

Lithium-Doped Titanium Dioxide-Based Multilayer Hierarchical Structure for Accelerating Nerve-Induced Bone Regeneration

Despite considerable advances in artificial bone tissues, the absence of neural network reconstruction in their design often leads to delayed or ineffective bone healing. Hence, we propose a multilayer hierarchical lithium (Li)-doped titanium dioxide structure, constructed through microarc oxidation combined with alkaline heat treatment. This structure can induce the sustained release of Li ions, mimicking the environment of neurogenic osteogenesis characterized by high brain-derived neurotrophic factor (BDNF) expression. During in vitro experiments, the structure enhanced the differentiation of Schwann cells (SCs) and the growth of human umbilical vein endothelial cells (HUVECs) and mouse embryo osteoblast progenitor cells (MC3T3-E1). Additionally, in a coculture system, the SC-conditioned media markedly increased alkaline phosphatase expression and the formation of calcium nodules, demonstrating the excellent potential of the material for nerve-induced bone regeneration. In an in vivo experiment based on a rat distal femoral lesion model, the structure substantially enhanced bone healing by increasing the density of the neural network in the tissue around the implant. In conclusion, this study elucidates the neuromodulatory pathways involved in bone regeneration, providing a promising method for addressing bone deformities.

The effect of magnesium ions synergistic with mineralized collagen on osteogenesis/angiogenesis properties by modulating macrophage polarizationin vitroandin vivo

In bone tissue engineering, the bone immunomodulatory properties of biomaterials are critical for bone regeneration, which is a synergistic process involving physiological activities like immune response, osteogenesis, and angiogenesis. The effect of the macrophage immune microenvironment on the osteogenesis and angiogenesis of various material extracts was examined in this experiment using Mg2+and Nano-hydroxyapatite/collagen (nHAC) in both a single application and a combined form. This studyin vitrorevealed that the two compounds combined significantly inhibited the NF-κB signaling pathway and reduced the release of inflammatory factors from macrophages when compared with the extraction phase alone. Additionally, by contributing to the polarization of macrophages towards the M2 type, the combined effects of the two materials can significantly improve osteogenesis/angiogenesis. The results ofin vivoexperiments confirmed that Mg2+/nHAC significantly promoted bone regeneration and angiogenesis. This study offers a promising method for enhancing bone graft material osseointegration.

Programmable Electro-Assembly of Collagen: Constructing Porous Janus Films with Customized Dual Signals for Immunomodulation and Tissue Regeneration in Periodontitis Treatment

Currently available guided bone regeneration (GBR) films lack active immunomodulation and sufficient osteogenic ability- in the treatment of periodontitis, leading to unsatisfactory treatment outcomes. Challenges remain in developing simple, rapid, and programmable manufacturing methods for constructing bioactive GBR films with tailored biofunctional compositions and microstructures. Herein, the controlled electroassembly of collagen under the salt effect is reported, which enables the construction of porous films with precisely tunable porous structures (i.e., porosity and pore size). In particular, bioactive salt species such as the anti-inflammatory drug diclofenac sodium (DS) can induce and customize porous structures while enabling the loading of bioactive salts and their gradual release. Sequential electro-assembly under pre-programmed salt conditions enables the manufacture of a Janus composite film with a dense and DS-containing porous layer capable of multiple functions in periodontitis treatment, which provides mechanical support, guides fibrous tissue growth, and acts as a barrier preventing its penetration into bone defects. The DS-containing porous layer delivers dual bio-signals through its morphology and the released DS, inhibiting inflammation and promoting osteogenesis. Overall, this study demonstrates the potential of electrofabrication as a customized manufacturing platform for the programmable assembly of collagen for tailored functions to adapt to specific needs in regenerative medicine.

3D-printed bredigite scaffolds with ordered arrangement structures promote bone regeneration by inducing macrophage polarization in onlay grafts

Bone tissue engineering scaffolds may provide a potential strategy for onlay bone grafts for oral implants. For determining the fate of scaffold biomaterials and osteogenesis effects, the host immune response is crucial. In the present study, bredigite (BRT) bioceramic scaffolds with an ordered arrangement structure (BRT-O) and a random morphology (BRT-R) were fabricated. The physicochemical properties of scaffolds were first characterized by scanning electron microscopy, mechanical test and micro-Fourier transform infrared spectroscopy. In addition, their osteogenic and immunomodulatory properties in an onlay grafting model were investigated. In vitro, the BRT-O scaffolds facilitated the macrophage polarization towards a pro-regenerative M2 phenotype, which subsequently facilitated the migration and osteogenic differentiation of bone marrow-derived mesenchymal stem cells. In vivo, an onlay grafting model was successfully established in the cranium of rabbits. In addition, the BRT-O scaffolds grafted on rabbit cranium promoted bone regeneration and CD68 + CD206 + M2 macrophage polarization. In conclusion, the 3D-printed BRT-O scaffold presents as a promising scaffold biomaterial for onlay grafts by regulating the local immune microenvironment.

An increase in Wharton's jelly membrane osteocompatibility by a genipin-cross-link

Wharton's Jelly (WJ) has attracted significant interest in the field of tissue healing thanks to its biological properties, including antibacterial activity and immunomodulation. However, due to the fast degradation and poor mechanical behavior in biological environment, its application in bone regeneration is compromised. Here, we proposed to use genipin as an efficient cross-linking agent to significantly improve the elasticity and the enzymatical stability of the WJ matrix. The degree of cross-linking, linear elastic moduli, and collagenase resistance varied over a wide range depending on genipin concentration. Furthermore, our results highlighted that an increase in genipin concentration led to a decreased surface wettability, therefore impairing cell attachment and proliferation. The genipin cross-linking prevented rapid in vitro and in vivo degradation, but led to an adverse host reaction and calcification. When implanted in the parietal bone defect, a limited parietal bone regeneration to the dura was observed. We conclude that genipin-cross-linked WJ is a versatile medical device however, a careful selection is required with regards to the genipin concentration.

Development, Characterization, and Antibacterial Analysis of the Selenium-Doped Bio-Glass-Collagen-Gelatin Composite Scaffold for Guided Bone Regeneration

Background Guided bone regeneration (GBR) is an often-used technique to aid the successful placement of dental implants in sites with deficient bone. The search for the ideal GBR membrane with bioactive components improving the regenerative outcomes is still on. In this study, a novel composite GBR membrane was developed using selenium-doped bio-glass, collagen, and gelatin. It was further characterized for surface, chemical, biocompatibility, and antibacterial properties. Methodology Selenium-doped bio-glass was prepared using the sol-gel method. The membrane was fabricated using an equal ratio of collagen and gelatin mixed with 1% selenium-doped bio-glass. The solution was poured to obtain a thin layer of the material which was lyophilized to obtain the final GBR membrane. The membrane was analyzed with scanning electron microscopy, energy dispersive X-ray (EDX) analysis, attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), zebrafish cytotoxicity test, and antibacterial assay. Results The membrane revealed good surface roughness with lamellar and fibrillar arrangement with a minute granular surface ideal for cell attachment and proliferation. The EDX analysis revealed the presence of carbon, oxygen, and nitrogen as predominant components with trace amounts of calcium, phosphorus, silica, and selenium. Fourier transform infrared spectroscopy analysis also proved the presence of collagen, gelatin, and bio-glass. The membrane revealed excellent biocompatibility with zebrafish growth at a normal rate with 90% viability maintained at 48, 72, and 96 hours and 95% viability at 120 hours. It also exhibited excellent antibacterial activity against Staphylococcus aureus and Escherichia coli with minimal growth of bacterial colonies. Conclusion The developed novel selenium bio-glass collagen and gelatin composite scaffold has a good surface and antibacterial properties along with excellent biocompatibility. Further cell line and in vivo studies should be conducted to explore its role in bone regeneration.

