Biomaterials Regulating Bone Hematoma for Osteogenesis

In situ osteogenic activation of mesenchymal stem cells by the blood clot biomimetic mechanical microenvironment

Blood clots (BCs) play a crucial biomechanical role in promoting osteogenesis and regulating mesenchymal stem cell (MSC) function and fate. This study shows that BC formation enhances MSC osteogenesis by activating Itgb1/Fak-mediated focal adhesion and subsequent Runx2-mediated bone regeneration. Notably, BC viscoelasticity regulates this effect by modulating Runx2 nuclear translocation. To mimic this property, a viscoelastic peptide bionic hydrogel named BCgel was developed, featuring a nanofiber network, Itgb1 binding affinity, BC-like viscoelasticity, and biosafety. The anticipated efficacy of BCgel is demonstrated by its ability to induce nuclear translocation of Runx2 and promote bone regeneration in both in vitro experiments and in vivo bone defect models with blood clot defect, conducted on rats as well as beagles. This study offers insights into the mechano-transduction mechanisms of MSCs during osteogenesis and presents potential guidelines for the design of viscoelastic hydrogels in bone regenerative medicine.

The Influence of Physiological Blood Clot on Osteoblastic Cell Response to a Chitosan-Based 3D Scaffold-A Pilot Investigation

BACKGROUND

The use of ex vivo assays associated with biomaterials may allow the short-term visualization of a specific cell type response inserted in a local microenvironment. Blood is the first component to come into contact with biomaterials, providing blood clot formation, being substantial in new tissue formation. Thus, this research investigated the physiological blood clot (PhC) patterns formed in 3D scaffolds (SCAs), based on chitosan and 20% beta-tricalcium phosphate and its effect on osteogenesis. Initially, SCA were inserted for 16 h in rats calvaria defects, and, after that, osteoblasts cells (OSB; UMR-106 lineage) were seeded on the substrate formed. The groups tested were SCA + OSB and SCA + PhC + OSB. Cell viability was checked by MTT and mineralized matrix formation in OSB using alizarin red (ARS). The alkaline phosphatase (ALP) and bone sialoprotein (BSP) expression in OSB was investigated by indirect immunofluorescence (IF). The OSB and PhC morphology was verified by scanning electron microscopy (SEM).

RESULTS

The SCA + PhC + OSB group showed greater cell viability (p = 0.0169). After 10 days, there was more mineralized matrix deposition (p = 0.0365) and high ALP immunostaining (p = 0.0021) in the SCA + OSB group. In contrast, BSP was more expressed in OSB seeded on SCA with PhC (p = 0.0033).

CONCLUSIONS

These findings show the feasibility of using PhC in ex vivo assays. Additionally, its inclusion in the experiments resulted in a change in OSB behavior when compared to in vitro assays. This "closer to nature" environment can completely change the scenario of a study.

Biocooperative Regenerative Materials by Harnessing Blood-Clotting and Peptide Self-Assembly

The immune system has evolved to heal small ruptures and fractures with remarkable efficacy through regulation of the regenerative hematoma (RH); a rich and dynamic environment that coordinates numerous molecular and cellular processes to achieve complete repair. Here, a biocooperative approach that harnesses endogenous molecules and natural healing to engineer personalized regenerative materials is presented. Peptide amphiphiles (PAs) are co-assembled with blood components during coagulation to engineer a living material that exhibits key compositional and structural properties of the RH. By exploiting non-selective and selective PA-blood interactions, the material can be immediately manipulated, mechanically-tuned, and 3D printed. The material preserves normal platelet behavior, generates and provides a continuous source of growth factors, and promotes in vitro growth of mesenchymal stromal cells, endothelial cells, and fibroblasts. Furthermore, using a personalized autologous approach to convert whole blood into PA-blood gel implants, bone regeneration is shown in a critical-sized rat calvarial defect. This study provides proof-of-concept for a biocooperative approach that goes beyond biomimicry by using mechanisms that Nature has evolved to heal as tools to engineer accessible, personalized, and regenerative biomaterials that can be readily formed at point of use.

