Bio-integrated scaffold facilitates large bone regeneration dominated by endochondral ossification.

Repair of large bone defects caused by severe trauma, non-union fractures, or tumor resection remains challenging because of limited regenerative ability. Typically, these defects heal through mixed routines, including intramembranous ossification (IMO) and endochondral ossification (ECO), with ECO considered more efficient. Current strategies to promote large bone healing via ECO are unstable and require high-dose growth factors or complex cell therapy that cause side effects and raise expense while providing only limited benefit. Herein, we report a bio-integrated scaffold capable of initiating an early hypoxia microenvironment with controllable release of low-dose recombinant bone morphogenetic protein-2 (rhBMP-2), aiming to induce ECO-dominated repair. Specifically, we apply a mesoporous structure to accelerate iron chelation, this promoting early chondrogenesis via deferoxamine (DFO)-induced hypoxia-inducible factor-1α (HIF-1α). Through the delicate segmentation of click-crosslinked PEGylated Poly (glycerol sebacate) (PEGS) layers, we achieve programmed release of low-dose rhBMP-2, which can facilitate cartilage-to-bone transformation while reducing side effect risks. We demonstrate this system can strengthen the ECO healing and convert mixed or mixed or IMO-guided routes to ECO-dominated approach in large-size models with clinical relevance. Collectively, these findings demonstrate a biomaterial-based strategy for driving ECO-dominated healing, paving a promising pave towards its clinical use in addressing large bone defects.

Advances in 3D Printing of Highly Bioadaptive Bone Tissue Engineering Scaffolds.

The number of patients with bone defects caused by trauma, bone tumors, and osteoporosis has increased considerably. The repair of irregular, recurring, and large bone defects poses a great challenge to clinicians. Bone tissue engineering is emerging as an appropriate strategy to replace autologous bone grafting in the repair of critically sized bone defects. However, the suitability of bone tissue engineering scaffolds in terms of structure, mechanics, degradation, and the microenvironment is inadequate. Three-dimensional (3D) printing is an advanced additive-manufacturing technology widely used for bone repair. 3D printing constructs personalized structurally adapted scaffolds based on 3D models reconstructed from CT images. The contradiction between the mechanics and degradation is resolved by altering the stacking structure. The local microenvironment of the implant is improved by designing an internal pore structure and a spatiotemporal factor release system. Therefore, there has been a boom in the 3D printing of personalized bone repair scaffolds. In this review, successful research on the preparation of highly bioadaptive bone tissue engineering scaffolds using 3D printing is presented. The mechanisms of structural, mechanical, degradation, and microenvironmental adaptations of bone prostheses and their interactions were elucidated to provide a feasible strategy for constructing highly bioadaptive bone tissue engineering scaffolds.

Photocurable 3D-printed PMBG/TCP biphasic scaffold mimicking vasculature for bone regeneration.

Mesoporous bioglass (MBG) with excellent osteointegration, osteoinduction, and biodegradability is a promising material for bone regeneration. However, its clinical application is hindered by complex processing and a lack of personalization, low mechanical strength, and uncontrollable degradation rate. In this study, we developed a double-bond-functionalized photocurable mesoporous bioglass (PMBG) sol that enabled ultrafast photopolymerization within 5 s. By further integrating nanosized tricalcium phosphate (TCP) particles through three-dimensional (3D) printing technology, we fabricated personalized and highly porous PMBG/TCP biphasic scaffolds. The mechanical properties and degradation behavior of the scaffolds were regulated by varying the amount of TCP doping. In vitro and in vivo experiments verified that PMBG/TCP scaffolds slowly released SiO44- and Ca2+, forming a vascularized bone regeneration microenvironment within the fully interconnected pore channels of the scaffold. This microenvironment promoted angiogenesis and accelerated bone tissue regeneration. Overall, this work demonstrates the solution to the problem of complex processing and lack of personalization in bioglass scaffolds, and the developed PMBG/TCP biphasic scaffold is an ideal material for bone regeneration applications with broad clinical prospects.

