NanoCRISPR-assisted biomimetic tissue-equivalent patch regenerates the intervertebral disc by inhibiting endothelial-to-mesenchymal transition

The integrity of the intervertebral disc (IVD), an immune-privileged organ protected by the blood-disc barrier, is compromised following annulus fibrosus (AF) injury. This breach facilitates angiogenesis, immune cell infiltration, and inflammation, accelerating intervertebral disc degeneration (IDD) and resulting in various clinical disorders. Current treatments fail to adequately address biological repair of AF defects and angiogenesis. Single-cell RNA sequencing analyses reveal that vascular endothelial growth factor (VEGF), secreted by IDD-associated fibrochondrocytes, is crucial in promoting angiogenesis by inducing endothelial-to-mesenchymal transition (EndoMT). This study proposes a nano-clustered regularly interspaced short palindromic repeats (CRISPR)-assisted AF patch with an aligned, polydopamine-modified nano-lamellae nanofibrous scaffold that replicates the hierarchical structure of natural AF, providing a conducive microenvironment for AF repair. A zeolitic imidazolate framework-8-based nanoCRISPR system encapsulates the CRISPR/CRISPR-associated protein 9 complex to target and eliminate VEGF-mediated angiogenic factors. In vitro studies demonstrate that the nanoCRISPR-assisted patch can enhance AF cell adhesion and migration, promote extracellular matrix deposition, knock out VEGF expression, and inhibit EndoMT. In vivo studies show its significant efficacy in promoting AF repair, inhibiting abnormal angiogenesis, and delaying IDD progression. This study presents a promising approach for structural and biological AF regeneration, addressing physical and angiogenic barriers in IVD regeneration.

Polydopamine-functionalized acellular fish scale scaffolds for accelerated bone tissue regeneration

The complex microenvironment changes in the bone defect site are the main reason for its refractory treatment, including the significant increase in the level of reactive oxygen species (ROS) and inflammatory dysregulation. There is an urgent need to develop some bioactive materials that can regulate the microenvironment and promote bone regeneration. This study proposed a new strategy for designing bone tissue engineering scaffolds based on fish scales and developed a polydopamine-functionalized acellular fish scale scaffold (PDA-AFS). The results showed that PDA-AFS had excellent mechanical properties, special three-dimensional surface topography, and biodegradability. In vitro results showed that PDA-AFS had good biocompatibility and cell adhesion ability, could effectively reduce ROS levels, and had immunomodulatory activity. More importantly, PDA-AFS can enhance osteogenic differentiation of bone marrow mesenchymal stem cells and promote endogenous bone regeneration in critical-sized calvarial bone defects. In addition, transcriptome analysis also provided clues to its possible osteogenic mechanism. Overall, we provide a new strategy for designing bone tissue engineering scaffolds based on fish scales for bone regeneration treatment of bone defects.

A cross-linked coating loaded with antimicrobial peptides for corrosion control, early antibacterial, and sequential osteogenic promotion on a magnesium alloy as orthopedic implants

Magnesium (Mg)-based alloys have been recognized as desirable biodegradable materials for orthopedic implants. However, their clinical application has been limited by rapid degradation rates, insufficient antibacterial and osteogenic-promotion properties. Herein, a MgF2 priming layer was first constructed on AZ31 surface. Then, dopamine and polyphenols (EGCG) were cross-linked onto this AZ31-F surface to promote osteogenesis and further enhance corrosion protection, followed by chemical grafting of antimicrobial peptides (AMPs) via Michael-addition and Schiff-base reaction to confer antibacterial properties. In vitro electrochemical corrosion tests showed that icorr of AZ31-FE/AMPs (4.36×10-7 A/cm2) is two orders of magnitude lower than that of AZ31 (4.17×10-5 A/cm2). In vitro immersion degradation showed that AZ31-FE/AMPs exhibited the lowest hydrogen release (2.38 mL) after 400 h immersion with the lowest hydrogen evolution rate among them. Further, AZ31-FE/AMPs displayed inhibitory effects against S. aureus and E. coil in the initial stage and even after 7 days immersion in PBS (antibacterial rate > 85 %). AZ31-FE/AMPs promoted ALP secretion and calcium nodule formation in MC3T3-E1 cells. Transcriptome sequencing results indicated that osteogenic promotion mechanism of AZ31-FE/AMPs in MC3T3-E1 may involve the PI3K-Akt signalling pathway. Further, AZ31-FE/AMPs enhanced new bone formation when implanted in a rat femoral bone defect model. This coating strategy addresses initial antibacterial and later osteogenesis needs based on the corrosion control, which is crucial for the surface design of Mg-based implants. STATEMENT OF SIGNIFICANCE: It is critical for magnesium-based orthopedic implants to achieve sequential functions in the bone repair process while controlling an appropriate degradation rate. A MgF2 priming layer/phenolic-amine grafted AMPs (antimicrobial peptides) duplex coating was constructed on AZ31 surface in this study. The MgF2 layer provided a basic corrosion protection to magnesium substrate, and dopamine and polyphenols (EGCG) were then cross-linked to the MgF2 pretreated AZ31 to promote osteogenesis and enhance corrosion resistance, followed by chemical grafting of AMPs to confer antibacterial property. This strategy effectively meets the initial need for infection resistance and later osteogenic promotion on the basis of controlling the substrate corrosion rate, thus holding significant implications for the surface design of magnesium-based implants.

Bioactive polymers: A comprehensive review on bone grafting biomaterials

The application of bone grafting materials in bone tissue engineering is paramount for treating severe bone defects. In this comprehensive review, we explore the significance and novelty of utilizing bioactive polymers as grafts for successful bone repair. Unlike metals and ceramics, polymers offer inherent biodegradability and biocompatibility, mimicking the native extracellular matrix of bone. While these polymeric micro-nano materials may face challenges such as mechanical strength, various fabrication techniques are available to overcome these shortcomings. Our study not only investigates diverse biopolymeric materials but also illuminates innovative fabrication methods, highlighting their importance in advancing bone tissue engineering.

Novel multi-functional microsphere scaffold with shape memory function for bone regeneration

Irregular bone defects caused by trauma and bone diseases provide a complex implant environment for surgery. Traditional implants often fail to integrate well with the surrounding bone defect interface, therefore, developing an artificial bone scaffold that can adapt to irregular bone defect boundaries is of significant importance for bone defect repair. This study successfully utilized a shape memory ternary copolymer polylactic acid-trimethylene carbonate-hydroxyacetic acid (PLLA-TMC-GA) and dopamine-modified nano-hydroxyapatite (PHA) composite to construct a temperature-responsive bone repair scaffold (PTG/PHA), thereby enhancing the interface compatibility between the implant and the surrounding environment. The addition of PHA has effectively improved the hydrophilicity of the stent and significantly increased its mechanical strength. Furthermore, the Sodium alginate (SA) hydrogel loaded with Icariin (Ica) coated on the stent surface promotes the growth and differentiation of bone cells through the drug-scaffold synergistic effect. Both in vivo and in vitro experiments have shown that the synergistic effect of the composite stent with Icariin significantly enhances the repair of bone defects. This study provides a promising tissue engineering method for the repair of irregular bone defects.

