Hua Ai

Biomedical applications of electrostatic layer-by-layer nano-assembly of polymers, enzymes, and nanoparticles.

The introduction of electrostatic layer-by-layer (LbL) self-assembly has shown broad biomedical applications in thin film coating, micropatterning, nanobioreactors, artificial cells, and drug delivery systems. Multiple assembly polyelectrolytes and proteins are based on electrostatic interaction between oppositely charged layers. The film architecture is precisely designed and can be controlled to 1-nm precision with a range from 5 to 1000 nm. Thin films can be deposited on any surface including many widely used biomaterials. Microencapsulation of micro/nanotemplates with multilayers enabled cell surface modification, controlled drug release, hollow shell formation, and nanobioreactors. Both in vitro and in vivo studies indicate potential applications in biology, pharmaceutics, medicine, and other biomedical areas.

Nano-encapsulation of furosemide microcrystals for controlled drug release

Furosemide microcrystals were encapsulated with polyions and gelatin to control the release of the drug in aqueous solutions. Charged linear polyions and gelatin were alternatively deposited on 5-microm drug microcrystals through layer-by-layer (LbL) assembly. Sequential layers of poly(dimethyldiallyl ammonium chloride) (PDDA) and poly(styrenesulfonate) (PSS) were followed by adsorption of two to six gelatin/PSS bilayers with corresponding capsule wall thicknesses ranging from 45 to 115 nm. The release of furosemide from the coated microparticles was measured in aqueous solutions of pH 1.4 and 7.4. At both pH values, the release rate of furosemide from the encapsulated particles was reduced by 50-300 times (for capsules coated with two to six bilayers) compared to uncoated furosemide. The results provide a method of achieving prolonged drug release through self-assembly of polymeric shells on drug microcrystals.

Biocompatibility of layer-by-layer self-assembled nanofilm on silicone rubber for neurons

Electrostatic layer-by-layer (LbL) self-assembly, a novel method for ultrathin film coating has been applied to silicone rubber to encourage nerve cell adhesion. The surfaces studied consisted of precursor layers, with alternating cationic poly(ethyleneimine) (PEI) and anionic sodium poly(styrenesulfonate) (PSS) followed by alternating laminin and poly-D-lysine (PDL) layers or fibronectin and PDL layers. Film growth increased linearly with the number of layers. Every fibronectin/PDL and laminin/PDL bilayer was 4.4 and 3.5 nm thick, respectively. All layers were more hydrophilic than the unmodified silicone rubber surface, as determined from contact angle measurements. Of the coatings studied, a PDL layer was the most hydrophilic. A multilayer film with composition [PSS/PEI]3+[fibronectin/PDL]4 or [PSS/PEI]3+[laminin/PDL]4 was highly favorable for neuron adhesion, in contrast to bare silicone rubber substrate. The film coated on silicone rubber is biocompatible for cerebellar neurons with active viability, as shown by lactate dehydrogenase (LDH) assay and fluorescence cellular metabolism observations. These results demonstrate that LbL self-assembly provides an effective approach to apply films with nanometer thickness to silicone rubber. Such only few nanometer thick films are biocompatible with neurons, and may be used to coat devises for long-term implant in the central nervous system.

Coating and selective deposition of nanofilm on silicone rubber for cell adhesion and growth.

