Biomimetic, Osteoconductive Non-mulberry Silk Fiber Reinforced Tricomposite Scaffolds for Bone Tissue Engineering

Engineering biomimetic silk fibroin hydrogel scaffolds with "organic-inorganic assembly" strategy for rapid bone regeneration

Although natural polymers have been widely used in constructing bone scaffolds, it still remains challenging to fabricate natural polymer-derived bone scaffolds with biomimetic mechanical properties as well as outstanding osteogenic properties for large-size and weight-bearing bone defects regeneration. Herein, an "organic-inorganic assembly" strategy is developed to construct silk fibroin (SF)-based bone scaffolds with the aforementioned merits. After secondary structure reshuffling, the 3.3-fold increment of β-sheet structures in SF hydrogel resulted in a 100-fold improvement of mineral-assembly efficacy via influencing the ion adsorption process and providing templates for mineral growth. Notably, abundant minerals were deposited within the hydrogel and also on the surface, which indicated entire mineral-assembly, which ensured the biomimetic mechanical properties of the digital light processing 3D printed SF hydrogel scaffolds with haversian-mimicking structure. In vitro experiments proved that the assembly between the mineral and SF results in rapid adhesion and enhanced osteogenic differentiation of human bone marrow-derived mesenchymal stem cells. In vivo experiments further proved that the mineral-assembled SF hydrogel scaffold could significantly enhance integration and bone regeneration at the weight-bearing site within one month. This SF-based "organic-inorganic assembly" strategy sheds light on constructing cell-free, growth factor-free and natural polymer-derived bone scaffolds with biomimetic 3D structure, mechanical properties and excellent osteogenic properties.

Biomimetic fabrication of sr-silk fibroin co-assembly hydroxyapatite based microspheres with angiogenic and osteogenic properties for bone tissue engineering

Bone defects caused by trauma, tumor resection, or developmental abnormalities are important issues in clinical practice. The vigorous development of tissue engineering technology provides new ideas and directions for regenerating bone defects. Hydroxyapatite (HAp), a bioactive ceramic, is extensively used in bone tissue engineering because of its excellent osteoinductive performance. However, its application is challenged by its single function and conventional environment-unfriendly synthesis methods. In this study, we successfully "green" synthesized sr-silk fibroin co-assembly hydroxyapatite nanoparticles (Sr-SF-HA) using silk fibroin (SF) as a biomineralized template, thus enabling it to have angiogenic activity and achieving the combination of organic and inorganic substances. Then, the rough composite microspheres loaded with Sr-SF-HA (CS/Sr-SF-HA) through electrostatic spraying technology and freeze-drying method were prepared. The CCK-8 test and live/dead cell staining showed excellent biocompatibility of CS/Sr-SF-HA. Alkaline phosphatase (ALP) staining, alizarin red staining (ARS), immunofluorescence, western blotting, and qRT-PCR test showed that CS/Sr-SF-HA activated the expression of related genes and proteins, thus inducing the osteogenic differentiation of rBMSCs. Moreover, tube formation experiments, scratch experiments, immunofluorescence, and qRT-PCR detection indicated that CS/Sr-SF-HA have good angiogenic activity. Furthermore, in vivo studies showed that the CS/Sr-SF-HA possesses excellent biocompatibility, vascular activity, as well as ectopic osteogenic ability in the subcutaneous pocket of rats. This study indicates that the construction of CS/Sr-SF-HA with angiogenic and osteogenic properties has great potential for bone tissue engineering.

Biomimetic Mineralization: From Microscopic to Macroscopic Materials and Their Biomedical Applications

Biomineralization is an attractive pathway to produce mineral-based biomaterials with high performance and hierarchical structures. To date, the biomineralization process and mechanism have been extensively studied, especially for the formation of bone, teeth, and nacre. Inspired by those, abundant biomimetic mineralized materials have been fabricated for biomedical applications. Those bioinspired materials generally exhibit great mechanical properties and biological functions. Nevertheless, substantial gaps remain between biomimetic materials and natural materials, particularly with respect to mechanical properties and mutiscale structures. This Review summarizes the recent progress of micro- and macroscopic biomimetic mineralization from the perspective of materials synthesis and biomedical applications. To begin with, we discuss the progress of biomimetic mineralization at the microscopic level. The mechanical strength, stability, and functionality of the nano- and micromaterials are significantly improved by introducing biominerals, such as DNA nanostructures, nanovaccines, and living cells. Next, numerous biomimetic strategies based on biomineralization at the macroscopic scale are highlighted, including in situ mineralization and bottom-up assembly of mineralized building blocks. Finally, challenges and future perspectives regarding the development of biomimetic mineralization are also presented with the aim of offering insights for the rational design and fabrication of next-generation biomimetic mineralized materials.

Injectable hydrogels for cartilage and bone tissue regeneration: A review

Annually, millions of patients suffer from irreversible injury owing to the loss or failure of an organ or tissue caused by accident, aging, or disease. The combination of injectable hydrogels and the science of stem cells have emerged to address this persistent issue in society by generating minimally invasive treatments to augment tissue function. Hydrogels are composed of a cross-linked network of polymers that exhibit a high-water retention capacity, thereby mimicking the wet environment of native cells. Due to their inherent mechanical softness, hydrogels can be used as needle-injectable stem cell carrier materials to mend tissue defects. Hydrogels are made of different natural or synthetic polymers, displaying a broad portfolio of eligible properties, which include biocompatibility, low cytotoxicity, shear-thinning properties as well as tunable biological and physicochemical properties. Presently, novel ongoing developments and native-like hydrogels are increasingly being used broadly to improve the quality of life of those with disabling tissue-related diseases. The present review outlines various future and in-vitro applications of injectable hydrogel-based biomaterials, focusing on the newest ongoing developments of in-situ forming injectable hydrogels for bone and cartilage tissue engineering purposes.

Kaempferol-loaded bioactive glass-based scaffold for bone tissue engineering: in vitro and in vivo evaluation

Due to the increasing prevalence of bone disorders among people especially in average age, the future of treatments for osseous abnormalities has been illuminated by scaffold-based bone tissue engineering. In this study, in vitro and in vivo properties of 58S bioactive glass-based scaffolds for bone tissue engineering (bare (B.SC), Zein-coated (C.SC), and Zein-coated containing Kaempferol (KC.SC)) were evaluated. This is a follow-up study on our previously published paper, where we synthesized 58S bioactive glass-based scaffolds coated with Kaempferol-loaded Zein biopolymer, and characterized from mostly engineering points of view to find the optimum composition. For this aim, in vitro assessments were done to evaluate the osteogenic capacity and biological features of the scaffolds. In the in vivo section, all types of scaffolds with/without bone marrow-derived stem cells (BMSC) were implanted into rat calvaria bone defects, and potential of bone healing was assessed using imaging, staining, and histomorphometric analyses. It was shown that, Zein-coating covered surface cracks leading to better mechanical properties without negative effect on bioactivity and cell attachment. Also, BMSC differentiation proved that the presence of Kaempferol caused higher calcium deposition, increased alkaline phosphatase activity, bone-specific gene upregulation in vitro. Further, in vivo study confirmed positive effect of BMSC-loaded KC.SC on significant new bone formation resulting in complete bone regeneration. Combining physical properties of coated scaffolds with the osteogenic effect of Kaempferol and BMSCs could represent a new strategy for bone regeneration and provide a more effective approach to repairing critical-sized bone defects.