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.

Photothermal driven BMSCs osteogenesis and M2 macrophage polarization on polydopamine-coated Ti3C2 nanosheets/poly(vinylidene fluoride trifluoroethylene) nanocomposite coatings

Mild thermal stimulation plays an active role in bone tissue repair and regeneration. In this work, a bioactive polydopamine/Ti3C2/poly(vinylidene fluoride trifluoroethylene) (PDA/Ti3C2/P(VDF-TrFE)) nanocomposite coating with excellent near-infrared light (NIR)-triggered photothermal effect was designed to improve the osteogenic ability of implants. By incorporating dopamine (DA)-modified Ti3C2 nanosheets into the P(VDF-TrFE) matrix and combining them with alkali initiated in situ polymerization, the resulting PDA/Ti3C2/P(VDF-TrFE) nanocomposite coating gained high adhesion strength on Ti substrate, excellent tribological and corrosion resistance properties, which was quite important for clinical application of implant coatings. Cell biology experiments showed that NIR-triggered mild thermal stimulation on the coating surface promoted cell spreading and growth of BMSCs, and also greatly upregulated the osteogenic markers, including Runt-Related Transcription Factor 2 (RUNX2), alkaline phosphatase (ALP), osteopontin (OPN), osteocalcin (OCN). Simultaneously, the synthesis of heat shock protein 47 (HSP47) was significantly promoted by the mild thermal stimulation, which strengthened the specific interaction between HSP47 and collagen Ⅰ (COL-Ⅰ), thereby activating the integrin-mediated MEK/ERK osteogenic differentiation signaling pathway. In addition, the results also showed that the mild thermal stimulation induced the polarization of macrophages towards M2 phenotype, which can attenuate the inflammatory response of injured bone tissue. Antibacterial results indicated that the coating exhibited an outstanding antibacterial ability against S. aureus and E. coli. Conceivably, the versatile implant bioactive coatings developed in this work will show great application potential for implant osseointegration.

3D Printing and Surface Engineering of Ti6Al4V Scaffolds for Enhanced Osseointegration in an In Vitro Study

Ti6Al4V superalloy is recognized as a good candidate for bone implants owing to its biocompatibility, corrosion resistance, and high strength-to-weight ratio. While dense metal implants are associated with stress shielding issues due to the difference in densities, stiffness, and modulus of elasticity compared to bone tissues, the surface of the implant/scaffold should mimic the properties of the bone of interest to assure a good integration with a strong interface. In this study, we investigated the additive manufacturing of porous Ti6Al4V scaffolds and coating modification for enhanced osteoconduction using osteoblast cells. The results showed the successful fabrication of porous Ti6Al4V scaffolds with adequate strength. Additionally, the surface treatment with NaOH and Dopamine Hydrochloride (DOPA) promoted the formation of Dopamine Hydrochloride (DOPA) coating with an optimized coating process, providing an environment that supports higher cell viability and growth compared to the uncoated Ti6Al4V scaffolds, as demonstrated by the higher proliferation ratios observed from day 1 to day 29. These findings bring valuable insights into the surface modification of 3D-printed scaffolds for improved osteoconduction through the coating process in solutions.

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

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

Biofabrication of biomimetic undulating microtopography at the dermal-epidermal junction and its effects on the growth and differentiation of epidermal cells

The undulating microtopography located at the junction of the dermis and epidermis of the native skin is called rete ridges (RRs), which plays an important role in enhancing keratinocyte function, improving skin structure and stability, and providing three-dimensional (3D) microenvironment for skin cells. Despite some progress in recent years, most currently designed and manufactured tissue-engineered skin models still cannot replicate the RRs, resulting in a lack of biological signals in the manufactured skin models. In this study, a composite manufacturing method including electrospinning, 3D printing, and functional coating was developed to produce the epidermal models with RRs. Polycaprolactone (PCL) nanofibers were firstly electrospun to mimic the extracellular matrix environment and be responsible for cell attachment. PCL microfibers were then printed onto top of the PCL nanofibers layer by 3D printing to quickly prepare undulating microtopography and finally the entire structures were dip-coated with gelatin hydrogel to form a functional coating layer. The morphology, chemical composition, and structural properties of the fabricated models were studied. The results proved that the multi-process composite fabricated models were suitable for skin tissue engineering. Live and dead staining, cell counting kit-8 (CCK-8) as well as histology (haematoxylin and eosin (HE) methodology) and immunofluorescence (primary and secondary antibodies combination assay) were used to investigate the viability, metabolic activity, and differentiation of skin cells forin vitroculturing.In vitroresults showed that each model had high cell viability, good proliferation, and the expression of differentiation marker. It was worth noting that the sizes of the RRs affected the cell growth status of the epidermal models. In addition, the unique undulation characteristics of the epidermal-dermal junction can be reproduced in the developed epidermal models. Overall, thesein vitrohuman epidermal models can provide valuable reference for skin transplantation, screening and safety evaluation of drugs and cosmetics.

3D Printing of Bone Substitutes Based on Vat Photopolymerization Processes: A Systematic Review

Treatment options for critically sized bone defects are currently limited to metal osteosynthesis, autologous bone grafting, or calcium-based implants to bridge the gap. Additive manufacturing techniques pose a possible alternative. The light-basedthree-dimensional printing process of vat photopolymerization (VP) is of particular interest since it enables the printing of complex scaffold architectures at high resolution. This review compares multiple vat photopolymerization processes as well as the employed resin components' interactions with musculoskeletal cells and tissue. The results show an outstanding printing capability, exceeding the potential of other printing methods. However, despite the availability of various biocompatible materials, neither the mechanical strength of bone nor the scale necessary for clinical application has been achieved so far when relying on single material constructs. One possible solution is the development of adaptive hybrid constructs produced with multimaterial VP.

Gelatin hydrogel reinforced with mussel-inspired polydopamine-functionalized nanohydroxyapatite for bone regeneration

Developing high-strength hydrogels with biocompatibility and bone conductibility is still desirable for bone regeneration. The nanohydroxyapatite (nHA) was incorporated into a dopamine-modified gelatin (Gel-DA) hydrogel system to create a highly biomimetic native bone tissue microenvironment. In addition, to further increase the cross-linking density between nHA and Gel-DA, nHA was functionalized by mussel-inspired polydopamine (PDA). Compared with nHA, adding polydopamine functionalized nHA (PHA) increased the compressive strength of Gel-Da hydrogel from 449.54 ± 180.32 kPa to 611.18 ± 211.86 kPa without affecting its microstructure. Besides, the gelation time of Gel-DA hydrogels with PHA incorporation (GD-PHA) was controllable from 49.47 ± 7.93 to 88.11 ± 31.18 s, contributing to its injectable ability in clinical applications. In addition, the abundant phenolic hydroxyl group of PHA was beneficial to the cell adhesion and proliferation of Gel-DA hydrogels, leading to the excellent biocompatibility of Gel-PHA hydrogels. Notably, the GD-PHA hydrogels could accelerate the bone repair efficiency in the rat model of the femoral defect. In conclusion, our results suggest the Gel-PHA hydrogel with osteoconductivity, biocompatibility, and enhanced mechanical properties is a potential bone repair material.

