Extracellular matrix-mimetic adhesive biomaterials for bone repair

Shape memory cycle conditions impact human bone marrow stromal cell binding to RGD- and YIGSR-conjugated poly (glycerol dodecanedioate)

Bioresorbable shape memory polymers (SMP) are an emerging class of polymers that can help address several challenges associated with minimally invasive surgery by providing a solution for structural tissue repair. Like most synthetic polymer networks, SMPs require additional biorelevance and modification for biomedical applications. Methodologies used to incorporate bioactive ligands must preserve SMP thermomechanics and ensure biofunctionality following in vivo delivery. We have previously described the development of a novel thermoresponsive bioresorbable SMP, poly (glycerol dodecanedioate) (PGD). In this study, cell-adhesive peptide sequences RGD and YIGSR were conjugated with PGD. We investigated 1) the impact of conjugated peptides on the fixity (Rf), recovery (Rr), and recovery rate (dRr/dT), 2) the impact of conjugated peptides on cell binding, and 3) the impact of the shape memory cycle (Tprog) on conjugated peptide functionality towards binding human bone marrow stromal cells (BMSC). Peptide conjugation conditions impact fixity but not the recovery or recovery rate (p < 0.01). Peptide-conjugated substrates increased cell attachment and proliferation compared with controls (p < 0.001). Using complementary integrin binding cell-adhesive peptides increased proliferation compared with using single peptides (p < 0.05). Peptides bound to PGD substrates exhibited specificity to their respective integrin targets. Following the shape memory cycle, peptides maintained functionality and specificity depending on the shape memory cycle conditions (p < 0.001). The dissipation of strain energy during recovery can drive differential arrangement of conjugated sequences impacting functionality, an important design consideration for functionalized SMPs. STATEMENT OF SIGNIFICANCE: Shape memory elastomers are an emerging class of polymers that are well-suited for minimally invasive repair of soft tissues. Tissue engineering approaches commonly utilize biodegradable scaffolds to deliver instructive cues, including cells and bioactive signals. Delivering these instructive cues on biodegradable shape memory elastomers requires modification with bioactive ligands. Furthermore, it is necessary to ensure the specificity of the ligands to their biological targets when conjugated to the polymer. Moreover, the bioactive ligand functionality must be conserved after completing the shape memory cycle, for applications in tissue engineering.

Integrin signalling in joint development, homeostasis and osteoarthritis

Integrins are key regulators of cell-matrix interactions during joint development and joint tissue homeostasis, as well as in the development of osteoarthritis (OA). The signalling cascades initiated by the interactions of integrins with a complex network of extracellular matrix (ECM) components and intracellular adaptor proteins orchestrate cellular responses necessary for maintaining joint tissue integrity. Dysregulated integrin signalling, triggered by matrix degradation products such as matrikines, disrupts this delicate balance, tipping the scales towards an environment conducive to OA pathogenesis. The interplay between integrin signalling and growth factor pathways further underscores the multifaceted nature of OA. Moreover, emerging insights into the role of endocytic trafficking in regulating integrin signalling add a new layer of complexity to the understanding of OA development. To harness the therapeutic potential of targeting integrins for mitigation of OA, comprehensive understanding of their molecular mechanisms across joint tissues is imperative. Ultimately, deciphering the complexities of integrin signalling will advance the ability to treat OA and alleviate its global burden.

Recent Advancements in Bone Tissue Engineering: Integrating Smart Scaffold Technologies and Bio-Responsive Systems for Enhanced Regeneration

In exploring the challenges of bone repair and regeneration, this review evaluates the potential of bone tissue engineering (BTE) as a viable alternative to traditional methods, such as autografts and allografts. Key developments in biomaterials and scaffold fabrication techniques, such as additive manufacturing and cell and bioactive molecule-laden scaffolds, are discussed, along with the integration of bio-responsive scaffolds, which can respond to physical and chemical stimuli. These advancements collectively aim to mimic the natural microenvironment of bone, thereby enhancing osteogenesis and facilitating the formation of new tissue. Through a comprehensive combination of in vitro and in vivo studies, we scrutinize the biocompatibility, osteoinductivity, and osteoconductivity of these engineered scaffolds, as well as their interactions with critical cellular players in bone healing processes. Findings from scaffold fabrication techniques and bio-responsive scaffolds indicate that incorporating nanostructured materials and bioactive compounds is particularly effective in promoting the recruitment and differentiation of osteoprogenitor cells. The therapeutic potential of these advanced biomaterials in clinical settings is widely recognized and the paper advocates continued research into multi-responsive scaffold systems.

Towards Stem Cell Therapy for Critical-Sized Segmental Bone Defects: Current Trends and Challenges on the Path to Clinical Translation

The management and reconstruction of critical-sized segmental bone defects remain a major clinical challenge for orthopaedic clinicians and surgeons. In particular, regenerative medicine approaches that involve incorporating stem cells within tissue engineering scaffolds have great promise for fracture management. This narrative review focuses on the primary components of bone tissue engineering-stem cells, scaffolds, the microenvironment, and vascularisation-addressing current advances and translational and regulatory challenges in the current landscape of stem cell therapy for critical-sized bone defects. To comprehensively explore this research area and offer insights for future treatment options in orthopaedic surgery, we have examined the latest developments and advancements in bone tissue engineering, focusing on those of clinical relevance in recent years. Finally, we present a forward-looking perspective on using stem cells in bone tissue engineering for critical-sized segmental bone defects.

Immobilizing c(RGDfc) on the surface of metal-phenolic networks by thiol-click reaction for accelerating osteointegration of implant

The limited osteointegration often leads to the failure of implant, which can be improved by fixing bioactive molecules onto the surface, such as arginyl-glycyl-aspartic acid (RGD): a cell adhesion motif. Metal-Phenolic Networks (MPNs) have garnered increasing attention from different disciplines in recent years due to their simple and rapid process for depositing on various substrates or particles with different shapes. However, the lack of cellular binding sites on MPNs greatly blocks its application in tissue engineering. In this study, we present a facile and efficient approach for producing PC/Fe@c(RGDfc) composite coatings through the conjugation of c(RGDfc) peptides onto the surface of PC/Fe-MPNs utilizing thiol-click reaction. By combined various techniques (ellipsometry, X-ray photoelectron spectroscopy, Liquid Chromatography-Mass Spectrometry, water contact angle, scanning electronic microscopy, atomic force microscopy) the physicochemical properties (composition, coating mechanism and process, modulus and hydrophilicity) of PC/Fe@c(RGDfc) surface were characterized in detail. In addition, the PC/Fe@c(RGDfc) coating exhibits the remarkable ability to positively modulate cellular attachment, proliferation, migration and promoted bone-implant integration in vivo, maintaining the inherent features of MPNs: anti-inflammatory, anti-oxidative properties, as well as multiple substrate deposition. This work contributes to engineering MPNs-based coatings with bioactive molecules by a facile and efficient thiol-click reaction, as an innovative perspective for future development of surface modification of implant materials.

The physiological effect of polystyrene nanoplastic particles on fish and human fibroblasts

Numerous studies have identified the detrimental effects for the biosphere of large plastic debris, the effect of microplastics (MPs) and nanoplastics (NPs) is less clear. The skin is the first point of contact with NPs, and skin fibroblasts have a vital role in maintaining skin structure and function. Here, a comparative approach is taken using three fibroblast cell lines from the zebrafish (SJD.1), human male newborn (BJ-5ta) and female adult (HDF/TERT164) and their response to polystyrene NP (PS-NPs) exposure is characterized. Cells were exposed to environmentally relevant PS-NP sizes (50, 500 and 1000 nm) and concentrations (0.001 to 10 μg/ml) and their uptake (1000 nm), and effect on cell viability, proliferation, migration, reactive oxygen species (ROS) production, apoptosis, alkaline phosphatase (ALP) and acid phosphatase (AP) determined. All fibroblasts took up PS-NPs, and a relationship between PS-NP particle size and concentration and the inhibition of proliferation and cell migration was identified. The inhibitory effect of PS-NPs on proliferation was more pronounced for human skin fibroblasts. The presence of PS-NPs negatively affected fibroblast migration in a time-, size- and concentration-dependent manner with larger PS-NPs at higher concentrations causing a more significant inhibition of cell migration, with human fibroblasts being the most affected. No major changes were detected in ROS production or apoptosis in NP challenged fibroblasts. While the ALP activity was increased in all fibroblast cell lines, only fish fibroblasts showed a significant increase in AP activity. The heterogeneous response of fibroblasts induced by PS-NPs was clearly revealed by the segregation of HDF, BJ.5ta and SJD.1 fibroblasts in principal component analysis. Our results demonstrate that PS-NP exposure adversely affected cellular processes in a cell-type and dose-specific manner in distinct fibroblast cell lines, emphasizing the need for further exploration of NP interactions with different cell types to better understand potential implications for human health.

