3,4-dihydroxyphenylalanine-assisted hydroxyapatite nanoparticle coating on polymer scaffolds for efficient osteoconduction

Hydroxyapatite nanoparticles-cell interaction: New approaches to disclose the fate of membrane-bound and internalised nanoparticles

Hydroxyapatite nanoparticles are popular tools in bone regeneration, but they have also been used for gene delivery and as anticancer drugs. Understanding their mechanism of action, particularly for the latter application, is crucial to predict their toxicity. To this end, we aimed to elucidate the importance of nanoparticle membrane interactions in the cytotoxicity of MG-63 cells using two different types of nanoparticles. In addition, conventional techniques for studying nanoparticle internalisation were evaluated and compared with newer and less exploited approaches. Hydroxyapatite and magnesium-doped hydroxyapatite nanoparticles were used as suspensions or compacted as specular discs. Comparison between cells seeded on the discs and those supplemented with the nanoparticles allowed direct interaction of the cell membrane with the material to be ruled out as the main mechanism of toxicity. In addition, standard techniques such as flow cytometry were inconclusive when used to assess nanoparticles toxicity. Interestingly, the use of intracellular calcium fluorescent probes revealed the presence of a high number of calcium-rich vesicles after nanoparticle supplementation in cell culture. These structures could not be detected by transmission electron microscopy due to their liquid content. However, by using cryo-soft X-ray imaging, which was used to visualise the cellular ultrastructure without further treatment other than vitrification and to quantify the linear absorption coefficient of each organelle, it was possible to identify them as multivesicular bodies, potentially acting as calcium stores. In the study, an advanced state of degradation of the hydroxyapatite and magnesium-doped hydroxyapatite nanoparticles within MG-63 cells was observed. Overall, we demonstrate that the combination of fluorescent calcium probes together with cryo-SXT is an excellent approach to investigate intracellular calcium, especially when found in its soluble form.

Application of artificial neural networks to predict Young's moduli of cartilage scaffolds: An in-vitro and micromechanical study

In this study, four-phase Gelatin-Polypyrrole-Akermanite-Magnetite scaffolds were fabricated and analyzed using in-vitro tests and numerical simulations. Such scaffolds contained various amounts of Magnetite bioceramics as much as 0, 5, 10, and 15 wt% of Gelatin-Polypyrrole-Akermanite biocomposite. X-ray diffraction analysis and Fourier transform infrared spectroscopy were conducted. Swelling and degradation of the scaffolds were studied by immersing them in phosphate-buffered saline, PBS, solution. Magnetite bioceramics decreased the swelling percent and degradation duration. By immersing scaffolds in simulated body fluid, the highest formation rate of Apatite was observed in the 15 wt% Magnetite samples. The mean pore size was in an acceptable range to provide suitable conditions for cell proliferation. MG-63 cells were cultured on extracts of the scaffolds for 24, 48, and 72 h and their surfaces for 24 h. Cell viabilities and cell morphologies were assessed. Afterward, micromechanical models with spherical and polyhedral voids and artificial neural networks were employed to predict Young's moduli of the scaffolds. Based on the results of finite element analyses, spherical-shaped void models made the best predictions of elastic behavior in the 0, 5 wt% Magnetite scaffolds compared to the experimental data. Results of the simulations and experimental tests for the ten wt% Magnetite samples were well matched in both micromechanical models. In the 15 wt% Magnetite sample, models with polyhedral voids could precisely predict Young's modulus of such scaffolds.

Characterizations and interfacial reinforcement mechanisms of multicomponent biopolymer based scaffold

