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

Lipoplex-Functionalized Thin-Film Surface Coating Based on Extracellular Matrix Components as Local Gene Delivery System to Control Osteogenic Stem Cell Differentiation

A gene-activated surface coating is presented as a strategy to design smart biomaterials for bone tissue engineering. The thin-film coating is based on polyelectrolyte multilayers composed of collagen I and chondroitin sulfate, two main biopolymers of the bone extracellular matrix, which are fabricated by layer-by-layer assembly. For further functionalization, DNA/lipid-nanoparticles (lipoplexes) are incorporated into the multilayers. The polyelectrolyte multilayer fabrication and lipoplex deposition are analyzed by surface sensitive analytical methods that demonstrate successful thin-film formation, fibrillar structuring of collagen, and homogenous embedding of lipoplexes. Culture of mesenchymal stem cells on the lipoplex functionalized multilayer results in excellent attachment and growth of them, and also, their ability to take up cargo like fluorescence-labelled DNA from lipoplexes. The functionalization of the multilayer with lipoplexes encapsulating DNA encoding for transient expression of bone morphogenetic protein 2 induces osteogenic differentiation of mesenchymal stem cells, which is shown by mRNA quantification for osteogenic genes and histochemical staining. In summary, the novel gene-functionalized and extracellular matrix mimicking multilayer composed of collagen I, chondroitin sulfate, and lipoplexes, represents a smart surface functionalization that holds great promise for tissue engineering constructs and implant coatings to promote regeneration of bone and other tissues.

Tailored Polyelectrolyte Multilayer Systems by Variation of Polyelectrolyte Composition and EDC/NHS Cross-Linking: Controlled Drug Release vs. Drug Reservoir Capabilities and Cellular Response for Improved Osseointegration

Polyelectrolyte multilayers (PEM) are versatile tools used to investigate fundamental interactions between material-related parameters and the resulting performance in stem cell differentiation, respectively, in bone tissue engineering. In the present study, we investigate the suitability of PEMs with a varying collagen content for use as drug carriers for the human bone morphogenetic protein 2 (rhBMP-2). We use three different PEM systems consisting either of the positively charged poly-L-lysine or the glycoprotein collagen type I and the negatively charged glycosaminoglycan heparin. For a specific modification of the loading capacity and the release kinetics, the PEMs were stepwise cross-linked before loading with cytokine. We demonstrate the possibility of immobilizing significant amounts of rhBMP-2 in all multilayer systems and to specifically tune its release via cross-linking. Furthermore, we prove that the drug release of rhBMP-2 plays only a minor role in the differentiation of osteoprogenitor cells. We find a significantly higher influence of the immobilized rhBMP-2 within the collagen-rich coatings that obviously represent an excellent mimicry of the native extracellular matrix. The cytokine immobilized in its bioactive form was able to achieve an increase in orders of magnitude both in the early stages of differentiation and in late calcification compared to the unloaded layers.

The Effect of the Topmost Layer and the Type of Bone Morphogenetic Protein-2 Immobilization on the Mesenchymal Stem Cell Response

Recombinant human bone morphogenetic protein-2 (rhBMP-2) plays a key role in the stem cell response, not only via its influence on osteogenesis, but also on cellular adhesion, migration, and proliferation. However, when applied clinically, its supra-physiological levels cause many adverse effects. Therefore, there is a need to concomitantly retain the biological activity of BMP-2 and reduce its doses. Currently, the most promising strategies involve site-specific and site-directed immobilization of rhBMP-2. This work investigated the covalent and electrostatic binding of rhBMP-2 to ultrathin-multilayers with chondroitin sulfate (CS) or diazoresin (DR) as the topmost layer. Angle-resolved X-ray photoelectron spectroscopy was used to study the exposed chemical groups. The rhBMP-2 binding efficiency and protein state were studied with time-of-flight secondary ion mass spectrometry. Quartz crystal microbalance, atomic force microscopy, and enzyme-linked immunosorbent assay were used to analyze protein–substrate interactions. The effect of the topmost layer was tested on initial cell adhesion and short-term osteogenesis marker expression. The results show the highest expression of selected osteomarkers in cells cultured on the DR-ended layer, while the cellular flattening was rather poor compared to the CS-ended system. rhBMP-2 adhesion was observed only on negatively charged layers. Cell flattening became more prominent in the presence of the protein, even though the osteogenic gene expression decreased.

