Polydopamine-Templated Hydroxyapatite Reinforced Polycaprolactone Composite Nanofibers with Enhanced Cytocompatibility and Osteogenesis for Bone Tissue Engineering

Polydopamine-induced biomimetic mineralization strategy to generate hydroxyapatite for the preparation of carbon fiber composites with excellent mechanical properties

Living organisms have developed a miraculous biomineralization strategy to form multistage organic-inorganic composites through the orderly assembly of hard/soft substances, achieving mechanical enhancement of materials from the nanoscale to the macroscale. Inspired by biominerals, this study used polydopamine (PDA) coating as a template to induce the growth of hydroxyapatite (HAP) on the surface of carbon fibers (CFs) for enhancing the interfacial properties of the CF/epoxy resin composites. This polydopamine-assisted hydroxyapatite formation (pHAF) biomimetic mineralization strategy constructs soft/hard ordered structure on the CF surface, which not only improves the chemical reaction activity of the CFs but also increases the fiber surface roughness. This, in turn, enhances the interaction and loading delivery among the fibers and the matrix. Compared to the untreated carbon fiber/epoxy resin (CF/EP) composites, the prepared composites showed a substantial enhancement in interlaminar shear strength (ILSS), flexural strength, and interfacial shear strength (IFSS), with improvements of 45.2 %, 46.9 %, and 60.5 %, respectively. This can be attributed to the HAP nanolayers increasing the adhesion and mechanical interlocking with the CFs to the matrix. This study provides an interface modification method of biomimetic mineralization for the preparation of high strength CF composites.

Bioinspired core-shell nanofiber drug-delivery system modulates osteogenic and osteoclast activity for bone tissue regeneration

Osteogenic-osteoclast coupling processes play a crucial role in bone regeneration. Recently, strategies that focus on multi-functionalized implant surfaces to enhance the healing of bone defects through the synergistic regulation of osteogenesis and osteoclastogenesis is still a challenging task in the field of bone tissue engineering. The aim of this study was to create a dual-drug release-based core-shell nanofibers with the intent of achieving a time-controlled release to facilitate bone regeneration. We fabricated core-shell P/PCL nanofibers using coaxial electrospinning, where alendronate (ALN) was incorporated into the core layer and hydroxyapatite (HA) into shell. The surface of the nanofiber construct was further modified with mussel-derived polydopamine (PDA) to induce hydrophilicity and enhance cell interactions. Surface characterizations confirmed the successful synthesis of PDA@PHA/PCL-ALN nanofibers endowed with excellent mechanical strength (20.02 ± 0.13 MPa) and hydrophilicity (22.56°), as well as the sustained sequential release of ALN and Ca ions. In vitro experiments demonstrated that PDA-functionalized core-shell PHA/PCL-ALN scaffolds possessed excellent cytocompatibility, enhanced cell adhesion and proliferation, alkaline phosphatase activity and osteogenesis-related genes. In addition to osteogenesis, the engineered scaffolds also significantly reduced osteoclastogenesis, such as tartrate-resistant acid phosphatase activity and osteoclastogenesis-related gene expression. After 12-week of implantation, it was observed that PDA@PHA/PCL-ALN nanofiber scaffolds, in a rat cranial defect model, significantly promoted bone repair and regeneration. Microcomputed tomography, histological examination, and immunohistochemical analysis collectively demonstrated that the PDA-functionalized core-shell PHA/PCL-ALN scaffolds exhibited exceptional osteogenesis-inducing and osteoclastogenesis-inhibiting effects. Finally, it may be concluded from our results that the bio-inspired surface-functionalized multifunctional, biomimetic and controlled release core-shell nanofiber provides a promising strategy to facilitate bone healing.

Electrospun fibers modified with polydopamine for enhancing human mesenchymal stem cell culture

In this study, we coated electrospun polycaprolactone (PCL) fibers with polydopamine (PDA) to modify their hydrophobicity and fabricated a matrix for culturing mesenchymal stem cells (MSCs). Additionally, we incorporated Arg-Gly-Asp (RGD) peptides into PDA to enhance MSCs culture performance on PCL fibers. PDA and RGD were successfully coated in one step by immersing the electrospun fibers in a coating solution, without requiring an additional surface activation process. The characteristics of functionalized PCL fibers were analyzed by scanning electron microscopy with energy-dispersive x-ray analysis, Fourier transform infrared spectroscopy, water contact angle measurement, and fluorescence measurements using a carboxylic-modified fluorescent microsphere. MSCs cultured on the modified PCL fibers demonstrated enhanced cell adhesion, proliferation, and osteogenic- and chondrogenic differentiation. This study provides insight into potential applications for scaffold fabrication in MSCs-based tissue engineering, wound dressing, implantation, and a deeper understanding of MSCs behaviorin vitro.

Bioinspired poly-dopamine/nano-hydroxyapatite: an upgrading biocompatible coat for 3D-printed polylactic acid scaffold for bone regeneration

Poly-lactic acid (PLA) has been proposed in dentistry for several regenerative procedures owing to its biocompatibility and biodegradability. However, the presence of methyl groups renders PLA hydrophobic, making the surface less ideal for cell attachment, and it does not promote tissue regeneration. Upgrading PLA with inductive biomaterial is a crucial step to increase the bioactivity of the PLA and allow cellular adhesion. Our purpose is to evaluate biocompatibility, bioactivity, cellular adhesion, and mechanical properties of 3D-printed PLA scaffold coated with poly-dopamine (PDA) and nano-hydroxyapatite (n-HA) versus PLA and PLA/n-HA scaffolds. The fused deposition modelling technique was used to print PLA, PLA with embedded n-HA particles, and PLA scaffold coated with PDA/n-HA by immersion. After matrices characterization for their chemical composition and surface properties, testing the compressive strength was pursued using a universal testing machine. The bioactivity of scaffolds was evaluated by monitoring the formation of calcium phosphate compounds after simulated body fluid immersion. The PLA/PDA/n-HA scaffold showed the highest compressive strength which was 29.11 ± 7.58 MPa with enhancing calcium phosphate crystals deposition with a specific calcium polyphosphate phase formed exclusively on PLA/PDA/n-HA. With cell viability assay, the PDA/n-HA-coated matrix was biocompatible with increase in the IC50, reaching ⁓ 176.8 at 72 without cytotoxic effect on the mesenchymal stem cells, promoting their adhesion and proliferation evaluated by confocal microscopy. The study explored the biocompatibility, bioactivity, and the cell adhesion ability of PDA/n-HA coat on a 3D-printed PLA scaffold that qualifies its use as a promising regenerative material.

Fabrication of Novel 3-D Nanocomposites of HAp-TiC-h-BN-ZrO2: Enhanced Mechanical Performances and In Vivo Toxicity Study for Biomedical Applications

Due to excellent biocompatibility, bioactivities, and osteoconductivity, hydroxyapatite (HAp) is considered as one of the most suitable biomaterials for numerous biomedical applications. Herein, HAp was fabricated using a bottom-up approach, i.e., a wet chemical method, and its composites with TiC, h-BN, and ZrO2 were fabricated by a solid-state reaction method with enhanced mechanical and biological performances. Structural, surface morphology, and mechanical behavior of the fabricated composites were characterized using various characterization techniques. Furthermore, transmission electron microscopy study revealed a randomly oriented rod-like morphology, with the length and width of these nanorods ranging from 78 to 122 and from 9 to 13 nm. Moreover, the mechanical characterizations of the composite HZBT4 (80HAp-10TiC-5h-BN-5ZrO2) reveal a very high compressive strength (246 MPa), which is comparable to that of the steel (250 MPa), fracture toughness (14.78 MPa m1/2), and Young's modulus (1.02 GPa). In order to check the biocompatibility of the composites, numerous biological tests were also performed on different body organs of healthy adult Sprague-Dawley rats. This study suggests that the composite HZBT4 could not reveal any significant influence on the hematological, serum biochemical, and histopathological parameters. Hence, the fabricated composite can be used for several biological applications, such as bone implants, bone grafting, and bone regeneration.

