Mussel-Inspired Polydopamine Coating: A General Strategy To Enhance Osteogenic Differentiation and Osseointegration for Diverse Implants

Mussel-inspired surface-engineering of 3D printed scaffolds employing bedecked transition metal for accelerated bone tissue regeneration

In modern civilization with fast work culture and uncontrolled lifestyles increase bone-related problems, moreover, lack of auto-regeneration of bone, indulge to formulate a suitable methodology to get rid of this problem. In this article, nanohydroxyapatite (nHA) decorated hierarchical titanium phosphate (TP) was synthesized by solvothermal process and incorporated into newly synthesized tartaric acid-based polyurethane (PU) through in situ technique. The porous 3D scaffold was fabricated by most advanced 3D printing technique with desired porous structure in a controlled manner. The biochemical properties of scaffold's surface were improved via immobilizing polydopamine (PDA) at ambient temperature. Elemental analysis indicated that TP-doped nanohybrid scaffolds experienced higher amount of PDA immobilization as compared to pristine and nHA-doped scaffolds. The unoccupied 'd' orbital of introduced Ti can form a coordinate bond with catechol groups of dopamine (DA) which augments PDA deposition on the scaffold's surface. Furthermore, the higher effective nuclear charge (Z⁎) of tetravalent Ti ion generates an effective dative bond with the urethane groups of PU chain which improves hardness and tensile strength (TS) of produced nanocomposites (PU/TP-nHA) remarkably by 71.3 % and 126 % compared to pristine PU. Ti-doped nanohybrid scaffolds, containing calcium and phosphate components with higher amounts of deposited PDA exhibited improved in vitro osteogenic bioactivity. Moreover, in vivo study expressed superior bone regeneration efficacy of the TP-doped nHA-integrated PU scaffold without showing any organ toxicity. Thus, the optimum level of TP-doped nHA with higher amount of PDA-immobilized PU nanohybrid scaffold would be a suitable bone graft substitute in bone regeneration applications.

3D Bioprinting of Prevascularized Bone Organoids for Rapid In Situ Cranial Bone Reconstruction

Despite rapid advances in the field of bone tissue engineering, cranial bone defects of critical size remain difficult to repair due to the limited self-regeneration capacity of the bone. Developmental engineering with mesenchymal stem cells (MSCs) aggregates has shown promise for enhanced bone regeneration; however, these MSCs aggregates require extended in vitro osteogenic induction time and lack sufficient vascularization to enable rapid in situ osteogenesis. To address these issues, a novel strategy is introduced for the large-scale generation of prevascularized bone organoids with self-organized vascularization and enhanced osteogenic properties by combining MSCs, human umbilical vein endothelial cells, and osteogenic microparticles. The osteogenic differentiation effects across different microparticles were systematically evaluated and identified graphene oxide as the most effective, which primarily promoted osteogenesis through the focal adhesion and PI3K/Akt pathway. Further, the prevascularized bone organoid-laden hydrogels can be 3D printed into complex tissue constructs with high cell density and osteogenic capacity. In vivo experiments confirmed that this approach promoted rapid vascularized bone tissue formation, achieving effective in situ regeneration and repair of cranial bone defects. This innovative developmental engineering strategy provides a promising, scalable, and effective approach to bone regeneration, advancing developmental tissue engineering for therapeutic applications.

3D-Printed Titanium Trabecular Scaffolds with Sustained Release of Hypoxia-Induced Exosomes for Dual-Mimetic Bone Regeneration

Current Ti-6Al-4V bone implants lack trabecular structure and pro‑angiogenic cues, both essential for regeneration. Herein, a dual biomimetic strategy is devised that integrates a 3D-printed biomimetic trabecular porous Ti-6Al-4V scaffold (BTPS) with exosome-loaded PEGDA/GelMA hydrogel microspheres (PGHExo) designed for sustained release. BTPS is designed using Voronoi algorithms and imaging data, and replicates the geometry and mechanical properties of natural bone. Hypoxia-induced human umbilical vein endothelial cell (HUVEC) derived exosomes (HExo) are encapsulated in PGHExo microspheres via microfluidic technology, enabling controlled release of HExo, and anchored onto BTPS using polydopamine (pDA) modification (BTPS&pDA@PGHExo). BTPS exhibited an elastic modulus of ≈3.2 GPa and a permeability of 11.52 × 10-8 mm2, mimicking natural bone. In vitro assays demonstrated that BTPS&pDA@PGHExo significantly enhanced osteogenesis and angiogenesis. mRNA-Seq analysis suggested that BTPS&pDA@PGHExo regulates osteogenic and angiogenic gene expression through the activation of pathways including MAPK, mTOR, HIF-1, and VEGF. In vivo, BTPS&pDA@PGHExo improved bone volume, density, and neovascularization in a rabbit model. This dual biomimetic strategy offers a promising clinical solution, addressing the limitations of conventional Ti-6Al-4V scaffolds and providing an innovative approach for personalized bone defect repair.

Overcoming biological inertness: multifaceted strategies to optimize PEEK bioactivity for interdisciplinary clinical applications

Polyether ether ketone (PEEK), characterized by a comparable elastic modulus to human bone with high wear resistance, radiolucency, and biocompatibility, demonstrates considerable promise for clinical applications. However, due to the significant limitations in clinical applications caused by the biological inertness of PEEK, it should first be modified to meet clinical needs. Currently, the field of PEEK modifications is rapidly advancing, with a particular emphasis on enhancing its biological properties. Most of the previous reviews have separately discussed strategies like antibacterial, osteogenic, and angiogenic enhancements for PEEK. This review combines cross-domain insights to update and synthesize recent research on PEEK composites, focusing on advanced multi-component sustained release platforms that mimic postoperative biological processes. Such temporal alignment between material functionality and physiological healing phases demonstrates unprecedented potential for expanding PEEK's clinical versatility.

Functional poly(ether-ketone-ketone) composite scaffold with enhanced cell-material interaction, anti-inflammatory and osteogenesis for facilitating osteointegration and bone regeneration

Bone defects resulting from trauma or disease remain a significant challenge in clinical practice, often requiring prolonged treatment. Poly(ether-ketone-ketone) (PEKK) is a commonly used implant material due to its excellent biocompatibility and mechanical properties, which are similar to those of bone. However, its biological inertness leads to poor anti-inflammatory and osteointegration properties, significantly hindering the bone repair process. In this study, a cryogel filled - PEKK/bioglass (BG) composite scaffold (SPBC) was prepared via 3D printing to provide immunomodulatory and bone integration performance. Compared with untreated PEKK, SPBC exhibited significant enhancements in surface properties, including higher hydrophilicity and roughness. Additionally, SPBC enhanced the adsorption of fibronectin and vitronectin on the scaffold surface and regulated the maturation of cytoskeleton and adhesion plaques by increasing the phosphorylation level of FAK at Y397, thereby promoting cell adhesion and spreading. Due to the release of bioactive ions, SPBC can significantly promote the polarization of RAW264.7 cells towards M2 and the secretion of anti-inflammatory cytokines, while also enhancing the proliferation and differentiation of rat mesenchymal stem cells (rMSCs) in vitro. Furthermore, the in vivo results confirmed the enhanced anti-inflammatory properties and the integration of SPBC with the host tissue. In summary, after surface modification and cryogel filling, SPBC demonstrated excellent anti-inflammatory and bone integration abilities, presenting potential for clinical application as an orthopedic implant scaffold.