Development of a system of heparin multilayers on titanium surfaces for dual growth factor release

The aim of the present study was to establish a modular platform of poly-L-lysine-heparin (PLL-Hep) polyelectrolyte multilayer (PEM) coatings on titanium surfaces for dual growth factor delivery of recombinant human bone morphogenic protein 2 (rhBMP2) and recombinant human vascular endothelial growth factor 165 (rhVEGF165) in clinically relevant quantities. Release characteristics for both growth factors differed significantly depending on film architecture. rhBMP2 induced activation of alkaline phosphatase in C2C12 cells and proliferation of human mesenchymal stem cells (hMSCs). rhVEGF mediated induction of von Willebrand factor (vWF) in hMSCs and proliferation of human umbilical vein endothelial cells. Osteogenic and angiogenic effects were modified by variation in cross-linking and architecture of the PEMs. By creating multilayer films with distinct zones, release characteristics and proportion of both growth factor delivery could be tuned and surface-activity modified to enhance angiogenic or osteogenic function in various ways. In summary, the system provides a modular platform for growth factor delivery that allows for individual composition and accentuation of angiogenic and osteogenic surface properties.

Half-life modeling of basic fibroblast growth factor released from growth factor-eluting polyelectrolyte multilayers

Growth factor-eluting polymer systems have been widely reported to improve cell and tissue outcomes; however, measurements of actual growth factor concentration in cell culture conditions are limited. The problem is compounded by a lack of knowledge of growth factor half-lives, which impedes efforts to determine real-time growth factor concentrations. In this work, the half-life of basic fibroblast growth factor (FGF2) was determined using enzyme linked immunosorbent assay (ELISA). FGF2 release from polyelectrolyte multilayers (PEMs) was measured and the data was fit to a simple degradation model, allowing for the determination of FGF2 concentrations between 2 and 4 days of culture time. After the first hour, the FGF2 concentration for PEMs assembled at pH = 4 ranged from 2.67 ng/mL to 5.76 ng/mL, while for PEMs assembled at pH = 5, the concentration ranged from 0.62 ng/mL to 2.12 ng/mL. CRL-2352 fibroblasts were cultured on PEMs assembled at pH = 4 and pH = 5. After 2 days, the FGF2-eluting PEM conditions showed improved cell count and spreading. After 4 days, only the pH = 4 assembly condition had higher cells counts, while the PEM assembled at pH = 5 and PEM with no FGF2 showed increased spreading. Overall, the half-life model and cell culture study provide optimal concentration ranges for fibroblast proliferation and a framework for understanding how temporal FGF2 concentration may affect other cell types.

Structured nanofilms comprising Laponite® and bone extracellular matrix for osteogenic differentiation of skeletal progenitor cells

Functionalized scaffolds hold promise for stem cell therapy by controlling stem cell fate and differentiation potential. Here, we have examined the potential of a 2-dimensional (2D) scaffold to stimulate bone regeneration. Solubilized extracellular matrix (ECM) from human bone tissue contains native extracellular cues for human skeletal cells that facilitate osteogenic differentiation. However, human bone ECM displays limited mechanical strength and degradation stability under physiological conditions, necessitating modification of the physical properties of ECM before it can be considered for tissue engineering applications. To increase the mechanical stability of ECM, we explored the potential of synthetic Laponite® (LAP) clay as a counter material to prepare a 2D scaffold using Layer-by-Layer (LbL) self-assembly. The LAP and ECM multilayer nanofilms (ECM/LAP film) were successfully generated through electrostatic and protein-clay interactions. Furthermore, to enhance the mechanical properties of the ECM/LAP film, application of a NaCl solution wash step, instead of deionized water following LAP deposition resulted in the generation of stable, multi-stacked LAP layers which displayed enhanced mechanical properties able to sustain human skeletal progenitor cell growth. The ECM/LAP films were not cytotoxic and, critically, showed enhanced osteogenic differentiation potential as a consequence of the synergistic effects of ECM and LAP. In summary, we demonstrate the fabrication of a novel ECM/LAP nanofilm layer material with potential application in hard tissue engineering.

