Enhanced in vivo osteogenesis by nanocarrier-fused bone morphogenetic protein-4

3D bioprinting of osteon-mimetic scaffolds with hierarchical microchannels for vascularized bone tissue regeneration

The integration of three-dimensional (3D) bioprinted scaffold's structure and function for critical-size bone defect repair is of immense significance. Inspired by the basic component of innate cortical bone tissue--osteons, many studies focus on biomimetic strategy. However, the complexity of hierarchical microchannels in the osteon, the requirement of mechanical strength of bone, and the biological function of angiogenesis and osteogenesis remain challenges in the fabrication of osteon-mimetic scaffolds. Therefore, we successfully built mimetic scaffolds with vertically central medullary canals, peripheral Haversian canals, and transverse Volkmann canals structures simultaneously by 3D bioprinting technology using polycaprolactone and bioink loading with bone marrow mesenchymal stem cells (BMSCs) and bone morphogenetic protein-4 (BMP-4). Subsequently, endothelial progenitor cells (EPCs) were seeded into the canals to enhance angiogenesis. The porosity and compressive properties of bioprinted scaffolds could be well controlled by altering the structure and canal numbers of the scaffolds. The osteon-mimetic scaffolds showed satisfactory biocompatibility and promotion of angiogenesis and osteogenesis in vitro and prompted the new blood vessels and new bone formation in vivo. In summary, this study proposes a biomimetic strategy for fabricating structured and functionalized 3D bioprinted scaffolds for vascularized bone tissue regeneration.

Three-dimensional bioprinting of multicell-laden scaffolds containing bone morphogenic protein-4 for promoting M2 macrophage polarization and accelerating bone defect repair in diabetes mellitus

Critical-sized bone defect repair in patients with diabetes mellitus remains a challenge in clinical treatment because of dysfunction of macrophage polarization and the inflammatory microenvironment in the bone defect region. Three-dimensional (3D) bioprinted scaffolds loaded with live cells and bioactive factors can improve cell viability and the inflammatory microenvironment and further accelerating bone repair. Here, we used modified bioinks comprising gelatin, gelatin methacryloyl (GelMA), and 4-arm poly (ethylene glycol) acrylate (PEG) to fabricate 3D bioprinted scaffolds containing BMSCs, RAW264.7 macrophages, and BMP-4-loaded mesoporous silica nanoparticles (MSNs). Addition of MSNs effectively improved the mechanical strength of GelMA/gelatin/PEG scaffolds. Moreover, MSNs sustainably released BMP-4 for long-term effectiveness. In 3D bioprinted scaffolds, BMP-4 promoted the polarization of RAW264.7 to M2 macrophages, which secrete anti-inflammatory factors and thereby reduce the levels of pro-inflammatory factors. BMP-4 released from MSNs and BMP-2 secreted from M2 macrophages collectively stimulated the osteogenic differentiation of BMSCs in the 3D bioprinted scaffolds. Furthermore, in calvarial critical-size defect models of diabetic rats, 3D bioprinted scaffolds loaded with MSNs/BMP-4 induced M2 macrophage polarization and improved the inflammatory microenvironment. And 3D bioprinted scaffolds with MSNs/BMP-4, BMSCs, and RAW264.7 cells significantly accelerated bone repair. In conclusion, our results indicated that implanting 3D bioprinted scaffolds containing MSNs/BMP-4, BMSCs, and RAW264.7 cells in bone defects may be an effective method for improving diabetic bone repair, owing to the direct effects of BMP-4 on promoting osteogenesis of BMSCs and regulating M2 type macrophage polarization to improve the inflammatory microenvironment and secrete BMP-2.

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The GelMA/gelatin/PEG/MSN composite bioinks showed satisfactory printability, mechanical stability, and biocompatibility.

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The sustained release of BMP-4 from MSNs induced M2 macrophage polarization and thereby inhibited inflammatory reactions.

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Loading of BMP-4 and secretion of BMP-2 by M2 type macrophages accelerated bone repair in DM bone defects.

Use of nanoparticles in skeletal tissue regeneration and engineering

Bone and osteochondral defects represent one of the major causes of disabilities in the world. Derived from traumas and degenerative pathologies, these lesions cause severe pain, joint deformity, and loss of joint motion. The standard treatments in clinical practice present several limitations. By producing functional substitutes for damaged tissues, tissue engineering has emerged as an alternative in the treatment of defects in the skeletal system. Despite promising preliminary clinical outcomes, several limitations remain. Nanotechnologies could offer new solutions to overcome those limitations, generating materials more closely mimicking the structures present in naturally occurring systems. Nanostructures comparable in size to those appearing in natural bone and cartilage have thus become relevant in skeletal tissue engineering. In particular, nanoparticles allow for a unique combination of approaches (e.g. cell labelling, scaffold modification or drug and gene delivery) inside single integrated systems for optimized tissue regeneration. In the present review, the main types of nanoparticles and the current strategies for their application to skeletal tissue engineering are described. The collection of studies herein considered confirms that advanced nanomaterials will be determinant in the design of regenerative therapeutic protocols for skeletal lesions in the future.

