Autonomous self-burying seed carriers for aerial seeding.

Aerial seeding can quickly cover large and physically inaccessible areas1 to improve soil quality and scavenge residual nitrogen in agriculture2, and for postfire reforestation3-5 and wildland restoration6,7. However, it suffers from low germination rates, due to the direct exposure of unburied seeds to harsh sunlight, wind and granivorous birds, as well as undesirable air humidity and temperature1,8,9. Here, inspired by Erodium seeds10-14, we design and fabricate self-drilling seed carriers, turning wood veneer into highly stiff (about 4.9 GPa when dry, and about 1.3 GPa when wet) and hygromorphic bending or coiling actuators with an extremely large bending curvature (1,854 m-1), 45 times larger than the values in the literature15-18. Our three-tailed carrier has an 80% drilling success rate on flat land after two triggering cycles, due to the beneficial resting angle (25°-30°) of its tail anchoring, whereas the natural Erodium seed's success rate is 0%. Our carriers can carry payloads of various sizes and contents including biofertilizers and plant seeds as large as those of whitebark pine, which are about 11 mm in length and about 72 mg. We compare data from experiments and numerical simulation to elucidate the curvature transformation and actuation mechanisms to guide the design and optimization of the seed carriers. Our system will improve the effectiveness of aerial seeding to relieve agricultural and environmental stresses, and has potential applications in energy harvesting, soft robotics and sustainable buildings.

Probing the Assembly of HDL Mimetic, Drug Carrying Nanoparticles Using Intrinsic Fluorescence.

Reconstituted high-density lipoprotein (HDL) containing apolipoprotein A-I (Apo A-I) mimics the structure and function of endogenous (human plasma) HDL due to its function and potential therapeutic utility in atherosclerosis, cancer, neurodegenerative diseases, and inflammatory diseases. Recently, a new class of HDL mimetics has emerged, involving peptides with amino acid sequences that simulate the the primary structure of the amphipathic alpha helices within the Apo A-I protein. The findings reported in this communication were obtained using a similar amphiphilic peptide (modified via conjugation of a myristic acid residue at the amino terminal aspartic acid) that self-assembles (by itself) into nanoparticles while retaining the key features of endogenous HDL. The studies presented here involve the macromolecular assembly of the myristic acid conjugated peptide (MYR-5A) into nanomicellar structures and its characterization via steady-state and time-resolved fluorescence spectroscopy. The structural differences between the free peptide (5A) and MYR-5A conjugate were also probed, using tryptophan fluorescence, FÓ§rster resonance energy transfer (FRET), dynamic light scattering, and gel exclusion chromatography. To our knowledge, this is the first report of a lipoprotein assembly generated from a single ingredient and without a separate lipid component. The therapeutic utility of these nanoparticles (due to their capablity to incorporate a wide range of drugs into their core region for targeted delivery) was also investigated by probing the role of the scavenger receptor type B1 in this process. SIGNIFICANCE STATEMENT: Although lipoproteins have been considered as effective drug delivery agents, none of these nanoformulations has entered clinical trials to date. A major challenge to advancing lipoprotein-based formulations to the clinic has been the availability of a cost-effective protein or peptide constituent, needed for the assembly of the drug/lipoprotein nanocomplexes. This report of a robust, spontaneously assembling drug transport system from a single component could provide the template for a superior, targeted drug delivery strategy for therapeutics of cancer and other diseases (Counsell and Pohland, 1982).

Evaluation of Artificial Tactile Sense in Mass Detection in Silicone Phantom for the Diagnosis of Prostate Tumor.

We analyzed the kinetic and kinematic variables of artificial tactile and artificial vibrotactile sensing test for mass detection in silicon phantom to determine tactile intensity and speed to obtain the best result in detecting the type and location of the mass. This study has utilized Artificial Tactile Sensing Instrument for Mass Detection (ATSIMD) in cylindrical silicone phantoms. The masses embedded in these samples were inserted in axial and environmental, deep and surface positions. The loading velocity, probe location, and the frequency of the applied force were considered as the independent variables in this study. It was found that for superficial mases the accuracy of detection at low speed 5 mm/sec, although dependent on the probe, but was 50% higher than under other conditions. For deep masses, with increasing mass depth, the accuracy of detection at medium speed of 8 mm/sec was 30% higher than at low speed. Mass detection by ATSIMD used in this study showed maximum efficiency at medium loading velocity. At low and high loading velocities, the dependence of mass detection on the probe location is related to the interaction of the testing method, tissue, and viscoelastic properties of the tissue.

