Surface functionalization of nanoporous alumina with bone morphogenetic protein 2 for inducing osteogenic differentiation of mesenchymal stem cells

Dopamine/DOPAC-assisted immobilization of bone morphogenetic protein-2 loaded Heparin/PEI nanogels onto three-dimentional printed calcium phosphate ceramics for enhanced osteoinductivity and osteogenicity

Nowadays, the three-dimensional (3D) printed calcium phosphate (CaP) ceramics have well-designed geometric structure, but suffer from relative weak osteoinductivity. Surface modification by incorporating bone morphogenetic protein-2 (BMP2) onto scaffolds is considered as an efficient approach to improve their bioactivity. However, high dose and uncontrolled burst release of BMP2 may cause undesired side effect. In the present study, porous BCP ceramics with inverse face-centred cube structure prepared by digital light processing (DLP)-based 3D printing technique were used as the substrates. BMP2 proteins were loaded in the self-assembled Heparin/PEI nanogels (NP/BMP2), and then immobilized onto BCP substrates through the intermediate mussel-derived bioactive dopamine and dihydroxyphenylacetic acid (DA/DOPAC) coating layers to construct functional BCP/layer/NP/BMP2 scaffolds. Our results showed that Heparin/PEI nanogel was a potent delivery system for BMP2, and BCP/layer/NP/BMP2 scaffolds exhibited the high loading capacity, controlled release rate, and sustained local delivery of BMP2. In vitro cell experiments with bone marrow stromal cells (BMSCs) found that BCP/layer/NP/BMP2 could promote cell proliferation, facilitate cell spreading, accelerate cell migration, up-regulate expression of osteogenic genes, and improve synthesis of osteoblast-related proteins. Moreover, the murine intramuscular implantation model suggested that BCP/layer/NP/BMP2 had a superior osteoinductive capacity, and the rat femoral condyle defect repair model showed that BCP/layer/NP/BMP2 could enhance in situ bone repair and regeneration. These findings demonstrate that the incorporation of BMP2 loaded Heparin/PEI nanogels to 3D printed scaffolds holds great promise in fabricating bone graft with a superior biological performance for orthopedic application.

Application of BMP in Bone Tissue Engineering

At present, bone nonunion and delayed union are still difficult problems in orthopaedics. Since the discovery of bone morphogenetic protein (BMP), it has been widely used in various studies due to its powerful role in promoting osteogenesis and chondrogenesis. Current results show that BMPs can promote healing of bone defects and reduce the occurrence of complications. However, the mechanism of BMP in vivo still needs to be explored, and application of BMP alone to a bone defect site cannot achieve good therapeutic effects. It is particularly important to modify implants to carry BMP to achieve slow and sustained release effects by taking advantage of the nature of the implant. This review aims to explain the mechanism of BMP action in vivo, its biological function, and how BMP can be applied to orthopaedic implants to effectively stimulate bone healing in the long term. Notably, implantation of a system that allows sustained release of BMP can provide an effective method to treat bone nonunion and delayed bone healing in the clinic.

Mesoporous Hydroxyapatite Nanoparticles Mediate the Release and Bioactivity of BMP-2 for Enhanced Bone Regeneration

Efficient delivery of bone morphogenetic protein-2 (BMP-2) with desirable bioactivity is still a great challenge in the field of bone regeneration. In this study, a silk fibroin/chitosan scaffold incorporated with BMP-2-loaded mesoporous hydroxyapatite nanoparticles (mHANPs) was prepared (SCH-L). BMP-2 was preloaded onto mHANPs with a high surface area before mixing with a silk fibroin/chitosan composite. Bare (without BMP-2) silk fibroin/chitosan/mHANP (SCH) scaffolds and SCH scaffolds with directly absorbed BMP-2 (SCH-D) were investigated in parallel for comparison. In vitro release kinetics indicated that BMP-2 released from the SCH-L scaffold showed a significantly lower initial burst release, followed by a more sustained release over time than the SCH-D scaffold. In vitro cell viability, osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), and the in vivo osteogenic effect of scaffolds in a rat calvarial defect were evaluated. The results showed that compared with bare SCH and SCH-D scaffolds, the SCH-L scaffold significantly promoted the osteogenic differentiation of BMSCs in vitro and induced more pronounced bone formation in vivo. Further studies demonstrated that the mHANP-mediated satisfactory conformational change and sustained release benefited the protection of the released BMP-2 bioactivity, as confirmed by alkaline phosphatase (ALP) activity and a mineralization deposition assay. More importantly, the interaction of BMP-2/mHANPs enhanced the binding ability of BMP-2 to cellular receptors, thereby maintaining its biological activity in osteogenic differentiation and osteoinductivity well, which contributed to the markedly promoted in vitro and in vivo osteogenic efficacy of the SCH-L scaffold. Taken together, these results provide strong evidence that mHANPs represent an attractive carrier for binding BMP-2 to scaffolds. The SCH-L scaffold shows promising potential for bone tissue regeneration applications.

