Enhanced Osteogenesis of ADSCs by the Synergistic Effect of Aligned Fibers Containing Collagen I

Role of Adipose-Derived Mesenchymal Stem Cells in Bone Regeneration

Bone regeneration involves multiple factors such as tissue interactions, an inflammatory response, and vessel formation. In the event of diseases, old age, lifestyle, or trauma, bone regeneration can be impaired which could result in a prolonged healing duration or requiring an external intervention for repair. Currently, bone grafts hold the golden standard for bone regeneration. However, several limitations hinder its clinical applications, e.g., donor site morbidity, an insufficient tissue volume, and uncertain post-operative outcomes. Bone tissue engineering, involving stem cells seeded onto scaffolds, has thus been a promising treatment alternative for bone regeneration. Adipose-derived mesenchymal stem cells (AD-MSCs) are known to hold therapeutic value for the treatment of various clinical conditions and have displayed feasibility and significant effectiveness due to their ease of isolation, non-invasive, abundance in quantity, and osteogenic capacity. Notably, in vitro studies showed AD-MSCs holding a high proliferation capacity, multi-differentiation potential through the release of a variety of factors, and extracellular vesicles, allowing them to repair damaged tissues. In vivo and clinical studies showed AD-MSCs favoring better vascularization and the integration of the scaffolds, while the presence of scaffolds has enhanced the osteogenesis potential of AD-MSCs, thus yielding optimal bone formation outcomes. Effective bone regeneration requires the interplay of both AD-MSCs and scaffolds (material, pore size) to improve the osteogenic and vasculogenic capacity. This review presents the advances and applications of AD-MSCs for bone regeneration and bone tissue engineering, focusing on the in vitro, in vivo, and clinical studies involving AD-MSCs for bone tissue engineering.

Substrate stiffness can affect the crosstalk between adipose derived mesenchymal stem cells and macrophages in bone tissue engineering

Purpose: This study aimed to explore the effect of biomaterials with different stiffness on Adipose Derived Mesenchymal Stem Cells (ADSC)-macrophage crosstalk in bone tissue engineering and its role in bone repair. Methods: Biomaterials with Young's modulus of 64 and 0.2 kPa were selected, and the crosstalk between ADSCs and macrophages was investigated by means of conditioned medium treatment and cell co-culture, respectively. Polymerase chain reaction (PCR) and flow cytometry were used to evaluate the polarization of macrophages. Alkaline phosphatase (ALP) and alizarin red staining (ARS) solutions were used to evaluate the osteogenic differentiation of ADSCs. Transwell assay was used to evaluate the chemotaxis of ADSCs and macrophages. Moreover, mass spectrometry proteomics was used to analyze the secreted protein profile of ADSCs of different substrates and macrophages in different polarization states. Results: On exploring the influence of biomaterials on macrophages from ADSCs on different substrates, we found that CD163 and CD206 expression levels in macrophages were significantly higher in the 64-kPa group than in the 0.2-kPa group in conditioned medium treatment and cell co-culture. Flow cytometry showed that more cells became CD163+ or CD206+ cells in the 64-kPa group under conditioned medium treatment or cell co-culture. The Transwell assay showed that more macrophages migrated to the lower chamber in the 64-kPa group. The proteomic analysis found that ADSCs in the 64-kPa group secreted more immunomodulatory proteins, such as LBP and RBP4, to improve the repair microenvironment. On exploring the influence of biomaterials on ADSCs from macrophages in different polarization states, we found that ALP and ARS levels in ADSCs were significantly higher in the M2 group than in the other three groups (NC, M0, and M1 groups) in both conditioned medium treatment and cell co-culture. The Transwell assay showed that more ADSCs migrated to the lower chamber in the M2 group. The proteomic analysis found that M2 macrophages secreted more extracellular remodeling proteins, such as LRP1, to promote bone repair. Conclusion: In bone tissue engineering, the stiffness of repair biomaterials can affect the crosstalk between ADSCs and macrophages, thereby regulating local repair immunity and affecting bone repair.

Aligned Lovastatin-loaded Electrospun Nanofibers Regulate Collagen Organization and Reduce Scar Formation

Excessive scar formation caused by cutaneous injury leads to pruritus, pain, contracture, dyskinesia, and unpleasant appearance. Functional wound dressings are designed to accelerate wound healing and reduce scar formation. In this study, we fabricated aligned or random polycaprolactone/silk fibroin electrospun nanofiber membranes with or without lovastatin loading, and then evaluated their scar-inhibitory effects on wounds under a specific tension direction. The nanofiber membranes exhibited good controlled-release performance, mechanical properties, hydrophilicity, and biocompatibility. Furthermore, nanofibers' perpendicular placement to the tension direction of the wound most effectively reduced scar formation (the scar area decreased by 66.9%) and promoted skin regeneration in vivo. The mechanism was associated with its aligned nanofibers regulated collagen organization in the early stage of wound healing. Moreover, lovastatin-loaded nanofibers inhibited myofibroblast differentiation and migration. Both tension direction-perpendicular topographical cues and lovastatin synergistically inhibited mechanical transduction and fibrosis progression, further reducing scar formation. In summary, our study may provide an effective scar prevention strategy in which individualized dressings can be designed according to the local mechanical force direction of patients' wounds, and the addition of lovastatin can further inhibit scar formation. STATEMENT OF SIGNIFICANCE: In vivo, cells and collagen are always arranged parallel to the tension direction. However, the aligned topographic cues themselves promote myofibroblast differentiation and exacerbate scar formation. Electrospun nanofibers' perpendicular placement to the tension direction of the wound most effectively reduces scar formation and promotes skin regeneration in vivo. The mechanism is associated with its tension direction-perpendicular nanofibers reregulate collagen organization in the early stage of wound healing. In addition, tension direction-perpendicular topographical cue and lovastatin could inhibit mechanical transduction and fibrosis progression synergistically, further reducing scar formation. This study proves that combining topographical cues of wound dressing and drugs would be a promising therapy for clinical scar management.

How Mechanical and Physicochemical Material Characteristics Influence Adipose-Derived Stem Cell Fate

Adipose-derived stem cells (ASCs) are a subpopulation of mesenchymal stem cells. Compared to bone marrow-derived stem cells, they can be harvested with minimal invasiveness. ASCs can be easily expanded and were shown to be able to differentiate into several clinically relevant cell types. Therefore, this cell type represents a promising component in various tissue engineering and medical approaches (e.g., cell therapy). In vivo cells are surrounded by the extracellular matrix (ECM) that provides a wide range of tissue-specific physical and chemical cues, such as stiffness, topography, and chemical composition. Cells can sense the characteristics of their ECM and respond to them in a specific cellular behavior (e.g., proliferation or differentiation). Thus, in vitro biomaterial properties represent an important tool to control ASCs behavior. In this review, we give an overview of the current research in the mechanosensing of ASCs and current studies investigating the impact of material stiffens, topography, and chemical modification on ASC behavior. Additionally, we outline the use of natural ECM as a biomaterial and its interaction with ASCs regarding cellular behavior.