Responsive biomimetic networks from polyisocyanopeptide hydrogels.

Mechanical responsiveness is essential to all biological systems down to the level of tissues and cells. The intra- and extracellular mechanics of such systems are governed by a series of proteins, such as microtubules, actin, intermediate filaments and collagen. As a general design motif, these proteins self-assemble into helical structures and superstructures that differ in diameter and persistence length to cover the full mechanical spectrum. Gels of cytoskeletal proteins display particular mechanical responses (stress stiffening) that until now have been absent in synthetic polymeric and low-molar-mass gels. Here we present synthetic gels that mimic in nearly all aspects gels prepared from intermediate filaments. They are prepared from polyisocyanopeptides grafted with oligo(ethylene glycol) side chains. These responsive polymers possess a stiff and helical architecture, and show a tunable thermal transition where the chains bundle together to generate transparent gels at extremely low concentrations. Using characterization techniques operating at different length scales (for example, macroscopic rheology, atomic force microscopy and molecular force spectroscopy) combined with an appropriate theoretical network model, we establish the hierarchical relationship between the bulk mechanical properties and the single-molecule parameters. Our results show that to develop artificial cytoskeletal or extracellular matrix mimics, the essential design parameters are not only the molecular stiffness, but also the extent of bundling. In contrast to the peptidic materials, our polyisocyanide polymers are readily modified, giving a starting point for functional biomimetic hydrogels with potentially a wide variety of applications, in particular in the biomedical field.

Transformation of Construction Cement to a Self-Healing Hybrid Binder.

A new biomimetic strategy to im prove the self-healing properties of Portland cement is presented that is based on the application of the biogenic inorganic polymer polyphosphate (polyP), which is used as a cement admixture. The data show that synthetic linear polyp, with an average chain length of 40, as well as natural long-chain polyP isolated from soil bacteria, has the ability to support self-healing of this construction material. Furthermore, polyP, used as a water-soluble Na-salt, is subject to Na+/Ca2+ exchange by the Ca2+ from the cement, resulting in the formation of a water-rich coacervate when added to the cement surface, especially to the surface of bacteria-containing cement/concrete samples. The addition of polyP in low concentrations (<1% on weight basis for the solids) not only accelerated the hardening of cement/concrete but also the healing of microcracks present in the material. The results suggest that long-chain polyP is a promising additive that increases the self-healing capacity of cement by mimicking a bacteria-mediated natural mechanism.

A Compatible Sensitivity Enhancement Strategy for Electrochemiluminescence Immunosensors Based on the Biomimetic Melanin-Like Deposition.

In this work, a compatible strategy was demonstrated for the enhancement of detection sensitivity of sandwich-type electrochemiluminescence (ECL) immunosensors. The enhanced signal response was based on the combination of biomimetic melanin-like deposition with the effective ECL quenching ability of quinone-rich biopolymers. Gold nanoparticle-loaded horseradish peroxidase (HRP) was used as a catalytic label for the secondary antibodies. The intrinsic catalytic property of HRP toward hydrogen peroxide (H2O2) generates reactive oxygen species, which highly promote the autopolymerization of catecholamines. The resulting fast deposition of quinone-rich biopolymers approaching the luminophor-incorporated sensing platform achieves an obvious ECL quenching. A broad-spectrum tumor marker alpha fetoprotein (AFP) was selected as a model analyte to demonstrate the feasibility of the proposed strategy. Under optimal conditions, a very low detection limit of 0.056 pg mL-1 was obtained. Two orders of magnitude enhancement was achieved in contrast to the signal response without the step of catalytic biopolymer deposition. The combination of compatible HRP labeling with unique melanin-like deposition has potential as a universal strategy in other ECL bioassays.

Phospholipid-Biomimetic Fluorescent Mitochondrial Probe with Ultrahigh Selectivity Enables In Situ and High-Fidelity Tissue Imaging.

