Covalently grafted BMP-7 peptide to reduce macrophage/monocyte activity: an in vitro study on cobalt chromium alloy.

Cobalt chromium (CoCr) alloy is widely used in orthopedic implants but its functional longevity is susceptible to inflammation related complications. Reduction of the development of chronic inflammation on the biomaterial surface would enhance direct bone-implant bonding and improve implant survival and long-term results. The BMP-7 peptide was derived from the knuckle epitope of bone morphogenic protein-7 (BMP-7) and was conjugated via a cysteine amino acid at the N-terminus. Mouse RAW 264.7 monocytes/macrophages were seeded on the CoCr substrates and inflammation was induced via lipopolysaccharide (LPS) challenge. The effects of BMP-7 peptide on inflammation were evaluated by measuring the expression of inflammatory markers like toll-like receptor-4 (TLR-4), tumor necrosis factor-α (TNF-α), and monocyte chemotactic protein-1 (MCP-1). ELISA and qPCR assays were used to study the inflammatory signals. BMP-7 signaling pathway activation was shown by the presence of phosphorylation of Smad1/5/8. Utilizing the reactivity of polydopamine films to immobilize BMP-7 peptide onto metal substrates may provide a promising approach for applications in situations where reduction of inflammation around implants would be beneficial in improving surgical outcome, bone healing, and implant integration.

Surface modification of titanium with curcumin: a promising strategy to combat fibrous encapsulation.

Fibrous encapsulation that prevents the direct contact between an implant and the bone can cause implant failure. However, prevention of fibrous encapsulation is difficult because of the lack of effective strategies which can selectively control the growth of fibroblasts and osteoblasts. Because curcumin, an extract from Curcuma longa, was recently found to reduce the formation of fibrous tissue, it is hypothesized that loading curcumin on implant surfaces would be efficacious in inhibiting fibrous encapsulation without adversely affecting the osteoblast functions. To prove this hypothesis, curcumin was loaded on to a titanium surface using poly(dopamine) as an anchor, and the behaviors of fibroblasts and osteoblasts on these curcumin-modified surfaces were investigated. Curcumin was successfully loaded on to titanium and showed a low release after incubation in phosphate-buffered saline for seven days. On the curcumin-modified surfaces, fibroblast proliferation was suppressed, and fibrous marker expressions as well as collagen synthesis were significantly reduced. These reductions were possibly because of the enhancement of fibroblast apoptosis induced by the surface curcumin. In contrast, no significant reduction in osteoblast functions was observed on the curcumin-modified substrates. These findings may provide a promising solution to reduce fibrous encapsulation, and thus may be highly beneficial for orthopaedic applications.

Accelerated bone growth in vitro by the conjugation of BMP2 peptide with hydroxyapatite on titanium alloy.

Titanium alloys have been widely used in orthopedic practice due to their inherent bioactivity, however it is still insufficient to truly and reliably incorporate into living bone. In this work, polydopamine film was employed to induce the growth of hydroxyapatite (HA) on titanium alloy to enhance its osteoconductivity. Bone morphogenetic protein-2 (BMP2) peptide was absorbed into the HA particles for osteoinductivity. The precipitation of HA and the existence of BMP2 peptide were examined by X-ray diffraction, X-ray photoelectron spectroscopy and fluorescence microscopy. The dissolution of HA and the release of BMP2 peptide were monitored by measuring the concentrations of calcium ions and BMP2 peptide in phosphate buffered saline solution, respectively. The effect of BMP2 peptide incorporated into HA coating on bone growth was evaluated in vitro by cell culture tests, including cell attachment, alkaline phosphatase (ALP) activity, and gene expression. The results show that the HA particles grown on the substrate are mediated by the polydopamine film. The BMP2 peptide is distributed uniformly on HA-coated substrate and released in a sustained manner. Moreover, the conjunction of HA and BMP2 peptide increases cell adhesion, ALP activity and gene expression of osteogenic markers, which are potentially useful in the development of enhanced orthopedic medical devices.

Anti-fibrosis effect of BMP-7 peptide functionalization on cobalt chromium alloy.