Optogenetic activation of mechanical nociceptions to enhance implant osseointegration

Orthopedic implants with high elastic modulus often suffer from poor osseointegration due to stress shielding, a phenomenon that suppresses the expression of intracellular mechanotransduction molecules (IMM) such as focal adhesion kinase (FAK). We find that reduced FAK expression under stress shielding is also mediated by decreased calcitonin gene-related peptide (CGRP) released from Piezo2+ mechanosensitive nerves surrounding the implant. To activate these nerves minimally invasively, we develop a fully implantable, wirelessly rechargeable optogenetic device. In mice engineered to express light-sensitive channels in Piezo2+ neurons, targeted stimulation of the L2-3 dorsal root ganglia (DRG) enhances localized CGRP release near the implant. This CGRP elevation activates the Protein Kinase A (PKA)/FAK signaling pathway in bone marrow mesenchymal stem cells (BMSCs), thereby enhancing osteogenesis and improving osseointegration. Here we show that bioelectronic modulation of mechanosensitive nerves offers a strategy to address implant failure, bridging neuroregulation and bone bioengineering.

A MnO2 nanosheets doping double crosslinked hydrogel for cartilage defect repair through alleviating inflammation and guiding chondrogenic differentiation

The inflammatory microenvironment and inferior chondrogenesis are major symptoms after cartilage defect. Although various modifications strategies associated with hydrogels exhibit remarkable capacity of pro-cartilage regeneration, the adverse effect by prolonging inflammation is still formidable to hamper potential biomedical applications of different hydrogel implants. Herein, inspired by the repair microenvironment of articular cartilage defects, an injectable, immunomodulatory, and chondrogenic L-MNS-CMDA hydrogel is prepared through grafting vinyl and catechol groups to chitosan macromolecules using amide reaction, then further loading MnO2 nanosheets (MNS). The double crosslinking of photopolymerization and catechol oxidative polymerization endows L-MNS-CMDA hydrogel with preferable mechanical property, affording a suitable mechanical support for cartilage defect repair. Additionally, the robust tissue adhesion capability stemming from catechol groups guarantees the long-term retention of the hydrogel in the defect site. Meanwhile, L-MNS-CMDA hydrogel decomposes exogenous and intracellular H2O2 into O2 and H2O, to effectively alleviate cellular oxidative stress caused by long-term hypoxia. Under the synergies of catechol groups and MNS, L-MNS-CMDA hydrogel not only inhibits macrophages polarizing into M1 phenotype, but encourages them turn into M2 phenotype, thereby, reconstructing an immunization friendly microenvironment to ultimately enhance cartilage regeneration. Predictably, the hydrogel markedly induces rat bone marrow mesenchymal stem cells differentiating into chondrocytes by expressing abundant glycosaminoglycan and type II collagen. A cartilage defect model of rat knee joint indicates that L-MNS-CMDA hydrogel visually regulate the early inflammatory response of post-implantation, and facilitate cartilage regeneration and recovery of joint function after 12 weeks of post-implantation. All in all, this multifunctional L-MNS-CMDA hydrogel exhibits superior immunomodulatory and chondrogenic properties, holding immense clinical potential in the treatment of cartilage defects.

A comparative study of polydopamine vs. glass ionomer cement for adhesion mechanisms on enamel and dentin using SEM and shear bond strength evaluation

Polydopamine (PD), inspired by the wet adhesion mechanism of mussel foot proteins, has emerged as a promising adhesive material with wide-ranging applications. This study aimed to compare the adhesive properties of PD and Glass Ionomer Cement (GIC) on enamel and dentin substrates, evaluating PD's potential as an alternative adhesive in dental practice. A total of 120 human premolars were prepared, with 80 teeth allocated for Scanning Electron Microscopy (SEM) analysis and 40 teeth reserved for shear bond strength testing. The 80 teeth for SEM were divided into four groups (n = 20 per group) based on the adhesive used (PD or GIC) and the substrate (enamel or dentin). The bond interfaces were analysed under SEM following adhesive self-polymerization. Statistical analysis using the Mann-Whitney U test (p < 0.05) revealed that GIC and PD showed more microcracks when bonded to dentin compared to enamel, with the PD-enamel group showing the fewest microcracks. For shear bond strength testing, the 40 remaining teeth were divided into four groups (n = 10 per group) according to the same adhesive-substrate combinations. The results analysed using the Kruskal-Wallis test (p < 0.001), indicated that PD bonded to enamel exhibited the highest bond strength, followed by PD-dentin, GIC-enamel, and GIC-dentin. These findings were consistent with the SEM analysis, demonstrating that PD provides superior bonding to enamel and outperforms GIC in both bond strength and interface quality. This study suggests that PD is a viable alternative to GIC, particularly for enamel bonding, and further research is recommended to assess its long-term clinical performance.

Alkaline etching assisted polydopamine coating for enhanced cell-material interactions on 3D printed polylactic acid scaffolds

The implant surface chemistry and topography are primary factors regulating the success and survival of bone scaffold. Surface modification is a promising alternative to enhance the biocompatibility and tissue response to augment the osteogenic functionalities of polyesters like PLA. The study employed the synergistic effect of alkaline hydrolysis and polydopamine (PDA) functionalization to enhance the cell-material interactions on 3D printed polylactic acid (PLA) scaffold. Comprehensive characterization of the modified PLA highlights the improvements in the physical, chemical and cell-material interactions upon two-step surface modification. The X-ray photoelectron spectroscopy (XPS) analysis substantiated enhanced PDA deposition with a ∼8.2% increase in surface N composition after surface etching due to homogeneous PDA deposition compared to the non-etched counterpart. The changes in surface chemistry and morphology upon dual surface modification complemented the human osteoblast (HOS) attachment and proliferation, with distinct cell morphology and spreading on PDA coated etched PLA (Et-PLAPDA) scaffolds. Moreover, substantial improvement in osteogenic differentiation of UMR-106 cells on etched PLA (Et-PLA) and Et-PLAPDA highlights the suitability of alkali etching-mediated PDA deposition to improve mineralization on PLA. Overall, the present work opens insights to modify scaffold surface composition, topography, hydrophilicity and roughness to regulate local cell adhesion to improve the osteogenic potential of PLA.

Nanozyme-Based Pump-free Microfluidic Chip for Colorectal Cancer Diagnosis via Circulating Cancer Stem Cell Detection

Circulating cancer stem cells (CCSCs) are subpopulations of cancer cells with high tumorigenicity, chemoresistance, and metastatic potential, which are also major drivers of disease progression. Herein, to achieve the prediction of tumor diagnosis and progression in colorectal cancer (CRC), a new, automated, and portable lateral displacement patterned pump-free (LP) microfluidic chip (LP-chip) with the CoPt3 nanozyme was established for CCSC capture and detection in peripheral blood and feces samples ex vivo. In this design, CoPt3@HA probes with functions of magnetic separation and colorimetric signal transduction by peroxidase-mimicking activity were applied for the capture of CCSCs and signal output in clinical samples. The generated colors of polydopamine (PDA) were quantifiable through the smartphone APP and visualizable by the naked eye in the test line (T line) and control line (C line) of the LP-chip. In the optimal experimental conditions, the CCSC concentration was sensitive to change in the range 0-105 cells mL-1, with a detection limit of 3 cells mL-1 (S/N = 3). Preliminary studies of clinical samples suggest that the platform has the potential for prediction of colorectal cancer progression and poor prognosis. Overall, the LP-chip provides potential strategies for timely diagnosis, therapeutic monitoring, and recurrence prediction to improve home-based patient care.

Immunomodulatory Biomaterials: Tailoring Surface Properties to Mitigate Foreign Body Reaction and Enhance Tissue Regeneration

The immune cells have demonstrated the ability to promote tissue repair by removing debris, breaking down the extracellular matrix, and regulating cytokine secretion profile. If the behavior of immune cells is not well directed, chronic inflammation and foreign body reaction (FBR) will lead to scar formation and loss of biomaterial functionality. The immunologic response toward tissue repair or chronic inflammation after injury and implantation can be modulated by manipulating the surface properties of biomaterials. Tailoring surface properties of biomaterials enables the regulation of immune cell fate such as adhesion, proliferation, recruitment, polarization, and cytokine secretion profile. This review begins with an overview of the role of immune cells in tissue healing and their interactions with biomaterials. It then discusses how the surface properties of biomaterials influence immune cell behavior. The core focus is reviewing surface modification methods to create innovative materials that reduce foreign body reactions and enhance tissue repair and regeneration by modulating immune cell activities. The review concludes with insights into future advancements in surface modification techniques and the associated challenges.