Three-Dimensional Printed Poly (Lactic-co-Glycolic Acid)-Magnesium Composite Scaffolds for the Promotion of Osteogenesis Through Immunoregulation

Scaffolds play an important role in bone tissue engineering. The ideal engineered scaffold needs to be biocompatible, bioactive, and able to regulate immune cells to enhance bone regeneration. In this study, magnesium (Mg)-contained poly(lactic-co-glycolic acid) (PLGA) scaffolds (hereinafter, referred to as PLGA-2Mg) were fabricated by 3-dimensional printing using a mixture of PLGA and MgSO 4 powder. Poly(lactic-co-glycolic acid) scaffolds (hereinafter, referred to as PLGA) were also fabricated by 3-dimensional printing and were used as control. The biocompatibility, immunoregulatory ability, and osteogenic properties of PLGA-2Mg were analyzed and compared with those of PLGA. The results indicate that the incorporation of Mg increased the Young modulus and surface roughness of the scaffold, but did not affect its degradation. The PLGA-2Mg further promoted the adhesion and proliferation of MC3T3-E1 cells compared with PLGA, which indicates its improved biocompatibility and bioactivity. In addition, PLGA-2Mg inhibited the polarization of RAW 264.7 cells toward the M1 phenotype by down-regulating the IL-1β , IL-6 , and iNOs gene expression when challenged with lipopolysaccharide stimulation. In contrast, it promoted the polarization of RAW 264.7 cells toward the M2 phenotype by up-regulating the TGF-β , IL-10 , and Arg-1 gene expression without lipopolysaccharide stimulation. Finally, MC3T3-E1 cells were cocultured with RAW 264.7 cells and scaffolds using a transwell system. It was found that the expression level of osteogenic-related genes ( ALP , COL-1 , BMP2 , and BSP ) was significantly upregulated in the PLGA-2Mg group compared with that in the PLGA group. Consequently, PLGA-2Mg with increased biocompatibility and bioactivity can promote osteogenesis through immunoregulation and has the potential to be used as a novel scaffold in bone tissue engineering.

Decellularized periosteum promotes guided bone regeneration via manipulation of macrophage polarization

Periosteum has shown potential as an effective barrier membrane for guided bone regeneration (GBR). However, if recognized as a "foreign body," insertion of a barrier membrane in GBR treatment will inevitably alter the local immune microenvironment and subsequently influence bone regeneration. The aim of this investigation was to fabricate decellularized periosteum (DP) and investigate its immunomodulatory properties in GBR. DP was successfully fabricated from periosteum from the mini-pig cranium. In vitro experiments indicated that the DP scaffold modulated macrophage polarization toward a pro-regenerative M2 phenotype, which in turn facilitated migration and osteogenic differentiation of bone marrow-derived mesenchymal stem cells. A rat GBR model with a cranial critical-size defect was established, and our in vivo experiment confirmed the beneficial effects of DP on the local immune microenvironment and bone regeneration. Collectively, the findings of this study indicate that the prepared DP possesses immunomodulatory properties and represents a promising barrier membrane for GBR procedures.

Li-Mg-Si bioceramics provide a dynamic immuno-modulatory and repair-supportive microenvironment for peripheral nerve regeneration

Biomaterials can modulate the local immune and repair-supportive microenvironments to promote peripheral nerve regeneration. Inorganic bioceramics have been widely used for regulating tissue regeneration and local immune response. However, little is known on whether inorganic bioceramics can have potential for enhancing peripheral nerve regeneration and what are the mechanisms underlying their actions. Here, the inorganic lithium-magnesium-silicon (Li-Mg-Si, LMS) bioceramics containing scaffolds are fabricated and characterized. The LMS-containing scaffolds had no cytotoxicity against rat Schwann cells (SCs), but promoted their migration and differentiation towards a remyelination state by up-regulating the expression of neurotrophic factors in a β-catenin-dependent manner. Furthermore, using single cell-sequencing, we showed that LMS-containing scaffolds promoted macrophage polarization towards the pro-regenerative M2-like cells, which subsequently facilitated the migration and differentiation of SCs. Moreover, implantation with the LMS-containing nerve guidance conduits (NGCs) increased the frequency of M2-like macrophage infiltration and enhanced nerve regeneration and motor functional recovery in a rat model of sciatic nerve injury. Collectively, these findings indicated that the inorganic LMS bioceramics offered a potential strategy for enhancing peripheral nerve regeneration by modulating the immune microenvironment and promoting SCs remyelination.

Resorbable Membranes for Guided Bone Regeneration: Critical Features, Potentials, and Limitations

Lack of horizontal and vertical bone at the site of an implant can lead to significant clinical problems that need to be addressed before implant treatment can take place. Guided bone regeneration (GBR) is a commonly used surgical procedure that employs a barrier membrane to encourage the growth of new bone tissue in areas where bone has been lost due to injury or disease. It is a promising approach to achieve desired repair in bone tissue and is widely accepted and used in approximately 40% of patients with bone defects. In this Review, we provide a comprehensive examination of recent advances in resorbable membranes for GBR including natural materials such as chitosan, collagen, silk fibroin, along with synthetic materials such as polyglycolic acid (PGA), polycaprolactone (PCL), polyethylene glycol (PEG), and their copolymers. In addition, the properties of these materials including foreign body reaction, mechanical stability, antibacterial property, and growth factor delivery performance will be compared and discussed. Finally, future directions for resorbable membrane development and potential clinical applications will be highlighted.

Immunomodulatory zinc-based materials for tissue regeneration

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

CaP-coated Zn-Mn-Li alloys regulate osseointegration via influencing macrophage polarization in the osteogenic environment

Immune response is an important factor in determining the fate of bone replacement materials, in which macrophages play an important role. It is a new idea to design biomaterials with immunomodulatory function to reduce inflammation and promote bone integration by regulating macrophages polarization. In this work, the immunomodulatory properties of CaP Zn-Mn-Li alloys and the specific mechanism of action were investigated. We found that the CaP Zn0.8Mn0.1Li alloy promoted the polarization of macrophages toward M2 and reduced inflammation, which could effectively upregulate osteogenesis-related factors and promote new bone formation, indicating the important role of macrophages polarization in biomaterial induction of osteogenesis. In vivo studies further demonstrated that CaP Zn0.8Mn0.1Li alloy could stimulate osteogenesis better than other Zn-Mn-Li alloys implantations by regulating macrophages polarization and reducing inflammation. In addition, transcriptome results showed that CaP Zn0.8Mn0.1Li played an important regulatory role in the life process of macrophages, activating Toll-like receptor signaling pathway, which participated in the activation and attenuation of inflammation, and accelerated bone integration. Thus, by preparing CaP coatings on the surface of Zn-Mn-Li alloys and combining the bioactive ingredient with controlled release, the biomaterial will be imbibed with beneficial immunomodulatory properties that promote bone integration.