Silk fibroin scaffolds: A promising candidate for bone regeneration

It remains a big challenge in clinical practice to repair large-sized bone defects and many factors limit the application of autografts and allografts, The application of exogenous scaffolds is an alternate strategy for bone regeneration, among which the silk fibroin (SF) scaffold is a promising candidate. Due to the advantages of excellent biocompatibility, satisfying mechanical property, controllable biodegradability and structural adjustability, SF scaffolds exhibit great potential in bone regeneration with the help of well-designed structures, bioactive components and functional surface modification. This review will summarize the cell and tissue interaction with SF scaffolds, techniques to fabricate SF-based scaffolds and modifications of SF scaffolds to enhance osteogenesis, which will provide a deep and comprehensive insight into SF scaffolds and inspire the design and fabrication of novel SF scaffolds for superior osteogenic performance. However, there still needs more comprehensive efforts to promote better clinical translation of SF scaffolds, including more experiments in big animal models and clinical trials. Furthermore, deeper investigations are also in demand to reveal the degradation and clearing mechanisms of SF scaffolds and evaluate the influence of degradation products.

Kartogenin Induced Adipose-Derived Stem Cell Exosomes Enhance the Chondrogenic Differentiation Ability of Adipose-Derived Stem Cells

Objective

The objective of this study is to explore the effect of kartogenin (KGN-)-pretreated adipose-derived stem cell-derived exosomes (ADSC-EXOs) on the chondrogenic differentiation ability of ADSCs.

Methods

Adipose-derived stem cells (ADSCs) were treated with different doses of KGN, and exosomes (EXOs) were extracted. EXOs were then identified using an electron microscope (EM), nanoparticle tracking analyzer, nanoparticle tracking analysis software, and exosomal protein markers. EXOs were labeled with the fluorescent dye PKH67 and their uptake by cells was evaluated. A cell counting kit-8 (CCK-8) assay, flow cytometry, clonogenic assay, and a cell scratch assay were used to detect the abilities of proliferation, apoptosis, clone formation, and migration of ADSCs, respectively. Subsequently, Alcian blue staining and toluidine blue staining were used to detect the chondrogenic differentiation ability of ADSCs in each group. Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot (WB) techniques were used to detect the expression of chondrogenic differentiation-related genes.

Results

In this study, ADSCs and KGN-induced ADSC-EXOs were successfully extracted and isolated. EXOs and ADSCs coculturing results showed that KGN-induced ADSC-EXOs can significantly promote proliferation, clone formation, migration, and chondrogenic differentiation of ADSCs and inhibit apoptosis. In addition, KGN-induced ADSC-EXOs can increase the expression of chondrogenic-related genes in ADSCs (Aggrecan, Collagen III, Collagen II, and SOX9), and can significantly decrease the expression of chondrolysis-related genes (MMP-3, ADAMTS4, and ADAMTS5).

Conclusion

KGN-induced ADSC-EXOs can enhance the chondrogenic differentiation ability of ADSCs by promoting cell proliferation and migration while inhibiting cell apoptosis. KGN treatment can also increase the expression of chondrogenic differentiation-related genes and decrease the expression of chondrolysis-related genes. These results provide a new approach to cartilage repair and regeneration.

The diameter factor of aligned membranes facilitates wound healing by promoting epithelialization in an immune way

Topographical properties, such as pattern and diameter, of biomaterials play important roles in influencing cell activities and manipulating the related immune response during wound healing. We prepared aligned electrospinning membranes with different fiber diameters, including 319 ± 100 nm (A300), 588 ± 132 nm (A600), and 1048 ± 130 nm (A1000), by adjusting the distance from the tip to the collector, the injection rate, and the concentration of the solution. The A300 membranes significantly improved cell proliferation and spreading and facilitated wound healing (epithelization and vascularization) with the regeneration of immature hair follicles compared to the other membranes. Transcriptomics revealed the underlying molecular mechanism that A300 could promote immune-related processes towards a pro-healing direction, significantly promoting keratinocyte migration and skin wound healing. All the results indicated that wound healing requires the active participation of the immune process, and that A300 was a potential candidate for guided skin regeneration applications.

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It is still unclear which diameter interval of aligned membranes is most suitable for tissue regeneration.

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Outstanding performances in the wound healing process was presented by the A300 membranes.

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The transcriptome revealed that A300 could promote immune related processes towards a pro-healing direction.

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A300 promoted keratinocytes migration and final wound healing partially through MMP12.

Bioprinting of Stem Cells in Multimaterial Scaffolds and Their Applications in Bone Tissue Engineering

Bioprinting stem cells into three-dimensional (3D) scaffolds has emerged as a new avenue for regenerative medicine, bone tissue engineering, and biosensor manufacturing in recent years. Mesenchymal stem cells, such as adipose-derived and bone-marrow-derived stem cells, are capable of multipotent differentiation in a 3D culture. The use of different printing methods results in varying effects on the bioprinted stem cells with the appearance of no general adverse effects. Specifically, extrusion, inkjet, and laser-assisted bioprinting are three methods that impact stem cell viability, proliferation, and differentiation potential. Each printing method confers advantages and disadvantages that directly influence cellular behavior. Additionally, the acquisition of 3D bioprinters has become more prominent with innovative technology and affordability. With accessible technology, custom 3D bioprinters with capabilities to print high-performance bioinks are used for biosensor fabrication. Such 3D printed biosensors are used to control conductivity and electrical transmission in physiological environments. Once printed, the scaffolds containing the aforementioned stem cells have a significant impact on cellular behavior and differentiation. Natural polymer hydrogels and natural composites can impact osteogenic differentiation with some inducing chondrogenesis. Further studies have shown enhanced osteogenesis using cell-laden scaffolds in vivo. Furthermore, selective use of biomaterials can directly influence cell fate and the quantity of osteogenesis. This review evaluates the impact of extrusion, inkjet, and laser-assisted bioprinting on adipose-derived and bone-marrow-derived stem cells along with the effect of incorporating these stem cells into natural and composite biomaterials.

Three-Dimensional Modeling of the Structural Microenvironment in Post-Traumatic War Wounds

BACKGROUND:

The development of post-traumatic heterotopic ossification (HO) is a common, undesirable sequela in patients with high-energy (war-related) extremity injuries. While inflammatory and osteoinductive signaling pathways are known to be involved in the development and progression of post-traumatic HO, features of the structural microenvironment within which the ectopic bone begins to form remain poorly understood. Thus, increasing our knowledge of molecular and structural changes within the healing wound may help elucidate the pathogenesis of post-traumatic HO and aid in the development of specific treatment and/or prevention strategies.

