Therapeutic-designed electrospun bone scaffolds: mesoporous bioactive nanocarriers in hollow fiber composites to sequentially deliver dual growth factors

Silicon-containing nanomedicine and biomaterials: materials chemistry, multi-dimensional design, and biomedical application

The invention of silica-based bioactive glass in the late 1960s has sparked significant interest in exploring a wide range of silicon-containing biomaterials from the macroscale to the nanoscale. Over the past few decades, these biomaterials have been extensively explored for their potential in diverse biomedical applications, considering their remarkable bioactivity, excellent biocompatibility, facile surface functionalization, controllable synthesis, etc. However, to expedite the clinical translation and the unexpected utilization of silicon-composed nanomedicine and biomaterials, it is highly desirable to achieve a thorough comprehension of their characteristics and biological effects from an overall perspective. In this review, we provide a comprehensive discussion on the state-of-the-art progress of silicon-composed biomaterials, including their classification, characteristics, fabrication methods, and versatile biomedical applications. Additionally, we highlight the multi-dimensional design of both pure and hybrid silicon-composed nanomedicine and biomaterials and their intrinsic biological effects and interactions with biological systems. Their extensive biomedical applications span from drug delivery and bioimaging to therapeutic interventions and regenerative medicine, showcasing the significance of their rational design and fabrication to meet specific requirements and optimize their theranostic performance. Additionally, we offer insights into the future prospects and potential challenges regarding silicon-composed nanomedicine and biomaterials. By shedding light on these exciting research advances, we aspire to foster further progress in the biomedical field and drive the development of innovative silicon-composed nanomedicine and biomaterials with transformative applications in biomedicine.

Poly(ε-caprolactone)/bioactive glass composite electrospun fibers for tissue engineering applications

In this work, composite electrospun fibers containing innovative bioactive glass nanoparticles were produced and characterized. Poly(ε-caprolactone), benign solvents, and sol-gel B- and Cu-doped bioactive glass powders were used to fabricate fibrous scaffolds. The retention of bioactive glass nanoparticles in the polymer matrix, the electrospinnability of this novel solution and the obtained electrospun composites were extensively characterized. As a result, composite electrospun fibers characterized by biocompatibility, bioactivity, and exhibiting overall properties adequate for both hard and soft tissue engineering applications, have been produced. The addition of these bioactive glass nanoparticles was, indeed, able to impart bioactive properties to the fibers. Cell culture studies show promising results, demonstrating proliferation and growth of cells on the composite fibers. Wettability, degradation rate, and mechanical performance were also tested and are in line with previous results.

Hollow channels scaffold in bone regenerative: a review

Bone substitute materials have been extensively used for bone regeneration over the past 50 years. The development of novel materials, fabrication technologies and the incorporation and release of regenerative cytokines, growth factors, cells and antimicrobials has been driven by the rapid development in the field of additive manufacturing technology. There are still however, significant challenges that need addressing, including ways to better mediate the rapid vascularization of bone scaffolds to enhance subsequent regeneration and osteogenesis. Increasing construct porosity can accelerate the development of blood vessels in the scaffold, but doing so also weakens the constructs mechanical properties. A novel design for promoting rapid vascularization is to fabricate custom-made hollow channels as bone scaffolds. Summarized here are the current developments in hollow channels scaffold, including their biological attributes, physio-chemical properties, and effects on regeneration. An overview of recent developments in scaffold fabrication as they relate to hollow channel constructs and their structural features will be introduced with an emphasis on attributes that enhance new bone and vessel formation. Furthermore, the potential to enhance angiogenesis and osteogenesis by replicating the structure of real bone will be highlighted.

Chitosan, polyethylene oxide/polycaprolactone electrospun core/shell nanofibrous mat containing rosuvastatin as a novel drug delivery system for enhancing human mesenchymal stem cell osteogenesis

Introduction: Due to the potential positive effects of rosuvastatin (RSV) on human mesenchymal stem cells (MSCs) osteogenesis and new bone regeneration, it is crucial to develop a suitable carrier that can effectively control the release profile of RSV. The primary objective of this study was to introduce a novel drug delivery system based on core/shell nanofibrous structures, enabling a sustained release of RSV. Methods: To achieve this, coaxial electrospinning was employed to fabricate chitosan (CS)+polyethylene oxide (PEO)/polycaprolactone (PCL) nanofibrous mats, wherein RSV was incorporated within the core of nanofibers. By optimizing the relevant parameters of the electrospinning process, the mats' surface was further modified using plasma treatment. The fibers' shape, structure, and thermal stability were characterized. The wettability, and degradation properties of the fabricated mats were also examined. In vitro studies were conducted to examine the release behavior of RSV. Additionally, the capability of MSCs to survive and differentiate into osteocytes when cultured on nanofibers containing RSV was evaluated. Results: Results demonstrated the successful fabrication of CS + PEO + RSV/PCL core/shell mats with a core diameter of approximately 370 nm and a shell thickness of around 70 nm under optimized conditions. Plasma treatment was found to enhance the wettability and drug-release behavior of the mats. The nanofibrous structure, serving as a carrier for RSV, exhibited increased proliferation of MSCs and enhanced osteogenic differentiation. Conclusion: Therefore, it can be concluded that CS + PEO + RSV/PCL core/shell nanofibrous structure can be utilized as a sustained-release platform for RSV over an extended period, making it a promising candidate for guided bone regeneration.

Mesoporous Bioactive Nanoparticles for Bone Tissue Applications

Research in nanomaterials with applications in bone regeneration therapies has experienced a very significant advance with the development of bioactive mesoporous nanoparticles (MBNPs). These nanomaterials consist of small spherical particles that exhibit chemical properties and porous structures that stimulate bone tissue regeneration, since they have a composition similar to that of conventional sol-gel bioactive glasses and high specific surface area and porosity values. The rational design of mesoporosity and their ability to incorporate drugs make MBNPs an excellent tool for the treatment of bone defects, as well as the pathologies that cause them, such as osteoporosis, bone cancer, and infection, among others. Moreover, the small size of MBNPs allows them to penetrate inside the cells, provoking specific cellular responses that conventional bone grafts cannot perform. In this review, different aspects of MBNPs are comprehensively collected and discussed, including synthesis strategies, behavior as drug delivery systems, incorporation of therapeutic ions, formation of composites, specific cellular response and, finally, in vivo studies that have been performed to date.

Role of FGF-18 in Bone Regeneration

In tissue engineering, three key components are cells, biological/mechanical cues, and scaffolds. Biological cues are normally proteins such as growth factors and their derivatives, bioactive molecules, and the regulators of a gene. Numerous growth factors such as VEGF, FGF, and TGF-β are being studied and applied in different studies. The carriers used to release these growth factors also play an important role in their functioning. From the early part of the 1990s, more research has beenconductedon the role of fibroblast growth factors on the various physiological functions in our body. The fibroblast growth factor family contains 22 members. Fibroblast growth factors such as 2, 9, and 18 are mainly associated with the differentiation of osteoblasts and in bone regeneration. FGF-18 stimulates the PI3K/ERK pathway and smad1/5/8 pathway mediated via BMP-2 by blocking its antagonist, which is essential for bone formation. FGF-18 incorporated hydrogel and scaffolds had showed enhanced bone regeneration. This review highlights these functions and current trends using this growth factor and potential outcomes in the field of bone regeneration.

