Silk-elastinlike protein-based hydrogels for drug delivery and embolization.

Silk-Elastinlike Protein-Based Polymers (SELPs) can form thermoresponsive hydrogels that allow for the generation of in-situ drug delivery matrices. They are produced by recombinant techniques, enabling exact control of monomer sequence and polymer length. In aqueous solutions SELP strands form physical crosslinks as a function of temperature increase without the addition of crosslinking agents. Gelation kinetics, modulus of elasticity, pore size, drug release, biorecognition, and biodegradation of SELP hydrogels can be controlled by placement of amino acid residues at strategic locations in the polymer backbone. SELP hydrogels have been investigated for delivery of a variety of bioactive agents including small molecular weight drugs and fluorescent probes, oligomers of glycosaminoglycans, polymeric macromolecules, proteins, plasmid DNA, and viral gene delivery systems. In this review we provide a background for use of SELPs in matrix-mediated delivery and summarize recent investigations of SELP hydrogels for controlled delivery of bioactive agents as well as their use as liquid embolics.

Protein-based polymer liquid embolics for cerebral aneurysms.

Cerebral aneurysms (CA), an abnormal bulge in the arteries that supply blood to the brain, are prone to rupture and can cause hemorrhagic stroke. Physicians can treat CA by blocking blood flow to the aneurysmal sac via clipping of the aneurysm neck via open procedure, or endovascular occlusion of the aneurysm with embolic materials to promote thrombus formation to prevent further inflow of blood into the aneurysm. Endovascular treatment options for CA still have significant limitations in terms of safety, usability in coagulopathic patients, and risks of device migration. Bioactive embolic therapies, consisting of non-toxic bioresorbable materials that encourage the growth of neointima across the aneurysm neck, are needed to improve the healing of CA. In this work, the bioinspired silk-elastinlike protein-based polymer (SELP 815K), was used to embolize aneurysms in a rabbit elastase model. SELP 815K effectively embolized the model aneurysms in vivo, achieving >90% occlusion, using commercial microcatheters. No device-associated adverse effects were observed in any of the animals, and SELP 815K showed no cytotoxicity. SELP embolization did not show any deleterious effects to local tissues, and features consistent with reendothelialization of the aneurysm neck were noted in histological examination one-month post-embolization. SELP 815K shows promise as an embolic treatment for unruptured CA. STATEMENT OF SIGNIFICANCE: Unruptured cerebral aneurysms are present in approximately 3% of the population, with a fatality rate of up to 65% upon rupture. In this work a silk-elastinlike protein polymer (SELP) is explored as a liquid embolic for occlusion of cerebral aneurysms. This embolic exists as a liquid at room temperature before rapidly forming a gel at physiological temperature. This shape filling property was used to successfully occlude cerebral aneurysms in rabbits, with stable occlusion persisting for over thirty days. SELP occlusions show evidence for reendothelialization of the aneurysm sac and provide an opportunity for delivery of bioactive agents to further improve treatments.

An Oligomeric Sulfated Hyaluronan and Silk-Elastinlike Polymer Combination Protects against Murine Radiation Induced Proctitis.

Semisynthetic glycosaminoglycan ethers (SAGEs) are short, sulfated hyaluronans which combine the natural properties of hyaluronan with chemical sulfation. In a murine model, SAGEs provide protection against radiation induced proctitis (RIP), a side effect of lower abdominal radiotherapy for cancer. The anti-inflammatory effects of SAGE have been studied in inflammatory diseases at mucosal barrier sites; however, few mechanisms have been uncovered necessitating high throughput methods. SAGEs were combined with silk-elastinlike polymers (SELPs) to enhance rectal accumulation in mice. After high radiation exposure to the lower abdominal area, mice were followed for 3 days or until they met humane endpoints, before evaluation of behavioral pain responses and histological assessment of rectal inflammation. RNA sequencing was conducted on tissues from the 3-day cohort to determine molecular mechanisms of SAGE-SELP. After 3 days, mice receiving the SAGE-SELP combination yielded significantly lowered pain responses and amelioration of radiation-induced rectal inflammation. Mice receiving the drug-polymer combination survived 60% longer than other irradiated mice, with a fraction exhibiting long term survival. Sequencing reveals varied regulation of toll like receptors, antioxidant activities, T-cell signaling, and pathways associated with pain. This investigation elucidates several molecular mechanisms of SAGEs and exhibits promising measures for prevention of RIP.

Avian lungs: A novel scaffold for lung bioengineering.

Allogeneic lung transplant is limited both by the shortage of available donor lungs and by the lack of suitable long-term lung assist devices to bridge patients to lung transplantation. Avian lungs have different structure and mechanics resulting in more efficient gas exchange than mammalian lungs. Decellularized avian lungs, recellularized with human lung cells, could therefore provide a powerful novel gas exchange unit for potential use in pulmonary therapeutics. To initially assess this in both small and large avian lung models, chicken (Gallus gallus domesticus) and emu (Dromaius novaehollandiae) lungs were decellularized using modifications of a detergent-based protocol, previously utilized with mammalian lungs. Light and electron microscopy, vascular and airway resistance, quantitation and gel analyses of residual DNA, and immunohistochemical and mass spectrometric analyses of remaining extracellular matrix (ECM) proteins demonstrated maintenance of lung structure, minimal residual DNA, and retention of major ECM proteins in the decellularized scaffolds. Seeding with human bronchial epithelial cells, human pulmonary vascular endothelial cells, human mesenchymal stromal cells, and human lung fibroblasts demonstrated initial cell attachment on decellularized avian lungs and growth over a 7-day period. These initial studies demonstrate that decellularized avian lungs may be a feasible approach for generating functional lung tissue for clinical therapeutics.