EMSL: Allison Campbell's Publications

Shaw WJ, AA Campbell, ML Paine, and M Snead. 2004. "The COOH terminus of the amelogenin, LRAP, is oriented next to the hydroxyapatite surface." Journal of Biological Chemistry 279(39):40263-40266. doi:10.1074/jbc.C400322200 Abstract The organic matrix in forming enamel consists largely of the amelogenin protein, self-assembled into nanospheres that are necessary to guide the formation of the unusually long and highly ordered hydroxyapatite (HAP) crystallites that constitute enamel. Despite its ability to direct crystal growth, the interaction of the amelogenin protein with HAP is unknown, though the charged C-terminus is often implicated in this function. To elucidate if the C-terminus is important in the binding and orientation of amelogenin with HAP, we used solid state NMR to determine the orientation of the C-terminus of an amelogenin splice variant, LRAP, which contains the charged C-terminus of the full protein, on the HAP surface. These experiments demonstrate that the sidechain methyl labeled residue, A46, is 8 Å from the HAP surface, under hydrated conditions, for the protein with and without phosphorylation. Modeling results are consistent with experimental measurements, resulting in an average 13Cala46-31P distance of 7.62 ± 1.8 Å for LRAP orientation onto the 100 face of HAP. The computational model also reveals that with 13Cala46 at this distance, the negatively charged residues are energetically favored to align themselves with the Ca2+ in the HAP lattice. The experimental results and supporting computational models provide direct evidence orienting the charged C-terminal region of the amelogenin protein on the HAP surface, optimized to exert control on developing enamel crystals.

Campbell AA. 2003. "Bioceramic Coatings for Orthopaedic Implants." Materials Today 6(11):26-30. Abstract During the past century, man-made materials and devices have been developed to the point at which they have been used successfully to replace and/or restore function to diseased or damaged tissues. In the field of orthopaedics, the use of metal implants has significantly improved the quality of life for countless individuals. Critical factors for implant success include proper design, material selection, and biocompatibility. While early research focused on the understanding biomechanical properties of the metal device, recent work has turned toward improving the biological properties of these devices. This has lead to the introduction of calcium phosphate (CaP) bioceramics as a bioactive interface between the bulk metal impart and the surrounding tissue. The first calcium phosphate coatings where produced via vapor phase routes but more recently, there has been the emergence of solution based and biomimetic methods. While each approach has its own intrinsic materials and biological properties, in general CaP coatings have the promise to improve implant biocompatibility and ultimately implant longevity.

Campbell AA, BL Deatherage, XS Li, BJ Nelson, CR Bottoni, and ES Dejong. 2002. "Hydroxyapatite Coatings Produced by Surface-Induced Mineralizaiton." In Biominetic Calcium Phosphate Coatings, pp. 47-54. Research Signpost, Trivandrum, India. Abstract The surface-induced mineralization (SIM) process is based on the observation that, in nature, organisms use biopolymers to produce ceramic composites such as teeth, bones, and shells. The SIM process involves modification of a surface to introduce surface functionalization followed by immersion in aqueous supersaturated calcium phosphate solutions. This room temperature process has advantages over conventional methods of calcium phosphate deposition in that uniform coatings are produced onto complex-shaped and/or microporous samples. Additionally, because it is a room temperature process, biological agents can be incorporated.

Dejong ES, TM Deberardino, DE Brooks, BJ Nelson, AA Campbell, CR Bottoni, AE Pusateri, RS Walton, CH Guymon, and AT Mcmanus. 2001. "Antimicrobial efficacy of external fixator pins coated with a lipid stabilized hydroxyapatite/chlorhexidine complex to prevent pin tract infection in a goat model." Journal of Trauma - injury infection, and critical care 50(6):1008-14. Abstract Background: Pin tract infection is a common complication of external fixation. An antiinfective external fixator pin might help to reduce the incidence of pin tract infection and improve pin fixation. Methods: Stainless steel and titanium external fixator pins, with and without a lipid stabilized hydroxyapatite/chlorhexidine coating, were evaluated in a goat model. Two pins contaminated with an identifiable Staphylococcus aureus strain were inserted into each tibia of 12 goats. The pin sites were examined daily. On day 14, the animals were killed, and the pin tips cultured. Insertion and extraction torques were measured. Results: Infection developed in 100% of uncoated pins, whereas coated pins demonstrated 4.2% infected, 12.5% colonized, and the remainder, 83.3%, had no growth (p < 0.01). Pin coating decreased the percent loss of fixation torque over uncoated pins (p = 0.04). Conclusion: These results demonstrate that the lipid stabilized hydroxyapatite/chlorhexidine coating was successful in decreasing infection and improving fixation of external fixator pins.

Campbell AA, L Song, XS Li, BJ Nelson, CR Bottoni, DE Brooks, and ES Dejong. 2000. "Development, Characterization, and Anti-Microbial Efficacy of Hydroxyapatite-Chlorhexidine Coatings Produced by Surface-Induced Mineralization." Journal of Biomedical Materials Research 53(4):400-407. Abstract The surface-induced mineralization (SIM) technique was used to produce hydroxyapatite (HAP) coatings on external fixation pins with the antimicrobial agent, chlorhexidine, incorporated within the coating. The SIM process involved surface modification of the substrate with organic functional groups followed by immersion in aqueous supersaturated calcium phosphate solutions. X-ray diffraction spectra confirmed that hydroxyapatite coatings were formed. Chlorhexidine was incorporated into the coating by placing the substrate into various chlorhexidine solutions in between mineralization cycles. Total uptake was measured by dissolution of the coating into a 0.1 M nitric acid solution and measuring the chlorhexidine concentration using UV spectroscopy at 251 nm. Release rates were measured by submersion of coated substrates into saline solutions and measuring chlorhexidine UV absorbency at 231 nm as a function of time. Results show an initial rapid release followed by a period of slower sustained release. The anti-microbial efficacy of the HAP-chlorhexidine coatings was evaluated in vitro using a staphylococcus aureus cell culture. Initial results show a large "kill zone" formed around the chlorhexidine/HAP coating versus HAP only or chlorhexidine/polyvinyl/nylon polymer coatings. This preliminary work clearly demonstrates that SIM HAP coatings have great potential to locally deliver antimicrobial agents, such as chlorhexidine, at implantation sites, which may greatly reduce the incidence of pin tract infection that occurs in external fixation.

Shaw WJ, JR Long, AA Campbell, PS Stayton, and GP Drobny. 2000. "A Solid State NMR Study of Dynamics in a Hydrated Salivary Peptide Adsorbed to Hydroxyapatite." Journal of the American Chemical Society 122(29):7118-7119. Abstract Proteins interact with biomineral surfaces to control crystal growth and final structure in biological systems ranging from seashell formation to teeth and bone. The elucidation of molecular recognition mechanisms at the organic-inorganic interface could provide inspiration for materials synthesis strategies. Solid state NMR (SSNMR) has been shown to be a powerful tool for determining the secondary structure of surface adsorbed proteins and can potentially provide important information on peptide dynamics at surfaces as a function of hydration.

Shaw WJ, JR Long, JL Dindot, AA Campbell, PS Stayton, and GP Drobny. 2000. "Determination of Statherin N-Terminal Peptide Conformation on Hydroxyapatite Crystals ." Journal of the American Chemical Society 122(8):1709-1716. Abstract Use of NMR DRAWS and REDOR techniques to elucidate protein structure when bound to hydroxyapatite surfcaes.

Campbell AA. 1999. "Interfacial Regulation of Crystallization in Aqueous Environments." Journal of Colloid and Interface Science 4(1):40-45.