Sustained Release of Nitric Oxide-Mediated Angiogenesis and Nerve Repair by Mussel-Inspired Adaptable Microreservoirs for Brain Traumatic Injury Therapy

Traumatic brain injury (TBI) triggers inflammatory response and glial scarring, thus substantially hindering brain tissue repair. This process is exacerbated by the accumulation of activated immunocytes at the injury site, which contributes to scar formation and impedes tissue repair. In this study, a mussel-inspired nitric oxide-release microreservoir (MINOR) that combines the features of reactive oxygen species (ROS) scavengers and sustained NO release to promote angiogenesis and neurogenesis is developed for TBI therapy. The injectable MINOR fabricated using a microfluidic device exhibits excellent monodispersity and gel-like self-healing properties, thus allowing the maintenance of its structural integrity and functionality upon injection. Furthermore, polydopamine in the MINOR enhances cell adhesion, significantly reduces ROS levels, and suppresses inflammation. Moreover, a nitric oxide (NO) donor embedded into the MINOR enables the sustained release of NO, thus facilitating angiogenesis and mitigating inflammatory responses. By harnessing these synergistic effects, the biocompatible MINOR demonstrates remarkable efficacy in enhancing recovery in mice. These findings benefit future therapeutic interventions for patients with TBI.

Bioactive material‑sodium alginate-polyvinyl alcohol composite film scaffold for bone tissue engineering application

Road accidents and infection-causing diseases during bone surgery are serious problems in orthopedics, and thus, addressing these pressing challenges is crucial. In the present study, the 70S30C calcium silicate bioactive material (BM) is synthesized by a sustainable approach employing a precipitation method using recycled rice husk and eggshells as a precursor of silica and calcium. Further, 70S30C BM is composited with sodium alginate (SA) and polyvinyl alcohol (PVA), and the films were prepared by solvent casting method. The composite films were prepared without the addition of acid, binder, and crosslinking agents. Further, the films were characterized by BET, XRD, ATR-FTIR, SEM, and EDS mapping. The in vitro bioactivity and biodegradation study is performed in the simulated body fluid (SBF). The in vitro haemolysis study is executed using human blood and the results demonstrate haemocompatibility of the composite films. The ex ovo CAM assay also exhibits good neovascularization. The in vitro and in vivo biocompatibility assay proves its non-toxic nature. Further, the in vivo study reveals that the engineered composite film demonstrates accelerated osteogenesis. This work broadens the orthopedic potential of the composite film and offers bioactivity, haemocompatibility, angiogenesis, non-toxicity, and in vivo osteogenesis which would serve as a potential candidate for bone tissue engineering application.

Effect of hematoma on early degradation behavior of magnesium after implantation

The corrosion of magnesium (Mg)-based bioabsorbable implanting devices is influenced by implantation environment which dynamically changes by biological response including wound healing. Understanding the corrosion mechanisms along the healing process is essential for the development of Mg-based devices. In this study, a hematoma model was created in a rat femur to analyze Mg corrosion with hematoma in the early stage of implantation. Pure Mg specimen (99.9%,ϕ1.2 × 6 mm) was implanted in rat femur under either hematoma or non-hematoma conditions. After a designated period of implantation, the specimens were collected and weighed. The insoluble salts formed on the specimen surfaces were analyzed using scanning electron microscopy, energy-dispersive x-ray spectroscopy, and Raman spectroscopy on days 1, 3, and 7. The results indicate that hematomas promote Mg corrosion and change the insoluble salt precipitation. The weight loss of the hematoma group (27.31 ± 5.91 µg mm-2) was significantly larger than that of the non-hematoma group (14.77 ± 3.28 µg mm-2) on day 7. In the non-hematoma group, carbonate and phosphate were detected even on day 1, but the only latter was detected on day 7. In the hematoma group, hydroxide was detected on day 1, followed by the formation of carbonate and phosphate on days 3 and 7. The obtained results suggest the hypoxic and acidic microenvironment in hematomas accelerates the Mg corrosion immediately after implantation, and the subsequent hematoma resorption process leads to the formation of phosphate and carbonate with organic molecules. This study revealed the risk of hematomas as an acceleration factor of the corrosion of Mg-based devices leading to the early implant failure. It is important to consider this risk in the design of Mg-based devices and to optimize surgical procedures controlling hemorrhage at implantation and reducing unexpected bleeding after surgery.

