Search

Although tissue engineering has been attracted greatly for healing of critical-sized bone defects, great efforts for improvement are still being made in scaffold design. In particular, bone regeneration would be enhanced if a scaffold precisely matches the contour of bone defects, especially if it could be implanted into the human body conveniently and safely. In this study, polyurethane/hydroxyapatite-based shape memory polymer (SMP) foam was fabricated as a scaffold substrate to facilitate bone regeneration. The minimally invasive delivery and the self-fitting behavior of the SMP foam were systematically evaluated to demonstrate its feasibility in the treatment of bone defects in vivo. Results showed that the SMP foam could be conveniently implanted into bone defects with a compact shape. Subsequently, it self-matched the boundary of bone defects upon shape-recovery activation in vivo. Micro-computed tomography determined that bone ingrowth initiated at the periphery of the SMP foam with a constant decrease towards the inside. Successful vascularization and bone remodeling were also demonstrated by histological analysis. Thus, our results indicate that the SMP foam demonstrated great potential for bone regeneration.

Major challenges in traditional wound closure methods (e.g. using sutures and skin staplers) remain inadequately unaddressed; these invasive treatments induce extra puncture wounds, anesthetic side effects, and severe scarring. Herein, an oxidized starch/gelatin-based shape memory hydrogel (OSG) was fabricated as a self-contracting wound dressing to facilitate noninvasive wound closure. The self-contracting properties were attributed by introducing crosslink net-points in the hydrogel polymer structure through Schiff base reaction between oxidized starch (OS) and gelatin. We systematically investigated the self-contracting properties to determine the feasibility of the hydrogel to treat wounds and promote wound closure noninvasively. Following elongation, OSGs could be entirely fixed in a temporary shape at 4 °C, and then contracted under infrared irradiation (IR) for shape memory activation near human physiological temperature (38 °C), providing sufficient recovery force (4 kPa) for successful noninvasive wound closure. Additionally, H&E staining revealed that thicker epidermis and dermis layers were achieved upon OSG treatment, confirming that the OSG facilitated tissue reconstruction in an in vivo rabbit model. Moreover, the OSG-treated wounds displayed smoother skin and no visible scarring compared to sutured wounds. Such excellent performance suggests that OSG hydrogel exhibits high potential as an alternative to medical sutures to facilitate noninvasive would closure.

A major complication of cortical bone grafting is nonunion at the host-graft junction. Many factors are thought to be involved in successful engraftment including the quality of the graft and the host response to it. In particular, the recipient osteoclasts (OCs) play a critical role by resorbing the engrafted bone. Thus, effective engraftment may depend on the inherent biological properties of the bone graft, which subsequently correlates with early and effective OC resorption. Normally, bone grafts are stored and processed by freezing, freeze-drying, irradiation, and lipid extraction. We sought to determine whether processing and storage affected bone quality, as evaluated by OC bone resorption. Cortical bone specimens from six human donors were either fresh, frozen at -75 degrees C, or had undergone combinations of freezing at -75 degrees C, freeze-drying, lipid extraction, irradiation, and treatment with hydrogen peroxide. Bone slices of 0.5-mm thickness taken from the surface, beneath the surface, and at a depth of 7.5 mm were incubated with isolated rabbit OCs and resorption lacunae were measured. We observed highest OC activity with fresh bone followed by frozen, partially processed, and fully processed bone. When allografts were stored at -75 degrees C for 12 months, there was up to a 4.2-fold reduction in OC activity on the surface layer. Additionally, we found reduced OC activity upon the outer surface bone compared to the inner layers. Removal of more than 0.5 mm of frozen and processed bone significantly improved OC activity. These results imply that inner bone layers of stored and processed bone allografts are protected against degradation of bone matrix components, except when frozen for extended periods of time. Taken together, these data suggest that bone allografts should be stored for less than 1 year and require the removal of at least 0.5 mm from their surface prior to transplantation.

