Hybridization kinetics between immobilized double-stranded DNA probes and targets containing embedded recognition segments.

We have investigated the time-dependent strand displacement activity of several targets with double-stranded DNA probes (dsProbes) of varying affinity. Here, the relative affinity of various dsProbes is altered through choices in hybridization length (11-15 bases) and the selective inclusion of center mismatches in the duplexes. While the dsProbes are immobilized on microspheres, the soluble, 15 base-long complementary sequence is presented either alone as a short target strand or as a recognition segment embedded within a longer target strand. Compared to the short target, strand displacement activity of the longer targets is slower, but still successful. Additionally, the longer targets exhibit modest differences in the observed displacement rates, depending on the location of recognition segment within the long target. Overall, our study demonstrates that the kinetics of strand displacement activity can be tuned through dsProbe sequence design parameters and is only modestly affected by the location of the complementary segment within a longer target strand.

Biomimetic human skin model patterned with rete ridges.

Rete ridges consist of undulations between the epidermis and dermis that enhance the mechanical properties and biological function of human skin. However, most human skin models are fabricated with a flat interface between the epidermal and dermal layers. Here, we report a micro-stamping method for producing human skin models patterned with rete ridges of controlled geometry. To mitigate keratinocyte-induced matrix degradation, telocollagen-fibrin matrices with and without crosslinks enable these micropatterned features to persist during longitudinal culture. Our human skin model exhibits an epidermis that includes the following markers: cytokeratin 14, p63, and Ki67 in the basal layer, cytokeratin 10 in the suprabasal layer, and laminin and collagen IV in the basement membrane. We demonstrated that two keratinocyte cell lines, one from a neonatal donor and another from an adult diabetic donor, are compatible with this model. We tested this model using an irritation test and showed that the epidermis prevents rapid penetration of sodium dodecyl sulfate. Gene expression analysis revealed differences in keratinocytes obtained from the two donors as well as between 2D (control) and 3D culture conditions. Our human skin model may find potential application for drug and cosmetic testing, disease and wound healing modeling, and aging studies.

DNA density-dependent assembly behavior of colloidal micelles.

A key advantage of DNA-mediated colloidal assembly is the ability to tune the strength of adhesion between particles based on sequence characteristics. In the current study, we have investigated DNA-mediated assembly of polystyrene colloidal particles as a function of sequence length, sequence fidelity, and probe density for DNA sequences patterned from the Salmonella genome. The results of our work indicate that the density of DNA probe strands heavily influences the ability of immobilized sequences to hybridize between surfaces of bidisperse colloidal particles. Incubating suspensions at higher temperatures (to minimize secondary structures that might otherwise compromise duplex formation) was also found to have less effect than duplex density on DNA-mediated particle assembly. We believe these results may add to the understanding and design considerations of directed particle assembly using DNA hybridization, especially in the submicrometer and micrometer size regime.

Impact of Isolated Burns on Major Organs: A Large Animal Model Characterized.

Severe burn results in systemic inflammatory response syndrome (SIRS) and multiple organ dysfunction (MOD). Currently, large-animal models of burn-induced SIRS/MOD mostly use secondary insults resulting in a paucity of knowledge on the effect of burn alone on different organ systems. The objective of the current study was to develop and characterize a large animal model of burn-induced SIRS over the course of 2 weeks. Yorkshire swine (n = 16) were randomized to sham controls (n = 4) or 40% total body surface area contact burns (n = 6 at 2 and 14 days post-burn). Blood chemistry and complete blood count analyses were performed at baseline and post-burn days 1, 2, 3, 7, 10, and 14. Upon euthanasia, tissue samples were taken for histopathology. Burns were found to be full thickness and did not re-epithelialize. SIRS was evidenced by increased body temperature, respiration rate, pulse, and white blood cell count for the duration of the experiment. Both acute liver injury and acute kidney injury were induced as determined biochemically and histologically. Histology also revealed atelectasis of the lungs which was associated with increased myeloperoxidase activity. Intestinal structure as well as enterocyte homeostasis was also disrupted. All of these organ abnormalities recovered to varying degrees by 14 days post-burn. We report a unique reproducible large animal model of burn-induced SIRS that can be tailored to specific organ systems for investigation into potential immunomodulatory interventions that prevent organ failure or promote organ recovery after burn injury.

Biopolymer/Calcium phosphate scaffolds for bone tissue engineering.

With nearly 30 years of progress, tissue engineering has shown promise in developing solutions for tissue repair and regeneration. Scaffolds, together with cells and growth factors, are key components of this development. Recently, an increasing number of studies have reported on the design and fabrication of scaffolding materials. In particular, inspired by the nature of bone, polymer/ceramic composite scaffolds have been studied extensively. The purpose of this paper is to review the recent progress of the naturally derived biopolymers and the methods applied to generate biomimetic biopolymer/calcium phosphate composites as well as their biomedical applications in bone tissue engineering.

Ontology analysis of global gene expression differences of human bone marrow stromal cells cultured on 3D scaffolds or 2D films.

Differences in gene expression of human bone marrow stromal cells (hBMSCs) during culture in three-dimensional (3D) nanofiber scaffolds or on two-dimensional (2D) films were investigated via pathway analysis of microarray mRNA expression profiles. Previous work has shown that hBMSC culture in nanofiber scaffolds can induce osteogenic differentiation in the absence of osteogenic supplements (OS). Analysis using ontology databases revealed that nanofibers and OS regulated similar pathways and that both were enriched for TGF-ß and cell-adhesion/ECM-receptor pathways. The most notable difference between the two was that nanofibers had stronger enrichment for cell-adhesion/ECM-receptor pathways. Comparison of nanofibers scaffolds with flat films yielded stronger differences in gene expression than comparison of nanofibers made from different polymers, suggesting that substrate structure had stronger effects on cell function than substrate polymer composition. These results demonstrate that physical (nanofibers) and biochemical (OS) signals regulate similar ontological pathways, suggesting that these cues use similar molecular mechanisms to control hBMSC differentiation.

Using double-stranded DNA probes to promote specificity in target capture.

The most prevalent nucleic acid detection schemes employ single-stranded sequences as probes for capture and detection of oligonucleotide targets in solution. In these systems elevated temperature conditions are generally used to enhance specificity and limit false positives from occurring with mismatched targets. In contrast, the current study uses a strand displacement approach between soluble targets and double-stranded DNA probes (dsProbes) immobilized on microspheres. In our approach the displacement of reporter strands from the dsProbes by the target of interest is promoted by the affinity differences between the reporter strand and the soluble DNA or RNA targets for the immobilized sequences. While displacement activity occurred readily in center mismatched dsProbes with a weaker intrinsic affinity, incorporating a two base-long single-stranded segment at the free end of the immobilized dsProbes resulted in target discrimination not observed for dsProbes possessing only a center mismatch.