Current Perspectives of Protein in Bone Tissue Engineering: Bone Structure, Ideal Scaffolds, Fabrication Techniques, Applications, Scopes, and Future Advances

In view of their exceptional approach, excellent inherent biocompatibility and biodegradability properties, and interaction with the local extracellular matrix, protein-based polymers have received attention in bone tissue engineering, which is a multidisciplinary field that repairs and regenerates fractured bones. Bone is a multihierarchical complex structure, and it performs several essential biofunctions, including maintaining mineral balance and structural support and protecting soft organs. Protein-based polymers have gained interest in developing ideal scaffolds as emerging biomaterials for bone fractured healing and regeneration, and it is challenging to design ideal bone substitutes as perfect biomaterials. Several protein-based polymers, including collagen, keratin, gelatin, serum albumin, etc., are potential materials due to their inherent cytocompatibility, controlled biodegradability, high biofunctionalization, and tunable mechanical characteristics. While numerous studies have indicated the encouraging possibilities of proteins in BTE, there are still major challenges concerning their biodegradability, stability in physiological conditions, and continuous release of growth factors and bioactive molecules. Robust scaffolds derived from proteins can be used to replace broken or diseased bone with a biocompatible substitute; proteins, being biopolymers, provide excellent scaffolds for bone tissue engineering. Herein, recent developments in protein polymers for cutting-edge bone tissue engineering are addressed in this review within 3-5 years, with a focus on the significant challenges and future perspectives. The first section discusses the structural fundamentals of bone anatomy and ideal scaffolds, and the second section describes the fabrication techniques of scaffolds. The third section highlights the importance of proteins and their applications in BTE. Hence, the recent development of protein polymers for state-of-the-art bone tissue engineering has been discussed, highlighting the significant challenges and future perspectives.

A multifunctional collagen-base bilayer membrane integrated with a bimetallic/polydopamine network for enhanced guided bone regeneration

The guided bone regeneration (GBR) technique is an effective treatment for small and medium-sized bone defects in the oral and maxillofacial region. However, currently available collagen membranes have limited functionality and are inadequate for clinical requirements. To address this challenge, this study pioneeringly developed a multifunctional bilayer membrane. Specifically, a bimetallic/polydopamine network (BPN), consisting of silver, magnesium, and dopamine, was successfully synthesized for the first time and integrated with collagen and hydroxyapatite. The resulting material was characterized, and its physicochemical properties, along with its barrier, osteogenic, angiogenic, antibacterial, hemostatic, and biosafety effects, were evaluated through both in vitro and in vivo studies. The results indicated that the BPN, composed of magnesium ions, silver nanoparticles (Ag NPs), and polydopamine (PDA), exhibited excellent thermal stability and slow release of silver and magnesium elements. The BPN/Col-HA membrane featured a bilayer structure with uniform distribution of silver and magnesium. It also demonstrated good hydrophilicity, suitable degradation and mechanical properties, as well as sustained release of silver and magnesium. In vitro experiments showed that the BPN/Col-HA membrane possessed desirable barrier, osteogenic, angiogenic, antibacterial, hemostatic, and biocompatible properties. In vivo results further confirmed its biosafety, hemostatic efficacy, and ability to effectively promote bone defect repair and angiogenesis. Thus, the BPN/Col-HA membrane emerges as a multifunctional GBR membrane with potential for clinical translation.

Phytic Acid-Gallium Network on a Polyimide Fiber Woven Fabric as an Artificial Ligament for Boosting Ligament-Bone Healing and Infection Treatment