Development of bioactive electrospun scaffolds suitable to support skin fibroblasts and release Lucilia sericata maggot excretion/secretion

Larval therapy has been reported to be beneficial in the treatment of chronic wounds by promoting granulation tissue formation, due to its antimicrobial properties and by degrading necrotic tissue. However, the use of live maggots is problematic for patient acceptance, and thus there is a need to develop materials which can release therapeutic biomolecules derived from maggot secretions to the wound bed. Here we describe the fabrication of a novel bioactive scaffold that can be loaded with Lucilia sericata maggot alimentary excretion/secretion fluids (L. sericata maggot E/S), and which can also provide structural stability for mammalian cell-growth and migration to support wound repair. Electrospun scaffolds were prepared from a poly(caprolactone)-poly(ethylene glycol)–block copolymer (PCL-b-PEG) blended with PCL with average fibre diameters of ~ 4 μm. The scaffolds were hydrophilic and were able to support viable fibroblasts that were able to infiltrate throughout the extent of the scaffold thickness. L. sericata maggot (E/S) was subsequently adsorbed to the surface and released over 21 days with retention of the protease activity that is responsible for supporting fibroblast migration. The incorporation of L. sericata maggot E/S on the surface of the electrospun fibres of PCL-PEG/PCL fibres is a novel approach with potential for future application to support skin wound healing within a clinical setting.

ROS-responsive PPGF nanofiber membrane as a drug delivery system for long-term drug release in attenuation of osteoarthritis

Excessive reactive oxygen species (ROS) are one of the leading mechanisms in the initiation and development of osteoarthritis (OA). However, conventional injection of ROS-responsive drug delivery systems (DDSs) such as nanoparticles and hydrogels usually cannot provide effective treatment due to rapid clearance and degradation or low bioavailability. In this study, a ROS-responsive nanofiber membrane named PLA/PEGDA-EDT@rGO-Fucoxanthin (PPGF) is fabricated by electrospinning, wherein PEGDA-EDT served as the ROS-responsive motif, reduced graphene oxide (rGO) as the drug carrier and fucoxanthin (Fx) as the antioxidative and anti-inflammatory agent. The results demonstrated that the PPGF nanofiber membrane exhibited sustained and long-term Fx release behavior (at least 66 days) in response to hydrogen peroxide (H₂O₂) in vitro. With low cytotoxicity and smart ROS responsiveness, PPGF showed excellent anti-inflammatory and antioxidative effects on IL-1β-induced chondrocytes by potent ROS scavenging potential and upregulation of antioxidative enzymes. It also demonstrated the attenuation of OA progression with the reduced Osteoarthritis Research Society International (OARSI) score by 93.17% in 8 weeks. The smart ROS-responsive, biodegradable and biocompatible nanofiber membranes possess great potential for OA therapy under arthroscopy.

Diabetic bone regeneration with nanoceria-tailored scaffolds by recapitulating cellular microenvironment: Activating integrin/TGF-β co-signaling of MSCs while relieving oxidative stress

Regenerating defective bone in patients with diabetes mellitus remains a significant challenge due to high blood glucose level and oxidative stress. Here we aim to tackle this issue by means of a drug- and cell-free scaffolding approach. We found the nanoceria decorated on various types of scaffolds (fibrous or 3D-printed one; named nCe-scaffold) could render a therapeutic surface that can recapitulate the microenvironment: modulating oxidative stress while offering a nanotopological cue to regenerating cells. Mesenchymal stem cells (MSCs) recognized the nanoscale (tens of nm) topology of nCe-scaffolds, presenting highly upregulated curvature-sensing membrane protein, integrin set, and adhesion-related molecules. Osteogenic differentiation and mineralization were further significantly enhanced by the nCe-scaffolds. Of note, the stimulated osteogenic potential was identified to be through integrin-mediated TGF-β co-signaling activation. Such MSC-regulatory effects were proven in vivo by the accelerated bone formation in rat calvarium defect model. The nCe-scaffolds further exhibited profound enzymatic and catalytic potential, leading to effectively scavenging reactive oxygen species in vivo. When implanted in diabetic calvarium defect, nCe-scaffolds significantly enhanced early bone regeneration. We consider the currently-exploited nCe-scaffolds can be a promising drug- and cell-free therapeutic means to treat defective tissues like bone in diabetic conditions.

Effect of Angiogenesis in Bone Tissue Engineering

The reconstruction of large skeletal defects is still a tricky challenge in orthopedics. The newly formed bone tissue migrates sluggishly from the periphery to the center of the scaffold due to the restrictions of exchange of oxygen and nutrition impotent cells osteogenic differentiation. Angiogenesis plays an important role in bone reconstruction and more and more studies on angiogenesis in bone tissue engineering had been published. Promising advances of angiogenesis in bone tissue engineering by scaffold designs, angiogenic factor delivery, in vivo prevascularization and in vitro prevascularization are discussed in detail. Among all the angiogenesis mode, angiogenic factor delivery is the common methods of angiogenesis in bone tissue engineering and possible research directions in the future.

(Bio)manufactured Solutions for Treatment of Bone Defects with Emphasis on US-FDA Regulatory Science Perspective

Bone defects, with second highest demand for surgeries around the globe, may lead to serious health issues and negatively influence patient lives. The advances in biomedical engineering and sciences have led to the development of several creative solutions for bone defect treatment. This review provides a brief summary of bone graft materials, an organized overview of top-down and bottom-up (bio)manufacturing approaches, plus a critical comparison between advantages and limitations of each method. We specifically discuss additive manufacturing techniques and their operation mechanisms in detail. Next, we review the hybrid methods and promising future directions for bone grafting, while giving a comprehensive US-FDA regulatory science perspective, biocompatibility concepts and assessments, and clinical considerations to translate a technology from a research laboratory to the market. The topics covered in this review could potentially fuel future research efforts in bone tissue engineering, and perhaps could also provide novel insights for other tissue engineering applications.