Culture of dental pulp stem cells on nanoporous alumina substrates modified by carbon nanotubes

PURPOSE

Alumina substrates are one of the commonly used scaffolds applied in cell culture, but in order to prevent formation of biofilm on the alumina substrate, these substrates are modified with carbon nanotube.

METHODS

The alumina substrate was made by a two-step anodization method and was then modified with carbon nanotubes by simple chemical reaction. The substrates were characterized with FTIR, SEM, EDX, 3D laser scanning digital microscope, contact angle (CA) and surface free energy (SFE). To determine how this modification influences the reduction of biofilm, biofilm of two various bacteria, Escherichia coli (E.coli) and Staphylococcus aureus (S. aureus), were investigated.

RESULTS

The biofilm on the modified substrate decreased due to the presence of carbon nanotubes and increased antibacterial properties. Dental pulp stem cells (DPSCs) were cultured onto flat alumina (FA) and nanoporous alumina-multiwalled carbon nanotubes (NAMC) substrates to examine how the chemical modification and surface topography affects growth of DPSCs.

CONCLUSION

Cell attachment and proliferation were investigated with SEM and Presto Blue assay, and the findings show that the NAMC substrates are suitable for cell culture.

Enhancement in sustained release of antimicrobial peptide and BMP-2 from degradable three dimensional-printed PLGA scaffold for bone regeneration

One of the goals of bone tissue engineering is to create scaffolds with well-defined, inter-connected pores, excellent biocompatibility and osteoinductive ability. Three-dimensional (3D)-printed polymer scaffold coated with bioactive peptide are an effective approach to fabricating ideal bone tissue engineering scaffolds for bone defect repair. However, the current strategy of adding bioactive peptides generally cause degradation to the polymer materials or damage the bioactivity of the biomolecules. Thus, in this study, we used a biomimetic process via poly(dopamine) coating to prepare functional 3D PLGA porous scaffolds with immobilized BMP-2 and ponericin G1 that efficiently regulate the osteogenic differentiation of preosteoblasts (MC3T3-E1) and simultaneously inhibit of pathogenic microbes, thereby enhancing biological activity. In this study, we analysed a 3D PLGA porous scaffold by scanning electron microscopy, water contact angle measurements, and materials testing. Subsequently, we examined the adsorption, release and in vitro antimicrobial activity of the 3D PLGA. Surface characterization showed that poly(dopamine) surface modification could more efficiently mediate the immobilization of BMP-2 and ponericin G1 onto the scaffold surfaces than physical adsorption, and that ponericin G1-immobilized 3D PLGA scaffolds were able to maintain long-term antibacterial activity. We evaluated the influence on cell adhesion, proliferation and differentiation by culturing MC3T3-E1 cells on different modified 3D PLGA scaffolds in vitro. The biological results indicate that MC3T3-E1 cell attachment and proliferation on BMP-2/ponericin G1-immobilized 3D PLGA scaffolds were much higher than those on other groups. Calcium deposition, and gene expression results showed that the osteogenic differentiation of cells was effectively improved by loading the 3D PLGA scaffold with BMP-2 and ponericin G1. In summary, our findings indicated that the polydopamine-assisted surface modification method can be a useful tool for grafting biomolecules onto biodegradable implants, and the dual release of BMP-2 and ponericin G1 can enhance the osteointegration of bone implants and simultaneously inhibit of pathogenic microbes. Therefore, we conclude that the BMP-2/ponericin G1-loaded PLGA 3D scaffolds are versatile and biocompatible scaffolds for bone tissue engineering.