Combined Effects of Polydopamine-Assisted Copper Immobilization on 3D-Printed Porous Ti6Al4V Scaffold for Angiogenic and Osteogenic Bone Regeneration

Numerous studies have demonstrated that biological compounds and trace elements such as dopamine (DA) and copper ions (Cu) could be modified onto the surfaces of scaffolds using a one-step immersion process which is simple, inexpensive and, most importantly, non-cytotoxic. The development and emergence of 3D printing technologies such as selective laser melting (SLM) have also made it possible for us to fabricate bone scaffolds with precise structural designs using metallic compounds. In this study, we fabricated porous titanium scaffolds (Ti) using SLM and modified the surface of Ti with polydopamine (PDA) and Cu. There are currently no other reported studies with such a combination for osteogenic and angiogenic-related applications. Results showed that such modifications did not affect general appearances and microstructural characteristics of the porous Ti scaffolds. This one-step immersion modification allowed us to modify the surfaces of Ti with different concentrations of Cu ions, thus allowing us to fabricate individualized scaffolds for different clinical scenarios. The modification improved the hydrophilicity and surface roughness of the scaffolds, which in turn led to promote cell behaviors of Wharton’s jelly mesenchymal stem cells. Ti itself has high mechanical strength, therefore making it suitable for surgical handling and clinical applications. Furthermore, the scaffolds were able to release ions in a sustained manner which led to an upregulation of osteogenic-related proteins (bone alkaline phosphatase, bone sialoprotein and osteocalcin) and angiogenic-related proteins (vascular endothelial growth factor and angiopoietin-1). By combining additive manufacturing, Ti6Al4V scaffolds, surface modification and Cu ions, the novel hybrid 3D-printed porous scaffold could be fabricated with ease and specifically benefited future bone regeneration in the clinic.

Mussel-inspired polydopamine decorated alginate dialdehyde-gelatin 3D printed scaffolds for bone tissue engineering application

This study utilized extrusion-based 3D printing technology to fabricate calcium-cross-linked alginate dialdehyde-gelatin scaffolds for bone regeneration. The surface of polymeric constructs was modified with mussel-derived polydopamine (PDA) in order to induce biomineralization, increase hydrophilicity, and enhance cell interactions. Microscopic observations revealed that the PDA layer homogeneously coated the surface and did not appear to induce any distinct change in the microstructure of the scaffolds. The PDA-functionalized scaffolds were more mechanically stable (compression strength of 0.69 ± 0.02 MPa) and hydrophilic (contact angle of 26) than non-modified scaffolds. PDA-decorated ADA-GEL scaffolds demonstrated greater durability. As result of the 18-days immersion in simulated body fluid solution, the PDA-coated scaffolds showed satisfactory biomineralization. Based on theoretical energy analysis, it was shown that the scaffolds coated with PDA interact spontaneously with osteocalcin and osteomodulin (binding energy values of -35.95 kJ mol-1 and -46.39 kJ mol-1, respectively), resulting in the formation of a protein layer on the surface, suggesting applications in bone repair. PDA-coated ADA-GEL scaffolds are capable of supporting osteosarcoma MG-63 cell adhesion, viability (140.18% after 7 days), and proliferation. In addition to increased alkaline phosphatase secretion, osteoimage intensity also increased, indicating that the scaffolds could potentially induce bone regeneration. As a consequence, the present results confirm that 3D printed PDA-coated scaffolds constitute an intriguing novel approach for bone tissue engineering.

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.

Versatile polyphenolic platforms in regulating cell biology

Polyphenolic materials are a class of fascinating and versatile bioinspired materials for biointerfacial engineering. In particular, due to the presence of active chemical groups, a series of unique physicochemical properties become accessible and tunable of the as-prepared polyphenolic platforms, which could delicately regulate the cell activities via cell-material contact-dependent interactions. More interestingly, polyphenols could also affect the cell behaviors via cell-material contact-independent manner, which arise due to their intrinsically functional characteristics (e.g., antioxidant and photothermal behaviors). As such, a comprehensive understanding on the relationship between material properties and desired biomedical applications, as well as the underlying mechanism at the cellular and molecular level would provide material design principles and accelerate the lab-to-clinic translation of polyphenolic platforms. In this review, we firstly give a brief overview of cell hallmarks governed by surrounding cues, followed by the introduction of polyphenolic material engineering strategies. Subsequently, a detailed discussion on cell-polyphenols contact-dependent interfacial interaction and contact-independent interaction was also carefully provided. Lastly, their biomedical applications were elaborated. We believe that this review could provide guidances for the rational material design of multifunctional polyphenols and extend their application window.

Additive Manufacturing Technologies for Fabrication of Biomaterials for Surgical Procedures in Dentistry: A Narrative Review

PURPOSE

To screen and critically appraise available literature regarding additive manufacturing technologies for bone graft material fabrication in dentistry.

MATERIAL AND METHODS

PubMed and Scopus were searched up to May 2021. Studies reporting the additive manufacturing techniques to manufacture scaffolds for intraoral bone defect reconstruction were considered eligible. A narrative review was synthesized to discuss the techniques for bone graft material fabrication in dentistry and the biomaterials used.

RESULTS

The databases search resulted in 933 articles. After removing duplicate articles (128 articles), the titles and abstracts of the remaining articles (805 articles) were evaluated. A total of 89 articles were included in this review. Reading these articles, 5 categories of additive manufacturing techniques were identified: material jetting, powder bed fusion, vat photopolymerization, binder jetting, and material extrusion.

CONCLUSIONS

Additive manufacturing technologies for bone graft material fabrication in dentistry, especially 3D bioprinting approaches, have been successfully used to fabricate bone graft material with distinct compositions.

c-Axis-Oriented Platelets of Crystalline Hydroxyapatite in Biomimetic Intrafibrillar Mineralization of Polydopamine-Functionalized Collagen Type I

Mineralized collagen fibrils are important basic building blocks of calcified tissues, such as bone and dentin. Polydopamine (PDA) can introduce functional groups, i.e., hydroxyl and amine groups, on the surfaces of type I collagen (Col-I) as possible nucleation sites of calcium phosphate (CaP) crystallization. Molecular bindings in between PDA and Col-I fibrils (Col-PDA) have been found to significantly reduce the interfacial energy. The wetting effect, mainly hydrophilicity due to the functional groups, escalates the degree of mineralization. The assembly of Col-I molecules into fibrils was initiated at the designated number of collagenous molecules and PDA. In contrast to the infiltration of amorphous calcium phosphate (ACP) precursors into the Col-I matrix by polyaspartic acid (pAsp), this collagen assembly process allows nucleation and ACP to exist in advance by PDA in the intrafibrillar matrix. PDA bound to specific sites, i.e., gap and overlap zones, by the regular arrangement of Col-I fibrils enhanced ACP nucleation and thus mineralization. As a result, the c-axis-oriented platelets of crystalline hydroxyapatite in the Col-I fibril matrix were observed in the enhanced mineralization through PDA functionalization.

