MICRO-AND NANOSPHERES FOR TISSUE ENGINEERING - Micro and Nanotechnologies in Engineering Stem Cells and Tissues - page 205

applications over the past decades. By incorporating different components, compo-
sites combine the advantages but eliminate the drawbacks of each component,
resulting in improved functionality and complexity. Representative examples
include inorganic-organic composites for bone reconstruction, which typically
combine biodegradable polymers with bioactive ceramics, resulting into materials
that improve the biological performance of polymers as well as provide bioceramics
with the ease of processing and controllable degradation. Composite micro- and
nanospheres have been fabricated by incorporating bioceramics (e.g., calcium
phosphates (CaPs)) with biopolymers (e.g., gelatin, PLGA), 37-44 which displayed
improved biological and physicochemical properties that include enhanced hydro-
philicity (compared with pure PLGA microspheres), 45 higher drug-loading effi-
ciency, 46 improved cytocompatibility, 45 reduced biodegradation and drug release
rates, 38 and strongly upregulated in vitro calcifying capability. 38
9.3 APPLICATIONS OF MICRO- AND NANOSPHERES
IN TISSUE ENGINEERING
9.3.1 Micro- and Nanospheres as Delivery Vehicles
9.3.1.1 Delivery of Biomolecules A critical challenge in tissue engineering is to
control the delivery of signaling biomolecules at the treatment sites to provide
instructive signals that regulate cell behavior and facilitate tissue regeneration. To
this end, complex and sophisticated delivery systems are required that allow for
sustained presence of therapeutic components at target tissues at the proper time.
Micro- and nanospheres have been studied most extensively for controlled delivery
of biomolecules owing to their inherently small size and corresponding large specific
surface area, high drug-loading efficiency, high reactivity toward surrounding tissues
in vivo, and high diffusibility and mobility of drug-loaded particles (Fig. 9.1). 4-8,13
FIGURE 9.1 The use of degradable microspheres as vehicles for biomolecule or cell
delivery (a), which can lead to subsequent cell proliferation and biomolecule release with the
degradation of carriers (b).