Zizyphus mauritiana seed extract: Paving the way for next-generation bone constructs with nano-fluorohydroxyapatite/carboxymethyl chitosan nanocomposite scaffold

This is the first study that explored the potential use of Zizyphus mauritiana seed extract (ZSE) to synthesize nano-fluorohydroxyapatite/carboxymethyl chitosan nanocomposite scaffolds at different concentrations (CFZ1, CFZ2 and CFZ3) using co-precipitation method. The proposed scaffolds showed presence of intermolecular H bonding interactions between the constituents, according to the FTIR. The mechanical studies revealed shore hardness of 72 ± 4.6 and optimal compressive modulus in case of CFZ3 [1654.48 ± 1.6 MPa], that was comparable with that of human cortical bone. The SEM, TEM and platelet adhesion images corroborated uniformly distributed needle like particles in case of CFZ3 with an average size ranging from 22 to 26 nm, linked rough morphology, and appropriate hemocompatibility. The markedly up regulation in the ALP activity and protein adsorption upon increasing ZSE concentration demonstrated that CFZ nanocomposite scaffolds were compatible with osteoblastic cells relative to CF nanocomposite. The cytotoxicity study indicated that CFZ nanocomposite do not induce toxicity over MG-63 and did not aggravate LDH leakage in contrast to CF. The histopathological investigations on albino rats confirmed significantly improved regeneration of bone in the repair of a critical-size [8 mm] calvarium defect. Therefore, CFZ3 nanocomposite scaffold represents a simple, off-the-shelf solution to the combined challenges associated with bone defects.

Cu-Sr Bilayer Bioactive Glass Nanoparticles/Polydopamine Functionalized Polyetheretherketone Enhances Osteogenic Activity and Prevents Implant-Associated Infections through Spatiotemporal Immunomodulation

Key factors contributing to implantation failures include implant-associated infections (IAIs) and insufficient osseointegration of the implants. Polyetheretherketone (PEEK) is widely used in orthopedics, yet its clinical applications are restricted due to its poor osteogenic and antibacterial properties as well as inadequate immune responses. To overcome these drawbacks, a novel spatiotemporal immunomodulation approach is proposed, chelating Cu-Sr bilayer bioactive glass nanoparticles (CS-BGNs) onto the PEEK surface via polydopamine (PDA). The CS-BGNs possess a bilayer core-shell structure where copper is distributed in the outer layer and strontium is clustered in the inner layer. The results show that CS-BGNs/PDA functionalized PEEK demonstrates a controlled and sequential release of Cu2+ and Sr2+ . In the early stage, Cu2+ from the outer layer releases rapidly, while Sr2+ from the inner layer releases in the late stage. This well-ordered release pattern modulates the phenotypic transition of macrophages, which induces M1 polarization in the early stage and M2 polarization in the late stage. Combined with the direct effects of Cu2+ and Sr2+ , the spatiotemporal immunomodulation not only benefits the early antibacterial and tissue-healing process, but also promotes the long-term process of osseointegration, providing new perspectives on the design of novel immunomodulatory biomaterials.

Multifunctional electrospun nanofibrous scaffold enriched with alendronate and hydroxyapatite for balancing osteogenic and osteoclast activity to promote bone regeneration

Electrospun composite nanofiber scaffolds are well known for their bone and tissue regeneration applications. This research is focused on the development of PVP and PVA nanofiber composite scaffolds enriched with hydroxyapatite (HA) nanoparticles and alendronate (ALN) using the electrospinning technique. The developed nanofiber scaffolds were investigated for their physicochemical as well as bone regeneration potential. The results obtained from particle size, zeta potential, SEM and EDX analysis of HA nanoparticles confirmed their successful fabrication. Further, SEM analysis verified nanofiber's diameters within 200-250 nm, while EDX analysis confirmed the successful incorporation of HA and ALN into the scaffolds. XRD and TGA analysis revealed the amorphous and thermally stable nature of the nanofiber composite scaffolds. Contact angle, FTIR analysis, Swelling and biodegradability studies revealed the hydrophilicity, chemical compatibility, suitable water uptake capacity and increased in-vitro degradation making it appropriate for tissue regeneration. The addition of HA into nanofiber scaffolds enhanced the physiochemical properties. Additionally, hemolysis cell viability, cell adhesion and proliferation by SEM as well as confocal microscopy and live/dead assay results demonstrated the non-toxic and biocompatibility behavior of nanofiber scaffolds. Alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP) assays demonstrated osteoblast promotion and osteoclast inhibition, respectively. These findings suggest that developed HA and ALN-loaded PVP/PVA-ALN-HA nanofiber composite scaffolds hold significant promise for bone regeneration applications.

Early In Vivo Osteogenic and Inflammatory Response of 3D Printed Polycaprolactone/Carbon Nanotube/Hydroxyapatite/Tricalcium Phosphate Composite Scaffolds

The development of advanced biomaterials and manufacturing processes to fabricate biologically and mechanically appropriate scaffolds for bone tissue is a significant challenge. Polycaprolactone (PCL) is a biocompatible and degradable polymer used in bone tissue engineering, but it lacks biofunctionalization. Bioceramics, such as hydroxyapatite (HA) and β tricalcium phosphate (β-TCP), which are similar chemically to native bone, can facilitate both osteointegration and osteoinduction whilst improving the biomechanics of a scaffold. Carbon nanotubes (CNTs) display exceptional electrical conductivity and mechanical properties. A major limitation is the understanding of how PCL-based scaffolds containing HA, TCP, and CNTs behave in vivo in a bone regeneration model. The objective of this study was to evaluate the use of three-dimensional (3D) printed PCL-based composite scaffolds containing CNTs, HA, and β-TCP during the initial osteogenic and inflammatory response phase in a critical bone defect rat model. Gene expression related to early osteogenesis, the inflammatory phase, and tissue formation was evaluated using quantitative real-time PCR (RT-qPCR). Tissue formation and mineralization were assessed by histomorphometry. The CNT+HA/TCP group presented higher expression of osteogenic genes after seven days. The CNT+HA and CNT+TCP groups stimulated higher gene expression for tissue formation and mineralization, and pro- and anti-inflammatory genes after 14 and 30 days. Moreover, the CNT+TCP and CNT+HA/TCP groups showed higher gene expressions related to M1 macrophages. The association of CNTs with ceramics at 10wt% (CNT+HA/TCP) showed lower expressions of inflammatory genes and higher osteogenic, presenting a positive impact and balanced cell signaling for early bone formation. The association of CNTs with both ceramics promoted a minor inflammatory response and faster bone tissue formation.

3D-printed porous functional composite scaffolds with polydopamine decoration for bone regeneration

Large size bone defects affect human health and remain a worldwide health problem that needs to be solved immediately. 3D printing technology has attracted substantial attention for preparing penetrable multifunctional scaffolds to promote bone reconditioning and regeneration. Inspired by the spongy structure of natural bone, novel porous degradable scaffolds have been printed using polymerization of lactide and caprolactone (PLCL) and bioactive glass 45S5 (BG), and polydopamine (PDA) was used to decorate the PLCL/BG scaffolds. The physicochemical properties of the PLCL/BG and PLCL/BG/PDA scaffolds were measured, and their osteogenic and angiogenic effects were characterized through a series of experiments both in vitro and in vivo. The results show that the PLCL/BG2/PDA scaffold possessed a good compression modulus and brilliant hydrophilicity. The proliferation, adhesion and osteogenesis of hBMSCs were improved in the PDA coating groups, which exhibited the best performance. The results of the SD rat cranium defect model indicate that PLCL/BG2/PDA obviously promoted osteointegration, which was further confirmed through immunohistochemical staining. Therefore, PDA decoration and the sustained release of bioactive ions (Ca, Si, P) from BG in the 3D-printed PLCL/BG2/PDA scaffold could improve surface bioactivity and promote better osteogenesis and angiogenesis, which may provide a valuable basis for customized implants in extensive bone defect repair applications.