Photocurable 3D-Printed PMBG/TCP Scaffold Coordinated with PTH (1-34) Bidirectionally Regulates Bone Homeostasis to Accelerate Bone Regeneration.

Bone defect repair remains a major clinical challenge that requires the construction of scaffolds that can regulate bone homeostasis. In this study, a photo-cured mesoporous bioactive glass (PMBG) precursor is developed as a tricalcium phosphate (TCP) agglomerant to obtain a double-phase PMBG/TCP scaffold via 3D printing. The scaffold exhibits multi-scale porous structures and large surface areas, making it a suitable carrier for the loading of parathyroid hormone (PTH) (1-34), which is used for the treatment of osteoporosis. In vitro and in vivo results demonstrate that PMBG/TCP scaffolds coordinated with PTH (1-34) can regulate bone homeostasis in a bidirectional manner to facilitate bone formation and inhibit bone resorption. Furthermore, bidirectional regulation of bone homeostasis by PTH (1-34) is achieved by inhibiting fibrogenic activation protein (FAP). Thus, PMBG/TCP scaffolds coordinated with PTH (1-34) are viable materials with considerable potential for application in the field of bone regeneration and provide an excellent solution for the design and development of clinical materials.

Tensile Test Coupled with an EBSD Study of a GH4169 Ring Rolled Product.

An in situ tensile test of the ring-rolled GH4169 alloy is performed to investigate the plastic deformation behavior at the micro level. Slip system activations are identified by slip traces captured by a scanning electron microscope and lattice orientation data acquired by electron backscattered diffraction. Our results demonstrated that the fraction of low-angle grain boundaries gradually increased upon tensile deformation, and the misorientation evolution in the grain interior was severely inhomogeneous. The Schmid factors at the grains of interest are calculated for comparison with the actual activated slip systems. Most of the slip system activation coincides with the Schmid law, as opposed to the initiation of other potential slip systems at some grains.

Bio-inspired, bio-degradable adenosine 5'-diphosphate-modified hyaluronic acid coordinated hydrophobic undecanal-modified chitosan for hemostasis and wound healing.

Uncontrolled hemorrhage and wound infection are crucial causes of trauma-associated death in both the military and the clinic. Therefore, developing an efficient and rapid hemostatic method with biocompatibility, easy degradation, and wound healing is of great importance and desirability. Inspired by spontaneous blood cell plug formation in the hemostasis process, an adenosine 5'-diphosphate modified pro-coagulation hyaluronic acid (HA-ADP) coordinated with enhanced antibacterial activity of undecanal-modified chitosan (UCS) was fabricated through physical electrostatic cross-linking and freeze-drying. The as-prepared hydrogel sponges showed a porous structure suitable for blood cell adhesion. In particular, the hydrogel exhibited excellent antibacterial ability and promoted the adhesion of platelets and red blood cells, thus inducing a prominent pro-coagulation ability via platelet activation, which exhibits a shorter hemostasis time (58.94% of control) in vitro. Compared with commercially available CELOX and gelatin sponge (GS), HA-ADP/UCS accelerates hemostasis and reduces blood loss in both rat tail amputation and rat artery injury models. Furthermore, all the samples exhibited superior cytocompatibility and biodegradability. Due to these performances, HA-ADP/UCS promoted full-thickness skin defect healing significantly in vivo. All the properties of HA-ADP/UCS suggest that it has great potential for translation as a clinical application material for hemostatic and wound healing.

Inherent Antibacterial and Instant Swelling ε-Poly-Lysine/ Poly(ethylene glycol) Diglycidyl Ether Superabsorbent for Rapid Hemostasis and Bacterially Infected Wound Healing.