Orthopedic metallic prosthetic implants are commonly made of cobalt chromium (CoCr) alloys. However, such metal-based implants are susceptible to fibrous capsule formation on the implant surface after implantation. At the bone-implant interface, this capsule can prevent implant integration, resulting in loosening and failure. Minimizing the development of such a capsule on the CoCr surface would improve direct bone-implant bonding leading to long-term implant functionality. We evaluated the anti-fibrosis effect of bone morphogenic protein-7 (BMP-7) peptide covalently bonded to CoCr alloy. This peptide, a biomimetic derivation of the knuckle epitope of BMP-7, was conjugated at the N-terminus with a cysteine amino acid. X-ray photoelectron spectroscopy (XPS) and probe binding assay were used to evaluate different stages of grafting and surface functionalization using polydopamine coating. Cellular functions were studied using fibroblast attachment, cell proliferation, and MTT assays. Fibroblasts were grown on functionalized and pristine CoCr substrates, and the efficacy of BMP-7 peptide on anti-fibrosis was analyzed via gene expression and protein expression of fibrosis markers ACTA2, Collagen 1A1, and fibronectin. The peptide functionalized substrates showed significant reduction of fibrosis markers expression after 1 week of incubation compared to controls. BMP-7 signaling pathway activation was shown by the presence of phosphorylation of Smad1/5/8. These findings may contribute to the improvement of CoCr implants in orthopedic surgery applications.

Collagen grafted 3D polycaprolactone scaffolds for enhanced cartilage regeneration.

Current surgical and repair treatments for articular cartilage defects still do not give satisfactory long-term results. Scaffold-based tissue engineering is the subject of much intensive interest. However, one major hurdle is that it is unable to accurately replicate the internal three dimensional (3D) microstructure of cartilage. In this work, a novel electrohydrodynamic printing (E-Jetting) technique was employed to fabricate 3D polycaprolactone (PCL) scaffolds, followed by collagen grafting mediated by polydopamine. Surface topography, chemical composition, and wettability of the scaffolds before and after surface functionalization were characterized. Porcine chondrocytes were seeded within the scaffolds for chondrogenesis evaluation. The results showed that a 3D PCL scaffold with controlled fibre diameter, orientation, and pore size was fabricated by the E-Jetting system. The surface functionalization made the PCL scaffold hydrophilic and favourable for cell attachment. The chondrocytes maintained their healthy phenotypes within the collagen grafted PCL scaffold. The increased production of sulfated glycosaminoglycan and highly expressed collagen type II demonstrated that collagen had a positive role in stimulating chondrogenesis and the collagen grafted PCL scaffold was effective in cartilage regeneration.

In vitro characterizations of mesoporous hydroxyapatite as a controlled release delivery device for VEGF in orthopedic applications.

Following bone implant surgery, prolonged ischemic conditions at the implant site often result in postsurgical complications like failure of osseointegration at the bone-implant interface which can lead to implant failure. Thus, restoration of the vascular supply is paramount to the proper development of the bone. High surface area mesostructured materials have been shown to be attractive candidates for bone regeneration to enhance cell adhesion and cell proliferation. This study uses hydroxyapatite, a naturally occurring mineral in the bone, fabricated to a range of suitable pore sizes, infused with vascular endothelial growth factor (VEGF), to be progressively released to stimulate revascularization. In this study, several characterizations including nitrogen adsorption analysis, Fourier-transformed infrared spectroscopy, X-ray diffraction, field emission scanning electron microscope, and transmission electron microscope were used to evaluate the synthesized mesoporous hydroxyapatite (MHA). The results showed that MHA can gradually release VEGF for enhancing revascularization, which is beneficial for orthopedic applications.

Cobalt chromium alloy with immobilized BMP peptide for enhanced bone growth.

Cobalt chromium (CoCr) alloys are widely used in orthopedic practice, however, lack of integration into the bone for long-term survival often occurs, leading to implant failure. Revision surgery to address such a failure involves increased risks, complications, and costs. Advances to enhancement of bone-implant interactions would improve implant longevity and long-term results. Therefore, we investigated the effects of BMP peptide covalently grafted to CoCr alloy on osteogenesis. The BMP peptide was derived from the knuckle epitope of bone morphogenic protein-2 (BMP-2) and was conjugated via a cysteine amino acid at the N-terminus. X-ray photoelectron spectroscopy and o-phthaldialdehyde were used to verify successful grafting at various stages of surface functionalization. Surface topography was evaluated from the surface profile determined by atomic force microscopy. Osteoblastic cells (MC3T3-E1) were seeded on the substrates, and the effects of BMP peptide on osteogenic differentiation were evaluated by measuring alkaline phosphatase (ALP) activity and calcium mineral deposition. The functionalized surfaces showed a twofold increase in ALP activity after 2 weeks incubation and a fourfold increase in calcium content after 3 weeks incubation compared to the pristine substrate. These findings are potentially useful in the development of improved CoCr implants for use in orthopedic applications.