Mussel-Based Biomimetic Strategies in Musculoskeletal Disorder Treatment: From Synthesis Principles to Diverse Applications

Musculoskeletal disorders are the second leading cause of disability worldwide, posing a huge global burden to the public sanitation system. Currently, tissue engineering-based approaches act as effective strategies, which are, however, challenging in limited application scenarios. Mussel-based biomimetic materials, exhibit numerous unique properties such as intense adhesion, biocompatibility, moisture resistance, and injectability, to name only a few, and have attracted extensive research interest. In particular, featuring state-of-the-art properties, mussel-inspired biomaterials have been widely explored in innumerable musculoskeletal disorder treatments including osteochondral defects, osteosarcoma, osteoarthritis, ligament rupture, and osteoporosis. Nevertheless, a comprehensive and timely discussion of their applications in musculoskeletal disorders is insufficient. In this review, we emphasize on (1) the main categories and characteristics of mussel foot proteins and their fundamental mechanisms for the spectacular adhesion in mussels; (2) the diverse synthetic methods and modification of various polymers; and (3) the emerging applications of mussel-biomimetic materials, the future perspectives, and challenges, especially in the area of musculoskeletal disorder. We envision that this review will provide a unique and insightful perspective to improve the development of a new generation of mussel biomimetic strategies.

Nanomaterial-assisted theranosis of bone diseases

Bone-related diseases refer to a group of skeletal disorders that are characterized by bone and cartilage destruction. Conventional approaches can regulate bone homeostasis to a certain extent. However, these therapies are still associated with some undesirable problems. Fortunately, recent advances in nanomaterials have provided unprecedented opportunities for diagnosis and therapy of bone-related diseases. This review provides a comprehensive and up-to-date overview of current advanced theranostic nanomaterials in bone-related diseases. First, the potential utility of nanomaterials for biological imaging and biomarker detection is illustrated. Second, nanomaterials serve as therapeutic delivery platforms with special functions for bone homeostasis regulation and cellular modulation are highlighted. Finally, perspectives in this field are offered, including current key bottlenecks and future directions, which may be helpful for exploiting nanomaterials with novel properties and unique functions. This review will provide scientific guidance to enhance the development of advanced nanomaterials for the diagnosis and therapy of bone-related diseases.

Synthesized bioactive lignin nanoparticles/polycaprolactone nanofibers: A novel nanobiocomposite for bone tissue engineering

The use of artificial biomaterial with enhanced bioactivity for osteostimulation is a major research concern at present days. In this research, antibacterial and osteostimulative core-shell lignin nanoparticles (LgNP) were synthesized from alkali lignin using tetrahydrofuran (THF) as solvent via a simultaneous pH and solvent shifting technology. Later, LgNP-loaded polycaprolactone (PCL) composite nanofibers were fabricated via the electrospinning technique. The addition of LgNP significantly increased the diameter of the nanofibers, ranging from 400 to 2200 nm. The addition of LgNP reduced the mechanical performance, crystallinity, and porosity of the nanofibers while improving surface wetting and swelling properties of the inherently hydrophobic PCL polymer. The prepared nanofibers showed excellent bactericidal efficacy against major bone infectious Gram-positive Staphylococcus aureus bacterial strains. The incorporation of LgNP imparted superior antioxidant activity and boosted the biodegradation process of the nanofibers. The deposition of biomineral apatite with platelet-like clustered protrusions having a Ca/P ratio of 1.67 was observed while incubating the scaffold in simulated body fluid. Based on the results of the LDH and WST-1 assay, it was demonstrated that the composite nanofibers are non-toxic to pre-osteoblastic cell line (MC3T3-E1) when they are placed in direct contact with the LgNP/PCL scaffold nanofibers. The MC3T3-E1 cells exhibited excellent proliferation and attachment on the prepared composite scaffold via filopodial and lamellipodial expansion with cell-secreted Ca deposition. According to the alkaline phosphatase activity test, LgNP/PCL nanofiber scaffolds significantly improved osteogenic differentiation of MC3T3-E1 cells compared to neat PCL nanofibers. Overall, our findings suggest that LgNP/PCL nanofiber scaffold could be a promising functional biomaterial for bone tissue engineering.

A Biomimetic Smart Nanoplatform as “Inflammation Scavenger” for Regenerative Therapy of Periodontal Tissue

Introduction

The functional reconstruction of periodontal tissue defects remains a clinical challenge due to excessive and prolonged host response to various endogenous and exogenous pro-inflammatory stimuli. Thus, a biomimetic nanoplatform with the capability of modulating inflammatory response in a microenvironment-responsive manner is attractive for regenerative therapy of periodontal tissue.

Methods

Herein, a facile and green design of engineered bone graft materials was developed by integrating a biomimetic apatite nanocomposite with a smart-release coating, which could realize inflammatory modulation by “on-demand” delivery of the anti-inflammatory agent through a pH-sensing mechanism.

Results

In vitro and in vivo experiments demonstrated that this biocompatible nanoplatform could facilitate the clearance of reactive oxygen species in human periodontal ligament stem cells under inflammatory conditions via inhibiting the production of endogenous proinflammatory mediators, in turn contributing to the enhanced healing efficacy of periodontal tissue. Moreover, this system exhibited effective antimicrobial activity against common pathogenic bacteria in the oral cavity, which is beneficial for the elimination of exogenous pro-inflammatory factors from bacterial infection during healing of periodontal tissue.

Conclusion

The proposed strategy provides a versatile apatite nanocomposite as a promising “inflammation scavenger” and propels the development of intelligent bone graft materials for periodontal and orthopedic applications.

Advancement in Analytical Techniques for Determining the Activity of β-Site Amyloid Precursor Protein Cleaving Enzyme 1

Alzheimer's disease (AD) is a degenerative disease of the central nervous system. The pathogenesis is still not fully clear. One of the main histopathological manifestations is senile plaques formed by β-amyloid (Aβ) accumulation. Aβ is generated from the sequential proteolysis of amyloid precursor protein (APP) by β-secretase [i.e. β-site APP cleaving enzyme 1 (BACE1)] and γ-secretase, with a rate-limiting step controlled by BACE1 activity. Therefore, inhibiting BACE1 activity has become a potential therapeutic strategy for AD. The development of reliable detection methods for BACE1 activity plays an important role in early diagnosis of AD and evaluation of the therapeutic effect of new drugs for AD. This article has reviewed the recent advances in BACE1 activity detection techniques. The challenges of applying these analysis techniques to early clinical diagnosis of AD and development trends of the detection techniques have been prospected.

Regulation of Macrophage Polarization Through Periodic Photo-Thermal Treatment to Facilitate Osteogenesis

The richened reactive oxygen species (ROS) and their derived excessive inflammation at bone injured sites hinder osteogenesis of endosseous Ti-based implants. Herein, anti-oxidized polydopamine (PDA) is deposited on hydrothermal growth formed hydroxyapatite (HA) nanorods on Ti to form a core-shell structural nanorod-like array with HA as a core and PDA as an amorphous shell (PDA@HA), showing not only ROS scavenging ability but also near-infrared (NIR) light derived photo-thermal effects. PDA@HA suppresses inflammation based on its ROS scavenging ability to a certain extent, while periodic photo-thermal treatment (PTT) at a mild temperature (41 ± 1 °C) further accelerates the transition of the macrophages (MΦs) adhered to PDA@HA from the pro-inflammatory (M1) phenotype to the anti-inflammatory (M2) phenotype in vitro and in vivo. Transcriptomic analysis reveals that the activation of the PI3K-Akt1 signaling pathway is responsible for the periodic PTT induced acceleration of the M1-to-M2 transition of MΦs. Acting on mesenchymal stem cells (MSCs) with paracrine cytokines of M2 macrophages, PDA@HA with mild PTT greatly promote the osteogenetic functions of MSCs and thus osteogenesis. This work paves a way of employing mildly periodic PTT to induce a favorable immunomodulatory microenvironment for osteogenesis and provides insights into its underlying immunomodulation mechanism.