Beta-TCP scaffolds with rationally designed macro-micro hierarchical structure improved angio/osteo-genesis capability for bone regeneration

The design of hierarchical porous structure in scaffolds is crucial for bone defect regenerative repair. However, bioceramic materials present a challenge in precisely constructing designed micropores owing to the limitation of forming process. To investigate micropore shape influences bone regeneration in bioceramic scaffolds with macropores, hierarchical porous scaffolds with interconnective macropores (~400 μm) and two types of micropores (spherical and fibrous) were prepared using a combination of direct ink writing (DIW) and template sacrifice methods. Compared to the scaffold with spherical micropores, the scaffold with highly interconnected fibrous micropores significantly improved cell adhesion and upregulated osteogenic and angiogenetic-related gene expression in mBMSCs and HUVECs, respectively. Furthermore, in vivo implantation experiments showed that hierarchical scaffolds with fibrous micropores accelerated the bone repair process significantly. This result can be attributed to the high interconnectivity of fibrous micropores, which promotes the transportation of nutrients and waste during bone regeneration. Our work demonstrates that hierarchical porous scaffold design, especially one with a fibrous micropore structure, is a promising strategy for improving the bone regeneration performance of bioceramic scaffolds.

Flaxseed mucilage/calcium phosphate composites as bioactive material for bone tissue regeneration

Biocompatible polymers are attractive material for the manufacturing of surgical implants which break down in vivo without the necessity for a consequent operation for removal. Elaboration of composite biomaterials scaffolds as artificial bone graft materials remains a major task in bioengineering. Flaxseed mucilage was used as bioactive polysaccharide for preparing composite scaffolds made of calcium phosphate embedded in mucilage matrix. Calcium chloride was mixed with mucilage followed by the addition of phosphate precursor to stimulate the in situ formation of calcium phosphate. The obtained scaffolds mucilage/calcium phosphate at different pHs (5 and 8) were characterized using FTIR, XRD, TGA, SEM/EDX and TEM. The results showed the formation of two phases: mucilage/dicalcium phosphate dihydrate (MU/brushite) and mucilage/hydroxyapatite (MU/HA). MTT test was applied to evaluate viability of MC3T3-E1 osteoblasts cells, and the formed hybrids at various pH conditions were classified as non-cytotoxic. These findings establish the potential of developed composite to be used as bone graft substitute materials.

Silk fibroin scaffolds: A promising candidate for bone regeneration

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

Biodegradable bioelectronics for biomedical applications

Biodegradable polymers have been widely used in tissue engineering with the potential to be replaced by regenerative tissue. While conventional bionic interfaces are designed to be implanted in living tissue and organs permanently, biocompatible and biodegradable electronic materials are now progressing a paradigm shift towards transient and regenerative bionic engineering. For example, biodegradable bioelectronics can monitor physiologies in a body, transiently rehabilitate disease symptoms, and seamlessly form regenerative interfaces from synthetic electronic devices to tissues by reducing inflammatory foreign-body responses. Conventional electronic materials have not readily been considered biodegradable. However, several strategies have been adopted for designing electroactive and biodegradable materials systems: (1) conductive materials blended with biodegradable components, (2) molecularly engineered conjugated polymers with biodegradable moieties, (3) naturally derived conjugated biopolymers, and (4) aqueously dissolvable metals with encapsulating layers. In this review, we endeavor to present the technical bridges from electrically active and biodegradable material systems to edible and biodegradable electronics as well as transient bioelectronics with pre-clinical bio-instrumental applications, including biodegradable sensors, neural and tissue engineering, and intelligent drug delivery systems.

Understanding the Interfacial Adhesion between Natural Silk and Polycaprolactone for Fabrication of Continuous Silk Biocomposites

The poor interfacial adhesion between silk fiber and polyester species remains a critical problem for the optimal mechanical performance of silk-reinforced polyester composites. Here, we investigated in quantitative terms the interfacial properties between natural silk fibers and polycaprolactone (PCL) at nano-, micro-, and macroscales and fabricated continuous silk-PCL composite filaments by melt extrusion and drawing processing of PCL melt at 100, 120, and 140 °C. Bombyx mori (Bm) silk, Antheraea pernyi (Ap) silk, and polyamide6 (PA6) fiber were compared to the composite with PCL. The Ap silk exhibited the highest surface energy, the best wettability, and the largest interfacial shear strength (IFSS) with PCL. The silk-PCL composite from the 120 °C melt processing displayed the highest tensile modulus, implying an optimal temperature for interfacial adhesion. The Raman imaging technique revealed in detail the nature of the physical fusion of the interface phase in these silk- and polyamide-reinforced PCL composites. This work is intended to lay a foundation for the design and processing of robust composites from continuous silk fibers and bioresorbable polyesters for potential structural biomaterials.

Nonmulberry silk fibroin-based biomaterials: Impact on cell behavior regulation and tissue regeneration

Silk fibroin (SF) is a promising biomaterial due to its good biocompatibility, easy availability, and high mechanical properties. Compared with mulberry silk fibroin (MSF), nonmulberry silk fibroin (NSF) isolated from typical nonmulberry silkworm silk exhibits unique arginine-glycine-aspartic acid (RGD) sequences with favorable cell adhesion enhancing effect. This inherent property probably makes the NSF more suitable for cell culture and tissue regeneration-related applications. Accordingly, various types of NSF-based biomaterials, such as particles, films, fiber mats, and 3D scaffolds, are constructed and their application potential in different biomedical fields is extensively investigated. Based on these promising NSF biomaterials, this review firstly makes a systematical comparison between the molecular structure and properties of MSF and typical NSF and highlights the unique properties of NSF. In addition, we summarize the effective fabrication strategies from degummed nonmulberry silk fibers to regenerated NSF-based biomaterials with controllable formats and their recent application progresses in cell behavior regulation and tissue regeneration. Finally, current challenges and future perspectives for the fabrication and application of NSF-based biomaterials are discussed. Related research and perspectives may provide valuable references for designing and modifying effective NSF-based and other natural biomaterials. STATEMENT OF SIGNIFICANCE: There exist many reviews about mulberry silk fibroin (MSF) biomaterials and their biomedical applications, while that about nonmulberry silk fibroin (NSF) biomaterials is scarce. Compared with MSF, NSF exhibits unique arginine-glycine-aspartic acid sequences with promising cell adhesion enhancing effect, which makes NSF more suitable for cell culture and tissue regeneration related applications. Focusing on these advanced NSF biomaterials, this review has systematically compared the structure and properties of MSF and NSF, and emphasized the unique properties of NSF. Following that, the effective construction strategies for NSF-based biomaterials are summarized, and their recent applications in cell behavior regulations and tissue regenerations are highlighted. Furthermore, current challenges and future perspectives for the fabrication and application of NSF-based biomaterials were discussed.