It is difficult for a single component biopolymer to meet the requirements of scaffold at present. The development of multicomponent biopolymer based scaffold provides an effective method to solve the issue based on the advantages of each kind of the biomaterials. However, the compatibility between different components might be very poor due to the difficulties in forming strong interfacial bonding, and thereby significantly degrading the integrated mechanical properties of the scaffold. In recent years, interface phase introduction, surface modification and in situ growth have been the major strategies for enhancing interfacial bonding. This article presents a comprehensive overview on the research in the area of constructing multicomponent biopolymer based scaffold and reinforcing their interfacial properties, and more importantly, the interfacial bonding mechanisms are systematically summarized. Detailly, interface phase introduction can build a bridge between biopolymer and other components to form strong interface bonding with the two phases under the action of interface phase. Surface modification can graft organic molecules or polymers containing functional groups onto other components to crosslink with biopolymer. In situ growth can directly in situ synthesize other components with the action of nucleating agent serving as an adherent platform for the nucleation and growth of other components to biopolymer surface by chemical bonding. In addition, the mechanical properties (including strength and modulus) and biological properties (including bioactivity, cytocompatibility and biosensing in vitro, and tissue compatibility, bone regeneration capacity in vivo) of multicomponent biopolymer based scaffold after interfacial reinforcing are also reviewed and discussed. Finally, suggestions for further research are given with highlighting the need for specific investigations to assess the interface formation, structure, properties, and more in vivo studies of scaffold before applications.

Titanium discs coated with 3,4-dihydroxy-l-phenylalanine promote osteogenic differentiation of human bone mesenchymal stem cells in vitro

The bioinspired material 3,4-dihydroxy-l-phenylalanine (DOPA) is commonly used as a basic layer in surface modification for osteogenesis; however, its effects on bone remodeling and the underlying mechanisms remain unclear. Here, we investigated the effect of DOPA-coated surfaces on human bone marrow-derived mesenchymal stem cells in vitro. Cells cultured on DOPA-modified titanium discs exhibited enhanced cellular adhesion and spreading compared with cells on non-treated surfaces. Moreover, DOPA-coating promoted greater cell proliferation and osteogenic differentiation, as determined using cell counting kit-8 (CCK-8) assay, alkaline phosphatase activity test and quantitative mineralization measurements. Furthermore, microarray analysis revealed that genes participating in focal adhesion were upregulated on DOPA-coated surfaces. Our results indicate that the application of a simple DOPA coating can promote osteogenic differentiation of osteoprogenitor cells, improving new bone formation and bone remodeling around implantable devices in tissue engineering.

Titanium discs with simple 3,4-dihydroxy-l-phenylalanine coating enhanced BM-MSC adhesion, spreading, proliferation and differentiation, and upregulated expression of genes involved in focal adhesion in vitro.

Improving Hydrophilicity and Inducing Bone-Like Apatite Formation on PPBES by Polydopamine Coating for Biomedical Application

Copoly(phthalazinone biphenyl ether sulfone) (PPBES) as a commercially available polyarylether is a promising orthopaedic implant material because its mechanical properties are similar to bone. However, the bioinert surface of polyarylether causes some clinical problems after implantation, which limits its application as an implant material. In this study, the surface of PPBES was modified by a biomineralization method of polydopamine-assisted hydroxyapatite formation (pHAF) to enhance its cytocompatibility. Polydopamine (PDA) coating, inspired by the adhesion mechanism of mussels, can readily endow PPBES with high hydrophilicity and the ability to integrate via the bone-like apatite coating. PPBES and PDA-coated PPBES were evaluated by scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and contact angle measurement. The water contact angles were reduced significantly after coating with PDA. PDA was successfully synthesized on PPBES and more PDA was obtained by increasing the temperature. Bone-like apatite on PPBES (apatite-coated PPBES) was confirmed by SEM and transmission electron microscopy (TEM). The cytotoxicity of pristine PPBES and apatite-coated PPBES were characterized by culturing of NIH-3T3 cells. Bone-like apatite synthesized by pHAF could further enhance cytocompatibility in vitro. This study provides a promising alternative for biofunctionalized PPBES with improved cytocompatibility for bone implant application.

