Fabrication and in vitro evaluation of the collagen/hyaluronic acid PEM coating crosslinked with functionalized RGD peptide on titanium

Protein-based layer-by-layer films for biomedical applications

The surface engineering of biomaterials is crucial for their successful (bio)integration by the body, i.e. the colonization by the tissue-specific cell, and the prevention of fibrosis and/or bacterial colonization. Performed at room temperature in an aqueous medium, the layer-by-layer (LbL) coating method is based on the alternating deposition of macromolecules. Versatile and simple, this method allows the functionalization of surfaces with proteins, which play a crucial role in several biological mechanisms. Possessing intrinsic properties (cell adhesion, antibacterial, degradable, etc.), protein-based LbL films represent a powerful tool to control bacterial and mammalian cell fate. In this article, after a general introduction to the LbL technique, we will focus on protein-based LbL films addressing different biomedical issues/domains, such as bacterial infection, blood contacting surfaces, mammalian cell adhesion, drug and gene delivery, and bone and neural tissue engineering. We do not consider biosensing applications or electrochemical aspects using specific proteins such as enzymes.

Layer-by-Layer Coatings of Collagen-Hyaluronic acid Loaded with an Antibacterial Manuka Honey Bioactive Compound to Fight Metallic Implant Infections

Implant-associated severe infections can result in catastrophic implant failures; thus, advanced antibacterial coatings are needed to combat infections. This study focuses on harnessing nature-inspired self-assembly of extracellular matrix (ECM)-like coatings on Ti alloy with a combination of jellyfish-derived collagen (J-COLL) and hyaluronic acid (HA) using our customized automated hybrid layer-by-layer apparatus. To improve the anti-infection efficacy of coatings, we have incorporated a natural antibacterial agent methylglyoxal (MGO, a Manuka honey compound) in optimized multilayer coatings. The obtainment of MGO-loaded multilayer coatings was successfully assessed by profilometry, contact angle, attenuated total reflectance (ATR)-Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. In vitro degradation confirmed the controlled release activity of MGO with a range of concentrations from 0.90 to 2.38 mM up to 21 days. A bacterial cell culture study using Escherichia coli (E. coli) and Staphylococcus epidermidis (S. epidermidis) confirmed that the MGO incorporated within layers 7 and 9 had a favorable effect on preventing bacterial growth and colonization on their surfaces. An in vitro cytocompatibility study confirmed that MGO agents included in the layers did not affect or reduce the cellular functionalities of L929 fibroblasts. In addition, MGO-loaded layers with Immortalized Mesenchymal Stem Cells (Y201 TERT-hMSCs) were found to favor the growth and differentiation of Y201 cells and promote calcium nodule formation. Overall, these surface coatings are promising candidates for delivering antimicrobial activity with bone-inducing functions for future bone tissue engineering applications.

Hyaluronic Acid-Based Bioconjugate Systems, Scaffolds, and Their Therapeutic Potential

In recent years, the development of hyaluronic acid or hyaluronan (HA) based scaffolds, medical devices, bioconjugate systems have expanded into a broad range of research and clinical applications. Research findings over the last two decades suggest that the abundance of HA in most mammalian tissues with distinctive biological roles and chemical simplicity for modifications have made it an attractive material with a rapidly growing global market. Besides its use as native forms, HA has received much interest on so-called "HA-bioconjugates" and "modified-HA systems". In this review, the importance of chemical modifications of HA, underlying rationale approaches, and various advancements of bioconjugate derivatives with their potential physicochemical, and pharmacological advantages are summarized. This review also highlights the current and emerging HA-based conjugates of small molecules, macromolecules, crosslinked systems, and surface coating strategies with their biological implications, including their potentials and key challenges discussed in detail.

Construction of an antibacterial low-defect hybrid layer by facile PEI electrostatic assembly promotes dentin bonding

Dentin bonding is the most common form of human tissue repair among tissue-biomaterial adhesions, concerning billions of people's oral health worldwide. However, insufficient adhesive infiltration in the demineralized dentin matrix (DDM) always produces numerous defects in the bonding interface termed the hybrid layer, which causes high levels of bacteria-related secondary dental diseases, and less than 50% of the bonding lasts more than 5 years. Therefore, it is urgent and vital to construct an antibacterial low-defect hybrid layer to solve the durability-related problems. A DDM with a hydrogel-like surface formed by the hydration of highly-anionic non-collagenous proteins (NCPs) is firstly used as a template to electrostatically assemble polyethyleneimine (PEI). The formation of a stable antibacterial polyelectrolyte complex of PEI/NCPs rapidly eliminates NCP hydration capacity and significantly improves the infiltration of various adhesives. Simultaneously, both the PEI during the assembly and the PEI-assembled DDM can directly destroy a biofilm of S. Mutans on the DDM. Consequently, a long-term antibacterial and low-defect hybrid layer is successfully created, which greatly improves the bonding effectiveness. This helps to improve the clinical treatment of bacteria-based dental diseases and the tooth-restoration repair effect and prevent secondary dental diseases, having significance in clinical dentistry and providing insights for other tissue-biomaterial adhesions.

