Abstract
One of the undeniable trends in modern bioengineering and nanotechnology is the use of various biomolecules, primarily of a polymeric nature, for the design and formulation of novel functional materials for controlled and targeted drug delivery, bioimaging and theranostics, tissue engineering, and other bioapplications. Biocompatibility, biodegradability, the possibility of replicating natural cellular microenvironments, and the minimal toxicity typical of biogenic polymers are features that have secured a growing interest in them as the building blocks for biomaterials of the fourth generation. Many recent studies showed the promise of the hard-templating approach for the fabrication of nano- and microparticles utilizing biopolymers. This review covers these studies, bringing together up-to-date knowledge on biopolymer-based multilayer capsules and beads, critically assessing the progress made in this field of research, and outlining the current challenges and perspectives of these architectures. According to the classification of the templates, the review sequentially considers biopolymer structures templated on non-porous particles, porous particles, and crystal drugs. Opportunities for the functionalization of biopolymer-based capsules to tailor them toward specific bioapplications is highlighted in a separate section.
Highlights
Capsules and Beads Made via Templating: Advantages, Hurdles and Perspectives
LbL deposition upon a non-porou achieved, the template undergoes dissolution, a polyelectrolyte multilayer capsule (PEMC) with internal gel-likeadsorb matrix; to this capsule is coined as aand, matrix-type capsule, template, the an polyelectrolytes the template surface following this, the tem or a microgel deposition upon a non-porous template, plate is eliminated, leaving a polymeric shell and a hollow lumen; these are known the polyelectrolytes adsorb to the template and,iffollowing this, is theable template is hollow-type capsules
Stable hollow PEMCs were formed with a slight increase in shell thickness, from 10–20 nm to 20–50 nm, which was attributed to alterations in polymer conformation on E.coli degradation
Summary
With the introduction of the versatile approach of the layer-by-layer (LbL) assembly of oppositely charged polyelectrolytes some decades ago, the research field has grown exponentially, owing to the ease of control over the layered film properties (i.e., film thickness, homogeneity, stability, porosity, etc.) [1,2,3,4,5,6,7,8,9,10] and the ability to coat surfaces of varying geometries [11,12,13,14]. LbL assembly can be achieved by a variety of methods, including traditional dip-coating [34], spray-coating [35,36], and spin-coating [37] approaches (Figure 1(1)–(3)). More recent emerging methodologies include that of microfluidic assisted approaches via the 2D coating of channels and the packing of 3D capsules [32,38,39], as well as “brushing”. Nanomaterials 2021, 11, 2502 the 2D coating of channels and the packing of 3D capsules [32,38,39], as well as “brushing”
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