Tissue engineered bone mimetics to study bone disorders ex vivo: Role of bioinspired materials

Recent advances in materials development and tissue engineering has resulted in a substantial number of bioinspired materials that recapitulate cardinal features of bone extracellular matrix (ECM) such as dynamic inorganic and organic environment(s), hierarchical organization, and topographical features. Bone mimicking materials, as defined by its self-explanatory term, are developed based on the current understandings of the natural bone ECM during development, remodeling, and fracture repair. Compared to conventional plastic cultures, biomaterials that resemble some aspects of the native environment could elicit a more natural molecular and cellular response relevant to the bone tissue. Although current bioinspired materials are mainly developed to assist tissue repair or engineer bone tissues, such materials could nevertheless be applied to model various skeletal diseases in vitro. This review summarizes the use of bioinspired materials for bone tissue engineering, and their potential to model diseases of bone development and remodeling ex vivo. We largely focus on biomaterials, designed to re-create different aspects of the chemical and physical cues of native bone ECM. Employing these bone-inspired materials and tissue engineered bone surrogates to study bone diseases has tremendous potential and will provide a closer portrayal of disease progression and maintenance, both at the cellular and tissue level. We also briefly touch upon the application of patient-derived stem cells and introduce emerging technologies such as organ-on-chip in disease modeling. Faithful recapitulation of disease pathologies will not only offer novel insights into diseases, but also lead to enabling technologies for drug discovery and new approaches for cell-based therapies.

Evaluation of the presence of MMP-2, TIMP-2, BMP2/4, and TGFβ3 in the facial tissue of children with cleft lip and palate

Cleft lip and palate (CLP) is the most common defect affecting the face. The treatment consists of surgical reconstruction of the anatomical structures of the cleft. Part of the surgical treatment is reconstruction of the alveolar bone by means of autogenic bone grafting (osteoplasty). This study aimed to evaluate the levels of expression of extracellular matrix remodeling factors in the facial tissue of children with a complete unilateral (CU) and a complete bilateral (CB) CLP to assess whether the wound healing process is adequate. Twenty-two CLP patients were enrolled in this study. Tissue samples were collected during alveolar osteoplasty for unilateral (n = 12) or bilateral (n = 10) cleft palate, (age range from 6 years 8 months to 12 years 2 months). Control material was obtained in the case of tooth extraction (age range from 6 years 9 months to 14 years 5 months). Immunohistochemistry was used to assess the levels of matrix metalloproteinase-2 (MMP-2), tissue inhibitor of metalloproteinase-2 (TIMP-2), bone morphogenetic proteins 2 and 4 (BMP2/4), and transforming growth factor β3 (TGFβ3). Numbers of positively stained cells were graded semi-quantitatively. Data were analysed using the Kraskel-Wallis rank test and the Bonferroni correction. The total number of MMP2-positive cells was significantly lower in the CBCLP and in the control group than in the CUCLP (p < 0.001 after the Bonferroni correction). The total number of TIMP2-positive cells was significantly higher in the CUCLP than in the CBCLP and in the control group (p < 0.001; p < 0.003 after the Bonferroni correction). The overall number of BMP2/4, TGFβ3-positive cells was significantly higher in the CUCLP than in the CBCLP and in the control group (p < 0.001 after the Bonferroni correction). The decrease of the relative amount of statistically significant BMP2/4, TGFβ3, MMP-2, TIMP-2 containing bone cells in CBCLP patients identifies affected alveolar bone regeneration and remodeling process.

Collagen-Binding Hepatocyte Growth Factor (HGF) alone or with a Gelatin- furfurylamine Hydrogel Enhances Functional Recovery in Mice after Spinal Cord Injury

The treatment of spinal cord injury (SCI) is currently a significant challenge. Hepatocyte growth factor (HGF) is a multipotent neurotrophic and neuroregenerative factor that can be beneficial for the treatment of SCI. However, immobilized HGF targeted to extracellular matrix may be more effective than diffusible, unmodified HGF. In this study, we evaluated the neurorestorative effects of an engineered HGF with a collagen biding domain (CBD-HGF). CBD-HGF remained in the spinal cord for 7 days after a single administration, while unmodified HGF was barely seen at 1 day. When a gelatin-furfurylamine (FA) hydrogel was applied on damaged spinal cord as a scaffold, CBD-HGF was retained in gelatin-FA hydrogel for 7 days, whereas HGF had faded by 1 day. A single administration of CBD-HGF enhanced recovery from spinal cord compression injury compared with HGF, as determined by motor recovery, and electrophysiological and immunohistochemical analyses. CBD-HGF alone failed to improve recovery from a complete transection injury, however CBD-HGF combined with gelatin-FA hydrogel promoted endogenous repair and recovery more effectively than HGF with hydrogel. These results suggest that engineered CBD-HGF has superior therapeutic effects than naïve HGF. CBD-HGF combined with hydrogel scaffold may be promising for the treatment of serious SCI.