Peptide-Based Biomaterials for Bone and Cartilage Regeneration

The healing of osteochondral defects (OCDs) that result from injury, osteochondritis, or osteoarthritis and bear lesions in the cartilage and bone, pain, and loss of joint function in middle- and old-age individuals presents challenges to clinical practitioners because of non-regenerative cartilage and the limitations of current therapies. Bioactive peptide-based osteochondral (OC) tissue regeneration is becoming more popular because it does not have the immunogenicity, misfolding, or denaturation problems associated with original proteins. Periodically, reviews are published on the regeneration of bone and cartilage separately; however, none of them addressed the simultaneous healing of these tissues in the complicated heterogeneous environment of the osteochondral (OC) interface. As regulators of cell adhesion, proliferation, differentiation, angiogenesis, immunomodulation, and antibacterial activity, potential therapeutic strategies for OCDs utilizing bone and cartilage-specific peptides should be examined and investigated. The main goal of this review was to study how they contribute to the healing of OCDs, either alone or in conjunction with other peptides and biomaterials.

Microenvironment-targeted strategy steers advanced bone regeneration

Treatment of large bone defects represents a great challenge in orthopedic and craniomaxillofacial surgery. Traditional strategies in bone tissue engineering have focused primarily on mimicking the extracellular matrix (ECM) of bone in terms of structure and composition. However, the synergistic effects of other cues from the microenvironment during bone regeneration are often neglected. The bone microenvironment is a sophisticated system that includes physiological (e.g., neighboring cells such as macrophages), chemical (e.g., oxygen, pH), and physical factors (e.g., mechanics, acoustics) that dynamically interact with each other. Microenvironment-targeted strategies are increasingly recognized as crucial for successful bone regeneration and offer promising solutions for advancing bone tissue engineering. This review provides a comprehensive overview of current microenvironment-targeted strategies and challenges for bone regeneration and further outlines prospective directions of the approaches in construction of bone organoids.

Applications of Polydopamine in Implant Surface Modification

There is great clinical demand for orthopedic and dental implant surface modification methods to prevent osseointegration failure and improve implant biological functions. Notably, dopamine (DA) can be polymerized to form polydopamine (PDA), which is similar to the adhesive proteins secreted by mussels, to form a stable bond between the bone surface and implants. Therefore, PDA has the potential to be used as an implant surface modification material with good hydrophilicity, roughness, morphology, mechanical strength, biocompatibility, antibacterial activity, cellular adhesion, and osteogenesis. In addition, PDA degradation releases DA into the surrounding microenvironment, which is found to play an important role in regulating DA receptors on both osteoblasts and osteoclasts during the bone remodeling process. Furthermore, the adhesion properties of PDA suggest its use as an intermediate layer in assisting other functional bone remodeling materials, such as nanoparticles, growth factors, peptides, and hydrogels, to form "dual modifications." The purpose of this review is to summarize the recent progress in research on PDA and its derivatives as orthopedic and dental implant surface modification materials and to analyze the multiple functions of PDA.

Optimizing the fabrication of a 3D high-resolution implant for neural stimulation

BACKGROUND

Tissue-integrated micro-electronic devices for neural stimulation hold great potential in restoring the functionality of degenerated organs, specifically, retinal prostheses, which are aimed at vision restoration. The fabrication process of 3D polymer-metal devices with high resolution and a high aspect-ratio (AR) is very complex and faces many challenges that impair its functionality.

APPROACH

Here we describe the optimization of the fabrication process of a bio-functionalized 3D high-resolution 1mm circular subretinal implant composed of SU-8 polymer integrated with dense gold microelectrodes (23μm pitch) passivated with 3D micro-well-like structures (20μm diameter, 3μm resolution). The main challenges were overcome by step-by-step planning and optimization while utilizing a two-step bi-layer lift-off process; bio-functionalization was carried out by N2 plasma treatment and the addition of a bio-adhesion molecule.

MAIN RESULTS

In-vitro and in-vivo investigations, including SEM and FIB cross section examinations, revealed a good structural design, as well as a good long-term integration of the device in the rat sub-retinal space and cell migration into the wells. Moreover, the feasibility of subretinal neural stimulation using the fabricated device was demonstrated in-vitro by electrical activation of rat's retina.

CONCLUSIONS

The reported process and optimization steps described here in detail can aid in designing and fabricating retinal prosthetic devices or similar neural implants.

Bioinspired Multi-Layer Biopolymer-Based Dental Implant Coating for Enhanced Osseointegration

The major drawbacks of metal-based implants are weak osseointegration and post-operational infections. These limitations restrict the long-term use of implants that may cause severe tissue damage and replacement of the implant. Recent strategies to enhance the osseointegration process require an elaborate fabrication process and suffer from post-operative complications. To address the current challenges taking inspiration from the extracellular matrix (ECM), the current study is designed to establish enhanced osseointegration with lowered risk of infection. Natural biopolymer pectin, peptide amphiphiles, and enzyme-mimicking fullerene moieties are governed to present an ECM-like environment around the implant surfaces. This multifunctional approach promotes osseointegration via inducing biomineralization and osteoblast differentiation. Application of the biopolymer-based composite to the metal surfaces significantly enhances cellular attachment, supports the mineral deposition, and upregulates osteoblast-specific gene expression. In addition to the osteoinductive properties of the constructed layers, the inherent antimicrobial properties of multilayer coating are also used to prevent infection possibility. The reported biopolymer-artificial enzyme composite demonstrates antimicrobial activity against Escherichia coli and Bacillus subtilis as a multifunctional surface coating.

Osteoblasts and Fibroblasts Interaction with a Porcine Acellular Dermal Matrix Membrane

The use of collagen membranes has remained the gold standard in GTR/GBR. In this study, the features and the biological activities of an acellular porcine dermis collagen matrix membrane applicable during dental surgery were investigated, and also by applying hydration with NaCl. Thus, two tested membranes were distinguished, the H-Membrane and Membrane, compared to the control cell culture plastic. The characterization was performed by SEM and histological analyses. In contrast, the biocompatibility was investigated on HGF and HOB cells at 3, 7, and 14 days by MTT for proliferation study; by SEM and histology for cell interaction study; and by RT-PCR for function-related genes study. In HOBs seeded on membranes, mineralization functions by ALP assay and Alizarin Red staining were also investigated. Results indicated that the tested membranes, especially when hydrated, can promote the proliferation and attachment of cells at each time. Furthermore, membranes significantly increased ALP and mineralization activities in HOBs as well as the osteoblastic-related genes ALP and OCN. Similarly, membranes significantly increased ECM-related and MMP8 gene expression in HGFs. In conclusion, the tested acellular porcine dermis collagen matrix membrane, mainly when it is hydrated, behaved as a suitable microenvironment for oral cells.

Molecular Modeling Insights into the Structure and Behavior of Integrins: A Review

Integrins are heterodimeric glycoproteins crucial to the physiology and pathology of many biological functions. As adhesion molecules, they mediate immune cell trafficking, migration, and immunological synapse formation during inflammation and cancer. The recognition of the vital roles of integrins in various diseases revealed their therapeutic potential. Despite the great effort in the last thirty years, up to now, only seven integrin-based drugs have entered the market. Recent progress in deciphering integrin functions, signaling, and interactions with ligands, along with advancement in rational drug design strategies, provide an opportunity to exploit their therapeutic potential and discover novel agents. This review will discuss the molecular modeling methods used in determining integrins' dynamic properties and in providing information toward understanding their properties and function at the atomic level. Then, we will survey the relevant contributions and the current understanding of integrin structure, activation, the binding of essential ligands, and the role of molecular modeling methods in the rational design of antagonists. We will emphasize the role played by molecular modeling methods in progress in these areas and the designing of integrin antagonists.