METHODS:

In this study, we performed high-resolution microscopy and biochemical analysis of tissues obtained from traumatic war wounds to characterize changes in the structural microenvironment. In addition, using an electrospinning approach, we modeled this microenvironment to reconstitute a three-dimensional type I collagen scaffold with non-woven, randomly oriented nanofibers where we evaluated the performance of primary mesenchymal progenitor cells.

RESULTS:

We found that traumatic war wounds are characterized by a disorganized, densely fibrotic collagen I matrix that influences progenitor cells adhesion, proliferation and osteogenic differentiation potential.

CONCLUSION:

Altogether, these results suggest that the structural microenvironment present in traumatic war wounds has the potential to contribute to the development of post-traumatic HO. Our findings may support novel treatment strategies directed towards modifying the structural microenvironment after traumatic injury.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13770-021-00355-y.

Silk Biomaterials for Bone Tissue Engineering

Silk is a natural fibrous polymer with application potential in regenerative medicine. Increasing interest remains for silk materials in bone tissue engineering due to their characteristics in biocompatibility, biodegradability and mechanical properties. Plenty of the in vitro and in vivo studies confirmed the advantages of silk in accelerating bone regeneration. Silk is processed into scaffolds, hydrogels, and films to facilitate different bone regenerative applications. Bioactive factors such as growth factors and drugs, and stem cells are introduced to silk-based matrices to create friendly and osteogenic microenvironments, directing cell behaviors and bone regeneration. The recent progress in silk-based bone biomaterials is discussed and focused on different fabrication and functionalization methods related to osteogenesis. The challenges and potential targets of silk bone materials are highlighted to evaluate the future development of silk-based bone materials.

Coaxial nanofibrous scaffolds mimicking the extracellular matrix transition in the wound healing process promoting skin regeneration through enhancing immunomodulation

Numerous studies have shown that scaffolds incorporated with extracellular matrix (ECM) proteins could regulate cell behaviors and improve wound healing. However, most ECM-containing scaffolds fail to capture the dynamic features of the native ECM. In this regard, nanofibrous scaffolds which mimic the composition transition of the ECM during wound healing may have great potential in promoting skin regeneration through dynamically modulating the microenvironment. Herein, we report a novel skin ECM-biomimetic coaxial nanofibrous scaffold for the repair of chronic wounds. Two essential ECM proteins, fibrinogen and collagen I, were incorporated into the shell and the core of nanofibers, respectively, to mimic the sequential appearance of fibrinogen and collagen I in the wound healing process. The regulation of the biomimetic coaxial scaffolds on adipose-derived mesenchymal stromal cells (ASCs) was compared with that of the PLGA/fibrinogen, PLGA/collagen I and PLGA uniaxial scaffolds. Our results showed that the biomimetic coaxial scaffolds remarkably promoted the immunomodulatory paracrine secretion of ASCs. By incubating macrophages with ASC conditioned medium, the enhanced immunomodulation of ASCs on the biomimetic coaxial scaffolds was confirmed by the enhanced M1-to-M2 polarization of macrophages. Furthermore, the biomimetic coaxial scaffolds effectively promoted wound repair through resolving inflammation in diabetic rats. These findings helped reveal the role of the dynamic ECM change in regulating wound healing and suggest the potential utility of the biomimetic coaxial scaffolds as a promising alternative to treat chronic wounds.

Biomaterial design strategies to address obstacles in craniomaxillofacial bone repair

Biomaterial design to repair craniomaxillofacial defects has largely focused on promoting bone regeneration, while there are many additional factors that influence this process. The bone microenvironment is complex, with various mechanical property differences between cortical and cancellous bone, a unique porous architecture, and multiple cell types that must maintain homeostasis. This complex environment includes a vascular architecture to deliver cells and nutrients, osteoblasts which form new bone, osteoclasts which resorb excess bone, and upon injury, inflammatory cells and bacteria which can lead to failure to repair. To create biomaterials able to regenerate these large missing portions of bone on par with autograft materials, design of these materials must include methods to overcome multiple obstacles to effective, efficient bone regeneration. These obstacles include infection and biofilm formation on the biomaterial surface, fibrous tissue formation resulting from ill-fitting implants or persistent inflammation, non-bone tissue formation such as cartilage from improper biomaterial signals to cells, and voids in bone infill or lengthy implant degradation times. Novel biomaterial designs may provide approaches to effectively induce osteogenesis and new bone formation, include design motifs that facilitate surgical handling, intraoperative modification and promote conformal fitting within complex defect geometries, induce a pro-healing immune response, and prevent bacterial infection. In this review, we discuss the bone injury microenvironment and methods of biomaterial design to overcome these obstacles, which if unaddressed, may result in failure of the implant to regenerate host bone.

Polydopamine-Ag composite surface guides HBMSCs adhesion and proliferation

Human bone marrow mesenchymal stem cells (HBMSCs) are regarded as an important resource in the field of maxillofacial bone regeneration because of their favorable properties when compared with other stem cells. Hence, finding suitable materials that could extend the application of HBMSCs has become an emerging medical topic and socioeconomic problem. In this work, polydopamine (PDA)-Ag surface was fabricated by PDA assisted photoreduction method, and the obtained PDA-Ag composite surface significantly promoted HBMSCs adhesion and proliferation. This effect is highly related to the amount of Ag nanoparticles (Ag NPs) present on the PDA surface. The behavior of HBMSCs on PDA-Ag surface could be spatially manipulated by controlling the distribution of Ag NPs on PDA surface (by controlling UV light). The general adhesion property allows the PDA-Ag surface to be fabricated on various substrates, making it a simple, general and controllable method for the fabrication of bioactive surface for HBMSCs.

A radial 3D polycaprolactone nanofiber scaffold modified by biomineralization and silk fibroin coating promote bone regeneration in vivo

The treatment and repair of large bone defects remains a major therapeutic challenge in the clinical setting. Nanofiber scaffolds fabricated via the electrospinning technique have been developed as a universal method for bone regeneration due to their suitable properties. However, traditional two-dimensional (2D) nanofiber mats are usually too dense, which may prevent cell infiltration and growth, thereby restricting their application. Herein, a three-dimensional (3D) polycaprolactone nanofiber scaffold was developed, modified by biomineralization and silk fibroin coating. The scaffold possessed a parallel array of nanofiber surfaces, mimicking the parallel structure of fibrils in natural bone tissue. Furthermore, the fabricated radially or laterally interconnected macrochannels were investigated to elucidate the effect of the scaffold structure on bone regeneration. In vitro studies revealed that the scaffolds could guide cell arrangement and that the radially aligned scaffold demonstrated a stronger ability to promote cell proliferation. In vivo results showed that the radially aligned scaffold could guide tissue arrangement and remodeling and support a significantly faster regeneration rate of bone tissue. Therefore, 3D-mineralized polycaprolactone nanofiber scaffolds with radially interconnected macrochannels and aligned nanofibers are expected to be used in tissue engineering, including in the repair of bone defects, cartilage or other composite tissues.

