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Biomedical subjects

Samuel I Stupp

Publications and source records attributed to Samuel I Stupp.

At least 37 records · Page 2Linked to original sources
PubMed2005

Synthesis of a poly(L-lysine)-calcium phosphate hybrid on titanium surfaces for enhanced bioactivity.

Titanium has been a successful implant material owing to its excellent strength to weight ratio, toughness, and bioinert oxide surface. Significant progress has been made on the improvement of titanium's bioactivity by coating its oxide surface with calcium phosphates and bioactive molecules. Here, we report on the coating of titanium with a poly(L-lysine)-calcium phosphate hybrid material with a nanoscale texture. This hybrid coating was grown by first nucleating seed crystals of calcium phosphate, directly on the Ti surface and then exposing this surface to solutions containing Ca(2+), PO(4)(3-), and poly(L-lysine). The resultant hybrid coating was characterized by electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, and elemental analysis. This material contained 14% by weight poly(L-lysine), and this organic component decreased greatly the dimensions of the surface features, thus enhancing surface area relative to the inorganic control. The highly textured hybrid material was more susceptible than the control to acidic and enzymatic degradation. The amino acid cysteine was covalently linked to the hybrid material, demonstrating the potential of this coating for further functionalization. These hybrid coatings may prove useful in enhancing the bioactivity of titanium.

Calcium Chloride↗
PubMed2005

Cellular response to zinc-containing organoapatite: an in vitro study of proliferation, alkaline phosphatase activity and biomineralization.

We present a series of experiments investigating the in vitro biological activity of zinc-containing organoapatite (ZnOA)-coated titanium meshes. ZnOA is a hydroxyapatite-based material that contains poly(l-lysine) and zinc ions and can be coated onto titanium by treating the metal surface with poly(amino acids) that allow for electrostatic bonding of the mineral to the titanium surface. Preosteoblastic mouse calyaria cells were cultured on ZnOA-coated titanium meshes in a three-dimensional (3D) bioreactor, which provides an in vitro culture environment that better simulates what cells experience in vivo, compared to traditional 2D cultures. Results of these studies show a time-dependent cascade of events leading to an earlier onset of alkaline phosphatase (ALP) expression and biomineralization of ZnOA-coated samples as compared to controls. After the observation of peak ALP levels in ZnOA-coated titanium samples, mineralized bone nodules were observed by scanning electron microscopy. Tetracycline staining confirmed that the observed mineral nodules were newly synthesized biomineral, and not due to the inorganic coating. ZnOA-coated titanium substrates represent a new class of materials for human repair that provide, mechanical stability, as well as chemical and biochemical signals to promote new bone growth.

3T3 Cells↗
PubMed2005

Supramolecular fluorophores for biological studies: phenylene vinylene-amino acid amphiphiles.

We report here on a family of self-assembling fluorescent organic amphiphiles with a biomolecular L-lysine hydrophile and a photonically active phenylene vinylene hydrophobe. Unlike conventional amphiphiles, these segmented dendrimers feature a rigid, branched hydrophobe, and have packing characteristics controlled by the ratio of cross-sectional areas of the hydrophobe and hydrophile. In dilute solution, the amphiphiles form supramolecular aggregates, which are easily taken in by cells through an endocytic pathway, and have no discernible effect on cell proliferation or morphology. An analogous pyrene-based amphiphile was cytotoxic, suggesting that cell survival may be linked either to the self-assembling nature of the amphiphiles, or to the specific properties of the phenylene vinylene segment. The combination of photonic and biological components in these amphiphiles provides great potential for applications in sensing or delivery of molecules to intracellular targets.

Amino Acids↗
PubMed2005

Presentation and recognition of biotin on nanofibers formed by branched peptide amphiphiles.

A branched peptide amphiphile system was designed for enhanced recognition of biotin on nanofibers formed by self-assembly of these molecules. Branching at a lysine residue was used to design peptide amphiphiles that are capable of presenting more than one epitope per molecule. We found that biotinylated branched structures form nanofibers that enhance recognition by the avidin protein receptor relative to similar nanostructures formed by linear peptide analogues. Biotin-avidin binding to the supramolecular nanofibers was characterized by measurement of fluorescence from nanofibers incubated with chromophore-conjugated avidin.