A 3D Printed Bone Tissue Engineering Scaffold Composed of Alginate Dialdehyde-Gelatine Reinforced by Lysozyme Loaded Cerium Doped Mesoporous Silica-Calcia Nanoparticles

A novel biomaterial comprising alginate dialdehyde-gelatine (ADA-GEL) hydrogel augmented by lysozyme loaded mesoporous cerium doped silica-calcia nanoparticles (Lys-Ce-MSNs) was 3D printed to create bioactive scaffolds. Lys-Ce-MSNs raised the mechanical stiffness of the hydrogel composite scaffold and induced surface apatite mineralization, when the scaffold was immersed in simulated body fluid (SBF). Moreover, the scaffolds could co-deliver bone healing (Ca and Si) and antioxidant ions (Ce), and Lys to achieve antibacterial (and potentially anticancer) properties. The nanocomposite hydrogel scaffolds could hold and deliver Lys steadily. Based on the in vitro results, the hydrogel nanocomposite containing Lys assured improved pre-osteoblast cell (MC3T3-E1) proliferation, adhesion, and differentiation, thanks to the biocompatibility of ADA-GEL, bioactivity of Ce-MSNs, and the stabilizing effect of Lys on the scaffold structure. On the other hand, the proliferation level of MG63 osteosarcoma cells decreased, likely due to the anticancer effect of Lys. Last but not least, cooperatively, alongside gentamicin (GEN), Lys brought about a proper antibacterial efficiency to the hydrogel nanocomposite scaffold against gram-positive and gram-negative bacteria. Taken together, ADA-GEL/Lys-Ce-MSN nanocomposite holds great promise for 3D printing of multifunctional hydrogel BTE scaffolds, able to induce bone regeneration, address infection, and potentially inhibit tumor formation and growth. This article is protected by copyright. All rights reserved.

Integrity of the ECM Influences the Bone Regenerative Property of ECM/Dicalcium Phosphate Composite Scaffolds

Due to the limitation of clinical autologous bone supply and other issues, the development of bone regeneration materials is still a hot topic. Natural tissue-derived bone repair materials have good biocompatibility and degradability, but their structure and properties are likely to be adversely affected during terminal sterilization. In this study, a composite scaffold consisting of the acellular extracellular matrix and dicalcium phosphate (ECM/DCP) was fabricated and terminally sterilized by γ-ray irradiation. In addition, the ECM/DCP scaffold was saturated with water and was also sterilized by γ-ray irradiation (RX-ECM/DCP). Results showed that the triple helix structure of collagen was better maintained in RX-ECM/DCP than in ECM/DCP. The thermal stability of RX-DCP/ECM was much better than that of ECP/ECM. The in vitro and in vivo performances of both types of scaffolds were also evaluated. The RX-ECM/DCP scaffold exhibited better in vitro bioactivity than that of the ECM/DCP scaffold as evidenced by more mineral formation in the simulated body fluid. In addition, RX-ECM/DCP also induced more effective bone regeneration than the ECM/DCP scaffold did in a rat calvarial defect model. Results sufficiently demonstrated that the addition of water to the scaffold could protect the structure of the ECM/DCP scaffold from being damaged by γ-ray irradiation during the terminal sterilization process. In summary, this study demonstrated a means to protect the ECM structure, which in turn led to the improvement of bone regenerative properties of the materials during γ-ray irradiation of ECM-based bone repair materials.

Application of vancomycin-impregnated calcium sulfate hemihydrate/nanohydroxyapatite/carboxymethyl chitosan injectable hydrogels combined with BMSC sheets for the treatment of infected bone defects in a rabbit model

BACKGROUND

The choice of bone substitutes for the treatment of infected bone defects (IBDs) has attracted the attention of surgeons for years. However, single-stage bioabsorbable materials that are used as carriers for antibiotic release, as well as scaffolds for BMSC sheets, need further exploration. Our study was designed to investigate the effect of vancomycin-loaded calcium sulfate hemihydrate/nanohydroxyapatite/carboxymethyl chitosan (CSH/n-HA/CMCS) hydrogels combined with BMSC sheets as bone substitutes for the treatment of IBDs.

METHODS

BMSCs were harvested and cultured into cell sheets. After the successful establishment of an animal model with chronic osteomyelitis, 48 New Zealand white rabbits were randomly divided into 4 groups. Animals in Group A were treated with thorough debridement as a control. Group B was treated with BMSC sheets. CSH/n-HA/CMCS hydrogels were implanted in the treatment of Group C, and Group D was treated with CSH/n-HA/CMCS+BMSC sheets. Gross observation and micro-CT 3D reconstruction were performed to assess the osteogenic and infection elimination abilities of the treatment materials. Histological staining (haematoxylin and eosin and Van Gieson) was used to observe inflammatory cell infiltration and the formation of collagen fibres at 4, 8, and 12 weeks after implantation.

RESULTS

The bone defects of the control group were not repaired at 12 weeks, as chronic osteomyelitis was still observed. HE staining showed a large amount of inflammatory cell infiltration around the tissue, and VG staining showed no new collagen fibres formation. In the BMSC sheet group, although new bone formation was observed by gross observation and micro-CT scanning, infection was not effectively controlled due to unfilled cavities. Some neutrophils and only a small amount of collagen fibres could be observed. Both the hydrogel and hydrogel/BMSCs groups achieved satisfactory repair effects and infection control. Micro-CT 3D reconstruction at 4 weeks showed that the hydrogel/BMSC sheet group had higher reconstruction efficiency and better bone modelling with normal morphology. HE staining showed little aggregation of inflammatory cells, and VG staining showed a large number of new collagen fibres.

CONCLUSIONS

Our preliminary results suggested that compared to a single material, the novel antibiotic-impregnated hydrogels acted as superior scaffolds for BMSC sheets and excellent antibiotic vectors against infection, which provided a basis for applying tissue engineering technology to the treatment of chronic osteomyelitis.

Superior processability of Antheraea mylitta silk with cryo-milling: Performance in bone tissue regeneration

Non-mulberry silk polymers have a promising future in biomedical applications. However, the dissolution of non-mulberry silk fiber is a still challenge and this poor processability has limited the use of this material. Here, we report a unique protocol to process the Antheraea mylitta (AM) silk fiber. We have shown that the cryo-milling of silk fiber reduces the beta sheet content by more than 10% and results in an SF powder that completely dissolves in routine solvents like trifluoroacetic acid (TFA) within few hours to form highly concentrated solutions (~20 wt%). Further, these solutions can be processed using conventional processing techniques such as electrospinning to form 3D scaffolds. Bombyx mori (BM) silk was used as a control sample in the study. In-vitro studies were also performed to monitor cell adhesion and proliferation and hMSCs differentiation into osteogenic lineage. Finally, the osteogenic potential of the scaffolds was also evaluated by a 4-week implantation study in rat calvarial model. The in-vitro and in-vivo results show that the processing techniques do not affect the biocompatibility of the material and the AM scaffolds support bone regeneration. Our results, thus, show that cryo-milling facilitates enhanced processability of non-mulberry silk and therefore expands its potential in biomedical applications.

