Controlled Molecular Organization of Surface Macromolecular Assemblies Based on Stimuli-Responsive Polypeptide Brushes

Humidity-Triggered Relaxation of Polyelectrolyte Complexes as a Robust Approach to Generate Extracellular Matrix Biomimetic Films

Generating a biofunctional film that can mimic the extracellular matrix (ECM) in an efficient and robust technique that may have great potential for medical devices, tissue engineering, and regenerative medicines. Herein, a facile approach to generate ECM biomimetic films based on the humidity-triggered relaxation of polyelectrolyte complex (PEC) nanoparticles is reported. The poly(l-lysine) and hyaluronan are precomplexed and sprayed onto a substrate, which, via a trigger of vaporous water, can be transformed into an even and stable film. The spontaneous polymer chain interfusion (diffusion coefficient ≈1.01 × 10^-9  cm²  s^-1 ) under saturated humidity, allowing for the rapid reorganization (within 30 min) of film morphology and structure is demonstrated. A controllable and scalable way for the loading of diversified bioactive agents, as well as on-demand modulation of stiffness is further presented. Moreover, the high-throughput arrays and programmed patterns can be easily completed, suggesting huge potentials that surpass those of state-of-the-art methods. Combined with high efficiency and flexible functionalization, it is believed that this approach should be beneficial for extending the practical applications of PEC films, such as medical implants, chip detectors, and so on.

Synthesis of antireflective silica coatings through the synergy of polypeptide layer-by-layer assemblies and biomineralization

We report a versatile approach to synthesize silica coatings with antireflective (AR) characteristics through the combination of a layer-by-layer (LbL) assembly technique and biomineralization. LbL assembled decanoyl-modified poly(l-lysine)/poly(l-glutamic acid) (PLL-g-Dec/PLGA) multilayer films were used as templates for silica mineralization, followed by calcination. The specific deposition of silica onto the LbL polypeptide assemblies through amine-catalyzed polycondensation resulted in silica coatings that exhibited the transcription of the nano-/microstructured polypeptide films and their film thickness and porosity can be tuned by varying the number of bilayers, degree of substitution, and PLL molecular weight. AR silica coatings exhibiting more than 6% increase in transmittance in the near UV/visible spectral range can be obtained at an optimized refractive index, thickness, and surface roughness. The abrasion test showed that the silica coatings exhibited sufficient structural durability due to continuous silica nanostructures and low surface roughness. This study demonstrated that nanostructured thin films can be synthesized for AR coatings using the synergy between the LbL assembly technique and biomineralization.

Chemoresponsive surface-tethered polypeptide brushes based on switchable secondary conformations

Surface-tethered chemoresponsive polypeptides prepared by surface-initiated vapor deposition polymerization were used to investigate conversion efficiency between α-helical and β-sheet conformations.

Use of surface properties to control the growth and differentiation of mouse fetal liver stem/progenitor cell colonies

Multilayers of poly-l-lysine/poly-l-glutamic acid (PLL/PLGA) were constructed by layer-by-layer deposition on an end-tethered cationic PLL brush film serving as an initial layer. Increasing the number of coupling layers increased the thickness and the hydration of the films, and decreased the films' shear modulus and serum adsorption. These films were used to culture primary mouse fetal liver cells. Fetal liver stem/progenitor cells (FLSPCs) were isolated and maintained on the PLGA-terminal PLL/PLGA surfaces, forming colonies with clear boundaries that were partially attached to the surface, with cross-sectional areas of ~500 to ~2500 μm(2) after 2 days culture. Long-term studies showed that the cluster size of colonies slowly expanded and was correlated with the surface properties. For example, on the thicker films with shear modulus, G, less than 5 kPa, FLSPCs cluster size was constrained within a small distribution with less than 4000 μm(2) of projected area, whereas on the thinner films with G > 30 kPa, clusters were expanded and widely distributed, with projected areas over 4000 um(2). Immunostaining studies suggested that clusters with a small size maintained the self-renewal characteristics of stem cells, while the expanded clusters were clearly the results of spontaneous differentiation, exhibiting hepatocyte-like properties. On PLL-terminal t-(PLL/PLGA) films, which are less favorable for stem cell cultures than PLGA-terminal t-(PLL/PLGA) films, the cluster size distribution was also correlated with the film thickness, with more clusters of small size preserved on the thicker films. We observed that a soft, hydrated, serum-free surface could restrict the FLSPC expansion, resulting in self-maintenance of FLSPC colonies.