Bone Tissue Engineering Scaffolds: Function of Multi-Material Hierarchically Structured Scaffolds

Bone tissue engineering (BTE) is a topic of interest for the last decade, and advances in materials, processing techniques, and the understanding of bone healing pathways have opened new avenues of research. The dual responsibility of BTE scaffolds in providing load-bearing capability and interaction with the local extracellular matrix to promote bone healing is a challenge in synthetic scaffolds. This article describes the usage and processing of multi-materials and hierarchical structures to mimic the structure of natural bone tissues to function as bioactive and load-bearing synthetic scaffolds. The first part of this literature review describes the physiology of bone healing responses and the interactions at different stages of bone repair. The following section reviews the available literature on biomaterials used for BTE scaffolds followed by some multi-material approaches. The next section discusses the impact of the scaffold's structural features on bone healing and the necessity of a hierarchical distribution in the scaffold structure. Finally, the last section of this review highlights the emerging trends in BTE scaffold developments that can inspire new tissue engineering strategies and truly develop the next generation of synthetic scaffolds.

Modeling of Biological Activity of PEO-Coated Titanium Implants with Conjugates of Cyclic RGD Peptide with Amino Acid Bisphosphonates

Titanium is considered to be the most essential metal in the field of implantology. The main factors determining metal biocompatibility, among others, include the morphology and chemical composition of the titanium surface. Therefore, the aim of this work was to develop approaches to control the biological activity of the titanium surface by creating coatings that combine both an inorganic phase with a given morphology and organic molecules containing an integrin-selective peptide that regulate cell adhesion and proliferation. As such, we synthesized new c(RGDfC) derivatives of amino acid bisphosphonates (four examples) with different bisphosphonate anchors and maleimide linkers. These molecules were deposited on a highly developed porous surface obtained via the plasma electrolytic oxidation (PEO) of coarse-grained and nanostructured titanium. In vitro studies demonstrated the increase in the viability degree of mesenchymal stem cells and fibroblasts on the surface of coarse-grained or nanostructured titanium modified with PEO and a c(RGDfC) derivative of ε-aminocaproic acid bisphophonate with an SMCC linker. As a result, the use of conjugates of amino acid bisphosphonates with a cyclic RGD peptide for the modification of PEO-coated titanium opens the ways for the effective control of the biological activity of the metal implant surface.

Peptides for Coating TiO2 Implants: An In Silico Approach

Titanium is usually used in the manufacturing of metal implants due to its biocompatibility and high resistance to corrosion. A structural and functional connection between the living bone and the surface of the implant, a process called osseointegration, is mandatory for avoiding prolonged healing, infections, and tissue loss. Therefore, osseointegration is crucial for the success of the implantation procedure. Osseointegration is a process mediated by bone-matrix progenitor cells' proteins, named integrins. In this study, we used an in silico approach to assemble and test peptides that can be strategically used in sensitizing TiO₂ implants in order to improve osseointegration. To do so, we downloaded PDB structures of integrins α5β1, αvβ3, and αIIbβ3; their biological ligands; and low-cost proteins from the Protein Data Bank, and then we performed a primary (integrin-protein) docking analysis. Furthermore, we modeled complex peptides with the potential to bind to the TiO₂ surface on the implant, as well as integrins in the bone-matrix progenitor cells. Then we performed a secondary (integrin-peptide) docking analysis. The ten most promising integrin-peptide docking results were further verified by molecular dynamics (MD) simulations. We recognized 82 peptides with great potential to bind the integrins, and therefore to be used in coating TiO₂ implants. Among them, peptides 1 (GHTHYHAVRTQTTGR), 3 (RKLPDATGR), and 8 (GHTHYHAVRTQTLKA) showed the highest binding stability during the MD simulations. This bioinformatics approach saves time and more effectively directs in vitro studies.

Bone regeneration materials and their application over 20 years: A bibliometric study and systematic review

Bone regeneration materials (BRMs) bring us new sights into the clinical management bone defects. With advances in BRMs technologies, new strategies are emerging to promote bone regeneration. The aim of this study was to comprehensively assess the existing research and recent progress on BRMs, thus providing useful insights into contemporary research, as well as to explore potential future directions within the scope of bone regeneration therapy. A comprehensive literature review using formal data mining procedures was performed to explore the global trends of selected areas of research for the past 20 years. The study applied bibliometric methods and knowledge visualization techniques to identify and investigate publications based on the publication year (between 2002 and 2021), document type, language, country, institution, author, journal, keywords, and citation number. The most productive countries were China, United States, and Italy. The most prolific journal in the BRM field was Acta Biomaterialia, closely followed by Biomaterials. Moreover, recent investigations have been focused on extracellular matrices (ECMs) (370 publications), hydrogel materials (286 publications), and drug delivery systems (220 publications). Research hotspots related to BRMs and extracellular matrices from 2002 to 2011 were growth factor, bone morphogenetic protein (BMP)-2, and mesenchymal stem cell (MSC), whereas after 2012 were composite scaffolds. Between 2002 and 2011, studies related to BRMs and hydrogels were focused on BMP-2, in vivo, and in vitro investigations, whereas it turned to the exploration of MSCs, mechanical properties, and osteogenic differentiation after 2012. Research hotspots related to BRM and drug delivery were fibroblast growth factor, mesoporous materials, and controlled release during 2002–2011, and electrospinning, antibacterial activity, and in vitro bioactivity after 2012. Overall, composite scaffolds, 3D printing technology, and antibacterial activity were found to have an important intersection within BRM investigations, representing relevant research fields for the future. Taken together, this extensive analysis highlights the existing literature and findings that advance scientific insights into bone tissue engineering and its subsequent applications.

Effectiveness of biomolecule-based bioactive surfaces, on os-seointegration of titanium dental implants: A systematic review and meta-analysis of in vivo studies

Titanium and alloy osseointegrated implants are used to replace missing teeth; however, some fail and are removed. Modifications of the implant surface with biologically active substances have been proposed. MEDLINE [via Pubmed], Embase and Web of Science were searched with the terms “titanium dental implants”, “surface properties”, “bioactive surface modifications”, “biomolecules”, “BMP”, “antibacterial agent”, “peptide”, “collagen”, “grown factor”, “osseointegration”, “bone apposition”, “osteogenic”, “osteogenesis”, “new bone formation”, “bone to implant contact”, “bone regeneration” and “in vivo studies”, until May 2022. A total of 10,697 references were iden-tified and 26 were included to analyze 1,109 implants, with follow-ups from 2 to 84 weeks. The ARRIVE guidelines and the SYRCLE tool were used to evaluate the methodology and scientific evidence. A meta-analysis was performed (RevMan 2020 software, Cochane Collaboration) with random effects that evaluated BIC at 4 weeks, with subgroups for the different coatings. The heterogeneity of the pooled studies was very high (95% CI, I2 = 99%). The subgroup of BMPs was the most favorable to coating. Surface modification of Ti implants by organic bioactive molecules seems to favor osseointegration in the early stages of healing, but long-term studies are necessary to corroborate the results of the experimental studies.