A review of current challenges and prospects of magnesium and its alloy for bone implant applications

Medical application materials must meet multiple requirements, and the designed implant must mimic the bone structure in shape and support the formation of bone tissue (osteogenesis). Magnesium (Mg) alloys, as a "smart" biodegradable material and as "the green engineering material in the twenty-first century", have become an outstanding bone implant material due to their natural degradability, smart biocompatibility, and desirable mechanical properties. Magnesium is recognised as the next generation of orthopaedic appliances and bioresorbable scaffolds. At the same time, improving the mechanical properties and corrosion resistance of magnesium alloys is an urgent challenge to promote the application of magnesium alloys. Nevertheless, the excessively quick deterioration rate generally results in premature mechanical integrity disintegration and local hydrogen build-up, resulting in restricted clinical bone restoration applicability. The condition of Mg bone implants is thoroughly examined in this study. The relevant approaches to boost the corrosion resistance, including purification, alloying treatment, surface coating, and Mg-based metal matrix composite, are comprehensively revealed. These characteristics are reviewed to assess the progress of contemporary Mg-based biocomposites and alloys for biomedical applications. The fabricating techniques for Mg bone implants also are thoroughly investigated. Notably, laser-based additive manufacturing fabricates customised forms and complicated porous structures based on its distinctive additive manufacturing conception. Because of its high laser energy density and strong controllability, it is capable of fast heating and cooling, allowing it to modify the microstructure and performance. This review paper aims to provide more insight on the present challenges and continued research on Mg bone implants, highlighting some of the most important characteristics, challenges, and strategies for improving Mg bone implants.

Silk-Based Bioengineered Diaphyseal Cortical Bone Unit Enclosing an Implantable Bone Marrow toward Atrophic Nonunion Grafting

Postnatal fracture healing of atrophic long bone diaphyseal nonunions remains a challenge for orthopedic surgeons. Paucity of autologous spongiosa has potentiated the use of tissue engineered bone grafts to improve success rates of bone marrow engraftment used in plate reosteosynthesis. Herein, the development and in vitro validation of a "sandwich-type" biofabricated diaphyseal cross-sectional unit, with an outer mechanically robust bioprinted cortical bone shell, encompassing an engineered bone marrow, are reported. Channelized silk fibroin blend sponges derived from Bombyx mori and Antheraea assama help in developing compartmentalized endosteum, exhibiting specialized osteoblasts (endosteal niche) and discontinuous endothelium (vascular niche). The cellular cross-talk between these two niches triggered via integrin-mediated cell adhesion, enables in preserving quiescence state of CD34⁺ /CD38^- hematopoietic stem cells and their recycling in the engineered marrow. The outer cortical bone strut is developed through multimaterial microextrusion bioprinting strategy. Osteogenically primed mesenchymal stem cells-laden silk fibroin-nano-hydroxyapatite bioink is bioprinted alongside paramagnetic Fe-doped bioactive glass-polycaprolactone blend thermoplastic ink, reinforcing it for mechanical stability. Pulsed magnetic field actuation positively influences the osteogenic commitment and maturation of the bioprinted constructs via mechanotransductory route. Therefore, the assembled engineered marrow and bioprinted cortical shell hold promise as potential orthobiologic substitutes toward atrophic nonunion repairs.

Generation of hybrid tissue engineered construct through embedding autologous chondrocyte loaded platelet rich plasma/alginate based hydrogel in porous scaffold for cartilage regeneration

Over the past decades, various attempts have been made to develop suitable tissue-engineered constructs to repair or regenerate the damaged or diseased articular cartilage. In the present study, we embedded Platelet rich plasma (PRP)/Sodium Alginate (SA) based hydrogel in porous 3D scaffold of chitosan (CH)/chondroitin sulfate (CS)/silk fibroin (SF) to develop hybrid scaffold for cartilage tissue construct generation with abilities to support shape recovery potential, facilitate uniform cells distribution and mimic gel like cartilage tissue extracellular matrix.The developed hybrid matrix shows suitable pore size (55-261 μm), porosity (77 ± 4.3%) and compressive strength (0.13 ± 0.04 MPa) for cartilage tissue construct generation and its applications. The developed SA/PRP-based cartilage construct exhibits higher metabolic activity, glycosaminoglycan deposition, expression of collagen type II, and aggrecan in comparison to SA based cell-scaffold construct. In-vivo animal study was also performed to investigate the biocompatibility and cartilage tissue regeneration potential of the developed construct. The obtained gross analysis of knee sample, micro-computed tomography, and histological analysis suggest that implanted tissue construct possess the superior potential to regenerate hyaline cartilage defect of thickness around 1.10 ± 0.36 mm and integrate with surrounding tissue at the defect site. Thus, the proposed strategy for the development of cartilage tissue constructs might be beneficial for the repair of full-thickness knee articular cartilage defects.

A Perfusion Bioreactor Model of Tumor-Induced Bone Disease Using Human Cells

Advanced solid tumors often metastasize to bone. Once established in bone, these tumors can induce bone destruction resulting in decreased quality of life and increased mortality. Neither 2D in vitro models nor 3D animal models sufficiently recapitulate the human bone-tumor microenvironment needed to fully understand the complexities of bone metastasis, highlighting the need for new models. A 3D in vitro humanized model of tumor-induced bone disease was developed by dynamically culturing human osteoblast, osteoclast, and metastatic cancer cells together within tissue-engineered bone constructs. Cell-mediated resorption can be observed by micro-computed tomography and can be quantified by change in mass. Taken together, these data can be used to investigate whether the metastatic cancer cells included in the model have the potential to drive osteoclastogenesis and cell-mediated resorption in vitro. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Fabricating bone-like scaffolds Basic Protocol 2: Preparing cells for the humanized model of TIBD Basic Protocol 3: Crafting a 3D in vitro humanized model of TIBD.

A silk composite fiber reinforced by telechelic-type polyalanine and its strengthening mechanism

A telechelic-type polyalanine was doped in silkworm silk fibroins to prepare reinforced composite fibers, which exhibited 42% and 51% higher mechanical properties than silk-only fibers in terms of tensile strength and toughness, respectively.

An Overview of Natural Polymers as Reinforcing Agents for 3D Printing

Three-dimensional (3D) printing, or additive manufacturing, is a group of innovative technologies that are increasingly employed for the production of 3D objects in different fields, including pharmaceutics, engineering, agri-food and medicines. The most processed materials by 3D printing techniques (e.g., fused deposition modelling, FDM; selective laser sintering, SLS; stereolithography, SLA) are polymeric materials since they offer chemical resistance, are low cost and have easy processability. However, one main drawback of using these materials alone (e.g., polylactic acid, PLA) in the manufacturing process is related to the poor mechanical and tensile properties of the final product. To overcome these limitations, fillers can be added to the polymeric matrix during the manufacturing to act as reinforcing agents. These include inorganic or organic materials such as glass, carbon fibers, silicon, ceramic or metals. One emerging approach is the employment of natural polymers (polysaccharides and proteins) as reinforcing agents, which are extracted from plants or obtained from biomasses or agricultural/industrial wastes. The advantages of using these natural materials as fillers for 3D printing are related to their availability together with the possibility of producing printed specimens with a smaller environmental impact and higher biodegradability. Therefore, they represent a “green option” for 3D printing processing, and many studies have been published in the last year to evaluate their ability to improve the mechanical properties of 3D printed objects. The present review provides an overview of the recent literature regarding natural polymers as reinforcing agents for 3D printing.

