Macroporous hydrogels upregulate osteogenic signal expression and promote bone regeneration.

The objective of this work was to investigate the effects of macroporous hydrogel architecture on the osteogenic signal expression and differentiation of human mesenchymal stem cells (hMSCs). In particular, we have proposed a tissue engineering approach for orbital bone repair based on a cyclic acetal biomaterial formed from 5-ethyl-5-(hydroxymethyl)-beta,beta-dimethyl-1,3-dioxane-2-ethanol diacrylate (EHD) and poly(ethylene glycol) diacrylate (PEGDA). The EHD monomer and PEGDA polymer may be fabricated into macroporous EH-PEG hydrogels by radical polymerization and subsequent porogen leaching, a novel technique for hydrophilic gels. We hypothesized that EH-PEG hydrogel macroporosity facilitates intercellular signaling among hMSCs. To investigate this phenomenon, hMSCs were loaded into EH-PEG hydrogels with varying pore size and porosity. The viability of hMSCs, the expression of bone morphogenetic protein-2 (BMP-2), BMP receptor type 1A, and BMP receptor type 2 by hMSCs, and the differentiation of hMSCs were then assessed. Results demonstrate that macroporous EH-PEG hydrogels support hMSCs and that this macroporous environment promotes a dramatic increase in BMP-2 expression by hMSCs. This upregulation of BMP-2 expression is associated by a more rapid hMSC differentiation, as measured by alkaline phosphatase expression. Altering hMSC interactions with the EH-PEG hydrogel surface, by the addition of fibronectin, did not appear to augment BMP-2 expression. We therefore speculate that EH-PEG hydrogel macroporosity facilitates autocrine and paracrine signaling by localizing endogenously expressed factors within the hydrogel's pores and thus promotes hMSC osteoblastic differentiation and bone regeneration.

The Regulatory Perspectives on Endoscopic Devices for Obesity.

The recent increase in US Food and Drug Administration-approved weight-loss devices has diversified obesity treatment options. The regulatory pathways for endoscopically placed weight-loss devices and considerations for clinical trials are discussed, including the benefit-risk paradigm intended to aid in weight-loss-device trial development. Also discussed is the benefit-risk analysis of recently approved endoscopic devices. A strategic priority of the FDA Center for Devices and Radiological Health is to increase the use of patient input in decision making. Thus, we consider how endoscopic weight-loss devices with profiles similar to those that have been approved may be viewed in a patient preference study.

Distribution and accumulation of 10 nm silver nanoparticles in maternal tissues and visceral yolk sac of pregnant mice, and a potential effect on embryo growth.

We examined the distribution of silver in pregnant mice and embryos/fetuses following intravenous injections of 10 nm silver nanoparticles (AgNPs) or soluble silver nitrate (AgNO3) at dose levels of 0 (citrate buffer control) or 66 µg Ag/mouse to pregnant mice on gestation days (GDs) 7, 8 and 9. Selected maternal tissues and all embryos/fetuses from control, AgNP- and AgNO3-treated groups on GD10 and control and AgNP-treated groups on GD16 were processed for the measurement of silver concentrations, intracellular AgNP localization, histopathology and gross examination of tissue morphology. Inductively-coupled plasma mass spectrometry revealed silver in all examined tissues following either AgNP or AgNO3 treatment, with highest concentrations of silver in maternal liver, spleen and visceral yolk sac (VYS), and lowest concentrations in embryos/fetuses. For VYS, mean silver concentration following AgNO3 treatment (4.87 ng Ag/mg tissue) was approximately two-fold that following AgNP treatment (2.31 ng Ag/mg tissue); for all other tissues examined, mean silver concentrations following either AgNP or AgNO3 treatment were not significantly different from each other (e.g. 2.57 or 2.84 ng Ag/mg tissue in maternal liver and 1.61 or 2.50 ng Ag/mg tissue in maternal spleen following AgNP or AgNO3 treatment, respectively). Hyperspectral imaging revealed AgNP aggregates in maternal liver, kidney, spleen and VYS from AgNP-treated mice, but not AgNO3-treated mice. Additionally, one or more embryos collected on GD10 from eight of ten AgNP-treated mice appeared small for their age (i.e. Theiler stage 13 [GD8.5] or younger). In the control group (N = 11), this effect was seen in embryos from only one mouse. In conclusion, intravenous injection of 10 nm AgNPs to pregnant mice resulted in notable silver accumulation in maternal liver, spleen and VYS, and may have affected embryonic growth. Silver accumulation in embryos/fetuses was negligible.