Polydopamine-Based Biomaterials in Orthopedic Therapeutics: Properties, Applications, and Future Perspectives

Polydopamine is a versatile and modifiable polymer, known for its excellent biocompatibility and adhesiveness. It can also be engineered into a variety of nanoparticles and biomaterials for drug delivery, functional modification, making it an excellent choice to enhance the prevention and treatment of orthopedic diseases. Currently, the application of polydopamine biomaterials in orthopedic disease prevention and treatment is in its early stages, despite some initial achievements. This article aims to review these applications to encourage further development of polydopamine for orthopedic therapeutic needs. We detail the properties of polydopamine and its biomaterial types, highlighting its superior performance in functional modification on nanoparticles and materials. Additionally, we also explore the challenges and future prospects in developing optimal polydopamine biomaterials for clinical use in orthopedic disease prevention and treatment.

Polydopamine Applications in Biomedicine and Environmental Science

This manuscript explores the multifaceted applications of polydopamine (PDA) across various scientific and industrial domains. It covers the chemical aspects of PDA and its potential in bone tissue engineering, implant enhancements, cancer treatment, and nanotechnology. The manuscript investigates PDA's roles in tissue engineering, cell culture technologies, surface modifications, drug delivery systems, and sensing techniques. Additionally, it highlights PDA's contributions to microfabrication, nanoengineering, and environmental applications. Through detailed testing and assessment, the study identifies limitations in PDA-related research, such as synthesis complexity, incomplete mechanistic understanding, and biocompatibility variability. It also proposes future research directions aimed at improving synthesis techniques, expanding biomedical applications, and enhancing sensing technologies to optimize PDA's efficacy and scalability.

Reactive oxygen-scavenging polydopamine nanoparticle coated 3D nanofibrous scaffolds for improved osteogenesis: Toward an aging in vivo bone regeneration model

Tissue engineered scaffolds aimed at the repair of critical-sized bone defects lack adequate consideration for our aging society. Establishing an effective aged in vitro model that translates to animals is a significant unmet challenge. The in vivo aged environment is complex and highly nuanced, making it difficult to model in the context of bone repair. In this work, 3D nanofibrous scaffolds generated by the thermally-induced self-agglomeration (TISA) technique were functionalized with polydopamine nanoparticles (PD NPs) as a tool to improve drug binding capacity and scavenge reactive oxygen species (ROS), an excessive build-up that dampens the healing process in aged tissues. PD NPs were reduced by ascorbic acid (rPD) to further improve hydrogen peroxide (H2O2) scavenging capabilities, where we hypothesized that these functionalized scaffolds could rescue ROS-affected osteoblastic differentiation in vitro and improve new bone formation in an aged mouse model. rPDs demonstrated improved H2O2 scavenging activity compared to neat PD NPs, although both NP groups rescued the alkaline phosphatase activity (ALP) of MC3T3-E1 cells in presence of H2O2. Additionally, BMP2-induced osteogenic differentiation, both ALP and mineralization, was significantly improved in the presence of PD or rPD NPs on TISA scaffolds. While in vitro data showed favorable results aimed at improving osteogenic differentiation by PD or rPD NPs, in vivo studies did not note similar improvements in ectopic bone formation an aged model, suggesting that further nuance in material design is required to effectively translate to improved in vivo results in aged animal models.

3D-Printed Demineralized Bone Matrix-Based Conductive Scaffolds Combined with Electrical Stimulation for Bone Tissue Engineering Applications

Bone is remodeled through a dynamic process facilitated by biophysical cues that support cellular signaling. In healthy bone, signaling pathways are regulated by cells and the extracellular matrix and transmitted via electrical synapses. To this end, combining electrical stimulation (ES) with conductive scaffolding is a promising approach for repairing damaged bone tissue. Therefore, "smart" biomaterials that can provide multifunctionality and facilitate the transfer of electrical cues directly to cells have become increasingly more studied in bone tissue engineering. Herein, 3D-printed electrically conductive composite scaffolds consisting of demineralized bone matrix (DBM) and polycaprolactone (PCL), in combination with ES, for bone regeneration were evaluated for the first time. The conductive composite scaffolds were fabricated and characterized by evaluating mechanical, surface, and electrical properties. The DBM/PCL composites exhibited a higher compressive modulus (107.2 MPa) than that of pristine PCL (62.02 MPa), as well as improved surface properties (i.e., roughness). Scaffold electrical properties were also tuned, with sheet resistance values as low as 4.77 × 105 Ω/sq for our experimental coating of the highest dilution (i.e., 20%). Furthermore, the biocompatibility and osteogenic potential of the conductive composite scaffolds were tested using human mesenchymal stromal cells (hMSCs) both with and without exogenous ES (100 mV/mm for 5 min/day four times/week). In conjunction with ES, the osteogenic differentiation of hMSCs grown on conductive DBM/PCL composite scaffolds was significantly enhanced when compared to those cultured on PCL-only and nonconductive DBM/PCL control scaffolds, as determined through xylenol orange mineral staining and osteogenic protein analysis. Overall, these promising results suggest the potential of this approach for the development of biomimetic hybrid scaffolds for bone tissue engineering applications.

Hierarchical Scaffold with Directional Microchannels Promotes Cell Ingrowth for Bone Regeneration

Bone regenerative scaffolds with a bionic natural bone hierarchical porous structure provide a suitable microenvironment for cell migration and proliferation. Here, a bionic scaffold (DP-PLGA/HAp) with directional microchannels is prepared by combining 3D printing and directional freezing technology. The 3D printed framework provides structural support for new bone tissue growth, while the directional pore embedded in the scaffolds provides an express lane for cell migration and nutrition transport, facilitating cell growth and differentiation. The hierarchical porous scaffolds achieve rapid infiltration and adhesion of bone marrow mesenchymal stem cells (BMSCs) and improve the expression of osteogenesis-related genes. The rabbit cranial defect experiment presents significant new bone formation, demonstrating that DP-PLGA/HAp offers an effective means to guide cranial bone regeneration. The combination of 3D printing and directional freezing technology might be a promising strategy for developing bone regenerative biomaterials.

Lysophosphatidic Acid/Polydopamine-Modified nHA Composite Scaffolds for Enhanced Osteogenesis via Upregulating the Wnt/Beta-Catenin Pathway

Guided bone regeneration (GBR) technology has been widely used for the regeneration of periodontal bone defects. However, the limited mechanical properties and bone regeneration potential of the currently available GBR membranes often limit their repair effectiveness. In this paper, serum-derived growth factor lysophosphatidic acid (LPA) nanoparticles and dopamine-decorative nanohydroxyapatite (pDA/nHA) particles were double-loaded into polylactic-glycolic acid/polycaprolactone (PLGA/PCL) scaffolds as an organic/inorganic biphase delivery system, namely, PP-pDA/nHA-LPA scaffolds. Physicochemical properties and osteogenic ability in vitro and in vivo were performed. Scanning electron microscopy and mechanical tests showed that the PP-pDA/nHA-LPA scaffolds had a 3D bionic scaffold structure with improved mechanical properties. In vitro cell experiments demonstrated that the PP-pDA/nHA-LPA scaffolds could significantly enhance the attachment, proliferation, osteogenic differentiation, and mineralization of MC3T3-E1 cells. In vivo, the PP-pDA/nHA-LPA scaffolds exhibited great cytocompatibility and cell recruitment ability in 2- and 4-week subcutaneous implantation experiments and significantly promoted bone regeneration in the periodontal defect scaffold implantation experiment. Moreover, LPA-loaded scaffolds were confirmed to enhance osteogenic activities by upregulating the expression of β-catenin and further activating the Wnt/β-catenin pathway. These results demonstrate that the biphase PP-pDA/nHA-LPA delivery system is a promising material for the GBR.

