Research
Thrusts
..... Nanostructures
..... Biomimetics
..... Bio-Nano
Laurie Gower - Our contribution to the field of biomimetic engineering is in the study of microstructural processing techniques utilized by organisms to deposit their hard tissues, such as bones, teeth, shells, diatom cell walls, etc.. In particular, biopolymers, such as proteins and polysaccharides, play a key role in both the formation of the mineral phase, as well as in the mechanical properties of the resulting composite, and is an active area of investigation. These biologically formed tissues, called biominerals, are actually polymer-ceramic composites, and have very different properties than the minerals produced synthetically because the highly regulated precipitation conditions lead to hierarchically structured composite materials. It is through molecular recognition at organic-inorganic interface that the nanoscopic level of architecture is regulated. Self-assembly of proteins and phospholipids leads to the formation of organic matrices which define where the mineral crystal will be deposited. For example, the matrix may be in the form of a template which controls the nucleation, and thus the location and orientation of the crystals. Alternatively, the matrix may form a compartment which imparts spatial restrictions to the growing mineral phase, and in essence "molds" the crystals (while under low temperature physiological conditions).
The research in our group is particularly interested in these concepts because we have discovered a polymer-induced liquid-precursor (PILP) mineralization process, in which the addition of small amounts of acidic polypeptides to a crystallizing reaction can lead to the formation of a liquid-phase mineral precursor, which due to its fluidic nature, can be molded and shaped by its surrounding container. Upon solidification of the precursor, non-equilibrium crystal morphologies can be generated. The hallmark of biomineralization is the highly unusual crystal morphologies that are generated, thus we have proposed that this PILP mechanism may play a key role in the biomineralization processes. Our research has been devoted to demonstrating this concept in vitro by simulating some of the unique morphologies that are found in biominerals, yet which have never been duplicated synthetically. Of particular relevance to nanotechnology are the following projects in our group:
- We are attempting to fabricate nanolaminated composites that mimic the structure of mollusk nacre (mother of pearl). Nacre reportedly has a thousand fold increase in fracture toughness relative to monolithic calcium carbonate, thus we seek to make such a nanolaminated bioceramic for application in dental restoratives.
- Bone has multiple levels of hierarchical structure, yet cannot be duplicated synthetically even at the most fundamental level of organization, which consists of nanoscopic crystals of hydroxyapatite embedded and arranged within a self-assembled collagenous matrix. We are attempting to fabricate a collagen-mineral composite with a nanostructured architecture that mimics bone. If this intrafibrillar mineralization can be achieved, a new bone-graft substitute material could be developed with load-bearing mechanical properties and optimal biocompatibility.
- Other projects in our group are related to patterning the deposition of the mineral phase using various organic templates. For example, we are preparing novel core-shell particles with controlled nanoporosity of the mineral shell that encapsulates an oily emulsion core, for controlled release applications (e.g. pharmaceutical agents, agricultural pesticides or fertilizer, industrial catalysts, etc).