Simple 3,4-Dihydroxy-L-Phenylalanine Surface Modification Enhances Titanium Implant Osseointegration in Ovariectomized Rats

Osteoporosis presents a challenge to the long-term success of osseointegration of endosseous implants. The bio-inspired 3,4-dihydroxy-L-phenylalanine (Dopa) coating is widely used as a basic layer to bind osteogenetic molecules that may improve osseointegration. To date, little attention has focused on application of Dopa alone or binding inhibitors of bone resorption in osteoporosis. Local use of a bisphosphonate such as zoledronic acid (ZA), an inhibitor of osteoclast-mediated bone resorption, has been proven to improve implant osseointegration. In this study, ovariectomized rats were divided into four groups and implanted with implants with different surface modifications: sandblasted and acid-etched (SLA), SLA modified with Dopa (SLA-Dopa), SLA modified with ZA (SLA-ZA), and SLA modified with Dopa and ZA (SLA-Dopa + ZA). Measurement of removal torque, micro-computed tomography and histology revealed a greater extent of bone formation around the three surface-modified implants than SLA-controls. No synergistic effect was observed for combined Dopa + ZA coating. Microarray analysis showed the Dopa coating inhibited expression of genes associated with osteoclast differentiation, similarly to the mechanism of action of ZA. Simple Dopa modification resulted in a similar improvement in osseointegration compared to ZA. Thus, our data suggest simple Dopa coating is promising strategy to promote osseointegration of implants in patients with osteoporosis.

Sphingosine-1-Phosphate Immobilized on Nanotopographical Scaffolds Improve Myogenic Differentiation

The skeletal muscle consists of highly aligned dense cables of collagen fibers with nanometer feature size to support muscle fibers. The skeletal myocyte can be greatly affected to differentiate by their surrounding topographical structure. To improve myogenic differentiation, we fabricated cell culture platform that sphingosine-1-phosphate (S1P) which regulated myocyte behavior is immobilized on a biomimetic nanopatterned polyurethaneacrylate (PUA) substrate using 3,4-dihydroxyphenylalanine (L-DOPA) for providing topographical and biological cues synergistically. In the present study, we hypothesized that cultured C2C12 cells can be induced to synergistically promote myogenic differenntiation on nanopatterned PUA-L-DOPA-S1P. We confirmed that nanopatterned PUA-L-DOPA-S1P has high hydrophilicity with a suitable range of water contact angle and small intensity of phosphate peak (P2p) by analyses of water contact analyzer and X-ray photoelectron spectroscopy. In addition, C2C12 cells culured on nanopatterned PUA-L-DOPA-S1P has well-oriented and organized myodubes formed with greater expression of myogenic regulatory factors such as MyoD and MyoG comapred to flat PUA groups. This functional platform which is not only provided topographical and biological cues has a suitable potential function to apply muscle cell niche as similar structure of muscle fiber but also utilized cell behavior within tissue engineered scaffolds and cellular microenvironment.

Enhanced bone formation in sheep vertebral bodies after minimally invasive treatment with a novel, PLGA fiber-reinforced brushite cement

BACKGROUND CONTEXT

Injectable, brushite-forming calcium phosphate cements (CPC) show potential for bone replacement, but they exhibit low mechanical strength. This study tested a CPC reinforced with poly(l-lactide-co-glycolide) acid (PLGA) fibers in a minimally invasive, sheep lumbar vertebroplasty model.

PURPOSE

The study aimed to test the in vivo biocompatibility and osteogenic potential of a PLGA fiber-reinforced, brushite-forming CPC in a sheep large animal model.

STUDY DESIGN/SETTING

This is a prospective experimental animal study.

METHODS

Bone defects (diameter: 5 mm) were placed in aged, osteopenic female sheep, and left empty (L2) or injected with pure CPC (L3) or PLGA fiber-reinforced CPC (L4; fiber diameter: 25 µm; length: 1 mm; 10% [wt/wt]). Three and 9 months postoperation (n=20 each), the structural and functional CPC effects on bone regeneration were documented ex vivo by osteodensitometry, histomorphometry, micro-computed tomography (micro-CT), and biomechanical testing.

RESULTS

Addition of PLGA fibers enhanced CPC osteoconductivity and augmented bone formation. This was demonstrated by (1) significantly enhanced structural (bone volume/total volume, shown by micro-CT and histomorphometry; 3 or 9 months) and bone formation parameters (osteoid volume and osteoid surface; 9 months); (2) numerically enhanced bone mineral density (3 and 9 months) and biomechanical compression strength (9 months); and (3) numerically decreased bone erosion (eroded surface; 3 and 9 months).

