Rachel L. Price

Selective bone cell adhesion on formulations containing carbon nanofibers.

Bone cell adhesion on novel carbon nanofibers and polycarbonate urethane/carbon nanofiber (PCU/CNF) composites is investigated in the present in vitro study. Carbon nanofibers have exceptional theoretical mechanical properties (such as high strength to weight ratios) that, along with possessing nanoscale fiber dimensions similar to crystalline hydroxyapatite found in physiological bone, suggest strong possibilities for use as an orthopedic/dental implant material. The effects of select properties of carbon fibers (specifically, dimension, surface energy, and chemistry) on osteoblast, fibroblast, chondrocyte, and smooth muscle cell adhesion were determined in the present in vitro study. Results provided evidence that smaller-scale (i.e., nanometer dimension) carbon fibers promoted osteoblast adhesion. Adhesion of other cells was not influenced by carbon fiber dimensions. Also, smooth muscle cell, fibroblast, and chondrocyte adhesion decreased with an increase in either carbon nanofiber surface energy or simultaneous change in carbon nanofiber chemistry. Moreover, greater weight percentages of high surface energy carbon nanofibers in the PCU/CNF composite increased osteoblast adhesion while at the same time decreased fibroblast adhesion.

Enhanced functions of osteoblasts on nanometer diameter carbon fibers

The present in vitro study investigated select functions (specifically, proliferation, synthesis of intracellular proteins, alkaline phosphatase activity, and deposition of calcium-containing mineral) of osteoblasts (the bone-forming cells) cultured on carbon fibers with nanometer dimensions. Carbon fiber compacts were synthesized to possess either nanophase (i.e., dimensions 100 nm or less) or conventional (i.e., dimensions larger than 100 nm) fiber diameters. Osteoblast proliferation increased with decreasing carbon fiber diameters after 3 and 7 days of culture. Moreover, compared to larger-diameter carbon fibers, osteoblasts synthesized more alkaline phosphatase and deposited more extracellular calcium on nanometer-diameter carbon fibers after 7, 14, and 21 days of culture. The results of the present study provided the first evidence of enhanced long-term (in the order of days to weeks) functions of osteoblasts cultured on nanometer-diameter carbon fibers; in this manner, carbon nanofibers clearly represent a unique and promising class of orthopedic/dental implant formulations with improved osseointegrative properties.

Nano-biotechnology: carbon nanofibres as improved neural and orthopaedic implants

For the continuous monitoring, diagnosis, and treatment of neural tissue, implantable probes are required. However, sometimes such neural probes (usually composed of silicon) become encapsulated with non-conductive, undesirable glial scar tissue. Similarly for orthopaedic implants, biomaterials (usually titanium and/or titanium alloys) often become encapsulated with undesirable soft fibrous, not hard bony, tissue. Although possessing intriguing electrical and mechanical properties for neural and orthopaedic applications, carbon nanofibres/nanotubes have not been widely considered for these applications to date. The present work developed a carbon nanofibre reinforced polycarbonate urethane (PU) composite in an attempt to determine the possibility of using carbon nanofibres (CNs) as either neural or orthopaedic prosthetic devices. Electrical and mechanical characterization studies determined that such composites have properties suitable for neural and orthopaedic applications. More importantly, cell adhesion experiments revealed for the first time the promise these materials have to increase neural (nerve cell) and osteoblast (bone-forming cell) functions. In contrast, functions of cells that contribute to glial scar-tissue formation for neural prostheses (astrocytes) and fibrous-tissue encapsulation events for bone implants (fibroblasts) decreased on PU composites containing increasing amounts of CNs. In this manner, this study provided the first evidence of the future that CN formulations may have towards interacting with neural and bone cells which is important for the design of successful neural probes and orthopaedic implants, respectively.

Enhanced functions of osteoblasts on nanostructured surfaces of carbon and alumina

It is of the utmost importance to increase the activity of bone cells on the surface of materials used in the design of orthopaedic implants. Increased activity of such cells can promote either integration of these materials into surrounding bone or complete replacement with naturally produced bone if biodegradable materials are used. Osteoblasts are bone-producing cells and, for that reason, are the cells of interest in initial studies of new orthopaedic implants. If these cells are functioning normally, they lay down bone matrix onto both existing bone and prosthetic materials implanted into the body. It is generally accepted that a successful material should enhance osteoblast function, leading to more bone deposition and, consequently, increased strength of the interface between the material and juxtaposed bone. The present study provided the first evidence of greater osteoblast function on carbon and alumina formulations that mimic the nano-dimensional crystal geometry of hydroxyapatite found in bone.