Mitochondrial-targeting and NIR-responsive Mn3O4@PDA@Pd-SS31 nanozymes reduce oxidative stress and reverse mitochondrial dysfunction to alleviate osteoarthritis

Mitochondrial reactive oxygen species (mROS) play a crucial role in the process of osteoarthritis (OA), which may be a promising target for therapy of OA. In this study, novel mitochondrial-targeting and SOD-mimic Mn3O4@PDA@Pd-SS31 nanozymes with near-infrared (NIR) responsiveness and synergistic cascade to scavenge mROS were designed for the therapy of OA. Results showed that the nanozymes accelerated the release of Pd and Mn3O4 under NIR irradiation, exhibiting enhanced activities of SOD and CAT mimic enzymes with reversed mitochondrial dysfunction and promoted mitophagy to effectively scavenge mROS from chondrocytes, modulate the microenvironment of oxidative stress, and eventually inhibit the inflammatory response. Nanozymes were excreted in vivo through intestinal metabolic pathway and had good biocompatibility, effectively reducing the inflammatory response and relieving articular cartilage degeneration in OA joints, with a reduction of 93.7 % and 93.8 % in OARSCI scores for 4 and 8 weeks respectively. Thus, this study demonstrated that the mitochondria targeting and NIR responsive Mn3O4@PDA@Pd-SS31 nanozymes could efficiently scavenge mROS, repair damaged mitochondrial function and promote cartilage regeneration, which are promising for the treatment of OA in clinical applications.

In vitro and in vivo studies on biodegradable Zn porous scaffolds with a drug-loaded coating for the treatment of infected bone defect

Additively manufactured biodegradable zinc (Zn) scaffolds have great potential to repair infected bone defects due to their osteogenic and antibacterial properties. However, the enhancement of antibacterial properties depends on a high concentration of dissolved Zn2+, which in return deteriorates osteogenic activity. In this study, a vancomycin (Van)-loaded polydopamine (PDA) coating was prepared on pure Zn porous scaffolds to solve the above dilemma. Compared with pure Zn scaffolds according to comprehensive in vitro tests, the PDA coating resulted in a slow degradation and inhibited the excessive release of Zn2+ at the early stage, thus improving cytocompatibility and osteogenic activity. Meanwhile, the addition of Van drug substantially suppressed the attachment and proliferation of S. aureus and E. coli bacterial. Furthermore, in vivo implantation confirmed the simultaneously improved osteogenic and antibacterial functions by using the pure Zn scaffolds with Van-loaded PDA coating. Therefore, it is promising to employ biodegradable Zn porous scaffolds with the proposed drug-loaded coating for the treatment of infected bone defects.

Pulmonary decellularized extracellular matrix (dECM) modified polyethylene terephthalate three-dimensional cell carriers regulate the proliferation and paracrine activity of mesenchymal stem cells

Introduction: Mesenchymal stem cells (MSCs) possess a high degree of self-renewal capacity and in vitro multi-lineage differentiation potential. Decellularized materials have garnered considerable attention due to their elevated biocompatibility, reduced immunogenicity, excellent biodegradability, and the ability to partially mimic the in vivo microenvironment conducive to cell growth. To address the issue of mesenchymal stem cells losing their stem cell characteristics during two-dimensional (2D) cultivation, this study established three-dimensional cell carriers modified with lung decellularized extracellular matrix and assessed its impact on the life activities of mesenchymal stem cells. Methods: This study employed PET as a substrate material, grafting with polydopamine (PDA), and constructing a decellularized extracellular matrix (dECM) coating on its surface, thus creating the PET/PDA/dECM three-dimensional (3D) composite carrier. Subsequently, material characterization of the cellular carriers was conducted, followed by co-culturing with human umbilical cord mesenchymal stem cells in vitro, aiming to investigate the material's impact on the proliferation and paracrine activity of mesenchymal stem cells. Results and Discussion: Material characterization demonstrated successful grafting of PDA and dECM materials, and it had complete hydrophilicity, high porosity, and excellent mechanical properties. The material was rich in various ECM proteins (collagen I, collagen IV , laminin, fibronectin, elastin), indicating good biocompatibility. In long-term in vitro cultivation (14 days) experiments, the PET/PDA/dECM three-dimensional composite carrier significantly enhanced adhesion and proliferation of human umbilical cord-derived mesenchymal stem cells (HUCMSCs), with a proliferation rate 1.9 times higher than that of cells cultured on tissue culture polystyrene (TCPS) at day 14. Furthermore, it effectively maintained the stem cell characteristics, expressing specific antigens for HUCMSCs. Through qPCR, Western blot, and ELISA experiments, the composite carrier markedly promoted the expression and secretion of key cell factors in HUCMSCs. These results demonstrate that the PET/PDA/dECM composite carrier holds great potential for scaling up MSCs' long-term in vitro cultivation and the production of paracrine factors.

Smart stimuli-responsive strategies for titanium implant functionalization in bone regeneration and therapeutics

With the increasing and aging of global population, there is a dramatic rise in the demand for implants or substitutes to rehabilitate bone-related disorders which can considerably decrease quality of life and even endanger lives. Though titanium and its alloys have been applied as the mainstream material to fabricate implants for load-bearing bone defect restoration or temporary internal fixation devices for bone fractures, it is far from rare to encounter failed cases in clinical practice, particularly with pathological factors involved. In recent years, smart stimuli-responsive (SSR) strategies have been conducted to functionalize titanium implants to improve bone regeneration in pathological conditions, such as bacterial infection, chronic inflammation, tumor and diabetes mellitus, etc. SSR implants can exert on-demand therapeutic and/or pro-regenerative effects in response to externally applied stimuli (such as photostimulation, magnetic field, electrical and ultrasound stimulation) or internal pathology-related microenvironment changes (such as decreased pH value, specific enzyme secreted by bacterial and excessive production of reactive oxygen species). This review summarizes recent progress on the material design and fabrication, responsive mechanisms, and in vitro and in vivo evaluations for versatile clinical applications of SSR titanium implants. In addition, currently existing limitations and challenges and further prospective directions of these strategies are also discussed.

2D silicene nanosheets-loaded coating for combating implant-associated infection

Implant-associated infection (IAI) is an unsolved problem in orthopaedics. Current therapies, including antibiotics and surgical debridement, can lead severe clinical and financial burdens on patients. Therefore, there is an urgent need to reinforce the inherent antibacterial properties of implants. Recently, two-dimensional (2D) silicene nanosheets (SNs) have gained increasing attention in biomedical fields owing to their considerable biocompatibility, biodegradability and strong photothermal-conversion performance. Herein, a dual-functional photosensitive coating on a Ti substrate (denoted as TPSNs) was rationally fabricated for bacterial inhibition and osteogenesis promotion. For the first time, SNs were loaded onto the surface of implants. Hyperthermia generated by the SNs and polydopamine (PDA) coating under 808 nm laser irradiation achieved the in vitro anti-bacterial efficiency of 90.7 ± 2.4 % for S. aureus and 88.0 ± 5.8 % for E. coli, respectively. In addition, TPSNs exhibited promising biocompatibility for the promotion of BMSC (bone marrow mesenchymal stem cells) proliferation and spreading. The presence of silicon (Si) in TPSNs contributed to the improved osteogenic differentiation of BMSCs, elevating the expressions of RUNX2 and OCN. In animal experiments, the combination of TPSNs with photothermal therapy (PTT) achieved an anti-bacterial efficiency of 89.2 % ± 1.6 % against S. aureus. Furthermore, TPSNs significantly improved bone-implant osseointegration in vivo. Overall, the development of a dual-functional TPSNs coating provides a new strategy for combating IAI.