CCL2 loaded microparticles promote acute patency in silk-based vascular grafts implanted in rat aortae

Cardiovascular disease is the leading cause of death worldwide, often associated with coronary artery occlusion. A common intervention for arterial blockage utilizes a vascular graft to bypass the diseased artery and restore downstream blood flow; however, current clinical options exhibit high long-term failure rates. Our goal was to develop an off-the-shelf tissue-engineered vascular graft capable of delivering a biological payload based on the monocyte recruitment factor C-C motif chemokine ligand 2 (CCL2) to induce remodeling. Bi-layered silk scaffolds consisting of an inner porous and outer electrospun layer were fabricated using a custom blend of Antherea Assama and Bombyx Mori silk (lyogel). Lyogel silk scaffolds alone (LG), and lyogel silk scaffolds containing microparticles (LGMP) were tested. The microparticles (MPs) were loaded with either CCL2 (LGMP+) or water (LGMP-). Scaffolds were implanted as abdominal aortic interposition grafts in Lewis rats for 1 and 8 weeks. 1-week implants exhibited patency rates of 50% (7/14), 100% (10/10), and 100% (5/5) in the LGMP-, LGMP+, and LG groups, respectively. The significantly higher patency rate for the LGMP+ group compared to the LGMP- group (p = 0.0188) suggests that CCL2 can prevent acute occlusion. Immunostaining of the explants revealed a significantly higher density of macrophages (CD68+ cells) within the outer vs. inner layer of LGMP- and LGMP+ constructs but not in LG constructs. After 8 weeks, there were no significant differences in patency rates between groups. All patent scaffolds at 8 weeks showed signs of remodeling; however, stenosis was observed within the majority of explants. This study demonstrated the successful fabrication of a custom blended silk scaffold functionalized with cell-mimicking microparticles to facilitate controlled delivery of a biological payload improving their in vivo performance. STATEMENT OF SIGNIFICANCE: This study outlines the development of a custom blended silk-based tissue-engineered vascular graft (TEVG) for use in arterial bypass or replacement surgery. A custom mixture of silk was formulated to improve biocompatibility and cellular binding to the tubular scaffold. Many current approaches to TEVGs include cells that encourage graft cellularization and remodeling; however, our technology incorporates a microparticle based delivery platform capable of delivering bioactive molecules that can mimic the function of seeded cells. In this study, we load the TEVGs with microparticles containing a monocyte attractant and demonstrate improved performance in terms of unobstructed blood flow versus blank microparticles. The acellular nature of this technology potentially reduces risk, increases reproducibility, and results in a more cost-effective graft when compared to cell-based options.

Silk biomaterials for vascular tissue engineering applications

Vascular tissue engineering is a rapidly growing field of regenerative medicine, which strives to find innovative solutions for vascular reconstruction. Considering the limited success of synthetic grafts, research impetus in the field is now shifted towards finding biologically active vascular substitutes bestowing in situ growth potential. In this regard, silk biomaterials have shown remarkable potential owing to their favorable inherent biological and mechanical properties. This review provides a comprehensive overview of the progressive development of silk-based small diameter (<6 mm) tissue-engineered vascular grafts (TEVGs), emphasizing their pre-clinical implications. Herein, we first discuss the molecular structure of various mulberry and non-mulberry silkworm silk and identify their favorable properties at the onset of vascular regeneration. The emergence of various state-of-the-art fabrication methodologies for the advancement of silk TEVGs is rationally appraised in terms of their in vivo performance considering the following parameters: ease of handling, long-term patency, resistance to acute thrombosis, stenosis and aneurysm formation, immune reaction, neo-tissue formation, and overall remodeling. Finally, we provide an update on the pre-clinical status of silk-based TEVGs, followed by current challenges and future prospects. STATEMENT OF SIGNIFICANCE: Limited availability of healthy autologous blood vessels to replace their diseased counterpart is concerning and demands other artificial substitutes. Currently available synthetic grafts are not suitable for small diameter blood vessels owing to frequent blockage. Tissue-engineered biological grafts tend to integrate well with the native tissue via remodeling and have lately witnessed remarkable success. Silk fibroin is a natural biomaterial, which has long been used as medical sutures. This review aims to identify several favorable properties of silk enabling vascular regeneration. Furthermore, various methodologies to fabricate tubular grafts are discussed and highlight their performance in animal models. An overview of our understanding to rationally improve the biological activity fostering the clinical success of silk-based grafts is finally discussed.

Functionalized Silk Vascular Grafts with Decellularized Human Wharton's Jelly Improves Remodeling via Immunomodulation in Rabbit Jugular Vein

Cell-free polymeric tissue-engineered vascular grafts (TEVGs) have shown great promise towards clinical translation; however, their limited bioactivity and remodeling ability challenge this cause. Here, a novel cell-free bioresorbable small diameter silk TEVG system functionalized with decellularized human Wharton's jelly (dWJ) matrix is developed and successfully implanted as interposition grafts into rabbit jugular vein. Implanted TEVGs remain patent for two months and integrate with host tissue, demonstrating neo-tissue formation and constructive remodeling. Mechanistic analysis reveals that dWJ matrix is a reservoir of various immunomodulatory cytokines (Interleukin-8, 6, 10, 4 and tumor necrosis factor alpha (TNF-α)), which aids in upregulating M2 macrophage-associated genes facilitating pro-remodeling behavior. Besides, dWJ treatment to human endothelial cells upregulates the expression of functional genes (cluster of differentiation 31 (CD31), endothelial nitric oxide synthase (eNOS), and vascular endothelial (VE)-cadherin), enables faster cell migration, and elevates nitric oxide (NO) production leading to the in situ development of endothelium. The dWJ functionalized silk TEVGs support increased host cell recruitment than control, including macrophages and vascular cells. It endows superior graft remodeling in terms of a dense medial layer comprising smooth muscle cells and elevates the production of extracellular matrix proteins (collagen and elastin). Altogether, these findings suggest that dWJ functionalization imitates the usefulness of cell seeding and enables graft remodeling.

Nonmulberry silk proteins: multipurpose ingredient in bio-functional assembly

The emerging field of tissue engineering and regenerative medicines utilising artificial polymers is facing many problems. Despite having mechanical stability, non-toxicity and biodegradability, most of them lack cytocompatibility and biocompatibility. Natural polymers (such as collagen, hyaluronic acid, fibrin, fibroin, and others), including blends, are introduced to the field to solve some of the relevant issues. Another natural biopolymer: silkworm silk gained special attention primarily due to its specific biophysical, biochemical, and material properties, worldwide availability, and cost-effectiveness. Silk proteins, namely fibroin and sericin extracted from domesticated mulberry silkwormBombyx mori, are studied extensively in the last few decades for tissue engineering. Wild nonmulberry silkworm species, originated from India and other parts of the world, also produce silk proteins with variations in their nature and properties. Among the nonmulberry silkworm species,Antheraea mylitta(Indian Tropical Tasar),A. assamensis/A. assama(Indian Muga), andSamia ricini/Philosamia ricini(Indian Eri), along withA. pernyi(Chinese temperate Oak Tasar/Tussah) andA. yamamai(Japanese Oak Tasar) exhibit inherent tripeptide motifs of arginyl glycyl aspartic acid in their fibroin amino acid sequences, which support their candidacy as the potential biomaterials. Similarly, sericin isolated from such wild species delivers unique properties and is used as anti-apoptotic and growth-inducing factors in regenerative medicines. Other characteristics such as biodegradability, biocompatibility, and non-inflammatory nature make it suitable for tissue engineering and regenerative medicine based applications. A diverse range of matrices, including but not limited to nano-micro scale structures, nanofibres, thin films, hydrogels, and porous scaffolds, are prepared from the silk proteins (fibroins and sericins) for biomedical and tissue engineering research. This review aims to represent the progress made in medical and non-medical applications in the last couple of years and depict the present status of the investigations on Indian nonmulberry silk-based matrices as a particular reference due to its remarkable potentiality of regeneration of different types of tissues. It also discusses the future perspective in tissue engineering and regenerative medicines in the context of developing cutting-edge techniques such as 3D printing/bioprinting, microfluidics, organ-on-a-chip, and other electronics, optical and thermal property-based applications.