Biomaterial functionalization with triple-helical peptides for tissue engineering

In the growing field of tissue engineering, providing cells in biomaterials with the adequate biological cues represents an increasingly important challenge. Yet, biomaterials with excellent mechanical properties often are often biologically inert to many cell types. To address this issue, researchers resort to functionalization, i.e. the surface modification of a biomaterial with active molecules or substances. Functionalization notably aims to replicate the native cellular microenvironment provided by the extracellular matrix, and in particular by collagen, its major component. As our understanding of biological processes regulating cell behaviour increases, functionalization with biomolecules binding cell surface receptors constitutes a promising strategy. Amongst these, triple-helical peptides (THPs) that reproduce the architectural and biological properties of collagen are especially attractive. Indeed, THPs containing binding sites from the native collagen sequence have successfully been used to guide cell response by establishing cell-biomaterial interactions. Notably, the GFOGER motif recognising the collagen-binding integrins is extensively employed as a cell adhesive peptide. In biomaterials, THPs efficiently improved cell adhesion, differentiation and function on biomaterials designed for tissue repair (especially for bone, cartilage, tendon and heart), vascular graft fabrication, wound dressing, drug delivery or immunomodulation. This review describes the key characteristics of THPs, their effect on cells when combined to biomaterials and their strong potential as biomimetic tools for regenerative medicine. STATEMENT OF SIGNIFICANCE: This review article describes how triple-helical peptides constitute efficient tools to improve cell-biomaterial interactions in tissue engineering. Triple helical peptides are bioactive molecules that mimic the architectural and biological properties of collagen. They have been successfully used to specifically recognize cell-surface receptors and provide cells seeded on biomaterials with controlled biological cues. Functionalization with triple-helical peptides has enabled researchers to improve cell function for regenerative medicine applications, such as tissue repair. However, despite encouraging results, this approach remains limited and under-exploited, and most functionalization strategies reported in the literature rely on biomolecules that are unable to address collagen-binding receptors. This review will assist researchers in selecting the correct tools to functionalize biomaterials in efforts to guide cellular response.

Bone: An Outstanding Composite Material

Bone is an outstanding, well-designed composite. It is constituted by a multi-level structure wherein its properties and behavior are dependent on its composition and structural organization at different length scales. The combination of unique mechanical properties with adaptive and self-healing abilities makes bone an innovative model for the future design of synthetic biomimetic composites with improved performance in bone repair and regeneration. However, the relation between structure and properties in bone is very complex. In this review article, we intend to describe the hierarchical organization of bone on progressively greater scales and present the basic concepts that are fundamental to understanding the arrangement-based mechanical properties at each length scale and their influence on bone’s overall structural behavior. The need for a better understanding of bone’s intricate composite structure is also highlighted.

Progress in Niobium Oxide-Containing Coatings for Biomedical Applications: A Critical Review

Typically, pure niobium oxide coatings are deposited on metallic substrates, such as commercially pure Ti, Ti6Al4 V alloys, stainless steels, niobium, TiNb alloy, and Mg alloys using techniques such as sputter deposition, sol-gel deposition, anodizing, and wet plasma electrolytic oxidation. The relative advantages and limitations of these coating techniques are considered, with particular emphasis on biomedical applications. The properties of a wide range of pure and modified niobium oxide coatings are illustrated, including their thickness, morphology, microstructure, elemental composition, phase composition, surface roughness and hardness. The corrosion resistance, tribological characteristics and cell viability/proliferation of the coatings are illustrated using data from electrochemical, wear resistance and biological cell culture measurements. Critical R&D needs for the development of improved future niobium oxide coatings, in the laboratory and in practice, are highlighted.

Enhanced Extracellular Matrix Deposition on Titanium Implant Surfaces: Cellular and Molecular Evidences

The surface structure of the titanium dental implants can modulate the activity of mesenchymal stem cells in order to promote the upregulation of osteoblastic related genes and the release of extracellular matrix (ECM) components. The present work was focused on the in vitro evaluation of the interaction of human periodontal ligament stem cells (hPDLSCs) and two different implant titanium surfaces topography (CTRL and TEST). This study was aimed at analyzing the cytotoxicity of the dental implant surfaces, the cellular adhesion capacity, and the improvement in the release of ECM molecules in an in vitro model. These parameters were carried out by means of the microscopic evaluation, viability assays, immunofluorescence, Western blot and RT-PCR investigations. The knowledge of the cell/implant interaction is essential for implant healing in order to obtain a more performing surfaces that promote the ECM release and provide the starting point to initiate the osseointegration process.

Advances in the application of mesenchymal stem cells, exosomes, biomimetic materials, and 3D printing in osteoporosis treatment

Owing to an increase in the aging population, osteoporosis has become a severe public health concern, with a high prevalence among the elderly and postmenopausal adults. Osteoporosis-related fracture is a major cause of morbidity and mortality in elderly and postmenopausal adults, posing a considerable socioeconomic burden. However, existing treatments can only slow down the process of osteoporosis, reduce the risk of fractures, and repair fractures locally. Therefore, emerging methods for treating osteoporosis, such as mesenchymal stem cell transplantation, exosome-driving drug delivery systems, biomimetic materials, and 3D printing technology, have received increasing research attention, with significant progress. Mesenchymal stem cells (MSCs) are pluripotent stem cells that can differentiate into different types of functional cells. Exosomes play a key role in regulating cell microenvironments through paracrine mechanisms. Bionic materials and 3D printed scaffolds are beneficial for the reconstruction and repair of osteoporotic bones and osteoporosis-related fractures. Stem cells, exosomes, and biomimetic materials represent emerging technologies for osteoporosis treatment. This review summarizes the latest developments in these three aspects.

Implantable blood clot loaded with BMP-2 for regulation of osteoimmunology and enhancement of bone repair

The treatment of large-area bone defects still faces many difficulties and challenges. Here, we developed a blood clot delivery platform loaded with BMP-2 protein (BMP-2@BC) for enhanced bone regeneration. Blood clot gel platform as natural biomaterials can be engineered from autologous blood. Once implanted into the large bone defect site, it can be used for BMP-2 local delivery, as well as modulating osteoimmunology by recruiting a great number of macrophages and regulating their polarization at different stages. Moreover, due to the deep-red color of blood clot gel, mild localized hyperthermia under laser irradiation further accelerated bone repair and regeneration. We find that the immune niche within the bone defect microenvironment can be modulated in a controllable manner by the blood clots implantation and laser treatment. We further demonstrate that the newly formed bone covered almost 95% of the skull defect area by our strategy in both mice and rat disease models. Due to the great biocompatibility, photothermal potential, and osteoimmunomodulation capacity, such technology shows great promise to be used in further clinical translation.

Decellularised extracellular matrix decorated PCL PolyHIPE scaffolds for enhanced cellular activity, integration and angiogenesis

Wound healing involves a complex series of events where cell–cell and cell-extracellular matrix (ECM) interactions play a key role. Wounding can be simple, such as the loss of the epithelial integrity, or deeper and more complex, reaching to subcutaneous tissues, including blood vessels, muscles and nerves. Rapid neovascularisation of the wounded area is crucial for wound healing as it has a key role in supplying oxygen and nutrients during the highly demanding proliferative phase and transmigration of inflammatory cells to the wound area. One approach to circumvent delayed neovascularisation is the exogenous use of pro-angiogenic factors, which is expensive, highly dose-dependent, and the delivery of them requires a very well-controlled system to avoid leaky, highly permeable and haemorrhagic blood vessel formation. In this study, we decorated polycaprolactone (PCL)-based polymerised high internal phase emulsion (PolyHIPE) scaffolds with fibroblast-derived ECM to assess fibroblast, endothelial cell and keratinocyte activity in vitro and angiogenesis in ex ovo chick chorioallantoic membrane (CAM) assays. Our results showed that the inclusion of ECM in the scaffolds increased the metabolic activity of three types of cells that play a key role in wound healing and stimulated angiogenesis in ex ovo CAM assays over 7 days. Herein, we demonstrated that fibroblast-ECM functionalised PCL PolyHIPE scaffolds appear to have great potential to be used as an active wound dressing to promote angiogenesis and wound healing.

Decellularisation of in vitro generated extracellular matrix (ECM) provides an effective way to stimulate angiogenesis and wound healing.