Polydopamine nanomaterials and their potential applications in the treatment of autoimmune diseases

The conventional treatment methods used for the management of autoimmune diseases (ADs) have limited efficacy and also exhibit significant side effects. Thus, identification of novel strategies to improve the efficacy and safety of ADs treatment is urgently required. Overactivated immune response and oxidative stress are common characteristics associated with ADs. Polydopamine (PDA), as a polymer material with good antioxidant and photothermal conversion properties, has displayed useful application potential against ADs. In addition, PDA possesses good biosafety, simple preparation, and easy functionalization, which is conducive for the pharmacological development of PDA nanomaterials with clinical transformation prospects. Here, we have first reviewed the preparation of PDA, the different functional integration strategies of PDA-based biomaterials, and their potential applications in ADs. Next, the mechanism of action of PDA in ADs has been elaborated in detail. Finally, the application opportunities and challenges linked with PDA nanomaterials for ADs treatment are discussed. This review is contributed to design reasonable and effective PDA nanomaterials for the diagnosis and treatment of ADs.

Polydopamine functionalized polyurethane shape memory sponge with controllable expansion performance triggered by near-infrared light for incompressible hemorrhage control

Uncontrolled expansion of shape memory sponges face a significant challenge in the treatment of lethal incompressible hemorrhage, which can lead to blood overflow or damage to the surrounding tissue. Herein, we developed a polydopamine functionalized polyurethane shape memory sponge (PDA-TPI-PU) with a controllable degree of expansion by near-infrared (NIR) light-triggered stimulation for the treatment of incompressible hemorrhage. The sponge has excellent liquid absorption performance and robust mechanical strength as well as good photothermal conversion ability. Under NIR light of 0.32 W/cm2, the maximum recovery rate of the fixed-shape compression sponge was 91% within 25 s in air and 80% within 25 s in blood. In the SD rat liver penetrating injury model, compared with commercial medical gelatin sponge and PVA sponge, the PDA-TPI-PU sponge could effectively control the bleeding under the NIR light irradiation and did not cause excessive compression of the wound. The sponge with these characteristics shows potential application prospects as a hemostatic material.

Synthesis, Characterization, and Induced Osteogenic Differentiation Effect of Collagen Membranes Functionalized by Polydopamine/Graphene Oxide for Bone Tissue Engineering

Collagen is one of the most common natural absorbable polymers, which is widely used as a barrier membrane in biomedical fields due to its many desirable biological properties. However, absorbable membranes such as collagen have their own disadvantages such as unpredictable degradation rates, poor rigidity leading to tissue collapse, and limited osteogenic properties and cell adhesion. In this study, a modified collagen membrane with a polydopamine-graphene oxide (PDA/GO) complex was synthesized to improve the characteristics of collagen for bone tissue engineering. The successful synthesis of PDA/GO on collagen membranes was verified using X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The wettability of PDA/GO-modified collagen membranes was considerably improved based on the characterization by water contact angle compared to the uncoated membranes and surface coatings solely by either PDA or GO. The modified PDA/GO coating also enhanced the mechanical properties such as tensile strength and biodegradation rate of collagen membranes. In addition, the PDA/GO coating effectively enhanced the biocompatibility of collagen membranes as verified by the enhanced proliferation and adhesion of human bone marrow stem cells (hBMSCs). Additionally, the effects of PDA/GO coating on the osteogenic differentiation of hBMSCs on collagen membranes were investigated through alkaline phosphatase (ALP) activity and reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The PDA/GO coating on collagen membranes resulted in a significant increase in osteogenic properties compared with the uncoated collagen membranes. According to the results of the current study, the combination of PDA and GO-modified collagen membranes could be used for bone tissue engineering and biomedical applications.

Limitation of the migration of plasticizers from medical devices through treatment with low-pressure cold plasma, polydopamine coating, and annealing

Poly(vinyl chloride) (PVC) is widely used in the manufacture of medical devices. The plasticizers added to PVC are potentially toxic for humans, likely to migrate, and thus unintentionally administered to patients. The objective of the present study was to reduce the migration of plasticizer (1,2-cyclohexanedicarboxylic acid, diisononylester (DINCH) or trioctyltrimellitate (TOTM)) from PVC by implementing a three-step surface treatment process: (i) pretreatment with low-pressure argon cold plasma, (ii) polydopamine coating, and (iii) post-treatment with cold plasma exposure or thermal treatment at 140 °C. Samples were then characterized in terms of the water contact angle (WCA) and the aspect in scanning electron microscopy. Plasticizer migration (n = 5) was measured using an HPLC technique with ultraviolet detection and found to depend on the treatment and the plasticizer. Plasticized PVC was hydrophobic, with a measured mean ± standard deviation WCA of 96.7 ± 3.6° for PVC-DINCH and 110.2 ± 5.8° for PVC-TOTM. Plasma post-treatment and thermal post-treatment were respectively associated with a mean decrease in migration of 38.3 ± 1.9% for DINCH and 61.5 ± 4.4% for TOTM. Our results are promising with regard to limiting the migration of plasticizers into the patient's blood and thus enabling the development of safer medical devices.

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.

Bioinspired Polymers: Transformative Applications in Biomedicine and Regenerative Medicine

Bioinspired polymers have emerged as a promising field in biomaterials research, offering innovative solutions for various applications in biomedical engineering. This manuscript provides an overview of the advancements and potential of bioinspired polymers in tissue engineering, regenerative medicine, and biomedicine. The manuscript discusses their role in enhancing mechanical properties, mimicking the extracellular matrix, incorporating hydrophobic particles for self-healing abilities, and improving stability. Additionally, it explores their applications in antibacterial properties, optical and sensing applications, cancer therapy, and wound healing. The manuscript emphasizes the significance of bioinspired polymers in expanding biomedical applications, addressing healthcare challenges, and improving outcomes. By highlighting these achievements, this manuscript highlights the transformative impact of bioinspired polymers in biomedical engineering and sets the stage for further research and development in the field.

Current surface modification strategies to improve the binding efficiency of emerging biomaterial polyetheretherketone (PEEK) with bone and soft tissue: A literature review

PURPOSE

The aim of this study was to review the literature on current surface modification strategies used to improve the binding efficiency of an emerging biological material, polyetheretherketone (PEEK), with bone and soft tissues.

STUDY SELECTION

This review was based on articles retrieved from PubMed, Google Scholar, Web of Science, and ScienceDirect databases. The main keywords used during the search were "polyetheretherketone (PEEK)," "implant," "surface modification," "biomaterials," "bone," "osseointegration," and "soft tissue."

RESULTS

The suitability of PEEK surface modification strategies has been critically analyzed and summarized here. Many cell and in vivo experiments in small animals have shown that the use of advanced modification technologies with appropriate surface modification strategies can effectively improve the surface inertness of PEEK, thereby improving its binding efficiency with bone and soft tissues.

CONCLUSIONS

Surface modifications of PEEK have revealed new possibilities for implant treatment; however, most results are based on in vitro or short-term in vivo evaluations in small animals. To achieve a broad application of PEEK in the field of oral implantology, more in vivo experiments and long-term clinical evaluations are needed to investigate the effects of various surface modifications on the tissue integration ability of PEEK to develop an ideal implant material.

Effect of polydopamine and fluoride ion coating on dental enamel remineralization: an in vitro study

BACKGROUND

Fluoride treatment is one of the most effective dental caries prevention methods. To continuously prevent dental caries, stably immobilizing the fluoride on the tooth enamel is highly desirable. This study aimed to evaluate the remineralization of tooth enamels by one-pot coating using polydopamine and fluoride ions.

METHODS

To prepare the enamel specimens for polydopamine- and fluoride ion-coating, they were treated with polydopamine- and fluoride-containing gels. The enamel specimens were collected from human molars in a blind manner (n = 100) and were randomized into five treatment groups (n = 20, each): 1) untreated, 2) polydopamine-coated, 3) fluoride-containing gel-treated, 4) F varnish-treated, and 5) polydopamine- and fluoride ion-coated enamels. Vickers hardness number (VHN), morphology, and fluoride contents of the specimens were measured before and after the pH-cycling regimen.