Polydopamine-treated hierarchical cellulosic fibers as versatile reinforcement of polybutylene succinate biocomposites for electromagnetic shielding

There is a need for scalable technologies to reduce electromagnetic pollution with materials of low density and low carbon footprint. Unfortunately, environmental adaptability, economic feasibility and lightweight are factors that are still far from optimal in most electromagnetic shielding materials. Herein, we address these challenges with polybutylene succinate (PBS) reinforced with bamboo fibers functionalized with Fe₃O₄ nanoparticles (Fe₃O₄-NPs) and polypyrrole (PPy). Such hybrid system was compatibilized via polydopamine (PDA) coupling, demonstrating magnetic, dielectric and interfacial polarization losses as well as distributed reflection, yielding a shielding effectiveness of ~36.9 dB. Simultaneously, the composite displayed gains in tensile strength and modulus (by 18 and 38%, respectively) combined with improved flexural strength and modulus (by 33% and 15%, respectively). Overall, this work demonstrates a new pathway toward low cost and lightweight bio-based materials for high-performance electromagnetic shielding.

Recent developments in mussel-inspired materials for biomedical applications

Over the decades, researchers have strived to synthesize and modify nature-inspired biomaterials, with the primary aim to address the challenges of designing functional biomaterials for regenerative medicine and tissue engineering. Among these challenges, biocompatibility and cellular interactions have been extensively investigated. Some of the most desirable characteristics for biomaterials in these applications are the loading of bioactive molecules, strong adhesion to moist areas, improvement of cellular adhesion, and self-healing properties. Mussel-inspired biomaterials have received growing interest mainly due to the changes in mechanical and biological functions of the scaffold due to catechol modification. Here, we summarize the chemical and biological principles and the latest advancements in production, as well as the use of mussel-inspired biomaterials. Our main focus is the polydopamine coating, the conjugation of catechol with other polymers, and the biomedical applications that polydopamine moieties are used for, such as matrices for drug delivery, tissue regeneration, and hemostatic control. We also present a critical conclusion and an inspired view on the prospects for the development and application of mussel-inspired materials.

Colonization versus encapsulation in cell-laden materials design: porosity and process biocompatibility determine cellularization pathways

Seeding materials with living cells has been-and still is-one of the most promising approaches to reproduce the complexity and the functionality of living matter. The strategies to associate living cells with materials are limited to cell encapsulation and colonization, however, the requirements for these two approaches have been seldom discussed systematically. Here we propose a simple two-dimensional map based on materials' pore size and the cytocompatibility of their fabrication process to draw, for the first time, a guide to building cellularized materials. We believe this approach may serve as a straightforward guideline to design new, more relevant materials, able to seize the complexity and the function of biological materials. This article is part of the theme issue 'Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 1)'.

Investigation of human adipose-derived stem-cell behavior using a cell-instructive polydopamine-coated gelatin-alginate hydrogel

Hydrogels can be fabricated and designed to exert direct control over stem cells' adhesion and differentiation. In this study, we have investigated the use of polydopamine (pDA)-treatment as a binding platform for bioactive compounds to create a versatile gelatin-alginate (Gel-Alg) hydrogel for tissue engineering applications. Precisely, pDA was used to modify the surface properties of the hydrogel and better control the adhesion and osteogenic differentiation of human adipose-derived stem cells (hASCs). pDA enabled the adsorption of different types of bioactive molecules, including a model osteoinductive drug (dexamethasone) as well as a model pro-angiogenic peptide (QK). The pDA treatment efficiently retained the drug and the peptide compared to the untreated hydrogel and proved to be effective in controlling the morphology, cell area, and osteogenic differentiation of hASCs. Overall, the findings of this study confirm the efficacy of pDA treatment as a valuable strategy to modulate the biological properties of biocompatible Gel-Alg hydrogels and further extend their value in regenerative medicine.

Digital Light Processing Bioprinted Human Chondrocyte-Laden Poly (γ-Glutamic Acid)/Hyaluronic Acid Bio-Ink towards Cartilage Tissue Engineering

Cartilage injury is the main cause of disability in the United States, and it has been projected that cartilage injury caused by osteoarthritis will affect 30% of the entire United States population by the year 2030. In this study, we modified hyaluronic acid (HA) with γ-poly(glutamic) acid (γ-PGA), both of which are common biomaterials used in cartilage engineering, in an attempt to evaluate them for their potential in promoting cartilage regeneration. As seen from the results, γ-PGA-GMA and HA, with glycidyl methacrylate (GMA) as the photo-crosslinker, could be successfully fabricated while retaining the structural characteristics of γ-PGA and HA. In addition, the storage moduli and loss moduli of the hydrogels were consistent throughout the curing durations. However, it was noted that the modification enhanced the mechanical properties, the swelling equilibrium rate, and cellular proliferation, and significantly improved secretion of cartilage regeneration-related proteins such as glycosaminoglycan (GAG) and type II collagen (Col II). The cartilage tissue proof with Alcian blue further demonstrated that the modification of γ-PGA with HA exhibited suitability for cartilage tissue regeneration and displayed potential for future cartilage tissue engineering applications. This study built on the previous works involving HA and further showed that there are unlimited ways to modify various biomaterials in order to further bring cartilage tissue engineering to the next level.

Surface engineering of biomaterials in orthopedic and dental implants: Strategies to improve osteointegration, bacteriostatic and bactericidal activities

BACKGROUND

The success of biomedical implants in orthopedic and dental applications is usually limited due to insufficient bone-implant integration, and implant-related infections. Biointerfaces are critical in regulating their interactions and the desirable performance of biomaterials in biological environment. Surface engineering has been widely studied to realize better control of the interface interaction to further enhance the desired behavior of biomaterials.

PURPOSE AND SCOPE

This review aims to investigate surface coating strategies in hard tissue applications to address insufficient osteointegration and implant-related infection problems.

SUMMARY

We first focused on surface coatings to enhance the osteointegration and biocompatibility of implants by emphasizing calcium phosphate-related, nanoscale TiO₂ -related, bioactive tantalum-based and biomolecules incorporated coatings. Different coating strategies such as plasma spraying, biomimetic deposition, electrochemical anodization and LENS are discussed. We then discussed techniques to construct anti-adhesive and bactericidal surface while emphasizing multifunctional surface coating techniques that combine potential osteointegration and antibacterial activities. The effects of nanotopography via TiO₂ coatings on antibacterial performance are interesting and included. A smart bacteria-responsive titanium dioxide nanotubes coating is also attractive and elaborated.

CONCLUSION

Developing multifunctional surface coatings combining osteogenesis and antimicrobial activity is the current trend. Surface engineering methods are usually combined to obtain hierarchical multiscale surface structures with better biofunctionalization outcomes.

