Intraluminal Guiding Structure of Nerve Conduits for Peripheral Nerve Regeneration

Peripheral nerve injury that can lead to disability affects millions of people worldwide annually. As the gold standard treatment of peripheral nerve injury, autologous nerve grafts are the most widely used and effective, but the clinical application of the treatment is greatly limited by many disadvantages. Tissue engineering nerve conduits gradually become promising autologous nerve grafts alternatives to promote the regeneration of injured nerves. This review places emphasis on tissue engineering designs of physical and topographic guiding structure inside nerve conduits in order to promote the migration of Schwann cells and directional regrowth of axons towards target organs. Various strategies of intraluminal guiding cues have been described and analyzed, including the incorporation with the tissue with natural basement membrane, collagen, microfilaments, intraluminal multi-channel and grooves in the inner wall. Recently, much progress has been made in the development of tissue engineering nerve conduits, but poor curative effect and deficiencies such as axon dispersion and malposition healing still remain unsolved, many crucial factors need to be considered in further research before clinical practices.

Membranous glomerulonephritis

It has been clear for several decades from comparison with the rodent model disease Heymann nephritis that membranous glomerulonephritis (MGN) is an immune condition in which antibodies, usually autoantibodies, bind to targets on the surface of podocytes. However, the antigen in Heymann nephritis, megalin, is not present on human podocytes. The first potential antigen was identified by studying rare examples of maternal alloimmunization, leading to congenital membranous nephropathy in the infant caused by antibodies to neutral endopeptidase. More recently, the target of autoantibody formation in most patients with primary MGN has been identified to be the phospholipase A2 receptor, PLA2R. Genome-wide association studies identify predisposing genetic loci at HLADQ and at the locus encoding the autoantigen itself. So antibodies to at least two different molecular targets can cause MGN, and it seems likely that there may be other targets in secondary types of MGN, and possibly haptenized or otherwise modified molecules are implicated in drug- and toxin-induced MGN. Once antibodies are fixed, animal models and human observations suggest that complement is involved in mediating tissue damage. However, immunoglobulin G4, not thought to fix complement, is the predominant isotype in human MGN, and the mechanisms are not fully unravelled. Podocyte injury is known to cause proteinuria. In MGN, antibody fixation or cell damage may stimulate production of extracellular matrix to account for the increased GBM thickness with ‘podocyte type’ basement membrane collagen isoforms, and ultimately cell death and glomerulosclerosis.

Combinatorial Tissue Engineering Partially Restores Function after Spinal Cord Injury

Hydrogel scaffolds provide a beneficial microenvironment in transected rat spinal cord. A combinatorial biomaterials based strategy provided a microenvironment that facilitated regeneration while reducing foreign body reaction to the 3-dimensional spinal cord construct. We used poly lactic-co-glycolic acid microspheres to provide sustained release of rapamycin from Schwann cell (SC)-loaded, positively charged oligo-polyethylene glycol fumarate scaffolds. Three dose formulations of rapamycin were compared to controls in 53 rats. We observed a dose-dependent reduction in the fibrotic reaction to the scaffold and improved functional recovery over 6 weeks. Recovery was replicated in a second cohort of 28 animals that included retransection injury. Immunohistochemical and stereological analysis demonstrated that blood vessel number, surface area, vessel diameter, basement membrane collagen, and microvessel phenotype within the regenerated tissue was dependent on the presence of SCs and rapamycin. TRITC-dextran injection demonstrated enhanced perfusion into scaffold channels. Rapamycin also increased the number of descending regenerated axons, as assessed by Fast Blue retrograde axonal tracing. These results demonstrate that normalization of the neovasculature was associated with enhanced axonal regeneration and improved function after spinal cord transection.