Bioactive Silk Fibroin-Based Hybrid Biomaterials for Musculoskeletal Engineering: Recent Progress and Perspectives

Musculoskeletal engineering has been considered as a promising approach to customize regenerated tissue (such as bone, cartilage, tendon, and ligament) via a self-healing performance. Recent advances have demonstrated the great potential of bioactive materials for regenerative medicine. Silk fibroin (SF), a natural polymer, is regarded as a remarkable bioactive material for musculoskeletal engineering thanks to its biocompatibility, biodegradability, and tunability. To improve tissue-engineering performance, silk fibroin is hybridized with other biomaterials to form silk-fibroin-based hybrid biomaterials, which achieve superior mechanical and biological performance. Herein, we summarize the recent development of silk-based hybrid biomaterials in musculoskeletal tissue with reasonable generalization and classification, mainly including silk fibroin-based inorganic and organic hybrid biomaterials. The applied inorganics are composed of calcium phosphate, graphene oxide, titanium dioxide, silica, and bioactive glass, while the polymers include polycaprolactone, collagen (or gelatin), chitosan, cellulose, and alginate. This article mainly focuses on the physical and biological performances both in vitro and in vivo study of several common silk-based hybrid biomaterials in musculoskeletal engineering. The timely summary and highlight of silk-fibroin-based hybrid biomaterials will provide a research perspective to promote the further improvement and development of silk fibroin hybrid biomaterials for improved musculoskeletal engineering.

Fabrication and in vitro evaluation of PCL/gelatin hierarchical scaffolds based on melt electrospinning writing and solution electrospinning for bone regeneration

As an emerging 3D printing technique, melt electrospinning writing (MEW) has been used to fabricate scaffolds with controllable structure and good mechanical strength for bone regeneration. However, how to further improve MEW scaffolds with nanoscale extracellular matrix (ECM) mimic structure and bioactivity is still challenging. In this study, we proposed a simple composite process by combining MEW and solution electrospinning (SE) to fabricate a micro/nano hierarchical scaffold for bone tissue engineering. The morphological results confirmed the hierarchical structure with both well-defined MEW microfibrous grid structure and SE random nanofiber morphology. The addition of gelatin nanofibers turned the scaffolds to be hydrophilic, and led to a slight enhancement of mechanical strength. Compared with PCL MEW scaffolds, higher cell adhesion efficiency, improved cell proliferation and higher osteoinductive ability were achieved for the MEW/SE composite scaffolds. Finally, multilayer composite scaffolds were fabricated by alternately stacking of MEW layer and SE layer and used to assess the effect on cell ingrowth in the scaffolds. The results showed that gelatin nanofibers did not inhibit cell penetration, but promoted the three-dimensional growth of bone cells. Thus, the strategy of the combined use of MEW and SE is a potential method to fabricate micro/nano hierarchical scaffolds to improve bone regeneration.

Preparation and evaluation of gellan gum hydrogel reinforced with silk fibers with enhanced mechanical and biological properties for cartilage tissue engineering

Various research about cartilage regeneration using biomaterials has been done recently. Particularly, gellan gum hydrogel (GG) is reported to be suitable as a biomaterial for cartilage tissue engineering (TE) for its water uptaking ability, producibility, and environmental resemblance of native cartilage. Despite these advantages, mechanical and cell adhesion properties are still difficult to modulate. Reinforcement is essential to overcome these problems. Herein, GG was modified by physically blending with different lengths of silk fiber (SF). As SF is expected to improve such disadvantages of GG, mechanical and biological properties were characterized to confirm its reinforcement ability. Mechanical properties such as degradation rate, swelling rate, compression strength, and viscosity were studied and it was confirmed that SF significantly reinforces the mechanical properties of GG. Furthermore, in vitro study was carried out to confirm morphology, biocompatibility, proliferation, and chondrogenesis of chondrocytes encapsulated in the hydrogels. Overall, chondrocytes in the GG blended with SF (SF/GG) showed enhanced cell viability and growth. According to this study, SF/GG can be a promising biomaterial for cartilage TE biomaterial.

Influence of Charge and Heat on the Mechanical Properties of Scaffolds from Ionic Complexation of Chitosan and Carboxymethyl Cellulose

As one of the most abundant, multifunctional biological polymers, polysaccharides are considered promising materials to prepare tissue engineering scaffolds. When properly designed, wetted porous scaffolds can have biomechanics similar to living tissue and provide suitable fluid transport, both of which are key features for in vitro and in vivo tissue growth. They can further mimic the components and function of glycosaminoglycans found in the extracellular matrix of tissues. In this study, we investigate scaffolds formed by charge complexation between anionic carboxymethyl cellulose and cationic protonated chitosan under well-controlled conditions. Freeze-drying and dehydrothermal heat treatment were then used to obtain porous materials with exceptional, unprecendent mechanical properties and dimensional long-term stability in cell growth media. We investigated how complexation conditions, charge ratio, and heat treatment significantly influence the resulting fluid uptake and biomechanics. Surprisingly, materials with high compressive strength, high elastic modulus, and significant shape recovery are obtained under certain conditions. We address this mostly to a balanced charge ratio and the formation of covalent amide bonds between the polymers without the use of additional cross-linkers. The scaffolds promoted clustered cell adhesion and showed no cytotoxic effects as assessed by cell viability assay and live/dead staining with human adipose tissue-derived mesenchymal stem cells. We suggest that similar scaffolds or biomaterials comprising other polysaccharides have a large potential for cartilage tissue engineering and that elucidating the reason for the observed peculiar biomechanics can stimulate further research.

Thymoquinone loading into hydroxyapatite/alginate scaffolds accelerated the osteogenic differentiation of the mesenchymal stem cells

Background

Phytochemical agents such as thymoquinone (TQ) have osteogenic property. This study aimed to investigate the synergic impact of TQ and hydroxyapatite on mesenchymal stem cell differentiation. Alginate was also used as drug vehicle.

Methods

HA scaffolds were fabricated by casting into polyurethane foam and sintering at 800 °C, and then, 1250 °C and impregnated by TQ containing alginate. The adipose-derived stem cells were aliquoted into 4 groups: control, osteogenic induced-, TQ and osteogenic induced- and TQ-treated cultures. Adipose derived-mesenchymal stem cells were mixed with alginate and loaded into the scaffolds

Results

The results showed that impregnation of HA scaffold with alginate decelerated the degradation rate and reinforced the mechanical strength. TQ loading in alginate/HA had no significant influence on physical and mechanical properties. Real-time RT-PCR showed significant elevation in collagen, osteopontin, and osteocalcin expression at early phase of differentiation. TQ also led to an increase in alkaline phosphatase activity. At long term, TQ administration had no impact on calcium deposition and proliferation rate as well as bone-marker expression.

Conclusion

TQ accelerates the differentiation of the stem cells into the osteoblasts, without changing the physical and mechanical properties of the scaffolds. TQ also showed a synergic influence on differentiation potential of mesenchymal stem cells.