Collagen-based scaffolds: An auspicious tool to support repair, recovery, and regeneration post spinal cord injury

Spinal cord injury (SCI) is a perplexing traumatic disease that habitually gives ride to permanent disability, motor, and sensory impairment. Despite the existence of several therapeutic approaches for the injured motor or sensory neurons, they can't promote axonal regeneration. Whether prepared by conventional or rapid prototyping techniques, scaffolds can be applied to refurbish the continuity of the injured site, by creating a suitable environment for tissue repair, axonal regeneration, and vascularization. Collagen is a multi-sourced protein, found in animals skin, tendons, cartilage, bones, and human placenta, in addition to marine biomass. Collagen is highly abundant in the extracellular matrix and is known for its biocompatibility, biodegradability, porous structure, good permeability, low immunogenicity and thus is extensively applied in the pharmaceutical, cosmetic, and food industries as well as the tissue engineering field. Collagen in scaffolds is usually functionalized with different ligands and factors such as, stem cells, embryonic or human cells to augment its binding specificity and activity. The review summarizes the significance of collagen-based scaffolds and their influence on regeneration, repair and recovery of spinal cord injuries.

Surface modification of a three-dimensional polycaprolactone scaffold by polydopamine, biomineralization, and BMP-2 immobilization for potential bone tissue applications

Three-dimensional (3D) bioprinting is a free-form fabrication technique enabling fine feature control for tissue engineering applications. Especially, 3D scaffolds capable of supporting cell attachment, proliferation, and osteogenic differentiation are a prerequisite for bone tissue regeneration. Herein, we elaborated this approach to produce a 3D polycaprolactone (PCL) scaffold with long-term osteogenic activity. Specifically, we coated polydopamine (PDA) on 3D PCL scaffolds, subsequently deposited hydroxyapatite (HA) nanoparticles via biomimetic mineralization, and finally immobilized bone morphogenetic protein-2 (BMP-2). Material properties were characterized and compared with various 3D scaffolds, including PCL, PDA-coated PCL (PCL/PDA), and PDA-coated and HA-deposited PCL (PCL/PDA/HA). In vitro cell culture studies with osteoblasts revealed that the PCL/PDA/HA scaffolds immobilized with BMP-2 showed long-term retention of BMP-2 (for up to 21 days) and significantly increased osteoblast proliferation and osteogenic differentiation, as evidenced by metabolic activity, alkaline phosphatase activity, and calcium deposition. We believe that this multifunctional osteogenic 3D scaffold will be useful for bone tissue engineering applications.

Recent Developments of Biomaterials for Additive Manufacturing of Bone Scaffolds

Recent years have witnessed surging demand for bone repair/regeneration implants due to the increasing number of bone defects caused by trauma, cancer, infection, and arthritis worldwide. In addition to bone autografts and allografts, biomaterial substitutes have been widely used in clinical practice. Personalized implants with precise and personalized control of shape, porosity, composition, surface chemistry, and mechanical properties will greatly facilitate the regeneration of bone tissue and satiate the clinical needs. Additive manufacturing (AM) techniques, also known as 3D printing, are drawing fast growing attention in the fabrication of implants or scaffolding materials due to their capability of manufacturing complex and irregularly shaped scaffolds in repairing bone defects in clinical practice. This review aims to provide a comprehensive overview of recent progress in the development of materials and techniques used in the additive manufacturing of bone scaffolds. In addition, clinical application, pre-clinical trials and future prospects of AM based bone implants are also summarized and discussed.

Applications of Polydopamine-Modified Scaffolds in the Peripheral Nerve Tissue Engineering

Peripheral nerve injury is a common and complicated traumatic disease in clinical neurosurgery. With the rapid advancement and development of medical technologies, novel tissue engineering provides alternative therapies such as nerve conduit transplantation. It has achieved significant outcomes. The scaffold surface modification is vital to the reconstruction of a pro-healing interface. Polydopamine has high chemical activity, adhesion, hydrophilicity, hygroscopicity, stability, biocompatibility, and other properties. It is often used in the surface modification of biomaterials, especially in the peripheral nerve regeneration. The present review discusses that polydopamine can promote the adhesion, proliferation, and differentiation of neural stem cells and the growth of neuronal processes. Polydopamine is widely used in the surface modification of nerve conduits and has a potential application prospect of repairing peripheral nerve injury. Polydopamine-modified scaffolds are promising in the peripheral nerve tissue engineering.

Nano-needle strontium-substituted apatite coating enhances osteoporotic osseointegration through promoting osteogenesis and inhibiting osteoclastogenesis

Implant loosening remains a major clinical challenge for osteoporotic patients. This is because osteoclastic bone resorption rate is higher than osteoblastic bone formation rate in the case of osteoporosis, which results in poor bone repair. Strontium (Sr) has been widely accepted as an anti-osteoporosis element. In this study, we fabricated a series of apatite and Sr-substituted apatite coatings via electrochemical deposition under different acidic conditions. The results showed that Ca and Sr exhibited different mineralization behaviors. The main mineralization products for Ca were CaHPO₄·2H₂O and Ca₃(PO₄)₂ with the structure changed from porous to spherical as the pH values increased. The main mineralization products for Sr were SrHPO₄ and Sr₅(PO₄)₃OH with the structure changed from flake to needle as the pH values increased. The in vitro experiment demonstrated that coatings fabricated at high pH condition with the presence of Sr were favorable to MSCs adhesion, spreading, proliferation, and osteogenic differentiation. In addition, Sr-substituted apatite coatings could evidently inhibit osteoclast differentiation and fusion. Moreover, the in vivo study indicated that nano-needle like Sr-substituted apatite coating could suppress osteoclastic activity, improve new bone formation, and enhance bone-implant integration. This study provided a new theoretical guidance for implant coating design and the fabricated Sr-substituted coating might have potential applications for osteoporotic patients.

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Ca²⁺ and Sr²⁺ showed different mineralization behaviors in acidic environments.

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Apatites fabricated at high pH conditions were beneficial to MSCs growth.

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Sr-substituted apatite exhibited superior anti-osteoclast activity ability.

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Sr-substituted apatite facilitated osteogenesis, bone growth, and osseointegration.

Effects of polydopamine coatings on nucleation modes of surface mineralization from simulated body fluid

Polydopamine (PDA) has been recently used as a versatile priming layer for further functionalization of a biomaterial surface, particularly in biomimetic mineralization of biomaterials. Yet most of the existing literature is on inorganic substrates and the underlying effects of the PDA layer coatings on the nucleation and mineralization process and the mineral-substrate interface have not been clearly identified. Here we aimed to investigate the effects of the PDA layer on the nucleation and growth and interfacial morphology of calcium phosphate mineral layer (CaP) from 10× simulated body fluid (10× SBF) on polymeric substrates. It is found that the nucleation of CaP on PDA-coated surface favors a mixed “islanding” and planar growth mode (Stranski–Krastanov) while the “islanding” mode (Volmer–Weber) was observed on the surface without PDA. This different early nucleation stage of mineralization was found to correlate with a more “bonded” interface between the mineral layer and the PDA-coated substrates, a slight increase in the interfacial strength and a different delamination mode. This study therefore provided new insights on how polydopamine priming layer influenced the mineralization process and the interface between the mineral layer and the substrate.