In mouse bone marrow cultures, the formation of osteoclast-like, that is, tartrate-resistant acid phosphatase-positive (TRAP+) and calcitonin (CT) receptor-positive multinucleated cells (MNCs), induced by 10(-10) to 10(-8) mol/L 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3], could be augmented by triiodothyronine (T3), which alone had no effect on osteoclast-like cell formation. The permissive effect of T3 increased the response to 1alpha,25(OH)2D3 by approximately one order of magnitude. Linear concentration dependence was observed between 10(-11) and 10(-8) mol/L T3. Importantly, inhibition of prostaglandin synthesis by indomethacin significantly impeded osteoclast-like cell formation by 1alpha,25(OH)2D3 and abrogated the effect of T3 thereon. Basal interleukin-6 (IL-6) production by cultured marrow cells was significantly stimulated by 1alpha,25(OH)2D3. However, even at an exceedingly high concentration of 20 ng/mL, IL-6 was ineffective in inducing osteoclast-like cell formation. Therefore, any hormonally induced rise in IL-6 release from bone marrow cells could not account for the observed changes in TRAP+ MNC numbers. Nevertheless, the stimulatory effect of 1alpha,25(OH)2D3 on osteoclastogenesis was partially dependent on IL-6 because it could be significantly blocked by a neutralizing monoclonal anti-IL-6 antibody, and to the same extent by a monoclonal anti-IL-6 receptor antibody. Unimpaired signaling through the IL-6/IL-6R system is also a prerequisite for the auxiliary effect of T3 on induction of osteoclast-like cells by 1alpha,25(OH)2D3. Our data provide evidence that 1alpha,25(OH)2D3 induces osteoclast-like cell formation, at least in part, in an IL-6-dependent mode of action, which is also subject to modulation by T3. The mechanism of interaction of the two hormones apparently involves joint stimulation of prostaglandin synthesis.

Amylin is a secretory product of pancreatic beta-cells which shares major sequence homology with calcitonin gene-related peptide. In neonatal mouse calvaria maintained in organ culture for 72 h, amylin inhibited basal (i.e., unstimulated) resorption in medium concentrations above 2.5 x 10(-9) M. In addition, amylin (> or = 1.0 x 10(-7) M) in a calcitonin-like fashion transiently inhibited bone resorption induced by 1.0 x 10(-8) M PTH ("escape phenomenon"). Pretreatment of calvarial bones with amylin (1.0 x 10(-8) - 1.0 x 10(-6) M) for 72 h attenuated the subsequent response to 1.0 x 10(-8) M PTH. Changes in location and appearance of osteoclasts in amylin-treated bones, as visualized by light microscopy, suggest that amylin inhibits bone resorption by causing a loss of specialized contact zones to the mineralized matrix in resorbing osteoclasts, and in addition, by preventing retraction of osteoblasts from the mineralized surface which impedes attachment of osteoclasts thereon.