Restoration of critical defects in the rabbit mandible using osteoblasts and vascular endothelial cells co-cultured with vascular stent-loaded nano-composite scaffolds

The success of large bone defect repair with tissue engineering technology depends mainly on angiogenesis and osteogenesis. In this study, we prepared poly-caprolactone/nano-hydroxyapatite/beta-calcium phosphate (PCL/nHA/β-TCP) composite scaffolds loaded with poly-(lactic-co-glycolic acid)/nano-hydroxyapatite/collagen/heparin sodium (PLGA/nHA/Col/HS) nanofiber small vascular stent by electrospinning and hot press forming-particle leaching methods. Supramolecular electrostatic self-assembly technology was used to modify the surfaces of small vascular stents to aid in hydrophilicity and anticoagulation. The surfaces of composite scaffolds were modified with an Arg-Gly-Asp (RGD) short peptide by physical adsorption to supply cell adhesion sites. The scaffolds were then combined with rabbit bone marrow-derived osteoblasts (OBs) and rabbit bone marrow-derived vascular endothelial cells (RVECs) to construct large, biologically active vascularized tissue-engineered bone in vitro; this bone was then used to repair critical bone defects in rabbit mandibles. Mechanical and biocompatibility testing results showed that PCL/nHA/β-TCP composite scaffolds loaded with small vascular stents had good surface structure, mechanical properties, biocompatibility, and bone-regeneration induction potential. Twelve weeks after implantation, histological analysis and X-ray scans showed that the use of osteoblasts and vascular endothelial cells co-cultured with PCL/nHA/β-TCP scaffolds was sufficient to repair critical defects in rabbit mandibles.

Recent advances in design and applications of biomimetic self-assembled peptide hydrogels for hard tissue regeneration

Abstract

The development of natural biomaterials applied for hard tissue repair and regeneration is of great importance, especially in societies with a large elderly population. Self-assembled peptide hydrogels are a new generation of biomaterials that provide excellent biocompatibility, tunable mechanical stability, injectability, trigger capability, lack of immunogenic reactions, and the ability to load cells and active pharmaceutical agents for tissue regeneration. Peptide-based hydrogels are ideal templates for the deposition of hydroxyapatite crystals, which can mimic the extracellular matrix. Thus, peptide-based hydrogels enhance hard tissue repair and regeneration compared to conventional methods. This review presents three major self-assembled peptide hydrogels with potential application for bone and dental tissue regeneration, including ionic self-complementary peptides, amphiphilic (surfactant-like) peptides, and triple-helix (collagen-like) peptides. Special attention is given to the main bioactive peptides, the role and importance of self-assembled peptide hydrogels, and a brief overview on molecular simulation of self-assembled peptide hydrogels applied for bone and dental tissue engineering and regeneration.

Graphic abstract

New trends in the development of multifunctional peptides to functionalize biomaterials

Improving cell-material interactions is a major goal in tissue engineering. In this regard, functionalization of biomaterials with cell instructive molecules from the extracellular matrix stands out as a powerful strategy to enhance their bioactivity and achieve optimal tissue integration. However, current functionalization strategies, like the use of native full-length proteins, are associated with drawbacks, thus urging the need of developing new methodologies. In this regard, the use of synthetic peptides encompassing specific bioactive regions of proteins represents a promising alternative. In particular, the combination of peptide sequences with complementary or synergistic effects makes it possible to address more than one biological target at the biomaterial surface. In this review, an overview of the main strategies using peptides to install multifunctionality on biomaterials is presented, mostly focusing on the combination of the RGD motif with other peptides sequences. The evolution of these approaches, starting from simple methods, like using peptide mixtures, to more advanced systems of peptide presentation, with very well defined chemical properties, are explained. For each system of peptide's presentation, three main aspects of multifunctionality-improving receptor selectivity, mimicking the extracellular matrix and preventing bacterial colonization while improving cell adhesion-are highlighted.

Three-Dimensional Printed BGS Treat a Large Bone Defect in a Rabbit Model

This study aimed to evaluate if the 3D printed bioactive glass porous scaffolds (BGS) can improve the reconstruction of the large bone defect. A rabbit model of large bone defects was established by making a 1.0 or 1.5 cm segmental defect in the middle of the femur bone. Then a 1.0 or 1.5 cm BGS was implanted into the bone defect. X-ray imaging showed that in both 1.0 and 1.5 cm groups, the newly formed bone tissue could be observed at 4 weeks after implantation, but a strengthened ossification trend could be observed at different time points. In the 1.0 cm group, a larger number of newly formed bone tissues were observed at 4 weeks, and in the 1.5 group, more newly formed bone tissues were found at 8 weeks. Nevertheless, ossified tissue generation on the BGS mainly completed at 12 weeks after implantation in both groups. The H&E staining revealed that the 3D BGS was easily degraded to form osteoid-like material in vivo, where the neo-ossification gradually occurred from the edge to the center. Immunohistochemical analysis showed that in the 1.0 group, protein expressions of three osteogenesis-related genes- BMP, collagen I and RUNX-2-all peaked at 8 weeks, and then gradually decreased at 12 and 18 weeks. In the 1.5 group, BMP and collagen I peaked at 18 weeks.

Bone physiological microenvironment and healing mechanism: Basis for future bone-tissue engineering scaffolds

Bone-tissue defects affect millions of people worldwide. Despite being common treatment approaches, autologous and allogeneic bone grafting have not achieved the ideal therapeutic effect. This has prompted researchers to explore novel bone-regeneration methods. In recent decades, the development of bone tissue engineering (BTE) scaffolds has been leading the forefront of this field. As researchers have provided deep insights into bone physiology and the bone-healing mechanism, various biomimicking and bioinspired BTE scaffolds have been reported. Now it is necessary to review the progress of natural bone physiology and bone healing mechanism, which will provide more valuable enlightenments for researchers in this field. This work details the physiological microenvironment of the natural bone tissue, bone-healing process, and various biomolecules involved therein. Next, according to the bone physiological microenvironment and the delivery of bioactive factors based on the bone-healing mechanism, it elaborates the biomimetic design of a scaffold, highlighting the designing of BTE scaffolds according to bone biology and providing the rationale for designing next-generation BTE scaffolds that conform to natural bone healing and regeneration.

Antibacterial Titanium Implants Biofunctionalized by Plasma Electrolytic Oxidation with Silver, Zinc, and Copper: A Systematic Review

Patients receiving orthopedic implants are at risk of implant-associated infections (IAI). A growing number of antibiotic-resistant bacteria threaten to hamper the treatment of IAI. The focus has, therefore, shifted towards the development of implants with intrinsic antibacterial activity to prevent the occurrence of infection. The use of Ag, Cu, and Zn has gained momentum as these elements display strong antibacterial behavior and target a wide spectrum of bacteria. In order to incorporate these elements into the surface of titanium-based bone implants, plasma electrolytic oxidation (PEO) has been widely investigated as a single-step process that can biofunctionalize these (highly porous) implant surfaces. Here, we present a systematic review of the studies published between 2009 until 2020 on the biomaterial properties, antibacterial behavior, and biocompatibility of titanium implants biofunctionalized by PEO using Ag, Cu, and Zn. We observed that 100% of surfaces bearing Ag (Ag-surfaces), 93% of surfaces bearing Cu (Cu-surfaces), 73% of surfaces bearing Zn (Zn-surfaces), and 100% of surfaces combining Ag, Cu, and Zn resulted in a significant (i.e., >50%) reduction of bacterial load, while 13% of Ag-surfaces, 10% of Cu-surfaces, and none of Zn or combined Ag, Cu, and Zn surfaces reported cytotoxicity against osteoblasts, stem cells, and immune cells. A majority of the studies investigated the antibacterial activity against S. aureus. Important areas for future research include the biofunctionalization of additively manufactured porous implants and surfaces combining Ag, Cu, and Zn. Furthermore, the antibacterial activity of such implants should be determined in assays focused on prevention, rather than the treatment of IAIs. These implants should be tested using appropriate in vivo bone infection models capable of assessing whether titanium implants biofunctionalized by PEO with Ag, Cu, and Zn can contribute to protect patients against IAI.