Binding Sites↗
PubMed2005

Self-assembled peptide amphiphile nanofibers conjugated to MRI contrast agents.

Self-assembled peptide amphiphile nanofibers have been investigated for their potential use as in vivo scaffolds for tissue engineering and drug delivery applications. We report here the synthesis of magnetic resonance (MR) active peptide amphiphile molecules that self-assemble into spherical and fiber-like nanostructures, enhancing T(1) relaxation time. This new class of MR contrast agents can potentially be used to combine high-resolution three-dimensional MR fate mapping of tissue-engineered scaffolds with targeting of specific cellular receptors.

Chelating Agents↗
PubMed2005

Enrichment of single-walled carbon nanotubes by diameter in density gradients.

The bulk enrichment and separation of single-walled carbon nanotubes (SWNTs) by diameter has been achieved through ultracentrifugation of DNA-wrapped SWNTs in aqueous density gradients. The separation is identified by the visual formation of colored bands of SWNTs in the density range of 1.11-1.17 g cm(-3). The optical absorbance spectra of the separated SWNTs indicate that SWNTs of decreasing diameter are increasingly more buoyant. This nondestructive and scalable separation strategy is expected to impact the fields of molecular electronics, optoelectronics, and sensing where SWNTs of a monodisperse band gap are essential.

Centrifugation, Density Gradient↗
PubMed2004

Synthesis, self-assembly, and characterization of supramolecular polymers from electroactive dendron rodcoil molecules.

We report here the synthesis and self-assembly of a series of three molecules with dendron rodcoil architecture that contain conjugated segments of oligo(thiophene), oligo(phenylene-vinylene), and oligo(phenylene). Despite their structural differences, all three molecules yield similar self-assembled structures. Electron and atomic force microscopy reveals the self-assembly of the molecules into high aspect ratio ribbon-like nanostructures which at low concentrations induce gelation in nonpolar solvent. Self-assembly results in a blue-shifted absorption spectrum and a red-shifted, quenched fluorescence spectrum, indicating aggregation of the conjugated segments within the ribbon-like structures. The assembly of these molecules into one-dimensional nanostructures is a route to pi-pi stacked supramolecular polymers for organic electronic functions. In the oligo(thiophene) derivative, self-assembly leads to a 3 orders of magnitude increase in the conductivity of iodine-doped films due to self-assembly. We also found that electric field alignment of these supramolecular assemblies can be used to create arrays of self-assembled nanowires on a device substrate.

Journal Article↗
PubMed2004

Semiconductor-encapsulated peptide-amphiphile nanofibers.

We report here on the use of peptide-amphiphile (PA) nanofibers displaying the S(P)RGD peptide sequence on their exterior as templates for the mineralization of cadmium sulfide (CdS). At low Cd:PA ratios, the nanofibers nucleate and organize quantum-confined 3-5 nm CdS nanocrystals into linear arrays. Tubular structures, in which the PA fibers are completely encapsulated by the semiconductor, are produced at higher Cd:PA ratios.

Cadmium Compounds↗
PubMed2004

Selective differentiation of neural progenitor cells by high-epitope density nanofibers.

Neural progenitor cells were encapsulated in vitro within a three-dimensional network of nanofibers formed by self-assembly of peptide amphiphile molecules. The self-assembly is triggered by mixing cell suspensions in media with dilute aqueous solutions of the molecules, and cells survive the growth of the nanofibers around them. These nanofibers were designed to present to cells the neurite-promoting laminin epitope IKVAV at nearly van der Waals density. Relative to laminin or soluble peptide, the artificial nanofiber scaffold induced very rapid differentiation of cells into neurons, while discouraging the development of astrocytes. This rapid selective differentiation is linked to the amplification of bioactive epitope presentation to cells by the nanofibers.