A two-phase and long-lasting multi-antibacterial coating enables titanium biomaterials to prevent implants-related infections

In clinical work, the main challenges for titanium (Ti) implantation are bacterial infection and aseptic loosening, which severely affect the survival rate of implants. The first 4 weeks post-operation is the infection peak phase of implants. Inhibiting implant infection caused by bacteria adhesion and proliferation during the early phase as well as promoting subsequent osteointegration is essential for implant success. Herein, we constructed a quaternary ammonium carboxymethyl chitosan (QCMC), collagen (COL Ⅰ) and hydroxyapatite (HAP) multilayers coating on Ti substrates via a modified layer-by-layer (LBL) technique and polymerization of dopamine. The QCMC/COL/HAP coating exhibited a multi-antibacterial property with a two-phase function: (1) At the first 4 weeks post-operation, the covalently bonded QCMC could be slowly degraded and demonstrated both contact-killing and release-killing properties during the infection peak phase; (2) At the second phase, osteogenesis and osseointegration-promotion capabilities were enhanced by HAP under the effective control of infection. The multifilm coating was degraded for more than 45 days under the action of collagenase Ⅰ, and displayed good biocompatibility in vivo and in vitro. Most importantly, the coating exhibited a long-lasting antibacterial activity for more than 3 months, against the main pathogenic bacteria of peri-implant infections. Both in vitro studies and in vivo animal models revealed a desirable osteogenic differentiation capacity of Ti-CCH. Therefore, our study reports a two-phase, long-lasting multi-antibacterial coating on Ti-CCH and indicates potential applications of the modified LBL strategy in orthopaedic fields, which is enlightening for developing practical implant and scaffold materials.

•

Developing a QCMC/COL/HAP multifilm coating via modified layer-by-layer technique and self-polymerization of dopamine.

•

The QCMC/COL/HAP coating exhibited desirable mechanical properties and excellent biocompatibility.

•

The release kinetics endowed the QCMC/COL/HAP coating with multi-antibacterial activity at the first phase after operation.

•

The QCMC/COL/HAP coating could improve osseointegration at the second phase of post-operation.

The Influence of Hyaluronic Acid Biofunctionalization of a Bovine Bone Substitute on Osteoblast Activity In Vitro

Bovine bone substitute materials (BSMs) are used for oral bone regeneration. The objective was to analyze the influence of BSM biofunctionalization via hyaluronic acid (HA) on human osteoblasts (HOBs). BSMs with ± HA were incubated with HOBs including HOBs alone as a negative control. On days 3, 7 and 10, cell viability, migration and proliferation were analyzed by fluorescence staining, scratch wound assay and MTT assay. On days 3, 7 and 10, an increased cell viability was demonstrated for BSM+ compared with BSM− and the control (each p ≤ 0.05). The cell migration was enhanced for BSM+ compared with BSM− and the control after day 3 and day 7 (each p ≤ 0.05). At day 10, an accelerated wound closure was found for the control compared with BSM+/− (each p < 0.05). The highest proliferation rate was observed for BSM+ on day 3 (p ≤ 0.05) followed by BSM− and the control (each p ≤ 0.05). At day 7, a non-significantly increased proliferation was shown for BSM+ while the control was higher than BSM− (each p < 0.05). The least proliferation activity was observed for BSM− (p < 0.05) at day 10. HA biofunctionalization of the BSMs caused an increased HOB activity and might represent a promising alternative to BSM− in oral bone regeneration.

Biocompatible Organic Coatings Based on Bisphosphonic Acid RGD-Derivatives for PEO-Modified Titanium Implants

Currently, significant attention is attracted to the problem of the development of the specific architecture and composition of the surface layer in order to control the biocompatibility of implants made of titanium and its alloys. The titanium surface properties can be tuned both by creating an inorganic sublayer with the desired morphology and by organic top coating contributing to bioactivity. In this work, we developed a composite biologically active coatings based on hybrid molecules obtained by chemical cross-linking of amino acid bisphosphonates with a linear tripeptide RGD, in combination with inorganic porous sublayer created on titanium by plasma electrolytic oxidation (PEO). After the addition of organic molecules, the PEO coated surface gets nobler, but corrosion currents increase. In vitro studies on proliferation and viability of fibroblasts, mesenchymal stem cells and osteoblast-like cells showed the significant dependence of the molecule bioactivity on the structure of bisphosphonate anchor and the linker. Several RGD-modified bisphosphonates of β-alanine, γ-aminobutyric and ε-aminocaproic acids with BMPS or SMCC linkers can be recommended as promising candidates for further in vivo research.