Polydopamine constructed interfacial molecular bridge in nano-hydroxylapatite/polycaprolactone composite scaffold

Nano-hydroxylapatite (nano-HAP)/polycaprolactone (PCL) composite scaffold is proved to possess great potential for bone tissue engineering application since the biocompatibility of PCL and the osteoinduction ability of nano-HAP. However, the interfacial bonding between nano-HAP and PCL is weak by reason of the difference in thermodynamic properties. Herein, nano-HAP was modified by polydopamine (PDA) and then added to the PCL matrix to enhance their interface bonding in bone scaffold manufactured by selective laser sintering (SLS). The results indicated that PDA acted as an interfacial molecular bridge between PCL and nano-HAP. On one hand, the amino groups of PDA formed hydrogen bonding with the hydroxyl groups of nano-HAP, and on the other hand, the catechol groups of PDA formed hydrogen bonding with the ester groups of PCL. Compared with the HAP/PCL scaffolds, the tensile and compressive strength of the P-HAP/PCL scaffolds loading 12 wt% P-HAP were increased by 10% and 16%, respectively. Meanwhile, the scaffold possessed great bioactivity and cytocompatibility that could accelerate the formation of apatite layers and promote the cell adhesion, proliferation and differentiation.

Biomimetic Design and Fabrication of Sericin-Hydroxyapatite Based Membranes With Osteogenic Activity for Periodontal Tissue Regeneration

The guided tissue regeneration (GTR) technique is a promising treatment for periodontal tissue defects. GTR membranes build a mechanical barrier to control the ingrowth of the gingival epithelium and provide appropriate space for the regeneration of periodontal tissues, particularly alveolar bone. However, the existing GTR membranes only serve as barriers and lack the biological activity to induce alveolar bone regeneration. In this study, sericin-hydroxyapatite (Ser-HAP) composite nanomaterials were fabricated using a biomimetic mineralization method with sericin as an organic template. The mineralized Ser-HAP showed excellent biocompatibility and promoted the osteogenic differentiation of human periodontal membrane stem cells (hPDLSCs). Ser-HAP was combined with PVA using the freeze/thaw method to form PVA/Ser-HAP membranes. Further studies confirmed that PVA/Ser-HAP membranes do not affect the viability of hPDLSCs. Moreover, alkaline phosphatase (ALP) staining, alizarin red staining (ARS), and RT-qPCR detection revealed that PVA/Ser-HAP membranes induce the osteogenic differentiation of hPDLSCs by activating the expression of osteoblast-related genes, including ALP, Runx2, OCN, and OPN. The unique GTR membrane based on Ser-HAP induces the differentiation of hPDLSCs into osteoblasts without additional inducers, demonstrating the excellent potential for periodontal regeneration therapy.

Mussel-inspired multifunctional surface through promoting osteogenesis and inhibiting osteoclastogenesis to facilitate bone regeneration

Osteogenesis and osteoclastogenesis are closely associated during the bone regeneration process. The development of multifunctional bone repair scaffolds with dual therapeutic actions (pro-osteogenesis and anti-osteoclastogenesis) is still a challenging task for bone tissue engineering applications. Herein, through a facile surface coating process, mussel-inspired polydopamine (PDA) is adhered to the surface of a biocompatible porous scaffold followed by the immobilization of a small-molecule activator (LYN-1604 (LYN)) and the subsequent in situ coprecipitation of hydroxyapatite (HA) nanocrystals. PDA, acting as an intermediate bridge, can provide strong LYN immobilization and biomineralization ability, while LYN targets osteoclast precursor cells to inhibit osteoclastic differentiation and functional activity, which endows LYN/HA-coated hybrid scaffolds with robust anti-osteoclastogenesis ability. Due to the synergistic effects of the LYN and HA components, the obtained three-dimensional hybrid scaffolds exhibited the dual effects of osteoclastic inhibition and osteogenic stimulation, thereby promoting bone tissue repair. Systematic characterization experiments confirmed the successful fabrication of LYN/HA-coated hybrid scaffolds, which exhibited an interconnected porous structure with nanoroughened surface topography, favorable hydrophilicity, and improved mechanical properties, as well as the sustained sequential release of LYN and Ca ions. In vitro experiments demonstrated that LYN/HA-coated hybrid scaffolds possessed satisfactory cytocompatibility, effectively promoting cell adhesion, spreading, proliferation, alkaline phosphatase activity, matrix mineralization, and osteogenesis-related gene and protein secretion, as well as stimulating angiogenic differentiation of endothelial cells. In addition to osteogenesis, the engineered scaffolds also significantly reduced osteoclastogenesis, such as tartrate-resistant acid phosphatase activity, F-actin ring staining, and osteoclastogenesis-related gene and protein secretion. More importantly, in a rat calvarial defect model, the newly developed hybrid scaffolds significantly promoted bone repair and regeneration. Microcomputed tomography, histological, and immunohistochemical analyses all revealed that the LYN/HA-coated hybrid scaffolds possessed not only reliable biosafety but also excellent osteogenesis-inducing and osteoclastogenesis-inhibiting effects, resulting in faster and higher-quality bone tissue regeneration. Taken together, this study offers a powerful and promising strategy to construct multifunctional nanocomposite scaffolds by promoting osteo/angiogenesis and suppressing osteoclastogenesis to accelerate bone regeneration.

Oxidized bacterial cellulose reinforced nanocomposite scaffolds for bone repair

Bone tissue engineering has been widely used in promoting the repair and regeneration of bone defects. Tissue-engineered bone scaffolds can simulate the extracellular matrix environment and induce the proliferation and differentiation of osteoblasts. The first issues to be considered when constructing bone repair scaffolds include biocompatibility, stress resistance, degradability and stability. Here, a low-cost manufacturing introduces a new bone repair composite scaffold (CS/OBC/nHAP). The scaffolds were composed of only natural derived components, including nano hydroxyapatite (nHAP) formed by in-situ crystallization of Ca²⁺/PO₄^2- solution and evenly dispersed in oxidized bacterial cellulose (OBC) and chitosan (CS) scaffolds. The experimental results showed that compared with CS/nHAP scaffold, CS/OBC/nHAP scaffold has significantly improve mechanical properties and water retention performance, and has a more stable degradation rate. Cell experiments showed that the CS/OBC/nHAP scaffold has good biocompatibility and significantly promote the proliferation of MC3T3-E1 cells. The rat skull defect model further proves that the CS/OBC/nHAP scaffold could induce the formation of bone tissue. Meanwhile, H&E staining experiment show that the CS/OBC/nHAP scaffold has good stability in vivo and could better promote the formation of bone tissue.

Chitosan-coated pore wall polycaprolactone three-dimensional porous scaffolds fabricated by porogen leaching method for bone tissue engineering: a comparative study on blending technique to fabricate scaffolds

One of the significant challenges in the fabrication of scaffolds for tissue engineering lies in the direct interaction of bioactive agents with cells in the scaffolds matrix, which curbs the effectiveness of bioactive agents resulting in diminished cell recognition and attachment ability of the scaffolds. Here, three-dimensional porous scaffolds were fabricated using polycaprolactone (PCL) and chitosan, by two approaches, i.e., blending and surface coating to compare their overall effectiveness. Blended scaffolds (Chi-PCL) were compared with the scaffolds fabricated using surface coating technique, where chitosan was coated on the pore wall of PCL scaffolds (C-PCL). The C-PCL exhibited a collective improvement in bioactivities of the stem cell on the scaffold, because of the cell compatible environment provided by the presence of chitosan over the scaffolds interface. The C-PCL showed the enhanced cell attachment and proliferation behavior of the scaffolds along with two-fold increase in hemolysis compatibility compared to Chi-PCL. Furthermore, the compression strength in C-PCL increased by 24.52% and 8.62% increase in total percentage porosity compared to Chi-PCL was attained. Along with this, all the bone markers showed significant upregulation in C-PCL scaffolds, which supported the surface coating technique over the conventional methods, even though the pore size of C-PCL was compromised by 19.98% compared with Chi-PCL.