Animals↗
PubMed2004

Modification of fibrous poly(L-lactic acid) scaffolds with self-assembling triblock molecules.

Molecular self-assembly offers an effective method to modify the surface properties of common biomaterials by presenting biologically relevant chemistry in a controlled, ordered fashion. This work reports on self-assembling triblock molecules containing rigid cholesteryl segments followed by flexible oligomers of L-(lactic acid) and second generation L-lysine dendrons. Second harmonic generation and small angle X-ray scattering indicate these molecules self-assemble into multilayer polar structures when cast from ethyl acetate solutions and segregate into polar polydomains when annealed. These self-assembled layers significantly improve water wettability when coated onto poly(L-lactic acid) fibers. Scaffolds formed from fibers modified by self-assembly enhance adhesion of 3T3 mouse calvaria cells and produce greater population growth rates. These results demonstrate the use of self-assembly to present biologically relevant chemistry on surfaces of biomaterials. Applications of this technology include the modification of substrates for cell culture, tissue engineering, and cell transplantation.

Acetates↗
PubMed2004

Gene expression in cancer cells is influenced by contact with bone cells in a novel coculture system that models bone metastasis.

Contact between bone cells and cancer cells (heterotypic cell contact) is thought to play a central role in the initial growth and progression of metastatic cells. Attempts at studying heterotypic contact in vitro and in vivo have been confounded by difficulty in controlling how and when heterotypic contact occurs between unlike cells. A novel model, the micropatterned coculture system, is described that quantifies and controls heterotypic contact between cancer cells and bone cells in vitro. The micropatterned coculture system is biocompatible, and is modified easily to accommodate two or more different populations of cells. Immunofluorescence of cocultures of prostate cancer-3 cells and osteoblasts show the precise control of cell interactions. Ribonucleic acid of sufficient quantity and quality is isolated readily from cells cocultured on the micropatterned coculture system. The expression of the metastasis associated genes urokinase plasminogen activator, insulinlike growth factor binding protein-1 and insulinlike growth factor binding protein-3 are regulated in response to heterotypic contact and soluble factors respectively. A model of bone metastasis based on the micropatterned coculture system technology will streamline the process for testing therapeutic agents, so that more molecules can be identified for animal and clinical testing at less cost and in less time than using conventional methods.

Animals↗
PubMed2003

Colonization of organoapatite-titanium mesh by preosteoblastic cells.

Titanium (Ti) and its alloys continue to serve as successful implant materials for skeletal repair because of their physical properties and biocompatibility. This study investigates the influence of organoapatite (OA), grown directly onto an L-shaped Ti mesh, on preosteoblastic cellular colonization. Unseeded mesh samples were placed on subconfluent layers of MC3T3-E1 murine calvaria cells and cultured for up to 2 weeks. Cells demonstrated accelerated colonization of the three-dimensional OA-Ti mesh substrates over bare Ti controls. Cells also showed significantly increased proliferation on the OA-Ti mesh over bare Ti controls. Cellular differentiation, measured by alkaline phosphatase and osteocalcin expression, was observed at late stages of the experiment with no notable differences between OA-Ti mesh and bare Ti controls. These results suggest that OA grown onto porous Ti substrates is capable of inducing accelerated colonization of unseeded implant structures by osteogenic cells.

Animals↗
PubMed2003

Aqueous self-assembly of unsymmetric Peptide bolaamphiphiles into nanofibers with hydrophilic cores and surfaces.

Unsymmetric peptide bolaamphiphiles that incorporate (l-glutamyl)3glycine at one terminus and either tetraethylene glycol or aspartic acid at the other were found to form hydrogels at low wt %, presumably by self-assembling into nanofibers presenting (l-glutamyl)3glycine at their surfaces and burying the second headgroup at their cores. Transmission electron microscopy measurements on 1 wt % gels negatively stained with phosphotungstic acid and positively stained with uranyl acetate show one-dimensional objects with diameters of 5 nm and lengths in excess of 1 mum. Circular dichroism and solid-state FTIR spectra indicate the adoption of beta-sheet structure within the nanofibers.