The application of hyaluronic acid in bone regeneration

Hyaluronic acid (HA) exists naturally as an important component of the extracellular matrix (ECM) in the human body. In recent decades, HA has been widely used in bone regeneration, and is currently a popular topic, particularly in the craniofacial and dental fields. From maxilla augmentation to craniofacial bone trauma, there is now a large demand for bone regenerative therapy. Serving as a cell-seeding scaffold or a carrier for bioactive components, hyaluronic acid-incorporated scaffolds and carriers in bone regeneration can be fabricated into either rigid or colloidal forms. Since the type of material used is a critical factor in the biological properties of a scaffold, HA derivatives or HA-incorporated composite scaffolds have shown excellent potential for improving osteogenesis and mineralization. Furthermore, in order to better enhance osteogenesis, local delivery carriers based on hyaluronic acid derivatives, rather than specifically serving as scaffolds, can be established by loading different osteoinductive or osteogenetic components and acquiring different release patterns. Such osteoinductive carriers immobilized on implant surfaces are also effective in improving osseointegration. Thus, as such a competent biomaterial, hyaluronic acid should be considered a promising tool in bone regeneration.

Approaches based on passive and active antibacterial coating on titanium to achieve antibacterial activity

Titanium (Ti) and its alloys are widely applied as orthopedic implants for hip and knee prosthesis, fixation, and dental implants. However, Ti and its alloys are bioinert and susceptible to bacteria and biofilm formation. Strategies for improving the antibacterial properties of Ti can be divided into two approaches, namely, passive coating and active coating on the Ti surface. Passive coating on Ti mainly kills the bacteria in contact but does not kill plankton or bacteria dwell in the bone tissue around the Ti implant. Active coating mainly involves the release of antibacterial agents to kill the bacteria, but this may result in the development of bacterial resistance. Both strategies include advantages and disadvantages. This article reviews the current and potential future approaches for improving antibacterial activity on Ti. We mainly focus on current approaches for fabricating antibacterial Ti and its limitations and countermeasures, and provide direction for further studies of biofunctionalization of Ti with antibacterial properties. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A:2531-2539, 2018.

The effect of surface immobilized NBD peptide on osteoclastogenesis of rough titanium plates in vitro and osseointegration of rough titanium implants in ovariectomized rats in vivo

Successful osseointegration in dental implants depends on balanced activation of osteoclasts and osteoblasts. Osteoporosis up-regulates osteoclast activity, so it is desirable to find effective interventions to inhibit osteoclastogenesis and enhance the osseointegration of implants under these conditions. It has been reported that the NF-κB essential modulator (NEMO)-binding domain (NBD) peptide can prevent osteoclast formation and bone resorption. In this study, we conjugated NBD peptide onto the surface of rough pure titanium (Ti) using the layer by layer technique. We analyzed the surface characteristics and determined the successful NBD integration by the presence of trivial granular structures, increased S elements and hydrophilia. Importantly, we first reported that Ti surface-conjugated NBD peptide retained its inhibitory effects on osteoclastogenesis by reducing osteoclast sealing zone formation and function. These effects were mediated by a reduction in NFATc1 expression, which in turn regulated integrin ανβ₃ and MMP9 by targeting the P65 signaling pathway. In vivo TRAP staining suggested NBD-coating decreased osteoclast formation with less pseudopodia. Micro-CT and histomorphometric analysis demonstrated that NBD-coating enhanced pronounced osseointegration in vivo in ovariectomized rats. This study holds great promise for in vivo use of immobilized NBD peptide and offers an effective therapeutic approach to select more suitable Ti-implant surface modifications for improving implant osseointegration in osteoporotic patients.

Successful osseointegration in dental implants depends on balanced activation of osteoclasts and osteoblasts.

Macrophage polarization, inflammatory signaling, and NF-κB activation in response to chemically modified titanium surfaces

Functionalization of titanium devices with various bioactive molecules enhances many of their properties as implants, including biocompatibility, which is typically assessed by macrophage activation and inflammation. However, functionalization requires prior introduction of reactive groups, to which bioactive agents can then be grafted. Thus, we investigated the inflammatory properties of titanium pretreated with NaOH, titanium pretreated with NaOH and then with 3-aminopropyl triethoxysilane, and titanium pretreated with dopamine. Inflammation, macrophage polarization, and activation of NF-κB signaling were assessed by real-time PCR and western blotting. The data demonstrate that silanized titanium is the least inflammatory, and promotes macrophage M2 polarization with modest engagement of the NF-κB signaling pathway. Importantly, silanization introduces a reactive amino group, providing more opportunities for further functionalization.