Caffeic Acid-coated Nanolayer on Mineral Trioxide Aggregate Potentiates the Host Immune Responses, Angiogenesis, and Odontogenesis

INTRODUCTION

The aim of this study was to investigate whether mineral trioxide aggregate (MTA) can be modified with caffeic acid (CA) to form caffeic acid/mineral trioxide aggregate (CAMTA) cement and to evaluate its physicochemical and biological properties as well as its capability in immune suppression and angiogenesis.

METHODS

MTA was immersed in trishydroxymethyl aminomethane buffer with CA to allow coating onto MTA powders. X-ray diffractometry and tensile stress-strain tests were conducted to assess for physical characteristics of CAMTA and to evaluate for successful modification of MTA. Then, the CAMTA cement was immersed in simulated body fluid to evaluate its hydroxyapatite formation capabilities and Si release profiles. In addition, RAW 264.7 cells and human dental pulp stem cells were used to evaluate CAMTA's immunosuppressive capabilities and cell responses, respectively. hDPSCs were also used to assess CAMTA's angiogenic capabilities.

RESULTS

The X-ray diffractometry results showed that CA can be successfully coated onto MTA without disrupting or losing MTA's original structural properties, thus allowing us to retain the initial advantages of MTA. CAMTA was shown to have higher mechanical properties compared with MTA and had rougher pitted surfaces, which were hypothesized to lead to enhanced adhesion, proliferation, and secretion of angiogenic- and odontogenic-related proteins. In addition, it was found that CAMTA was able to enhance hydroxyapatite formation and immunosuppressive capabilities compared with MTA.

CONCLUSIONS

CAMTA cements were found to have improved physicochemical and biological characteristics compared with their counterpart. In addition, CAMTA cements had enhanced odontogenic, angiogenic, and immunosuppressive properties compared with MTA. All of the results of this study proved that CAMTA cements could be a biomaterial for future clinical applications and tissue engineering use.

Mussel-inspired polydopamine-mediated surface modification of freeze-cast poly (ε-caprolactone) scaffolds for bone tissue engineering applications

There are many methods used to fabricate the scaffolds for tissue regeneration, among which freeze casting has attracted a great deal of attention due to the capability to create a unidirectional structure. In this study, polycaprolactone (PCL) scaffolds were fabricated by freeze-casting technology in order to create porous microstructure with oriented open-pore channels. To induce biomineralization, and to improve hydrophilicity and cell interactions, mussel-inspired polydopamine (PDA) was coated on the surface of the freeze-cast PCL constructs. Then, the synergistic effects of oriented microstructure and deposited layer on efficient reconstruction of injured bone were studied. Microscopic observations demonstrated that, the coated layer did not show any special change in lamellar microstructure of the scaffolds. Water-scaffold interactions were evaluated by contact angle measurements, and they demonstrated strong enhancement in the hydrophilicity of the polymeric scaffolds after PDA coating. Biodegradation ratio and water uptake evaluation confirmed an increase in the measured values after PDA precipitation. The biomineralization of the PDA-coated scaffolds was characterized by field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) and X-ray diffraction (XRD). Obtained results confirmed biomineralization of the constructs after a 28-day immersion in a simulated body fluid (SBF) solution. Mechanical analysis demonstrated higher compressive strength after PDA coating. L929 fibroblast cell viability and attachment illustrated that PDA-coated PCL scaffolds are able to support cell adhesion and proliferation. The increased secretion of alkaline phosphatase (ALP) after culturing osteosarcoma cell lines (MG-63) revealed the initial capability of scaffolds to induce bone regeneration. Therefore, the PDA-coated scaffolds introduce a promising approach for bone tissue engineering application.

Mussel-inspired polydopamine induced the osteoinductivity to ice-templating PLGA-gelatin matrix for bone tissue engineering application

In this study, poly(lactic-co-glycolic acid) (PLGA)-gelatin scaffolds were fabricated using the freeze-casting technique. Polydopamine (PDA) coating was applied on the surface of scaffolds to enhance the hydrophilicity, bioactivity, and cellular behavior of the composite constructs. Further, the synergistic effect of PDA coating and lamellar microstructure of scaffolds was evaluated on the promotion of properties. Based on morphological observations, freeze-casting constructs showed lamellar pore channels while the uniformity and pore size were slightly affected by deposition of PDA. The hydrophilicity and swelling capacity of the scaffolds were assessed using contact angle measurement and phosphate buffered saline absorption ratio. The results indicated a significant increment in water-matrix interactions following surface modification. The evaluation of the biodegradation ratio revealed the higher degree of degradation in PDA-coated samples owing to the presence of hydrophilic functional groups in the chemical structure of PDA. On the other hand, the bioactivity potential of PDA in the simulated body fluid solution confirmed the possibility of using coated constructs as a bone reconstructive substitute. The improvement of cellular attachment and filopodia formation in PDA-contained matrixes was the other benefit of the coating process. Furthermore, cellular proliferation and ALP activity were enhanced after PDA coating. The suggested PDA-coated PLGA-gelatin scaffolds can be applied in bone tissue regeneration.

Effect of Bone Morphogenic Protein-2-Loaded Mesoporous Strontium Substitution Calcium Silicate/Recycled Fish Gelatin 3D Cell-Laden Scaffold for Bone Tissue Engineering

Bone has a complex hierarchical structure with the capability of self-regeneration. In the case of critical-sized defects, the regeneration capabilities of normal bones are severely impaired, thus causing non-union healing of bones. Therefore, bone tissue engineering has since emerged to solve problems relating to critical-sized bone defects. Amongst the many biomaterials available on the market, calcium silicate-based (CS) cements have garnered huge interest due to their versatility and good bioactivity. In the recent decade, scientists have attempted to modify or functionalize CS cement in order to enhance the bioactivity of CS. Reports have been made that the addition of mesoporous nanoparticles onto scaffolds could enhance the bone regenerative capabilities of scaffolds. For this study, the main objective was to reuse gelatin from fish wastes and use it to combine with bone morphogenetic protein (BMP)-2 and Sr-doped CS scaffolds to create a novel BMP-2-loaded, hydrogel-based mesoporous SrCS scaffold (FGSrB) and to evaluate for its composition and mechanical strength. From this study, it was shown that such a novel scaffold could be fabricated without affecting the structural properties of FGSr. In addition, it was proven that FGSrB could be used for drug delivery to allow stable localized drug release. Such modifications were found to enhance cellular proliferation, thus leading to enhanced secretion of alkaline phosphatase and calcium. The above results showed that such a modification could be used as a potential alternative for future bone tissue engineering research.