Osteogenic potential of recombinant human bone morphogenetic protein-9/absorbable collagen sponge (rhBMP-9/ACS) in rat critical size calvarial defects

OBJECTIVES

It has been reported that bone morphogenetic protein (BMP)-9 has potent osteoinductive properties among the BMP family by adenovirus-transfection experiments. We very recently reported that absorbable collagen sponge (ACS) as a carrier for recombinant human (rh) BMP-9, compared with chitosan sponge, was suitable for inducing bone healing/regeneration by BMP-9 in a rat calvarial defect model. The aim of this study was to evaluate different doses of rhBMP-9/ACS on new bone formation in rat critical size calvarial defects.

MATERIALS AND METHODS

Bilateral calvarial defects (n = 32) were surgically created in 16 wistar rats and randomly filled with one of the following materials: (1) absorbable collagen sponge (ACS) alone; (2) 1 μg-rhBMP-9/ACS (L-rhBMP-9/ACS); (3) 5 μg-rhBMP-9/ACS (H-rhBMP-9/ACS); and (4) blank defects (control). The animals were sacrificed 8 weeks postsurgery for radiographic and histomorphometric analyses.

RESULTS

Bone volume and defect closure were statistically higher in the rhBMP-9/ACS-implanted (L-rhBMP-9/ACS and H-rhBMP-9/ACS) groups when compared with ACS-alone group (p < 0.05). Furthermore, defects filled with H-rhBMP-9/ACS showed the highest levels of newly formed bone area (NBA) and NBA/total defect area among all groups. No significant differences in any of the radiographic and histometric parameters could be observed between both concentrations of rhBMP-9.

CONCLUSIONS

Within the limits of this study, it can be concluded that rhBMP-9/ACS-induced bone formation can be reached with as little as 1 μg/site in rat critical size calvarial defects.

CLINICAL RELEVANCE

RhBMP-9 could be a potential therapeutic growth factor for future bone regenerative procedures.

Taking cues from the extracellular matrix to design bone-mimetic regenerative scaffolds

There is an ongoing need for effective materials that can replace autologous bone grafts in the clinical treatment of bone injuries and deficiencies. In recent years, research efforts have shifted away from a focus on inert biomaterials to favor scaffolds that mimic the biochemistry and structure of the native bone extracellular matrix (ECM). The expectation is that such scaffolds will integrate with host tissue and actively promote osseous healing. To further enhance the osteoinductivity of bone graft substitutes, ECM-mimetic scaffolds are being engineered with a range of growth factors (GFs). The technologies used to generate GF-modified scaffolds are often inspired by natural processes that regulate the association between endogenous ECMs and GFs. The purpose of this review is to summarize research centered on the development of regenerative scaffolds that replicate the fundamental collagen-hydroxyapatite structure of native bone ECM, and the functionalization of these scaffolds with GFs that stimulate critical events in osteogenesis.

FGF8 signaling sustains progenitor status and multipotency of cranial neural crest-derived mesenchymal cells in vivo and in vitro

The cranial neural crest (CNC) cells play a vital role in craniofacial development and regeneration. They are multi-potent progenitors, being able to differentiate into various types of tissues. Both pre-migratory and post-migratory CNC cells are plastic, taking on diverse fates by responding to different inductive signals. However, what sustains the multipotency of CNC cells and derivatives remains largely unknown. In this study, we present evidence that FGF8 signaling is able to sustain progenitor status and multipotency of CNC-derived mesenchymal cells both in vivo and in vitro. We show that augmented FGF8 signaling in pre-migratory CNC cells prevents cell differentiation and organogenesis in the craniofacial region by maintaining their progenitor status. CNC-derived mesenchymal cells with Fgf8 overexpression or control cells in the presence of exogenous FGF8 exhibit prolonged survival, proliferation, and multi-potent differentiation capability in cell cultures. Remarkably, exogenous FGF8 also sustains the capability of CNC-derived mesenchymal cells to participate in organogenesis such as odontogenesis. Furthermore, FGF8-mediated signaling strongly promotes adipogenesis but inhibits osteogenesis of CNC-derived mesenchymal cells in vitro. Our results reveal a specific role for FGF8 in the maintenance of progenitor status and in fate determination of CNC cells, implicating a potential application in expansion and fate manipulation of CNC-derived cells in stem cell-based craniofacial regeneration.