An integrated multi-layer 3D-fabrication of PDA/RGD coated graphene loaded PCL nanoscaffold for peripheral nerve restoration

As a conductive nanomaterial, graphene has huge potentials in nerve function restoration by promoting electrical signal transduction and metabolic activities with unique topological properties. Polydopamine (PDA) and arginylglycylaspartic acid (RGD) can improve cell adhesion in tissue engineering. Here we report an integrated 3D printing and layer-by-layer casting (LBLC) method in multi-layered porous scaffold fabrication. The scaffold is composed of single-layered graphene (SG) or multi-layered graphene (MG) and polycaprolactone (PCL). The electrically conductive 3D graphene scaffold can significantly improve neural expression both in vitro and in vivo. It promotes successful axonal regrowth and remyelination after peripheral nerve injury. These findings implicate that graphene-based nanotechnology have great potentials in peripheral nerve restoration in preclinical and clinical application.

An in vivo study on the effect of coating stability on osteointegration performance of collagen/hyaluronic acid multilayer modified titanium implants

Aseptic loosening of implant is one of the main causes of Ti-based implant failure. In our previous work, a novel stable collagen/hyaluronic acid (Col/HA) multilayer modified titanium coatings (TCs) was developed by layer-by-layer (LBL) covalent immobilization technique, which showed enhanced biological properties compared with TCs that were physically absorbed with Col/HA multilayer in vitro. In this study, a rabbit model with femur condyle defect was employed to compare the osteointegration performance of them. Results indicated that Col/HA multilayer with favourable stability could better facilitate osteogenesis around implants and bone-implant contact. The Col/HA multilayer covalent-immobilized TC may reduce aseptic loosening of implant.

•

Stability of Col/HA multilayer could promote the growth of trabecular bone around implants.

•

New bone was induced to grow into the hole of Col/HA multilayer covalently immobilized TC implants.

•

New bone contacted with Col/HA multilayer covalently immobilized TC implants closely.

PTH coatings on titanium surfaces improved osteogenic integration by increasing expression levels of BMP-2/Runx2/Osterix

The aim of this experiment was to assemble parathyroid hormone (PTH) coatings on titanium surfaces and evaluate the effect on implant osseointegration.

The synergistic effect of type I collagen and hyaluronic acid on the biological properties of Col/HA-multilayer-modified titanium coatings: an in vitro and in vivo study

The synergistic effect on osseointegration is existed between Type I collagen (ColI) and hyaluronic acid (HA), and the early osseogenetic activity of ColI/HA multilayer modified titanium coatings (TC) is higher than that ColI modified TC and HA modified TC.

Targeted delivery of doxorubicin to tumour tissues by a novel legumain sensitive polygonal nanogel

Targeted delivery of cytotoxic drugs to tumour tissue has great importance for successful chemotherapy. Legumain is an asparaginyl endopeptidase that is highly up-regulated in a number of solid tumours. The aim of this work was to prepare a novel hyaluronic acid (HA) based legumain sensitive nanogel for the delivery of doxorubicin with a high targeting efficiency both in vitro and in vivo. The legumain sensitive property is achieved by the conjugation of doxorubicin with HA via a legumain substrate peptide bridge. This HA derivative is further crosslinked in a water/oil solvent system to form a polygonal nanogel. Doxorubicin released in the tumour tissue is sustained thanks to the combined action of legumain and hyaluronidase, which are both overexpressed in tumour tissues. Hyaluronic acid could act as a targeting agent to CD44 (HA receptor), which further improved the in vivo target effect and enhanced in vitro cellular uptake. The developed nanogel exhibited a high therapeutic index that improved tumour inhibition effects and reduced system toxicity in a lung cancer mice model. These results highlighted the advantages of using this multi-functional material for a successful delivery of doxorubicin against cancer.

Biofunctionalization of titanium with bacitracin immobilization shows potential for anti-bacteria, osteogenesis and reduction of macrophage inflammation