In situ and directly imaging mitochondria in tissues instead of isolated cells can offer more native and accurate information. Particularly, in the clinical diagnose of mitochondrial diseases such as mitochondrial myopathy, it is a routine examination item to directly observe mitochondrial morphology and number in muscle tissues from patients. However, it is still a challenging task because the selectivity of available probes is inadequate for exclusively tissue imaging. Inspired by the chemical structure of amphiphilic phospholipids in mitochondrial inner membrane, we synthesized a phospholipid-biomimetic amphiphilic fluorescent probe (Mito-MOI) by modifying a C18-alkyl chain to the lipophilic side of carbazole-indolenine cation. Thus, the phospholipid-like Mito-MOI locates at mitochondrial inner membrane through electrostatic interaction between its cation and inner membrane negative charge. Simultaneously, the C18-alkyl chain, as the second targeting group, is deeply embedded into the hydrophobic region of inner membrane through hydrophobic interaction. Therefore, the dual targeting groups (cation and C18-alkyl chain) actually endow Mito-MOI with ultrahigh selectivity. As expected, high-resolution microscopic photos showed that Mito-MOI indeed stained mitochondrial inner membrane. Moreover, in situ and high-fidelity tissue imaging has been achieved, and particularly, four kinds of mitochondria and their crystal-like structure in muscle tissues were visualized clearly. Finally, the dynamic process of mitochondrial fission in living cells has been shown. The strategy employing dual targeting groups should have reference value for designing fluorescent probes with ultrahigh selectivity to various intracellular membranous components.

Real-time analysis of composite magnetic nanoparticle disassembly in vascular cells and biomimetic media.

The fate of nanoparticle (NP) formulations in the multifaceted biological environment is a key determinant of their biocompatibility and therapeutic performance. An understanding of the degradation patterns of different types of clinically used and experimental NP formulations is currently incomplete, posing an unmet need for novel analytical tools providing unbiased quantitative measurements of NP disassembly directly in the medium of interest and in conditions relevant to specific therapeutic/diagnostic applications. In the present study, this challenge was addressed with an approach enabling real-time in situ monitoring of the integrity status of NPs in cells and biomimetic media using Förster resonance energy transfer (FRET). Disassembly of polylactide-based magnetic NPs (MNPs) was investigated in a range of model biomimetic media and in cultured vascular cells using an experimentally established quantitative correlation between particle integrity and FRET efficiency controlled through adjustments in the spectral overlap between two custom-synthesized polylactide-fluorophore (boron dipyrromethene) conjugates incorporated in MNPs. The results suggest particle disassembly governed by diffusion-reaction processes with kinetics strongly dependent on conditions promoting release of oligomeric fragments from the particle matrix. Thus, incubation in gels simulating the extracellular environment and in protein-rich serum resulted in notably lower and higher MNP decomposition rates, respectively, compared with nonviscous liquid buffers. The diffusion-reaction mechanism also is consistent with a significant cell growth-dependent acceleration of MNP processing in dividing vs. contact-inhibited vascular cells. The FRET-based analytical strategy and experimental results reported herein may facilitate the development and inform optimization of biodegradable nanocarriers for cell and drug delivery applications.

Quantification of therapeutic miRNA mimics in whole blood from nonhuman primates.

MRX34, a microRNA (miRNA)-based therapy for cancer, has recently entered clinical trials as the first clinical candidate in its class. It is a liposomal nanoparticle loaded with a synthetic mimic of the tumor suppressor miRNA miR-34a as the active pharmaceutical ingredient. To understand the pharmacokinetic properties of the drug and to rationalize an optimal dosing regimen in the clinic, a method is needed to quantitatively detect the miRNA mimic. Here, we report the development and qualification of a quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assay in support of pharmacokinetic and toxicokinetic assessments in the nonhuman primate. Detection and quantification were performed on total ribonucleic acid (RNA) isolated from whole blood. The qualified range of the standard curve spans 6 orders of magnitude from 2.5 × 10(-7) to 2.5 × 10(-1) ng per reverse transcription (RT) reaction, corresponding to an estimated blood concentration from 6.2 × 10(-5) to 6.2 × 10(1) ng/mL. Our results demonstrate that endogenous as well as the exogenous miR-34a can be accurately and precisely quantified. The assay was used to establish the pharmacokinetic profile of MRX34, showing a favorable residence time and exposure of the miRNA mimic in whole blood from nonhuman primates.

Structural characterization of inorganic biomaterials.

Composite materials with unique architectures are ubiquitous in nature, e.g., marine shells, sponge spicules, bones, and dentine. These structured organic-inorganic systems are generated through self-assembly of organic matter (usually proteins or lipids) into scaffolds, onto which the inorganic component is deposited in organized hierarchical structures of sizes spanning several orders of magnitude. The development of bio-inspired materials is possible through the design of synthetic bottom-up self-assembly methods. Knowledge of the structure is required in order to assess the efficiency of their design and evaluate their properties. This chapter reviews the main methods used for structure determination of natural and synthetic inorganic biomaterials, namely, X-ray diffraction and scattering and electron diffraction and microscopy (TEM, SEM), as well as the AFM and CSLM microscopy methods. Moreover, spectroscopic (IR, NMR, and Raman) and thermal methods are presented. Examples of biomimetic synthetic materials are used to show the contribution of single or multiple techniques in the elucidation of their structure.