Roles of the fibroblast growth factor signal transduction system in tissue injury repair

Following injury, tissue autonomously initiates a complex repair process, resulting in either partial recovery or regeneration of tissue architecture and function in most organisms. Both the repair and regeneration processes are highly coordinated by a hierarchy of interplay among signal transduction pathways initiated by different growth factors, cytokines and other signaling molecules under normal conditions. However, under chronic traumatic or pathological conditions, the reparative or regenerative process of most tissues in different organs can lose control to different extents, leading to random, incomplete or even flawed cell and tissue reconstitution and thus often partial restoration of the original structure and function, accompanied by the development of fibrosis, scarring or even pathogenesis that could cause organ failure and death of the organism. Ample evidence suggests that the various combinatorial fibroblast growth factor (FGF) and receptor signal transduction systems play prominent roles in injury repair and the remodeling of adult tissues in addition to embryonic development and regulation of metabolic homeostasis. In this review, we attempt to provide a brief update on our current understanding of the roles, the underlying mechanisms and clinical application of FGFs in tissue injury repair.

Multifunctional GelMA platforms with nanomaterials for advanced tissue therapeutics

Polymeric hydrogels are fascinating platforms as 3D scaffolds for tissue repair and delivery systems of therapeutic molecules and cells. Among others, methacrylated gelatin (GelMA) has become a representative hydrogel formulation, finding various biomedical applications. Recent efforts on GelMA-based hydrogels have been devoted to combining them with bioactive and functional nanomaterials, aiming to provide enhanced physicochemical and biological properties to GelMA. The benefits of this approach are multiple: i) reinforcing mechanical properties, ii) modulating viscoelastic property to allow 3D printability of bio-inks, iii) rendering electrical/magnetic property to produce electro-/magneto-active hydrogels for the repair of specific tissues (e.g., muscle, nerve), iv) providing stimuli-responsiveness to actively deliver therapeutic molecules, and v) endowing therapeutic capacity in tissue repair process (e.g., antioxidant effects). The nanomaterial-combined GelMA systems have shown significantly enhanced and extraordinary behaviors in various tissues (bone, skin, cardiac, and nerve) that are rarely observable with GelMA. Here we systematically review these recent efforts in nanomaterials-combined GelMA hydrogels that are considered as next-generation multifunctional platforms for tissue therapeutics. The approaches used in GelMA can also apply to other existing polymeric hydrogel systems.

Potent Particle-Based Vehicles for Growth Factor Delivery from Electrospun Meshes: Fabrication and Functionalization Strategies for Effective Tissue Regeneration

Functionalization of electrospun meshes with growth factors (GFs) is a common strategy for guiding specific cell responses in tissue engineering. GFs can exert their intended biological effects only when they retain their bioactivity and can be subsequently delivered in a temporally controlled manner. However, adverse processing conditions encountered in electrospinning can potentially disrupt GFs and diminish their biological efficacy. Further, meshes prepared using conventional approaches often promote an initial burst and rely solely on intrinsic fiber properties to provide extended release. Sequential delivery of multiple GFs─a strategy that mimics the natural tissue repair cascade─is also not easily achievable with traditional fabrication techniques. These limitations have hindered the effective use and translation of mesh-based strategies for tissue repair. An attractive alternative is the use of carrier vehicles (e.g., nanoparticles, microspheres) for GF incorporation into meshes. This review presents advances in the development of particle-integrated electrospun composites for safe and effective delivery of GFs. Compared to traditional approaches, we reveal how particles can protect GF activity, permit the incorporation of multiple GFs, decouple release from fiber properties, help achieve spatiotemporal control over delivery, enhance surface bioactivity, exert independent biological effects, and augment matrix mechanics. In presenting innovations in GF functionalization and composite engineering strategies, we also discuss specific in vitro and in vivo biological effects and their implications for diverse tissue engineering applications.

Current Biomaterial-Based Bone Tissue Engineering and Translational Medicine

Bone defects cause significant socio-economic costs worldwide, while the clinical "gold standard" of bone repair, the autologous bone graft, has limitations including limited graft supply, secondary injury, chronic pain and infection. Therefore, to reduce surgical complexity and speed up bone healing, innovative therapies are needed. Bone tissue engineering (BTE), a new cross-disciplinary science arisen in the 21st century, creates artificial environments specially constructed to facilitate bone regeneration and growth. By combining stem cells, scaffolds and growth factors, BTE fabricates biological substitutes to restore the functions of injured bone. Although BTE has made many valuable achievements, there remain some unsolved challenges. In this review, the latest research and application of stem cells, scaffolds, and growth factors in BTE are summarized with the aim of providing references for the clinical application of BTE.

Multi-functional silica-based mesoporous materials for simultaneous delivery of biologically active ions and therapeutic biomolecules

Mesoporous silica-based materials, especially mesoporous bioactive glasses (MBGs), are being highly considered for biomedical applications, including drug delivery and tissue engineering, not only because of their bioactivity and biocompatibility but also due to their tunable composition and potential use as drug delivery carriers owing to their controllable nanoporous structure. Numerous researches have reported that MBGs can be doped with various therapeutic ions (strontium, copper, magnesium, zinc, lithium, silver, etc.) and loaded with specific biomolecules (e.g., therapeutic drugs, antibiotics, growth factors) achieving controllable loading and release kinetics. Therefore, co-delivery of ions and biomolecules using a single MBG carrier is highly interesting as this approach provides synergistic effects toward improved therapeutic outcomes in comparison to the strategy of sole drug or ion delivery. In this review, we discuss the state-of-the-art in the field of mesoporous silica-based materials used for co-delivery of ions and therapeutic drugs with osteogenesis/cementogenesis, angiogenesis, antibacterial and anticancer properties. The analysis of the literature reveals that specially designed mesoporous nanocarriers can release multiple ions and drugs at therapeutically safe and relevant levels, achieving the desired biological effects (in vivo, in vitro) for specific biomedical applications. It is expected that this review on the ion/drug co-delivery concept using MBG carriers will shed light on the advantages of such co-delivery systems for clinical use. Areas for future research directions are identified and discussed. STATEMENT OF SIGNIFICANCE: Many studies in literature focus on the potential of single drug or ion delivery by mesoporous silica-based materials, exploiting the bioactivity, biocompatibility, tunable composition and controllable nanoporosity of these materials. Recenlty, studies have adopted the "dual-delivery" concept, by designing multi-functional mesoporous silica-based systems which are capable to deliver both biologically active ions and biomolecules (growth factors, drugs) simultaneously in order to achieve synergy of their complementary therapeutic activities. This review summarizes the state of the art in the field, with focus on osteogenesis/cementogenesis, angiogenesis, antibacterial and anticancer properties, and discusses the challenges and prospects for further progress in this area, expecting to generate broader interest in the technology for applications in disease treatment and regenerative medicine.

Rationally design of electrospun polysaccharides polymeric nanofiber webs by various tools for biomedical applications: A review

Nanofibers have a particular benefit when delivering a spectrum of therapeutic drugs for diverse biomedical applications. Nanofibers are easily fabricated from cellulose acetate, chitosan, polycaprolactone, and other polymers with regulated morphology and release profiles due to nanotechnology's recent advancement. This review will provide the latest approaches to the fabrication of electrospun nanofibers containing herbal extracts, antimicrobial peptides, and antibiotics for wound-healing potential. Besides, synthesis and evaluation of nanofibrous mats, including conducting polymer and evaluate their possibility for wound healing. In addition, nanofibers are loaded with some drugs for skin cancer treatment and contain growth factors for tissue regeneration. Also, the current two-dimensional nanofibers limitations and the various techniques for convert two-dimensional to three-dimension nanofibers to avoid these drawbacks. Moreover, the future direction in improving the three-dimensional structure and functionality has been including.