Titanium has been widely used in the orthopedic and dental fields, however, the inert nature of Ti makes it unsuitable for application in promoting bone cell growth，osteogenic differentiation and antibacterial ability. The aims of the current study were to investigate the antimicrobial activity and biofunction of the polypeptide antibiotic bacitracin, and obtain a multi-biofunctional titanium implant by covalently-immobilizing titanium with the bacitracin. The results showed that the bacitracin possessed low minimum inhibitory concentration (MIC) to both Staphylococcus aureus and Methicillin-resistant Staphylococcus aureus (MRSA), with the non-cytotoxicity concentration up to 500μg/mL to human bone marrow mesenchymal stem cells (hBMSCs), furthermore, the bacitracin could improve the osteogenic differentiation of hBMSCs. The results of Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) indicated that bacitracin had been covalently immobilized on the surface of titanium. Immobilized bacitracin could improve the hydrophilic of immobilized titanium. The results of antimicrobial assay demonstrated that the covalently-immobilized bacitracin also had excellent antimicrobial property, and the bacitracin immobilized titanium could inhibit bacterial adhesion and colonization. The results of cell biology experiments proved that the bacitracin immobilized titanium could improve hBMSCs' adhesion, proliferation and osteogenic differentiation. We also found that the macrophages were difficult to spread or activate on the surface of bacitracin immobilized titanium, and the secretion of inflammatory factors had been inhibited. In conclusion, the novel bacitracin immobilized titanium has multi-biofunctions including outstanding antibacterial properties, excellent cell biology performance, and restraining inflammation, which has exciting application prospect.

Effect of Assembly pH on Polyelectrolyte Multilayer Surface Properties and BMP-2 Release

The effect of solution pH during layer-by-layer assembly of polyelectrolyte multilayer (PEM) coatings on properties relevant to orthopedic implant success was investigated. Bone morphogenetic protein 2 (BMP-2), a potent osteoconductive growth factor, was adsorbed onto the surface of anodized titanium, and PEM coatings prepared from solutions of poly-l-histidine and poly(methacrylic acid) were built on top of the BMP-2. High levels of BMP-2 released over several months were achieved. Approximately 2 μg/cm(2) of BMP-2 were initially adsorbed on the anodized titanium and a pH-dependent release behavior was observed, with more stable coatings assembled at pH = 6-7. Three different diffusion regimes could be determined from the release profiles: an initial burst release, a sustained release regime, and a depletion regime. BMP-2 was shown to maintain bioactivity after release from a PEM and the presence of a PEM was shown to preserve BMP-2 structure. No visible change was observed in surface roughness as the assembly pH was varied, whereas the surface energy decreased for samples prepared at more basic pH. These results indicate that the initial BMP-2 layer affects PEM surface structure, but not the functional groups exposed on the surface.

Spatially-controlled distribution of HACC in mineralized collagen coatings for improving rhBMP-2 loading and release behavior

In this study, mineralized collagen (COL) coatings with controlled loading and release of bone morphogenetic protein (rhBMP-2) as well as enhanced osteogenic differentiation were successfully achieved via the spatially-control of hydroxypropyltrimethyl ammonium chloride chitosan (HACC) within the coatings. The distribution of HACC in the inner part (HACC-IN) or the outer part (HACC-OUT) of the coatings were adjusted by different potential values and negative/positive alternations during alternating potentials assisted electrochemical deposition (AP-ECD). It was found that rhBMP-2 loading capacity was remarkably enhanced with the increased incorporation of HACC due to their strong interaction, and the release behavior was also tuned by HACC location. In general, HACC-IN coatings showed a prominent improvement in cytocompatibility and osteogenic differentiation. The main reason is considered that the inner location of HACC can eliminate the negative effect of HACC to initial cellular adhesion and bring to a sustained rhBMP-2 release behavior due to kinetic modification. An optimized coating in this work could load as high as 4644ng/cm(2) rhBMP-2 and release only 25% for 14 days, which consequently leads to a better osteogenic differentiation. This study has thus inspired another promising protocol for designing growth factor incorporated bioactive coatings for bone implants with improved osteointegration.

Fabrication, characterization, and biological assessment of multilayer laminin γ2 DNA coatings on titanium surfaces

The purpose of this work was to fabricate a multilayer laminin γ2 DNA coating on a titanium surface and evaluate its biological properties. A multilayer laminin γ2 DNA coating was fabricated on titanium using a layer-by-layer assembly technique. The rate of coating degradation was evaluated by detecting the amount of cDNA remaining. Surface analysis using X-ray photoelectron spectroscopy, atomic force microscopy, and surface contact angle measurements revealed the multilayer structure to consist of cationic lipid and confirmed that a laminin γ2 DNA layer could be fabricated on titanium via the layer-by-layer assembly process. The transfection efficiency was highest for five layers in the multilayer structure. HEK293 cells cultured on the multilayer films displayed significantly higher adhesion activity than the control group. The expression of laminin γ2 and the co-localization of integrin β4 and plectin were more obvious in HN4 cells cultured on the multilayer laminin γ2 DNA coating, while weak immunoreactivities were observed in the control group. We concluded that the DNA-loaded multilayer provided a surface with good biocompatibility and that the multilayer laminin γ2 DNA coating might be effective in improving cell adhesion and the formation of hemidesmosomes on titanium surfaces.