Retrieval of relevant parameters of natural multilayer systems by means of bio-inspired optimization strategies.

Natural photonic structures exhibit remarkable color effects such as metallic appearance and iridescence. A rigorous study of the electromagnetic response of such complex structures requires to accurately determine some of their relevant optical parameters, such as the refractive indices of the materials involved. In this paper, we apply different heuristic optimization strategies to retrieve the real and imaginary parts of the refractive index of the materials comprising natural multilayer systems. Through some examples, we compare the performances of the inversion methods proposed and show that these kinds of algorithms have a great potential as a tool to investigate natural photonic structures.

Use of ethylene glycol to evaluate gradient performance in gradient-intensive diffusion MR sequences.

Imaging a phantom of known dimensions is a widely used and simple method for calibrating MRI gradient strength. However, full-range characterization of gradient response is not achievable using this approach. Measurement of the apparent diffusion coefficient of a liquid with known diffusivity allows for calibration of gradient amplitudes across a wider dynamic range. An important caveat is that the temperature dependence of the liquid's diffusion characteristics must be known, and the temperature of the calibration phantom must be recorded. In this report, we demonstrate that the diffusion coefficient of ethylene glycol is well described by Arrhenius-type behavior across the typical range of ambient MRI magnet temperatures. Because of ethylene glycol's utility as an NMR chemical-shift thermometer, the same (1)H MR spectroscopy measurements that are used for gradient calibration also simultaneously "report" the sample temperature. The high viscosity of ethylene glycol makes it well-suited for assessing gradient performance in demanding diffusion-weighted imaging and spectroscopy sequences.

Biomimetic hydrogels gate transport of calcium ions across cell culture inserts.

Control of the in vitro spatiotemporal availability of calcium ions is one means by which the microenvironments of hematopoietic stem cells grown in culture may be reproduced. The effects of cross-linking density on the diffusivity of calcium ions through cell culture compatible poly(2-hydroxyethyl methacrylate) [poly(HEMA)]-based bioactive hydrogels possessing 1.0 mol% 2-methacryloyloxyethyl phosphorylcholine (MPC), 5 mol% N,N-(dimethylamino)ethylmethacrylate (DMAEMA) and ca. 17 mol% n-butyl acrylate (n-BA) have been investigated to determine if varying cross-link density is a viable approach to controlling transport of calcium across hydrogel membranes. Cross-linking density was varied by changing the composition of cross-linker, tetraethyleneglycol diacrylate (TEGDA). The hydrogel membranes were formed by sandwich casting onto the external surface of track-etched polycarbonate membranes (T = 10 µm, φ = 0.4 µm pores) of cell culture inserts, polymerized in place by UV light irradiation and immersed in buffered (0.025 HEPES, pH 7.4) 0.10 M calcium chloride solution. The transport of calcium ions across the hydrogel membrane was monitored using a calcium ion selective electrode set within the insert. Degree of hydration (21.6 ± 1.0%) and void fraction were found to be constant across all cross-linking densities. Diffusion coefficients, determined using time-lag analysis, were shown to be strongly dependent on and to exponentially decrease with increasing cross-linking density. Compared to that found in buffer (2.0-2.5 × 10⁻6 cm²/s), diffusion coefficients ranged from 1.40 × 10⁻6 cm²/s to 1.80 × 10⁻7 cm²/s and tortuosity values ranged from 1.7 to 10.0 for the 1 and 12 mol% TEGDA cross-linked hydrogels respectively. Changes in tortuosity arising from variations in cross-link density were found to be the primary modality for controlling diffusivity through novel n-BA containing poly(HEMA)-based bioactive hydrogels.

Low modulus biomimetic microgel particles with high loading of hemoglobin.