Regulation of Macrophage Polarization on Chiral Potential Distribution of CFO/P(VDF-TrFE) Films

Surface potentials of biomaterials have been shown to regulate cell fate commitment. However, the effects of chirality-patterned potential distribution on macrophage polarization are still only beginning to be explored. In this work, we demonstrated that the chirality-patterned potential distribution of CoFe₂O₄/poly(vinylidene fluoride-trifluoroethylene) (CFO/P(VDF-TrFE)) films could significantly down-regulate the M1 polarization of bone marrow-derived macrophages (BMDMs). Specifically, the dextral-patterned surface potential distribution simultaneously up-regulated the expression of M2-related markers of BMDMs. The results were attributed to the sensitive difference of integrin subunits (α₅β₁ and α_vβ₃) to the dextral- and sinistral-patterned surface potential distribution, respectively. The interaction difference between the integrin subunits and surface potential distribution altered the cell adhesion and cytoskeletal structure and thereby the polarization behavior of BMDMs. This work, therefore, emphasizes the importance of chirality of potential distribution on cell behavior and provides a new strategy to regulate the immune response of biomaterials.

Engineering exosomes and biomaterial-assisted exosomes as therapeutic carriers for bone regeneration

Mesenchymal stem cell-based therapy has become an effective therapeutic approach for bone regeneration. However, there are still limitations in successful clinical translation. Recently, the secretome of mesenchymal stem cells, especially exosome, plays a critical role in promoting bone repair and regeneration. Exosomes are nanosized, lipid bilayer-enclosed structures carrying proteins, lipids, RNAs, metabolites, growth factors, and cytokines and have attracted great attention for their potential application in bone regenerative medicine. In addition, preconditioning of parental cells and exosome engineering can enhance the regenerative potential of exosomes for treating bone defects. Moreover, with recent advancements in various biomaterials to enhance the therapeutic functions of exosomes, biomaterial-assisted exosomes have become a promising strategy for bone regeneration. This review discusses different insights regarding the roles of exosomes in bone regeneration and summarizes the applications of engineering exosomes and biomaterial-assisted exosomes as safe and versatile bone regeneration agent delivery platforms. The current hurdles of transitioning exosomes from bench to bedside are also discussed.

Metal-phenolic networks acted as a novel bio-filler of a barrier membrane to improve guided bone regeneration via manipulating osteoimmunomodulation

A guided bone tissue regeneration membrane (GBRM) is traditionally viewed as an inert physical barrier to isolate soft tissue from the bone defect area. However, as a "foreign body", the implantation of a GBRM would inevitably modulate immune response and subsequently affect bone dynamics. Herein, we developed strontium ion (Sr²⁺)-based metal-phenolic network complexes (MPNs) as a novel type of bio-filler to manipulate the osteoimmunomodulation of the advanced GBRM. For controllable delivery of Sr²⁺ depending on the difference in affinity between phenolic ligands and Sr²⁺, tannic acid (TA), epigallocatechin gallate (EGCG), and epigallocatechin (EGC) were selected to chelate with Sr²⁺. The formed MPNs were incorporated into PCL nanofibrous membranes by blending electrospinning. Among them, TA/Sr based MPN particles displayed the most sustainable release profile of phenolic ligands and Sr²⁺. Further investigations demonstrated that Sr²⁺ could not only directly promote osteogenic differentiation of BMSCs, but also manipulate an anti-inflammatory osteoimmune microenvironment in a synergistic manner with TA, thus enhancing osteogenesis and inhibiting bone resorption. The rat alveolar bone defect model also confirmed that the TA/Sr nanoparticle modified membrane displayed better bone regeneration performance than the pure PCL membrane via inhibiting bone resorption. This work provides a new platform for controllable delivery of bioactive nutrient elements, and holds great promise for advancing multi-functional biocomposites.

Barrier Membranes for Guided Bone Regeneration (GBR): A Focus on Recent Advances in Collagen Membranes

Guided bone regeneration (GBR) has become a clinically standard modality for the treatment of localized jawbone defects. Barrier membranes play an important role in this process by preventing soft tissue invasion outgoing from the mucosa and creating an underlying space to support bone growth. Different membrane types provide different biological mechanisms due to their different origins, preparation methods and structures. Among them, collagen membranes have attracted great interest due to their excellent biological properties and desired bone regeneration results to non-absorbable membranes even without a second surgery for removal. This work provides a comparative summary of common barrier membranes used in GBR, focusing on recent advances in collagen membranes and their biological mechanisms. In conclusion, the review article highlights the biological and regenerative properties of currently available barrier membranes with a particular focus on bioresorbable collagen-based materials. In addition, the advantages and disadvantages of these biomaterials are highlighted, and possible improvements for future material developments are summarized.

Functionalized multidimensional biomaterials for bone microenvironment engineering applications: Focus on osteoimmunomodulation

As bone biology develops, it is gradually recognized that bone regeneration is a pathophysiological process that requires the simultaneous participation of multiple systems. With the introduction of osteoimmunology, the interplay between the immune system and the musculoskeletal diseases has been the conceptual framework for a thorough understanding of both systems and the advancement of osteoimmunomodulaty biomaterials. Various therapeutic strategies which include intervention of the surface characteristics or the local delivery systems with the incorporation of bioactive molecules have been applied to create an ideal bone microenvironment for bone tissue regeneration. Our review systematically summarized the current research that is being undertaken in the field of osteoimmunomodulaty bone biomaterials on a case-by-case basis, aiming to inspire more extensive research and promote clinical conversion.

3D printed Ti-5Cu alloy accelerates osteogenic differentiation of MC3T3-E1 cells by stimulating the M2 phenotype polarization of macrophages

Ti-5Cu alloy has been proved to have excellent mechanical properties and cell compatibility and has certain antibacterial properties due to the addition of Cu. However, there are few studies on the effects of Ti-5Cu alloy on macrophage polarization and immune-related bone formation. In this study, we prepared Ti-5Cu alloy by three-dimensional printing technology and found that Ti-5Cu alloy presented a much smoother surface compared with Ti. In addition, the CCK-8 results indicated the Ti-5Cu alloy had no cytotoxicity to RAW264.7 cells by co-culture. The results of inductively coupled plasma mass spectrometry showed that the concentration of Cu²⁺ was 0.133 mg/L after 7 days of co-culture, and the CCK-8 results proved that Cu²⁺ had no cytotoxicity to RAW264.7 at this concentration. Then, we studied the effects of Ti-5Cu alloy on macrophage polarization; it was shown that the Ti-5Cu alloy is more prone to modulate the RAW264.7 polarization towards the M2 phenotype and the conditioned medium derived from Ti-5Cu alloy significantly promoted the proliferation and osteogenic differentiation of MC3T3-E1 cells. However, when the expression of Oncostatin M (OSM) gene of RAW264.7 was knocked down, the osteogenic differentiation of MC3T3-E1 cells was decreased. This suggests that the OSM secreted by RAW264.7 co-cultured with Ti-5Cu alloy could accelerate the osteogenic differentiation of MC3T3-E1 cells by acting on OSMR/gp130 receptors.