Incorporation of FGF-2 into Pharmaceutical Grade Fucoidan/Chitosan Polyelectrolyte Multilayers

Biopolymer polyelectrolyte multilayers are a commonly studied soft matter system for wound healing applications due to the biocompatibility and beneficial properties of naturally occurring polyelectrolytes. In this work, a popular biopolymer, chitosan, was combined with the lesser known polysaccharide, fucoidan, to create a multilayer film capable of sequestering growth factor for later release. Fucoidan has been shown to act as a heparin-mimic due to similarities in the structure of the two molecules, however, the binding of fibroblast growth factor-2 to fucoidan has not been demonstrated in a multilayer system. This study assesses the ability of fucoidan to bind fibroblast growth factor-2 within a fucoidan/chitosan polyelectrolyte multilayer structure using attenuated total internal reflectance infrared spectroscopy and quartz crystal microbalance with dissipation monitoring. The fibroblast growth factor-2 was sequestered into the polyelectrolyte multilayer as a cationic layer in the uppermost layers of the film structure. In addition, the diffusion of fibroblast growth factor-2 into the multilayer has been assessed.

Surface modification of titanium with collagen/hyaluronic acid and bone morphogenetic protein 2/7 heterodimer promotes osteoblastic differentiation

The aim of this study was to evaluate the effects of a collagen/hyaluronic acid coating without or with incorporated heterodimeric bone morphogenetic protein 2/7 (BMP2/7) on in-vitro osteoblastic differentiation on titanium discs. The multilayer collagen/hyaluronic acid coatings without or without incorporated BMP2/7 were deposited on titanium discs via a layer-by-layer technique. The effects of the coatings were evaluated by assessing the alkaline phosphatase (ALP) activity (an early osteoblastic differentiation marker) and the osteocalcin expression (a late osteoblastic differentiation marker). The expression levels of the osteoblastic genes, such as alkaline phosphatase 2 (AKP2) and osteocalcin (OC) were detected using real-time RT-PCR. ALP activity and OC expression were significantly increased when cells were cultured with collagen/hyaluronic acid+BMP2/7 heterodimer (p<0.05). The same result was found in cells with the expression of a BMP2/7 fusion gene, OC and AKP2. These results indicated that collagen/hyaluronic acid+BMP2/7 heterodimer-coated discs might have the potential to greatly enhance osseointegration than a either BMP2 or BMP7 solution or a mixture of BMP2 and BMP7 BMP2/7.

Weak polyelectrolyte-based multilayers via layer-by-layer assembly: Approaches, properties, and applications

Layer-by-layer (LbL) assembly is a nanoscale technique with great versatility, simplicity and molecular-level processing of various nanoscopic materials. Weak polyelectrolytes have been used as major building blocks for LbL assembly providing a fundamental and versatile tool to study the underlying mechanisms and practical applications of LbL assembly due to its pH-responsive charge density and molecular conformation. Because of high-density uncompensated charges and high-chain mobility, weak polyelectrolyte exponential multilayer growth is considered one of the fastest developing areas for organized molecular films. In this article, we systematically review the current status and developments of weak polyelectrolyte-based multilayers including all-weak-polyelectrolyte multilayers, weak polyelectrolytes/other components (e.g. strong polyelectrolytes, neutral polymers, and nanoparticles) multilayers, and exponentially grown weak polyelectrolyte multilayers. Several key aspects of weak polyelectrolytes are highlighted including the pH-controllable properties, the responsiveness to environmental pH, and synergetic functions obtained from weak polyelectrolyte/other component multilayers. Throughout this review, useful applications of weak polyelectrolyte-based multilayers in drug delivery, tunable biointerfaces, nanoreactors for synthesis of nanostructures, solid state electrolytes, membrane separation, and sensors are highlighted, and promising future directions in the area of weak polyelectrolyte-based multilayer assembly such as fabrication of multi-responsive materials, adoption of unique building blocks, investigation of internal molecular-level structure and mechanism of exponentially grown multilayers, and exploration of novel biomedical and energy applications are proposed.