Biomimetic cues from poly(lactic-co-glycolic acid)/hydroxyapatite nano-fibrous scaffolds drive osteogenic commitment in human mesenchymal stem cells in the absence of osteogenic factor supplements

Mimicking the complex hierarchical architecture of the 'osteon', the functional unit of cortical bone, from the bottom-up offers the possibility of generating mature bone tissue in tissue engineered bone substitutes. In this work, a modular 'bottom-up' approach has been developed to assemble bone niche-mimicking nanocomposite scaffolds composed of aligned electrospun nanofibers of poly(lactic-co-glycolic acid) (PLGA) encapsulating aligned rod-shape nano-sized hydroxyapatite (nHA). By encoding axial orientation of the nHA within these aligned nanocomposite fibers, significant improvements in mechanical properties, surface roughness, hydrophilicity and in vitro simulated body fluid (SBF) mineral deposition were achieved. Moreover, these hierarchical scaffolds induced robust formation of bone hydroxyapatite and osteoblastic maturation of human bone marrow-derived mesenchymal stem cells (hBMSCs) in growth media that was absent of any soluble osteogenic differentiation factors. The results of this investigation confirm that these tailored, aligned nanocomposite fibers, in the absence of media-bone inductive factors, offer the requisite biophysical and biochemical cues to hBMSCs to promote and support their differentiation into mature osteoblast cells and form early bone-like tissue in vitro.

Maneuvering the Migration and Differentiation of Stem Cells with Electrospun Nanofibers

Electrospun nanofibers have been extensively explored as a class of scaffolding materials for tissue regeneration, because of their unique capability to mimic some features and functions of the extracellular matrix, including the fibrous morphology and mechanical properties, and to a certain extent the chemical/biological cues. This work reviews recent progress in applying electrospun nanofibers to direct the migration of stem cells and control their differentiation into specific phenotypes. First, the physicochemical properties that make electrospun nanofibers well-suited as a supporting material to expand stem cells by controlling their migration and differentiation are introduced. Then various systems are analyzed in conjunction with mesenchymal, neuronal, and embryonic stem cells, as well as induced pluripotent stem cells. Finally, some perspectives on the challenges and future opportunities in combining electrospun nanofibers with stem cells are offered to address clinical issues.

Acellular pericardium: A naturally hierarchical, osteoconductive, and osteoinductive biomaterial for guided bone regeneration

There is great demand for an improved barrier membrane with osteogenic potential for guided bone regeneration (GBR). Natural acellular porcine pericardium (APP) is increasingly used in regenerative medicine as a kind of common extracellular matrix materials. This study aimed to investigate its potential application in GBR, especially its osteoconductive and osteoinductive properties. Bio-Gide (BG), a commercial collagen membrane, was set as the control group. APP samples were characterized by physicochemical analyses and their biological effects on human bone mesenchymal stem cells (hBMSCs) and human gingival fibroblasts (hGFs) were also examined. Additionally, the osteogenic potential of APP was tested on a bilateral critical-sized calvarial defect model. We discovered that the smooth surface of APP tended to recruit more hBMSCs. Moreover, promoted proliferation and osteogenic differentiation of hBMSCs was detected on this side of APP, with increased alkaline phosphatase activity and upregulated expression of bone-specific genes. Besides, the rough side of APP showed good biocompatibility and barrier function with hGFs. Histologic observation and analysis of calvarial defect healing over 4 weeks revealed enhanced bone regeneration under APP compared with BG and the control group. The results of this study indicate that APP is a potential osteoconductive and osteoinductive biomaterial for GBR.

Three-Dimensional Printing and Electrospinning Dual-Scale Polycaprolactone Scaffolds with Low-Density and Oriented Fibers to Promote Cell Alignment

Complex and hierarchically functionalized scaffolds composed of micro- and nanoscale structures are a key goal in tissue engineering. The combination of three-dimensional (3D) printing and electrospinning enables the fabrication of these multiscale structures. This study presents a polycaprolactone 3D-printed and electrospun scaffold with multiple mesh layers and fiber densities. The results show successful fabrication of a dual-scale scaffold with the 3D-printed scaffold acting as a gap collector with the printed microfibers as the electrodes and the pores a series of insulating gaps resulting in aligned nanofibers. The electrospun fibers are highly aligned perpendicular to the direction of the printed fiber and form aligned meshes within the pores of the scaffold. Mechanical testing showed no significant difference between the number of mesh layers whereas the hydrophobicity of the scaffold increased with increasing fiber density. Biological results indicate that increasing the number of mesh layers improves cell proliferation, migration, and adhesion. The aligned nanofibers within the microscale pores allowed enhanced cell bridging and cell alignment that was not observed in the 3D-printed only scaffold. These results demonstrate a facile method of incorporating low-density and aligned fibers within a 3D-printed scaffold that is a promising development in multiscale hierarchical scaffolds where alignment of cells can be desirable.

Wood-Derived Hybrid Scaffold with Highly Anisotropic Features on Mechanics and Liquid Transport toward Cell Migration and Alignment

Fantastic structures in nature have inspired much incredible research. Wood, a typical model of anisotropy and hierarchy, has been widely investigated for its mechanical properties and water extraction abilities, although applications in biological areas remain challenging. Delignified wood composite with in situ deposited hydroxyapatite (HAp) and infiltrated polycaprolactone (PCL) is hereby fabricated in an attempt to mimic natural bone. The inherent structure and properties of wood are carefully preserved during the fabrication, showing anisotropic mechanical properties in the radial direction (420 MPa) and longitudinal direction (20 MPa). In addition, it also performs directional liquid transport, effectively inducing the migration and alignment of cells to simulate the uniform seeding behavior of various cells in natural bone. Moreover, the synergistic effect of blended HAp and PCL largely promotes cell proliferation and osteogenic differentiation, providing a promising candidate for bone regeneration materials.

ECM-mimicking nanofibrous matrix coaxes macrophages toward an anti-inflammatory phenotype: Cellular behaviors and transcriptome analysis

An in-depth understanding of biomaterial cues to selectively polarize macrophages is beneficial in the design of "immuno-informed" biomaterials that positively interact with the immune system to dictate a favorable macrophage response following implantation. Given the promising future of ECM-mimicking nanofibrous biomaterials in biomedical application, it is essential to elucidate how their intrinsic cues, especially the nanofibrous architecture, affect macrophages. In the present study, we evaluated how the nanofibrous architecture of a gelatin matrix modulated macrophage responses from the perspectives of cellular behaviors and a transcriptome analysis. In our results, the nanofibrous surface attenuated M1 polarization and down-regulated the inflammatory responses of macrophages compared with a smooth surface. Besides, the cell-material interaction was up-regulated and the adhered macrophages tended to maintain an original, non-polarized state on the nanofibrous matrix. Accordingly, whole transcriptome analysis revealed that nanofibrous architecture up-regulated the pathways related to ECM-receptor interaction and down-regulated pathways related to pro-inflammation. This study provides a panoramic view of the interaction between macrophages and nanofibers, and offers valuable information for the design of immunomodulatory ECM-mimicking biomaterials for tissue regeneration.