Kurzbeschreibung: Einleitung: Die ausgepragten Beschwerden der Patienten und die damit verbundenen hohen Kosten fur das Gesundheitssystem nach traumatischen Knochenverletzungen, Osteoporose oder osteolytischen Knochenmetastasen, unterstreichen die Wichtigkeit der Entwicklung neuer Ansatze in der Knochenwiederherstellung. Bei groseren Knochenverlusten ist es notwendig Knochentransplantate beziehungsweise Knochenersatzmaterialien einzusetzen. Viele fuhren jedoch zu verschiedenen Komplikationen wie, unter anderem, Reaktionen des Immunsystems, Abstosung und auf diesem Weg ubertragbaren Infektionskrankheiten. Es ist notwendig, neue Strategien in der Knochenregeneration zu entwickeln. Um optimale Regeneration zu gewahrleisten, mussen die Eigenschaften der neuen Knochenersatzmaterialien vollstandig geklart sein. Ziel der Studie: Untersuchung der Faktoren, die in die Anhaftung an und die Reaktion von Osteoklasten (OC) auf mineralisierte Substrate beeinflussen, um die besten Bedingungen fur die fruhen Stadien der Knochenregeneration zu schaffen. Methoden: OC aus Kaninchen oder aus muriner Cokultur von OB mit OC-Vorstufen aus dem Knochenmark, wurden auf Knochen, Elfenbein, Koralle, Muschelschalen und Glas kultiviert. Die Organisation des Zytoskeletts wurde bei verschiedenen Temperaturbehandlungen der Substrate (auser Glas) bei 50°C, 200°C, 400° oder 600°C analysiert. Durch die Temperaturbehandlung wurden Modifikationen der Zusammensetzung der Substrate, wie Proteingehalt oder kristalliner Struktur, erreicht. Die Zellen wurden nach der Kultur auf den jeweiligen Substraten fixiert und das Aktin-haltige Zytoskelett wurde durch Rhodamin-Phalloidin mittels Fluoreszenzmikroskopie sichtbar gemacht. Resultat: Unabhangig von der Temperaturbehandlung, wurden keine schadigenden Effekte der Substrate (Aragonit, Calcit, Perlmutt, Knochen, Elfenbein) auf OC festgestellt. Interessanterweise, hafteten OC stark an Knochen, Elfenbein und den anderen kalzifizierten Substraten, unabhangig von geandertem Proteingehalt oder modifizierter kristalliner Struktur. OC entwickelten auf allen Substraten (ebenfalls unabhangig von der Temperaturbehandlung) Sealing zones, mit Ausnahme der Glasoberflachen, die als Kontrolle dienten. Bemerkenswerterweise wurden „podosomen belts“ auf allen Substraten, inklusive Knochen, entdeckt. Diese Entdeckung widerspricht fruheren Untersuchungen, nach denen „podosomen belts“ nicht auf Knochen erscheinen. Zusammengefasst zeigen die Ergebnisse, dass der Ausloseimpuls fur die Bildung von Sealing zones durch OC weder Apatit noch Kalziumphosphat ist. Kalziumkarbonat ist ausreichend um die Entstehung von Sealing zones zu ermoglichen. Schlussfolgerung: Die Substrate Aragonit, Calcit und Perlmutt sind in ahnlicher Weise wie Knochen von OC abbaubar, eine Erkenntnis die in die Entwicklung neuer Knochenersatzmaterialien einfliesen sollte. Offenlegung von Interessenskonflikten: Keine

The adenylate cyclase activator forskolin (1–10 μmol L ) inhibited 45 Ca release from parathyroid hormone (PTH; 10 nmol L ) stimulated prelabeled neonatal mouse calvaria in short term culture (24 h). This effect of forskolin was potentiated by rolipram, Ro 20-1724, and isobutyl-methylxanthine, three structurally different inhibitors of cyclic AMP phosphodiesterase. Forskolin (10 μmol L ) and calcitonin (30 mU/mL) inhibited the mobilization of stable calcium and inorganic phosphate as well as the release of the lysomal enzymes beta-glucuronidase and beta-N-acetylglucosaminidase from PTH-stimulated unlabeled bones. Osteoclasts in PTH-stimulated calvaria showed active ruffled borders with numerous membrane infoldings. Treatment of PTH-stimulated bones with forskolin and calcitonin resulted in a rapid (2 h) loss of the active ruffled border. In addition, forskolin and calcitonin induced similar changes with respect to the number and size distribution of cytoplasmic vesicles in PTH-activated osteoclasts. After 24 h, all signs of osteoclast inactivation were still prominent, whereas after 48 h of treatment with forskolin or calcitonin, the reappearance of a ruffled border on a number of osteoclasts signaled an escape from the inhibitory action of both calcitonin or forskolin. These data indicate that forskolin inhibits bone resorption by a cyclic AMP dependent mechanism and that the effect of forskolin and calcitonin on bone resorption and osteoclast morphology are comparable. These observations lend further support to the view that cyclic AMP may be an intracellular mediator of the inhibitory action of calcitonin on multinucleated osteoclasts.