Helix formation in the polymer brush

This work considers the physics of a brush formed by polymers capable of undergoing a helix-coil transition. A self-consistent field approximation for strongly stretched polymer chains is used in combination with a lattice model of the interaction energy in helix-coil mixtures. Crowding-induced chain stretching stabilizes helix formation at moderate tethering densities while high tethering density causes sufficiently strong stretching to unravel segments of the helix, resulting in distinct layers of monomer density and helical content. Compared to a random-coil brush at low-to-moderate tethering density, a helicogenic brush is less resistant to compression in the direction perpendicular to stretching due to easy alignment of helices and fewer unfavorable interactions between helical segments. At higher tethering density, the abovementioned stretch-induced decrease in helical content resists further compression. The proposed model is useful for understanding an emerging class of biomaterials that utilize helix-forming polymer brushes to induce shape changes or to stabilize biofunctional helical peptide sequences.

Layer-by-layer polypeptide macromolecular assemblies-mediated synthesis of mesoporous silica and gold nanoparticle/mesoporous silica tubular nanostructures

A simple and versatile approach is proposed to use the LbL-assembled polypeptide macromolecular assemblies as mediating agents and templates for directed growth of gold nanoparticles and biomimetic silica mineralization, allowing the synthesis of polypeptide/silica and polypeptide/gold nanoparticle/silica composite materials, as well as mesoporous silica (meso-SiO2) and gold nanoparticle/mesoporous silica (Au NP/meso-SiO2). The formation of tubular nanostructures was demonstrated by silicification and growth of gold nanoparticles within macromolecular assemblies formed by poly(L-lysine) (PLL) and poly(L-glutamic acid) (PLGA) using polycarbonate membranes as templates. The experimental data revealed that the silicified macromolecular assemblies adopted mainly sheet/turn conformation. The as-prepared mesoporous silica materials possessed well-defined tubular structures with pore size and porosity depending on the size of sheet/turn aggregates, which is a function of the molecular weight of polypeptides. The directed growth of Au NP and subsequent silica mineralization in the macromolecular assembly resulted in Au NP/meso-SiO2 tubes with uniform nanoparticle size and the as-prepared materials exhibited promising catalytic activity toward the reduction of p-nitrophenol. This approach provides a facile and general method to synthesize organic-inorganic composite materials, oxide and metal-oxide nanomaterials with different compositions and structures.

Surface-initiated vapor deposition polymerization of poly(gamma-benzyl-L-glutamate): optimization and mechanistic studies

Surface-initiated vapor deposition polymerization (SI-VDP) is a very effective approach to synthesize grafted poly(amino acids). In this study, we developed an SI-VDP system with pressure and temperature control and demonstrated highly efficient surface-grafting of poly(gamma-benzyl-L-glutamate) (PBLG) on a silicon wafer at pressure 1000 times larger than those in prior reports. More importantly, we developed new methods to quantitatively investigate mechanistic details of the SI-VDP process. First, we monitored the amount of vaporized monomer and developed a VDP reaction profile (VDPRP) method to study the major monomer reservoir processes. Next, we developed a quantitative Fourier transform infrared analysis of both as-deposited PBLG and chemisorbed PBLG films in addition to ellipsometric data to evaluate the major substrate surface processes. We observed two classes of characteristic features (pulses or two peaks) of VDPRPs, which depended upon the monomer temperature, and proposed possible mechanisms. We also found that the two peaks of VDPRPs can selectively track different reservoir processes in real time. For surface processes, we proposed possible mechanisms to obtain the surface-grafted PBLG that are expected to have either high packing density with mostly alpha-helix segments or low packing density with both random coil and alpha-helix segments.

Mixing a sol and a precipitate of block copolymers with different block ratios leads to an injectable hydrogel

A facile method to obtain a thermoreversible physical hydrogel was found by simply mixing an aqueous sol of a block copolymer with a precipitate of a similar copolymer but with a different block ratio. Two ABA-type triblock copolymers poly(D,L-lactic acid-co-glycolic acid)-B-poly(ethylene glycol)-B-poly(D,L-lactic acid-co-glycolic acid) (PLGA-PEG-PLGA) were synthesized. One sample in water was a sol in a broad temperature region, while the other in water was just a precipitate. The mixture of these two samples with a certain mix ratio underwent, however, a sol-to-gel-to-precipitate transition upon an increase of temperature. A dramatic tuning of the sol-gel transition temperature was conveniently achieved by merely varying mix ratio, even in the case of a similar molecular weight. Our study indicates that the balance of hydrophobicity and hydrophilicity within this sort of amphiphilic copolymers is critical to the inverse thermal gelation in water resulting from aggregation of micelles. The availability of encapsulation and sustained release of lysozyme, a model protein by the thermogelling systems was confirmed. This "mix" method provides a very convenient approach to design injectable thermogelling biomaterials with a broad adjustable window, and the novel copolymer mixture platform is potentially used in drug delivery and other biomedical applications.