A recently developed method for surface modification, layer-by-layer (LbL) assembly, has been applied to silicone, and its ability to encourage endothelial cell growth and control cell growth patterns has been examined. The surfaces studied consisted of a precursor, with alternating cationic polyethyleneimine (PEI) and anionic sodium polystyrene sulfonate (PSS) layers followed by alternating gelatin and poly-d-lysine (PDL) layers. Film growth increased linearly with the number of layers. Each PSS/PEI bilayer was 3 nm thick, and each gelatin/PDL bilayer was 5 nm thick. All layers were more hydrophilic than the unmodified silicone rubber surface, as determined from contact angle measurements. The contact angle was primarily dictated by the outermost layer. Of the coatings studied, gelatin was the most hydrophilic. A film of (PSS/PEI)4/(gelatin/PDL)4/ gelatin was highly favorable for cell adhesion and growth, in contrast to films of (PSS/PEI)8 or (PSS/PEI)8/PSS. Cell growth patterns were successfully controlled by selective deposition of microspheres on silicone rubber, using microcontact printing with a silicone stamp. Cell adhesion was confined to the region of microsphere deposition. These results demonstrate that the LbL self-assembly technique provides a general approach to coat and selectively deposit films with nanometer thickness on silicone rubber. Furthermore, they show that this method is a viable technique for controlling cellular adhesion and growth.

GELATIN–GLUTARALDEHYDE CROSS-LINKING ON SILICONE RUBBER TO INCREASE ENDOTHELIAL CELL ADHESION AND GROWTH

SummarySilicone is a biomaterial that is widely used in many areas because of its high optical clarity, its durability, and the ease with which it can be cast. However, these advantages are counterbalanced by strong hydrophobicity. Gelatin cross-linking has been used as a hydrophilic coating on many biomaterials but not on silicone rubber. In this study two gelatin glutaraldehyde (GA) cross-linking methods were used to coat a hydrophilic membrane on silicone rubber. In method I, gelatin and GA were mixed in three different proportions (64:1, 128:1, and 256:1) before coating. In method II, a newly formed 5% gelatin membrane was cross-linked with a 2.5% GA solution. All coatings were hydrophilic, as determined from the measurement of contact angle for a drop of water on the surface. Bovine coronary arterial endothelial cells were shown to grow well on the surface modified by method II at 72 h. In method I, the cells grew well for gelatin-GA proportions of 64:1 and 128:1 at 72 h. No cell attachment on untreated silicone rubber was observed by the third d of seeding. The results indicated that both methods of gelatin-GA cross-linking provided a hydrophilic surface on silicone for endothelial cell adhesion and growth in vitro.

Using microfabrication and electrostatic layer-by-layer (LbL) self-assembly technologies to improve the growth and alignment of smooth muscle cells

Smooth muscle cells (SMCs) were cultured on polydimethylsiloxane (PDMS) based cell culture substrates. Two types of experiments were performed to address the cell behaviors on these substrates. One was culturing smooth muscle cells on bare PDMS flat surfaces and gelatin coated PDMS flat surfaces deposited using electrostatic layer-by-layer self-assembly technology. The other was culturing smooth muscle cells on two microstructured PDMS microchannel substrates and PDMS flat surface substrates. The microchannels are 5-/spl mu/m channels (line width = 5 /spl mu/m, spacing width = 5 /spl mu/m, depth = 5 /spl mu/m) and 100-/spl mu/m channels (line width = 100 /spl mu/m, spacing width = 100 /spl mu/m, depth = 50 /spl mu/m) respectively. All substrates were coated with multilayers (50 nm in thickness) of gelatin using electrostatic layer-by-layer self-assembly technology in order to improve the attachment of the cells. We concluded that surface treatment, such as gelatin coating, is able to help smooth muscle cells attach on PDMS substrates. Accordingly, it will increase the potential growth of cells on the engineered PDMS substrates. Second, smooth muscle cells showed a clear preference of alignment long the channel sidewall on the 100-/spl mu/m channel substrate as compared to that on the flat surface substrate. Microchannels are able to align the growth of smooth muscle cells, and the ability of controlling the alignment depends on the dimension of the microstructures, as well as the surface treatment for increasing cell attachment. Microfabrication and electrostatic layer-by-layer self-assembly technologies have significant potential for application in the field of tissue engineering.

