Generation of Alginate Microspheres for Biomedical Applications

Summary

In the following sections, we outline procedures for the preparation of alginate microspheres for use in biomedical applications. We specifically illustrate a technique for creating multilayered alginate microspheres for the dual purpose of cell and protein encapsulation as a potential treatment for type 1 diabetes.

Abstract

Alginate-based materials have received considerable attention for biomedical applications because of their hydrophilic nature, biocompatibility, and physical architecture. Applications include cell encapsulation, drug delivery, stem cell culture, and tissue engineering scaffolds. In fact, clinical trials are currently being performed in which islets are encapsulated in PLO coated alginate microbeads as a treatment of type I diabetes. However, large numbers of islets are required for efficacy due to poor survival following transplantation. The ability to locally stimulate microvascular network formation around the encapsulated cells may increase their viability through improved transport of oxygen, glucose and other vital nutrients. Fibroblast growth factor-1 (FGF-1) is a naturally occurring growth factor that is able to stimulate blood vessel formation and improve oxygen levels in ischemic tissues. The efficacy of FGF-1 is enhanced when it is delivered in a sustained fashion rather than a single large-bolus administration. The local long-term release of growth factors from islet encapsulation systems could stimulate the growth of blood vessels directly towards the transplanted cells, potentially improving functional graft outcomes. In this article, we outline procedures for the preparation of alginate microspheres for use in biomedical applications. In addition, we describe a method we developed for generating multilayered alginate microbeads. Cells can be encapsulated in the inner alginate core, and angiogenic proteins in the outer alginate layer. The release of proteins from this outer layer would stimulate the formation of local microvascular networks directly towards the transplanted islets.

Protocol

The protocol here describes a three-step procedure for generating multilayered alginate microbeads (Figure 1). First, alginate microbeads are formed (Figure 2A). This procedure is described in section 1 below. Cells or proteins can be added to the microbeads in this step in order to act as a delivery system. The next step involves the formation of a permselective layer on the microbeads and is described in section 2. The final step involves the formation of an additional alginate layer and is described in section 3. This layer forms on the outside of the surface of the beads (Figure 2B) can be used to encapsulate....

Discussion

Alginate is a natural, acidic polysaccharide extracted from algae and is composed of units of 1,4'-β-D-mannuronic acid (M) and α-L-guluronic acid (G) ^2,3. Simple gelation occurs when divalent cations, such as Ca²⁺, Sr²⁺, or Ba²⁺ interact with G-monomers forming ionic bridges between adjacent alginate chains. Microbeads of alginate have been utilized to deliver a variety of proteins, including fibroblast growth factor-1 (FGF-1), nerve growth factor, leukemia inhibiti.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Pronova Ultrapure LVG alginate	Nova-Matrix	4200006	A variety of alginate formulations are available. The choice of alginate influences the end properties of the microbeads, including size, mechanical properties, and transport. The composition used should be optimized for a given application.
Pronova Ultrapure LVM alginate	Nova-Matrix	4200206	A variety of alginate formulations are available. The choice of alginate influences the end properties of the microbeads, including size, mechanical properties, and transport. The composition used should be optimized for a given application.
Poly-L-ornithine hydrochloride	Sigma-Aldrich	P2533