Macroporous hydrogel scaffolds and their characterization by optical coherence tomography.

A simple porogen-leaching method to fabricate macroporous cyclic acetal hydrogel cell scaffolds is presented. Optical coherence tomography (OCT) was applied for nondestructive imaging and quantitative characterization of the scaffold structures. High-resolution OCT reveals the microstructures of the engineered tissue scaffolds in three dimensions. It also enables subsequent image processing to investigate quantitatively several key morphological design parameters for macroporous scaffolds, including the volume porosity, pore interconnectivity, and pore size. Two image-processing algorithms were adapted: three-dimensional labeling was applied to assess the interconnectivity, and erosion was applied to assess the pore size. Scaffolds with different design parameters were imaged, characterized, and compared. OCT imaging and image processing successfully discriminated scaffolds made from different formulations in terms of volume porosity, interconnectivity, and pore size. The cell viability and their spread across the scaffolds were confirmed by the fluorescence microscopy co-registered with OCT.

Challenges associated with regeneration of orbital floor bone.

Orbital floor fractures are a serious consequence of craniofacial trauma and account for ∼60%-70% of all orbital fractures. Unfortunately, the body's natural response to orbital floor defects generally may not restore proper function and facial aesthetics, which is complicated by the thin bone and adjacent sinuses. Current clinical treatments include alloplastic implants and autologous grafts; however, each has associated disadvantages and sequelae. This review has outlined necessary components for a successful tissue-engineered construct for orbital floor repair. In addition, current successes and progress in the literature specific to orbital floors and craniofacial research have been reviewed. Finally, challenges and future directions have been described.

Cyclic acetal hydroxyapatite nanocomposites for orbital bone regeneration.

We have incorporated hydroxyapatite nanoparticles within cyclic acetal hydrogels to create nanocomposites that can be used to repair surgically created orbital floor defects in a rabbit animal model. Nanosized hydroxyapatite particles may improve tissue engineering scaffold properties because they have similar length scale of many cellular and molecular components and therefore can enhance cellular adhesion and migration. We hypothesize that inclusion of nanosized hydroxyapatite particles (20-70 nm) within cyclic acetal hydrogels would support bone defect repair. The objectives of our study include (1) characterization of nanocomposites in vitro, (2) investigation of tissue response and capsule tissue surrounding nanocomposites in vivo, and (3) investigation of the potential of nanocomposites to facilitate bone formation at 7- and 28-day time points in vivo. Experimental nanocomposite groups consisted of 0, 10, and 50 ng/mL nanosized hydroxyapatite. In vitro results indicated uniform dispersion of nanoparticles within nanocomposites and increased compressive moduli of nanocomposites with increase in nanoparticle concentration and bone marrow stromal cell viability within nanocomposites. In vivo results at day 7 indicated a tissue response of mild to increased inflammatory cells and presence of immature fibrous tissue. At day 28, tissue response consisted of mild inflammatory response and mature tissue. Quantitative results at day 7 indicated no difference in total bone percentage area between groups. The results also indicated that the tissue capsule surrounding the 0, 10, and 50 ng group implants had no clear organization. Quantitative results at day 28 indicated that the tissue capsule surrounding the 0, 10, and 50 ng group implants was an organized layer and the bone percentage for the 50 ng group was significantly higher than that of the remaining groups. Initial results indicated that our nanocomposites initiate a positive in vivo response in terms of bone growth. However, the percentage of bone area compared with the total area was low at both time points. Thus, in our study, even after addition of nanoparticles to cyclic acetal hydrogels, their biocompatible properties were maintained. On the other hand, addition of nanoparticles to cyclic acetal hydrogels did not lead to complete restoration of orbital floor defects.

Osteogenic differentiation of bone marrow stromal cells induced by coculture with chondrocytes encapsulated in three-dimensional matrices.