Bioactive LbL-assembled multilayer nanofilms upregulate tenogenesis and angiogenesis enabling robust healing of degenerative rotator cuff tendons in vivo

Degenerative changes to rotator cuff tendons are often diagnosed in elderly patients. Spontaneous healing of degenerative tendons is rather inefficient as a result of the lack of a suitable microenvironment for tendon stem cell differentiation and vascularization. Herein, multilayer hyaluronic acid/chitosan (HA/CS) nanofilms were assembled by a layer-by-layer assembly method onto aligned poly(ε-caprolactone) (PCL) nanofibers for use in healing degenerative tendons. Materials testing showed that the number of layers of HA/CS nanofilms could adjust the hydrophilicity and wettability of the nanofibrous membranes. In vitro, the optimal 8-layer (termed as 8LP) membrane afforded aligned morphology of tendon stem/progenitor cells (TSPCs) and up-regulated mRNA expression of tenogenic markers (SCX, BGN). In a rabbit model with disorganized rotator cuff tendons, the 8LP group up-regulated mRNA levels of collagen I/III and tenascin (TNC) at 6 weeks, but not 12 weeks, post-surgery as compared to the native PCL group. Next, vascular endothelial growth factor-loaded 8LP (termed as 8LP-V) was prepared. Compared to 8LP, 8LP-V produced higher levels of angiogenesis in the tendons at 6 or 12 weeks post-surgery, thus supplying endogenous pre-tendon growth factors (TGF-β, IGF-1) to further enhance tenogenic transcriptional factors. As a result, 8LP-V yielded thicker collagen fibers and/or higher tendon stiffness as compared to the 8LP and clinical pericardial patch groups. This study highlights the rational design of LbL-assembled multilayer HA/CS films to upregulate tenogenesis for robust healing of degenerative rotator cuff tendons.

Impact of molecular weight on polyelectrolyte multilayer assembly and surface properties

Polyelectrolyte multilayers (PEMs) are a versatile category of materials due to their ability to modify surface properties for applications ranging from protective coatings to improved cell adhesion. Polyelectrolyte choice, including its structure and molecular weight (MW), is known to greatly influence PEM assembly and surface properties. In this work, poly(acrylic acid)/poly-l-lysine PEMs using three pairs of MWs (1.8k/15-30k, 100k/120k, and 250k/275k) were studied to determine the effects of their MWs on PEM assembly, topography and surface energy. PEMs assembly was monitored in a quartz crystal microbalance with dissipation, resulting in masses of 3.90 ± 0.87 µg/cm², 10.80 ± 4.189 µg/cm², and 30.04 ± 13.68 µg/cm² for 10 bilayers of low, medium, and high MW pairs, respectively. The low MW PEM was more rigid. Low and high MW PEMs exhibited higher roughness than medium MW, caused by polyelectrolyte stripping. Surface energy remained constant with bilayer count in the low and high MW PEMs, but steadily increased in the medium MW PEM. Differences between medium MW PEMs from low and high MW systems indicate that, while PEM properties change with MW, they are not monotonically correlated and are instead related to changes in internal charge distributions and the resultant stripping that may occur.

Combining Top-Down and Bottom-Up with Photodegradable Layer-by-Layer Films

Layer-by-layer (LbL) self-assembly of polymer coatings is a bottom-up fabrication technique with broad applicability across a wide range of materials and applications that require control over interfacial properties. While most LbL coatings are chemically uniform in directions both tangent and perpendicular to their substrate, control over the properties of surface coatings as a function of space can enhance their function. To contribute to this rapidly advancing field, our group has focused on the top-down spatiotemporal control possible with photochemically reactive LbL coatings, harnessed through charge-shifting polyelectrolytes enabled by photocleavable ester pendants. The photolysis of the photocleavable esters degrades LbL films containing these polyelectrolytes. The chemical structures of the photocleavable groups dictate the wavelengths responsible for disrupting these coatings, ranging from ultraviolet to near-infrared in our work. In addition, spatially segregating reactive groups into "compartments" within LbL films has enabled us to fabricate reactive free-standing polymer films and multiheight photopatterned coatings. Overall, by combining bottom-up and top-down approaches, photoreactive LbL films enable precise control over the interfacial properties of polymer and composite coatings.

Layer-by-layer assembly of nanofilms to control cell functions

Control of cell functions by layer-by-layer assembly has a great challenge in tissue engineering and biomedical applications. We summarize current hot approaches in this review.