One of the goals of bone tissue engineering is to create scaffolds with well-defined, inter-connected pores, excellent biocompatibility and osteoinductive ability.

Collagen and fibronectin surface modification of nanoporous anodic alumina and macroporous silicon for endothelial cell cultures

BACKGROUND

The ability to direct the cellular response by means of biomaterial surface topography is important for biomedical applications. Substrate surface topography has been shown to be an effective cue for the regulation of cellular response. Here, the response of human aortic endothelial cells to nanoporous anodic alumina and macroporous silicon with collagen and fibronectin functionalization has been studied.

METHODS

Confocal microscopy and scanning electron microscopy were employed to analyse the effects of the material and the porosity on the adhesion, morphology, and proliferation of the cells. Cell spreading and filopodia formation on macro- and nanoporous material was characterized by atomic force microscopy. We have also studied the influence of the protein on the adhesion.

RESULTS

It was obtained the best results when the material is functionalized with fibronectin, regarding cells adhesion, morphology, and proliferation.

CONCLUSION

These results permit to obtain chemical modified 3D structures for several biotechnology applications such as tissue engineering, organ-on-chip or regenerative medicine.

Nano-Pore Size of Alumina Affects Osteoblastic Response

The rapid development and application of nanotechnology to biological interfaces has impacted the bone implant field, allowing researchers to finely modulate the interface between biomaterials and recipient tissues. In the present study, oxidative anodization was exploited to generate two alumina surfaces with different pore diameters. The former displayed surface pores in the mean range of 16-30 nm, while in the latter pores varied from to 65 to 89 nm. The samples were characterized by Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive X-ray spectroscopy (EDX) analysis prior to being tested with pre-osteoblastic MC3T3-E1 cells. In vitro cell response was studied in terms of early cell adhesion, viability, and morphology, including focal adhesion quantification. Both the alumina samples promoted higher cell adhesion and viability than the control condition represented by the standard culture dish plastic. Osteogenic differentiation was assessed through alkaline phosphatase activity and extracellular calcium deposition, and it was found that of the two nano-surfaces, one was more efficient than the other. By comparing for the first time two nano-porous alumina surfaces with different pore diameters, our data supported the role of nano-topography in inducing cell response. Modulating a simple aspect of surface texture may become an attractive route for guiding bone healing and regeneration around implantable metals.

Osteogenic differentiation of 3D cultured mesenchymal stem cells induced by bioactive peptides

OBJECTIVES

Bioactive peptides derived from receptor binding motifs of native proteins are a potent source of bioactive molecules that can induce signalling pathways. These peptides could substitute for osteogenesis promoting supplements. The work presented here compares three kinds of bioactive peptides derived from collagen III, bone morphogenetic protein 7 (BMP-7) and BMP-2 with their potential osteogenic activity on the model of porcine mesenchymal stem cells (pMSCs).

MATERIALS AND METHODS

pMSCs were cultured on electrospun polycaprolactone nanofibrous scaffolds with different concentrations of the bioactive peptides without addition of any osteogenic supplement. Analysis of pMSCs cultures included measurement of the metabolic activity and proliferation, immunofluorescence staining and also qPCR.

RESULTS

Results showed no detrimental effect of the bioactive peptides to cultured pMSCs. Based on qPCR analysis, the bioactive peptides are specific for osteogenic differentiation with no detectable expression of collagen II. Our results further indicate that peptide derived from BMP-2 protein promoted the expression of mRNA for osteocalcin (OCN) and collagen I significantly compared to control groups and also supported deposition of OCN as observed by immunostaining method.

CONCLUSION

The data suggest that bioactive peptide with an amino acid sequence of KIPKASSVPTELSAISTLYL derived from BMP-2 protein was the most potent for triggering osteogenic differentiation of pMSCs.