Osteogenic Differentiation of Adipose-Derived Stromal Cells: From Bench to Clinics

In addition to mesenchymal stem cells, adipose-derived stem/stromal cells (ASCs) are an attractive source for a large variety of cell-based therapies. One of their most important potential applications is related to the regeneration of bone tissue thanks to their capacity to differentiate in bone cells. However, this requires a proper control of their osteogenic differentiation, which depends not only on the initial characteristics of harvested cells but also on the conditions used for their culture. In this review, we first briefly describe the preclinical and clinical trials using ASCs for bone regeneration and present the quantitative parameters used to characterize the osteogenic differentiation of ASCs. We then focus on the soluble factors influencing the osteogenic differentiation of ACS, including the steroid hormones and various growth factors, notably the most osteoinductive ones, the bone morphogenetic proteins (BMPs). Impact statement Adipose-derived stromal/stem cells are reviewed for their use in bone regeneration.

Potential of electrospun cationic BSA fibers to guide osteogenic MSC differentiation via surface charge and fibrous topography

Large or complex bone fractures often need clinical treatments for sufficient bone repair. New treatment strategies have pursued the idea of using mesenchymal stromal cells (MSCs) in combination with osteoinductive materials to guide differentiation of MSCs into bone cells ensuring complete bone regeneration. To overcome the challenge of developing such materials, fundamental studies are needed to analyze and understand the MSC behavior on modified surfaces of applicable materials for bone healing. For this purpose, we developed a fibrous scaffold resembling the bone/bone marrow extracellular matrix (ECM) based on protein without addition of synthetic polymers. With this biomimetic in vitro model we identified the fibrous structure as well as the charge of the material to be responsible for its effects on MSC differentiation. Positive charge was introduced via cationization that additionally supported the stability of the scaffold in cell culture, and acted as nucleation point for mineralization during osteogenesis. Furthermore, we revealed enhanced focal adhesion formation and osteogenic differentiation of MSCs cultured on positively charged protein fibers. This pure protein-based and chemically modifiable, fibrous ECM model allows the investigation of MSC behavior on biomimetic materials to unfold new vistas how to direct cells' differentiation for the development of new bone regenerating strategies.

Triple PLGA/PCL Scaffold Modification Including Silver Impregnation, Collagen Coating, and Electrospinning Significantly Improve Biocompatibility, Antimicrobial, and Osteogenic Properties for Orofacial Tissue Regeneration

Biodegradable synthetic scaffolds hold great promise for oral and craniofacial guided tissue regeneration and bone regeneration. To overcome the limitations of current scaffold materials in terms of osteogenic and antimicrobial properties, we have developed a novel silver-modified/collagen-coated electrospun poly-lactic-co-glycolic acid/polycaprolactone (PLGA/PCL) scaffold (PP-pDA-Ag-COL) with improved antimicrobial and osteogenic properties. Our novel scaffold was generated by electrospinning a basic PLGA/PCL matrix, followed by silver nanoparticles (AgNPs) impregnation via in situ reduction, polydopamine coating, and then coating by collagen I. The three intermediate materials involved in the fabrication of our scaffolds, namely, PLGA/PCL (PP), PLGA/PCL-polydopamine (PP-pDA), and PLGA/PCL-polydopamine-Ag (PP-pDA-Ag), were used as control scaffolds. Scanning electron micrographs and mechanical testing indicated that the unique three-dimensional structures with randomly oriented nanofibrous electrospun scaffold architectures, the elasticity modulus, and the tensile strength were maintained after modifications. CCK-8 cell proliferation analysis demonstrated that the PP-pDA-Ag-COL scaffold was associated with higher MC3T3 proliferation rates than the three control scaffolds employed. Scanning electron and fluorescence light microscopy illustrated that PP-pDA-Ag-COL scaffolds significantly enhanced MC3T3 cell adhesion compared to the control scaffolds after 12 and 24 h culture, in tandem with the highest β1 integrin expression levels, both at the mRNA level and the protein level. Alkaline phosphatase activity, BMP2, and RUNX2 expression levels of MC3T3 cells cultured on PP-pDA-Ag-COL scaffolds for 7 and 14 days were also significantly higher when compared to controls (P < 0.001). There was a wider antibacterial zone associated in PP-pDA-Ag-COL and PP-pDA-Ag scaffolds versus control scaffolds (P < 0.05), and bacterial fluorescence was reduced on the Ag-modified scaffolds after 24 h inoculation against Staphylococcus aureus and Streptococcus mutans. In a mouse periodontal disease model, the PP-pDA-Ag-COL scaffold enhanced alveolar bone regeneration (31.8%) and was effective for periodontitis treatment. These results demonstrate that our novel PP-pDA-Ag-COL scaffold enhanced biocompatibility and osteogenic and antibacterial properties and has therapeutic potential for alveolar/craniofacial bone regeneration.

Synergistic effects of thermal treatment and encapsulation of calcium phosphate nanoparticles on enhancing dimensional stability and osteogenic induction potential of free-standing PLGA electrospun membranes

Limited dimensional stability and osteogenic induction property of poly (lactide-co-glycolide) (PLGA) electrospun membranes hampered their applications in bone tissue engineering. Thermal treatment of fixed PLGA membranes at 50 °C for 2 h and further immersion in 75% ethanol at free-standing state were adopted in order to obtain a high stability and well-maintained fiber morphology. After the process, free-standing membranes were stable during incubation in PBS at 37 °C, the volumetric ratio was 59.0%, fibers became curved, and the average diameter was 816 nm. For as-electrospun PLGA membranes, the volumetric ratio was only 35.3%, showing that thermal treatment was effective to improve the dimensional stability. The addition of calcium phosphate nanoparticles in P5-T-F further increased the volumetric ratio (64.0%) and significantly improved the mechanical properties. The mineralization capacity of PLGA membranes was enhanced because of thermal treatment. Hemolysis ratios of all samples were ∼2% indicating good hemocompatibility of PLGA electrospun membranes. Proliferation of adipose derived stem cells from rats (rADSCs) on treated PLGA membranes was significantly faster than that on untreated one, especially for sample P-T-F. In addition to thermal treatment, the addition of calcium phosphate nanoparticles showed synergistic effects on improving mineralization property and osteogenic differentiation of rADSCs. When compared with P-T-F, P5-T-F had 153.0% higher ALP activity and 518% higher calcium mineral deposition based on alizarin red assay. Thermal treatment along with encapsulation of calcium phosphate nanoparticles in PLGA electrospun membranes demonstrated a great prospect for applications in bone tissue engineering.