Development of carboxymethylcellulose based composites for bone tissue engineering

The present study focuses on the development of carboxymethylcellulose (CMC)–biphasic calcium phosphate (BCP) composite scaffolds through the freeze-drying process for bone tissue engineering applications. Citric acid or fumaric acid was added as the cross-linker of CMC to improve the stability of composite scaffolds. The effect of change in freezing temperature (−20, −40 or −80°C) on the pore morphology, swelling ability and mechanical properties of composite scaffolds was studied. Cross-linked scaffolds showed an increased thermal degradation temperature compared with non-cross-linked scaffolds. All the composite scaffolds showed a porous structure with homogeneous blending of CMC and BCP. Cross-linked scaffolds showed appreciable swelling ability and stability in phosphate-buffered saline, while non-cross-linked scaffolds were unstable for 24 h. Cross-linked scaffolds had lower compressive strength than non-cross-linked scaffolds under dry conditions. However, in the hydrated state, only citric acid-cross-linked scaffolds were stable with improved compressive strength of 64 ± 4, 57 ± 4 and 67 ± 4 kPa when processed at −20, −40 and −80°C, respectively. Furthermore, three-dimensional culture of Saos-2 cells on citric acid-cross-linked scaffolds showed their suitability for cell proliferation and osteogenic differentiation. Therefore, citric acid-cross-linked CMC–BCP composite scaffolds may be promising scaffolds for bone tissue engineering applications.

The Materiobiology of Silk: Exploring the Biophysical Influence of Silk Biomaterials on Directing Cellular Behaviors

Biophysical properties of the extracellular environment dynamically regulate cellular fates. In this review, we highlight silk, an indispensable polymeric biomaterial, owing to its unique mechanical properties, bioactive component sequestration, degradability, well-defined architectures, and biocompatibility that can regulate temporospatial biochemical and biophysical responses. We explore how the materiobiology of silks, both mulberry and non-mulberry based, affect cell behaviors including cell adhesion, cell proliferation, cell migration, and cell differentiation. Keeping in mind the novel biophysical properties of silk in film, fiber, or sponge forms, coupled with facile chemical decoration, and its ability to match functional requirements for specific tissues, we survey the influence of composition, mechanical properties, topography, and 3D geometry in unlocking the body's inherent regenerative potential.

Silk Biomaterials for Bone Tissue Engineering

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

Controlled delivery of bone morphogenic protein-2-related peptide from mineralised extracellular matrix-based scaffold induces bone regeneration

Ideal bone tissue engineering scaffolds composed of extracellular matrix (ECM) require excellent osteoconductive ability to imitate the bone environment. We developed a mineralised tissue-derived ECM-modified true bone ceramic (TBC) scaffold for the delivery of aspartic acid-modified bone morphogenic protein-2 (BMP-2) peptide (P28) and assessed its osteogenic capacity. Decellularized ECM from porcine small intestinal submucosa (SIS) was coated onto the surface of TBC, followed by mineralisation modification (mSIS/TBC). P28 was subsequently immobilised onto the scaffolds in the absence of a crosslinker. The alkaline phosphatase activity and other osteogenic differentiation marker results showed that osteogenesis of the P28/mSIS/TBC scaffolds was significantly greater than that of the TBC and mSIS/TBC groups. In addition, to examine the osteoconductive capability of this system in vivo, we established a rat calvarial bone defect model and evaluated the new bone area and new blood vessel density. Histological observation showed that P28/mSIS/TBC exhibited favourable bone regeneration efficacy. This study proposes the use of mSIS/TBC loaded with P28 as a promising osteogenic scaffold for bone tissue engineering applications.

Systematic Review of Silk Scaffolds in Musculoskeletal Tissue Engineering Applications in the Recent Decade

During the past decade, various novel tissue engineering (TE) strategies have been developed to maintain, repair, and restore the biomechanical functions of the musculoskeletal system. Silk fibroins are natural polymers with numerous advantageous properties such as good biocompatibility, high mechanical strength, and low degradation rate and are increasingly being recognized as a scaffolding material of choice in musculoskeletal TE applications. This current systematic review examines and summarizes the latest research on silk scaffolds in musculoskeletal TE applications within the past decade. Scientific databases searched include PubMed, Web of Science, Medline, Cochrane library, and Embase. The following keywords and search terms were used: musculoskeletal, tendon, ligament, intervertebral disc, muscle, cartilage, bone, silk, and tissue engineering. Our Review was limited to articles on musculoskeletal TE, which were published in English from 2010 to September 2019. The eligibility of the articles was assessed by two reviewers according to prespecified inclusion and exclusion criteria, after which an independent reviewer performed data extraction and a second independent reviewer validated the data obtained. A total of 1120 articles were reviewed from the databases. According to inclusion and exclusion criteria, 480 articles were considered as relevant for the purpose of this systematic review. Tissue engineering is an effective modality for repairing or replacing injured or damaged tissues and organs with artificial materials. This Review is intended to reveal the research status of silk-based scaffolds in the musculoskeletal system within the recent decade. In addition, a comprehensive translational research route for silk biomaterial from bench to bedside is described in this Review.

Metal-Protein Hybrid Materials with Desired Functions and Potential Applications

Metal nanohybrids are fast emerging functional nanomaterials with advanced structures, intriguing physicochemical properties, and a broad range of important applications in current nanoscience research. Significant efforts have been devoted toward design and develop versatile metal nanohybrid systems. Among numerous biological components, diverse proteins offer avenues for making advanced multifunctional systems with unusual properties, desired functions, and potential applications. This review discusses the rational design, properties, and applications of metal-protein nanohybrid materials fabricated from proteins and inorganic components. The construction of functional biomimetic nanohybrid materials is first briefly introduced. The properties and functions of these hybrid materials are then discussed. After that, an overview of promising application of biomimetic metal-protein nanohybrid materials is provided. Finally, the key challenges and outlooks related to this fascinating research area are also outlined.

HA/MgO nanocrystal-based hybrid hydrogel with high mechanical strength and osteoinductive potential for bone reconstruction in diabetic rats

Bone repair and regeneration processes are markedly impaired in diabetes mellitus (DM). Intervening approaches similar to those developed for normal healing conditions have been adopted to combat DM-associated bone regeneration. However, limited outcomes were achieved for these approaches. Hence, together with osteoconductive hydroxyapatite (HA) nanocrystals, osteoinductive magnesium oxide (MgO) nanocrystals were uniformly mounted into the network matrix of an organic hydrogel composed of cysteine-modified γ-polyglutamic acid (PGA-Cys) to construct a hybrid and rough hydrogel scaffold. It was hypothesized that the HA/MgO nanocrystal hybrid hydrogel (HA/MgO-H) scaffold can significantly promote bone repair in DM rats via the controlled release of Mg²⁺. The HA/MgO-H scaffold exhibited a sponge-like morphology with porous 3D networks inside it and displayed higher mechanical strength than a PGA-Cys scaffold. Meanwhile, the HA/MgO-H scaffold gradually formed a tough hydrogel with G' of more than 1000 Pa after hydration, and its high hydration swelling ratio was still retained. Moreover, after the chemical degradation of the dispersed MgO nanocrystals, slow release of Mg²⁺ from the hydrogel matrix was achieved for up to 8 weeks because of the chelation between Mg²⁺ and the carboxyl groups of PGA-Cys. In vitro cell studies showed that the HA/MgO-H scaffold could not only effectively promote the migration and proliferation of BMSCs but could also induce osteogenic differentiation. Moreover, in the 8th week after implanting the HA/MgO-H scaffold into femur bone defect zones of DM rats, more effective bone repair was presented by micro-CT imaging. The bone mineral density (397.22 ± 16.36 mg cm^-3), trabecular thickness (0.48 ± 0.07 mm), and bone tissue volume/total tissue volume (79.37 ± 7.96%) in the HA/MgO-H group were significantly higher than those in the other groups. Moreover, higher expression of COL-I and OCN after treatment with HA/MgO-H was also displayed. The bone repair mechanism of the HA/MgO-H scaffold was highly associated with reduced infiltration of pro-inflammatory macrophages (CD80⁺) and higher angiogenesis (CD31⁺). Collectively, the HA/MgO-H scaffold without the usage of bioactive factors may be a promising biomaterial to accelerate bone defect healing under diabetes mellitus.