A network analysis of angiogenesis/osteogenesis-related growth factors in bone tissue engineering based on in-vitro and in-vivo data: A systems biology approach

The principal purpose of tissue engineering is to stimulate the injured or unhealthy tissues to revive their primary function through the simultaneous use of chemical agents, cells, and biocompatible materials. Still, choosing the appropriate protein as a growth factor (GF) for tissue engineering is vital to fabricate artificial tissues and accelerate the regeneration procedure. In this study, the angiogenesis and osteogenesis-related proteins' interactions are studied using their related network. Three major biological processes, including osteogenesis, angiogenesis, and angiogenesis regulation, were investigated by creating a protein-protein interaction (PPI) network (45 nodes and 237 edges) of bone regeneration efficient proteins. Furthermore, a gene ontology and a centrality analysis were performed to identify essential proteins within a network. The higher degree in this network leads to higher interactions between proteins and causes a considerable effect. The most highly connected proteins in the PPI network are the most remarkable for their employment. The results of this study showed that three significant proteins including prostaglandin endoperoxide synthase 2 (PTGS2), TEK receptor tyrosine kinase (TEK), and fibroblast growth factor 18 (FGF18) were involved simultaneously in osteogenesis, angiogenesis, and their positive regulatory. Regarding the available literature, the results of this study confirmed that PTGS2 and FGF18 could be used as a GF in bone tissue engineering (BTE) applications to promote angiogenesis and osteogenesis. Nevertheless, TEK was not used in BTE applications until now and should be considered in future works to be examined in-vitro and in-vivo.

Protein Adsorption on SiO2-CaO Bioactive Glass Nanoparticles with Controllable Ca Content

Bioactive glass nanoparticles (BGNs) are emerging multifunctional building blocks for various biomedical applications. In this study, the primary aim was to develop monodispersed binary SiO2-CaO BGNs with controllable Ca content. We successfully synthesized such spherical BGNs (size ~110 nm) using a modified Stöber method. Our results showed that the incorporated Ca did not significantly affect particle size, specific surface area, and structure of BGNs. Concentrations of CaO in BGN compositions ranging from 0 to 10 mol% could be obtained without the gap between actual and nominal compositions. For this type of BGNs (specific surface area 30 m2/g), the maximum concentration of incorporated CaO appeared to be ~12 mol%. The influence of Ca content on protein adsorption was investigated using bovine serum albumin (BSA) and lysozyme as model proteins. The amount of adsorbed proteins increased over time at the early stage of adsorption (<2 h), regardless of glass composition and protein type. Further incubation of BGNs with protein-containing solutions seemed to induce a reduced amount of adsorbed proteins, which was more significant in BGNs with higher Ca content. The results indicate that the Ca content in BGNs is related to their protein adsorption behavior.

Multidrug-loaded electrospun micro/nanofibrous membranes: Fabrication strategies, release behaviors and applications in regenerative medicine

Electrospun micro/nanofibrous membranes (EFMs) have been widely investigated as local drug delivery systems. Multiple drugs can be simultaneously incorporated into one EFM to create synergistic effects, reduce side effects, and play their respective roles in the complex physiological processes of tissue regeneration and postoperative adhesion prevention. Due to the versatile electrospinning techniques, sustained and programmed release behaviors of multiple drugs could be achieved by modulating the structure of the EFMs and the location of the drugs. In this review, various multidrug incorporation approaches based on electrospinning are overviewed. In particular, the advantages and limitations of each drug incorporation technique, the methods to control drug release and the effect of one drug release on another are discussed. Then the applications of multidrug-loaded EFMs in regenerative medicine, including wound healing, bone regeneration, vascular tissue engineering, nerve regeneration, periodontal regeneration and adhesion prevention are comprehensively reviewed. Finally, the future perspectives and challenges in the research of multidrug-loaded EFMs are discussed.

Porous bioactive glass micro- and nanospheres with controlled morphology: developments, properties and emerging biomedical applications

In recent years, porous bioactive glass micro/nanospheres (PBGSs) have emerged as attractive biomaterials in various biomedical applications where such engineered particles provide suitable functions, from tissue engineering to drug delivery. The design and synthesis of PBGSs with controllable particle size and pore structure are critical for such applications. PBGSs have been successfully synthesized using melt-quenching and sol-gel based methods. The morphology of PBGSs is controllable by tuning the processing parameters and precursor characteristics during the synthesis. In this comprehensive review on PBGSs, we first overview the synthesis approaches for PBGSs, including both melt-quenching and sol-gel based strategies. Sol-gel processing is the primary technology used to produce PBGSs, allowing for control over the chemical compositions and pore structure of particles. Particularly, the influence of pore-forming templates on the morphology of PBGSs is highlighted. Recent progress in the sol-gel synthesis of PBGSs with sophisticated pore structures (e.g., hollow mesoporous, dendritic fibrous mesoporous) is also covered. The challenges regarding the control of particle morphology, including the influence of metal ion precursors and pore expansion, are discussed in detail. We also highlight the recent achievements of PBGSs in a number of biomedical applications, including bone tissue regeneration, wound healing, therapeutic agent delivery, bioimaging, and cancer therapy. Finally, we conclude with our perspectives on the directions of future research based on identified challenges and potential new developments and applications of PBGSs.

Advances in Growth Factor Delivery for Bone Tissue Engineering

Shortcomings related to the treatment of bone diseases and consequent tissue regeneration such as transplants have been addressed to some extent by tissue engineering and regenerative medicine. Tissue engineering has promoted structures that can simulate the extracellular matrix and are capable of guiding natural bone repair using signaling molecules to promote osteoinduction and angiogenesis essential in the formation of new bone tissues. Although recent studies on developing novel growth factor delivery systems for bone repair have attracted great attention, taking into account the complexity of the extracellular matrix, scaffolding and growth factors should not be explored independently. Consequently, systems that combine both concepts have great potential to promote the effectiveness of bone regeneration methods. In this review, recent developments in bone regeneration that simultaneously consider scaffolding and growth factors are covered in detail. The main emphasis in this overview is on delivery strategies that employ polymer-based scaffolds for spatiotemporal-controlled delivery of both single and multiple growth factors in bone-regeneration approaches. From clinical applications to creating alternative structural materials, bone tissue engineering has been advancing constantly, and it is relevant to regularly update related topics.

Combinatorial effect of nano whitlockite/nano bioglass with FGF-18 in an injectable hydrogel for craniofacial bone regeneration

Comparing the bone regeneration potential of nano whitlockite or nano bioglass in combination with FGF-18, loaded in an injectable, shear-thinning chitin/PLGA hydrogel for craniofacial bone regeneration.