Improved osteoblast viability in the presence of smaller nanometre dimensioned carbon fibres

Carbon nanofibres have been proposed as a possible new orthopaedic/dental implant material due to their unique mechanical, electrical, and cytocompatibility properties. Specifically, these fibres have dimensions (diameters ranging between 60 and 200?nm and aspect ratios of about 500) similar to hydroxyapatite crystals and collagen fibres found in bone. More importantly, previous in vitro studies have provided evidence that nanophase (?nm diameter) carbon fibres enhance osteoblast (the bone-producing cell) function over conventional (>100?nm diameter) carbon fibres and current orthopaedic implant materials such as titanium, Ti6Al4V, and CoCrMo. However, articulating components of orthopaedic implant materials may generate harmful wear debris. To determine, for the first time, the influence of carbon nanofibre wear debris on osteoblast viability, direct contact toxicity studies were performed in the present in vitro study. Not surprisingly, the results from direct-contact toxicity studies over a 24?h time period provided evidence of time-?and concentration-dependent cell viability decreases when exposed to carbon nanofibres. Most importantly, the results from this study provided the first evidence that nanophase carbon fibres were less detrimental to osteoblast viability compared to larger diameter conventional carbon fibres. For this reason, this in vitro study provided continuing evidence of the promise of nanophase materials (particularly, carbon nanofibres) in improving orthopaedic implant efficiency.

Carbon Nanofiber Surface Roughness Increases Osteoblast Adhesion

The present study demonstrated for the first time desirable cytocompatibility properties of carbon nanofibers pertinent for bone prosthetic applications. Specifically, osteoblast (boneforming cells), fibroblast (cells contributing to callus formation and fibrous encapsulation events that result in implant loosening), chondrocyte (cartilage-forming cells), and smooth muscle cell (for comparison purposes) adhesion were determined on carbon nanofibers in the present in vitro study. Results provided evidence that nanometer dimension carbon fibers promoted select osteoblast adhesion, in contrast to the performance of conventional carbon fibers. Moreover, adhesion of other cells was not influenced by carbon fiber dimensions. To determine properties that selectively enhanced osteoblast adhesion, similar cell adhesion assays were performed on poly-lactic-co-glycolic (PLGA) casts of carbon fiber compacts previously tested. Compared to PLGA casts of conventional carbon fibers, results provided the first evidence of enhanced select osteoblast adhesion on PLGA casts of nanophase carbon fibers. The summation of these results demonstrate that due to a high degree of nanometer surface roughness, carbon fibers and PLGA with nanometer surface dimensions may be optimal materials to selectively increase osteoblast adhesion necessary for successful orthopedic implant applications.

Increased adhesion on carbon nanofiber/polymer composite materials

Previous studies have shown that nanometer dimension materials (such as carbon nanofibers) increase the adhesion of osteoblasts (bone matrix-producing cells) compared to their micron dimension counterparts. It was the purpose of the present study to observe the effect of variable weight percents of carbon nanofibers in a PLGA (poly(dl-lactide/glycolide) 50:50 wt. %) polymer composite on osteoblast adhesion. Specifically, 0.5, 1.0, and 5.0 wt % of carbon nanofibers were chosen as the variable weight percents and pure PLGA, pure carbon nanofiber, and etched glass substrates were used as controls. Results have provided evidence that osteoblast adhesion increases as the percent of carbon nanofibers increases in PLGA composites.

Increased Osteoblast and Decreased Smooth Muscle Cell Adhesion on Biologically-inspired Carbon Nanofibers

Osteoblast (the bone-forming cells) and smooth muscle cell adhesion was investigated on carbon nanofiber formulations of various diameters (specifically, from 60 to 200 nm) and surface energies (from 25 to 140 mJ/m 2 ) in the present in vitro study. Results provided the first evidence that osteoblast adhesion increased with decreased carbon nanofiber diameter after 1 hour. In contrast, smooth muscle cell adhesion was not dependent on carbon nanofiber diameter. Moreover, the present study demonstrated that smooth muscle cell adhesion decreased with increased carbon nanofiber surface energy after 1 hour. Alternatively, osteoblast adhesion was not affected by carbon nanofiber surface energy. Since adhesion is a crucial prerequisite for subsequent functions of cells (such as the deposition of bone by osteoblasts), the present results of controlled adhesion of both osteoblasts and a competitive cell line (i.e., smooth muscle cells) demonstrate that carbon nanofibers with small diameters and high surface energies may become the next-generation of orthopedic implant materials to enhance new bone synthesis. These criteria may prove critical in the clinical success of bone prostheses.