(Jake Barralet, Hung-Wen Li, Marc McKee, Jay Nadeau, Satya Prakash, Maryam Tabrizian, Hojatollah Vali, and Paul Wiseman)
The connection between advanced materials and Biology arises from the fact that the nanoscale is the scale at which the smallest man made structures readily interact with the large macromolecules of living systems, thus opening the possibility of novel hybrid materials, devices, and systems. The focus of research at MIAM comprises three main general areas: genetic control of bone interfaces and biomineralization, biorecognition and the development of biosensors, and ultra fast imaging techniques of both biomolecules and of protein expression patterns that correlate with cellular function.
The organizing principle behind current studies of biomineralization in vertebrates is that it is an active, biological process, regulated by specific extra cellular matrix proteins such as osteopontin, bone sialoprotein, matrix Gla protein and Phex [M. Murshed, M. Mckee et al. ”Extracellular matrix mineralization is regulated locally; different roles of two gla-containing proteins”, J. Cell Bio. 165, 625 (2004)]. Regulation of biomineralization by proteins is also being studied in invertebrate, calcium carbonate-containing systems which include eggshell and seashells. Of course, these studies have numerous direct applications to medicine, including pathological mineralization such as it is observed in kidney stones, arthritis, vascular calcification (including atherosclerosis) and dental plaque (calculus) [S.A. Steitz, M. McKee et al. “Osteopontin inhibits mineral deposition and promotes regression of ectopic calcification”, Am. J. Pathol. 161, 2035 (2002)]. At the interface with materials science, the elucidation of protein control of tissue mineralization will enable progress in the design and development of a new generation, implantable biomaterials that incorporate bioactive organic moieties such as small peptides and/or intact proteins in order to guide and accelerate tissue healing and mineralization [C.D. Hoemann, M. McKee ”Tissue engineering of cartilage using an injectable and adhesive chitosan-based cell-delivery vehicle”, Osteoarthritis and Cartilage 13, 318 (2005)].
An important aspect of the research on implantable biomaterials is the study of their biocompatibility and sterilization which at MIAM focuses on the use of naturally-derived polysaccharides and bioceramics as delivery systems and as matrix. Surface treatment is one of the main routes to improve the biocompatibility and hemocompatibility of biomaterials. Electropolishing, plasma polymer deposition and laser surface treatment, and electrodeposition are but a few of the techniques used to increase either corrosion resistance or biocompatibility of metal and polymer based biomaterials [B. Thierry, M. Tabrizian et al. ”Bioactive coatings of endovascular stents based on polyelectrolyte multilayers”, Biomacromolecules 4, 1564 (2003)].
A particular application concerns the development of Bioceramics, and in particular the low temperature syntheses of nanocrystalline and amorphous inorganic, cold setting materials (cements), and their precipitation to create new or improved materials or devices for tissue repair or delivery [L.M. Grover, J. Barralet et al. “The mechanical properties and microstructures of cement formed from pyrophosphoric and orthophosphoric acids”. Key Eng. Mat. 17, 125 (2005)]. Bioceramics based research on tissue engineering focuses on new ways to build three dimensional structures by using micro scaffolds as building blocks, as for example the use of calcium cross linked alginate as a tissue engineering scaffold [M.A. Lawson, J. Barralet et al. “Adhesion and growth of bone marrow stromal cells on modified alginate hydrogels”. Tissue Eng. 10, 1480 (2004)].
At the materials end of the research, crystal growth studies are being conducted to assess the effect on growth speed and morphology from solution content of proteins known to regulate biomineralization.
Nanostructured platforms are being developed with applications in gene/protein therapy and tissue engineering in mind. As was the case above, nanoparticles currently in use are based on natural polysaccharides and LbL-lipid systems. Suitably functionalized, applications that are being currently pursued include their use as gene carrier, or as injectable delivery system of growth factors for in situ bone regeneration [K.L. Douglas and M. Tabrizian, “Effect of experimental parameters on the formation of alginate-chitosan nanoparticles and evaluation of their potential application as DNA carrier”. J. Biomat. Sci. Polymer edition 16, 43 (2005)].