Interplay of Substrate Conductivity, Cellular Microenvironment, and Pulsatile Electrical Stimulation toward Osteogenesis of Human Mesenchymal Stem Cells in Vitro

The influences of physical stimuli such as surface elasticity, topography, and chemistry over mesenchymal stem cell proliferation and differentiation are well investigated. In this context, a fundamentally different approach was adopted, and we have demonstrated the interplay of inherent substrate conductivity, defined chemical composition of cellular microenvironment, and intermittent delivery of electric pulses to drive mesenchymal stem cell differentiation toward osteogenesis. For this, conducting polyaniline (PANI) substrates were coated with collagen type 1 (Coll) alone or in association with sulfated hyaluronan (sHya) to form artificial extracellular matrix (aECM), which mimics the native microenvironment of bone tissue. Further, bone marrow derived human mesenchymal stem cells (hMSCs) were cultured on these moderately conductive (10(-4)-10(-3) S/cm) aECM coated PANI substrates and exposed intermittently to pulsed electric field (PEF) generated through transformer-like coupling (TLC) approach over 28 days. On the basis of critical analysis over an array of end points, it was inferred that Coll/sHya coated PANI (PANI/Coll/sHya) substrates had enhanced proliferative capacity of hMSCs up to 28 days in culture, even in the absence of PEF stimulation. On the contrary, the adopted PEF stimulation protocol (7 ms rectangular pulses, 3.6 mV/cm, 10 Hz) is shown to enhance osteogenic differentiation potential of hMSCs. Additionally, PEF stimulated hMSCs had also displayed different morphological characteristics as their nonstimulated counterparts. Concomitantly, earlier onset of ALP activity was also observed on PANI/Coll/sHya substrates and resulted in more calcium deposition. Moreover, real-time polymerase chain reaction results indicated higher mRNA levels of alkaline phosphatase and osteocalcin, whereas the expression of other osteogenic markers such as Runt-related transcription factor 2, Col1A, and osteopontin exhibited a dynamic pattern similar to control cells that are cultured in osteogenic medium. Taken together, our experimental results illustrate the interplay of multiple parameters such as substrate conductivity, electric field stimulation, and aECM coating on the modulation of hMSC proliferation and differentiation in vitro.

Oriented collagen nanocoatings for tissue engineering

Collagens are among the most widely present and important proteins composing the human total body, providing strength and structural stability to various tissues, from skin to bone. In this paper, we report an innovative approach to bioactivate planar surfaces with oriented collagen molecules to promote cells proliferation and alignment. The Langmuir-Blodgett technique was used to form a stable collagen film at the air-water interface and the Langmuir-Schaefer deposition was adopted to transfer it to the support surface. The deposition process was monitored by estimating the mass of the protein layers after each deposition step. Collagen films were then structurally characterized by atomic force, scanning electron and fluorescent microscopies. Finally, collagen films were functionally tested in vitro. To this aim, 3T3 cells were seeded onto the silicon supports either modified or not (control) by collagen film deposition. Cells adhesion and proliferation on collagen films were found to be greater than those on control both after 1 (p<0.05) and 7 days culture. Moreover, the functionalization of the substrate surface triggered a parallel orientation of cells when cultured on it. In conclusion, these data demonstrated that the Langmuir-Schaefer technique can be successfully used for the deposition of oriented collagen films for tissue engineering applications.

Poly(dopamine)-assisted immobilization of Arg-Gly-Asp peptides, hydroxyapatite, and bone morphogenic protein-2 on titanium to improve the osteogenesis of bone marrow stem cells

Osteointegration of titanium implants in bone defects is clinically important for long-term performance of orthopaedic implants. In this work, we developed a facile and effective "one-pot" deposition method based on dopamine polymerization for the development of cell-adhesive, osteoconductive, and osteoinductive titanium implants. Arg-Gly-Asp (RGD)-conjugated polymers, hydroxyapatite (HAp) nanoparticles, and bone morphogenic protein-2 (BMP-2) were mixed with an alkaline dopamine solution, and then, titanium substrates were immersed in the mixture for an hour. During poly(dopamine) coating, the three types of bioactive substances were immobilized on the titanium surfaces. Our results indicate that RGD conjugation enhanced the adhesion of human bone marrow stem cell line, while HAp incorporation facilitated cellular osteodifferentiation. The immobilization of BMP-2 induced the osteogenesis of the stem cells, indicated by reverse-transcriptase polymerase chain reaction (RT-PCR) analysis. The mineralization on the deposited substrates was also enhanced greatly. This functionalized layer on titanium substrate promoted mesenchymal stem cell to osteoblast and improved osteogenic differentiation and mineralization. In conclusion, the surface modification method shows a great potential for enhancement of osteointegration of orthopaedic and dental implants.