Severe traumatic bleeding control and wound-related anti-infection play a crucial role in saving lives and promoting wound healing for both the military and the clinic. In this contribution, an inherent antibacterial and instant swelling ε-poly-lysine/poly (ethylene glycol) diglycidyl ether (EPPE) superabsorbent was developed by a simple mild ring-opening reaction. The as-prepared EPPE1 displayed a porous structure and rough surface and exhibited instant water-triggered expansion with approximately 6300% swelling ratio in deionized water. Moreover, EPPE1 presented efficient pro-coagulation capacity by hemadsorption that can facilitate blood cell gathering and activation in vitro and exhibited a shorter in vivo hemostasis time than that of commercial gelatin sponge and CELOX in both rat tail amputation and noncompressible rat liver lethal defect model. Also, EPPE1 showed excellent antibacterial capacity, prominent biocompatibility, and great biodegradability. Additionally, EPPE1 significantly promotes in vivo wound healing in a full-thickness skin defect model due to its great hemostasis behavior and remarkable bactericidal performance. Hence, EPPE has great potential for serving as an extensively applied hemostatic agent under varied clinical conditions.

Bioinspired, Injectable, Quaternized Hydroxyethyl Cellulose Composite Hydrogel Coordinated by Mesocellular Silica Foam for Rapid, Noncompressible Hemostasis and Wound Healing.

Massive bleeding control and anti-infection are the major challenges for urgent trauma with deep and noncompressible hemorrhage in both clinic and battlefield. Inspired by the coordinated primarily blood clot formation and secondly coagulation cascade activation in natural hemostasis process, an injectable, quaternized hydroxyethyl cellulose/mesocellular silica foam (MCF) hydrogel sponge (QHM) for both hemorrhage control and antibacterial activities were prepared via one-pot radical graft copolymerization. The as-prepared QHMs exhibited instant water-triggered expansion and superabsorbent capacity and thereby effectively facilitated blood components concentration. Moreover, the QHM1 with appropriate amount of MCF (9.82 w/w %) could further activate the coagulation factors. Synergistically, the QHM1 could reduce the plasma clotting time to 59 ± 4% in vitro and showed less blood loss than commercially available hemostatics in vivo noncompressible hemorrhage models of lethal rabbit-liver defect. Furthermore, the QHM with a quaternary ammonium groups density of 2.732 mmol/g exhibited remarkable antibacterial activities and excellent cytocompatibility. With the efficient hemostasis efficacy and excellent antibacterial behavior, QHM dramatically facilitated the wound healing in a full-thickness skin defect model in vivo. Thus, this QHM represents a promising hemostatic in more widespread clinical application.

Multicellularity-interweaved bone regeneration of BMP-2-loaded scaffold with orchestrated kinetics of resorption and osteogenesis.

Synchronization of material resorption and new bone formation is vital to achieve harmonious bone regeneration in the treatment of large bone defects. To exposit the resorption/osteogenesis properties in the guided bone repairing, rhBMP-2-loaded trimodal macro/micro/nano-porous bioactive glass scaffolds (TMS-rhBMP-2) were set as substrate model. We penetratingly investigated the particular function of hierarchical structure and incorporated rhBMP-2 in the resorption/osteogenesis, and dissected the cellular interplay throughout the regenerative procedure. The results suggested that rhBMP-2 significantly facilitated osteoclastogenesis-mediated scaffold degradation and strikingly up-regulated mesenchymal stem cells (MSCs)-involved osteogenesis in vitro. Further gene microarray and related proteins expression indicated that in the presence of rhBMP-2, MSCs rather than differentiated MSCs could exert synergistic effects on osteoclastogenesis, osteoclasts maturation and resorptive function; meanwhile, rhBMP-2-induced MSCs osteogenesis was also strengthened by the osteoclasts. In vivo micro-CT, X-ray, kinetic and histological analyses qualitatively and quantitively demonstrated the optimized coupling of bioresorption/osteogenesis and the most rapid regeneration in TMS-rhBMP-2. Consequently, with rhBMP-2 acted as ignitor and MSCs/osteoclasts interaction as booster, a harmonious bone regeneration was obtained. Besides, long-term magnetic resonance imaging (MRI) in virtue of Gd3+ suggested that the degradation products mainly distributed in liver and spleen, verifying the accumulation/discharge profiles and safety application of TMS-rhBMP-2 system in vivo. This study will not merely provide guidance for the design of clinical bone repairing materials, but shed substantial light on the multicell-mediated tissue regeneration.