Mussel-inspired functionalization of electrospun scaffolds with polydopamine-assisted immobilization of mesenchymal stem cells-derived small extracellular vesicles for enhanced bone regeneration

Mesenchymal stem cells-derived small extracellular vesicles (MSCs-sEV) have shown promising prospects as a cell-free strategy for bone tissue regeneration. Here, a bioactive MSCs-sEV-loaded electrospun silk fibroin/poly(ε-caprolactone) (SF/PCL) scaffold was synthesized via a mussel-inspired immobilization strategy assisted by polydopamine (pDA). This pDA modification endowed the as-prepared scaffold with high loading efficiency and sustained release profile of sEV. In addition, the fabricated composite scaffold exhibited good physiochemical, mechanical, and biocompatible properties. In vitro cellular experiments indicated that the MSCs-sEV-loaded composite scaffold promoted the adhesion and spreading of preosteoblast and endothelial cells, as well as enhanced osteogenic differentiation and angiogenic activity. In vivo experiments showed that the functionalized electrospun scaffolds promoted bone regeneration in a rat calvarial bone defect model. Results suggest that the developed MSCs-sEV-anchored pDA-modified SF/PCL electrospun scaffolds possess high application potential in bone tissue engineering owing to their powerful pro-angiogenic and -osteogenic capacities, cell-free bioactivity, and cost effectiveness.

2-Dodecylmalonic acid-mediated synthesis of mineralized hydroxyapatite amicable for bone cell growth on orthopaedic implant

The present study illustrates the use of 2-dodecylmalonic acid (MA) as a template in biomineralization-inspired synthesis of hydroxyapatite nanoparticles (HANPs). HANPs synthesized in presence of various concentrations of MA displayed varying particle size and shape. The smallest particle size (22-27 nm) was obtained for MA₂-HANP synthesized in presence of 37 µM MA. The critical micelle concentration (CMC) for MA at pH 9.0 relevant for mineralization was ∼35 µM. AFM analysis revealed that at a low concentration of 10 µM and pH 9.0, MA could generate oblong-shaped aggregates. At 40 µM, comparable to the concentration used to generate MA₂-HANP, the amphiphile self-assembled to form a spherical soft scaffold, which likely regulated spatial confinement of ions during mineralization and generated small size HANPs. Osteoblast-like MG-63 cells seeded on titanium wire (TW) coated with MA₂-HANP-incorporated collagen type I (H-TW) displayed enhanced cell proliferation, high expression of osteogenic differentiation marker genes (Col I, ALP, OCN and Runx2) and copious calcium mineral deposition after 14 days of growth. The nuanced role of the self-assembly process of an amphiphilic template in HANP mineralization unravelled in the present study can guide future scaffold design for biomineralization-inspired synthesis of HANPs tailored for bone tissue engineering applications.

Aptamer-mediated synthesis of multifunctional nano-hydroxyapatite for active tumour bioimaging and treatment

OBJECTIVES

The nano-hydroxyapatite (nHAp) is widely used to develop imaging probes and drug carriers due to its excellent bioactivity and biocompatibility. However, traditional methods usually need cumbersome and stringent conditions such as high temperature and post-modification to prepare the functionalized nHAp, which do not benefit the particles to enter cells due to the increased particle size. Herein, a biomimetic synthesis strategy was explored to achieve the AS1411-targeted tumour dual-model bioimaging using DNA aptamer AS1411 as a template. Then, the imaging properties and the biocompatibility of the synthesized AS-nFAp:Gd/Tb were further investigated.

MATERIALS AND METHODS

The AS-nFAp:Gd/Tb was prepared under mild conditions through a one-pot procedure with AS1411 as a template. Besides, the anticancer drug DOX was loaded to AS-nFAp:Gd/Tb so as to achieve the establishment of a multifunctional nano-probe that integrated the tumour diagnosis and treatment. The AS-nFAp:Gd/Tb was characterized by transmission electron microscopy (TEM), energy disperse X-ray Spectroscopy (EDS) mapping, X-ray photoelectron spectroscopy (XPS) spectrum, X-ray diffraction (XRD), fourier-transformed infrared (FTIR) spectroscopy, capillary electrophoresis analyses, zeta potential and particle sizes. The in vitro magnetic resonance imaging (MRI) and fluorescence imaging were performed on an MRI system and a confocal laser scanning microscope, respectively. The potential of the prepared multifunctional nHAp for a targeted tumour therapy was investigated by a CCK-8 kit. And the animal experiments were conducted on the basis of the guidelines approved by the Animal Care and Use Committee of Sichuan University, China.

RESULTS

In the presence of AS1411, the as-prepared AS-nFAp:Gd/Tb presented a needle-like morphology with good monodispersity and improved imaging performance. Furthermore, due to the specific binding between AS1411 and nucleolin up-expressed in cancer cells, the AS-nFAp:Gd/Tb possessed excellent AS1411-targeted fluorescence and MRI imaging properties. Moreover, after loading chemotherapy drug DOX, in vitro and in vivo studies showed that DOX@AS-nFAp:Gd/Tb could effectively deliver DOX to tumour tissues and exert a highly effective tumour inhibition without systemic toxicity compared with pure DOX.

CONCLUSIONS

The results indicated that the prepared multifunctional nHAp synthesized by a novel biomimetic strategy had outstanding capabilities of recognition and treatment for the tumour and had good biocompatibility; hence, it might have a potential clinical application in the future.

The efficiency of PCL/HAp electrospun nanofibers in bone regeneration: a review

Electrospinning is a method which produces various nanofiber scaffolds for different tissues was attractive for researchers. Nanofiber scaffolds could be made from several biomaterials and polymers. Quality and virtues of final scaffolds depend on used biomaterials (even about single substance, the origin is effective), additives (such as some molecules, ions, drugs, and inorganic materials), electrospinning parameter (voltage, injection speed, temperature, …), etc. In addition to its benefits, which makes it more attractive is the possibility of modifications. Common biomaterials in bone tissue engineering such as poly-caprolactone (PCL), hydroxyapatite (HAp), and their important features, electrospinning nanofibers were widely studied. Related investigations indicate the critical role of even small parameters (like the concentration of PCL or HAp) in final product properties. These changes also, cause deference in cell proliferation, adhesion, differentiation, and in vivo repair process. In this review was focussed on PCL/HAp based nanofibers and additives that researchers used for scaffold improvement. Then, reviewing properties of gained nanofibers, their effect on cell behaviour, and finally, their valency in bone tissue engineering studies (in vitro and in vivo).

Bovine Serum Albumin-Directed Fabrication of Nanohydroxyapatite with Improved Stability and Biocompatibility

Nanohydroxyapatite (nHAp) has gained considerable concerns due to its vast potential in biomedical applications such as drug delivery, tissue engineering and bone repair. However, the preparation of HAp nanostructures in a controllable manner under environment-friendly reaction conditions remains a challenge. In recent years, the use of biological macromolecules or proteins as templates in the production of nanomaterials has gained more attention due to the relatively mild physical conditions needed for biomimetic synthesis. In this study, a novel nHAp was fabricated by employing bovine serum albumin (BSA) as template under mild condition. After that, the as-obtained nanostructured materials which have well-defined structures and morphologies were characterized by various methods. Furthermore, the rod-like shaped hydroxyapatite demonstrated improved stability properties, as well as cell viability and biocompatibility, compared to BSA free synthesized c-HAp. We expect that this pleasantly novel research will render new insights into the fabrication strategies of nanomaterials and be of practical importance for the expanding biological application.