Nanostructured interface and microfluidic systems are also being designed and built through surface molecular engineering and nanolithography with the goal of developing biorecognition systems for real time assays. Current research aims at improving biochips used with Quartz Crystal Microgravimetry and Surface Plasmon Systems (SPR) systems. Integration of the biorecognition surfaces, with microfluidic control and optoelectronic packaging of the SPR system would lead to effective, real time, detection of biomarkers and toxins[P.O. Bagnaninchi, M. Tabrizian et al. “Complex permittivity measurement as a new noninvasive tool for monitoring In vitro tissue engineering and cell signature through the detection of cell proliferation, differentiation, and pretissue formation”. IEEE Trans. NanoBioSci. 3, 243 (2004)].
Major breakthroughs in our understanding of cell cycle, regulation, and function may well follow the introduction of sophisticated imaging techniques to a plethora of in vivo studies. These techniques have been developed in the materials sciences over the last few years, but they are now increasingly finding widespread application in a number of biological studies. They include advanced laser scanning fluorescence microscopy (both single photon confocal, and nonlinear two photon fluorescence laser scanning microscopy), the use of quantum dots as potential sensitive probes, image correlation spectroscopy, and image cross correlation spectroscopy. These imaging techniques are enabling detailed studies of the molecular mechanisms involved in cellular adhesion, and how cells dynamically regulate adhesion receptors to control cellular migration [B. Hebert, P. Wiseman et al. “Spatiotemporal image correlation Spectroscopy (STICS) theory, verification, and application to protein velocity mapping in living CHO cells”. Biophys. J. 88, 3601 (2005)]. Cellular adhesion and migration play fundamental roles in the normal development of tissue architecture in organisms and are also known to function abnormally in certain diseases such as the progression of cancers from a single localized growth to dispersed, invasive metastases. Adhesion complexes are dynamic structures, not static, and are actively assembled and disassembled by the cells in different locations in the membrane in order to facilitate traction needed for cell migration. Real time imaging provides invaluable insights into the mechanism of cell adhesion and migration [P. Wiseman et al. “Spatial mapping of integrin interactions and dynamics during cell migration by Image Correlation Microscopy”. J. Cell Sci. 117, 5521 (2004)].
In essence, current imaging techniques allow probing important biological processes at the single molecule level, including the study of single molecule biophysical or biochemical properties, detailed analysis of enzyme activity, and a number of macromolecular interactions (protein-DNA and protein-protein interactions). In effect, single molecule techniques observe the distributions and time trajectories of individual molecules, information that is lost in the ensemble average, and thus provide valuable insights into the microscopic mechanisms behind function. A topic currently under investigation includes biological molecular machines that are responsible for DNA recombination and repair, including imaging the mechanistic details of these DNA processing proteins, the exploration of their regulatory architecture, with the aim of elucidating the general mechanism of protein/DNA interaction [T.T. Perkins , H.W. Li et al. “Forward and reverse motion of single RecBCD molecules on DNA”. Biophys. J. 86, 1640 (2004)].
Finally, research is under way toward the development of artificial cells to achieve micro encapsulation, biomaterial and medical device engineering, tissue engineering, and cell therapy [T. Chang and S. Prakash, “Procedures for microencapsulation of enzymes, cells and genetically engineered microorganisms”. Molec. Biotech. 17, 249 (2001)]. The focus is to design artificial cell microcapsules that are capable of targeting specific sites, and then encapsulating genetically engineered cells, microorganisms, enzymes, small peptides, DNA, and active drugs. Research is conducted to advance our understanding of the basic mechanisms that govern the use of microcapsules for oral delivery of therapeutic agents [Y. Wei, S. Prakash et al. “Artificial cell microcapsule for oral delivery of live bacterial cells for therapy: design, preparation, and in-vitro characterization”. J. Pharmacy and Pharmaceutical Sci. 7, 315 (2004)], and to develop support systems for artificial liver and kidney [T. Haque, S. Prakash et al, “In vitro study of alginate-chitosan microcapsules: an alternative to liver cell transplants for the treatment of liver failure”, Biotechnology Lett. 27, 317 (2005)].