Promoting Osteogenic Differentiation of Human Adipose-Derived Stem Cells by Altering the Expression of Exosomal miRNA

Human adipose-derived stem cells (ADSCs) can release exosomes; however, their specific functions remain elusive. In this study, we verified that exosomes derived from osteogenically differentiated ADSCs can promote osteogenic differentiation of ADSCs. Furthermore, in order to investigate the importance of exosomal microRNAs (miRNAs) in osteogenic differentiation of ADSCs, we used microarray assays to analyze the expression profiles of exosomal miRNAs derived from undifferentiated as well as osteogenically differentiated ADSCs; 201 miRNAs were upregulated and 33 miRNAs were downregulated between the two types of exosomes. Additionally, bioinformatic analyses, which included gene ontology analyses, pathway analysis, and miRNA-mRNA-network investigations, were performed. The results of these analyses revealed that the differentially expressed exosomal miRNAs participate in multiple biological processes, such as gene expression, synthesis of biomolecules, cell development, differentiation, and signal transduction, among others. Moreover, we found that these differentially expressed exosomal miRNAs connect osteogenic differentiation to processes such as axon guidance, MAPK signaling, and Wnt signaling. To the best of our knowledge, this is the first study to identify and characterize exosomal miRNAs derived from osteogenically differentiated ADSCs. This study confirms that alterations in the expression of exosomal miRNAs can promote osteogenic differentiation of ADSCs, which also provides the foundation for further research on the regulatory functions of exosomal miRNAs in the context of ADSC osteogenesis.

Nanolamellar Tantalum Interfaces in the Osteoblast Adhesion

The design of topographically patterned surfaces is considered to be a preferable approach for influencing cellular behavior in a controllable manner, in particular to improve the osteogenic ability of bone regeneration. In this study, we fabricated nanolamellar tantalum (Ta) surfaces with lamellar wall thicknesses of 40 and 70 nm. The cells attached to nanolamellar Ta surfaces exhibited higher protein adsorption and expression of β1 integrin, as compared to the nonstructured bulk Ta, which facilitated the initial cell attachment and spreading. We thus, as expected, observed significantly enhanced osteoblast adhesion, growth, and alkaline phosphatase activity on nanolamellar Ta surfaces. However, the beneficial effects of nanolamellar structures on osteogenesis became weaker as the lamellar wall thickness increased. The interaction between cells and Ta surfaces was examined through adhesion forces using atomic force microscopy. Our findings indicated that the Ta surface with a lamellar wall thickness of 40 nm exhibited the strongest stimulatory effect. The observed strongest adhesion force between the cell-attached tip and the Ta surface with a 40 nm thick lamellar wall encouraged the much stronger binding of cells with the surface and thus well-attached, -stretched, and -grown cells. We attributed this to the increase in the available contact area of cells with the thinner nanolamellar Ta surface. The increased contact area allowed the enhancement of the cell surface interaction strength and, thus, improved osteoblast adhesion. This study suggests that the thin nanolamellar topography shows immense potential in improving the clinical performance of dental and orthopedic implants.

Enhanced osteoinduction of electrospun scaffolds with assemblies of hematite nanoparticles as a bioactive interface

Purpose

Electrospun scaffolds have been studied extensively for their potential use in bone tissue engineering. However, their hydrophobicity and relatively low matrix stiffness constrain their osteoinduction capacities. In the present study, we studied polymer electrospun scaffolds coated with hydrophilic hematite nanoparticles (αFeNPs) constructed using layer-by-layer (LbL) assembly to construct a bioactive interface between the scaffolds and cells, to improve the osteoinduction capacities of the scaffolds.

Materials and methods

The morphology of the αFeNPs was assessed. Surface properties of the scaffolds were tested by X-ray photoelectron spectroscopy (XPS), surface water contact angle, and in vitro protein adsorption test. The stiffness of the coating was tested using an atomic force microscope (AFM). In vitro cell assays were performed using rat adipose-derived stem cells (ADSCs).

Results

Morphology characterizations showed that αFeNPs assembled on the surface of the scaffold, where the nano assemblies improved hydrophilicity and increased surface roughness, with increased surface stiffness. Enhanced initial ADSC cell spread was found in the nano assembled groups. Significant enhancements in osteogenic differentiation, represented by enhanced alkaline phosphatase (ALP) activities, elevated expression of osteogenic marker genes, and increased mineral synthesis by the seeded ADSCs, were detected. The influencing factors were attributed to the better hydrophilicity, rougher surface topography, and harder interface stiffness. In addition, the presence of nanoparticles was believed to provide better cell adhesion sites.

Conclusion

The results suggested that the construction of a bioactive interface by LbL assembly using αFeNPs on traditional scaffolds should be a promising method for bone tissue engineering.

Magnetic Cell-Scaffold Interface Constructed by Superparamagnetic IONP Enhanced Osteogenesis of Adipose-Derived Stem Cells

One of the key factors in tissue engineering and regenerative medicine is to optimize the interaction between seed cells and scaffolds such that the cells can grow in naturally biomimetic conditions. Their similarity to macromolecules and many unique properties mean that functional nanoparticles have promising potential for the modification and improvement of traditional scaffolds to obtain excellent biocompatibility, tunable stiffness, physical sensing, and stimulus-response capabilities. In the present study, we report magnetic poly(lactic- co-glycolic acid)/polycaprolactone (PLGA/PCL) scaffolds that were fabricated using a combination of the electrospinning technique and layer-by-layer assembly of superparamagnetic iron oxide nanoparticles (IONPs). PLGA/PCL scaffolds assembled with gold nanoparticles were prepared using the same method for comparison. The results showed that the assembled film of nanoparticles on the surface greatly enhanced the hydrophilicity and increased the elastic modulus of the scaffold, which subsequently improved the osteogenesis of the stem cells. Furthermore, the magnetic property of the IONPs proved to be the key factor in enhancing osteogenic differentiation, which explained the superior osteogenic capacity of the magnetic scaffolds compared with that of the gold nanoparticle-assembled scaffold. These results demonstrated the importance of magnetic nanomaterials as a bioactive interface between cells and scaffolds and will promote the design of biomaterials to improve tissue engineering and regenerative medicine efficacy.