RESULTS

Polydopamine- and fluoride ion-coated enamels showed the highest fluoride content and lowest VHN reduction among the samples. The fluoride content of the polydopamine/fluoride ion (PD/F)-coated enamel was increased to 182 ± 6.6%, which was far higher than that of the uncoated enamel (112.3 ± 32.8%, P < 0.05). The changes in the VHN values (ΔVHN) of PD/F-coated enamel substrates showed a slight reduction in the VHN (-3.6%, P < 0.05), which was far lower than that in the control group (-18.9%, P < 0.05). In addition, scanning electron microscopy clearly supported the effect of polydopamine- and fluoride ion-coatings on the remineralization of enamel specimens.

CONCLUSION

Our findings suggest that one-pot treatments with polydopamine and fluoride ions could significantly enhance remineralization by inhibiting enamel demineralization through the prolonged retention of fluoride ions.

Polyetheretherketone development in bone tissue engineering and orthopedic surgery

Polyetheretherketone (PEEK) has been widely used in the medical field as an implant material, especially in bone tissue engineering and orthopedic surgery, in recent years. This material exhibits superior stability at high temperatures and is biosecured without harmful reactions. However, the chemical and biological inertness of PEEK still limits its applications. Recently, many approaches have been applied to improve its performance, including the modulation of physical morphology, chemical composition and antimicrobial agents, which advanced the osteointegration as well as antibacterial properties of PEEK materials. Based on the evolution of PEEK biomedical devices, many studies on the use of PEEK implants in spine surgery, joint surgery and trauma repair have been performed in the past few years, in most of which PEEK implants show better outcomes than traditional metal implants. This paper summarizes recent studies on the modification and application of biomedical PEEK materials, which provides further research directions for PEEK implants.

Combined photothermal and sonodynamic therapy using a 2D black phosphorus nanosheets loaded coating for efficient bacterial inhibition and bone-implant integration

Surgical site infection (SSI) remains a major threat for implant failure in orthopedics. Herein, we report a dual-functional coating on Ti implants (named Ti/PDA/BP) with the integration of two-dimensional (2D) photo-sono sensitive black phosphorus nanosheets (BPNSs) and polydopamine (PDA) for efficient bacterial inhibition and bone-implant integration. For the first time, we employ BPNSs as generators of reactive radicals (ROS) under ultrasound (US) stimuli for implant associated infection. Additionally, the application of PDA improves the stability of BPNSs, the biocompatibility and photothermal performance of this hybrid coating. The as-prepared Ti/PDA/BP coating exhibits superior biocompatibility, bioactivity, photothermal and sonodynamic conversion abilities. Owing to the synergistic effect of hyperthermia and ·OH, Ti/PDA/BP damages the membrane and antioxidant system of Staphylococcus aureus, reaching a high antibacterial activity of 96.6% in vitro and 97.3% in vivo with rapid 10 min NIR irradiation and 20 min US treatment. In addition, we firstly unveil the significant effect of Ti/PDA/BP-based sonodynamic therapy (SDT) on bacterial membrane and oxidative stress at the transcriptome level. Moreover, the Ti/PDA/BP coating remarkably promotes osteogenesis in vitro and bone-implant osseointegration in vivo. Overall, development of Ti/PDA/BP bioactive coating provides a new strategy for combating the implant associated infection.

Fabrication of bFGF/polydopamine-loaded PEEK implants for improving soft tissue integration by upregulating Wnt/β-catenin signaling

The difficulties associated with polyetheretherketone (PEEK) implants and soft tissue integration for craniomaxillofacial bone repair have led to a series of complications that limit the clinical benefits. In this study, 3D printed multi-stage microporous PEEK implants coated with bFGF via polydopamine were fabricated to enhance PEEK implant-soft tissue integration. Multistage microporous PEEK scaffolds prepared by sulfonation of concentrated sulfuric acid were coated with polydopamine, and then used as templates for electrophoretic deposition of bFGF bioactive factors. Achieving polydopamine and bFGF sustained release, the composite PEEK scaffolds possessed good mechanical properties, hydrophilicity, protein adhesion properties. The in vitro results indicated that bFGF/polydopamine-loaded PEEK exhibited good biocompatibility to rabbit embryonic fibroblasts (REF) by promoting cell proliferation, adhesion, and migration. Ribonucleic acid sequencing (RNA-seq) revealed that bFGF/polydopamine-loaded PEEK implants significantly upregulated the expression of genes and proteins associated with soft tissue integration and activated Wnt/β-catenin signaling in biological processes, but related expression of genes and proteins was significantly downregulated when the Wnt/β-catenin signaling was inhibited. Furthermore, in vivo bFGF/polydopamine-loaded PEEK implants exhibited excellent performance in improving the growth and adhesion of the surrounding soft tissue. In summary, bFGF/polydopamine-loaded PEEK implants possess soft tissue integration properties by activating the Wnt/β-catenin signaling, which have a potential translational clinical application in the future.

3D-Printed conductive polymeric scaffolds with direct current electrical stimulation for enhanced bone regeneration

Various methods have been used to treat bone defects caused by genetic disorders, injury, or disease. Yet, there is still great need to develop alternative approaches to repair damaged bone tissue. Bones naturally exhibit piezoelectric potential, or the ability to convert mechanical stresses into electrical impulses. This phenomenon has been utilized clinically to enhance bone regeneration in conjunction with electrical stimulation (ES) therapies; however, oftentimes with critical-sized bone defects, the bioelectric potential at the site of injury is compromised, resulting in less desirable outcomes. In the present study, the potential of a 3D-printed conductive polymer blend to enhance bone formation through restoration of the bioelectrical microenvironment was evaluated. A commercially available 3D printer was used to create circular, thin-film scaffolds consisting of either polylactide (PLA) or a conductive PLA (CPLA) composite. Preosteoblast cells were seeded onto the scaffolds and subjected to direct current ES via a purpose-built cell culture chamber. It was found that CPLA scaffolds had no adverse effects on cell viability, proliferation or differentiation when compared with control scaffolds. The addition of ES, however, resulted in a significant increase in the expression of osteocalcin, a protein indicative of osteoblast maturation, after 14 days of culture. Furthermore, xylenol orange staining also showed the presence of increased mineralized calcium nodules in cultures undergoing stimulation. This study demonstrates the potential for low-cost, conductive scaffolding materials to support cell viability and enhance in vitro mineralization in conjunction with ES.

Evaluation of cell adhesion and osteoconductivity in bone substitutes modified by polydopamine

Bones damaged due to disease or accidents can be repaired in different ways. Tissue engineering has helped with scaffolds made of different biomaterials and various methods. Although all kinds of biomaterials can be useful, sometimes their weakness in cellular activity or osteoconductivity prevents their optimal use in the fabrication of bone scaffolds. To solve this problem, we need additional processes, such as surface modification. One of the common methods is coating with polydopamine. Polydopamine can not only cover the weakness of the scaffolds in terms of cellular properties, but it can also create or increase osteoconductivity properties. Polydopamine creates a hydrophilic layer on the surface of scaffolds due to a large number of functional groups such as amino and hydroxyl groups. This layer allows bone cells to anchor and adheres well to the surfaces. In addition, it creates a biocompatible environment for proliferation and differentiation. Besides, the polydopamine coating makes the surfaces chemically active by catechol and amine group, and as a result of their presence, osteoconductivity increases. In this mini-review, we investigated the characteristics, structure, and properties of polydopamine as a modifier of bone substitutes. Finally, we evaluated the cell adhesion and osteoconductivity of different polydopamine-modified bone scaffolds.