Probiotic bacteria cell surface-associated protein mineralized hydroxyapatite incorporated in porous scaffold: In vitro evaluation for bone cell growth and differentiation

There is a high demand for synthesis of biocompatible hydroxyapatite nanoparticle (HANP), which is a key component in bone tissue engineering scaffolds. The present study describes a facile route of HANP synthesis through mineralization of the cell surface-associated protein (CSP) from the human probiotic lactic acid bacteria (LAB) Lactobacillus rhamnosus GG. CSP extract from the LAB (consisting of ~66 kDa, ~47 kDa, ~40 kDa and ~25 kDa protein) was mineralized to yield spindle-shaped HANPs having an average particle length of 371 nm as evidenced in FETEM analysis. CSP-mineralized HANPs (CSP-HANPs) were characterized by FTIR and BET analysis, while XRD and SAED analysis indicated their crystalline nature. Mechanistic studies suggested the key role of ~25 kDa CSP (F4SP) in mineralization. In contrast to CSP-HANPs, F4SP-mineralized crystalline HA was plate-shaped having an average length of 1.68 μm and breadth of 0.95 μm. HANP mineralization at the whole-cell (WC) level resulted in clusters of aggregated HANPs (WC-HANPs) adhering onto L. rhamnosus GG cells as evident in FETEM, FESEM and AFM analysis. FETEM analysis revealed that the desorbed WC-HANPs recovered by cell lysis were needle-shaped, with a particle size distribution of 70-110 nm. Given that CSP-HANPs were non-toxic to cultured HEK 293 cells and osteoblast-like MG-63 cells, chitosan-gelatin (CG) scaffold incorporated with 15% w/v CSP-HANP (H-CG) was generated and tested for bone cell growth. H-CG exhibited a favorable pore size distribution (160-230 μm), overall porosity (~84%) and biodegradation profile. H-CG scaffold was conducive to osteogenesis and rendered enhanced proliferation, alkaline phosphatase (ALP) activity, calcium mineralization and heightened marker gene expression (ALP, Col I, Runx2 and OCN) in seeded MG-63 cells. CSP sourced from a safe probiotic LAB is thus a viable and effective mineralization template for synthesis of biocompatible HANPs that can be leveraged for bone tissue engineering applications.

An In Vitro Evaluation of the Hierarchical Micro/Nanoporous Structure of a Ti3Zr2Sn3Mo25Nb Alloy after Surface Dealloying

A process to dealloy a Ti-3Zr-2Sn-3Mo-25Nb (TLM) titanium alloy to create a porous surface structure has been reported in this paper aiming to enhance the bioactivity of the alloy. A simple nanoporous topography on the surface was produced through dealloying the as-solution treated TLM alloy. In contrast, dealloying the as-cold rolled alloy created a hierarchical micro/nanoporous topography. SEM and XPS were performed to characterize the topography and element chemistry of both porous structures. The roughness, hydrophilicity, protein adsorption, cell adhesion, proliferation, and osteogenic differentiation were tested. The elements of Zr, Mo, Sn, and Nb were depleted at the nanoporous TLM surface with a diameter of 15.6 ± 2.3 nm. Dissolving the microscale α phase from the alloy surface contributed to the formation of the microscale grooves on the surface. The simple nanoporous topographical surface exhibited hydrophilicity and higher protein adsorption ability, which facilitated the early adhesion of osteoblasts compared with the hierarchical micro/nanoporous surface. On the other hand, the hierarchical micro/nanoporous surface improved cell proliferation and differentiation and still retained the contact guidance function, which implied good bonding for osseointegration. This research revealed the effect of phase composition on the surface morphology of dealloying titanium alloy and the synergistic effect of micron and nanometer topography on the function of osteoblasts. This paper therefore provides insights into the surface topological design of titanium-based biomaterials with improved biocompatibility.

Electropsun Polycaprolactone Fibres in Bone Tissue Engineering: A Review

Regeneration of bone tissue requires novel load bearing, biocompatible materials that support adhesion, spreading, proliferation, differentiation, mineralization, ECM production and maturation of bone-forming cells. Polycaprolactone (PCL) has many advantages as a biomaterial for scaffold production including tuneable biodegradation, relatively high mechanical toughness at physiological temperature. Electrospinning produces nanofibrous porous matrices that mimic many properties of natural tissue extracellular matrix with regard to surface area, porosity and fibre alignment. The biocompatibility and hydrophilicity of PCL nanofibres can be improved by combining PCL with other biomaterials to form composite scaffolds for bone regeneration. This work reviews the most recent research on synthesis, characterization and cellular response to nanofibrous PCL scaffolds and the composites of PCL with other natural and synthetic materials for bone tissue engineering.

Research Progress of Thermosensitive Hydrogel in Tumor Therapeutic

Compared with traditional tumor therapy strategies, hydrogel as a drug reservoir system can realize on-demand drug release and deep tissue penetration ability. It also exhibits great tumor-site retention to enhance the permeability and retention effect of tumor treatment. This can significantly overcome the drug's resistance and severe side effects. Inorganic/organic composite hydrogel has attracted wide attention due to its combined effects, enhancing therapeutic effects against various kinds of tumors. In situ injectable hydrogel can securely restrict the drugs in the lesion sites without leakage and guarantee better biosafety. Moreover, hydrogel possesses interconnected macropores which can provide enough space for nutrient transport, cellular activity, and cell-cell interactions. Thermal therapy is an effective strategy for tumor therapy due to its minimal invasiveness and high selectivity. Because the location temperature can be precisely controlled and helps avoid the risks of destroying the body's immune system and ablate normal cells, thermal therapy exhibits significant treatment outcomes. Nonetheless, when the cellular temperature reaches approximately 43 °C, it causes long-term cell inactivation. Based on these merits, thermosensitive hydrogel formulation with adaptive functions shows excellent efficacy, unlimited tissue penetration capacity, and few deleterious side effects. Furthermore, the thermosensitive hydrogel has unique physical properties under the external stimuli, which is the ideal drug delivery system for on-demand release in tumor treatment. This article will review the state of the thermosensitive hydrogel in clinic application for cancer therapy.

Silk-based hybrid microfibrous mats as guided bone regeneration membranes

LAPONITE® (LAP) nanoplatelets were incorporated within a regenerated silk fibroin (RSF) microfibrous mat via electrospinning, which exhibited better cell adhesion and proliferation of bone marrow mesenchymal stem cells (BMSCs) than the pristine RSF ones.

Bifunctional scaffolds of hydroxyapatite/poly(dopamine)/carboxymethyl chitosan with osteogenesis and anti-osteosarcoma effect

Bifunctional scaffolds prepared by hydroxyapatite/poly(dopamine)/carboxymethyl chitosan with good osteogenesis and anti-osteosarcoma effect is promising for bone tumor therapy.

In vitro performance of 3D printed PCL-TCP degradable spinal fusion cage

Spinal fusion cages are commonly used to treat spinal diseases caused by degenerative changes, deformities, and trauma. At present, most of the main clinical spinal fusion cage products are non-degradable and still cause some undesirable side effects, such as the stress shielding phenomenon, interference with postoperative medical imaging, and obvious foreign body sensation in patients. Degradable spinal fusion cages have promising potential with extensive perspectives. The purpose of this study was to fabricate a degradable spinal fusion cage from both polycaprolactone (PCL) and high-proportion beta-tricalcium phosphate (β-TCP), using the highly personalised, accurate, and rapid fused deposition modelling 3 D printing technology. PCL and β-TCP were mixed in three different ratios (60:40, 55:45, and 50:50). Both in vitro degradation and cell experiments proved that all cages with the different PCL:β-TCP ratios met the mechanical properties of human cancellous bone while maintaining their structural integrity. The biological activity of the cages improved with higher amounts of the β-TCP content. This study also showed that a spinal fusion cage with high β-TCP content and suitable mechanical properties can be manufactured using extruding rods and appropriate models, providing a new solution for the design of degradable spinal fusion cages.

Biodegradable materials for bone defect repair

Compared with non-degradable materials, biodegradable biomaterials play an increasingly important role in the repairing of severe bone defects, and have attracted extensive attention from researchers. In the treatment of bone defects, scaffolds made of biodegradable materials can provide a crawling bridge for new bone tissue in the gap and a platform for cells and growth factors to play a physiological role, which will eventually be degraded and absorbed in the body and be replaced by the new bone tissue. Traditional biodegradable materials include polymers, ceramics and metals, which have been used in bone defect repairing for many years. Although these materials have more or fewer shortcomings, they are still the cornerstone of our development of a new generation of degradable materials. With the rapid development of modern science and technology, in the twenty-first century, more and more kinds of new biodegradable materials emerge in endlessly, such as new intelligent micro-nano materials and cell-based products. At the same time, there are many new fabrication technologies of improving biodegradable materials, such as modular fabrication, 3D and 4D printing, interface reinforcement and nanotechnology. This review will introduce various kinds of biodegradable materials commonly used in bone defect repairing, especially the newly emerging materials and their fabrication technology in recent years, and look forward to the future research direction, hoping to provide researchers in the field with some inspiration and reference.

