Colloidal systems toward 3D cell culture scaffolds

Three-dimensional porous scaffolds are essential for the development of tissue engineering and regeneration, as biomimetic supports to recreate the microenvironment present in natural tissues. To successfully achieve the growth and development of a specific kind of tissue, porous matrices should be able to influence cell behavior by promoting close cell-cell and cell-matrix interactions. To achieve this goal, the scaffold must fulfil a set of conditions, including ordered interconnected porosity to promote cell diffusion and vascularization, mechanical strength to support the tissue during continuous ingrowth, and biocompatibility to avoid toxicity. Among various building approaches to the construction of porous matrices, selected strategies afford hierarchical scaffolds with such defined properties. The control over porosity, microstructure or morphology, is crucial to the fabrication of high-end, reproducible scaffolds for the target application. In this review, we provide an insight into recent advances toward the colloidal fabrication of hierarchical scaffolds. After identifying the main requirements for scaffolds in biomedical applications, conceptual building processes are introduced. Examples of tissue regeneration applications are provided for different scaffold types, highlighting their versatility and biocompatibility. We finally provide a prospect about the current state of the art and limitations of porous scaffolds, along with challenges that are to be addressed, so these materials consolidate in the fields of tissue engineering and drug delivery.

Modular segmented hyperbranched copolymers

Modular segmented hyperbranched polymers, amenable to facile post-polymerization functionalization, were created via two distinct approaches.

Layer-by-Layer Approach to (2+1)D Photonic Crystal Superlattice with Enhanced Crystalline Integrity

Large-area polystyrene (PS) colloidal monolayers with high mechanical strength are created by a combination of the air/water interface self-assembly and the solvent vapor annealing technique. Layer-by-layer (LBL) stacking of these colloidal monolayers leads to the formation of (2+1)D photonic crystal superlattice with enhanced crystalline integrity. By manipulating the diameter of PS spheres and the repetition period of the colloidal monolayers, flexible control in structure and stop band position of the (2+1)D photonic crystal superlattice has been realized, which may afford new opportunities for engineering photonic bandgap materials. Furthermore, an enhancement of 97.3% on light output power of a GaN-based light emitting diode is demonstrated when such a (2+1)D photonic crystal superlattice employed as a back reflector. The performance enhancement is attributed to the photonic bandgap enhancement and good angle-independence of the (2+1)D photonic crystal superlattice.

Liquid Crystal Elastomer Microspheres as Three-Dimensional Cell Scaffolds Supporting the Attachment and Proliferation of Myoblasts

We report that liquid crystal elastomers (LCEs), often portrayed as artificial muscles, serve as scaffolds for skeletal muscle cell. A simultaneous microemulsion photopolymerization and cross-linking results in nematic LCE microspheres 10-30 μm in diameter that when conjoined form a LCE construct that serves as the first proof-of-concept for responsive LCE muscle cell scaffolds. Confocal microscopy experiments clearly established that LCEs with a globular, porous morphology permit both attachment and proliferation of C2C12 myoblasts, while the nonporous elastomer morphology, prepared in the absence of a microemulsion, does not. In addition, cytotoxicity and proliferation assays confirm that the liquid crystal elastomer materials are biocompatible promoting cellular proliferation without any inherent cytotoxicity.

Biomineralization-inspired synthesis of functional organic/inorganic hybrid materials: organic molecular control of self-organization of hybrids

Biomineralization-inspired synthesis of functional organic/inorganic hybrid materials. Molecularly controlled mechanisms of biomineralization and application of the processes towards future material synthesis are introduced.

Shape-tailored polymer colloids on the road to become structural motifs for hierarchically organized materials

Anisometric polymer colloids are likely to behave differently when compared with centrosymmetric particles. Their study may not only shine new light on the organization of matter; they may also serve as building units with specific symmetries and complexity to build new materials from them. Polymer colloids of well-defined complex geometries can be obtained by packing a limited number of spherical polymer particles into clusters with defined configurations. Such supracolloidal architectures can be fabricated at larger scales using narrowly dispersed emulsion droplets as templates. Assemblies built from at least two different types of particles as elementary building units open perspectives in selective targeting of colloids with specific properties, aiming for mesoscale building blocks with tailor-made morphologies and multifunctionality. Polymer colloids with defined geometries are also ideal to study shape-dependent properties such as the diffusion of complex particles.

Controllable fabrication of nanocrystal-loaded photonic crystals with a polymerizable macromonomer via the CCTP technique

We report an alternative strategy for fabricating nanocrystal-loaded photonic crystals with a polymerizable macromonomer via catalytic chain-transfer polymerization (CCTP) in which CoBF acted as a chain-transfer agent (CTAs). First, monodisperse, functionalized PS-co-PMAA microspheres with polystyrene (PS) cores and poly(methacrylic acid) (PMAA) shells were controllably prepared using styrene and the as-prepared PMAA macromonomer by surfactant-free emulsion polymerization. Then Cd(0.4)Zn(0.6)S nanocrystals capped with as-prepared PMAA macromonomer were synthesized by an in situ growth method. Finally, Cd(0.4)Zn(0.6)S nanocrystal-loaded PS-co-PMAA microspheres hybrids were obtained through simply mixing an aqueous solution of PS-co-PMAA microspheres with an aqueous solution of Cd(0.4)Zn(0.6)S nanocrystals in the appropriate proportions; the multianchor -COOH groups on the surface of core-shell PS-co-PMAA microspheres favor incorporation with Cd(0.4)Zn(0.6)S nanocrystals. Scanning electron microscopy (SEM) images confirm that PS-co-PMAA microspheres are uniformly surrounded by Cd(0.4)Zn(0.6)S nanocrystals. In addition, discrete electronic and photonic states can be combined both with PS-co-PMAA photonic crystals and fluorescent semiconductor Cd(0.4)Zn(0.6)S nanocrystals.

Covalent and physical cross-linking of photonic crystals with 10-fold-enhanced chemomechanical stability

We report opal photonic crystals that are self-assembled from functional polymer particles. We randomly copolymerized functional side-chain monomers containing motifs that form homodimers or heterobridges. These include ether or methylene bridges, hydrazone bridges, acids for anhydride formation, low- T g copolymers or physical cross-links by hydrogen bonds and/or polarity. To generate particles that are monodisperse, spherical, and functionalized, we combined emulsifier-free synthesis with swelling synthesis steps. Laser diffraction from centimeter-sized beams, white-light interferometry, and atomic force microscopy demonstrates symmetry and homogeneity across the entire crystal without the loss of interstitial volume. Compared to the stability of nonfunctional particles, the stability of the crystal against immersion in water and isopropanol was enhanced from 10 to a perfect 100%. One of the successful approaches (methylene bridges from N-methylolmethacrylamid) is triggered by thermal activation, but as shown, this is operative far from the trivial regime of sintering. We demonstrate successful infiltration with and solvation of a laser-polymerizable resin, thus enabling the processing of 3D photonic waveguide structures.