Hybrid Mineral/Organic Material Induces Bone Bridging and Bone Volume Augmentation in Rat Calvarial Critical Size Defects

In craniofacial bone defects, the promotion of bone volume augmentation remains a challenge. Finding strategies for bone regeneration such as combining resorbable minerals with organic polymers would contribute to solving the bone volume roadblock. Here, dicalcium phosphate dihydrate, chitosan and hyaluronic acid were used to functionalize a bone-side collagen membrane. Despite an increase in the release of inflammatory mediators by human circulating monocytes, the in vivo implantation of the functionalized membrane allowed the repair of a critical-sized defect in a calvaria rat model with de novo bone exhibiting physiological matrix composition and structural organization. Microtomography, histological and Raman analysis combined with nanoindentation testing revealed an increase in bone volume in the presence of the functionalized membrane and the formation of woven bone after eight weeks of implantation; these data showed the potential of dicalcium phosphate dihydrate, chitosan and hyaluronic acid to induce an efficient repair of critical-sized bone defects and establish the importance of thorough multi-scale characterization in assessing biomaterial outcomes in animal models.

A Bilayer Membrane Doped with Struvite Nanowires for Guided Bone Regeneration

Guided bone regeneration (GBR) therapy demonstrates a prominent curative effect on the management of craniomaxillofacial (CMF) bone defects. In this study, a GBR membrane consisting of a microporous layer and a struvite-nanowire-doped fibrous layer is constructed via non-solvent induced phase separation, followed by an electrospinning procedure to treat critical-sized calvarial defects. The microporous layer shows selective permeability for excluding the rapid-growing non-osteogenic tissues and potential wound stabilization. The nanowire-like struvite is synthesized as the deliverable therapeutic agent within the fibrous layer to facilitate bone regeneration. Such a membrane displays a well-developed heterogeneous architecture, satisfactory mechanical performance, and long-lasting characteristics. The in vitro biological evaluation reveals that apart from being a strong barrier, the bilayer struvite-laden membrane can actively promote cellular adhesion, proliferation, and osteogenic differentiation. Consequently, the multifunctional struvite-doped membranes are applied to treat 5 mm-sized bilateral calvarial defects in rats, resulting in overall improved healing outcomes compared with the untreated or the struvite-free membrane-treated group, which is characterized by enhanced osteogenesis and significantly increased new bone formation. The encouraging preclinical results reveal the great potential of the bilayer struvite-doped membrane as a clinical GBR device for augmenting large-area CMF bone reconstruction.

Microporous structures on mineralized collagen mediate osteogenesis by modulating the osteo-immune response of macrophages

It is a new hot pot in tissue engineering and regenerative medicine to study the effects of physicochemical properties of implanted biomaterials on regulating macrophage polarization to promote bone regeneration. In this study, we designed and fabricated mineralized collagen (MC) with different microporous structures via in vitro biomimetic mineralization method. The microporous structures, mechanical properties, shore hardness and water contact angle measurements were tested. Live/dead cell staining, CCK-8 assay, phalloidine staining, staining of focal adhesions were used to detect cell behavior. ELISA, qRT-PCR, ALP, and alizarin red staining (ARS) were performed to appraise osteogenic differentiation and investigated macrophage response and their subsequent effects on the osteogenic differentiation. The results showed that RAW264.7 and MC3T3-E1 cells were able to survive on the MC. MC with the microporous structure of approximately 84 μm and 70%–80% porosity could promote M2 macrophage polarization and increase the expression level of TGF-β and VEGF. Moreover, the gene expression of the osteogenic markers ALP, COL-1, and OCN increased. Therefore, MC with different microporous structures mediated osteoimmunomodulation in bone regeneration. These data will provide a new idea of biomaterials inducing bone repair and direct the optimal design of novel immune biomaterials, development, and rational usage.

Various Coated Barrier Membranes for Better Guided Bone Regeneration: A Review

A good barrier membrane is one of the important factors for effective guided bone/tissue regeneration (GBR/GTR) in the case of periodontal bone defects. Several methods are being discussed to overcome and improve the shortcomings of commercially available membranes. One of the methods is to coat the membrane with bioactive materials. In this study, 41 studies related to coated membranes for GBR/GTR published in the last 5 years were reviewed. These studies reported coating the membrane with various bioactive materials through different techniques to improve osteogenesis, antimicrobial properties, and physical/mechanical properties. The reported studies have been classified and discussed based on the purpose of coating. The goal of the most actively studied research on coating or surface modification of membranes is to improve new bone formation. For this purpose, calcium phosphate, bioactive glass, polydopamine, osteoinduced drugs, chitosan, platelet-rich fibrin, enamel matrix derivatives, amelotin, hyaluronic acid, tantalum, and copper were used as membrane coating materials. The paradigm of barrier membranes is changing from only inert (or biocompatible) physical barriers to bioactive osteo-immunomodulatory for effective guided bone and tissue regeneration. However, there is a limitation that there exists only a few clinical studies on humans to date. Efforts are needed to implement the use of coated membranes from the laboratory bench to the dental chair unit. Further clinical studies are needed in the patients’ group for long-term follow-up to confirm the effect of various coating materials.

Mesenchymal Stem Cell-Derived Extracellular Vesicles for Bone Defect Repair

The repair of critical bone defects is a hotspot of orthopedic research. With the development of bone tissue engineering (BTE), there is increasing evidence showing that the combined application of extracellular vesicles (EVs) derived from mesenchymal stem cells (MSCs) (MSC-EVs), especially exosomes, with hydrogels, scaffolds, and other bioactive materials has made great progress, exhibiting a good potential for bone regeneration. Recent studies have found that miRNAs, proteins, and other cargo loaded in EVs are key factors in promoting osteogenesis and angiogenesis. In BTE, the expression profile of the intrinsic cargo of EVs can be changed by modifying the gene expression of MSCs to obtain EVs with enhanced osteogenic activity and ultimately enhance the osteoinductive ability of bone graft materials. However, the current research on MSC-EVs for repairing bone defects is still in its infancy, and the underlying mechanism remains unclear. Therefore, in this review, the effect of bioactive materials such as hydrogels and scaffolds combined with MSC-EVs in repairing bone defects is summarized, and the mechanism of MSC-EVs promoting bone defect repair by delivering active molecules such as internal miRNAs is further elucidated, which provides a theoretical basis and reference for the clinical application of MSC-EVs in repairing bone defects.

Barrier Membrane in Regenerative Therapy: A Narrative Review

Guided bone and tissue regeneration remains an integral treatment modality to regenerate bone surrounding teeth and dental implants. Barrier membranes have been developed and produced commercially to allow space for bone regeneration and prevent the migration of unwanted cells. Ideal membrane properties, including biocompatibility, sufficient structural integrity and suitable shelf life with easy clinical application, are important to ensure good clinical regenerative outcomes. Membranes have various types, and their clinical application depends on the origin, material, structure and properties. This narrative review aims to describe the currently available barrier membranes in terms of history, main features, types, indication and clinical application and classify them into various groups. Various membranes, including those which are resorbable and non-resorbable, synthetic, added with growth factors and composed of modern materials, such as high-grade polymer (Polyetheretherketone), are explored in this review.