Siliceous mesostructured cellular foams/poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) composite biomaterials for bone regeneration

Osteoinductive and biodegradable composite biomaterials for bone regeneration were prepared by combining poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) with siliceous mesostructured cellular foams (SMC), using the porogen leaching method. Surface hydrophilicity, morphology, and recombinant human bone morphogenetic protein 2 adsorption/release behavior of the SMC/PHBHHx scaffolds were analyzed. Results of scanning electron microscopy indicated that the SMC was uniformly dispersed in the PHBHHx scaffolds, and SMC modification scaffolds have an interconnected porous architecture with pore sizes ranging from 200 to 400 μm. The measurements of the water contact angles suggested that the incorporation of SMC into PHBHHx improves the hydrophilicity of the composite. In vitro studies with simulated body fluid show great improvements to bioactivity and biodegradability versus pure PHBHHx scaffolds. Cell adhesion and cell proliferation on the scaffolds was also evaluated, and the new tools provide a better environment for human mesenchymal stem cell attachment, spreading, proliferation, and osteogenic differentiation on PHBHHx scaffolds. Moreover, micro-computed tomography and histological evaluation confirmed that the SMC/PHBHHx scaffolds improved the efficiency of new bone regeneration with excellent biocompatibility and biodegradability and faster and more effective osteogenesis in vivo.

Mussel-inspired human gelatin nanocoating for creating biologically adhesive surfaces

Recombinant human gelatin was conjugated with dopamine using carbodiimide as a surface modifier. This dopamine-coupled human gelatin (D-rhG) was characterized by ¹H-nuclear magnetic resonance, mass spectroscopy, and circular dichroism. D-rhG-coated surface properties were analyzed by physicochemical methods. Additionally, cell attachment and growth on the modified surfaces was assessed using human umbilical endothelial cells. Binding of gelatin onto titanium was significantly enhanced by dopamine conjugation. The thickness of the D-rhG coating depended on the treatment pH; thicker layers were formed at higher pH values, with a maximum thickness of 30 nm. D-rhG enhanced the binding of collagen-binding vascular endothelial growth factor and cell adhesion as compared with gelatin alone, even at the same surface concentration. The D-rhG surface modifier enhanced substrate binding by creating an adhesive nanointerface that increased specific protein binding and cell attachment.

The applications of buckminsterfullerene C60 and derivatives in orthopaedic research

Abstract Buckminsterfullerene C60 and derivatives have been extensively explored in biomedical research due to their unique structure and unparalleled physicochemical properties. C60 is characterized as a "free radical sponge" with an anti-oxidant efficacy several hundred-fold higher than conventional anti-oxidants. Also, the C60 core has a strong electron-attracting ability and numerous functional compounds with widely different properties can be added to this fullerene cage. This review focused on the applications of C60 and derivatives in orthopaedic research, such as the treatment of cartilage degeneration, bone destruction, intervertebral disc degeneration (IVDD), vertebral bone marrow disorder, radiculopathy, etc., as well as their toxicity in vitro and in vivo. We suggest that C60 and derivatives, especially the C60 cores coupled with functional groups presenting new biological and pharmacological activities, are advantageous in orthopaedic research and will be promising in clinical performance for musculoskeletal disorders treatment; however, the pharmacokinetics and toxicology of these agents as local/systemic administration need to be carefully determined.

A novel, visible light-induced, rapidly cross-linkable gelatin scaffold for osteochondral tissue engineering

Osteochondral injuries remain difficult to repair. We developed a novel photo-cross-linkable furfurylamine-conjugated gelatin (gelatin-FA). Gelatin-FA was rapidly cross-linked by visible light with Rose Bengal, a light sensitizer, and was kept gelled for 3 weeks submerged in saline at 37°C. When bone marrow-derived stromal cells (BMSCs) were suspended in gelatin-FA with 0.05% Rose Bengal, approximately 87% of the cells were viable in the hydrogel at 24 h after photo-cross-linking, and the chondrogenic differentiation of BMSCs was maintained for up to 3 weeks. BMP4 fusion protein with a collagen binding domain (CBD) was retained in the hydrogels at higher levels than unmodified BMP4. Gelatin-FA was subsequently employed as a scaffold for BMSCs and CBD-BMP4 in a rabbit osteochondral defect model. In both cases, the defect was repaired with articular cartilage-like tissue and regenerated subchondral bone. This novel, photo-cross-linkable gelatin appears to be a promising scaffold for the treatment of osteochondral injury.