Hydroxyapatite Nanoparticles Fortified Xanthan Gum-Chitosan Based Polyelectrolyte Complex Scaffolds for Supporting the Osteo-Friendly Environment

Nanoparticle-reinforced polymer-based scaffolding matrices as artificial bone-implant materials are potential suitors for bone regenerative medicine as they simulate the native bone. In the present work, a series of bioinspired, osteoconductive tricomposite scaffolds made up of nano-hydroxyapatite (NHA) embedded xanthan gum-chitosan (XAN-CHI) polyelectrolyte complex (PEC) are explored for their bone-regeneration potential. The Fourier transform infrared spectroscopy studies confirmed complex formation between XAN and CHI and showed strong interactions between the NHA and PEC matrix. The X-ray diffraction studies indicated regulation of the nanocomposite (NC) scaffold crystallinity by the physical cues of the PEC matrix. Further results exhibited that the XAN-CHI/NHA5 scaffold, with a 50/50 (polymer/NHA) ratio, has optimized porous structure, appropriate compressive properties, and sufficient swelling ability with slower degradation rates, which are far better than those of CHI/NHA and other XAN-CHI/NHA NC scaffolds. The simulated body fluid studies showed XAN-CHI/NHA5 generated apatite-like surface structures of a Ca/P ratio ∼1.66. Also, the in vitro cell-material interaction studies with MG-63 cells revealed that relative to the CHI/NHA NC scaffold, the cellular viability, attachment, and proliferation were better on XAN-CHI/NHA scaffold surfaces, with XAN-CHI/NHA5 specimens exhibiting an effective increment in cell spreading capacity compared to XAN-CHI/NHA4 and XAN-CHI/NHA6 specimens. The presence of an osteo-friendly environment is also indicated by enhanced alkaline phosphatase expression and protein adsorption ability. The higher expression of extracellular matrix proteins, such as osteocalcin and osteopontin, finally validated the induction of differentiation of MG-63 cells by tricomposite scaffolds. In summary, this study demonstrates that the formation of PEC between XAN and CHI and incorporation of NHA in XAN-CHI PEC developed tricomposite scaffolds with robust potential for use in bone regeneration applications.

In vitro and in vivo evaluation of structurally-controlled silk fibroin coatings for orthopedic infection and in-situ osteogenesis

Biomedical device-associated infections (BAI) and osteosynthesis are two main complications following the orthopedic implant surgery, especially while infecting bacteria form a mature biofilm, which can protect the organisms from the host immune system and antibiotic therapy. Comparing with the single antibiotics therapeutic method, the combination of silver nanoparticles (AgNPs) and conventional antibiotics exert a high level of antibacterial activity. Nevertheless, one major issue that extremely restricts the potential application of AgNP/antiviotics is the uncontrolled release. Moreover, the lack of osteogenic ability may cause the osteosynthesis. Thus, herein we fabricated a structure-controlled drug-loaded silk fibroin (SF) coating that can achieve the size and release control of AgNPs and high efficient osteogenesis. Three comparative SF-based coatings were fabricated: α-structured coating (α-helices 32.7%,), m-structured coating (β-sheets 28.3%) and β-structured coating (β-sheets 41%). Owning to the high content of α-helices structure and small AgNPs (20 nm), α-structured coating displayed better protein adsorption and hydrophilicity, as well as pH-dependent and long-lasting antibacterial performance. In vitro studies demonstrated that α coating showed biocompatibility (cellular attachment, spreading and proliferation), high ALP expression, collagen secretion and calcium mineralization. Moreover, after one month subcutaneous implantation in vivo, α-structured coating elicited minimal, comparable inflammatory response. Additionally, in a rabbit femoral defect model, α-structured coating displayed a significant improvement on the generation of new-born bone and bonding between the new bone and the tissue, implying a rapid and durable osteointegration. Expectedly, this optimized structure-controlled SF-based coating can be an alternative and prospective solution for the current challenges in orthopedics. STATEMENT OF SIGNIFICANCE: In this study, an AgNPs/Gentamycin-loaded structured-controlled silk fibroin coatings were constructed on Ti implant's surface to guarantee the success of implantation even in the face of bacterial infection. In comparison, the α-structured coating had the lowest content of β-sheets structure (19.0%) and the smallest particle size of AgNPs (~ 20 nm), and owned pH-responsive characteristic due to reversible α-helices structural. Thanks to pH-responsive release of Ag⁺, the α-structure coating could effectively inhibit adhesive bacteria and kill planktonic bacteria by releasing a large amount of reactive oxygen radicals. Through in vitro biological results (cell proliferation, differentiation and osteogenic gene expression) and in vivo rabbit femur implantation results, the α-structure coating had good biocompatible and osteogenic properties.

Comprehensive Survey on Nanobiomaterials for Bone Tissue Engineering Applications

One of the most important ideas ever produced by the application of materials science to the medical field is the notion of biomaterials. The nanostructured biomaterials play a crucial role in the development of new treatment strategies including not only the replacement of tissues and organs, but also repair and regeneration. They are designed to interact with damaged or injured tissues to induce regeneration, or as a forest for the production of laboratory tissues, so they must be micro-environmentally sensitive. The existing materials have many limitations, including impaired cell attachment, proliferation, and toxicity. Nanotechnology may open new avenues to bone tissue engineering by forming new assemblies similar in size and shape to the existing hierarchical bone structure. Organic and inorganic nanobiomaterials are increasingly used for bone tissue engineering applications because they may allow to overcome some of the current restrictions entailed by bone regeneration methods. This review covers the applications of different organic and inorganic nanobiomaterials in the field of hard tissue engineering.

Bio-surface coated titanium scaffolds with cancellous bone-like biomimetic structure for enhanced bone tissue regeneration

In view of the fact that titanium (Ti)-based implants still face the problem of loosening and failure of the implants caused by the slow biological response, the low osseointegration rate and the implant bacterial infection in clinical application, we designed a cancellous bone-like biomimetic Ti scaffold using the template accumulated by sugar spheres as a pore-forming agent. And based on a modified surface mineralization process and mussel-like adhesion mechanism, a silicon-doped calcium phosphate composite coating (Van-pBNPs/pep@pSiCaP) with Vancomycin (Van)-loaded polydopamine (pDA)-modified albumin nanoparticles (Van-pBNPs) and cell adhesion peptides (GFOGER) was constructed on the surface of Ti scaffold for mimicking the extracellular matrix (ECM) microenvironment of natural bone matrix to induce greater tissue regeneration. The in vitro study demonstrated that this porous Ti scaffold with functional bio-surface could distinctly facilitate cell early adhesion and spreading, and activate the expression of α2β1 integrin receptor on the cell membrane through promoting the formation of focal adhesions (FAs) in bone marrow stromal cells (BMSCs), thus mediating greater osteogenic cell differentiation. And it could also effectively inhibit the adhesion and growth of Staphylococcus epidermidis, exhibiting good antibacterial properties. Moreover, the Van-pBNPs/pep@pSiCaP-Ti scaffolds showed enhanced in vivo bone-forming ability due to the contributions of bioactive chemical components and the natural cancellous bone-like macrostructure. This work offers a promising structural and functional bio-inspired strategy for designing metal implants with desirable ability of osteoinduction synergistically with antibacterial efficacy for promoting bone regeneration and infection prevention simultaneously. STATEMENT OF SIGNIFICANCE: This manuscript describes a new method for making porous Ti scaffolds with a natural cancellous bone-like structure. Besides, a functional bio-surface was constructed on the bionic structure, mimicking some of the functions of the collagen-rich organic matrix and inorganic CaP nanocrystallites of native ECM of bone in chemical components and biological activities. This interconnected inter-pore opening structure encouraged the migration of cells among open macro-pores within the scaffold. In addition, the functionalized surface not only improved early cell adhesion, spreading, stimulated greater osteogenic differentiation of bone-forming cells, but also endowed the scaffold with excellent antibacterial effect. The biomimetic metal implant with multiple biomedical functions designed in this study has a great clinical application potential. This study represents a feasible method for the preparation of biomimetic structure of metal implants and the improvement of their surface biological activity.