Regulation of Macrophage Polarization by Mineralized Collagen Coating to Accelerate the Osteogenic Differentiation of Mesenchymal Stem Cells

Osteogenesis on the interface between the implant and host bone is a synergistic processing of multiple systems involved in immune response, angiogenesis, osteogenesis, etc. However, regulation of the osteoimmune microenvironment on the implant surface to accelerate the osteogenesis through manipulating the polarization of macrophage phenotype is still beginning to be explored. We here demonstrate that macrophage phenotype is able to be regulated by decoration of mineralized collagen (MC) coating on the titanium implant surface via triggering the integrin-related cascade pathway of macrophages. Furthermore, regulation of the macrophage polarization and construction of the osteoimmune microenvironment by MC coating would subsequently accelerate the osteogenic differentiation of the mesenchymal stem cells. This work therefore emphasizes the importance of the osteoimmune microenvironment on osteogenesis and provides a promising strategy to improve the osteointegration of implants.

Hierarchical Intrafibrillarly Mineralized Collagen Membrane Promotes Guided Bone Regeneration and Regulates M2 Macrophage Polarization

Mineralized collagen has been introduced as a promising barrier membrane material for guided bone regeneration (GBR) due to its biomimetic nanostructure. Immune interaction between materials and host significantly influences the outcome of GBR. However, current barrier membranes are insufficient for clinical application due to limited mechanical or osteoimmunomodulatory properties. In this study, we fabricated hierarchical intrafibrillarly mineralized collagen (HIMC) membrane, comparing with collagen (COL) and extrafibrillarly mineralized collagen (EMC) membranes, HIMC membrane exhibited preferable physicochemical properties by mimicking the nanostructure of natural bone. Bone marrow mesenchymal stem cells (BMSCs) seeded on HIMC membrane showed superior proliferation, adhesion, and osteogenic differentiation capacity. HIMC membrane induced CD206+Arg-1+ M2 macrophage polarization, which in turn promoted more BMSCs migration. In rat skull defects, HIMC membrane promoted the regeneration of new bone with more bone mass and more mature bone architecture. The expression levels of Runx2 and osterix and CD68 + CD206 + M2 macrophage polarization were significantly enhanced. HIMC membrane provides an appropriate osteoimmune microenvironment to promote GBR and represents a promising material for further clinical application.

Antibacterial and Immunomodulatory Properties of Acellular Wharton’s Jelly Matrix

Of all biologic matrices, decellularized tissues have emerged as a promising tool in the field of regenerative medicine. Few empirical clinical studies have shown that Wharton’s jelly (WJ) of the human umbilical cord promotes wound closure and reduces wound-related infections. In this scope, we herein investigated whether decellularized (DC)-WJ could be used as an engineered biomaterial. In comparison with devitalized (DV)-WJ, our results showed an inherent effect of DC-WJ on Gram positive (S. aureus and S. epidermidis) and Gram negative (E. coli and P. aeruginosa) growth and adhesion. Although DC-WJ activated the neutrophils and monocytes in a comparable magnitude to DV-WJ, macrophages modulated their phenotypes and polarization states from the resting M0 phenotype to the hybrid M1/M2 phenotype in the presence of DC-WJ. M1 phenotype was predominant in the presence of DV-WJ. Finally, the subcutaneous implantation of DC-WJ showed total resorption after three weeks of implantation without any sign of foreign body reaction. These significant data shed light on the potential regenerative application of DC-WJ in providing a suitable biomaterial for tissue regenerative medicine and an ideal strategy to prevent wound-associated infections.

Novel insights into nanomaterials for immunomodulatory bone regeneration

Bone defect repair caused by trauma, congenital malformation, tumors, infection or systemic diseases remains the focus of attention in regeneration medicine. Recent advances in osteoimmunology indicate that immune cells and correlative cytokines modulate the delicate balance between osteoblasts and osteoclasts and induce a favorable microenvironment for bone regeneration. With superior attributes that imitate the three-dimensional architecture of natural bone, excellent fabricability, mechanical and biological properties, nanomaterials (NMs) are becoming attractive in the field of bone tissue engineering. Particularly, it could be an effective strategy for immunomodulatory bone regeneration by engineering NMs involved in composition nature, nanoarchitectural morphology, surface chemistry, topography and biological molecules, whose mechanisms potentially refer to regulating the phenotype of high-plastic immune cells and inducing cytokine secretion to accelerate osteogenesis. Despite these prominent achievements, the employment of NMs is poorly translated into clinical trials due to the lack of knowledge about the interaction between NMs and the immune system. For this reason, we sketch out the hierarchical structure of bone and its natural healing process, followed by discussion about the effects of immune cells on bone regeneration. Novel horizons focusing on recent progressions in the architectural and physicochemical performances of NMs and their impacts on the body defence mechanism are also emphasized, hoping to provide novel insights for the fabrication of bone graft materials in tissue engineering.

Attapulgite-doped electrospun PCL scaffolds for enhanced bone regeneration in rat cranium defects

Electrospun PCL scaffolds have been widely used for tissue engineering as they have shown great potential to mimic the structure of the natural extracellular matrix (ECM). However, the small pore size and low bioactivity of the scaffolds limit cell migration and tissue formation. In this study, PCL (polycaprolactone), PCL/PEG (polyethylene glycol), and PCL/PEG/ATP (nano-attapulgite) scaffolds were fabricated via electrospinning. To increase the porosity of the scaffolds, they were washed to remove water-soluble PEG fibers. Then the porous structure was measured using scanning electron microscopy (SEM) and atomic force microscopy (AFM), which showed an increased porosity when PEG fibers were removed in PCL/PEG and PCL/PEG/ATP scaffolds. Moreover, the mechanical properties were also analyzed in dry and wet conditions. In vitro mouse multipotent mesenchymal precursor cells were used to assess the biocompatibility of the scaffolds, and osteogenesis was analyzed using CCK-8 and real-time PCR (RT-PCR) methods. Moreover, in vivo μCT, histological and immunohistochemical analyses were conducted to evaluate new bone formation in rat cranium defect models. Washed PCL/PEG/ATP scaffolds were implanted into the cranium defects in rats for 4 or 8 weeks, better cell infiltration was observed in these scaffolds than in unwashed ones. The result demonstrated that washed PCL/PEG/ATP scaffold facilitated the differentiation of MSCs into osteoblasts compared with PCL scaffold, as proved by the increased expression of osteogenic key genes as well as Smad1, Smad4, and Smad5. Furthermore, in vivo studies demonstrated that using the ATP-doped electrospun PCL scaffold can improve the bone regeneration of rat cranium defects. Particularly, the PCL/ATP-30% scaffold has the best effect compared to the other scaffolds. The enhanced osteogenesis and bone repair were related to the PCL/ATP activated BMP/Smad signaling pathway.