Tannic acid-loaded mesoporous silica for rapid hemostasis and antibacterial activity.

Massive blood loss and bacterial infection are major challenges for global public health. In this study, we developed tannic acid (TA)-loaded mesoporous silica (MS) nanoparticles for both hemorrhage control and effective antibacterium via covalent conjugation and electrostatic adsorption. The TA-absorbed MS could significantly relieve hemolysis and facilitate blood contact, therefore efficiently promoting protein adhesion and the contact activation pathway of the coagulation cascade with desirable hemostasis. Comparably, with increasing TAs absorption, the bleeding control and antibacterial performance were improved simultaneously, especially for 15TMS. Hemostasis tests demonstrated that the 15TMS could reduce the hemostatic time by 65% both in vitro and in vivo, with lower blood loss and could exhibit better antibacterial activities against Staphylococcus aureus and Staphylococcus epidermidis as well as promote wound healing. However, the TAs-loaded MS via chemical grafting (15T-g-MS) significantly reduced the surface area of MS, by replacing the Si-OH on the MS, and thus it exhibited worse bleeding control and antibacterial efficacy than 15TMS. Furthermore, all the samples exhibited excellent cell viability. Based on these results, it can be concluded that the 15TMS would be a promising material platform for designing hemostats in more extensive clinical application.

A Novel Droplet-Fabricated Mesoporous Silica-Based Nanohybrid Granules for Hemorrhage Control.

Uncontrolled hemorrhage is one of the leading cause for death in both civilian and military trauma. The zeolite-based hemostatic agent currently available in clinic exhibits great exothermic reaction and poor biodegradability. To overcome these limitations, in this study, we developed a novel mesoporous silica (MS)-based calcium alginate nanohybrid granule (p-MS/CA) for hemorrhage control. The p-MS/CA was prepared by an in situ pore-forming, droplet process and the granule prepared was 2-3 mm in size with rough and macroporous surface. The p-MS/CA could significantly accelerate water absorption and block off the damaged tissue, and thereby efficiently promoted platelet and plasma protein adhesion, enhanced wound adherence, facilitated the contact activation pathway of coagulation cascade with desirable hemostasis. Hemostasis test demonstrated that the p-MS/CA granule could reduce about 50% hemostatic time both in vitro and vivo and decrease blood loss. Meanwhile, the nanocomposite of p-MS/CA exhibited excellent cell viability and did not induce hemolysis. Furthermore, the preparation process for multipore p-MS/CA is low-cost, quick and easy to achieve large-scale production. Owing to the superior hemostatic performance and simple preparation process, we believe that this study will provide an alternative approach for hemorrhage control in some specific injury types, and have immense potential for commercial and clinical application.

Surface Topography Regulates Osteogenic Differentiation of MSCs via Crosstalk between FAK/MAPK and ILK/ß-Catenin Pathways in a Hierarchically Porous Environment.

The response of mesenchymal stem cell (MSCs) to elaborate microarchitectured topographies in three-dimensional environment and the underlying molecular mechanism remain poorly understood. Here, with hierarchical mesoporous bioactive glass (MBG) scaffolds as substrate model, we show the effects of specific, elaborate microtextured topographies (micrograiny, microporous and hybrid micrograiny/microporous surface) on MSCs osteogenesis and the molecular mechanism involved. With a similar size and density, the microporous surface was more favorable for the MSC osteogenesis, and the hybrid micrograiny/microporous surface exhibited a synergetic effect. All the microscaled topographies facilitated expression of integrin subunits, focal adhesion complexes, and up-regulated FAK/MAPK and ILK/ß-catenin signaling pathways. Separately blocking FAK/MAPK and ILK/ß-catenin cascade dramatically attenuated the heightened ß-catenin signaling, and the phosphorylation of ERK1/2 and P38, respectively, indicating a typical crosstalk between FAK/MAPK and ILK/ß-catenin signalings was involved. Correlating the MSCs response with the specific topographical cues, it can be inferred that the micrograiny/microporous topographies induced FAs assembly and homeostasis, and thus FAK/MAPK and ILK/ß-catenin signalings played critical role in regulating MSCs osteogenic differentiation. The findings, therefore, have significant implications in better understanding of the MSCs fate in a 3D environment and provided guidance of the development of novel biomaterial for bone regeneration.