Osteogenic Peptides and Attachment Methods Determine Tissue Regeneration in Modified Bone Graft Substitutes

The inclusion of biofunctional molecules with synthetic bone graft substitutes has the potential to enhance tissue regeneration during treatment of traumatic bone injuries. The clinical use of growth factors has though been associated with complications, some serious. The use of smaller, active peptides has the potential to overcome these problems and provide a cost-effective, safe route for the manufacture of enhanced bone graft substitutes. This review considers the design of peptide-enhanced bone graft substitutes, and how peptide selection and attachment method determine clinical efficacy. It was determined that covalent attachment may reduce the known risks associated with growth factor-loaded bone graft substitutes, providing a predictable tissue response and greater clinical efficacy. Peptide choice was found to be critical, but even within recognised families of biologically active peptides, the configurations that appeared to most closely mimic the biological molecules involved in natural bone healing processes were most potent. It was concluded that rational, evidence-based design of peptide-enhanced bone graft substitutes offers a pathway to clinical maturity in this highly promising field.

The enzymatic hydrolysates from deer sinew promote MC3T3-E1 cell proliferation and extracellular matrix synthesis by regulating multiple functional genes

Background

Deer Sinew serves as a medicinal food, and has been used for treating skeletal diseases, especially bone diseases in a long history. Thus, it could become an alternative option for the prevention and therapeutic remedy of bone-related diseases. In our previous study, we established an optimal extraction process of the enzymatic hydrolysates from Chinese Sika deer sinews (DSEH), and we demonstrated that DSEH significantly promoted the proliferation of MC3T3-E1 cells (an osteoblast-like cell line) with a certain dose-effect relationship. However, the precise molecular mechanism of deer sinew in regulating bone strength is still largely unknown. The aim of this study was to explore the underlying molecular mechanism of DSEH on MC3T3-E1 cells proliferation and extracellular matrix synthesis.

Methods

Preparation and quality control were performed as previously described. The effect of DSEH at different administrated concentrations on cell proliferation was measured using both CCK-8 and MTT assays, and the capacity of DSEH on extracellular matrix synthesis was detected by Alizarin red staining and quantification. The gene expression pattern change of MC3T3-E1 cells under the treatment of DSEH was investigated by RNA-seq analysis accompanied with validation methods.

Results

We demonstrated that DSEH promoted MC3T3-E1 cell proliferation and extracellular matrix synthesis by regulating multiple functional genes. DSEH significantly increased the expression levels of genes that promoted cell proliferation such as Gstp1, Timp1, Serpine1, Cyr61, Crlf1, Thbs1, Ctgf, P4ha2, Sod3 and Nqo1. However, DSEH significantly decreased the expression levels of genes that inhibited cell proliferation such as Mt1, Cdc20, Gas1, Nrp2, Cmtm3, Dlk2, Sema3a, Rbm25 and Hspb6. Furthermore, DSEH mildly increased the expression levels of osteoblast gene markers.

Conclusions

Our findings suggest that DSEH facilitate MC3T3-E1 cell proliferation and extracellular matrix synthesis to consolidate bone formation and stability, but prevent MC3T3-E1 cells from oxidative stress-induced damage, apoptosis and further differentiation. These findings deepened the current understanding of DSEH on regulating bone development, and provided theoretical support for the discovery of optional prevention and treatment for bone-related diseases.

Connective tissue growth factor promotes chemotaxis of preosteoblasts through integrin α5 and Ras during tensile force-induced intramembranous osteogenesis

In vertebrates, new bone formation via intramembranous osteogenesis is a critical biological event for development, remodeling, and fracture healing of bones. Chemotaxis of osteoblast lineage cells is an essential cellular process in new bone formation. Connective tissue growth factor (CTGF) is known to exert chemotactic properties on various cells; however, details of CTGF function in the chemotaxis of osteoblast lineage cells and underlying molecular biological mechanisms have not been clarified. The aim of the present study was to evaluate the chemotactic properties of CTGF and its underlying mechanisms during active bone formation through intramembranous osteogenesis. In our mouse tensile force-induced bone formation model, preosteoblasts were aggregated at the osteogenic front of calvarial bones. CTGF was expressed at the osteogenic front, and functional inhibition of CTGF using a neutralizing antibody suppressed the aggregation of preosteoblasts. In vitro experiments using μ-slide chemotaxis chambers showed that a gradient of CTGF induced chemotaxis of preosteoblastic MC3T3-E1 cells, while a neutralizing integrin α5 antibody and a Ras inhibitor inhibited the CTGF-induced chemotaxis of MC3T3-E1 cells. These findings suggest that the CTGF-integrin α5-Ras axis is an essential molecular mechanism to promote chemotaxis of preosteoblasts during new bone formation through intramembranous osteogenesis.

3-D Cell Culture Systems in Bone Marrow Tissue and Organoid Engineering, and BM Phantoms as In Vitro Models of Hematological Cancer Therapeutics-A Review

We review the state-of-the-art in bone and marrow tissue engineering (BMTE) and hematological cancer tissue engineering (HCTE) in light of the recent interest in bone marrow environment and pathophysiology of hematological cancers. This review focuses on engineered BM tissue and organoids as in vitro models of hematological cancer therapeutics, along with identification of BM components and their integration as synthetically engineered BM mimetic scaffolds. In addition, the review details interaction dynamics of various BM and hematologic cancer (HC) cell types in co-culture systems of engineered BM tissues/phantoms as well as their relation to drug resistance and cytotoxicity. Interaction between hematological cancer cells and their niche, and the difference with respect to the healthy niche microenvironment narrated. Future perspectives of BMTE for in vitro disease models, BM regeneration and large scale ex vivo expansion of hematopoietic and mesenchymal stem cells for transplantation and therapy are explained. We conclude by overviewing the clinical application of biomaterials in BM and HC pathophysiology and its challenges and opportunities.

A Review of Bioactive Glass/Natural Polymer Composites: State of the Art

Collagen, gelatin, silk fibroin, hyaluronic acid, chitosan, alginate, and cellulose are biocompatible and non-cytotoxic, being attractive natural polymers for medical devices for both soft and hard tissues. However, such natural polymers have low bioactivity and poor mechanical properties, which limit their applications. To tackle these drawbacks, collagen, gelatin, silk fibroin, hyaluronic acid, chitosan, alginate, and cellulose can be combined with bioactive glass (BG) nanoparticles and microparticles to produce composites. The incorporation of BGs improves the mechanical properties of the final system as well as its bioactivity and regenerative potential. Indeed, several studies have demonstrated that polymer/BG composites may improve angiogenesis, neo-vascularization, cells adhesion, and proliferation. This review presents the state of the art and future perspectives of collagen, gelatin, silk fibroin, hyaluronic acid, chitosan, alginate, and cellulose matrices combined with BG particles to develop composites such as scaffolds, injectable fillers, membranes, hydrogels, and coatings. Emphasis is devoted to the biological potentialities of these hybrid systems, which look rather promising toward a wide spectrum of applications.

Review of Integrin-Targeting Biomaterials in Tissue Engineering

The ability to direct cell behavior has been central to the success of numerous therapeutics to regenerate tissue or facilitate device integration. Biomaterial scientists are challenged to understand and modulate the interactions of biomaterials with biological systems in order to achieve effective tissue repair. One key area of research investigates the use of extracellular matrix-derived ligands to target specific integrin interactions and induce cellular responses, such as increased cell migration, proliferation, and differentiation of mesenchymal stem cells. These integrin-targeting proteins and peptides have been implemented in a variety of different polymeric scaffolds and devices to enhance tissue regeneration and integration. This review first presents an overview of integrin-mediated cellular processes that have been identified in angiogenesis, wound healing, and bone regeneration. Then, research utilizing biomaterials are highlighted with integrin-targeting motifs as a means to direct these cellular processes to enhance tissue regeneration. In addition to providing improved materials for tissue repair and device integration, these innovative biomaterials provide new tools to probe the complex processes of tissue remodeling in order to enhance the rational design of biomaterial scaffolds and guide tissue regeneration strategies.