The development of an artificial ligament with a multifunction of promoting bone formation, inhibiting bone resorption, and preventing infection to obtain ligament-bone healing for anterior cruciate ligament (ACL) reconstruction still faces enormous challenges. Herein, a novel artificial ligament based on a PI fiber woven fabric (PIF) was fabricated, which was coated with a phytic acid-gallium (PA-Ga) network via a layer-by-layer assembly method (PFPG). Compared with PIF, PFPG with PA-Ga coating significantly suppressed osteoclastic differentiation, while it boosted osteoblastic differentiation in vitro. Moreover, PFPG obviously inhibited fibrous encapsulation and bone absorption while accelerating new bone regeneration for ligament-bone healing in vivo. PFPG remarkably killed bacteria and destroyed biofilm, exhibiting excellent antibacterial properties in vitro as well as anti-infection ability in vivo, which were ascribed to the release of Ga ions from the PA-Ga coating. The cooperative effect of the surface characteristics (e.g., hydrophilicity/surface energy and protein absorption) and sustained release of Ga ions for PFPG significantly enhanced osteogenesis while inhibiting osteoclastogenesis, thereby achieving ligament-bone integration as well as resistance to infection. In summary, PFPG remarkably facilitated osteoblastic differentiation, while it suppressed osteoclastic differentiation, thereby inhibiting osteoclastogenesis for bone absorption while accelerating osteogenesis for ligament-bone healing. As a novel artificial ligament, PFPG represented an appealing option for graft selection in ACL reconstruction and displayed considerable promise for application in clinics.

Enhancing osteogenesis and angiogenesis functions for Ti-24Nb-4Zr-8Sn scaffolds with methacrylated gelatin and deferoxamine

Repair of large bone defects remains challenge for orthopedic clinical treatment. Porous titanium alloys have been widely fabricated by the additive manufacturing, which possess the elastic modulus close to that of human cortical bone, good osteoconductivity and osteointegration. However, insufficient bone regeneration and vascularization inside the porous titanium scaffolds severely limit their capability for repair of large-size bone defects. Therefore, it is crucially important to improve the osteogenic function and vascularization of the titanium scaffolds. Herein, methacrylated gelatin (GelMA) were incorporated with the porous Ti-24Nb-4Zr-8Sn (Ti2448) scaffolds prepared by the electron beam melting (EBM) method (Ti2448-GelMA). Besides, the deferoxamine (DFO) as an angiogenic agent was doped into the Ti2448-GelMA scaffold (Ti2448-GelMA/DFO), in order to promote vascularization. The results indicate that GelMA can fully infiltrate into the pores of Ti2448 scaffolds with porous cross-linked network (average pore size: 120.2 ± 25.1 μm). Ti2448-GelMA scaffolds facilitated the differentiation of MC3T3-E1 cells by promoting the ALP expression and mineralization, with the amount of calcium contents ∼2.5 times at day 14, compared with the Ti2448 scaffolds. Impressively, the number of vascular meshes for the Ti2448-GelMA/DFO group (∼7.2/mm2) was significantly higher than the control group (∼5.3/mm2) after cultivation for 9 h, demonstrating the excellent angiogenesis ability. The Ti2448-GelMA/DFO scaffolds also exhibited sustained release of DFO, with a cumulative release of 82.3% after 28 days. Therefore, Ti2448-GelMA/DFO scaffolds likely provide a new strategy to improve the osteogenesis and angiogenesis for repair of large bone defects.

Biomaterials for Drug Delivery and Human Applications

Biomaterials embody a groundbreaking paradigm shift in the field of drug delivery and human applications. Their versatility and adaptability have not only enriched therapeutic outcomes but also significantly reduced the burden of adverse effects. This work serves as a comprehensive overview of biomaterials, with a particular emphasis on their pivotal role in drug delivery, classifying them in terms of their biobased, biodegradable, and biocompatible nature, and highlighting their characteristics and advantages. The examination also delves into the extensive array of applications for biomaterials in drug delivery, encompassing diverse medical fields such as cancer therapy, cardiovascular diseases, neurological disorders, and vaccination. This work also explores the actual challenges within this domain, including potential toxicity and the complexity of manufacturing processes. These challenges emphasize the necessity for thorough research and the continuous development of regulatory frameworks. The second aim of this review is to navigate through the compelling terrain of recent advances and prospects in biomaterials, envisioning a healthcare landscape where they empower precise, targeted, and personalized drug delivery. The potential for biomaterials to transform healthcare is staggering, as they promise treatments tailored to individual patient needs, offering hope for improved therapeutic efficacy, fewer side effects, and a brighter future for medical practice.