Microporous density-mediated response of MSCs on 3D trimodal macro/micro/nano-porous scaffolds via fibronectin/integrin and FAK/MAPK signaling pathways.

The microporous architecture of biomaterials/scaffolds plays a critical role in cellular behaviors of marrow stromal cells in the field of tissue regeneration, but the role of microporous density in this process and its underlying molecular mechanism are poorly understood. In the present work, a series of three-dimensional (3D) trimodal macro/micro/nano-porous MBG scaffolds (TMSs) with different microporous densities were developed to investigate the influence of microporous density on the attachment, proliferation and osteogenic differentiation of rat bone marrow stromal cells (rBMSCs), and the fundamental molecular mechanism was explored. The results demonstrated that scaffolds with micropores significantly promoted initial cell adhesion, ALP activity and osteogenesis-related gene/protein expressions, especially the one with 20% microporous density (TMS 20). We found that the appropriate microporous density modulated the adsorption of fibronectin (Fn), and in turn facilitated integrin receptor binding affinity, focal adhesion complex formation and subsequent FAK/MAPK signaling pathway activation. Based on these studies, it can be confirmed that microporous density contributes to the regulation of cellular response, which can provide a new insight into the design of future bone substitutes in a 3D environment.

PEGylated poly(glycerol sebacate)-modified calcium phosphate scaffolds with desirable mechanical behavior and enhanced osteogenic capacity.

UNLABELLED: Calcium phosphate (CaP) scaffolds have been widely used as bone graft substitutes, but undesirable mechanical robustness and bioactivity greatly hamper its availability in clinic application. To address these issues, PEGylated poly (glycerol sebacate) (PEGS), a hydrophilic elastomer, was used to modify a model calcium phosphate cement (CPC) scaffold for bone regeneration in this study. The PEGS pre-polymer with PEG content from 0% to 40% was synthesized and was subsequently coated onto the pre-fabricated CPC scaffolds by facile infiltration and thermal-crosslink process. Compression strength and toughness of the CPC/PEGS composite scaffold (defined as CPX/Y, X referred to the PEG content in PEGS and Y referred to PEGS amount in final scaffold) were effectively tailored with increasing coating amount and PEG content, and CPX/Y exhibited an optimal compressive strength of 3.82MPa and elongation at break of 13.20%, around 5-fold and 3-fold enhancement compared to the CPC. In vitro cell experiment with BMSCs as model indicated that coating and PEG-modified synchronously facilitated cell attachment and proliferation in a dose-dependent manner. Particularly, osteogenic differentiation of BMSCs on PEGS/CPC scaffold was strongly enhanced, especially for CP20/18. Further in vivo experiments confirmed that PEGS/CPC induced promoted osteogenesis in striking contrast to CPC and PGS/CPC. Collectively, hybrids scaffolds (around 18% coating amount and PEG content from 20% to 40%) with the combination of enhanced mechanical behavior and up-regulated cellular response were optimized and PEGS/CaP scaffolds can be deemed as a desirable option for bone tissue engineering. STATEMENT OF SIGNIFICANCE: Insufficient mechanical robustness and bioactivity still limit the availability of calcium phosphate (CaP) scaffolds in clinic application. Herein, calcium phosphate cement (CPC) scaffold, as a model CaP-matrix material, was modified with PEGylated PGS (PEGS) polymers by facile infiltration and thermal-crosslink process. Such biomimetic combination of PEGS and CaP-matrix porous scaffold was first explored, without affecting its porous structure. In this study, CPC scaffold was endowed with robust mechanical behavior and promoted bioactivity by simultaneously optimizing the amount of polymer-coating and the PEG content in PGS. In rat critical-sized calvarial defects repairing, osteogenic efficacy of PEGS/CPC further demonstrated the potential for application in bone tissue regeneration. The design concept proposed in this study might provide new insights into the development of future tissue engineering materials.