Alanine↗
PubMed2003

Assembling a lasing hybrid material with supramolecular polymers and nanocrystals.

The combination of bottom-up and top-down processes to organize nanophases in hybrid materials is a key strategy to create functional materials. We found that oxide and sulphide nanocrystals become spontaneously dispersed in organic media during the self-assembly of nanoribbon supramolecular polymers. These nanoribbon polymers form by self-assembly of dendron rodcoil molecules, which contain three molecular blocks with dendritic, rod-like, and coil-like architectures. In an electric field these supramolecular assemblies carrying bound nanocrystals migrate to the positive electrode in an etched channel and align in the field. In the system containing ZnO nanocrystals as the inorganic component, both phases are oriented in the hybrid material forming an ultraviolet lasing medium with a lower threshold relative to pure ZnO nanocrystals.

Crystallization↗
PubMed2003

Self-assembly combining two bioactive peptide-amphiphile molecules into nanofibers by electrostatic attraction.

We describe a new approach to peptide-amphiphile (PA) nanofiber preparation that allows PAs with different bioactive amino acid sequences to be combined into a single fiber. Oppositely charged PAs are synthesized separately and then mixed to produce gels of nanofiber networks at physiological pH. Transmission electron microscopy reveals the formation of fibers approximately 7 nm in diameter and several micrometers long in these dimeric systems. On the basis of NMR and microscopy, we suggest that these nanofibers are cylindrical micelles of mixed composition, formed due to electrostatic attraction between the oppositely charged PAs. This strategy for self-assembly may be useful in cell therapies that can be implemented without invasive surgery or in in vitro tissue engineering.

Amino Acid Sequence↗
PubMed2002

Self-assembling biomaterials: liquid crystal phases of cholesteryl oligo(L-lactic acid) and their interactions with cells.

We report here on the synthesis and characterization of a series of self-assembling biomaterials with molecular features designed to interact with cells and scaffolds for tissue regeneration. The molecules of these materials contain cholesteryl moieties, which have universal affinity for cell membranes, and short chains of lactic acid, a common component of biodegradable tissue engineering matrices. The materials were synthesized in good yields with low polydispersities in the range of 1.05-1.15, and their characterization was carried out by small-angle x-ray diffraction, transmission electron microscopy, electron diffraction, differential scanning calorimetry, and atomic force microscopy. These molecular materials form layered structures that can be described as smectic phases and can also order into single-crystal stacks with an orthorhombic unit cell. Their layer spacings range from 58 to 99 A, corresponding to bilayers of oligomers with an average of 10 and 37 lactic acid residues, respectively. The self-organized layered structures were found to promote improved fibroblast adhesion and spreading, although the specific mechanism for this observed response remains unknown. The ability of self-assembling materials to present ordered and periodic bulk structures to cells could be a useful strategy in tissue engineering.

Animals↗
PubMed2002

Dendron rodcoils: synthesis of novel organic hybrid structures.

Convergent and divergent syntheses of novel organic hybrid structures termed dendron rodcoils (DRC) containing dendritic, rodlike, and coillike segments are described. The aryl ester dendron masked with 32 trifluoromethyl groups is prepared via a convergent approach using 5-(tert-butyldimethylsiloxy)isophthalic acid as the monomer unit. The activation of the focal point of the dendron allows for successful coupling between the dendron and the diblock rodcoil molecules synthesized separately. In another example, the dendritic block is grown via divergent strategy from the terminus of rodcoil using 3,5-bis(tert-butyldimethylsiloxy)benzoic acid as an AB(2) monomer. A combination of catalyzed esterification reactions and silyl deprotection chemistry proved to be a very efficient method for construction of these nanosized structures with unusual molecular architecture. Both synthetic strategies allowed for the preparation of DRCs with nearly monodisperse dendritic blocks as demonstrated by NMR, MALDI-TOF, and GPC measurements.

Journal Article↗