Zn/Sr dual ions-collagen co-assembly hydroxyapatite enhances bone regeneration through procedural osteo-immunomodulation and osteogenesis

The immune microenvironment induced by biomaterials played vital roles in bone regeneration. Hydroxyapatite (HA) and its ion-substituted derivates represent a large class of core inorganic materials for bone tissue engineering. Although ion substitution was proved to be a potent way to grant HA more biological functions, few studies focused on the immunomodulatory properties of ion-doped HA. Herein, to explore the potential osteoimmunomodulatory effects of ion-doped HA, zinc and strontium co-assembled into HA through a collagen template biomimetic way (ZnSr-Col-HA) was successfully achieved. It was found that ZnSr-Col-HA could induce a favorable osteo-immune microenvironment by stimulating macrophages. Furthermore, ZnSr-Col-HA demonstrated a procedural promoting effect on osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) in vitro. Specifically, the osteo-immune microenvironment acted as a dominant factor in promoting osteogenic gene expressions at the early stage through OSM signal pathway. Whereas the direct stimulating effects on BMSCs by Zn²⁺/Sr²⁺ were more effectively at the later stage with Nfatc1/Maf and Wnt signals activated. In vivo study confirmed strong promoting effects of ZnSr-Col-HA on critical-sized cranial defect repair. The current study indicated that such a combined biomaterial design philosophy of dual ion-doping and biomimetic molecular co-assembly to endow HA applicable osteoimmunomodulatory characteristics might bring up a new cutting-edge concept for bone regeneration study.

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Zn/Sr dual ions-collagen co-assembly hydroxyapatite (ZnSr-Col-HA) was achieved via a molecular template biomimetic way.

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A procedural promoting effect of ZnSr-Col-HA on osteogenic differentiation of BMSCs was firstly found.

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A novel material design philosophy was proposed for dual ions-doped biomimetic HA with osteoimmunomodulatory properties.

Ultrastructural and Physicochemical Characterization of a Non-Crosslinked Type 1 Bovine Derived Collagen Membrane

In this work, in vitro testing was used to study the properties of non-crosslinked type 1 bovine derived collagen membranes used in bone regeneration surgery. Collagen membranes were prepared, their surface roughness was quantified by interferometry, their morphology was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), their wettability was measured by the contact angle technique, their mechanical properties were investigated by tensile testing, their phase transformation temperatures were measured by Differential Scanning Calorimetry (DSC), and their biocompatibility was evaluated by immunological testing. The calorimetry tests showed that the membrane is formed only by type 1 collagen. The SEM observations showed that the morphology consists of layers of highly organized collagen fibers and patterns of striated fibrils typical of type 1 collagen. The small contact angle showed that the membrane is hydrophilic, with the possibility of rapid absorption of body fluids. The tensile tests showed that the membrane has enough elasticity, ductility, and mechanical strength for use in tissue regeneration. With the immunostaining technique, it was possible to confirm the membrane biocompatibility.

The antigenicity of silk-based biomaterials: sources, influential factors and applications

Silk is an ancient material with essential roles in numerous biomedical applications, such as tissue regeneration and drug delivery, because of its excellent tunable mechanical properties and diverse physical structures. In addition to the necessary functionalities for biomedical applications, another critical factor for materials applied in biology is the appropriate immune interactions with the body. This review focuses on the immune responses of silk-based materials applied in biomedical applications, specifically antigenicity. The factors affecting the antigenicity of silk-based materials are complicated and are related to the composition and structural characteristics of the materials. At the same time, the composition of silk-based materials varies with its species sources, such as silkworms, spiders, honey bees, or engineered recombinant silk. Additionally, different processing methods are used to fabricate different material formats, such as films, hydrogels, scaffolds, particles, and fibers, resulting in different structural characteristics. Furthermore, the resulting body reactions are also different with different degrees of the immune response. Silk protein typically induces a mild immune response, and immunogenicity can play active roles in osteogenesis, angiogenesis, and protection from inflammation. However, there are some rare reports of severe immune responses caused by silk, which can result in an allergic response or tissue necrosis. The source of allergenicity in silk-based materials is currently under-studied and how to regulate and eliminate the overreaction of the immune system is essential for further applications. Overall, the diverse characteristics of silk-based materials mostly show beneficial bioresponses with mild immunogenicity, and the tunable properties make it applicable in immune-related biomedical applications.

Immunomodulatory bioactive glasses for tissue regeneration

The regulatory functions of the immune response in tissue healing, repair, and regeneration have been evidenced in the last decade. Immune cells play central roles in immune responses toward inducing favorable tissue regenerative processes. Modulating and controlling the immune cell responses (particularly macrophages) is an emerging approach to enhance tissue regeneration. Bioactive glasses (BGs) are multifunctional materials exhibiting osteogenic, angiogenic, and antibacterial properties, being increasingly investigated for various tissue regeneration scenarios, including bone regeneration and wound healing. On the other hand, the immunomodulatory effects of BGs in relation to regenerating tissues have started to be understood, and key knowledge is emerging. This is the first review article summarizing the immunomodulatory effects of BGs for tissue repair and regeneration. The immune response to BGs is firstly introduced, discussing potential mechanisms regarding the immunomodulation effects induced by BGs. Moreover, the interactions between the immune cells involved in the immunomodulation process and BGs (dissolution products) are summarized in detail. Particularly, a well-regulated and timely switch of macrophage phenotype from pro-inflammatory to anti-inflammatory is crucial to constructive tissue regeneration through modulating osteogenesis, osteoclastogenesis, and angiogenesis. The influence of BG characteristics on macrophage responses is discussed. We highlight the strategies employed to harness macrophage responses for enhanced tissue regeneration, including the incorporation of active ions, surface functionalization, and controlled release of immunomodulatory molecules. Finally, we conclude with our perspectives on future research challenges and directions in the emerging field of immunomodulatory BGs for tissue regeneration. STATEMENT OF SIGNIFICANCE: Immunomodulatory effects of bioactive glasses (BGs) in relation to bone regeneration and wound healing have started to be understood. We summarize those studies which have focused on immunomodulatory BGs for tissue regeneration. We first introduce the potential mechanisms of the immunomodulation effects induced by BGs. Interactions between the cells involved in immunomodulation processes and BGs (and their dissolution products, biologically active ions) are elaborated. We highlight the strategies employed to modulate macrophage responses for enhancing tissue regeneration, including incorporation of active ions, surface functionalization, and controlled release of immunomodulatory agents. This is the first review article summarizing and outlining the immunomodulatory effects of BGs for tissue regeneration. We anticipate that increasing research efforts will start to emerge in the area of immunomodulatory BGs.