Natural and Synthetic Polymers for Bone Scaffolds Optimization

Bone tissue is the structural component of the body, which allows locomotion, protects vital internal organs, and provides the maintenance of mineral homeostasis. Several bone-related pathologies generate critical-size bone defects that our organism is not able to heal spontaneously and require a therapeutic action. Conventional therapies span from pharmacological to interventional methodologies, all of them characterized by several drawbacks. To circumvent these effects, tissue engineering and regenerative medicine are innovative and promising approaches that exploit the capability of bone progenitors, especially mesenchymal stem cells, to differentiate into functional bone cells. So far, several materials have been tested in order to guarantee the specific requirements for bone tissue regeneration, ranging from the material biocompatibility to the ideal 3D bone-like architectural structure. In this review, we analyse the state-of-the-art of the most widespread polymeric scaffold materials and their application in in vitro and in vivo models, in order to evaluate their usability in the field of bone tissue engineering. Here, we will present several adopted strategies in scaffold production, from the different combination of materials, to chemical factor inclusion, embedding of cells, and manufacturing technology improvement.

Alternating ring-opening copolymerization of epoxides with saturated and unsaturated cyclic anhydrides: reduced viscosity poly(propylene fumarate) oligomers for use in cDLP 3D printing

A ring-opening copolymerization of propylene oxide with saturated and unsaturated anhydrides using Mg(BHT)₂(THF)₂ catalyst followed by an isomerization yields poly(propylene fumarate) (PPF) oligomers with improved properties for 3D printing.

Engineered 3D Polymer and Hydrogel Microenvironments for Cell Culture Applications

The realization of biomimetic microenvironments for cell biology applications such as organ-on-chip, in vitro drug screening, and tissue engineering is one of the most fascinating research areas in the field of bioengineering. The continuous evolution of additive manufacturing techniques provides the tools to engineer these architectures at different scales. Moreover, it is now possible to tailor their biomechanical and topological properties while taking inspiration from the characteristics of the extracellular matrix, the three-dimensional scaffold in which cells proliferate, migrate, and differentiate. In such context, there is therefore a continuous quest for synthetic and nature-derived composite materials that must hold biocompatible, biodegradable, bioactive features and also be compatible with the envisioned fabrication strategy. The structure of the current review is intended to provide to both micro-engineers and cell biologists a comparative overview of the characteristics, advantages, and drawbacks of the major 3D printing techniques, the most promising biomaterials candidates, and the trade-offs that must be considered in order to replicate the properties of natural microenvironments.

Review of Polymeric Materials in 4D Printing Biomedical Applications

The purpose of 4D printing is to embed a product design into a deformable smart material using a traditional 3D printer. The 3D printed object can be assembled or transformed into intended designs by applying certain conditions or forms of stimulation such as temperature, pressure, humidity, pH, wind, or light. Simply put, 4D printing is a continuum of 3D printing technology that is now able to print objects which change over time. In previous studies, many smart materials were shown to have 4D printing characteristics. In this paper, we specifically review the current application, respective activation methods, characteristics, and future prospects of various polymeric materials in 4D printing, which are expected to contribute to the development of 4D printing polymeric materials and technology.

Additive Manufacturing of Nerve Decellularized Extracellular Matrix-Contained Polyurethane Conduits for Peripheral Nerve Regeneration

The nervous system is the part of our body that plays critical roles in the coordination of actions and sensory information as well as communication between different body parts through electrical signal transmissions. Current studies have shown that patients are likely to experience a functional loss if they have to go through a nerve repair for >15 mm lesion. The ideal treatment methodology is autologous nerve transplant, but numerous problems lie in this treatment method, such as lack of harvesting sites. Therefore, researchers are attempting to fabricate alternatives for nerve regeneration, and nerve conduit is one of the potential alternatives for nerve regeneration. In this study, we fabricated polyurethane/polydopamine/extracellular matrix (PU/PDA/ECM) nerve conduits using digital light processing (DLP) technology and assessed for its physical properties, biodegradability, cytocompatibility, neural related growth factor, and proteins secretion and expression and its potential in allowing cellular adhesion and proliferation. It was reported that PU/PDA/ECM nerve conduits were more hydrophilic and allowed enhanced cellular adhesion, proliferation, expression, and secretion of neural-related proteins (collagen I and laminin) and also enhanced expression of neurogenic proteins, such as nestin and microtubule-associated protein 2 (MAP2). In addition, PU/PDA/ECM nerve conduits were reported to be non-cytotoxic, had sustained biodegradability, and had similar physical characteristics as PU conduits. Therefore, we believed that PU/PDA/ECM nerve conduits could be a potential candidate for future nerve-related research or clinical applications.

3D Printing of Amino Resin-based Photosensitive Materials on Multi-parameter Optimization Design for Vascular Engineering Applications

Cardiovascular diseases are currently the most common cause of death globally and of which, the golden treatment method for severe cardiovascular diseases or coronary artery diseases are implantations of synthetic vascular grafts. However, such grafts often come with rejections and hypersensitivity reactions. With the emergence of regenerative medicine, researchers are now trying to explore alternative ways to produce grafts that are less likely to induce immunological reactions in patients. The main goal of such studies is to produce biocompatible artificial vascular grafts with the capability of allowing cellular adhesion and cellular proliferation for tissues regeneration. The Design of Experimental concepts is employed into the manufacturing process of digital light processing (DLP) 3D printing technology to explore near-optimal processing parameters to produce artificial vascular grafts with vascular characteristics that are close to native vessels by assessing for the cause and effect relationships between different ratios of amino resin (AR), 2-hydroxyethyl methacrylate (HEMA), dopamine, and curing durations. We found that with proper optimization of fabrication procedures and ratios of materials, we are able to successfully fabricate vascular grafts with good printing resolutions. These had similar physical properties to native vessels and were able to support cellular adhesion and proliferation. This study could support future studies in exploring near-optimal processes for fabrication of artificial vascular grafts that could be adapted into clinical applications.

The mussel-inspired assisted apatite mineralized on PolyJet material for artificial bone scaffold

With the development of three-dimensional (3D) printing, many commercial 3D printing materials have been applied in the fields of biomedicine and medical. MED610 is a clear, biocompatible PolyJet material that is medically certified for bodily contact. In this study, the polydopamine (PDA)/hydroxyapatite (HA) coating was added to the printed MED610 objects to evaluate its physical properties, cell proliferation, cell morphology, and alkaline phosphatase expression level. The results show that the PDA/HA coating helps printed objects to enhance the hardness, biocompatibility, and osteogenic differentiation potential. We expect that PDA/HA coatings contribute to the applicability of MED610 in biomedical and medical applications.