Cell Type Influences Local Delivery of Biomolecules from a Bioinspired Apatite Drug Delivery System

Recently, the benefit of step-wise sequential delivery of fibroblast growth factor-2 (FGF-2) and bone morphogenetic protein-2 from a bioinspired apatite drug delivery system on mouse calvarial bone repair was demonstrated. The thicknesses of the nanostructured poly-l-Lysine/poly-l-Glutamic acid polyelectrolyte multilayer (PEM) and the bone-like apatite barrier layer that make up the delivery system, were varied. The effects of the structural variations of the coating on the kinetics of cell access to a cytotoxic factor delivered by the layered structure were evaluated. FGF-2 was adsorbed into the outer PEM, and cytotoxic antimycin-A (AntiA) was adsorbed to the substrate below the barrier layer to detect the timing of the cell access. While MC3T3-E1 osteoprogenitor cells accessed AntiA after three days, the RAW 264.7 macrophage access occurred within 4 h, unless the PEM layer was removed, in which case the results were reversed. Pits were created in the coating by the RAW 264.7 macrophages and initiated delivery, while the osteoprogenitor cell access to drugs occurred through a solution-mediated coating dissolution, at junctions between the islands of crystals. Macrophage-mediated degradation is therefore a mechanism that controls drug release from coatings containing bioinspired apatite.

Multilayered coating of titanium implants promotes coupled osteogenesis and angiogenesis in vitro and in vivo

We used surface-modified titanium (Ti) substrates with a multilayered structure composed of chitosan-catechol (Chi-C), gelatin (Gel) and hydroxyapatite (HA) nanofibers, which were previously shown to improve osteogenesis, as a platform to investigate the interaction of osteogenesis and angiogenesis during bone healing. Combined techniques of Transwell co-culture, wound healing assay, enzyme linked immunosorbent assay (ELISA), quantitative real-time polymerase chain reaction (qRT-PCR), western blotting and immunohistochemical staining were used to evaluate adhesion, morphology and migration of adipose-derived mesenchymal stem cells (Ad-MSCs) and human umbilical vein endothelial cells (HUVECs) grown on different Ti substrates. We investigated the effect of substrates on the osteogenic differentiation of Ad-MSCs and reciprocal paracrine effects of Ad-MSCs on HUVECs or vice versa. The multilayered Ti substrates directly regulated the cellular functions of Ad-MSCs and angiogenic HUVECs and mediated communication between them by enhancing paracrine effects via cell-matrix interactions in vitro. The in vivo results showed that the change of microenvironment induced by surface-modified Ti implants promoted the adhesion, recruitment and proliferation of MSCs and facilitated coupled osteogenesis and angiogenesis in bone healing. The study proved that multilayer-film-coated Ti substrates positively mediated cellular biological function in vitro and improved bone healing in vivo.

STATEMENT OF SIGNIFICANCE

Recent studies have revealed that osteogenesis and angiogenesis are coupled, and that communication between osteoblasts and endothelial cells is essential for bone healing and remodeling processes; however, these conclusions only result from in vitro studies or in vivo studies using transgenic murine models. Relatively little is known about the communication between osteoblasts and endothelial cells in peri-implants during bone healing processes. Our results revealed the cellular/molecular mechanism of how multilayered Ti substrates mediate reciprocal paracrine effects between adipose-derived mesenchymal stem cells and human umbilical vein endothelial cells; moreover, the interactions between the cell-matrix and peri-implant was proven in vivo with enhanced bone healing. This study contributes to our understanding of the fundamental mechanisms of angiogenesis and osteogenesis that affect peri-implantation, and thus, provides new insights into the design of future high-quality orthopedic implants.

Quantitative Rheometry of Thin Soft Materials Using the Quartz Crystal Microbalance with Dissipation

In the inertial limit, the resonance frequency of the quartz crystal microbalance (QCM) is related to the coupled mass on the quartz sensor through the Sauerbrey expression that relates the mass to the change in resonance frequency. However, when the thickness of the film is sufficiently large, the relationship becomes more complicated and both the frequency and damping of the crystal resonance must be considered. In this regime, a rheological model of the material must be used to accurately extract the adhered film's thickness, shear modulus, and viscoelastic phase angle from the data. In the present work we examine the suitability of two viscoelastic models, a simple Voigt model ( Physica Scripta 1999, 59, 391-396) and a more realistic power-law model ( Langmuir 2015, 31, 4008-4017), to extract the rheological properties of a thermoresponsive hydrogel film. By changing temperature and initial dry film thickness of the gel, the operation of QCM was traversed from the Sauerbrey limit, where viscous losses do not impact the frequency, through the regime where the QCM response is sensitive to viscoelastic properties. The density-shear modulus and the viscoelastic phase angle from the two models are in good agreement when the shear wavelength ratio, d/λ _n, is in the range of 0.05-0.20, where d is the film thickness and λ _n is the wavelength of the mechanical shear wave at the n^th harmonic. We further provide a framework for estimating the physical properties of soft materials in the megahertz regime by using the physical behavior of polyelectrolyte complexes. This provides the user with an approximate range of allowable film thicknesses for accurate viscoelastic analysis with either model, thus enabling better use of the QCM-D in soft materials research.

