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Orthopedic implant failure has been attributed mainly to loosening of the implant from host bone, which may be due to poor bonding of the implant material to bone tissue, as well as to bacterial infection. One promising strategy to enhance tissue integration is to develop a selective biointeractive surface that simultaneously enhances bone cell function while decreasing bacterial adhesion. In this in vitro study, the surfaces of titanium alloy substrates were functionalized by first covalently grafting carboxymethyl chitosan (CMCS), followed by the conjugation of bone morphogenetic protein-2 (BMP-2) to the CMCS-grafted surface. Bacterial adhesion on the substrates was assayed with Staphylococcus aureus and Staphylococcus epidermidis . Cell functions were investigated using osteoblasts and human bone marrow-derived mesenchymal stem cells. The results showed that bacterial adhesion on both the CMCS and CMCS-BMP-2 functionalized surfaces was significantly reduced compared to that on the pristine substrates. In addition, the CMCS-BMP-2 modified substrates significantly promoted attachment, alkaline phosphatase activity, and calcium mineral deposition of both osteoblast and human bone marrow-derived mesenchymal stem cells. The achievement of the dual functions of bacterial adhesion reduction and cell function promotion by the CMCS-BMP-2 modified titanium substrates illustrates the good potential of such surfaces for enhancement of tissue integration and implant longevity.

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Adipose-derived stem cells (ADSCs) have great potential as a cell source for tissue engineering and regenerative medicine because they are easier to obtain, have lower donor-site morbidity and are available in larger numbers than stem cells harvested using bone marrow aspiration. Until now, little has been known about how nanotopography affects the proliferation and endothelial differentiation of ADSCs. In the present study, two nanograting substrates with a period (ridge and groove) of about 250 and 500 nm, respectively, were fabricated on quartz and their effect on ADSC fate was investigated. The results showed that proliferation of ADSCs on nanograting substrates decreased while cell attachment was not significantly affected compared to a flat substrate. Endothelial differentiation of ADSCs on both flat and nanograting substrates can be induced with vascular endothelial growth factor, as shown by immunofluorescent staining. Quantitative real-time PCR analysis showed significantly enhanced upregulation of vWF, PECAM-1 and VE-cadherin at the gene level by ADSCs on the nanograting substrates. In vitro angiogenesis assay on Matrigel showed that nanograting substrates enhanced capillary tube formation. This study highlights the beneficial influence of nanotopography on the differentiation of ADSC into endothelial cells which play an important role in vascularization.

Poly (lactic-co-glycolic acid) (PLGA) is a biodegradable polymer used to make resorbable sutures, and is also used in other applications in tissue engineering. Being an artificial polymer, its degradation rate can be tailored to suit its application. It can be easily moulded into structures with suitable mechanical strength and degrades into relatively harmless products in the body. Its adjustable degradation rate also makes it a potentially excellent controlled release delivery device. However, the functionalization of PLGA with bioactive molecules usually requires extensive chemical modification. Chemical modification may compromise the mechanical strength of PLGA and inactivate the bioactive molecules. In this paper, a study is done to investigate the coating of an angiogenic factor on unmodified PLGA suture substrates for the differentiation of human mesenchymal stem cells (hMSC) into endothelial cells (EC). The results show that the method used to anchor vascular endothelial growth factor (VEGF) onto the PLGA surface can enable the gradual release of VEGF from the substrate into solution to induce the differentiation of hMSCs into ECs. Thus, this method can potentially be used to coat PLGA materials like sutures, meshes and scaffolds, rendering them functional as effective controlled release delivery devices for a wide range of bioactive molecules.

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.

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.

Circulating progenitor cells are known to home to various organs to repair injured tissues or to routinely replace old cells and maintain tissue integrity. Similarly, circulating progenitor bone cells can possibly home to a bone implant, differentiate, and eventually osteointegrate with the prosthesis. Osteointegration of bone cells with the prosthesis can help to reduce the risk of implant failure due to constant movement between bone tissue and implant surface. In this study, we aim to investigate if immobilized bone morphogenetic protein-2 (BMP2) on chitosan-grafted titanium substrate (Ti-CS-BMP2) will enhance bone marrow-derived mesenchymal stem cell (BMMSC) adhesion onto the substrate surface and further induce their differentiation into osteoblasts. The results show that our Ti-CS-BMP2 substrate is able to retain adsorbed BMP2, and is capable of slow release of this growth factor. Despite the lesser number of BMMSCs initially attached onto the Ti-CS-BMP2 substrates and consequently the lower level of cell proliferation, Ti-CS-BMP2 cells had the highest level of ALP activity. RT-PCR results show that Ti-CS-BMP2 cells had a relatively higher level of transcription activity of Runx2, compared with that of bone cell-derived osteoblasts (BC-OB), an indication that the BMMSCs were actively differentiating into osteoblasts. Finally, alizarin red staining reveals the presence of calcium deposits in the differentiated cells. Hence our Ti-CS-BMP2 substrates possess an osteoconductive effect and can possibly be used to fabricate bone implants that can osteointegrate with host bone tissue.