Production of Alginate Sub‐micron Particles and Their Biological Application

Abstract

Alginate includes several kinds of carbohydrate polymers with variable properties originating from various seaweeds. Because it is derived from several origins, including Laminaria hyperborean, Laminaria digitata, Laminaria japonica, Ascophyllum nodosum, and Macrocystis pyrifera, 1 and structured by the atypical appearance of two building blocks, D-mannuronic aid and L-guluronic acid, 2 there are over 200 kinds of commercially available alginates reaching a commercial value of 125 million US dollars in around 2008. 3,4 Although bacterial fermentation can produce alginate with defined chemical and physical properties, 5 the approximate annual production, about 38 000 tons worldwide, mainly depends on various seaweeds. 4 Because of its low cost, negligible toxicity and biocompatibility, alginate has attracted much attention not only for research but also for biomedical applications. 6 Wound dressing is one of the emerging applications of alginate, which makes use of its hydro-buffering ability. 7 Sustained release of incorporated functional materials is a key function of alginate for accelerated wound healing of bone and cartilage as well as for the regeneration of muscles and nerves and the pancreas and liver. 6 More recently, miniaturized cell culture techniques have focused on alginate for its easy molding properties in addition to its biocompatibility. Combined with microfluidic control, alginate has been used to form beads, 8 strings, 9 and even coils, 10 and cells encapsulated within alginate were shown to thrive well. [11][12][13][14] Alginate forms gels from 0.5 to 3% solutions which is still very viscous. The high viscosity of ungelled solution makes it impossible for microfluidic devices to fabricate micron-level flow layers. 15 Consequently, general alginate particles are made dropwise, which results in several hundred micrometer-sized 16 or millimeter-sized particles, 17 and the smallest alginate particles made by microfluidic focusing techniques are limited to be more than several tens of micrometers reducing the scope of potential applications. 15,18,19 A sonication method was also tried to make micron-sized alginate beads which could be transfected into cells; however, the method was only partly successful making several micrometer-sized particles with heterogeneity. 20,21 Considering the previous and potent applications, alginate particles of less than a micrometer will provide new practical applications in addition to their use in research. 15 Alginate solution is easily gelled by the addition of divalent cations such as calcium. 22,23 Therefore, the most popular way to make gelled alginate structures is just mixing with or dumping into cation solution, generally calcium chloride, at ambient temperature. Instantaneous surface gelation ensures the solidification of the overall structures, of which the inner alginate would be gelled by the diffused cations. 23 Therefore, the initial state of mixing with cation solution is the point of shape formation.In this report, we produced alginate particle smal...