Effectiveness of Core-Shell Nanofibers Incorporating Amphotericin B by Solution Blow Spinning Against Leishmania and Candida Species

The aim of this study was to develop polymeric nanofibers for controlled administration of Amphotericin B (AmpB), using the solution centrifugation technique, characterizing its microstructural and physical properties, release rate, and activity against Leishmania and Candida species. The core-shell nanofibers incorporated with AmpB were synthesized by Solution Blow Spinning (SBS) and characterized by scanning electron microscopy (SEM), differential scanning calorimetry, X-Ray diffraction, and drug release assay. In vitro leishmanicidal and antifungal activity were also evaluated. Fibrous membranes with uniform morphology and smooth surfaces were produced. The intensity of the diffraction peaks becomes slightly more pronounced, assuming the increased crystallization in PLA/PEG at high AmpB loadings. Drug release occurred and the solutions with nanofibers to encourage greater incorporation of AmpB showed a higher concentration. In the results of the experiment with promastigotes, the wells treated with nanofibers containing concentrations of AmpB at 0.25, 0.5, and 1%, did not have any viable cells, similar to the positive control. Various concentrations of AmpB improved the inhibition of fungal growth. The delivery system based on PLA/PEG nanofibers was properly developed for AmpB, presenting a controlled release and a successful encapsulation, as well as antifungal and antileishmanial activity.

FGF/FGFR signaling in health and disease

Growing evidences suggest that the fibroblast growth factor/FGF receptor (FGF/FGFR) signaling has crucial roles in a multitude of processes during embryonic development and adult homeostasis by regulating cellular lineage commitment, differentiation, proliferation, and apoptosis of various types of cells. In this review, we provide a comprehensive overview of the current understanding of FGF signaling and its roles in organ development, injury repair, and the pathophysiology of spectrum of diseases, which is a consequence of FGF signaling dysregulation, including cancers and chronic kidney disease (CKD). In this context, the agonists and antagonists for FGF-FGFRs might have therapeutic benefits in multiple systems.

Nanostructured Biomaterials for Bone Regeneration

This review article addresses the various aspects of nano-biomaterials used in or being pursued for the purpose of promoting bone regeneration. In the last decade, significant growth in the fields of polymer sciences, nanotechnology, and biotechnology has resulted in the development of new nano-biomaterials. These are extensively explored as drug delivery carriers and as implantable devices. At the interface of nanomaterials and biological systems, the organic and synthetic worlds have merged over the past two decades, forming a new scientific field incorporating nano-material design for biological applications. For this field to evolve, there is a need to understand the dynamic forces and molecular components that shape these interactions and influence function, while also considering safety. While there is still much to learn about the bio-physicochemical interactions at the interface, we are at a point where pockets of accumulated knowledge can provide a conceptual framework to guide further exploration and inform future product development. This review is intended as a resource for academics, scientists, and physicians working in the field of orthopedics and bone repair.

Fabrication of poly(acrylic acid) grafted-chitosan/polyurethane/magnetic MIL-53 metal organic framework composite core-shell nanofibers for co-delivery of temozolomide and paclitaxel against glioblastoma cancer cells

In the present study, the magnetic MIL-53 nanometal organic framework particles (NMOFs) were incorporated into poly(acrylic acid) grafted-chitosan/polyurethane (PA-g-CS/PU) core-shell nanofibers for controlled release of temozolomide (TMZ) and paclitaxel (PTX) against U-87 MG glioblastoma cells during chemotherapy/hyperthermia combined method. The synthesized magnetic MIL-53 NMOFs and NMOF-loaded nanofibers were characterized using X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), Fourier transformed infrared (FTIR), vibrating-sample magnetometer (VSM) and scanning electron microscopy (SEM) analysis. The TMZ and PTX release profiles from magnetic MIL-53 5 wt% loaded-CS-g-PAA-PTX-TMZ/PU fibers were investigated under acidic and physiological pH at temperatures of 37 and 43 °C. The effect of hyperthermia on the release rate of TMZ and PTX from magnetic nanofibers was investigated. An alternating magnetic field could induce the mild hyperthermia (43 °C) for the cells treated with magnetic MIL-53 5 wt% loaded-CS-g-PAA-PTX-TMZ/PU fibers during 10 min. The release data were best described by the non-Fickian diffusion of Korsmeyer-Peppas equation. The cell viability, flowcytometry and Bcl-2, Bax expression levels were investigated to obtain the optimum nanofibrous carrier for apoptosis of U-87 MG cells in vitro. The obtained results indicated that the synthesized magnetic MIL-53 NMOFs loaded- PA-g-CS/PU/TMZ-PTX nanofibers (shell flow rate: 0.8 mLh^-1) could be used as a targeted delivery of anticancer agents with maximum apoptosis of 49.6% of U-87 MG glioblastoma cells under AMF during chemotherapy/hyperthermia combination therapy.

The response of host blood vessels to graded distribution of macro-pores size in the process of ectopic osteogenesis

Angiogenesis is of great importance to bone regeneration, but it remains a significant challenge to induce sufficient angiogenesis and osteogenesis within bone grafts for large bone defect healing. The aim of this study is to investigate the effects of hydroxyapatite (HA) scaffold via a novel graded pore distribution approach on vascularization and osteoinduction. Two types of graded porous scaffolds were fabricated by sugar templates-leaching techniques: (1) one with large pores of 1100-1250 μm in the center and small pores of 500-650 μm at the periphery (HALS); (2) the other with small pores of 500-650 μm in the center and large pores of 1100-1250 μm at the periphery (HASL). In vivo data showed different pore size distribution had a remarkable impact on blood vessel formation during bone formation, which led to distinct localization of new bone within the defects. After one month of implantation, the diameters of the blood vessels infiltrated on the periphery of HASL were substantially larger than those in the center though the host blood vessels were successful in infiltrating throughout the whole scaffold. In contrast, vascularization within HALS appeared to be poor with very few blood vessels formed in the center, indicating heterogeneous vascularization in the scaffolds. After 3 months of implantation, we found that HASL induced more homogeneous bone formation in the whole bone graft but new bone was only found at the periphery of HALS. This study suggests that the pores size distribution in graded scaffolds cannot only affected early stage vascularization, but also influence late stage bone formation and remodeling. The architecture of larger pores at the periphery of graded scaffold may be capable of enhancing angiogenesis and osteogenesis during large size bone defect healing.

