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Our laboratory is currently exploring synthetic oligo(poly(ethylene glycol)fumarate) (OPF)-based biomaterials as a means to deliver fibroblasts to promote regeneration of central/partial defects in tendons and ligaments. In order to further modulate the swelling and degradative characteristics of OPF-based hydrogels, OPF crosslinking via a radically initiated, mixed-mode reaction involving poly(ethylene glycol) (PEG)-diacrylate and PEG-dithiol was investigated. Results demonstrate that mixed-mode hydrogels containing OPF can be formed and that the presence of 20 wt.% PEG-dithiol increases swelling and decreases degradation time vs. 10 wt.% PEG-dithiol and non-thiol-containing hydrogels (20% thiol fold swelling 28.7 ± 0.8; 10% thiol fold swelling 11.6 ± 1.4; non-thiol 8.7 ± 0.2; 20% thiol-containing hydrogels degrade within 15 days in vitro ). After encapsulation, tendon/ligament fibroblasts remained largely viable over 8 days of static culture. While the presence of PEG-dithiol did not significantly affect cellularity or collagen production within the constructs over this time period, image analysis revealed that the 20% PEG-dithiol gels did appear to promote cell clustering, with greater values for aggregate area observed by day 8. These experiments suggest that mixed-mode OPF-based hydrogels may provide an interesting alternative as a cell carrier for engineering a variety of soft orthopedic tissues, particularly for applications when it is important to encourage cell–cell contact.

Recently there has been an increased interest in the effects of paracrine signaling between groups of cells, particularly in the context of better understanding how stem cells contribute to tissue repair. Most current 3D co-culture methods lack the ability to effectively separate two cell populations after the culture period, which is important for simultaneously analyzing the reciprocal effects of each cell type on the other. Here, we detail the development of a 3D hydrogel co-culture system that allows us to culture different cell types for up to 7 days and subsequently separate and isolate the different cell populations using enzyme-sensitive glues. Separable 3D co-culture laminates were prepared by laminating PEG-based hydrogels with enzyme-degradable hydrogel adhesives. Encapsulated cell populations exhibited good segregation with well-defined interfaces. Furthermore, constructs can be separated on-demand upon addition of the appropriate enzyme, while cell viability remains high throughout the culture period, even after laminate separation. This platform offers great potential for a variety of basic cell signaling studies as the incorporation of an enzyme-sensitive adhesive interface allows the on-demand separation of individual cell populations for immediate analysis or further culture to examine persistence of co-culture effects and paracrine signaling on cell populations.

Computerized tomography (CT) was performed on 256 children with seizure disorders. The incidence of abnormal scans was closely related to seizure type, and permitted separation of patients into a low-yield and a high-yield group. Low-yield groups included children with idiopathic generalized seizures, children in whom both the neurologic examination and electroencephalogram (EEG) were normal, and children with a generalized seizure of unknown etiology in whom the neurologic examination and the EEG were normal. The high-yield groups included children with partial seizures with elementary symptomatology, partial seizures with complex symptomatology, generalized seizures with known etiology, neonates with seizures, and children whose seizures began as neonates. The overall incidence of abnormalities in the entire group was 33 percent. An abnormal neurologic examination increased the incidence of abnormal CT scans to 64 percent. EEGs were abnormal in 65 percent of the children, but only focal slowing resulted in a significant increase in the incidence of abnormal CT scans. Seven children (2.7 percent) had intracranial abnormalities requiring surgery. If the neurologic examination and EEG were normal, the yield of abnormal CT scans was only 5 percent of the total.