Applications of the electrostatic layer-by-layer self-assembly technique in biomedical engineering

The electrostatic layer-by-layer (LbL) self-assembly technique has shown broad applications in biomedical engineering including: 1) Controlled Drug Release: Furosemide microcrystals have been encapsulated with polyions to control the release of the drug in aqueous solutions. The release of furosemide was slowed (up to 300 times) after encapsulation. 2) Artificial cells: Platelets were coated with polyions, nanoparticles, or antibodies through LbL self-assembly, and targeting of anti-IgG shelled platelets based on antigen-antibody recognition was demonstrated. 3) Biocompatible Nanofilms: Nanofilms of gelatin, Poly-D-lysine, collagen, fibronectin, laminin, hyaluronic acid, or heparin were coated on a PDMS substrate through LbL assembly. A film thickness could be controlled with nanometer accuracy by varying the number of layers. The film was hydrophilic and biocompatible for cell adhesion and growth. 4) Micropatterning: Micropatterning of microspheres and nanospheres was achieved on PDMS substrate through LbL assembly. Cell adhesion on micropatterns was observed. 5) Bio/Nano-Reactors: Multiple layers of nanoparticles were coated on 420 nm diameter nanospheres and then glucose oxidase (GOx) multilayers were fabricated to form high surface area colloidal biocatalysts. The GOx catalytic activity of the biocolloids increased proportionally with the number of silica layers. Biocolloids also exhibited magnetic properties.

Culturing smooth muscle cells on modified PDMS substrates

Polydimethylsiloxane (PDMS) is a popular biocompatible material to be used in cell culture area. However, due to its hydrophobic surface property, cells cannot grow on its bare surface very well. In this paper, electrostatic layer-by-layer (LbL) self-assembly technology was used to coat thin films of hydrophilic and biocompatible materials, poly(dimethyldiallylammonium chloride) (PDDA), poly(styrene sulfonate) (PSS), and gelatin, on the surface of cell culture substrate to increase the growth and alignment of smooth muscle cells (SMCs).

Micropatterning of micro/nanospheres on PDMS by using layer-by-layer self-assembly

Recently, microcontact printing has been used as a new method for building complex patterns. Unlike patterning self-assembled monolayers, we introduced a method to pattern micro/nano structures on PDMS without the help of metal thin film coating and alkanethiol solution. In this study, polycation poly(ethylenimine) and polyanion poly(styrenesulfonate) were used as ink solution to form an ultrathin film on PDMS stamp through electrostatic layer-by-layer self-assembly. The multilayer film of (PEI/PSS)/sub 3//PEI was assembled with a thickness of 12 nm. Then negatively charged 4.5-/spl mu/m microspheres or 45-nm fluorescence nanospheres were adsorbed on the precursor film through the LbL technique. Finally, microspheres or nanospheres were patterned on PDMS substrate through contact printing. Positively charged poly-D-lysine was adsorbed on patterned microspheres through electrostatic interaction. Then bovine coronary arterial endothelial cells were seeded on micropatterns of PDL. In conclusion, charged polyions could be used as an ink solution for PDMS stamps in micropatterning of micro/nanospheres on PDMS substrate.

Coating bio-nanofilm on PDMS through layer-by-layer self-assembly

PDMS is a popular biomaterial, and its surface modification with biocompatible ultrathin films may have potential applications in many biomedical areas. The technique of electrostatic Layer-by-Layer (LbL) assembly of polyions has been widely used in recent years to form ultrathin films. In this study, cationic Poly(ethyleneimine) (PEI) and anionic poly(styrene sulfonate) (PSS) were alternately adsorbed onto PDMS through LbL self-assembly. Then poly-D-lysine, gelatin, collagen, fibronectin, laminin, hyaluronic acid, and heparin were coated on PDMS through LbL assembly by alternate adsorption with oppositely charged polyelectrolytes. The film coated on PDMS was hydrophilic compared to the PDMS substrate, as verified through contact angle measurement. The film thickness could be controlled precisely with an accuracy of nanometers by varying the number of layers. The protein nanofilm was biocompatible, enabling endothelial cells, nerve cells, hepatocytes, or smooth muscle cells to adhere and grow. No cell growth was found on the unmodified PDMS substrate.