Fabrication and in vitro evaluation of stable collagen/hyaluronic acid biomimetic multilayer on titanium coatings

Layer-by-layer (LBL) self-assembly technique has been proved to be a highly effective method to immobilize the main components of the extracellular matrix such as collagen and hyaluronic acid on titanium-based implants and form a polyelectrolyte multilayer (PEM) film by electrostatic interaction. However, the formed PEM film is unstable in the physiological environment and affects the long-time effectiveness of PEM film. In this study, a modified LBL technology has been developed to fabricate a stable collagen/hyaluronic acid (Col/HA) PEM film on titanium coating (TC) by introducing covalent immobilization. Scanning electron microscopy, diffuse reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to characterize the PEM film. Results of Sirius red staining demonstrated that the chemical stability of PEM film was greatly improved by covalent cross-linking. Cell culture assays further illustrated that the functions of human mesenchymal stem cells, such as attachment, spreading, proliferation and differentiation, were obviously enhanced by the covalently immobilized Col/HA PEM on TCs compared with the absorbed Col/HA PEM. The improved stability and biological properties of the Col/HA PEM covalently immobilized TC may be beneficial to the early osseointegration of the implants.

Polyelectrolyte multilayer coating with two regulatory molecules on titanium: construction and its biological effects

Aim: This study aimed at constructing a novel disulfide-crosslinked collagen I/hyaluronic acid polyelectrolyte multilayer (PEM) coating incorporated with bFGF and arginine–glycine–aspartic acid on titanium via the layer-by-layer technique, and evaluating its biological effects. Materials & methods: The surface topography and components, thickness, degradation behaviors and bFGF release profiles of the PEM coating were investigated. The effects of the PEM coating on osteoprogenitor cell growth and bone implant interfacial binding strength in the rabbit femur model were evaluated separately. Results: The formation of disulfide bonds improved the stability of the PEM coating, resulting in a coating that can release bFGF in a slow and sustained manner. Biological evaluations revealed that the resultant PEM coating on titanium promoted various cell behaviors and enhanced the binding strength. Conclusion: The employed cotreatment regimen enabled bFGF and arginine–glycine–aspartic acid to have a synergistic effect on the cell responses, which, in turn, improved the osseointegration.

Original submitted 26 January 2012; Revised submitted 10 June 2012; Published online 5 February 2013

Naturally and synthetic smart composite biomaterials for tissue regeneration

The development of smart biomaterials for tissue regeneration has become the focus of intense research interest. More opportunities are available by the composite approach of combining the biomaterials in the form of biopolymers and/or bioceramics either synthetic or natural. Strategies to provide smart capabilities to the composite biomaterials primarily seek to achieve matrices that are instructive/inductive to cells, or that stimulate/trigger target cell responses that are crucial in the tissue regeneration processes. Here, we review in-depth, recent developments concerning smart composite biomaterials available for delivery systems of biofactors and cells and scaffolding matrices in tissue engineering. Smart composite designs are possible by modulating the bulk and surface properties that mimic the native tissues, either in chemical (extracellular matrix molecules) or in physical properties (e.g. stiffness), or by introducing external therapeutic molecules (drugs, proteins and genes) within the structure in a way that allows sustainable and controllable delivery, even time-dependent and sequential delivery of multiple biofactors. Responsiveness to internal or external stimuli, including pH, temperature, ionic strength, and magnetism, is another promising means to improve the multifunctionality in smart scaffolds with on-demand delivery potential. These approaches will provide the next-generation platforms for designing three-dimensional matrices and delivery systems for tissue regenerative applications.

Hyaluronic acid stimulates the formation of calcium phosphate on CoCrMo alloy in simulated physiological solution

The behaviour of CoCrMo alloy has been studied in two simulated physiological solutions-NaCl and Hanks' solutions-each containing the sodium salt of hyaluronic acid. Hyaluronic acid is a component of synovial joint fluid, so the behaviour of orthopaedic alloys in its presence needs to be assessed. Electrochemical methods, X-ray photoelectron spectroscopy and scanning electron microscopy have been used to analyse the composition, thickness and morphology of any layers formed on the alloy. The addition of hyaluronic acid shifts the corrosion potential and increases the value of polarization resistance. The presence of hyaluronic acid in simulated Hanks' physiological solution stimulates the formation of a calcium phosphate layer, opening up the possibility for tailoring the surface properties of CoCrMo alloy. The viability of human osteoblast-like was determined using the Alamar(®) Blue Assay, while the osteogenic activity was evaluated by alkaline phosphatase activity. The presence of hyaluronic acid affects the alkaline phosphatase activity.