Mussel-Inspired Lego Approach for Controlling the Wettability of Surfaces with Colorless Coatings

The control of surface wettability with polyphenol coatings has been at the forefront of materials research since the late 1990s, when robust underwater adhesion was linked to the presence of L-DOPA-a catecholic amino acid-in unusually high amounts, in the sequences of several mussel foot proteins. Since then, several successful approaches have been reported, although a common undesired feature of most of them is the presence of a remnant color and/or the intrinsic difficulty in fine-tuning and controlling the hydrophobic character. We report here a new family of functional catechol-based coatings, grounded in the oxidative condensation of readily available pyrocatechol and thiol-capped functional moieties. The presence of at least two additional thiol groups in their structure allows for polymerization through the formation of disulfide bonds. The synthetic flexibility, together with its modular character, allowed us to: (I) develop coatings with applications exemplified by textiles for oil-spill water treatment; (II) develop multifunctional coatings, and (III) fine-tune the WCA for flat and textile surfaces. All of this was achieved with the application of colorless coatings.

In Situ Facile Synthesis of Low-Cost Biogenic Eggshell-Derived Nanohydroxyapatite/Chitosan Biocomposites for Orthopedic Implant Applications

In situ facile synthesis and the characterization of nanohydroxyapatite/chitosan (nHAP/CS) biocomposites were investigated for examining their potential applications in orthopedic implant technology. Firstly, the bare nHAP, europium-doped hydroxyapatite (Eu-nHAP), yttrium-doped hydroxyapatite (Y-nHAP), and Eu- and Y-codoped hydroxyapatite (Eu,Y-nHAP) nanoparticles were synthesized by the wet precipitation technique using biowaste-eggshell-derived calcium oxide powders. Then, through ultrasonication using the nanohydroxyapatite/chitosan mixtures (molar ratio = 1:2), the nHAP/CS, Eu-nHAP/CS, Y-nHAP/CS, and Eu,Y-nHAP/CS biocomposites were fabricated. Among them, Eu,Y-nHAP/CS showed higher cell viability (94.9%), higher solubility (pH = 7.6 after 21 days), and greater antibacterial activity than those of the other composites. In addition, Eu,Y-nHAP/CS exhibited improved mechanical properties compared with the other composites. For example, the nanoindentation test displayed the Eu,Y-nHAP/CS-coated 316L stainless steel implant to possess a higher Young's modulus value (9.24 GPa) and greater hardness value (300.71 MPa) than those of the others. The results indicate that the biomass-eggshell-derived Eu,Y-doped nHAP is of good use for orthopedic implant applications.

The Application of Black Phosphorus Nanomaterials in Bone Tissue Engineering

Recently, research on and the application of nanomaterials such as graphene, carbon nanotubes, and metal-organic frameworks has become increasingly popular in tissue engineering. In 2014, a two-dimensional sheet of black phosphorus (BP) was isolated from massive BP crystals. Since then, BP has attracted significant attention as an emerging nanomaterial. BP possesses many advantages such as light responsiveness, electrical conductivity, degradability, and good biocompatibility. Thus, it has broad prospects in biomedical applications. Moreover, BP is composed of phosphorus, which is a key bone tissue component with good biocompatibility and osteogenic repair ability. Thereby, BP exhibits excellent advantages for application in bone tissue engineering. In this review, the structure and the physical and chemical properties of BP are described. In addition, the current applications of BP in bone tissue engineering are reviewed to aid the future research and application of BP.

Design of Cefotaxime Sodium-Loaded Polydopamine Coatings with Controlled Surface Roughness for Titanium Implants

The success rate of dental implants is limited by peri-implant infection and insufficient osseointegration. Therefore, reducing the occurrence of peri-implantitis and promoting osseointegration are in demand. A roughened surface has commonly been applied to improve the osseointegration of implants, but it will accelerate the attachment of bacteria. We have developed novel antibiotic-decorated titanium (Ti) surfaces by the immobilization of dopamine and cefotaxime sodium (CS) simultaneously. Moreover, the surface roughness of the polydopamine (PDA)/CS coating was controlled by the changes in polymerization times as determined by atomic force microscopy. Then, all antibiotic-grafted Ti surfaces could effectively prevent the adhesion and proliferation of both Escherichia coli and Streptococcus mutans in comparison to the pristine control. For the culture and osteogenic differentiation of human umbilical mesenchymal stem cells (hUMSCs) on the substrate surface, PDA/CS coating with polymerization times less than 30 min showed acceptable biocompatibility, but the upregulation of marker genes and proteins was detected when the polymerization time was more than 30 min. Moreover, the best calcium deposition results were found in the 30 min PDA/CS group with or without the addition of osteogenic factors. Therefore, our PDA/CS coating with a polymerization time of 30 min holds great potential to design dental implants with dual bacteriostatic and osteogenic properties.

Mussel-inspired biomaterials: From chemistry to clinic

After several billions of years, nature still makes decisions on its own to identify, develop, and direct the most effective material for phenomena/challenges faced. Likewise, and inspired by the nature, we learned how to take steps in developing new technologies and materials innovations. Wet and strong adhesion by Mytilidae mussels (among which Mytilus edulis-blue mussel and Mytilus californianus-California mussel are the most well-known species) has been an inspiration in developing advanced adhesives for the moist condition. The wet adhesion phenomenon is significant in designing tissue adhesives and surgical sealants. However, a deep understanding of engaged chemical moieties, microenvironmental conditions of secreted proteins, and other contributing mechanisms for outstanding wet adhesion mussels are essential for the optimal design of wet glues. In this review, all aspects of wet adhesion of Mytilidae mussels, as well as different strategies needed for designing and fabricating wet adhesives are discussed from a chemistry point of view. Developed muscle-inspired chemistry is a versatile technique when designing not only wet adhesive, but also, in several more applications, especially in the bioengineering area. The applications of muscle-inspired biomaterials in various medical applications are summarized for future developments in the field.

Adhesive Gelatin-Catechol Complex Reinforced Poly(Acrylic Acid) Hydrogel with Enhanced Toughness and Cell Affinity for Cartilage Regeneration

The repair of cartilage damage caused by trauma, wear, or degenerative deformation remains a major challenge in modern medicine. Therefore, it is essential to develop a mechanically compatible and bioactive scaffold for cartilage tissue regeneration. In this study, a mussel-inspired, tough, adhesive polydopamine/gelatin-poly(acrylic acid) (PDA/Gel-PAA) composite hydrogel was developed for cartilage regeneration. The hydrogel achieved a high compressive strength of up to 0.67 MPa and a toughness of 420 J/m2 because of the unique chemical-physical cross-linking structure by introducing the PDA/Gel complex into the PAA network. PAA chains with rich carboxyl groups mimic the negatively charged glycosaminoglycans (GAGs) in the natural cartilage extracellular matrix (ECM), leading to strong water retention in the hydrogel. The incorporation of the PDA/Gel complex with catechol groups on PDA and arginine-glycine-aspartic acid (RGD) sequences on gelatin chains provided abundant adhesive motifs to improve the cell affinity and tissue adhesiveness of PAA, thereby facilitating the adhesion and proliferation of bone marrow stromal cells (BMSCs). In addition, transforming growth factor-β3 (TGFβ3) was stably immobilized and released from the PDA/Gel-PAA hydrogel. Thus, adhesive hydrogels can provide a suitable microenvironment to promote cell migration in the defect area and induce chronogenesis for cartilage regeneration.

Surface polydopamine modification of bone defect repair materials: Characteristics and applications

Bone defects are a common challenge for clinical orthopedic surgeons. The existing bone defect repair materials are difficult to achieve satisfactory osseointegration between the material and the bone. Therefore, it is increasingly important to find effective methods to improve the integration of the materials with the bone and thus facilitate bone defect repair. Researchers have found that polydopamine (PDA) has a structure and properties similar to the adhesive proteins secreted by mussels in nature, with good biocompatibility, bioactivity, hydrophilicity, bio-adhesion and thermal stability. PDA is therefore expected to be used as a surface modification material for bone repair materials to improve the bonding of bone repair materials to the bone surface. This paper reviews research related to PDA-modified bone repair materials and looks at their future applications.