Rotary-jet spun polycaprolactone/nano-hydroxyapatite scaffolds modified by simulated body fluid influenced the flexural mode of the neoformed bone

Polycaprolactone (PCL) is a biocompatible, biodegradable synthetic polymer which in combination with nanohydroxyapatite (nHAp) can give rise to a low cost, nontoxic bioactive product with excellent mechanical properties and slow degradation. Here we produced, characterized and evaluated in vivo the bone formation of PCL/nHAp scaffolds produced by the rotary jet spinning technique. The scaffolds produced were firstly soaked into simulated body fluid for 21 days to also obtain nHAp onto PCL/nHAp scaffolds. Afterwards, the scaffolds were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy and Raman spectroscopy. For in vivo experiments, 20 male Wistar rats were used and randomly divided in 4 experimental groups (n = 5). A critical defect of 3 mm in diameter was made in the tibia of the animals, which were filled with G1 control (clot); G2-PCL scaffold; G3-PCL/nHAp (5%) scaffold; G4-PCL/nHAp (20%) scaffold. All animals were euthanized 60 days after surgery, and the bone repair in the right tibiae were evaluated by radiographic analysis, histological analysis and histomorphometric analysis. While in the left tibias, the areas of bone repair were submitted to the flexural strength test. Radiographic and histomorphometric analyses no showed statistical difference in new bone formation between the groups, but in the three-point flexural tests, the PCL/nHAp (20%) scaffold positively influenced the flexural mode of the neoformed bone. These findings indicate that PCL/nHAp (20%) scaffold improve biomechanical properties of neoformed bone and could be used for bone medicine regenerative.

Three-Dimensional Electrodeposition of Calcium Phosphates on Porous Nanofibrous Scaffolds and Their Controlled Release of Calcium for Bone Regeneration

To mimic the bone matrix of mineralized collagen and to impart microporous structure to facilitate cell migration and bone regeneration, we developed a nanofibrous (NF) polymer scaffold with highly interconnected pores and three-dimensional calcium phosphate coating utilizing an electrodeposition technique. The mineral content, morphology, crystal structure, and chemical composition could be tailored by adjusting the deposition temperature, voltage, and duration. A higher voltage and a higher temperature led to a greater rate of mineralization. Furthermore, nearly linear calcium releasing kinetics was achieved from the mineralized 3D scaffolds. The releasing rate was controlled by varying the initial electrodeposition conditions. A higher deposition voltage and temperature led to slower calcium release, which was associated with the highly crystalline and stoichiometric hydroxyapatite content. This premineralized NF scaffold enhanced bone regeneration over the control scaffold in a subcutaneous implantation model, which was associated with released calcium ions in facilitating osteogenic cell proliferation.

A Synthetic Graft With Multilayered Co-Electrospinning Nanoscaffolds for Bridging Massive Rotator Cuff Tear in a Rat Model

BACKGROUND

Graft bridging is used in massive rotator cuff tear (MRCT); however, the integration of graft-tendon and graft-bone is still a challenge.

HYPOTHESIS

A co-electrospinning nanoscaffold of polycaprolactone (PCL) with an "enthesis-mimicking" (EM) structure could bridge MRCT, facilitate tendon regeneration, and improve graft-bone healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

First, we analyzed the cytocompatibility of the electrospinning nanoscaffolds, including aligned PCL (aPCL), nonaligned PCL (nPCL), aPCL-collagen I, nPCL-collagen II, and nPCL-nanohydroxyapatite (nHA). Second, for the EM condition, nPCL-collagen II and nPCL-nHA were electrospun layer by layer at one end of the aPCL-collagen I; for the control condition, the nPCL was electrospun on the aPCL. In 40 mature male rats, resection of both the supraspinatus and infraspinatus tendons was performed to create MRCT, and the animals were divided randomly into EM and control groups. In both groups, one end of the layered structure was fixed on the footprint of the rotator cuff, whereas the other end of the layered structure was sutured with the tendon stump. The animals were euthanized for harvesting of tissues for histologic and biomechanical analysis at 4 weeks or 8 weeks postoperatively.

RESULTS

All scaffolds showed good cytocompatibility in vitro. The graft-tendon tissue in the EM group had more regularly arranged cells, denser tissue, a significantly higher tendon maturing score, and more birefringence compared with the control group at 8 weeks after operation. Newly formed fibrocartilage could be observed at the graft-bone interface in both groups by 8 weeks, but the EM group had a higher graft-bone healing score and significantly more newly formed fibrocartilage than the control group. An enthesis-like structure with transitional layers was observed in the EM group at 8 weeks. Biomechanically, the values for maximum failure load and stiffness of the tendon-graft-bone complex were significantly higher in the EM group than in the control group at 8 weeks.

CONCLUSION

The co-electrospinning nanoscaffold of aPCL-collagen I could be used as a bridging graft to improve early graft-tendon healing for MRCT in a rat model and enhance early enthesis reconstruction in combination with a multilayered structure of nPCL-collagen II and nPCL-nHA.

CLINICAL RELEVANCE

We constructed a graft to bridge MRCT, enhance graft-tendon healing and graft-bone healing, and reconstruct the enthesis structure.

Polydopamine regulated hydroxyapatite microspheres grown in the three-dimensional honeycomb-like mollusk shell-derived organic template for osteogenesis

Layered osteochondral composite scaffolds are considered as a promising strategy for the treatment of osteochondral defects. However, the insufficient osseous support and integration of the subchondral bone layer frequently result in the failure of osteochondral repair. Therefore, it is essentially important to explore new subchondral bone constructs tailored to support bone integration and healing. In this study, a novel three-dimensional porous biomimetic construct (HA/pDA-OTMS) was successfully developed by polydopamine (pDA) regulating hydroxyapatite (HA) microspheres grown in the honeycomb-like mollusk shell-derived organic template (OTMS). The biomimetic OTMS had good mechanical properties, high toughness, biodegradability and excellent biocompatibility. Moreover, the long-range ordered cavity structure of OTMS allowed the smallest material to create the largest and most stable geometric space, endowing it high HA loading capacity. The modification of pDA on OTMS surface effectively promoted the mineral nucleation of HA in the micro-nano cavities of OTMS. The compression mechanical tests showed that the combination of inorganic HA and organic pDA-OTMS greatly improved the mechanical properties of the construct. Additionally, the HA/pDA-OTMS composite provided adequate 3-D support for osteoblast cell attachment, proliferation and differentiation, as well as significantly up-regulated the expression of osteogenesis-related genes. These results demonstrated that as-prepared HA/pDA-OTMS constructs with combined mechanical strength and excellent osteogenic activity show great application prospects in subchondral bone regeneration.

Biological Factors, Metals, and Biomaterials Regulating Osteogenesis through Autophagy

Bone loss raises great concern in numerous situations, such as ageing and many diseases and in both orthopedic and dentistry fields of application, with an extensive impact on health care. Therefore, it is crucial to understand the mechanisms and the determinants that can regulate osteogenesis and ensure bone balance. Autophagy is a well conserved lysosomal degradation pathway, which is known to be highly active during differentiation and development. This review provides a revision of the literature on all the exogen factors that can modulate osteogenesis through autophagy regulation. Metal ion exposition, mechanical stimuli, and biological factors, including hormones, nutrients, and metabolic conditions, were taken into consideration for their ability to tune osteogenic differentiation through autophagy. In addition, an exhaustive overview of biomaterials, both for orthopedic and dentistry applications, enhancing osteogenesis by modulation of the autophagic process is provided as well. Already investigated conditions regulating bone regeneration via autophagy need to be better understood for finely tailoring innovative therapeutic treatments and designing novel biomaterials.