Anti-Fibronectin Aptamer Modifies Blood Clot Pattern and Stimulates Osteogenesis: An Ex Vivo Study

BACKGROUND

Scaffold (SCA) functionalization with aptamers (APT) provides adsorption of specific bioactive molecules on biomaterial surfaces. The aim of this study was to observe if SCA enriched with anti-fibronectin APT can favor coagulum (PhC) and osteoblasts (OSB) differentiation.

METHODS

20 μg of APT was functionalized on SCA by simple adsorption. For PhC formation, SCAs were inserted into rat calvaria defects for 17 h. Following proper transportation (buffer solution PB), OSBs (UMR-106 lineage) were seeded over PhC + SCAs with and without APT. Cells and PhC morphology, PhC cell population, protein labeling and gene expression were observed in different time points.

RESULTS

The APT induced higher alkaline phosphatase and bone sialoprotein immunolabeling in OSB. Mesenchymal stem cells, leukocytes and lymphocytes cells were detected more in the APT group than when scaffolds were not functionalized. Additionally, an enriched and dense fibrin network and different cell types were observed, with more OSB and white blood cells in PhC formed on SCA with APT. The gene expression showed higher transforming growth factor beta 1 (TGF-b1) detection in SCA with APT.

CONCLUSIONS

The SCA functionalization with fibronectin aptamers may alter key morphological and functional features of blood clot formation, and provides a selective expression of proteins related to osteo differentiation. Additionally, aptamers increase TGF-b1 gene expression, which is highly associated with improvements in regenerative therapies.

Autologous blood clots: a natural biomaterial for wound healing

Repair after injury in mammalian tissue involves a complex cascade of events, with the formation of local blood clots being essential for the initial phases of wound healing. As a result, emerging research has sought to harness this biological activity to generate a pro-regenerative biomaterial to speed up wound healing. According to recent studies, “blood clots” created in vitro can be employed as an orthobiologic-based biomaterial for promoting tissue regeneration. Even though such research is still in its early phases, numerous studies show encouraging results that suggest autologous blood clots created in vitro might be a valuable treatment for soft tissue and orthopedic injuries. In this article, we discuss the function of blood clots in physiologic healing, how exogenous material can affect this process, and the most recent clinical research that proposes the use of autologous blood clots as a therapeutically beneficial biomaterial.

Titanium surface interacting with blood clot enhanced migration and osteogenic differentiation of bone marrow mesenchymal stem cells

Introduction: Blood clot formation is the initial phase upon implantation, and the feature of blood clot orchestrates the following complement system activation, coagulation cascade, and bone marrow mesenchymal stromal cells (BMSCs) recruitment. This study aimed to investigate the effect of implant surface on blood-material interactions and subsequent BMSC cellular behaviors. Methods: This study was established to imitate the physiological process of implantation in vivo and in vitro. Whole blood was incubated with polished titanium (PT) surfaces and sandblasted and double acid-etching (SLA) surfaces for 10 min or 2 h, then seeded with BMSCs. The adhesion, proliferation, migration, and differentiation of cells were studied at specific time points. Titanium implants were implanted into the tibia in vivo and were screwed out after implantation. The activation of the coagulation cascade, platelets, complement system, and clot networks were assessed and further quantitatively analyzed. Results: Compared with the PT surface, the SLA surface induced the earlier and stronger blood coagulation cascade and formed a more stratified clots network with fibrinogen, platelets, and CD14 positive cell. The adhesion, proliferation, and migration of BMSCs were enhanced by pre-incubated surfaces. The higher levels of the osteogenic-related genes, ALP activity, and calcium nodule formation were showed on SLA surfaces with blood incubation. Conclusion: SLA titanium surfaces play a role in influencing the formation of blood clots and coordinating surface-blood interactions and cell biological processes. These findings provide the idea of modifying the blood clots formed on the implant surface by biomaterials modification and thus has implications for the development of better osteogenic biomaterials.