Attachment of Ultralow Amount of Engineered Plant Viral Nanoparticles to Mesenchymal Stem Cells Enhances Osteogenesis and Mineralization

Hydrogel-based materials are widely used to mimic the extracellular matrix in bone tissue engineering, although they often lack biofunctional cues. In the authors' previous work, Potato virus X (PVX), a flexible rod-shaped biocompatible plant virus nanoparticle (VNP) with 1270 coat protein subunits, is genetically modified to present functional peptides for generating a bone substitute. Here, PVX is engineered to present mineralization- and osteogenesis-associated peptides and laden in hydrogels at a concentration lower by two orders of magnitude. Its competence in mineralization is demonstrated both on 2D surfaces and in hydrogels and the superiority of enriched peptides on VNPs is verified and compared with free peptides and VNPs presenting fewer functional peptides. Alkaline phosphatase activity and Alizarin red staining of human mesenchymal stem cells increase 1.2-1.7 times when stimulate by VNPs. Engineered PVX adheres to cells, exhibiting a stimulation of biomimetic peptides in close proximity to the cells. The retention of VNPs in hydrogels is monitored and more than 80% of VNPs remain inside after several washing steps. The mechanical properties of VNP-laden hydrogels are investigated, including viscosity, gelling temperature, and compressive tangent modulus. This study demonstrates that recombinant PVX nanoparticles are excellent candidates for hydrogel nanocomposites in bone tissue engineering.

Integrin-Targeting Peptides for the Design of Functional Cell-Responsive Biomaterials

Integrins are a family of cell surface receptors crucial to fundamental cellular functions such as adhesion, signaling, and viability, deeply involved in a variety of diseases, including the initiation and progression of cancer, of coronary, inflammatory, or autoimmune diseases. The natural ligands of integrins are glycoproteins expressed on the cell surface or proteins of the extracellular matrix. For this reason, short peptides or peptidomimetic sequences that reproduce the integrin-binding motives have attracted much attention as potential drugs. When challenged in clinical trials, these peptides/peptidomimetics let to contrasting and disappointing results. In the search for alternative utilizations, the integrin peptide ligands have been conjugated onto nanoparticles, materials, or drugs and drug carrier systems, for specific recognition or delivery of drugs to cells overexpressing the targeted integrins. Recent research in peptidic integrin ligands is exploring new opportunities, in particular for the design of nanostructured, micro-fabricated, cell-responsive, stimuli-responsive, smart materials.

Conditioning of 3D Printed Nanoengineered Ionic-Covalent Entanglement Scaffolds with iP-hMSCs Derived Matrix

Additive manufacturing is a promising method for producing customized 3D bioactive constructs for regenerative medicine. Here, 3D printed highly osteogenic scaffolds using nanoengineered ionic-covalent entanglement ink (NICE) for bone tissue engineering are reported. This NICE ink consists of ionic-covalent entanglement reinforced with Laponite, a 2D nanosilicate (nSi) clay, allowing for the printing of anatomic-sized constructs with high accuracy. The 3D printed structure is able to maintain high structural stability in physiological conditions without any significant swelling or deswelling. The presence of nSi imparts osteoinductive characteristics to the NICE scaffolds, which is further augmented by depositing pluripotent stem cell-derived extracellular matrix (ECM) on the scaffolds. This is achieved by stimulating human induced pluripotent stem cell-derived mesenchymal stem cells (iP-hMSCs) with 2-chloro-5-nitrobenzanilide, a PPARγ inhibitor that enhances Wnt pathway, resulting in the deposition of an ECM characterized by high levels of collagens VI and XII found in anabolic bone. The osteoinductive characteristics of these bioconditioned NICE (bNICE) scaffolds is demonstrated through osteogenic differentiation of bone marrow derived human mesenchymal stem cells. A significant increase in the expression of osteogenic gene markers as well as mineralized ECM are observed on bioconditioned NICE (bNICE) scaffolds compared to bare scaffolds (NICE). The bioconditioned 3D printed scaffolds provide a unique strategy to design personalized bone grafts for in situ bone regeneration.

Platelet-rich plasma inhibits osteoblast apoptosis and actin cytoskeleton disruption induced by gingipains through upregulating integrin β1

The aim of this study was to explore the effects of platelet-rich plasma on gingipain-caused changes in cell morphology and apoptosis of osteoblasts. Mouse osteoblasts MC3T3-E1 cells were treated with gingipain extracts from Porphyromonas gingivalis in the presence or absence of platelet-rich plasma. Apoptosis was detected with terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining. F-actin was determined by phalloidin-fluorescent staining and observed under confocal microscopy. Western blot analysis was used to detect integrin β1, F-actin, and G-actin protein expressions. A knocking down approach was used to determine the role of integrin β1. The platelet-rich plasma protected osteoblasts from gingipain-induced apoptosis in a dose-dependent manner, accompanied by upregulation of integrin β1. Platelet-rich plasma reversed the loss of F-actin integrity and decrease of F-actin/G-actin ratio in osteoblasts in the presence of gingipains. By contrast, the effects of platelet-rich plasma were abrogated by knockdown of integrin β1. The platelet-rich plasma failed to reduce cell apoptosis and reorganize the cytoskeleton after knockdown of integrin β1. In conclusion, platelet-rich plasma inhibits gingipain-induced osteoblast apoptosis and actin cytoskeleton disruption by upregulating integrin β1 expression.

Peptide Chitosan/Dextran Core/Shell Vascularized 3D Constructs for Wound Healing

Three-dimensional (3D) bioprinting has emerged to create novel cell-based therapies for regenerative medicine applications. Vascularized networks within engineered constructs are required, and toward this end, we report a promising strategy using core-shell (c/s) extrusion 3D-bioprinting technology that employs biomimetic biomaterials to construct regenerative, prevascularized scaffolds for wound care. A custom-designed cell-responsive bioink consisting of a 13% (w/v) cell-laden gelatin methacryloyl (GelMA) shell surrounding a peptide-functionalized, succinylated chitosan (C)/dextran aldehyde (D) cell-laden core was successfully bioprinted resulting in organized microdesigns exhibiting excellent cell viability and subsequent vessel formation. Our templating strategy takes advantage of GelMA's intrinsic thermoreversible properties of low degree of acryloyl functionalization used in combination with a lightly, chemically cross-linked peptide-CD core to serve as temporal structural supports that stabilize during extrusion onto a cooled platform. Mechanical integrity was further strengthened layer-by-layer via GelMA UV photo-cross-linking. We report the first example of GelMA used in combination with a peptide-CD bioink to c/s 3D-bioprint regenerative, prevascularized constructs for wound care. Particular cell adhesion and proteolytic peptide-CD functionalized pair combinations, P15/MMP-2 and P15/cRGD, were found to significantly increase growth of human bone-marrow-derived mesenchymal stems cells (hBMSCs) and human umbilical vein endothelial cells (HUVECs). The constructs delivered two cell types: hBMSCs in the shell bioink and HUVECs within the core bioink. Cord-like, natural microvascularization was shown with endothelial cell marker expression as confirmed by immunofluorescence (IF) staining exhibiting tubelike structures. In addition, in vitro skin wound healing activity of the construct showed a ∼twofold rate of wound closure. Overall, c/s 3D-bioprinted, peptide-CD/GelMA constructs provided the appropriate microenvironment for in vitro stem and endothelial cell viability, delivery, and differentiation. We foresee these custom constructs as representing a fundamental step toward engineering larger scale regenerative, prevascularized tissues.

The primary cilium directs osteopontin-induced migration of mesenchymal stem cells by regulating CD44 signaling and Cdc42 activation

The primary cilium acts as a sensory organelle with diverse receptors and ion channels to detect extracellular cues and regulate cellular functions, including cell migration. The migration of mesenchymal stem cells (MSCs) to bone remodeling sites is important for bone homeostasis. Recently, we have suggested that osteopontin (OPN) is a significant chemoattractant in MSC migration to bone remodeling sites. The objective of this study was to determine whether the primary cilium acts as a chemoattractant sensory unit to detect OPN cues and control MSC migration. We found that the loss of primary cilium induced by silencing of IFT88 reduced OPN-induced migration of MSCs. The effect of IFT88 silencing on cellular attachment, spreading, and proliferation was negligible. The loss of primary cilium did not affect the level of integrinβ1 or CD44, two known receptors for OPN. Interestingly, CD44 was localized to the primary cilium by OPN stimulus. Knockdown of IFT88 or CD44 dysregulated OPN-induced signaling activation and abolished OPN-induced Cdc42 activation. Our findings suggest that the primary cilium acts as a chemoattractant sensor for OPN to regulate MSC migration by controlling not only CD44-mediated OPN signaling, but also Cdc42-mediated actin cytoskeleton rearrangement.

