Engineering chemoattractant gradients using chemokine-releasing polysaccharide microspheres

Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA.
Biomaterials (Impact Factor: 8.56). 04/2011; 32(21):4903-13. DOI: 10.1016/j.biomaterials.2011.03.027
Source: PubMed

ABSTRACT Spatial and temporal concentration gradients of chemoattractants direct many biological processes, especially the guidance of immune cells to tissue sites during homeostasis and responses to infection. Such gradients are ultimately generated by secretion of attractant proteins from single cells or collections of cells. Here we describe cell-sized chemoattractant-releasing polysaccharide microspheres, capable of mimicking chemokine secretion by host cells and generating sustained bioactive chemokine gradients in their local microenvironment. Exploiting the common characteristic of net cationic charge and reversible glycosaminoglycan binding exhibited by many chemokines, we synthesized alginate hydrogel microspheres that could be loaded with several different chemokines (including CCL21, CCL19, CXCL12, and CXCL10) by electrostatic adsorption. These polysaccharide microspheres subsequently released the attractants over periods ranging from a few hours to at least 1 day when placed in serum-containing medium or collagen gels. The generated gradients were able to attract cells more than hundreds of microns away to make contact with individual microspheres. This versatile system for chemoattractant delivery could find applications in immunotherapy, vaccines and fundamental chemotaxis studies in vivo and in vitro.

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Available from: Darrell J Irvine, Sep 27, 2015
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    • "Microbeads can be used to sequester soluble molecules [11] and encapsulate cells [12] [13] [14]. These capabilities are used in tissue engineering and regenerative medicine to selectively differentiate stem cells [15] [16] [17] and create soluble factor concentration gradients to guide cell migration [18] [19]. One of the primary advantages of microbeads over bulk scaffolds for tissue engineering applications is that the surface areato-volume ratio is small enough to allow rapid transport of nutrients and waste of the encapsulated cells [20]. "
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    ABSTRACT: Alginate can be used to encapsulate mammalian cells and for the slow release of small molecules. Packaging alginate as microbead structures allows customizable delivery for tissue engineering, drug release, or contrast agents for imaging. However, state-of-the-art microbead fabrication has a limited range in achievable bead sizes, and poor control over bead placement, which may be desired to localize cellular signaling or delivery. Herein, we present a novel, laser-based method for single-step fabrication and precise planar placement of alginate microbeads. Our results show that bead size is controllable within 8%, and fabricated microbeads can remain immobilized within 2% of their target placement. Demonstration of this technique using human breast cancer cells shows that cells encapsulated within these microbeads survive at a rate of 89.6%, decreasing to 84.3% after five days in culture. Infusing rhodamine dye into microbeads prior to fluorescent microscopy shows their 3D spheroidal geometry and the ability to sequester small molecules. Microbead fabrication and patterning is compatible with conventional cellular transfer and patterning by laser direct-write, allowing location-based cellular studies. While this method can also be used to fabricate microbeads en masse for collection, the greatest value to tissue engineering and drug delivery studies and applications lies in the pattern registry of printed microbeads.
    Biofabrication 11/2013; 5(4):045006. DOI:10.1088/1758-5082/5/4/045006 · 4.29 Impact Factor
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    • "Microbeads possess versatile applicability as probes for biomolecule screening [1], vehicles for targeted drug delivery [2] [3], microtools for cell manipulation [4] and microbioreactors for scalable cell culture systems [5] [6]. For example, positioning of cell-laden or protein-conjugated beads from blueprinted patterns can greatly enhance spatial detection in bioMEMS sensor technology [7] [8] [9], and the arrangement of drug-loaded microbeads allows for the formation of spatially defined concentration gradients [10]. In addition, recent work has made it possible to encapsulate cells in physiologically relevant biomaterials capable of directing biological processes [11] [12]. "
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    ABSTRACT: Fabrication of heterogeneous microbead patterns on a bead-by-bead basis promotes new opportunities for sensors, lab-on-a-chip technology and cell-culturing systems within the context of customizable constructs. Laser direct-write (LDW) was utilized to target and deposit solid polystyrene and stem cell-laden alginate hydrogel beads into computer-programmed patterns. We successfully demonstrated single-bead printing resolution and fabricated spatially-ordered patterns of microbeads. The probability of successful microbead transfer from the ribbon surface increased from 0 to 80% with decreasing diameter of 600 to 45 µm, respectively. Direct-written microbeads retained spatial pattern registry, even after 10 min of ultrasonication treatment. SEM imaging confirmed immobilization of microbeads. Viability of cells encapsulated in transferred hydrogel microbeads achieved 37 ± 11% immediately after the transfer process, whereas randomly-patterned pipetted control beads achieved a viability of 51 ± 25%. Individual placement of >10 µm diameter microbeads onto planar surfaces has previously been unattainable. We have demonstrated LDW as a valuable tool for the patterning of single, micrometer-diameter beads into spatially-ordered patterns.
    Biofabrication 05/2012; 4(2):025006. DOI:10.1088/1758-5082/4/2/025006 · 4.29 Impact Factor
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    ABSTRACT: Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) microspheres have been previously found to support the proliferation and differentiation of a variety of neuronal cells; however, to establish functional neural networks and tissue integration, the cells on the microspheres have to be connected. It was found that neurites bridged the microspheres but these connections were fragile. Thus, the neurons on PHBV microspheres (neuron–microspheres) were encapsulated in a laminin–collagen hydrogel to promote and protect the bridging formations. Bridges were found across the continuous surface between microspheres in contact (surface bridges), and in the gel space between microspheres (suspended bridges). This neuron–microsphere–hydrogel construct increased the proportion of bridge-forming neurites by 31% as compared to neuron–microspheres alone. Furthermore, the neuron–microsphere–hydrogel was found to increase the proportion of suspended bridges by 3.5 times. The surface bridges were subsequently verified to form from neurites extending across continuous surfaces, and thus packing microspheres closer to generate more continuous surfaces increased surface bridging by 70%. However, seeding cells into the gel space did not increase the proportion of suspended bridges but this still increased the overall proportion of bridges by 21%. Images of neurites in the gel space suggested that suspended bridges could have formed instead from neurites extending out of microsphere surfaces into the gel space. This is the first study to focus on neurite bridging and microspheres as scaffolds supported by hydrogel. Furthermore, a novel neurite guidance cue was found in the form of continuous surfaces.
    Soft Matter 11/2011; 7(24):11372-11379. DOI:10.1039/C1SM06473H · 4.03 Impact Factor
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