Engineered Injectable Cell-Laden Chitin/Chitosan Hydrogel with Adhesion and Biodegradability for Calvarial Defect Regeneration

Trade-off of high-strength and dynamic crosslinking of hydrogels remains an enormous challenge. Motivated by the self-healing property of biological tissues, the strategy of combining multiple dynamic bond mechanisms and a polysaccharide network is proposed to fabricate biomimetic hydrogels with sufficient mechanical strength, injectability, biodegradability, and self-healing property for bone reconstruction engineering. Stable acylhydrazone bonds endowed hydrogels with robust mechanical strength (>10 kPa). The integration of dynamic imine bonds and acylhydrazone bonds optimized the reversible characteristic to protect the cell during the injection and mimicked ECM microenvironment for cell differentiation as well as rapid adapting bone defect area. Furthermore, due to the slow enzymatic hydrolysis kinetics of chitosan and the self-healing properties of resulting networks, hydrogels exhibited a satisfactory biodegradation period (>8 weeks) that highly matches with bone regeneration. Additionally, rBMSC-laden hydrogels exhibited splendid osteogenic induction and bone reconstruction without prefabrication scaffolds and incubation, demonstrating tremendous potential for clinical application. This work proposes an efficient strategy for the construction of a low-cost multifunctional hydrogel, making polysaccharide-based hydrogels as the optimal carrier for enabling cellular functions in bone repair.

Nanotopographical cues for regulation of macrophages and osteoclasts: emerging opportunities for osseointegration

Nanotopographical cues of bone implant surface has direct influences on various cell types during the establishment of osseointegration, a prerequisite of implant bear-loading. Given the important roles of monocyte/macrophage lineage cells in bone regeneration and remodeling, the regulation of nanotopographies on macrophages and osteoclasts has arisen considerable attentions recently. However, compared to osteoblastic cells, how nanotopographies regulate macrophages and osteoclasts has not been properly summarized. In this review, the roles and interactions of macrophages, osteoclasts and osteoblasts at different stages of bone healing is firstly presented. Then, the diversity and preparation methods of nanotopographies are summarized. Special attentions are paid to the regulation characterizations of nanotopographies on macrophages polarization and osteoclast differentiation, as well as the focal adhesion-cytoskeleton mediated mechanism. Finally, an outlook is indicated of coordinating nanotopographies, macrophages and osteoclasts to achieve better osseointegration. These comprehensive discussions may not only help to guide the optimization of bone implant surface nanostructures, but also provide an enlightenment to the osteoimmune response to external implant.

Genipin modified lyophilized platelet-rich fibrin scaffold for sustained release of growth factors to promote bone regeneration

Lyophilized platelet-rich fibrin (L-PRF) was shown to further activate resident platelets in platelet-rich fibrin causing a higher amount of growth factors release. However, it still required further experimental studies to resolve the uncontrolled degradation and burst release problem. In this study, the nature crosslinker genipin is introduced to improve the performance of L-PRF scaffold. We used a series of gradient concentration genipin solutions to react with L-PRF. The crosslinking degree, micro morphology, mean pore size, water absorption and mechanical properties of the crosslinked scaffold were evaluated. In order to study the effect of genipin modification on the release kinetics of growth factors from L-PRF, we detected the release of platelet-derived growth factor, vascular endothelial growth factor and transforming growth factor in vitro by ELISA. To investigate the biodegradability of the crosslinked L-PRF in vivo, the scaffolds were transplanted subcutaneously into backs of rats, and the materials were recovered at 1, 2 and 4 weeks after implantation. The biodegradation, inflammatory reaction and biocompatibility of the scaffolds were examined by histological staining. Finally, the genipin crosslinked/uncrosslinked L- Platelet-rich fibrin scaffolds were implanted with freshly prepared SHED cell sheets into rat critical size calvarial defects and the skull samples were recovered to examine the treatment efficacy of genipin crosslinked L-PRF by histologic and radiographic approaches. Results of this study indicated that genipin can be used to modify L-PRF at room temperature at a very low concentration. Genipin-modified L-PRF shows better biomechanical performance, slower biodegradation, good bioavailable and sustained release of growth factors. The 0.01% w/v and 0.1% w/v genipin crosslinked L-PRF have good porous structure and significantly promote cell proliferation and enhance the expression of key genes in osteogenesis in vitro, and work best in promoting bone regeneration in vivo.