Endochondral ossification implicates chondrocyte signaling as an important factor in directing the osteogenic differentiation of mesenchymal stem cells in vivo. In this study, the osteoinductive capabilities of articular chondrocytes suspended in alginate hydrogels were analyzed via coculture with bone marrow stromal cells (BMSCs). In particular, the effect of chondrocyte coculture time on the mechanism underlying this osteogenic induction was examined. Chondrocytes were suspended in alginate beads and cultured above BMSCs in monolayer. Beads containing chondrocytes were removed after 1, 10, or 21 days of coculture. Quantitative reverse transcriptase polymerase chain reaction was used to assess the expression of alkaline phosphatase, bone morphogenetic protein-2, and osteocalcin by BMSCs after days 1, 8, 14, and 21. Calcium deposition was also assayed to characterize the extent of mineralization within cultures. Results indicate that osteogenic differentiation of BMSCs is initiated upon brief exposure to chondrocyte signaling, but requires continued exposure in order to progress fully and maintain an osteoblastic phenotype.

Tissue response and orbital floor regeneration using cyclic acetal hydrogels.

Orbital floor injuries are a common form of traumatic craniofacial injury that may not heal properly through the body's endogenous response. Reconstruction is often necessary, and an optimal method does not exist. We propose a tissue engineering approach for orbital bone repair based upon a cyclic acetal biomaterial formed from 5-ethyl-5-(hydroxymethyl)-beta,beta-dimethyl-1,3-dioxane-2-ethanol diacrylate (EHD) and poly(ethylene glycol) diacrylate (PEGDA). The EHD monomer and PEGDA polymer may be fabricated into an EH-PEG hydrogel by radical polymerization. The objectives of this work were to study (1) the tissue response to EH-PEG hydrogels in an orbital bone defect and (2) the induction of bone formation by delivery of bone morphogenetic protein-2 (BMP-2) from EH-PEG hydrogels. EH-PEG hydrogels were fabricated and implanted into an 8-mm rabbit orbital floor defect. Experimental groups included unloaded EH-PEG hydrogels, and EH-PEG hydrogels containing 0.25 microg and 2.5 microg BMP-2/implant. Results demonstrated that the unloaded hydrogel was initially bordered by a fibrin clot and then by fibrous encapsulation. BMP-2 loaded EH-PEG hydrogels, independent of concentration, were surrounded by fibroblasts at both time points. Histological analysis also demonstrated that significant bone growth was present at the 2.5 microg BMP-2/implant group at 28 days. This work demonstrates that the EH-PEG construct is a viable option for use and delivery of BMP-2 in vivo.

Cyclic acetal hydrogel system for bone marrow stromal cell encapsulation and osteodifferentiation.

Many systems have been proposed for the encapsulation of bone marrow stromal cells (BMSCs) within degradable hydrogels. Here, we use a novel cyclic acetal-based biomaterial formed from 5-ethyl-5-(hydroxymethyl)-beta,beta-dimethyl-1,3-dioxane-2-ethanol diacrylate (EHD) and poly(ethylene glycol) diacrylate (PEGDA). A cyclic acetal-based hydrogel may be preferred as cyclic acetals hydrolytically degraded into diols and carbonyls as primary degradation products, which may not affect local acidity, unlike other widely investigated polymers. The EHD monomer and PEGDA polymer may be fabricated into a EH-PEG hydrogel by radical polymerization initiated by the ammonium persulfate (APS) and N,N,N',N'-tetramethylethylenediamine (TEMED) system. The objective of this work is to determine whether the components utilized in the fabrication of EH-PEG hydrogels as well as the EH-PEG hydrogels permit BMSC viability, metabolic activity, and osteodifferentiation. Cell viability and metabolic activity were assessed after 30 min, 1 h, and 3 h of exposure to pertinent concentrations of the initiator system (10-20 mM). Osteodifferentiation was assessed by alkaline phosphatase and osteocalcin expression after a short exposure to the initiator system to simulate the encapsulation process. Lastly, cell viability was assessed immediately after encapsulation and after 7 days of culture within the EH-PEG hydrogels. Results indicate that the metabolic activity and viability of BMSCs are minimally affected, and that osteodifferentiation is not significantly affected by the APS-TEMED initiator system. Also, encapsulated BMSCs maintained viability within EH-PEG hydrogels for 7 days. This work demonstrates that the EH-PEG hydrogel is a viable option for the encapsulation and osteodifferentiation of BMSCs.