The promotion of osseointegration of titanium surfaces by coating with silk protein sericin

A promising strategy to influence the osseointegration process around orthopaedic titanium implants is the immobilization of bioactive molecules. This recruits appropriate interaction between the surface and the tissue by directing cells adhesion, proliferation, differentiation and active matrix remodelling. In this study, we aimed to investigate the functionalization of metallic implant titanium with silk protein sericin. Titanium surface was immobilized with non-mulberry Antheraea mylitta sericin using glutaraldehyde as crosslinker. To analyse combinatorial effects the sericin immobilized titanium was further conjugated with integrin binding peptide sequence Arg-Gly-Asp (RGD) using ethyl (dimethylaminopropyl) carbodiimide and N-hydroxysulfosuccinimide as coupling agents. The surface of sericin immobilized titanium was characterized biophysically. Osteoblast-like cells were cultured on sericin and sericin/RGD functionalized titanium and found to be more viable than those on pristine titanium. The enhanced adhesion, proliferation, and differentiation of osteoblast cells were observed. RT-PCR analysis showed that mRNA expressions of bone sialoprotein, osteocalcin and alkaline phosphatase were upregulated in osteoblast cells cultured on sericin and sericin/RGD immobilized titanium substrates. Additionally, no significant amount of pro-inflammatory cytokines TNF-α, IL-1β and nitric oxide production were recorded when macrophages cells and osteoblast-macrophages co culture cells were grown on sericin immobilized titanium. The findings demonstrate that the sericin immobilized titanium surfaces are potentially useful bioactive coated materials for titanium-based medical implants.

Construction of microenvironment onto titanium substrates to regulate the osteoblastic differentiation of bone marrow stromal cells in vitro and osteogenesis in vivo

To mimic the extracellular matrix of natural bone, apatite/gelatin composite was deposited onto nanostructured titanium substrates via a coprecipitation method, which was pretreated by potassium hydroxide and heat treatment to generate an anticorrosive nanostructured layer. The successful formation of the apatite/gelatin nanocomposite onto titanium surfaces was revealed by Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, atomic force microscopy (AFM), and thin film X-ray diffraction (TF-XRD) measurements, respectively. The immunofluorescence staining of vinculin revealed that the apatite/gelatin nanocomposite deposited titanium substrate was favorable for cell adhesion. More importantly, bone marrow stromal cells cultured onto the apatite/gelatin nanocomposite deposited titanium substrates displayed significantly higher (p < 0.05 or p < 0.01) proliferation and differentiation levels of alkaline phosphatase, mRNA expressions of osteocalcin (OC), osteopontin (OPN), and collagen type I (Col I), and OC content after culture for 7, 14, and 21 days, respectively, which was also revealed by the immunofluorescence analysis of OC and OPN expression. The deposition of apatite/gelatin nanocomposite improved bone density (p < 0.05) and bone-implant contact rate (p < 0.05), which was reflected by microcomputed tomography analysis and histological evaluation in vivo using a rabbit model. This work provides an approach to fabricate high-performance titanium-based implants with enhanced bone osseointegration.

Umbilical cord stem cells released from alginate-fibrin microbeads inside macroporous and biofunctionalized calcium phosphate cement for bone regeneration

The need for bone repair has increased as the population ages. The objectives of this study were to (1) develop a novel biofunctionalized and macroporous calcium phosphate cement (CPC) containing alginate-fibrin microbeads encapsulating human umbilical cord mesenchymal stem cells (hUCMSC) and, for the first time, (2) investigate hUCMSC proliferation and osteogenic differentiation inside the CPC. A macroporous CPC was developed using calcium phosphate powder, chitosan, and a gas-foaming porogen. Five types of CPC were fabricated: a CPC control, CPC+0.05% fibronectin (Fn), CPC+0.1% Fn, CPC+0.1% arginine-glycine-aspartate (RGD), and CPC+0.1% Fn+0.1% RGD. Alginate-fibrin microbeads containing 10(6) hUCMSC per ml were encapsulated in the CPC paste. After the CPC had set, the degradable microbeads released hUCMSC within it. The hUCMSC proliferated inside the CPC, with the cell density after 21 days being 4-fold that on day1. CPC+0.1% RGD had the highest cell density, which was 4-fold that of the CPC control. The released cells differentiated along the osteogenic lineage and synthesized bone mineral. The hUCMSC inside the CPC+0.1% RGD construct expressed the genes alkaline phosphatase, osteocalcin and collagen I, at twice the level of the CPC control. Mineral synthesis by hUCMSC inside the CPC+0.1% RGD construct was 2-fold that in the CPC control. RGD and Fn incorporation in the CPC did not compromise its strength, which matched the reported strength of cancellous bone. In conclusion, degradable microbeads released hUCMSC which proliferated, differentiated and synthesized minerals inside the macroporous CPC. The CPC with RGD greatly enhanced cell function. The novel biofunctionalized and macroporous CPC-microbead-hUCMSC construct is promising for bone tissue engineering applications.