Enhanced wound healing in diabetic rats by nanofibrous scaffolds mimicking the basketweave pattern of collagen fibrils in native skin

Nanofibrous scaffolds that offer proper microenvironmental cues to promote the healing process are highly desirable for patients with chronic wounds. Although studies have shown that fiber organization regulates cell behaviors in vitro, little is known about its effects on the wound healing process in vivo. Most of the nanofibrous scaffolds currently used in skin repair are randomly oriented. Herein, inspired by the basketweave-like pattern of collagen fibrils in native skin, we fabricated biomimetic nanofibrous scaffolds with crossed fiber organization via electrospinning. The regulation of crossed nanofibrous scaffolds on fibroblasts was compared with that of aligned and random nanofibrous scaffolds. Unexpectedly, crossed nanofibrous scaffolds induced different cellular responses in fibroblasts, including differences in cellular morphology, migration and wound healing related gene expression, in comparison to either aligned or random nanofibrous scaffolds. More importantly, the regulation of nanofibrous scaffolds with different fiber organizations on wound repair was systematically investigated in diabetic rats. While the healing processes were enhanced by all nanofibrous scaffolds, wounds treated with crossed nanofibrous scaffolds achieved the best healing outcome, which was evidenced by the resolution of inflammation, the accelerated migration of fibroblasts and keratinocytes, and the promotion of angiogenesis. These findings helped reveal the role of fiber organization in regulating the wound healing process in vivo and suggest the potential utility of biomimetic crossed nanofibrous scaffolds for the repair of chronic wounds.

Thermally induced self-agglomeration 3D scaffolds with BMP-2-loaded core-shell fibers for enhanced osteogenic differentiation of rat adipose-derived stem cells

Introduction

Scaffold structure plays a vital role in cell behaviors. Compared with two-dimensional structure, 3D scaffolds can mimic natural extracellular matrix (ECM) and promote cell–cell and cell–matrix interactions. The combination of osteoconductive scaffolds and osteoinductive growth factors is considered to have synergistic effects on bone regeneration.

Materials and methods

In this study, core–shell poly(lactide-co-glycolide) (PLGA)/polycaprolactone (PCL)–BMP-2 (PP–B) fibrous scaffolds were prepared through coaxial electrospinning. Next, we fabricated 3D scaffolds based on PP–B fibers with thermally induced self-agglomeration (TISA) method and compared with conventional PLGA/PCL scaffolds in terms of scaffold morphology and BMP-2 release behaviors. Then, rat adipose-derived stem cells (rADSCs) were seeded on the scaffolds, and the effects on cell proliferation, cell morphology, and osteogenic differentiation of rADSCs were detected.

Results

The results demonstrated that 3D scaffold incorporated with BMP-2 significantly increased proliferation and osteogenic differentiation of rADSCs, followed by PP–B group.

Conclusion

Our findings indicate that scaffolds with 3D structure and osteoinductive growth factors have great potential in bone tissue engineering.

Cell-Sheet-Derived ECM Coatings and Their Effects on BMSCs Responses

Extracellular matrix (ECM) provides a dynamic and complex environment to determine the fate of stem cells. In this work, light harvested cell sheets were treated with paraformaldehyde or ethanol, which eventually become ECM. Such ECM was then immobilized on titanium substrates via polydopamine chemistry. Their effects on bone marrow mesenchymal stromal cells (BMSCs) behaviors were investigated. It was found that paraformaldehyde-treated ECM coating (PT-ECM) showed a well-maintained microstructure, whereas that of ethanol-treated (ET-ECM) was completely changed. As a result, different amide structures and distributions of ECM components, such as laminin and collagen I, were exhibited. Alkaline phosphatase activity, osteocalcin secretion, related gene expression, and mineral deposition were evaluated for BMSCs cultured on both ECM coatings. PT-ECM was demonstrated to promote osteogenic differentiation much more efficiently than that of ET-ECM. That is ascribed to the preservation of native ECM milieu of PT-ECM. Such ECM acquirement and immobilization method could establish surfaces being able to direct stem cell responses on various materials. That shows promising potential in bone tissue engineering and other related biomedical applications.

Materials-Directed Differentiation of Mesenchymal Stem Cells for Tissue Engineering and Regeneration

Cell-based therapies are a promising alternative to grafts and organ transplantation for treating tissue loss or damage due to trauma, malfunction, or disease. Over the past two decades, mesenchymal stem cells (MSCs) have attracted much attention as a potential cell population for use in regenerative medicine. While the proliferative capacity and multilineage potential of MSCs provide an opportunity to generate clinically relevant numbers of transplantable cells, their use in tissue regenerative applications has met with relatively limited success to date apart from secreting paracrine-acting factors to modulate the defect microenvironment. Presently, there is significant effort to engineer the biophysical properties of biomaterials to direct MSC differentiation and further expand on the potential of MSCs in tissue engineering, regeneration, and repair. Biomaterials can dictate MSC differentiation by modulating features of the substrate including composition, mechanical properties, porosity, and topography. The purpose of this review is to highlight recent approaches for guiding MSC fate using biomaterials and provide a description of the underlying characteristics that promote differentiation toward a desired phenotype.

Biomimetic Domain-Active Electrospun Scaffolds Facilitating Bone Regeneration Synergistically with Antibacterial Efficacy for Bone Defects

To improve bone regeneration in oral microenvironment, we generated a novel biodegradable, antibacterial, and osteoconductive electrospun PLGA/PCL membrane as an ideal osteogenic scaffold. The novel three-layer membranes were structured with serial layers of electrospun chlorhexidine-doped-PLGA/PCL (PPC), PLGA/PCL (PP), and β-tricalcium phosphate-doped-PLGA/PCL (PPβ). To characterize osteoconductive properties of these membranes, MC3T3-E1 (MC) cultures were seeded onto the membranes for 14 days for evaluation of cell proliferation, morphology and gene/protein expression. In addition, MC cells were cultured onto different surfaces of the three-layer membranes, PPC layer facing MC cells (PPβ-PP-PPC) and PPβ layer facing MC cells (PPC-PP-PPβ) to evaluate surface-material effects. Membrane properties and structures were evaluated. Antibacterial properties against Streptococcus mutans and Staphylococcus aureus were determined. Scanning electron microscope demonstrated smaller interfiber spaces of PPC and PPβ-PP-PPC compared to PPβ, PPC-PP-PPβ, and PP. PPC and PPβ-PP-PPC exhibited hydrophilic property. The three-layer membranes (PPC-PP-PPβ and PPβ-PP-PPC) demonstrated significantly higher Young's modulus (94.99 ± 4.03 MPa and 92.88 ± 4.03 MPa) compared to PP (48.76 ± 18.15 MPa) or PPC (7.92 ± 3.97 MPa) (p < 0.05). No significant difference of cell proliferation was found among any groups at any time point (p > 0.05). Higher expression of integrins were detected at 12 h of cultures on PPC-PP-PPβ compared to the controls. Promoted osteoconductive effects of PPC-PP-PPβ were revealed by alkaline phosphatase assays and Western blot compared with the controls at 7 and 14 days. PPC, PPC-PP-PPβ and PPβ-PP-PPC exhibited a significantly wider antibacterial zone against the tested bacteria compared to PP and PPβ (p < 0.05). These results suggested that the three-layer electrospun membranes demonstrated superior properties: higher strength, better cell adhesion, and promoted osteoconductive properties compared to single-layer membrane: however, antibacterial properties were exhibited in three-layer electrospun membranes and chlorhexidine-doped single-layer membrane. We concluded that the novel three-layer membranes could be used as a biocompatible scaffold for intraoral bone regeneration due to its enhanced osteoconductive activity and antibacterial effect.