Development of mussel-inspired 3D-printed poly (lactic acid) scaffold grafted with bone morphogenetic protein-2 for stimulating osteogenesis

3D printing is a versatile technique widely applied in tissue engineering due to its ability to manufacture large quantities of scaffolds or constructs with various desired architectures. In this study, we demonstrated that poly (lactic acid) (PLA) scaffolds fabricated via fused deposition not only retained the original interconnected microporous architectures, the scaffolds also exhibited lower lactic acid dissolution as compared to the freeze-PLA scaffold. The 3D-printed scaffolds were then grafted with human bone morphogenetic protein-2 (BMP-2) via the actions of polydopamine (PDA) coatings. The loading and release rate of BMP-2 were monitored for a period of 35 days. Cellular behaviors and osteogenic activities of co-cultured human mesenchymal stem cells (hMSCs) were assessed to determine for efficacies of scaffolds. In addition, we demonstrated that our fabricated scaffolds were homogenously coated with PDA and well grafted with BMP-2 (219.1 ± 20.4 ng) when treated with 250 ng/mL of BMP-2 and 741.4 ± 127.3 ng when treated with 1000 ng/mL of BMP-2. This grafting enables BMP-2 to be released in a sustained profile. From the osteogenic assay, it was shown that the ALP activity and osteocalcin of hMSCs cultured on BMP-2/PDA/PLA were significantly higher when compared with PLA and PDA/PLA scaffolds. The methodology of PDA coating employed in this study can be used as a simple model to immobilize multiple growth factors onto different 3D-printed scaffold substrates. Therefore, there is potential for generation of scaffolds with different unique modifications with different capabilities in regulating physiochemical and biological properties for future applications in bone tissue engineering.

Substitutions of strontium in bioactive calcium silicate bone cements stimulate osteogenic differentiation in human mesenchymal stem cells

Calcium silicate cements have been considered as alternative bone substitutes owing to its extraordinary bioactivity and osteogenicity. Unfortunately, the major disadvantage of the cements was the slow degradation rate which may limit the efficiency of bone regeneration. In this study, we proposed a facile method to synthesize degradable calcium silicate cements by incorporating strontium into the cements through solid-state sintering. The effects of Sr incorporation on physicochemical and biological properties of the cements were evaluated. Although, our findings revealed that the incorporation of strontium retarded the hardening reaction of the cements, the setting time of different cements (11-19 min) were in the acceptable range for clinical use. The presence of Sr in the CS cements would hampered the precipitation of calcium phosphate products on the surface after immersion in SBF, however, a layer of precipitated calcium phosphate products can be formed on the surface of the Sr-CS cement within 1 day immersion in SBF. More importantly, the degradation rate of the cements increased with increasing content of strontium, consequentially raised the levels of released strontium and silicon ions. The elevated dissolving products may contribute to the enhancement of the cytocompatibility, alkaline phosphatase activity, osteocalcin secretion, and mineralization of human Wharton's jelly mesenchymal stem cells. Together, it is concluded that the strontium-incorporated calcium silicate cement might be a promising bone substitute that could accelerate the regeneration of irregularly shaped bone defects.

Fabrication of hierarchically porous silk fibroin-bioactive glass composite scaffold via indirect 3D printing: Effect of particle size on physico-mechanical properties and in vitro cellular behavior

In order to regenerate bone defects, bioactive hierarchically scaffolds play a key role due to their multilevel porous structure, high surface area, enhanced nutrient transport and diffusion. In this study, novel hierarchically porous silk fibroin (SF) and silk fibroin-bioactive glass (SF-BG) composite were fabricated with controlled architecture and interconnected structure, by combining indirect three-dimensional (3D) inkjet printing and freeze-drying methods. Further, the effect of 45S5 Bioactive glass particles of different sizes (<100 nm and 6 μm) on mechanical strength and cell behavior was investigated. The results demonstrated that the hierarchical structure in this scaffold was composed of two levels of pores in the order of 500-600 μm and 10-50 μm. The prepared SF-BG composite scaffolds utilized by nano and micro particles possessed mechanical properties with a compressive strength of 0.94 and 1.2 MPa, respectively, in dry conditions. In a wet condition, the hierarchically porous scaffolds did not exhibit any fluctuation after compression load cell and were incredibly flexible, with excellent mechanical stability. The SF-BG composite scaffold with nanoparticles presented a significant 50% increase in attachment of human bone marrow stem cells in comparison with SF and SF-BG scaffold with microparticles. Moreover, SF-BG scaffolds promoted alkaline phosphatase activity as compared to SF scaffolds without BG particles on day 14. In brief, the 3D porous silk fibroin-based composites containing BG nanoparticles with excellent mechanical properties are promising scaffolds for bone tissue regeneration in high load-bearing applications.

Highly porous polycaprolactone scaffolds doped with calcium silicate and dicalcium phosphate dihydrate designed for bone regeneration

Polycaprolactone (PCL), dicalcium phosphate dihydrate (DCPD) and/or calcium silicates (CaSi) have been used to prepare highly porous scaffolds by thermally induced phase separation technique (TIPS). Three experimental mineral-doped formulations were prepared (PCL-10CaSi, PCL-5CaSi-5DCPD, PCL-10CaSi-10DCPD); pure PCL scaffolds constituted the control group. Scaffolds were tested for their chemical-physical and biological properties, namely thermal properties by differential scanning calorimetry (DSC), mechanical properties by quasi-static parallel-plates compression testing, porosity by a standard water-absorption method calcium release, alkalinizing activity, surface microchemistry and micromorphology by Environmental Scanning electronic Microscopy (ESEM), apatite-forming ability in Hank Balanced Saline Solution (HBSS) by Energy Dispersive X-ray Spectroscopy (EDX) and micro-Raman, and direct contact cytotoxicity. All mineral-doped scaffolds released calcium and alkalinized the soaking medium, which may favor a good biological (osteogenic) response. ESEM surface micromorphology analyses after soaking in HBSS revealed: pure PCL, PCL-10CaSi and PCL-10CaSi-10DCPD kept similar surface porosity percentages but different pore shape modifications. PCL-5CaSi-5DCPD revealed a significant surface porosity increase despite calcium phosphates nucleation (p < 0.05). Micro-Raman spectroscopy detected the formation of a B-type carbonated apatite (Ap) layer on the surface of PCL-10CaSi-10DCPD aged for 28 days in HBSS; a similar phase (but of lower thickness) formed also on PCL-5CaSi-5DCPD and PCL; the deposit formed on PCL-10CaSi was mainly composed of calcite. All PCL showed bulk open porosity higher than 94%; however, no relevant brittleness was observed in the materials, which retained the possibility to be handled without collapsing. The thermo-mechanical properties showed that the reinforcing and nucleating action of the inorganic fillers CaSi and DCPD improved viscoelastic properties of the scaffolds, as confirmed by the increased value of storage modulus and the slight increase in the crystallization temperature for all the biomaterials. A detrimental effect on the mechanical properties was observed in samples with the highest amount of inorganic particles (PCL-10CaSi-10DCPD). All the scaffolds showed absence of toxicity, in particular PCL-10CaSi-10DCPD. The designed scaffolds are biointeractive (release biologically relevant ions), nucleate apatite, possess high surface and internal open porosity and can be colonized by cells, creating a bone forming osteoblastic microenvironment and appearing interesting materials for bone regeneration purposes.