Biological responses to immobilized microscale and nanoscale surface topographies

Cellular responses are highly influenced by biochemical and biomechanical interactions with the extracellular matrix (ECM). Due to the impact of ECM architecture on cellular responses, significant research has been dedicated towards developing biomaterials that mimic the physiological environment for design of improved medical devices and tissue engineering scaffolds. Surface topographies with microscale and nanoscale features have demonstrated an effect on numerous cellular responses, including cell adhesion, migration, proliferation, gene expression, protein production, and differentiation; however, relationships between biological responses and surface topographies are difficult to establish due to differences in cell types and biomaterial surface properties. Therefore, it is important to optimize implant surface feature characteristics to elicit desirable biological responses for specific applications. The goal of this work was to review studies investigating the effects of microstructured and nanostructured biomaterials on in vitro biological responses through fabrication of microscale and nanoscale surface topographies, physico-chemical characterization of material surface properties, investigation of protein adsorption dynamics, and evaluation of cellular responses in specific biomedical applications.

Inkjet printed periodical micropatterns made of inert alumina ceramics induce contact guidance and stimulate osteogenic differentiation of mesenchymal stromal cells

Bioinert high performance ceramics exhibit detrimental features for implant components with direct bone contact because of their low osseointegrating capability. We hypothesized that periodical microstructures made of inert alumina ceramics can influence the osteogenic differentiation of human mesenchymal stromal cells (hMSC). In this study, we manufactured pillared arrays made of alumina ceramics with periodicities as low as 100μm and pillar heights of 40μm employing direct inkjet printing (DIP) technique. The response of hMSC to the microstructured surfaces was monitored by measuring cell morphology, viability and formation of focal adhesion complexes. Osteogenic differentiation of hMSCs was investigated by alkaline phosphatase activity, mineralization assays and expression analysis of respective markers. We demonstrated that MSCs react to the pillars with contact guidance. Subsequently, cells grow onto and form connections between the microstructures, and at the same time are directly attached to the pillars as shown by focal adhesion stainings. Cells build up tissue-like constructs with heights up to the micropillars resulting in increased cell viability and osteogenic differentiating properties. We conclude that periodical micropatterns on the micrometer scale made of inert alumina ceramics can mediate focal adhesion dependent cell adhesion and stimulate osteogenic differentiation of hMSCs.

Gelatin Tight-Coated Poly(lactide-co-glycolide) Scaffold Incorporating rhBMP-2 for Bone Tissue Engineering

Surface coating is the simplest surface modification. However, bioactive molecules can not spread well on the commonly used polylactone-type skeletons; thus, the surface coatings of biomolecules are typically unstable due to the weak interaction between the polymer and the bioactive molecules. In this study, a special type of poly(lactide-co-glycolide) (PLGA)-based scaffold with a loosened skeleton was fabricated by phase separation, which allowed gelatin molecules to more readily diffuse throughout the structure. In this application, gelatin modified both the internal substrate and external surface. After cross-linking with glutaraldehyde, the surface layer gelatin was tightly bound to the diffused gelatin, thereby preventing the surface layer gelatin coating from falling off within 14 days. After gelatin modification, PLGA scaffold demonstrated enhanced hydrophilicity and improved mechanical properties (i.e., increased compression strength and elastic modulus) in dry and wet states. Furthermore, a sustained release profile of recombinant human bone morphogenetic protein-2 (rhBMP-2) was achieved in the coated scaffold. The coated scaffold also supported the in vitro attachment, proliferation, and osteogenesis of rabbit bone mesenchymal stem cells (BMSCs), indicating the bioactivity of rhBMP-2. These results collectively demonstrate that the cross-linked-gelatin-coated porous PLGA scaffold incorporating bioactive molecules is a promising candidate for bone tissue regeneration.

Fabrication and characterization of silk fibroin/chitosan/Nano γ-alumina composite scaffolds for tissue engineering applications

A series of silk fibroin/chitosan/Nano γ-alumina composite scaffolds have been prepared using the lyophilization technique for tissue engineering. These were then characterized using SEM, XRD, EDX, FTIR and TGA.