CONCLUSIONS

The PLGA fiber-reinforced CPC is highly biocompatible and its PLGA fiber component enhanced bone formation. Also, PLGA fibers improve the mechanical properties of brittle CPC, with potential applicability in load-bearing areas.

The preosteoblast response of electrospinning PLGA/PCL nanofibers: effects of biomimetic architecture and collagen I

Constructing biomimetic structure and incorporating bioactive molecules is an effective strategy to achieve a more favorable cell response. To explore the effect of electrospinning (ES) nanofibrous architecture and collagen I (COL I)-incorporated modification on tuning osteoblast response, a resorbable membrane composed of poly(lactic-co-glycolic acid)/poly(caprolactone) (PLGA/PCL; 7:3 w/w) was developed via ES. COL I was blended into PLGA/PCL solution to prepare composite ES membrane. Notably, relatively better cell response was delivered by the bioactive ES-based membrane which was fabricated by modification of 3,4-dihydroxyphenylalanine and COL I. After investigation by field emission scanning electron microscopy, Fourier transform infrared spectroscopy, contact angle measurement, and mechanical test, polyporous three-dimensional nanofibrous structure with low tensile force and the successful integration of COL I was obtained by the ES method. Compared with traditional PLGA/PCL membrane, the surface hydrophilicity of collagen-incorporated membranes was largely enhanced. The behavior of mouse preosteoblast MC3T3-E1 cell infiltration and proliferation on membranes was studied at 24 and 48 hours. The negative control was fabricated by solvent casting. Evaluation of cell adhesion and morphology demonstrated that all the ES membranes were more favorable for promoting the cell adhesion and spreading than the casting membrane. Cell Counting Kit-8 assays revealed that biomimetic architecture, surface topography, and bioactive properties of membranes were favorable for cell growth. Analysis of β1 integrin expression level by immunofluorescence indicated that such biomimetic architecture, especially COL I-grafted surface, plays a key role in cell adhesion and proliferation. The real-time polymerase chain reaction suggested that both surface topography and bioactive properties could facilitate the cell adhesion. The combined effect of biomimetic architecture with enhanced surface activity by 3,4-dihydroxyphenylalanine-assisted modification and COL I incorporation of PLGA/PCL electrospun membranes could successfully fill osteogenic defects and allow for better cell proliferation and differentiation.

Modelling the nanomechanical response of a micro particle-matrix system for nanoindentation tests

A lot of experimental, numerical simulation and analytical modelling work has been done on how the substrate affects the measured hardness and elastic modulus of the coating/substrate system for nanoindentation tests. Little work has been done on the elastic-plastic behaviour of micro particle-matrix systems. Clifford et al have proposed an empirical model to describe the spatially dependent composite modulus during nanoindentation tests for linear elastic particles embedded in a linear elastic matrix. However, no such models have been developed for elastic-plastic composites. In this study, finite element simulations were used to determine the elastic modulus and hardness of hard particles embedded in a soft matrix and vice versa. An extended Clifford model has been developed to determine the elastic modulus and hardness for elastic-plastic composites with various particle shapes and volume fractions.

Peptide decorated nano-hydroxyapatite with enhanced bioactivity and osteogenic differentiation via polydopamine coating

To be better used as implant materials in bone graft substitutes, bioactivity and osteogenesis of nano-hydroxyapatite (nano-HA) need to be further enhanced. Inspired by adhesive proteins in mussels, here we developed a novel bone forming peptide decorated nano-HA material. In this study, nano-HA was coated by one-step pH-induced polymerization of dopamine, and then the peptide was grafted onto polydopamine (pDA) coated nano-HA (HA-pDA) through catechol chemistry. Our results demonstrated that the peptide-conjugated nano-HA crystals could induce the adhesion and proliferation of MG-63 cells. Moreover, the highly alkaline phosphatase activity of the functionalized nano-HA indicated that the grafted peptide could maintain its biological activity after immobilization onto the surface of HA-pDA, especially at the concentration of 100μg/mL. These modified nano-HA crystals with better bioactivity and osteogenic differentiation hold great potential to be applied as bioactive materials in bone repairing, bone regeneration and bio-implant coating applications.