Growth-Factor-Releasing Polyelectrolyte Multilayer Films to Control the Cell Culture Environment

Polyelectrolyte multilayers (PEMs) are of great interest as cell culture surfaces because of their ability to modify topography and surface energy and release biologically relevant molecules such as growth factors. In this work, fibroblast growth factor 2 (FGF2) was adsorbed directly onto polystyrene, plasma-treated polystyrene, and glass surfaces with a poly(methacrylic acid) and poly-l-histidine PEM assembled above it. Up to 14 ng/cm² of FGF2 could be released from plasma-treated polystyrene surfaces over the course of 7 days with an FGF2 solution concentration of 100 μg/mL applied during the adsorption process. This release rate could be modulated by adjusting the adsorption concentration, decreasing to as low as 2 ng/cm² total release over 7 days using a 12.5 μg/mL FGF2 solution. The surface energy and roughness could also be regulated using the adsorbed PEM. These properties were found to be substrate- and first-layer-dependent, supporting current theories of PEM assembly. When released, FGF2 from the PEMs was found to significantly enhance fibroblast proliferation as compared to culture conditions without FGF2. The results showed that growth factor release profiles and surface properties are easily controllable through modification of the PEM assembly steps and that these strategies can be effectively applied to common cell culture surfaces to control the cell fate.

Cell Guidance on Nanostructured Metal Based Surfaces

Metal surface nanostructuring to guide cell behavior is an attractive strategy to improve parts of medical implants, lab-on-a-chip, soft robotics, self-assembled microdevices, and bionic devices. Here, we discus important parameters, relevant trends, and specific examples of metal surface nanostructuring to guide cell behavior on metal-based hybrid surfaces. Surface nanostructuring allows precise control of cell morphology, adhesion, internal organization, and function. Pre-organized metal nanostructuring and dynamic stimuli-responsive surfaces are used to study various cell behaviors. For cells dynamics control, the oscillating stimuli-responsive layer-by-layer (LbL) polyelectrolyte assemblies are discussed to control drug delivery, coating thickness, and stiffness. LbL films can be switched "on demand" to change their thickness, stiffness, and permeability in the dynamic real-time processes. Potential applications of metal-based hybrids in biotechnology and selected examples are discussed.

Regulation of Cell Signaling Factors Using PLGA Nanoparticles Coated/Loaded with Genes and Proteins for Osteogenesis of Human Mesenchymal Stem Cells

Transfection of specific genes and transportation of proteins into cells have been a focus of stem cell differentiation research. However, it is not easy to regulate codelivery of a gene and a protein into cells. For codelivery into undifferentiated cells (human mesenchymal stem cells (hMSCs)), we used biodegradable carriers loaded with Runt-related transcription factor 2 (RUNX2) protein and coated with bone morphogenetic protein 2 (BMP2) plasmid DNA (pDNA) to induce osteogenesis. The released gene and protein were first localized in the cytosol of transfected hMSCs, and the gene then moved into the nucleus. The levels of internalized PLGA nanoparticles were tested using different doses and incubation durations. Then, transfection of BMP2 pDNA was confirmed by determining mRNA and protein levels and acquiring cell images. The same techniques were used to assess osteogenesis of hMSCs both in vitro and in vivo upon internalization of PLGA NPs carrying the BMP2 gene and RUNX2 protein. Detection of specific genes and proteins demonstrated that cells transfected with PLGA NPs carrying both the BMP2 gene and RUNX2 protein were highly differentiated compared with other samples. Histological and immunofluorescence analyses demonstrated that transfection of PLGA nanoparticles carrying both the BMP2 gene and RUNX2 protein dramatically enhanced osteogenesis of hMSCs.