Fabrication of a Cell-Friendly Poly(dimethylsiloxane) Culture Surface via Polydopamine Coating

In this study, we fabricated a poly(dimethylsiloxane) (PDMS) surface coated with polydopamine (PDA) to enhance cell adhesion. PDA is well known for improving surface adhesion on various surfaces due to the abundant reactions enabled by the phenyl, amine, and catechol groups contained within it. To confirm the successful surface coating with PDA, the water contact angle and X-ray photoelectron spectroscopy were analyzed. Human umbilical vein endothelial cells (HUVECs) and human-bone-marrow-derived mesenchymal stem cells (MSCs) were cultured on the PDA-coated PDMS surface to evaluate potential improvements in cell adhesion and proliferation. HUVECs were also cultured inside a cylindrical PDMS microchannel, which was constructed to mimic a human blood vessel, and their growth and performance were compared to those of cells grown inside a rectangular microchannel. This study provides a helpful perspective for building a platform that mimics in vivo environments in a more realistic manner.

Mussel-Inspired Polydopamine-Based Multilayered Coatings for Enhanced Bone Formation

Repairing bone defects remains a challenge in clinical practice and the application of artificial scaffolds can enhance local bone formation, but the function of unmodified scaffolds is limited. Considering different application scenarios, the scaffolds should be multifunctionalized to meet specific demands. Inspired by the superior adhesive property of mussels, polydopamine (PDA) has attracted extensive attention due to its universal capacity to assemble on all biomaterials and promote further adsorption of multiple external components to form PDA-based multilayered coatings with multifunctional property, which can induce synergistic enhancement of new bone formation, such as immunomodulation, angiogenesis, antibiosis and antitumor property. This review will summarize mussel-inspired PDA-based multilayered coatings for enhanced bone formation, including formation mechanism and biofunction of PDA coating, as well as different functional components. The synergistic enhancement of multiple functions for better bone formation will also be discussed. This review will inspire the design and fabrication of PDA-based multilayered coatings for different application scenarios and promote deeper understanding of their effect on bone formation, but more efforts should be made to achieve clinical translation. On this basis, we present a critical conclusion, and forecast the prospects of PDA-based multilayered coatings for bone regeneration.

Application of biomolecules modification strategies on PEEK and its composites for osteogenesis and antibacterial properties

As orthopedic and dental implants, polyetheretherketone (PEEK) is expected to be a common substitute material of titanium (Ti) and its alloys due to its good biocompatibility, chemical stability, and elastic modulus close to that of bone tissue. It could avoid metal allergy and bone resorption caused by the stress shielding effect of Ti implants, widely studied in the medical field. However, the lack of biological activity is not conducive to the clinical application of PEEK implants. Therefore, the surface modification of PEEK has increasingly become one of the research hotspots. Researchers have explored various biomolecules modification methods to effectively enhance the osteogenic and antibacterial activities of PEEK and its composites. Therefore, this review mainly summarizes the recent research of PEEK modified by biomolecules and discusses the further research directions to promote the clinical transformation of PEEK implants.

Heterostructured Metal-Organic Frameworks/Polydopamine Coating Endows Polyetheretherketone Implants with Multimodal Osteogenicity and Photoswitchable Disinfection

Clinically, bacteria-induced contagion and insufficient osseointegrative property inevitably elicit the failure of orthopedic implants. Herein, a heterostructured coating consisting of simvastatin (SIM)-laden metal-organic frameworks and polydopamine nanolayers is created on a porous bioinert polyetheretherketone implant. The heterostructured coating significantly promotes cytocompatibility and osteogenic differentiation through multimodal osteogenicity mechanisms of zinc ion (Zn²⁺ ) therapy, SIM drug therapy, and surface micro-/nano-topological stimulation. Under the illumination of near-infrared (NIR) light, singlet oxygen (¹ O₂ ) and local hyperthermia are produced; besides, NIR light dramatically accelerates the release of Zn²⁺ ions from heterostructured coatings. Gram-positive and -negative bacteria are effectively eradicated by the synergy of photothermal/photodynamic effects and photo-induced accelerated delivery of Zn²⁺ ions. The superior osteogenicity and osseointegration, as well as photoswitchable disinfection controlled by NIR light are corroborated via in vivo results. This work highlights the great potential of photoresponsive heterostructured orthopedic implants in treatment of the noninvasive bone reconstruction of bacteria-associated infectious tissues through multimodal phototherapy and photoswitchable ion-therapy.

TiO2 Nanotubes Functionalized with Icariin for an Attenuated In Vitro Immune Response and Improved In Vivo Osseointegration

Due to their superior mechanical and chemical properties, titanium (Ti) and its alloys have been widely used as orthopedic implantable devices. However, their bioinertness represents a limitation, which can be overcome by employing various surface modifications, such as TiO₂ nanotube (TNT) fabrication via electrochemical anodization. Anodic TNTs present tunable dimensions and unique structures, turning them into feasible drug delivery platforms. In the present work, TNTs were loaded with icariin (Ica) through an adhesive intermediate layer of polydopamine (DP), and their in vitro and in vivo biological performance was evaluated. The successful fabrication of the modified surfaces was verified by scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), and contact angle measurements (CA), while the in vitro release of Ica was evaluated via UV-VIS spectrophotometry. In terms of in vitro behaviour, comparative studies on RAW 264.7 macrophages demonstrated that the TNT substrates, especially TNT-DP-Ica, elicited a lower inflammatory response compared to the Ti support. Moreover, the in vivo implantation studies evinced generation of a reduced fibrotic capsule around this implant and increased thickness of the newly formed bone tissue at 1 month and 3 months post-implantation, respectively. Overall, our results indicate that the controlled release of Ica from TNT surfaces could result in an improved osseointegration process.

Additive Manufacturing in Orthopedics: A Review

Additive manufacturing is an advanced manufacturing manner that seems like the industrial revolution. It has the inborn benefit of producing complex formations, which are distinct from traditional machining technology. Its manufacturing strategy is flexible, including a wide range of materials, and its manufacturing cycle is short. Additive manufacturing techniques are progressively used in bone research and orthopedic operation as more innovative materials are developed. This Review lists the recent research results, analyzes the strengths and weaknesses of diverse three-dimensional printing strategies in orthopedics, and sums up the use of varying 3D printing strategies in surgical guides, surgical implants, surgical predictive models, and bone tissue engineering. Moreover, various postprocessing methods for additive manufacturing for orthopedics are described.

Oxygen-Carrying and Antibacterial Fluorinated Nano-Hydroxyapatite Incorporated Hydrogels for Enhanced Bone Regeneration

Insufficient oxygen availability in tissue engineering is one of the major factors for the failure of clinical transplantation. One potential strategy to conquer this limitation is the fabrication of spontaneous and continuous oxygen supplying scaffolds for in situ tissue regeneration. In this work, a versatile fluorine-incorporating hydrogel is designed which can not only timely and continuously supply oxygen for mesenchymal stem cells (MSCs) to overcome deficient oxygen before vascularization in scaffolds, but can present a higher antibacterial capability to avoid bacterial infections. The HAp@PDA-F nanoparticles are first prepared and then incorporated with the quaternized and methacrylated chitosan forming CS/HAp@PDA-F by photo-crosslinking. In vitro results indicate that CS/HAp@PDA-F hydrogel has outstanding mechanical performance, moreover, it also has the oxygen-carrying ability to prolong survival ability, enhance proliferation activity, and preserve osteogenic differentiation potency and promote osteogenic-related genes expression of rat bone mesenchymal stem cells (rBMSCs) under hypoxic environment. Furthermore, the CS/HAp@PDA-F hydrogel can inhibit the growth of Staphylococcus aureus and Escherichia coli, providing a good antibacterial activity. Additionally, in vivo experiments demonstrate higher bone volume and bone mineral density, and more new bone tissue generation in CS/HAp@PDA-F group than in CS/HAp@PDA group. These results indicate that the rational design of fluorinated hydrogel possesses a good clinical application prospect for bone regeneration.