The Roles of Exosomes upon Metallic Ions Stimulation in Bone Regeneration

Metallic ions have been widely investigated and incorporated into bone substitutes for bone regeneration owing to their superior capacity to induce angiogenesis and osteogenesis. Exosomes are key paracrine mediators that play a crucial role in cell-to-cell communication. However, the role of exosomes in metallic ion-induced bone formation and their underlying mechanisms remain unclear. Thus, this review systematically analyzes the effects of metallic ions and metallic ion-incorporated biomaterials on exosome secretion from mesenchymal stem cells (MSCs) and macrophages, as well as the effects of secreted exosomes on inflammation, angiogenesis, and osteogenesis. In addition, possible signaling pathways involved in metallic ion-mediated exosomes, followed by bone regeneration, are discussed. Despite limited investigation, metallic ions have been confirmed to regulate exosome production and function, affecting immune response, angiogenesis, and osteogenesis. Although the underlying mechanism is not yet clear, these insights enrich our understanding of the mechanisms of the metallic ion-induced microenvironment for bone regeneration, benefiting the design of metallic ion-incorporated implants.

Poly-Alanine-ε-Caprolacton-Methacrylate as Scaffold Material with Tuneable Biomechanical Properties for Osteochondral Implants

An aging population and injury-related damage of the bone substance lead to an increasing need of innovative materials for the regeneration of osteochondral defects. Biodegradable polymers form the basis for suitable artificial implants intended for bone replacement or bone augmentation. The great advantage of these structures is the site-specific implant design, which leads to a considerable improvement in patient outcomes and significantly reduced post-operative regeneration times. Thus, biomechanical and biochemical parameters as well as the rate of degradation can be set by the selection of the polymer system and the processing technology. Within this study, we developed a polymer platform based on the amino acid Alanine and ε-Caprolacton for use as raw material for osteochondral implants. The biomechanical and degradation properties of these Poly-(Alanine-co-ε-Caprolacton)-Methacrylate (ACM) copolymers can be adjusted by changing the ratio of the monomers. Fabrication of artificial structures for musculo-skeletal tissue engineering was done by Two-Photon-Polymerization (2PP), which represents an innovative technique for generating defined scaffolds with tailor-made mechanical and structural properties. Here we show the synthesis, physicochemical characterization, as well as first results for structuring ACM using 2PP technology. The data demonstrate the high potential of ACM copolymers as precursors for the fabrication of biomimetic implants for bone-cartilage reconstruction.

Fabrication of a bio-instructive scaffold conferred with a favorable microenvironment allowing for superior implant osseointegration and accelerated in situ vascularized bone regeneration via type H vessel formation

The potential translation of bio-inert polymer scaffolds as bone substitutes is limited by the lack of neovascularization upon implantation and subsequently diminished ingrowth of host bone, most likely resulted from the inability to replicate appropriate endogenous crosstalk between cells. Human umbilical vein endothelial cell-derived decellularized extracellular matrix (HdECM), which contains a collection of angiocrine biomolecules, has recently been demonstrated to mediate endothelial cells(ECs) - osteoprogenitors(OPs) crosstalk. We employed the HdECM to create a PCL (polycaprolactone)/fibrin/HdECM (PFE) hybrid scaffold. We hypothesized PFE scaffold could reconstitute a bio-instructive microenvironment that reintroduces the crosstalk, resulting in vascularized bone regeneration. Following implantation in a rat femoral bone defect, the PFE scaffold demonstrated early vascular infiltration and enhanced bone regeneration by microangiography (μ-AG) and micro-computational tomography (μ-CT). Based on the immunofluorescence studies, PFE mediated the endogenous angiogenesis and osteogenesis with a substantial number of type H vessels and osteoprogenitors. In addition, superior osseointegration was observed by a direct host bone-PCL interface, which was likely attributed to the formation of type H vessels. The bio-instructive microenvironment created by our innovative PFE scaffold made possible superior osseointegration and type H vessel-related bone regeneration. It could become an alternative solution of improving the osseointegration of bone substitutes with the help of induced type H vessels, which could compensate for the inherent biological inertness of synthetic polymers.

