Diffusion in the extracellular space (ECS) of the brain is constrained by the volume fraction and the tortuosity and a modified diffusion equation represents the transport behavior of many molecule...

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Diffusion in brain extracellular space.

To better direct repair following spinal cord injury (SCI), we designed an implant modeled after the intact spinal cord consisting of a multicomponent polymer scaffold seeded with neural stem cells. Implantation of the scaffold–neural stem cells unit into an adult rat hemisection model of SCI promoted long-term improvement in function (persistent for 1 year in some animals) relative to a lesion-control group. At 70 days postinjury, animals implanted with scaffold-plus-cells exhibited coordinated, weight-bearing hindlimb stepping. Histology and immunocytochemical analysis suggested that this recovery might be attributable partly to a reduction in tissue loss from secondary injury processes as well as in diminished glial scarring. Tract tracing demonstrated corticospinal tract fibers passing through the injury epicenter to the caudal cord, a phenomenon not present in untreated groups. Together with evidence of enhanced local GAP-43 expression not seen in controls, these findings suggest a possible regeneration component. These results may suggest a new approach to SCI and, more broadly, may serve as a prototype for multidisciplinary strategies against complex neurological problems.

https://www.pnas.org/content/pnas/99/5/3024.full.pdf

Functional recovery following traumatic spinal cord injury mediated by a unique polymer scaffold seeded with neural stem cells.

https://ir.ymlib.yonsei.ac.kr/bitstream/22282913/144077/1/T200207005.pdf

Functional recovery following traumatic spinal cord injury mediated by a unique polymer scaffold seeded with neural stem cells

The role of porous media in modeling flow and heat transfer in biological tissues

Diffusion plays a crucial role in brain function The spaces between cells can be likened to the water phase of a foam and many substances move within this complicated region Diffusion in this interstitial space can be accurately modelled with appropriate modifications of classical equations and quantified from measurements based on novel micro-techniques Besides delivering glucose and oxygen from the vascular system to brain cells, diffusion also moves informational substances between cells, a process known as volume transmission Deviations from expected results reveal how local uptake, degradation or bulk flow may modify the transport of molecules Diffusion is also essential to many therapies that deliver drugs to the brain The diffusion-generated concentration distributions of well-chosen molecules also reveal the structure of brain tissue This structure is represented by the volume fraction (void space) and the tortuosity (hindrance to diffusion imposed by local boundaries or local viscosity) Analysis of these parameters also reveals how the local geometry of the brain changes with time or under pathological conditions Theoretical and experimental approaches borrow from classical diffusion theory and from porous media concepts Earlier studies were based on radiotracers but the recent methods use a point-source paradigm coupled with micro-sensors or optical imaging of macromolecules labelled with fluorescent tags These concepts and methods are likely to be applicable elsewhere to measure diffusion properties in very small volumes of highly structured but delicate material

https://iopscience.iop.org/article/10.1088/0034-4885/64/7/202/pdf

Diffusion and related transport mechanisms in brain tissue

A biocompatible heterogeneous hydrogel of poly [N-(2-hydroxypropyl) methacrylamide] (PHPMA), was evaluated for its ability to promote tissue repair and enhance axonal regrowth across lesion cavities in the brain and spinal cord in adult and juvenile (P17 P21) rats. Incorporation of PHPMA hydrogels into surrounding host tissue was examined at the ultrastructural level and using immunohistochemical techniques. In addition, and in parallel to these studies, diffusion parameters (volume fraction and tortuosity of the gel network) of the PHPMA hydrogels were evaluated pre- to postimplantation using an in vivo real-time iontophoretic method. The polymer hydrogels were able to bridge tissue defects created in the brain or spinal cord, and supported cellular ingrowth, angiogenesis, and axonogenesis within the structure of the polymer network. As a result, a reparative tissue grew within the porous structure of the gel, composed of glial cells, blood vessels, axons and dendrites, and extracellular biological matrices, such as laminin and/or collagen. Consistent with matrix deposition and tissue formation within the porous structure of the PHPMA hydrogels, there were measurable changes in the diffusion characteristics of the polymers. Extracellular space volume decreased and tortuosity increased within implanted hydrogels, attaining values similar to that seen in developing neural tissue. PHPMA polymer hydrogel matrices thus show neuroinductive and neuroconductive properties. They have the potential to repair tissue defects in the central nervous system by replacing lost tissue and by promoting the formation of a histotypic tissue matrix that facilitates and supports regenerative axonal growth. () ()

Neural tissue formation within porous hydrogels implanted in brain and spinal cord lesions: ultrastructural, immunohistochemical, and diffusion studies.

Diffusion constraints and neuron-glia interaction during aging.

‘The definitive version is available at www3.interscience.wiley.com '. Copyright Wiley-Liss, Inc. DOI: 10.1002/hipo.1101 [Full text of this article is not available in the UHRA]

Z. Simonova

Papers

Neural tissue formation within porous hydrogels implanted in brain and spinal cord lesions: ultrastructural, immunohistochemical, and diffusion studies.

Diffusion constraints and neuron-glia interaction during aging.

Learning deficits in aged rats related to decrease in extracellular volume and loss of diffusion anisotropy in hippocampus.

Postnatal hypobaric hypoxia in rats impairs water maze learning and the morphology of neurones and macroglia in cortex and hippocampus

Astrocytes, oligodendroglia, extracellular space volume and geometry in rat fetal brain grafts