Bioinspired trimodal macro/micro/nano-porous scaffolds loading rhBMP-2 for complete regeneration of critical size bone defect.

Critical size bone defects raise great demands for efficient bone substitutes. Mimicking the hierarchical porous architecture and specific biological cues of natural bone has been considered as an effective strategy to facilitate bone regeneration. Herein, a trimodal macro/micro/nano-porous scaffold loaded with recombinant human bone morphogenetic protein-2 (rhBMP-2) was developed. With mesoporous bioactive glass (MBG) as matrix, a trimodal MBG scaffold (TMS) with enhanced compressive strength (4.28 MPa, porosity of 80%) was prepared by a "viscosity controlling" and "homogeneous particle reinforcing" multi-template process. A 7.5 nm, 3D cubic (Im3m) mesoporous structure was tailored for a "size-matched entrapment" of rhBMP-2 to achieve sustained release and preserved bioactivity. RhBMP-2-loaded TMS (TMS/rhBMP-2) induced excellent cell attachment, ingrowth and osteogenesis in vitro. Further in vivo ectopic bone formation and orthotopic rabbit radius critical size defect results indicated that compared to the rhBMP-2-loaded bimodal macro/micro- and macro/nano-porous scaffolds, TMS/rhBMP-2 exhibited appealing bone regeneration capacity. Particularly, in critical size defect, complete bone reconstruction with rapid medullary cavity reunion and sclerotin maturity was observed on TMS/rhBMP-2. On the basis of these results, TMS/rhBMP-2 developed here represents a promising bone substitute for clinical application and the concepts proposed in this study might provide new thoughts on development of future orthopedic biomaterials. STATEMENT OF SIGNIFICANCE: Limited self-regenerating capacity of human body makes the reconstruction of critical size bone defect a significant challenge. Current bone substitutes often exhibit undesirable therapeutic efficacy due to poor osteoconductivity or low osteoinductivity. Herein, TMS/rhBMP-2, an advanced mesoporous bioactive glass (MBG) scaffold with osteoconductive trimodal macro/micro/nano-porosity and osteoinductive rhBMP-2 delivery was developed. The preparative and mechanical problems of hierarchical MBG scaffold were solved without affecting its excellent biocompatibilities, and rhBMP-2 immobilization in sizematched mesopores was first explored. Combining structural and biological cues, TMS/rhBMP-2 achieved a complete regeneration with rapid medullary cavity reunion and sclerotin maturity in rabbit radius critical size defects. The design conceptions proposed in this study might provide new thoughts on development of future orthopedic biomaterials.

Kaolin-reinforced 3D MBG scaffolds with hierarchical architecture and robust mechanical strength for bone tissue engineering.

Three-dimensional mesoporous bioglass (3D MBG) scaffolds with mesoporous structures and highly interconnected macroporous networks are considered as ideal biomaterials for skeletal tissue applications. However, their inherent brittleness and poor mechanical strength greatly hamper their performance and clinical application. Here, using a modified polyurethane foam (PU) templating method with utilization of kaolin as binder, a new facile method for preparation of 3D MBG scaffolds with excellent mechanical strength, mineralization ability and desirable cellular response is proposed. The developed hybrid MBG-XK (where X refers to the final dry weight of kaolin in the scaffold) scaffolds with 85% porosity exhibited a high compressive strength from 2.6 to 6.0 MPa with increasing content of kaolin (5-20%), about 100 times higher than that of the traditional PU-template MBG scaffold. With the addition of kaolin, the MBG-10K scaffold exhibited a more stable and desirable pH environment, and an enhanced protein adsorption capacity. Furthermore, with rat bone marrow stromal cells as a model, in vitro cell culture experiments indicated that, compared with MBG, the prepared MBG-XK scaffolds possessed comparable cell proliferation, penetration capacity, enhanced cell attachment and osteogenic differentiation, especially for MBG-10K.