A practical guide for evaluating the osteoimmunomodulatory properties of biomaterials

Biomaterials offer a promising approach to repair bone defects. Whereas traditional studies predominantly focused on optimizing the osteogenic capacity of biomaterials, less focus has been on the immune response elicited by them. However, the immune and skeletal systems extensively interact, a concept which is referred to as 'osteoimmunology'. This realization has fuelled the development of biomaterials with favourable osteoimmunomodulatory (OIM) properties, aiming to modulate the immune response and to support bone regeneration, thereby affecting the success of an implant. Given the plethora of in vitro assays used to evaluate the OIM properties of biomaterials, it may be challenging to select the right methods to produce conclusive results. In this review, we aim to provide a comprehensive and practical guide for researchers interested in studying the OIM properties of biomaterials in vitro. After a concise overview of the concept of osteoimmunology, emphasis is put on the methodologies that are regularly used to evaluate the OIM properties of biomaterials. First, a description of the most commonly used cell types and cell culture media is provided. Second, typical experimental set-ups and their relevant characteristics are discussed. Third, a detailed overview of the generally used methodologies and readouts, including cell type-specific markers and time points of analysis, is given. Finally, we highlight the promise of advanced approaches, namely microarrays, bioreactors and microfluidic-based systems, and the potential that these may offer to the osteoimmunology field. STATEMENT OF SIGNIFICANCE: Osteoimmunology focuses on the connection and communication between the skeletal and immune systems. This interaction has been recognized to play an important role in the clinical success of biomaterials, which has resulted in an increasing amount of research on the osteoimmunomodulatory (OIM) properties of biomaterials. However, the amount of literature makes it challenging to extract the information needed to design experiments from beginning to end, and to compare obtained results to existing work. This article intends to serve as a guide for those aiming to learn more about the commonly used experimental approaches in the field. We cover early-stage choices, such as cell types and experimental set-ups, but also discuss specific assays, including cell markers and time points of analysis.

A novel coating with universal adhesion and inflammation-responsive drug release functions to manipulate the osteoimmunomodulation of implants

The immune response elicited by the bone endoprosthesis is currently considered an important factor that affects its interfacial osteointegration. In this work, a metal-phenolic-based drug-loaded coating with universal adhesion properties and intelligent drug delivery feature was created to promote osteointegration by manipulating a beneficial osteoimmune microenvironment. A novel pro-drug with inflammation-responsive release function was firstly synthesized via the esterification reaction between tannic acid (TA) and indometacin (IND), and then the coating was developed by chelating it with Fe3+. In the normal biological environment, the coating was stable, while, in the inflammatory environment, the release of TA and IND motifs could be triggered by the overexpressed esterase. The released TA and IND displayed synergistic effects on macrophage polarization, leading to a downregulation expression of pro-inflammatory cytokines, and an upregulation expression of anti-inflammatory cytokines and osteogenic-related factors. When stimulated by a conditioned medium generated by macrophages seeded onto the coating, the osteogenic differentiation potential of BMSCs was significantly enhanced. Finally, the designed coating significantly promoted the osteointegration of the implant, demonstrated by the increase of the bone-implant contact by two times. Additionally, the coating was substrate-independent and can be formed within seconds without special equipment, thus, it showed great potential applications to endow advanced hard tissue implants with favorable osteoimmunomodulation.

Substituted Hydroxyapatite, Glass, and Glass-Ceramic Thin Films Deposited by Nanosecond Pulsed Laser Deposition (PLD) for Biomedical Applications: A Systematic Review

The deposition of thin films of bioactive materials is the most common approach to improve the bone bonding ability of an implant surface. With this purpose, several wet and plasma assisted deposition methods were proposed in the scientific literature. In this review, we considered films obtained by nanosecond Pulsed Laser Deposition (PLD). Since hydroxyapatite (HA) has composition and structure similar to that of the mineral component of the bone, the initial studies focused on the selection of experimental conditions that would allow the deposition of films that retain HA stoichiometry and crystallinity. However, biological apatite was found to be a poorly crystalline and multi-substituted mineral; consequently, the attention of researchers was oriented towards the deposition of substituted HA, glass (BG), and glass-ceramic (BGC) bioactive materials to exploit the biological relevance of foreign ions and crystallinity. In this work, after a description of the nanosecond ablation and film growth of ceramic materials, we reported studies on the mechanism of HA ablation and deposition, evidencing the peculiarities of PLD. The literature concerning the PLD of ion substituted HA, BG, and BGC was then reviewed and the performances of the coatings were discussed. We concluded by describing the advantages, limitations, and perspectives of PLD for biomedical applications.

Periosteal Tissue Engineering: Current Developments and Perspectives

Periosteum, a highly vascularized bilayer connective tissue membrane plays an indispensable role in the repair and regeneration of bone defects. It is involved in blood supply and delivery of progenitor cells and bioactive molecules in the defect area. However, sources of natural periosteum are limited, therefore, there is a need to develop tissue-engineered periosteum (TEP) mimicking the composition, structure, and function of natural periosteum. This review explores TEP construction strategies from the following perspectives: i) different materials for constructing TEP scaffolds; ii) mechanical properties and surface topography in TEP; iii) cell-based strategies for TEP construction; and iv) TEP combined with growth factors. In addition, current challenges and future perspectives for development of TEP are discussed.

Inflammation and biomaterials: role of the immune response in bone regeneration by inorganic scaffolds

The regulatory role of the immune system in maintaining bone homeostasis and restoring its functionality, when disturbed due to trauma or injury, has become evident in recent years. The polarization of macrophages, one of the main constituents of the immune system, into the pro-inflammatory or anti-inflammatory phenotype has great repercussions for cellular crosstalk and the subsequent processes needed for proper bone regeneration such as angiogenesis and osteogenesis. In certain scenarios, the damaged osseous tissue requires the placement of synthetic bone grafts to facilitate the healing process. Inorganic biomaterials such as bioceramics or bioactive glasses are the most widely used due to their resemblance to the mineral phase of bone and superior osteogenic properties. The immune response of the host to the inorganic biomaterial, which is of an exogenous nature, might determine its fate, leading either to active bone regeneration or its failure. Therefore, various strategies have been employed, like the modification of structural/chemical features or the incorporation of bioactive molecules, to tune the interplay with the immune cells. Understanding how these particular modifications impact the polarization of macrophages and further osteogenic and osteoclastogenic events is of great interest in view of designing a new generation of osteoimmunomodulatory materials that support the regeneration of osseous tissue during all stages of bone healing.

Surface modified small intestinal submucosa membrane manipulates sequential immunomodulation coupled with enhanced angio- and osteogenesis towards ameliorative guided bone regeneration

Constructing bioactive guided bone regeneration (GBR) membranes that possess biological multifunctionality is becoming increasingly attractive and promising to meet higher requirements for bone healing. Given the biological responses following implantation, GBR process originates from an early inflammation-driven reaction adjacent to implanted membranes surface. However, to date there is relatively little attention paid to the critical immunoregulatory functions in traditionally designed GBR membranes. Herein, for the first time, we manipulate immunomodulatory properties of the widely-used native small intestinal submucosa (SIS) membrane by incorporating strontium-substituted nanohydroxyapatite coatings and/or IFN-γ to its surface. In vitro results reveal the obtained novel membrane SIS/SrHA/IFN-γ not only promote functions of endothelial cells and osteoblasts directly, but also energetically mediate a sequential M1-M2 macrophages transition to concurrently facilitate angiogenesis and osteogenesis. Moreover, in vivo outcomes of subcutaneous implantation and cranial defects repair further confirm its superior capacity to promote vascularization and in situ bone regeneration than pristine SIS through immunomodulation. These results demonstrate a sequential immunomodulatory strategy renders modified SIS membranes acting as a robust immunomodulator rather than a traditional barrier to significantly ameliorate in vivo GBR outcomes and hence provide important implications that may facilitate concerns on immunomodulatory properties for future GBR developments.

