Two complementary strategies can be used in the fabrication of molecular biomaterials. In the 'top-down' approach, biomaterials are generated by stripping down a complex entity into its component parts (for example, paring a virus particle down to its capsid to form a viral cage). This contrasts with the 'bottom-up' approach, in which materials are assembled molecule by molecule (and in some cases even atom by atom) to produce novel supramolecular architectures. The latter approach is likely to become an integral part of nanomaterials manufacture and requires a deep understanding of individual molecular building blocks and their structures, assembly properties and dynamic behaviors. Two key elements in molecular fabrication are chemical complementarity and structural compatibility, both of which confer the weak and noncovalent interactions that bind building blocks together during self-assembly. Using natural processes as a guide, substantial advances have been achieved at the interface of nanomaterials and biology, including the fabrication of nanofiber materials for three-dimensional cell culture and tissue engineering, the assembly of peptide or protein nanotubes and helical ribbons, the creation of living microlenses, the synthesis of metal nanowires on DNA templates, the fabrication of peptide, protein and lipid scaffolds, the assembly of electronic materials by bacterial phage selection, and the use of radiofrequency to regulate molecular behaviors.

A 16-residue peptide [(Ala-Glu-Ala-Glu-AlaLys-Ala-Lys)2J has a characteristic 13-sheet circular dichroism spectrum in water. Upon the addition of salt, the peptide spontaneously assembles to form a macroscopic membrane. The membrane does not dissolve in heat or in acidic or alkaline solutions, nor does it dissolve upon addition of guanidine hydrochloride, SDS/urea, or a variety of proteolytic enzymes.Scanning EM reveals a network of interwoven framents ""10-20 nm in diameter. An important component of the stability is probably due to formation of complementary ionic bonds between glutamic and lysine side chains. This phenomenon may be a model for studying the insoluble peptides found in certain neurological disorders. It may also have implications for biomaterials and origin-of-life research.Peptides of alternating hydrophilic and hydrophobic amino acid residues have a tendency to adopt a (3-sheet structure. The complete sequence of (Ala-Glu-Ala-Glu-Ala-Lys-AlaLys)2 (EAK16) was originally found in a region of alternating hydrophobic and hydrophilic residues in zuotin, a yeast protein that was initially identified for its ability to bind preferentially to left-handed Z-DNA (1). Previous studies with alternating amphiphilic-peptide polymers-e.g., poly-(Val-Lys), poly(Glu-Ala), poly(Tyr-Glu), poly(Lys-Phe), poly(Lys-Leu)-and oligopeptides [(Val-Glu-Val-Orn)j_3]-Val (2-7) have shown that these polymers can adopt (3-sheet structures and can aggregate, depending upon pH, salt, and time. However, self-complementary EAK16 is distinctive in that it forms an insoluble macroscopic membrane. MATERIALS AND METHODSPeptides. The Glu-Ala-Lys peptides were synthesized by a peptide synthesizer (Applied Biosystems), purified by reverse-phase HPLC, and eluted by a linear gradient of 5-80% acetonitrile/0.1% trifluoacetic acid. The peptide stock solutions were dissolved in water (1-5 mg/ml) or in 23% acetonitrile (10 mg/ml). The concentrations of the peptides were determined by dissolving dried peptide in water (wt/vol) and centrifuging the solution. A portion of the solution was then analyzed by hydrolysis with internal controls. The sequence of the peptides was confirmed by microsequencing. The composition of the peptides was confwrmed by hydrolytic analysis. Ala-Glu-Ala-Lys-Ala-Glu-Ala-Glu-Ala-Lys-AlaLys (EAK12) and EAK16 are acetylated and aminated at the N-and C-terminal ends, respectively. Blocking of both N and C termini of EAK16 appears nonessential for membrane formation.CD Measurement. CD spectra were gathered on an Aviv model 6ODS spectropolarimeter with 6OHDS software for data processing. Because EAK16 contains both positively and negatively charged residues, the peptide itself can serve as a buffer. CD samples were prepared by diluting stock peptide solution (1-5 mg/ml) in water.Membrane Preparations. The membranes were prepared as follows: 5-10 ,4 of the stock solution of EAK16 peptide (1-5 mg/ml) was added to 0.5-1.0 ml of phosphate-buffered saline (150 mM NaCl/10 mM sodium phosphate, pH 7.4) with 0.00001% Con...

A new type of self-assembling peptide (sapeptide) scaffolds that serve as substrates for neurite outgrowth and synapse formation is described. These peptide-based scaffolds are amenable to molecular design by using chemical or biotechnological syntheses. They can be tailored to a variety of applications. The sapeptide scaffolds are formed through the spontaneous assembly of ionic self-complementary ␤-sheet oligopeptides under physiological conditions, producing a hydrogel material. The scaffolds can support neuronal cell attachment and differentiation as well as extensive neurite outgrowth. Furthermore, they are permissive substrates for functional synapse formation between the attached neurons. That primary rat neurons form active synapses on such scaffold surfaces in situ suggests these scaffolds could be useful for tissue engineering applications. The buoyant sapeptide scaffolds with attached cells in culture can be transported readily from one environment to another. Furthermore, these peptides did not elicit a measurable immune response or tissue inflammation when introduced into animals. These biological materials created through molecular design and self assembly may be developed as a biologically compatible scaffold for tissue repair and tissue engineering.biological materials ͉ cell attachment ͉ molecular material design ͉ primary neurons ͉ PC12 cells