Functional analysis of bioactivated and antiinfective PDLLA – coated surfaces

Abstract

Common scaffold surfaces such as titanium can have side effects; for example, infections, cytotoxicity, impaired osseointegration, or low regeneration rates for bone tissue. These effects lead to poor implant integration or even implant loss. Therefore, bioactive implants are promising instruments in tissue regeneration. Osteoinductive elements-such as growth factors and anti-infectives-support wound healing and bone growth and thereby enable faster osseointegration, even in elderly patients. In this study, titanium surfaces were coated with a poly-(d,l-lactide) (PDLLA) layer containing different concentrations of copolymer-protected gene vectors (COPROGs) to locally provide bone morphogenetic protein-2 (BMP-2) or activated anti-infective agents, such as chlorhexidine gluconate, triclosan, and metronidazole, to prevent peri-implantitis. The coated titanium implants were then loaded with osteoblasts, NIH 3T3 fibroblasts, and human mesenchymal stem cells in 96-well plates. When shielded by COPROGs as a protective layer and resuspended in PDLLA, BMP-2-encoding pDNA at relatively low doses (5.63 µg/implant) induced the local expression of BMP-2. A linear dose dependence, which is common for recombinant growth factors, was not found, probably due to the retention property of the PDLLA surface. PDLLA, in general, successfully retains additional elements, such as osteoconductive growth factors (BMP-2) and anti-infective agents, which was demonstrated using metronidazole, and thus prevents the systemic application of excessive doses. These bioactive implant surfaces that provide the local release of therapeutic gene vectors or anti-infective agents allow the controlled stimulation of the implant and scaffold osseointegration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1672-1683, 2017.

Comparative analysis of bone regeneration behavior using recombinant human BMP‐2 versus plasmid DNA of BMP‐2

“…Under the assumption that previous in vitro results are transferable to in vivo findings, we found that this limited expression level seems to be sufficient to induce NB, because of endogenous BMP‐2 release by nontransfected cells via the paracrine stimulation of cells by the gene‐activated surface within the initial 14 days postsurgery. By the gene therapeutic approach, transgene‐derived low amounts of BMP2 are produced after local transfection of cells which then can activate additional endogenous BMP2 production in non‐transfected target cells …”

“…This transfection process, however, leads to a cascade of cell differentiation and mitosis of transfected osteoprogenitor cells, which thereby enhances GF release over a longer period of time (for detailed data, please refer to Ref. ). Endogenous BMP‐2 expression, evoked by gene vectors, is more physiological in terms of, for example, host‐specific glycosylation, because of de novo synthesis by local host cells …”

“…RhBMP‐2 and pBMP‐2 have been widely investigated in preclinical settings and proven to influence osteogenesis positively by stimulating local cell growth and differentiation, although in different ways. Basing our work on previous studies in vivo and in vitro concerning the optimization of applied doses, we have now applied rhBMP‐2 and pBMP‐2 in mandibular critical size defects (CSD) of Sprague–Dawley rats and evaluated bone regeneration after four different time points. The aim of this study has been to generate and compare two different bone‐inducing surface coatings based on BMP‐2 as an osteoinductive GF in an attempt to solve the problem as to which is better: proteins or genes.…”

Biomaterial substrate modifications that influence cell-material interactions to prime cellular responses to nonviral gene delivery

“…Similar to chemical modifications, physical modifications of the substrate impact cell-material interactions by altering the interface, yet maintain bulk material properties such as biocompatibility and hardness. Physical characteristics of the substrate have been shown to affect cellular adhesion, spreading, migration, proliferation, and morphology, presumably by spatially confining adsorbed ECM proteins and cells 40,96…”

“…For example, some applications include coating a vascular stent with poly(lactic-co-glycolic acid) (PLGA) bilayer nanoparticles and DNA encoding vascular endothelial growth factor to prevent restenosis, 34 loading a collagen patch with bPEI and DNA encoding platelet-derived growth factor-BB to increase wound healing, 35 or coating a titanium (Ti) bone implant with poly-(d,l-lactide) and polymer vectors complexed with DNA plasmids encoding bone morphogenetic protein-2 (BMP-2) to encourage osseointegration. 36 To use a cell-material interface to prime cells for more efficient transfection, substrate properties can be tuned through chemical modifications such as the addition of natural coatings, ligands, or functional side groups, and/or physical modifications such as topography or stiffness. The cell-material interface is known to influence cell behaviors that are innately controlled by the extracellular matrix (ECM) proteins 37 that adsorb onto a culture surface or exist natively in tissue.…”