We synthesized extremely deformable red blood cell-like microgel particles and loaded them with bovine hemoglobin (Hb) to potentiate oxygen transport. With similar shape and size as red blood cells (RBCs), the particles were fabricated using the PRINT (particle replication in nonwetting templates) technique. Low cross-linking of the hydrogel resulted in very low mesh density for these particles, allowing passive diffusion of hemoglobin throughout the particles. Hb was secured in the particles through covalent conjugation of the lysine groups of Hb to carboxyl groups in the particles via EDC/NHS coupling. Confocal microscopy of particles bound to fluorescent dye-labeled Hb confirmed the uniform distribution of Hb throughout the particle interior, as opposed to the surface conjugation only. High loading ratios, up to 5 times the amount of Hb to polymer by weight, were obtained without a significant effect on particle stability and shape, though particle diameter decreased slightly with Hb conjugation. Analysis of the protein by circular dichroism (CD) spectroscopy showed that the secondary structure of Hb was unperturbed by conjugation to the particles. Methemoglobin in the particles could be maintained at a low level and the loaded Hb could still bind oxygen, as studied by UV-vis spectroscopy. Hb-loaded particles with moderate loading ratios demonstrated excellent deformability in microfluidic devices, easily deforming to pass through restricted pores half as wide as the diameter of the particles. The suspension of concentrated particles with a Hb concentration of 5.2 g/dL showed comparable viscosity to that of mouse blood, and the particles remained intact even after being sheared at a constant high rate (1000 1/s) for 10 min. Armed with the ability to control size, shape, deformability, and loading of Hb into RBC mimics, we will discuss the implications for artificial blood.

Preliminary evaluation of particle systems visualization on the skin surface by scanning electron microscopy and transparency profilometry.

BACKGROUND: There is a rising debate concerning the possible side effects arising from the use of particles at nanosize since the production of nanomaterials is increasing worldwide. Nanoparticles are able to enter the body through the skin, lungs or intestinal tract, depositing in several organs, and the risk associated with exposure to them, the routes of entry and the molecular mechanisms of any cytotoxicity need to be well understood. The aim of this work was to evaluate the suitability of skin replica as a method to study the colloidal systems visualization and distribution on skin surface. METHODS: Solid lipid nanoparticles (SLN) were used as carrier systems. Skin replicas on healthy volunteers, before and after SLN application, were prepared and visualized using profilometry and scanning electron microscopy (SEM). RESULTS: The results obtained in our study show that skin replica represents a suitable method to study the colloidal systems and their interaction with the skin surface. CONCLUSION: Profilometry enabled us to observe the systems distribution on a cutaneous texture. In addition, SEM, thanks to its high magnifications and field depth, allowed us to evaluate particles' distribution on the skin texture and the interaction between particles of different compositions and replica silicone.

A synthetic cartilage extracellular matrix model: hyaluronan and collagen hydrogel relaxivity, impact of macromolecular concentration on dGEMRIC.

OBJECTIVE: To develop and characterize the MR properties of a synthetic model for cartilage extra-cellular matrix using hydrogels and to determine the concentration dependence of spin-lattice (T1) and spin-spin (T2) relaxation times of hydrogels and their glycosaminoglycan and collagen components in the presence and absence of gadopentetate dimeglumine (Gd-DTPA) for use in dGEMRIC. MATERIALS AND METHODS: T1 and T2 measurements were made at 3 Tesla on a range of gelatin (i.e., collagen) and hyaluronan (i.e., glycosaminoglycan) solutions (6.25-100 g/l), alone, together in a composite, and as dityramine-bridged hydrogels. Relaxivity was calculated as a function of macromolecular concentration. RESULTS: Even at the highest concentrations, gelatin and hyaluronan solutions had T1 and T2 values significantly larger than those reported for cartilage. Only composite hydrogels with gelatin and hyaluronan concentrations naturally found in cartilage resulted in T1 values, but not T2 values, representative of cartilage. Relaxivities were slightly dependent on both hyaluronan concentration (R1 = 0.0027 l g(-1) s(-1); R2 = 0.025 l g(-1) s(-1)) and gelatin concentration (R1 = 0.0032 l g(-1) s(-1); R2 = 0.020 l g(-1) s(-1)) alone and as a composite (R1 = 0.0068 l g(-1) s(-1); R2 = 0.101 l g(-1) s(-1)). Gd-DTPA relaxivities were dependent upon macromolecular concentration and varied by 14-32% (R1 = 4.24 to 5.55 mM(-1) s(-1); R2 = 4.60 to 6.27 mM(-1) s(-1)) over the range of cartilage biochemistry. CONCLUSIONS: Without the contrast agent, hyaluronan and gelatin, alone or in a composite, have a very small impact on the relaxivities of the model system. The impact on R1 was approximately tenfold less than on R2. In contrast, macromolecular concentrations above 50 g/l significantly impacted Gd-DTPA relaxivity and should be accounted for when measuring the glycosaminoglycan content of cartilage in vivo using dGEMRIC.