Small Extracellular Vesicles from Lipopolysaccharide-Preconditioned Dental Follicle Cells Promote Periodontal Regeneration in an Inflammatory Microenvironment

Lipopolysaccharide (LPS)-induced inflammatory microenvironment can enhance the dental follicle cells (DFCs) proliferation, differentiation, and adhesion abilities beneficial to periodontal regeneration, which possibly attributes the success to exosomes according to recent studies. This study aimed to investigate the therapeutic efficacy and underlying mechanisms of LPS-preconditioned DFC-derived small extracellular vesicles (sEVs), which enriched exosomes for periodontal regeneration in an inflammatory microenvironment. LPS preconditioning could significantly increase the secretion of sEVs derived from DFCs. Both LPS-preconditioned dental follicle cell-derived sEV (L-D-sEV) and DFC-derived sEV (D-sEV) promoted the proliferation of periodontal ligament cells from periodontitis (p-PDLCs) with a dose-dependent and saturable manner and also enhanced the migration and differentiation of p-PDLCs. Furthermore, L-D-sEV showed a modest benefit than D-sEV to promote p-PDLCs differentiation. In vivo, an L-D-sEV-loaded hydrogel applied in the treatment of periodontitis was beneficial to repair lost alveolar bone in the early stage of treatment and to maintain the level of alveolar bone in the late stage of treatment in experimental periodontitis rats, which could partly decrease the expression of the RANKL/OPG ratio. In conclusion, L-D-sEV was beneficial to p-PDLCs forming an integrity periodontal tissue. The biological injectable L-D-sEV-loaded hydrogel could be used as a treatment method for experimental periodontitis in rats, promoting periodontal tissue regeneration and providing a new alternative cell therapy method for periodontal tissue regeneration.

Tuning the immune reaction to manipulate the cell-mediated degradation of a collagen barrier membrane

In order to elicit a desired barrier function in guided bone regeneration (GBR) or guided tissue regeneration (GTR), a barrier membrane has to maintain its integrity for a certain period of time to guarantee the regeneration of target tissue. Due to the complexity and variety of clinical conditions, the healing time required for tissue regeneration varies from one case to another, which implies the need for tailoring the barrier membranes to diverse conditions via manipulating their degradation property. As a "non-self" biomaterial, a barrier membrane will inevitably trigger host-membrane immune response after implantation, which entails the activation of phagocytic cells. In the degradation process of a barrier membrane, the cell-mediated degradation may play a more vital role than enzymatic and physicochemical dissolution; however, limited studies have been carried out on this topic. In this context, we investigated the cell-mediated degradation and illustrated the possible key cells and mediators for immunomodulation via in vivo and in vitro studies. We discovered that IL-13, a key cytokine mainly released by T helper 2 cells (Th2), induced the formation of foreign body giant cells (FBGCs), thus resulting in membrane degradation. Neutralizing IL-13 could suppress membrane degradation and formation of FBGC. The contributions of this study are (1) unveiling the immune mechanisms underlying the cell-mediated collagen membrane degradation; (2) allowing the formation of an "immunodegradation" strategy to develop an "immune-smart" barrier membrane to manipulate its degradation; (3) providing the key regulatory immune cells and cytokines for the immunomodulation target in collagen membrane degradation. STATEMENT OF SIGNIFICANCE: The significance of this research includes.

Mesoporous Hydroxyapatite Nanoparticles Mediate the Release and Bioactivity of BMP-2 for Enhanced Bone Regeneration

Efficient delivery of bone morphogenetic protein-2 (BMP-2) with desirable bioactivity is still a great challenge in the field of bone regeneration. In this study, a silk fibroin/chitosan scaffold incorporated with BMP-2-loaded mesoporous hydroxyapatite nanoparticles (mHANPs) was prepared (SCH-L). BMP-2 was preloaded onto mHANPs with a high surface area before mixing with a silk fibroin/chitosan composite. Bare (without BMP-2) silk fibroin/chitosan/mHANP (SCH) scaffolds and SCH scaffolds with directly absorbed BMP-2 (SCH-D) were investigated in parallel for comparison. In vitro release kinetics indicated that BMP-2 released from the SCH-L scaffold showed a significantly lower initial burst release, followed by a more sustained release over time than the SCH-D scaffold. In vitro cell viability, osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), and the in vivo osteogenic effect of scaffolds in a rat calvarial defect were evaluated. The results showed that compared with bare SCH and SCH-D scaffolds, the SCH-L scaffold significantly promoted the osteogenic differentiation of BMSCs in vitro and induced more pronounced bone formation in vivo. Further studies demonstrated that the mHANP-mediated satisfactory conformational change and sustained release benefited the protection of the released BMP-2 bioactivity, as confirmed by alkaline phosphatase (ALP) activity and a mineralization deposition assay. More importantly, the interaction of BMP-2/mHANPs enhanced the binding ability of BMP-2 to cellular receptors, thereby maintaining its biological activity in osteogenic differentiation and osteoinductivity well, which contributed to the markedly promoted in vitro and in vivo osteogenic efficacy of the SCH-L scaffold. Taken together, these results provide strong evidence that mHANPs represent an attractive carrier for binding BMP-2 to scaffolds. The SCH-L scaffold shows promising potential for bone tissue regeneration applications.

In vitro biocompatibility of biohybrid polymers membrane evaluated in human gingival fibroblasts

The biohybrid polymer membrane (BHM) is a new biomaterial designed for the treatment of soft periodontal tissue defects. We aimed to evaluate the in vitro biocompatibility of the membrane in human gingival fibroblasts and the capability to induce cell adhesion, migration, differentiation and improving the production of the extracellular matrix. BHM and Mucograft® collagen matrix (MCM) membranes were punched into 6 mm diameter round discs and placed in 96‐well plates. Human primary gingival fibroblasts were seeded on the membranes or tissue culture plastic (TCP) serving as the control. Cell proliferation/viability and morphology were evaluated after 3, 7, and 14 days of culture by cell counting kit (CCK)‐8 assay and scanning electron microscopy, respectively. Additionally, the gene expression of transforming growth factor (TGF)‐β1, focal adhesion kinase (FAK), collagen type 1 (Col1), alpha‐smooth muscle actin (α‐SMA), and fibroblasts growth factor (FGF)‐2 was analyzed at 3, 7, and 14 days of culture by qPCR. Cell proliferation on BHM was significantly higher than on MCM and similar to TCP. Gene expression of TGF‐β1, FAK, Col1, and α‐SMA were significantly increased on BHM compared to TCP at most investigated time points. However, the gene expression of FGF‐2 was significantly decreased on BHM at Day 7 and recovered at Day 14 to the levels similar to TCP. The finding of this study showed that BHM is superior for gingival fibroblasts in terms of adhesion, proliferation, and gene expression, suggesting that this membrane may promote the healing of soft periodontal tissue.