Biomimetic and osteogenic 3D silk fibroin composite scaffolds with nano MgO and mineralized hydroxyapatite for bone regeneration

Artificial bioactive materials have received increasing attention worldwide in clinical orthopedics to repair bone defects that are caused by trauma, infections or tumors, especially dedicated to the multifunctional composite effect of materials. In this study, a weakly alkaline, biomimetic and osteogenic, three-dimensional composite scaffold (3DS) with hydroxyapatite (HAp) and nano magnesium oxide (MgO) embedded in fiber (F) of silkworm cocoon and silk fibroin (SF) is evaluated comprehensively for its bone repair potential in vivo and in vitro experiments, particularly focusing on the combined effect between HAp and MgO. Magnesium ions (Mg²⁺) has long been proven to promote bone tissue regeneration, and HAp is provided with osteoconductive properties. Interestingly, the weak alkaline microenvironment from MgO may also be crucial to promote Sprague-Dawley (SD) rat bone mesenchymal stem cells (BMSCs) proliferation, osteogenic differentiation and alkaline phosphatase (ALP) activities. This SF/F/HAp/nano MgO (SFFHM) 3DS with superior biocompatibility and biodegradability has better mechanical properties, BMSCs proliferation ability, osteogenic activity and differentiation potential compared with the scaffolds adding HAp or MgO alone or neither. Similarly, corresponding meaningful results are also demonstrated in a model of distal lateral femoral defect in SD rat. Therefore, we provide a promising 3D composite scaffold for promoting bone regeneration applications in bone tissue engineering.

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.

3D printing of silk microparticle reinforced polycaprolactone scaffolds for tissue engineering applications

Polycaprolactone (PCL) scaffolds have been widely investigated for tissue engineering applications, however, they exhibit poor cell adhesion and mechanical properties. Subsequently, PCL composites have been produced to improve the material properties. This study utilises a natural material, Bombyx mori silk microparticles (SMP) prepared by milling silk fibre, to produce a composite to enhance the scaffolds properties. Silk is biocompatible and biodegradable with excellent mechanical properties. However, there are no studies using SMPs as a reinforcing agent in a 3D printed thermoplastic polymer scaffold. PCL/SMP (10, 20, 30 wt%) composites were prepared by melt blending. Rheological analysis showed that SMP loading increased the shear thinning and storage modulus of the material. Scaffolds were fabricated using a screw-assisted extrusion-based additive manufacturing system. Scanning electron microscopy and X-ray microtomography was used to determine scaffold morphology. The scaffolds had high interconnectivity with regular printed fibres and pore morphologies within the designed parameters. Compressive mechanical testing showed that the addition of SMP significantly improved the compressive Young's modulus of the scaffolds. The scaffolds were more hydrophobic with the inclusion of SMP which was linked to a decrease in total protein adsorption. Cell behaviour was assessed using human adipose derived mesenchymal stem cells. A cytotoxic effect was observed at higher particle loading (30 wt%) after 7 days of culture. By day 21, 10 wt% loading showed significantly higher cell metabolic activity and proliferation, high cell viability, and cell migration throughout the scaffold. Calcium mineral deposition was observed on the scaffolds during cell culture. Large calcium mineral deposits were observed at 30 wt% and smaller calcium deposits were observed at 10 wt%. This study demonstrates that SMPs incorporated into a PCL scaffold provided effective mechanical reinforcement, improved the rate of degradation, and increased cell proliferation, demonstrating potential suitability for bone tissue engineering applications.

Comparing the regeneration potential between PLLA/Aragonite and PLLA/Vaterite pearl composite scaffolds in rabbit radius segmental bone defects

Mussel-derived nacre and pearl, which are natural composites composed CaCO₃ platelets and interplatelet organic matrix, have recently gained interest due to their osteogenic potential. The crystal form of CaCO₃ could be either aragonite or vaterite depending on the characteristics of mineralization template within pearls. So far, little attention has been paid on the different osteogenic capacities between aragonite and vaterite pearl. In the current work, aragonite or vaterite pearl powders were incorporated into poly-l-lactic acid (PLLA) scaffold as bio-functional fillers for enhanced osteogenesis. In intro results revealed that PLLA/aragonite scaffold possessed stronger stimulatory effect on SaOS-2 cell proliferation and differentiation, evidenced by the enhanced cell viability, alkaline phosphatase activity, collagen synthesis and gene expressions of osteogenic markers including osteocalcin, osteopotin and bone sialoprotein. The bone regeneration potential of various scaffolds was evaluated in vivo employing a rabbit critical-sized radial bone defect model. The X-ray and micro-CT results showed that significant bone regeneration and bridging were achieved in defects implanted with composite scaffolds, while less bone formation and non-bridging were found for pure PLLA group. Histological evaluation using Masson's trichrome and hematoxylin/eosin (H&E) staining indicated a typical endochondral bone formation process conducted at defect sites treated with composite scaffolds. Through three-point bending test, the limbs implanted with PLLA/aragonite scaffold were found to bear significantly higher bending load compared to other two groups. Together, it is suggested that aragonite pearl has superior osteogenic capacity over vaterite pearl and PLLA/aragonite scaffold can be employed as a potential bone graft for bone regeneration.

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PLLA/pearl powder composite scaffolds with interconnected pores were fabricated.

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PLLA/aragonite scaffold stimulated SaOS-2 cell proliferation and differentiation.

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PLLA/aragonite scaffold promoted bone regeneration in vivo.

Drug Delivery Based on Nanotechnology for Target Bone Disease

Bone diseases are a serious problem in modern human life. With the coming acceleration of global population ageing, this problem will become more and more serious. Due to the specific physiological characteristics and local microenvironment of bone tissue, it is difficult to deliver drugs to the lesion site. Therefore, the traditional orthopedic medicine scheme has the disadvantages of high drug frequency, large dose and relatively strong side effects. How to target deliver drugs to the bone tissue or even target cells is the focus of the development of new drugs. Nano drug delivery system with a targeting group can realize precise delivery of orthopedic drugs and effectively reduce the systemic toxicity. In addition, the application of bone tissue engineering scaffolds and biomedical materials to realize in situ drug delivery also are research hotspot. In this article, we briefly review the application of nanotechnology in targeted therapies for bone diseases.