Directing Stem Cell Commitment by Amorphous Calcium Phosphate Nanoparticles Incorporated in PLGA: Relevance of the Free Calcium Ion Concentration

The microenvironment of mesenchymal stem cells (MSCs) is responsible for the modulation in MSC commitment. Nanocomposites with an inorganic and an organic component have been investigated, and osteogenesis of MSCs has been attributed to inorganic phases such as calcium phosphate under several conditions. Here, electrospun meshes and two-dimensional films of poly(lactic-co-glycolic acid) (PLGA) or nanocomposites of PLGA and amorphous calcium phosphate nanoparticles (PLGA/aCaP) seeded with human adipose-derived stem cells (ASCs) were analyzed for the expression of selected marker genes. In a two-week in vitro experiment, osteogenic commitment was not found to be favored on PLGA/aCaP compared to pure PLGA. Analysis of the medium revealed a significant reduction of the Ca²⁺ concentration when incubated with PLGA/aCaP, caused by chemical precipitation of hydroxyapatite (HAp) on aCaP seeds of PLGA/aCaP. Upon offering a constant Ca²⁺ concentration, however, the previously observed anti-osteogenic effect was reversed: alkaline phosphatase, an early osteogenic marker gene, was upregulated on PLGA/aCaP compared to pristine PLGA. Hence, in addition to the cell–material interaction, the material–medium interaction was also important for the stem cell commitment here, affecting the cell–medium interaction. Complex in vitro models should therefore consider all factors, as coupled impacts might emerge.

Boosting the Osteogenic and Angiogenic Performance of Multiscale Porous Polycaprolactone Scaffolds by In Vitro Generated Extracellular Matrix Decoration

Tissue engineering (TE)-based bone grafts are favorable alternatives to autografts and allografts. Both biochemical properties and the architectural features of TE scaffolds are crucial in their design process. Synthetic polymers are attractive biomaterials to be used in the manufacturing of TE scaffolds, due to various advantages, such as being relatively inexpensive, enabling precise reproducibility, possessing tunable mechanical/chemical properties, and ease of processing. However, such scaffolds need modifications to improve their limited interaction with biological tissues. Structurally, multiscale porosity is advantageous over single-scale porosity; therefore, in this study, we have considered two key points in the design of a bone repair material; (i) manufacture of multiscale porous scaffolds made of photocurable polycaprolactone (PCL) by a combination of emulsion templating and three-dimensional (3D) printing and (ii) decoration of these scaffolds with the in vitro generated bone-like extracellular matrix (ECM) to create biohybrid scaffolds that have improved biological performance compared to PCL-only scaffolds. Multiscale porous scaffolds were fabricated, bone cells were cultured on them, and then they were decellularized. The biological performance of these constructs was tested in vitro and in vivo. Mesenchymal progenitors were seeded on PCL-only and biohybrid scaffolds. Cells not only showed improved attachment on biohybrid scaffolds but also exhibited a significantly higher rate of cell growth and osteogenic activity. The chick chorioallantoic membrane (CAM) assay was used to explore the angiogenic potential of the biohybrid scaffolds. The CAM assay indicated that the presence of the in vitro generated ECM on polymeric scaffolds resulted in higher angiogenic potential and a high degree of tissue infiltration. This study demonstrated that multiscale porous biohybrid scaffolds present a promising approach to improve bioactivity, encourage precursors to differentiate into mature bones, and to induce angiogenesis.

Combining Biologically Active β-Lactams Integrin Agonists with Poly(l-lactic acid) Nanofibers: Enhancement of Human Mesenchymal Stem Cell Adhesion

Regulating stem cell adhesion and growth onto functionalized biomaterial scaffolds is an important issue in the field of tissue engineering and regenerative medicine. In this study, new electrospun scaffolds of poly(l-lactic acid) (PLLA), as bioresorbable polymer, and β-lactam compounds agonists of selected integrins, as functional components with cell adhesive properties, are designed. The new β-lactam-PLLA scaffolds contribute significantly in guiding protein translation involved in human bone marrow mesenchymal stem cells (hBM-MSC) adhesion and integrin gene expression. Scanning electron microscopy, confocal laser scanning microscopy, and Western Blot analyses reveal that GM18-PLLA shows the best results, promoting cell adhesion by significantly driving changes in focal adhesion proteins distribution (β₁ integrin and vinculin) and activation (pFAK), with a notable increase of GM18-targets subunits integrin gene expression, α₄ and β₁. These novel functionalized submicrometric fibrous scaffolds demonstrate, for the first time, the powerful combination of selective β-lactams agonists of integrins with biomimetic scaffolds, suggesting a designed rule that could be suitably applied to tissue repair and regeneration.

Effect of focal adhesion kinase inhibition on osteoblastic cells grown on titanium with different topographies

Objective

The present study aimed to investigate the participation of focal adhesion kinases (FAK) in interactions between osteoblastic cells and titanium (Ti) surfaces with three different topographies, namely, untreated (US), microstructured (MS), and nanostructured (NS).

Methodology

Osteoblasts harvested from the calvarial bones of 3-day-old rats were cultured on US, MS and NS discs in the presence of PF-573228 (FAK inhibitor) to evaluate osteoblastic differentiation. After 24 h, we evaluated osteoblast morphology and vinculin expression, and on day 10, the following parameters: gene expression of osteoblastic markers and integrin signaling components, FAK protein expression and alkaline phosphatase (ALP) activity. A smooth surface, porosities at the microscale level, and nanocavities were observed in US, MS, and NS, respectively.

Results

FAK inhibition decreased the number of filopodia in cells grown on US and MS compared with that in NS. FAK inhibition decreased the gene expression of Alp, bone sialoprotein, osteocalcin, and ALP activity in cells grown on all evaluated surfaces. FAK inhibition did not affect the gene expression of Fak, integrin alpha 1 ( Itga1 ) and integrin beta 1 ( Itgb1 ) in cells grown on MS, increased the gene expression of Fak in cells grown on NS, and increased the gene expression of Itga1 and Itgb1 in cells grown on US and NS. Moreover, FAK protein expression decreased in cells cultured on US but increased in cells cultured on MS and NS after FAK inhibition; no difference in the expression of vinculin was observed among cells grown on all surfaces.

Conclusions

Our data demonstrate the relevance of FAK in the interactions between osteoblastic cells and Ti surfaces regardless of surface topography. Nanotopography positively regulated FAK expression and integrin signaling pathway components during osteoblast differentiation. In this context, the development of Ti surfaces with the ability to upregulate FAK activity could positively impact the process of implant osseointegration.

CoCrMo surface modifications affect biocompatibility, adhesion, and inflammation in human osteoblasts

In this study, different surface modifications were performed on a Cobalt-Chrome-Molybdenum (CoCrMo) alloy and the effects on cell viability and cytotoxicity as well as the adhesion potential of human osteoblasts (hFOB) and their inflammation reaction were investigated in vitro. CoCrMo discs were coated with TiN, with polished and porous coated surfaces, or with pure titanum (cpTi) surfaces and examined by Scanning Electron Microscopy to evaluate surface modifications. In vitro cell viability, adhesion behaviour, and expression of inflammation markers of hFOB human osteoblasts were measured via CellTiter-Glo, CytoTox, ELISA, and RT-PCR respectively. All results were compared to CoCrMo without surface modifications. The biocompatibility data showed high compatibility for the TiN hard coatings. Likewise, the porous surface coating increased cell viability significantly, compared to an untreated CoCrMo alloy. None of the investigated materials influenced cytotoxicity. Different surface modifications did not influence expression of fibronectin, although TiN, porous surface coatings and polished surfaces showed highly significant reductions in integrin subunit expression. In addition to the regulation of adhesion potential these three surfaces stimulated an anti-inflammatory response by osteocytes. Improved biocompatibility and adhesion properties may contribute to better osteointegration of prosthetics.