Reactions of Subcutaneous Connective Tissue to Mineral Trioxide Aggregate, Biodentine®, and a Newly Developed BioACTIVE Base/Liner

AIM

There is an increasing interest in the application of BioACTIVE materials to achieve hard tissue formation and maintain pulp vitality. Mineral trioxide aggregate (MTA) and Biodentine® are BioACTIVE materials used for pulp capping. Recently, dental researchers have produced BioACTIVE glass-incorporated light-curable pulp capping material. The study is aimed at evaluating the subcutaneous connective tissue reactions to MTA, Biodentine®, ACTIVA BioACTIVE Base/Liner. These materials were placed in polyethylene tubes and implanted into the dorsal connective tissue of Sprague Dawley rats. The presence of inflammation, predominant cell type, calcification, and thickness of fibrous connective tissue was recorded by histological examination 7, 30, and 60 days after the implantation procedure. Scores were defined as follows: 0 = none or few inflammatory cells, no reaction; 1 = <25 cells, mild reaction; 2 = 25 to 125 cells, moderate reaction; and 3 = ≥125 cells, severe reaction. Fibrous capsule thickness, necrosis, and formation of calcification were recorded. ANOVA and post hoc Dunnett's tests were used for statistically analyses (p < 0.05).

RESULTS

In terms of oedema, inflammation, fibrous capsule, and necrosis, no significant differences were found in any time period for any material. MTA and Biodentine® showed higher calcification than in the ACTIVA BioACTIVE on day 30, and the difference was statistically significant (p < 0.05). After 60 days, while calcification was not seen in the control group, it was observed in the test groups. There was a statistically significant difference between the control and the others.

CONCLUSION

All materials were well tolerated by the tissues in the 60-day evaluation period. One notable finding is the presence of dystrophic calcification in the connective tissue adjacent to the newly developed BioACTIVE Base/Liner material. Therefore, this new BioACTIVE Base/Liner material may be safely recommended to clinicians as a pulp capping material.

Electrospun Poly (Aspartic Acid)-Modified Zein Nanofibers for Promoting Bone Regeneration

Background

Critical-sized bone defects raise great challenges. Zein is of interest for bone regeneration, but it has limited ability to stimulate cell proliferation. In this regard, a poly (aspartic acid) (PAsp)-zein hybrid is promising, as PAsp can promote rat bone marrow stromal cell (rBMSCs) proliferation and osteogenic differentiation. This research aimed to develop electrospun PAsp-modified zein nanofibers to realize critical-sized bone defects repair.

Methods

Three groups of PAsp-modified zein nanofibers were prepared, they were PAsp grafting percentages of 0% (zein), 5.32% (ZPAA-1), and 7.63% (ZPAA-2). Using rBMSCs as in vitro cell model and SD rats as in vivo animal model, fluorescence staining, SEM, CCK-8, ALP, ARS staining, μCT and histological analysis were performed to verify the biological and osteogenic activities for PAsp-modified zein nanofibers.

Results

As the Asp content increased from 0% to 7.63%, the water contact angle decreased from 129.8 ± 2.3° to 105.5 ± 2.5°. SEM, fluorescence staining and CCK-8 assay showed that ZPAA-2 nanofibers had a superior effect on rBMSCs spreading and proliferation than did zein and ZPAA-1 nanofibers, ALP activity and ARS staining showed that ZPAA-2 can improve rBMSCs osteogenic differentiation. In vivo osteogenic activities was evaluated by μCT analysis, HE, Masson and immunohistochemical staining, indicating accelerated bone formation in ZPAA-2 SD rats after 4 and 8 weeks treatment, with a rank order of ZPAA-2 > ZPAA-1 > zein group. Moreover, the semiquantitative results of the Masson staining revealed that the maturity of the new bone was higher in the ZPAA-2 group than in the other groups.

Conclusion

Electrospun PAsp-modified zein can provide a suitable microenvironment for osteogenic differentiation of rBMSCs, as well as for bone regeneration; the optimal membrane appears to have a PAsp grafting percentage of 7.63%.

Mesoporous bioactive glasses for bone healing and biomolecules delivery

Impact of bone diseases and injury is increasing at an enormous rate during the past decades due to increase in road traffic accidents and other injuries. Bioactive glasses have excellent biocompatibility and osteoconductivity that makes it suitable for bone regeneration. Researches and studies conducted on several bioactive glasses gives an insight on the need of multi-disciplinary approaches involving various scientific fields to attain its full potential. Of late, a next generation bioactive glass called as mesoporous bioactive glass (MBG) has been developed with higher specific surface area and control over mesoporous structure that presents a new material for bone regeneration. A brief discussion and overview on the potential use of MBG as a suitable material for bone tissue regeneration and biomolecule delivery is included. Additionally, possible control of the structural and functional property based on composition and fabrication techniques are also covered. According to recent researches, MBG-implant interaction with bone forming cells for cellular growth and differentiation as well as its effect on delivery of growth factor, both in vitro and in vivo, are optimistic; yet, the complete efficacy of this material is still to be explored. Hence, in this article we will review the current development and its applications for bone tissue engineering (TE).

Sequential drug delivery for liver diseases

The liver performs critical physiological functions such as metabolism/detoxification and blood homeostasis/biliary excretion. A high degree of blood access means that a drug's resident time in any cell is relatively short. This short drug exposure to cells requires local sequential delivery of multiple drugs for optimal efficacy, potency, and safety. The high metabolism and excretion of drugs also impose both technical challenges and opportunities to sequential drug delivery. This review provides an overview of the sequential events in liver regeneration and the related liver diseases. Using selected examples of liver cancer, hepatitis B viral infection, fatty liver diseases, and drug-induced liver injury, we highlight efforts made for the sequential delivery of small and macromolecular drugs through different biomaterials, cells, and microdevice-based delivery platforms that allow fast delivery kinetics and rapid drug switching. As this is a nascent area of development, we extrapolate and compare the results with other sequential drug delivery studies to suggest possible application in liver diseases, wherever appropriate.

Scaffold-mediated sequential drug/gene delivery to promote nerve regeneration and remyelination following traumatic nerve injuries

Neural tissue regeneration following traumatic injuries is often subpar. As a result, the field of neural tissue engineering has evolved to find therapeutic interventions and has seen promising outcomes. However, robust nerve and myelin regeneration remain elusive. One possible reason may be the fact that tissue regeneration often follows a complex sequence of events in a temporally-controlled manner. Although several other fields of tissue engineering have begun to recognise the importance of delivering two or more biomolecules sequentially for more complete tissue regeneration, such serial delivery of biomolecules in neural tissue engineering remains limited. This review aims to highlight the need for sequential delivery to enhance nerve regeneration and remyelination after traumatic injuries in the central nervous system, using spinal cord injuries as an example. In addition, possible methods to attain temporally-controlled drug/gene delivery are also discussed for effective neural tissue regeneration.