Effect of calcium on the morphology and functionality of whey protein nanofibrils.

Self-assembly of amyloid-like nanofibrils during heating of bovine whey proteins at 80 °C and pH 2 is accelerated by the presence of NaCl and/or CaCl(2), but the rheological consequences of accelerated self-assembly are largely unknown. This investigation focused on the impact of CaCl(2) on the evolution of rheological properties and fibril morphology of heated whey protein isolate (WPI), both during self-assembly at high temperature and after cooling. Continuous rotational rheometry of heated 2% w/w WPI showed a nonlinear effect of CaCl(2) on the viscosity of fibril dispersions, which we attributed to effects on fibril flexibility and thus the balance between intrafibril and interfibril entanglements. Small-amplitude oscillatory measurements made in situ during heating of 10% w/w WPI at 80 °C suggest that CaCl(2) is not involved in either fibril structure or gel structure, and this was confirmed with dialysis experiments.

Peptide mixtures can self-assemble into large amyloid fibers of varying size and morphology.

Peptide mixtures spontaneously formed micrometer-sized fibers and ribbons from aqueous solution. Hydrolyzed gliadin produced short, slightly elliptical fibers while hydrolyzed wheat gluten, a mixture of gliadin and glutenin, formed round fibers of similar size. Mixing hydrolyzed gliadin with increasing molar amounts of myoglobin or amylase resulted in longer, wider fibers that transitioned from round to rectangular cross section. Fiber size, morphology, and modulus were controlled by peptide mixture composition. Fourier transform infrared (FT-IR) spectroscopy results showed that peptides experienced α to ß transitions forming an elementary cross-ß peptide secondary structure, indicative of amyloids. Large fiber formation was observed to be dependent on hydrophobic packing between constituent peptides. A model was developed to show how the fiber morphology was influenced by the peptides in the mixture.

On the design of composite protein-quantum dot biomaterials via self-assembly.

Incorporation of nanoparticles during the hierarchical self-assembly of protein-based materials can impart function to the resulting composite materials. Herein we demonstrate that the structure and nanoparticle distribution of composite fibers are sensitive to the method of nanoparticle addition and the physicochemical properties of both the nanoparticle and the protein. Our model system consists of a recombinant enhanced green fluorescent protein-Ultrabithorax (EGFP-Ubx) fusion protein and luminescent CdSe-ZnS core-shell quantum dots (QDs), allowing us to optically assess the distribution of both the protein and nanoparticle components within the composite material. Although QDs favorably interact with EGFP-Ubx monomers, the relatively rough surface morphology of composite fibers suggests EGFP-Ubx-QD conjugates impact self-assembly. Indeed, QDs templated onto EGFP-Ubx film post-self-assembly can be subsequently drawn into smooth composite fibers. Additionally, the QD surface charge impacts QD distribution within the composite material, indicating that surface charge plays an important role in self-assembly. QDs with either positively or negatively charged coatings significantly enhance fiber extensibility. Conversely, QDs coated with hydrophobic moieties and suspended in toluene produce composite fibers with a heterogeneous distribution of QDs and severely altered fiber morphology, indicating that toluene severely disrupts Ubx self-assembly. Understanding factors that impact the protein-nanoparticle interaction enables manipulation of the structure and mechanical properties of composite materials. Since proteins interact with nanoparticle surface coatings, these results should be applicable to other types of nanoparticles with similar chemical groups on the surface.

Three-dimensional spatial patterning of proteins in hydrogels.

The ability to create three-dimensional biochemical environments that mimic those in vivo is valuable for the elucidation of fundamental biological phenomena and pathways. To this end, we designed a system in which proteins can be photochemically patterned in three dimensions within hydrogels under physiological conditions. Fibroblast growth factor-2 (FGF2) was immobilized within agarose hydrogels that were modified with two-photon labile 6-bromo-7-hydroxycoumarin-protected thiols. Two different methods were developed for FGF2 immobilization. The first procedure relies on the protein containing free cysteines for the formation of disulfide bonds with photoexposed agarose thiols. The second procedure takes advantage of the femtomolar binding partners, human serum albumin (HSA) and albumin binding domain (ABD), which have K(D) values of ~10(-14) M. Here HSA-maleimide was chemically bound to photoexposed agarose thiols, and then the FGF2-ABD fusion protein was added to form a stable complex with the immobilized HSA. The use of orthogonal, physical binding pairs allows protein immobilization under mild conditions and can be broadly applied to any protein expressed as an ABD fusion.