Polyphosphate-crosslinked collagen scaffolds for hemostasis and alveolar bone regeneration after tooth extraction

Post-extraction bleeding and alveolar bone resorption are the two frequently encountered complications after tooth extraction that result in poor healing and rehabilitation difficulties. The present study covalently bonded polyphosphate onto a collagen scaffold (P-CS) by crosslinking. The P-CS demonstrated improved hemostatic property in a healthy rat model and an anticoagulant-treated rat model. This improvement is attributed to the increase in hydrophilicity, increased thrombin generation, platelet activation and stimulation of the intrinsic coagulation pathway. In addition, the P-CS promoted the in-situ bone regeneration and alveolar ridge preservation in a rat alveolar bone defect model. The promotion is attributed to enhanced osteogenic differentiation of bone marrow stromal cells. Osteogenesis was improved by both polyphosphate and blood clots. Taken together, P-CS possesses favorable hemostasis and alveolar ridge preservation capability. It may be used as an effective treatment option for post-extraction bleeding and alveolar bone loss.

Statement of significance

Collagen scaffold is commonly used for the treatment of post-extraction bleeding and alveolar bone loss after tooth extraction. However, its application is hampered by insufficient hemostatic and osteoinductive property. Crosslinking polyphosphate with collagen produces a modified collagen scaffold that possesses improved hemostatic performance and augmented bone regeneration potential.

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Polyphosphate-crosslinked collagen scaffold (P-CS) showed better hemostatic effect in healthy or anticoagulant-treated rats.

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The promoted bone regeneration ability of P-CS might also be related to the clot alteration caused by polyphosphate.

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P-CS has therapeutic potential in bleeding control and alveolar ridge preservation after tooth extraction.

Hydrogel composite scaffolds with an attenuated immunogenicity component for bone tissue engineering applications

Xenogeneic bones are potential templates for bone regeneration. In this study, decellularized porcine bone powder with attenuated immunogenicity was incorporated into a photocurable hydrogel, gelatin methacryloyl (GelMA), to obtain scaffolds with good mechanical properties for bone tissue engineering. The decellularized bone powder (DCB)-GelMA hybrid scaffolds had higher compressive strength and stiffness values when the DCB content was increased. In vitro evaluations revealed the biocompatibility of these scaffolds. The scaffolds could induce human bone marrow mesenchymal stem cells (hMSCs) to undergo osteogenic differentiation even in the absence of an induction medium. The efficiency of the scaffolds for bone regeneration applications was further evaluated using an in vivo cranial bone defect model in rats. Micro-CT images showed that the hybrid scaffolds with 20% DCB content had the best effect in promoting new bone regeneration. Thus, it was concluded that the DCB-GelMA hybrid scaffolds have high potential in bone tissue engineering applications.

Early osteoimmunomodulatory effects of magnesium-calcium-zinc alloys

Today, substantial attention is given to biomaterial strategies for bone regeneration, and among them, there is a growing interest in using immunomodulatory biomaterials. The ability of a biomaterial to induce neo vascularization and macrophage polarization is a major factor in defining its success. Magnesium (Mg)-based degradable alloys have attracted significant attention for bone regeneration owing to their biodegradability and potential for avoiding secondary removal surgeries. However, there is insufficient evidence in the literature regarding the early inflammatory responses to these alloys in vivo. In this study, we investigated the early body responses to Mg-0.45wt%Zn-0.45wt%Ca pin-shaped alloy (known as ZX00 alloy) in rat femora 2, 5, and 10 days after implantation. We used 3D micro computed tomography (µCT), histological, immunohistochemical, histomorphometrical, and small angle X-ray scattering (SAXS) analyses to study new bone formation, early macrophage polarization, neo vascularization, and bone quality at the implant bone interface. The expression of macrophage type 2 biological markers increased significantly after 10 days of Mg alloy implantation, indicating its potential in stimulating macrophage polarization. Our biomineralization results using µCT as well as histological stained sections did not indicate any statistically significant differences between different time points for both groups. The activity of alkaline phosphatase (ALP) and Runt-related transcription factor 2 (Runx 2) biological markers decreased significantly for Mg group, indicating less osteoblast activity. Generally, our results supported the potential of ZX00 alloy to enhance the expression of macrophage polarization in vivo; however, we could not observe any statistically significant changes regarding biomineralization.