Alginate: properties and biomedical applications

Hydrogels for biomedical applications.

Hydrophilic polymers are the center of research emphasis in nanotechnology because of their perceived “intelligence”. They can be used as thin films, scaffolds, or nanoparticles in a wide range of biomedical and biological applications. Here we highlight recent developments in engineering uncrosslinked and crosslinked hydrophilic polymers for these applications. Natural, biohybrid, and synthetic hydrophilic polymers and hydrogels are analyzed and their thermodynamic responses are discussed. In addition, examples of the use of hydrogels for various therapeutic applications are given. We show how such systems’ intelligent behavior can be used in sensors, microarrays, and imaging. Finally, we outline challenges for the future in integrating hydrogels into biomedical applications.

/pdf/hydrogels-in-biology-and-medicine-from-molecular-principles-3lowrzjjsl.pdf

Hydrogels in Biology and Medicine: From Molecular Principles to Bionanotechnology†

We have used the pH-induced self-assembly of a peptide-amphiphile to make a nanostructured fibrous scaffold reminiscent of extracellular matrix. The design of this peptide-amphiphile allows the nanofibers to be reversibly cross-linked to enhance or decrease their structural integrity. After cross-linking, the fibers are able to direct mineralization of hydroxyapatite to form a composite material in which the crystallographic c axes of hydroxyapatite are aligned with the long axes of the fibers. This alignment is the same as that observed between collagen fibrils and hydroxyapatite crystals in bone.

http://science.sciencemag.org/content/sci/294/5547/1684.full.pdf

Self-assembly and mineralization of peptide-amphiphile nanofibers

Hydrogel delivery systems can leverage therapeutically beneficial outcomes of drug delivery and have found clinical use. Hydrogels can provide spatial and temporal control over the release of various therapeutic agents, including small-molecule drugs, macromolecular drugs and cells. Owing to their tunable physical properties, controllable degradability and capability to protect labile drugs from degradation, hydrogels serve as a platform in which various physiochemical interactions with the encapsulated drugs control their release. In this Review, we cover multiscale mechanisms underlying the design of hydrogel drug delivery systems, focusing on physical and chemical properties of the hydrogel network and the hydrogel-drug interactions across the network, mesh, and molecular (or atomistic) scales. We discuss how different mechanisms interact and can be integrated to exert fine control in time and space over the drug presentation. We also collect experimental release data from the literature, review clinical translation to date of these systems, and present quantitative comparisons between different systems to provide guidelines for the rational design of hydrogel delivery systems.

/pdf/designing-hydrogels-for-controlled-drug-delivery-3k03j5j2j9.pdf

Designing hydrogels for controlled drug delivery.

Single implantation of microencapsulated islets into rats with streptozotocin-induced diabetes corrected the diabetic state for 2 to 3 weeks. The microencapsulated islets remained morphologically and functionally intact throughout long-term culture studies lasting over 15 weeks.

https://science.sciencemag.org/content/sci/210/4472/908.full.pdf

Microencapsulated islets as bioartificial endocrine pancreas

Two experiments were conducted to examine the efficacy of microencapsulation of bovine spermatozoa for use in artificial insemination. In Exp. 1, sperm were encapsulated at three different concentrations (45, 90 and 180 X 10(6) sperm/ml) in either .75- or 1.5-mm (diameter) microcapsules and incubated in vitro for 24 h at 37 C. Unencapsulated samples of each concentration served as controls. Capsule contents were evaluated for percentage of sperm motility and intact acrosomes at 2, 12 and 24 h of incubation. Capsule fragility was evaluated after 24 h incubation. Viability of spermatozoa was not influenced by sperm concentration or capsule size, and compared with controls, cellular injury after encapsulation was not apparent. Fragility of capsules was unaffected by capsule size; however, as the sperm concentration increased, integrity of the capsules decreased (P less than .05). In Exp. 2, using frozen-thawed semen, the effect of egg yolk content, presence of glycerol and viability of spermatozoa on the success of microencapsulation was measured. The extender was 2.9% sodium citrate with glycerol (7% v/v) and either 0, 5, 10 or 15% egg yolk (v/v). Uniformity of capsules in size and shape was evaluated subjectively. Capsule integrity and uniformity were unaffected by glycerol, sperm viability or egg yolk level up to 10% v/v; however, encapsulation of spermatozoa in 15%-yolk buffer increased the heterogeneity in capsule size and shape. Viability of encapsulated spermatozoa was maximal for extenders containing 10 or 15% yolk v/v. Reduced viability for the 5% yolk extender was due to pre-encapsulation injury associated with freezing. Microencapsulation procedures are compatible with sperm viability and can be adapted to an acceptable extender system used in artificial insemination.

Microencapsulation of Bovine Spermatozoa

Microencapsulation of living cells and tissues. 1983 review and update

This report deals with the primary problem in cardiac transplantation, homograft rejection, in its acute and chronic forms. Experience is drawn from 125 orthotopic cardiac transplants in dogs and from 4 human cases. The electrocardiogram is the most reliable indicator of an impending rejection crisis; elevation of lactic dehydrogenase (LDH) isozymes may add confirmation. Treatment of the rejection crisis requires transiently high doses of prednisone in addition to maintenance doses of azathioprine. Experimental data suggest the additional value of graft irradiation. The acute pathologic process is characterized early by infiltration with mononuclear cells. These cells are associated with injury to vascular endothelium which results in interstitial hemorrhage and edema and anoxic injury to the muscle fibers. The chronic form of rejection is manifested by coronary arterial narrowing due to intimai proliferation or thrombus formation, which results presumably from immunologic damage to the endothelium.

Franklin Lim

Papers

Microencapsulated islets as bioartificial endocrine pancreas

Microencapsulation of Bovine Spermatozoa

Microencapsulation of living cells and tissues. 1983 review and update

Rejection of the cardiac transplant

Microencapsulated islets in diabetic rats.