Supercritical CO2 foamed composite scaffolds incorporating bioactive lipids promote vascularized bone regeneration via Hif-1α upregulation and enhanced type H vessel formation

Bone tissue engineering has substantial potential for the treatment of massive bone defects; however, efficient vascularization coupled with bone regeneration still remains a challenge in this field. In the current study, supercritical carbon dioxide (scCO₂) foaming technique was adopted to fabricate mesoporous bioactive glasses (MBGs) particle-poly (lactic-co-glycolic acid) (PLGA) composite scaffolds with appropriate mechanical and degradation properties as well as in vitro bioactivity. The MBG-PLGA scaffolds incorporating the bioactive lipid FTY720 (designated as FTY/MBG-PLGA) exhibited simultaneously sustained release of the bioactive lipid and ions. In addition to providing a favorable microenvironment for cellular adhesion and proliferation, FTY/MBG-PLGA scaffolds significantly facilitated the in vitro osteogenic differentiation of rBMSCs and also markedly stimulated the upregulation of Hif-1α expression via the activation of the Erk1/2 pathway, which mediated the osteogenic and pro-angiogenic effects on rBMSCs. Furthermore, FTY/MBG-PLGA extracts induced superior in vitro angiogenic performance of HUVECs. In vivo evaluation of critical-sized rat calvarial bone defects indicated that FTY/MBG-PLGA scaffolds potently promoted vascularized bone regeneration. Notably, the significantly enhanced formation of type H vessels (CD31^hiEmcn^hi neo-vessels) was observed in newly formed bone tissue in FTY/MBG-PLGA group, strongly suggesting that FTY720 and therapeutic ions released from the scaffolds synergistically induced more type H vessel formation, which indicated the coupling of angiogenesis and osteogenesis to achieve efficiently vascularized bone regeneration. Overall, the results indicated that the foamed porous MBG-PLGA scaffolds incorporating bioactive lipids achieved desirable vascularization-coupled bone formation and could be a promising strategy for bone regenerative medicine. STATEMENT OF SIGNIFICANCE: Efficacious coupling of vascularizationandbone formation is critical for the restoration of large bone defects. Anoveltechnique was used to fabricate composite scaffolds incorporating bioactive lipids which possessedsynergistic cues of bioactive lipids and therapeutic ions to potently promotebone regenerationas well as vascularization. The underlying molecular mechanism for the osteogenic and pro-angiogenic effects of the compositescaffolds was unveiled. Interestingly, the scaffolds were furtherfoundto enhance the formation oftype H capillarieswithin the bone healing microenvironment to couple angiogenesis to osteogenesis to achieve satisfyingvascularizedbone regeneration.These findings provide a novel strategy to develop efficiently vascularized engineering constructs to treat massive bone defects.

Biomaterial-assisted local and systemic delivery of bioactive agents for bone repair

Although bone tissues possess an intrinsic capacity for repair, there are cases where bone healing is either impaired or insufficient, such as fracture non-union, osteoporosis, osteomyelitis, and cancers. In these cases, treatments like surgical interventions are used, either alone or in combination with bioactive agents, to promote tissue repair and manage associated clinical complications. Improving the efficacy of bioactive agents often requires carriers, with biomaterials being a pivotal player. In this review, we discuss the role of biomaterials in realizing the local and systemic delivery of biomolecules to the bone tissue. The versatility of biomaterials enables design of carriers with the desired loading efficiency, release profile, and on-demand delivery. Besides local administration, systemic administration of drugs is necessary to combat diseases like osteoporosis, warranting bone-targeting drug delivery systems. Thus, chemical moieties with the affinity towards bone extracellular matrix components like apatite minerals have been widely utilized to create bone-targeting carriers with better biodistribution, which cannot be achieved by the drugs alone. Bone-targeting carriers combined with the desired drugs or bioactive agents have been extensively investigated to enhance bone healing while minimizing off-target effects. Herein, these advancements in the field have been systematically reviewed. STATEMENT OF SIGNIFICANCE: Drug delivery is imperative when surgical interventions are not sufficient to address various bone diseases/defects. Biomaterial-assisted delivery systems have been designed to provide drugs with the desired loading efficiency, sustained release, and on-demand delivery to enhance bone healing. By surveying recent advances in the field, this review outlines the design of biomaterials as carriers for the local and systemic delivery of bioactive agents to the bone tissue. Particularly, biomaterials that bear chemical moieties with affinity to bone are attractive, as they can present the desired bioactive agents to the bone tissue efficiently and thus enhance the drug efficacy for bone repair.

Sintered electrospun polycaprolactone for controlled model drug delivery

Electrospinning has been used widely for drug delivery applications due to its versatility and ease of modification of spun fiber properties. Net drug loading and release is typically limited by the inherent surface-area of the sample. In a relatively novel approach, sintering of electrospun fiber was used to create a capsule favoring long-term delivery. We showed that electrospun polycaprolactone (PCL) retained its initial morphology out to 1042 days of in vitro exposure, illustrating its potential for extended performance. Sintering decreased the electrospun pore size by 10- and 28-fold following 56 and 57 °C exposures, respectively. At 58 and 59 °C, the PCL capsules lost all apparent surface porosity, but entrapped pores were observed in the 58 °C cross-section. The use of Rhodamine B (RhB, 479.02 g mol^-1), Rose Bengal (RB, 1017.64 g mol^-1) and albumin-fluorescein isothiocyanate conjugate from bovine serum (BSA-FITC, ~66,000 g mol^-1) as model compounds demonstrated that release (RhB > RB ≫ BSA-FITC) is controlled both by molecular weight and available porosity. Interestingly, the ranking of release following sintering was 57 > 56 > 59 > 58 °C; COMSOL simulations explored the effects of capsule wall thickness and porosity on release rate. It was hypothesized that model drug adsorption on the available fiber surface-area (57 versus 56 °C) and entrapped porosity (59 versus 58 °C) could have also attributed to the observed ranking of release rates. While the 56 and 57 °C exposures allowed the bulk of the release to occur in <1 day, the capsules sintered at 58 and 59 °C exhibited release that continued after 12 days of exposure.

Materials Science and Design Principles of Growth Factor Delivery Systems in Tissue Engineering and Regenerative Medicine

Growth factors (GFs) are signaling molecules that direct cell development by providing biochemical cues for stem cell proliferation, migration, and differentiation. GFs play a key role in tissue regeneration, but one major limitation of GF-based therapies is dosage-related adverse effects. Additionally, the clinical applications and efficacy of GFs are significantly affected by the efficiency of delivery systems and other pharmacokinetic factors. Hence, it is crucial to design delivery systems that provide optimal activity, stability, and tunable delivery for GFs. Understanding the physicochemical properties of the GFs and the biomaterials utilized for the development of biomimetic GF delivery systems is critical for GF-based regeneration. Many different delivery systems have been developed to achieve tunable delivery kinetics for single or multiple GFs. The identification of ideal biomaterials with tunable properties for spatiotemporal delivery of GFs is still challenging. This review characterizes the types, properties, and functions of GFs, the materials science of widely used biomaterials, and various GF loading strategies to comprehensively summarize the current delivery systems for tunable spatiotemporal delivery of GFs aimed for tissue regeneration applications. This review concludes by discussing fundamental design principles for GF delivery vehicles based on the interactive physicochemical properties of the proteins and biomaterials.

