Temperature-induced ultradense PEG polyelectrolyte surface grafting provides effective long-term bioresistance against mammalian cells, serum, and whole blood.

We report a facile method of generating ultradense poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) surface by using high temperature alone, which in turn provides dramatic improvement in resisting nonspecific bioadsorption. X-ray photoelectron spectroscopy (XPS) revealed that the surface graft density increased ~4 times higher on the surface prepared at 80 °C compared to 20 °C. The studies from small-angle X-ray scattering (SAXS) and the effect of varying ionic strength during/post assemblies at 20 and 80 °C indicated that the "cloud point grafting effect" is not the cause for obtaining high density grafting. Stringent long-term bioresistance tests have been conducted and the temperature-induced PLL-g-PEG surfaces have achieved (1) zero mammalian cell adsorption/migration for up to 36 days and (2) extremely close-to-zero protein adsorptions have been observed even after 36 days in 10% serum media and 24 h in whole blood within the ultrasensitive detection limit of time-of-flight secondary ion mass spectrometry (ToF-SIMS).

Guidance of stem cell fate on 2D patterned surfaces.

Stem cells possess unique abilities as they can renew themselves for extended periods of time and have the capacity to differentiate into a variety of lineages. They hold promise for treating a plethora of diseases ranging from musculoskeletal defects to myocardial infarction and to neural disorders. Understanding how to control the fate decision of these cells to self-renew or differentiate is paramount in stem cell tissue engineering. Recently, significant progress has been made in guiding stem cell differentiation in vitro, and we are beginning to understand the complex interplay of factors that control their fate. Here, we highlight the recent approaches for guidance of stem cells through patterning of surfaces at the micro- and nanoscale. Particular attention is given to chemical patterning of substrates with adhesion ligands and physical patterning with a variety of topographical features. These surface-mediated biochemical and mechanical cues have proven influential in altering a wide range of stem cell phenotypes. This approach to guide or ultimately control stem cells by surface patterning has enormous potential implications in cell therapies and regenerative medicine.

Micro- and nanoengineering approaches to control stem cell-biomaterial interactions.

As our population ages, there is a greater need for a suitable supply of engineered tissues to address a range of debilitating ailments. Stem cell based therapies are envisioned to meet this emerging need. Despite significant progress in controlling stem cell differentiation, it is still difficult to engineer human tissue constructs for transplantation. Recent advances in micro- and nanofabrication techniques have enabled the design of more biomimetic biomaterials that may be used to direct the fate of stem cells. These biomaterials could have a significant impact on the next generation of stem cell based therapies. Here, we highlight the recent progress made by micro- and nanoengineering techniques in the biomaterials field in the context of directing stem cell differentiation. Particular attention is given to the effect of surface topography, chemistry, mechanics and micro- and nanopatterns on the differentiation of embryonic, mesenchymal and neural stem cells.

High-throughput screening of microscale pitted substrate topographies for enhanced nonviral transfection efficiency in primary human fibroblasts.

Optimization of nonviral gene delivery typically focuses on the design of particulate carriers that are endowed with desirable membrane targeting, internalization, and endosomal escape properties. Topographical control of cell transfectability, however, remains a largely unexplored parameter. Emerging literature has highlighted the influence of cell-topography interactions on modulation of many cell phenotypes, including protein expression and cytoskeletal behaviors implicated in endocytosis. Using high-throughput screening of primary human dermal fibroblasts cultured on a combinatorial library of microscale topographies, we have demonstrated an improvement in nonviral transfection efficiency for cells cultured on dense micropit patterns compared to smooth substrates, as verified with flow cytometry. A 25% increase in GFP(+) cells was observed independent of proliferation rate, accompanied by SEM and confocal microscopy characterization to help explain the phenomenon qualitatively. This finding encourages researchers to investigate substrate topography as a new design consideration for the optimization of nonviral transfection systems.

A combinatorial screening of human fibroblast responses on micro-structured surfaces.

Biomaterial surfaces structured with topographical features have been predicted to play an important role in the next generation of biomedical implants. Specific trends with regard to the influence of the topographical effect on cellular behavior are however challenging to establish due to differences in the topographical features and geometries in the various studies. Here, we demonstrate the use of a highly versatile combinatorial screening approach to identify the effect of 169 distinct surface topographies, consisting of pillars, on fibroblast proliferation and mechanical response. Altering the inter-pillar gap size of the structures revealed a significant change in fibroblast proliferation and identified obvious stress-induced changes in the cytoskeleton and focal adhesion morphology. Larger (4-6 µm) inter-pillar gap sizes reduced fibroblast proliferation and elicited a strong elongation leading to a disruption of the actin cytoskeleton anchored primarily to focal adhesions located between the pillars. Smaller (1-2 µm) inter-pillar gap sizes, on the contrary, caused the fibroblasts to proliferate comparable to cells on a non-structured surface with cells having a clear actin cytoskeleton attached to focal adhesions located mostly on top of the pillars. The approach reveals a strong correlation between the exact topographical periodicities and cellular responses such as cell proliferation, cell morphology and focal adhesion.

Gold ions bio-released from metallic gold particles reduce inflammation and apoptosis and increase the regenerative responses in focal brain injury.

Traumatic brain injury results in loss of neurons caused as much by the resulting neuroinflammation as by the injury. Gold salts are known to be immunosuppressive, but their use are limited by nephrotoxicity. However, as we have proven that implants of pure metallic gold release gold ions which do not spread in the body, but are taken up by cells near the implant, we hypothesize that metallic gold could reduce local neuroinflammation in a safe way. Bio-liberation, or dissolucytosis, of gold ions from metallic gold surfaces requires the presence of disolycytes i.e. macrophages and the process is limited by their number and activity. We injected 20-45 mum gold particles into the neocortex of mice before generating a cryo-injury. Comparing gold-treated and untreated cryolesions, the release of gold reduced microgliosis and neuronal apoptosis accompanied by a transient astrogliosis and an increased neural stem cell response. We conclude that bio-liberated gold ions possess pronounced anti-inflammatory and neuron-protective capacities in the brain and suggest that metallic gold has clinical potentials. Intra-cerebral application of metallic gold as a pharmaceutical source of gold ions represents a completely new medical concept that bypasses the blood-brain-barrier and allows direct drug delivery to inflamed brain tissue.