Preparation of well-distributed titania nanopillar arrays on Ti6Al4V surface by induction heating for enhancing osteogenic differentiation of stem cells

Great effort has recently been devoted to the preparation of nanoscale surfaces on titanium-based implants to achieve clinically fast osteoinduction and osseointegration, which relies on the unique characteristics of the nanostructure. In this work, we used induction heating treatment (IHT) as a rapid oxidation method to fabricate a porous nanoscale oxide layer on the Ti6Al4V surface for better medical application. Well-distributed vertical nanopillars were yielded by IHT for 20-35 s on the alloy surface. The composition of the oxides contained rutile/anatase TiO₂ and a small amount of Al₂O₃ between the TiO₂ grain boundaries (GBs). This technology resulted in a reduction and subsequent increase of surface roughness of 26-32 nm when upregulating the heating time, followed by the successive enhancement of the thickness, wettability and adhesion strength of the oxidation layer to the matrix. The surface hardness also distinctly rose to 554 HV in the IHT-35 s group compared with the 350 HV of bare Ti6Al4V. The massive small-angle GBs in the bare alloy promoted the formation of nanosized oxide crystallites. The grain refinement and deformation texture reduction further improved the mechanical properties of the matrix after IHT. Moreover, in vitro experiments on a mesenchymal stem cell (BMSC) culture derived from human bone marrow for 1-7 days indicated that the nanoscale layers did not cause cytotoxicity, and facilitated cell differentiation in osteoblasts by enhancing the gene and osteogenesis-related protein expressions after 1-3 weeks of culturing. The increase of the IHT time slightly advanced the BMSC proliferation and differentiation, especially during long-term culture. Our findings provide strong evidence that IHT oxidation technology is a novel nanosurface modification technology, which is potentially promising for further clinical development.

Nano-biphasic calcium phosphate/polyvinyl alcohol composites with enhanced bioactivity for bone repair via low-temperature three-dimensional printing and loading with platelet-rich fibrin

Background and aim

As a newly emerging three-dimensional (3D) printing technology, low-temperature robocasting can be used to fabricate geometrically complex ceramic scaffolds at low temperatures. Here, we aimed to fabricate 3D printed ceramic scaffolds composed of nano-biphasic calcium phosphate (BCP), polyvinyl alcohol (PVA), and platelet-rich fibrin (PRF) at a low temperature without the addition of toxic chemicals.

Methods

Corresponding nonprinted scaffolds were prepared using a freeze-drying method. Compared with the nonprinted scaffolds, the printed scaffolds had specific shapes and well-connected internal structures.

Results

The incorporation of PRF enabled both the sustained release of bioactive factors from the scaffolds and improved biocompatibility and biological activity toward bone marrow-derived mesenchymal stem cells (BMSCs) in vitro. Additionally, the printed BCP/PVA/PRF scaffolds promoted significantly better BMSC adhesion, proliferation, and osteogenic differentiation in vitro than the printed BCP/PVA scaffolds. In vivo, the printed BCP/PVA/PRF scaffolds induced a greater extent of appropriate bone formation than the printed BCP/PVA scaffolds and nonprinted scaffolds in a critical-size segmental bone defect model in rabbits.

Conclusion

These experiments indicate that low-temperature robocasting could potentially be used to fabricate 3D printed BCP/PVA/PRF scaffolds with desired shapes and internal structures and incorporated bioactive factors to enhance the repair of segmental bone defects.

Facile Strategy to Generate Aligned Polymer Nanofibers: Effects on Cell Adhesion

Structure of polymer fiber membranes plays a vital role in controlling cell responses as applied to immobilize targets for specific cell interactions. Electrospinning is a simple and powerful method to prepare polymer fiber membranes with scales from nano- to micrometers. In this report, a facile yet versatile strategy has been developed for fabricating polymer nanofiber membranes with well-aligned structures using a glass sheet between the needle and a static drum as the collector. Effects of solution concentration, polymer molecular weight, applied voltage, and collection distance on the morphologies of the formed fibers were systematically studied. Adhesion of cells (e.g., mouse melanoma cells B16-F10 and fibroblast cells NIH-3T3) on the fiber membrane has been further investigated. Our results show that cell morphologies varied from elongated to spherical on the random fiber membrane when the pore area of membrane decreased. In contrast, on the membrane with aligned morphology, when decreasing the gap width of fiber membrane, cell is found to keep elongated state and spread along the alignment direction. This work provides a facile yet effective strategy to engineer surface structures of the fiber membranes for controlling cell adhesion.

Osteocytogenesis: Roles of Physicochemical Factors, Collagen Cleavage, and Exogenous Molecules

Osteocytes, the most abundant cell type in mammalian bone, are generally considered as the terminally differentiated cells of osteoblasts that are progressively self-buried or passively embedded in bone matrix. Emerging evidence reveals the essential functions of osteocytes in bone homeostasis and mechanotransduction. However, our knowledge on osteocytes, especially their formation, remains scarce. In this regard, the current review mainly focuses on several key factors that drive the osteocytic differentiation of osteoblasts, that is, osteocytogenesis. Available literature has demonstrated the involvement of physicochemical factors such as matrix composition, oxygen tension, and mechanical stress in the osteoblast-to-osteocyte transition. During cell migration and matrix remodeling, the matrix metalloproteinase-dependent collagen cleavage would play an "active" role in maturation and maintenance of the osteocytes. Besides, some in vitro methodologies are also established to induce the transformation of osteoblastic cell lines and primary mesenchymal cells to preosteocytes through cell transfection or addition of exogenous molecules (e.g., fibroblast growth factor-2, retinoic acid), which could potentiate the effort to form functional bone substitutes through elevated osteocytogenesis. Thus, advances of new technologies would enable comprehensive and in-depth understanding of osteocytes and their development, which in turn help promote the research on osteocyte biology and osteopathology.

Improved cell adhesion and osteogenesis using a PLTGA (poly l-lactide, 1,3-trimethylene carbonate, and glycolide) terpolymer by gelatin-assisted hydroxyapatite immobilization for bone regeneration

Schematic illustration of the procedures for preparing the GEL/HAP-coated PLTGA film, and representative images of the improved cellular behaviors.

Poly(l-lactide) melt spun fiber-aligned scaffolds coated with collagen or chitosan for guiding the directional migration of osteoblasts in vitro

PLLA melt spun fiber-aligned scaffolds coated with collagen or chitosan enhance the viability, spreading, alignment and mobility of osteoblasts.