Additive manufacturing of bone scaffolds

Additive manufacturing (AM) can obtain not only customized external shape but also porous internal structure for scaffolds, both of which are of great importance for repairing large segmental bone defects. The scaffold fabrication process generally involves scaffold design, AM, and post-treatments. Thus, this article firstly reviews the state-of-the-art of scaffold design, including computer-aided design, reverse modeling, topology optimization, and mathematical modeling. In addition, the current characteristics of several typical AM techniques, including selective laser sintering, fused deposition modeling (FDM), and electron beam melting (EBM), especially their advantages and limitations are presented. In particular, selective laser sintering is able to obtain scaffolds with nanoscale grains, due to its high heating rate and a short holding time. However, this character usually results in insufficient densification. FDM can fabricate scaffolds with a relative high accuracy of pore structure but with a relative low mechanical strength. EBM with a high beam-material coupling efficiency can process high melting point metals, but it exhibits a low-resolution and poor surface quality. Furthermore, the common post-treatments, with main focus on heat and surface treatments, which are applied to improve the comprehensive performance are also discussed. Finally, this review also discusses the future directions for AM scaffolds for bone tissue engineering.

Composite Hydrogels with the Simultaneous Release of VEGF and MCP-1 for Enhancing Angiogenesis for Bone Tissue Engineering Applications

Rapid new microvascular network induction was critical for bone regeneration, which required the spatiotemporal delivery of growth factors and transplantation of endothelial cells. In this study, the linear poly(d,l-lactic-co-glycolic acid)-b-methoxy poly(ethylene glycol) (PLGA-mPEG) block copolymer microspheres were prepared for simultaneously delivering vascular endothelial growth factor (VEGF) and monocyte chemotactic protein-1 (MCP-1). Then, vascular endothelial cells (VECs) with growth factor loaded microspheres were composited into a star-shaped PLGA-mPEG block copolymer solution. After this, composite hydrogel (microspheres ratio: 5 wt%) was formed by increasing the temperature to 37 °C. The release profiles of VEGF and MCP-1 from composite hydrogels in 30 days were investigated to confirm the different simultaneous delivery systems. The VECs exhibited a good proliferation in the composite hydrogels, which proved that the composite hydrogels had a good cytocompatibility. Furthermore, in vivo animal experiments showed that the vessel density and the mean vessel diameters increased over weeks after the composite hydrogels were implanted into the necrosis site of the rabbit femoral head. The above results suggested that the VECs-laden hydrogel composited with the dual-growth factor simultaneous release system has the potential to enhance angiogenesis in bone tissue engineering.

Tunable 3D Nanofiber Architecture of Polycaprolactone by Divergence Electrospinning for Potential Tissue Engineering Applications

The creation of biomimetic cell environments with micro and nanoscale topographical features resembling native tissues is critical for tissue engineering. To address this challenge, this study focuses on an innovative electrospinning strategy that adopts a symmetrically divergent electric field to induce rapid self-assembly of aligned polycaprolactone (PCL) nanofibers into a centimeter-scale architecture between separately grounded bevels. The 3D microstructures of the nanofiber scaffolds were characterized through a series of sectioning in both vertical and horizontal directions. PCL/collagen (type I) nanofiber scaffolds with different density gradients were incorporated in sodium alginate hydrogels and subjected to elemental analysis. Human fibroblasts were seeded onto the scaffolds and cultured for 7 days. Our studies showed that the inclination angle of the collector had significant effects on nanofiber attributes, including the mean diameter, density gradient, and alignment gradient. The fiber density and alignment at the peripheral area of the 45°-collector decreased by 21% and 55%, respectively, along the z-axis, while those of the 60°-collector decreased by 71% and 60%, respectively. By altering the geometry of the conductive areas on the collecting bevels, polyhedral and cylindrical scaffolds composed of aligned fibers were directly fabricated. By using a four-bevel collector, the nanofibers formed a matrix of microgrids with a density of 11%. The gradient of nitrogen-to-carbon ratio in the scaffold-incorporated hydrogel was consistent with the nanofiber density gradient. The scaffolds provided biophysical stimuli to facilitate cell adhesion, proliferation, and morphogenesis in 3D.

Current state of fabrication technologies and materials for bone tissue engineering

A range of traditional and free-form fabrication technologies have been investigated and, in numerous occasions, commercialized for use in the field of regenerative tissue engineering (TE). The demand for technologies capable of treating bone defects inherently difficult to repair has been on the rise. This quest, accompanied by the advent of functionally tailored, biocompatible, and biodegradable materials, has garnered an enormous research interest in bone TE. As a result, different materials and fabrication methods have been investigated towards this end, leading to a deeper understanding of the geometrical, mechanical and biological requirements associated with bone scaffolds. As our understanding of the scaffold requirements expands, so do the capability requirements of the fabrication processes. The goal of this review is to provide a broad examination of existing scaffold fabrication processes and highlight future trends in their development. To appreciate the clinical requirements of bone scaffolds, a brief review of the biological process by which bone regenerates itself is presented first. This is followed by a summary and comparisons of commonly used implant techniques to highlight the advantages of TE-based approaches over traditional grafting methods. A detailed discussion on the clinical and mechanical requirements of bone scaffolds then follows. The remainder of the manuscript is dedicated to current scaffold fabrication methods, their unique capabilities and perceived shortcomings. The range of biomaterials employed in each fabrication method is summarized. Selected traditional and non-traditional fabrication methods are discussed with a highlight on their future potential from the authors' perspective. This study is motivated by the rapidly growing demand for effective scaffold fabrication processes capable of economically producing constructs with intricate and precisely controlled internal and external architectures. STATEMENT OF SIGNIFICANCE: The manuscript summarizes the current state of fabrication technologies and materials used for creating scaffolds in bone tissue engineering applications. A comprehensive analysis of different fabrication methods (traditional and free-form) were summarized in this review paper, with emphasis on recent developments in the field. The fabrication techniques suitable for creating scaffolds for tissue engineering was particularly targeted and their use in bone tissue engineering were articulated. Along with the fabrication techniques, we emphasized the choice of materials in these processes. Considering the limitations of each process, we highlighted the materials and the material properties critical in that particular process and provided a brief rational for the choice of the materials. The functional performance for bone tissue engineering are summarized for different fabrication processes and the choice of biomaterials. Finally, we provide a perspective on the future of the field, highlighting the knowledge gaps and promising avenues in pursuit of effective scaffolds for bone tissue engineering. This extensive review of the field will provide research community with a reference source for current approaches to scaffold preparation. We hope to encourage the researchers to generate next generation biomaterials to be used in these fabrication processes. By providing both advantages and disadvantage of each fabrication method in detail, new fabrication techniques might be devised that will overcome the limitations of the current approaches. These studies should facilitate the efforts of researchers interested in generating ideal scaffolds, and should have applications beyond the repair of bone tissue.