Biomedical subjects

Jack Lemons

Publications and source records attributed to Jack Lemons.

8 recordsLinked to original sources

PubMed2005

Surface modification of surface sol-gel derived titanium oxide films by self-assembled monolayers (SAMs) and non-specific protein adsorption studies.

Biological events occurring at the implant-host interface, including protein adsorption are mainly influenced by surface properties of the implant. Titanium alloys, one of the most widely used implants, has shown good biocompatibility primarily through its surface oxide. In this study, a surface sol-gel process based on the surface reaction of metal alkoxides with a hydroxylated surface was used to prepare ultrathin titanium oxide (TiOx) coatings on silicon wafers. The oxide deposited on the surface was then modified by self-assembled monolayers (SAMs) of silanes with different functional groups. Interesting surface morphology trends and protein adhesion properties of the modified titanium oxide surfaces were observed as studied by non-specific protein binding of serum albumin. The surface properties were investigated systematically using water contact angle, ellipsometry, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) measurements. Results showed that the surface sol-gel process predominantly formed homogeneous, but rough and porous titanium oxide layers. The protein adsorption was dependent primarily on the silane chemistry, packing of the alkyl chains (extent of van der Waals interaction), morphology (porosity and roughness), and wettability of the sol-gel oxide. Comparison was made with a thermally evaporated TiOx-Ti/Si-wafer substrate (control). This method further extends the functionalization of surface sol-gel derived TiOx layers for possible titanium alloy bioimplant surface modification.

Adsorption↗

PubMed2005

Dual-energy x-ray absorptiometry analysis of implants in rat tibiae.

Dual energy x-ray absorptiometry (DXA) was evaluated for its ability to measure changes in bone mineral density in isolated rat tibiae. This technique is available for in vivo use to potentially augment or replace some aspects of conventional histomorphometric techniques used for the evaluation of metallic implant-to-bone interfaces. Known quantities of hydroxyapatite powder, representing various bone densities, were measured using DXA in a series of 3 experiments: (1) the hydroxyapatite powder was placed within a plastic tube, (2) the hydroxyapatite was placed within an excised rat tibia, and (3) hydroxyapatite powder was placed within a rat tibia with soft tissue overlying it. Statistical analysis (analysis of variance) showed significant differences in bone mineral density among groups that varied by only 5% hydroxyapatite density within the plastic tubes. The system detected hydroxyapatite changes of 20% within the tibiae with and without overlying soft tissue (P < 0.05). These data were consistent and linear (R > 0.90). Although DXA analysis has been widely used in clinical and research applications for detection of osteoporosis, its use for documenting bone growth around implants has not been widely reported. The use of such a technique could have substantial benefits for both the clinical and research arenas. These data show that DXA analysis to identify bone density changes adjacent to implants has significant applications in small animal research models.

Absorptiometry, Photon↗

PubMed2005

Corrosion on spinal implants.

OBJECTIVE: Modular spine implants are used as an aid to obtaining fusion, but fretting and corrosion occur between modular components in a biologic environment. METHODS: Forty-eight spinal implant constructs manufactured by a variety of companies were retrieved from 47 patients and were subjected to surface analysis stereomicroscopy. RESULTS: Stainless-steel implants (n = 23) had either semirigid constructs with mild or no surface alteration (n = 7) or rigid constructs with moderate or severe alteration (n = 16). Surface damage was consistent with previously observed mechanically assisted crevice corrosion phenomena. Titanium alloy implants (n = 25) showed no significant corrosion but had three constructs with fatigue failure of anchoring screws. One cobalt alloy construct showed no evidence of corrosion. CONCLUSIONS: Long-term effects of fretting and corrosion are unclear, and minimization of these phenomena seems justified. Selection of modular components with similar materials and surface finish may help the surgeon minimize localized changes over time. Stainless-steel implants with rigid interconnections and those with different surface finishes between rods and connectors are most susceptible to corrosion.

Alloys↗

PubMed2004

Examination of surface and material properties of explanted zirconia femoral heads.

The crystalline structure of Zirconia femoral heads provides for superior fracture toughness when compared with alumina. Transformation of the crystalline structure that takes place with time in service may produce changes in the surface and biomechanical properties of these implants. This study examines surface and mechanical property changes of Zirconia femoral heads that occur with time in situ. Eighteen retrieved Zirconia femoral heads were compared to 5 factory-sealed controls. The retrieved implants demonstrated significant transformation to a monoclinic phase. This phase transformation was associated with decreased surface hardness. There was evidence of increased surface roughness with increasing time of implantation. The phase transformation that takes place in Zirconia femoral heads may render these implants less desirable as a bearing surface in total hip arthroplasty.

Femur Head↗

PubMed2004

An amino acid-modified and non-HEMA containing glass-ionomer cement.

It is known that unreacted 2-hydroxyethyl methacrylate (HEMA) in current resin modified glass ionomer cements (RMGICs) shows potential cytotoxicity to pulp and surrounding tissues. Elimination of HEMA could make RMGICs more attractive for dental applications. In this research, novel six acrylate and methacrylate derivatives of amino acids were synthesized, characterized and used for replace HEMA in RMGICs. The experimental RMGICs were formulated with vinyl-containing polymer, amino acid derivative, water, and commercial Fuji II LC glass. Among all the derivatives, methacryloyl beta-alanine (MBA) was selected for further formulations due to its relatively low solution viscosity and high CS. Effects of polymer content and powder/liquid, P/L, ratio were significant. The formulation with liquid composition of 50/25/25 (polymer/MBA/water) and P/L ratio of 2.7/1 was found the optimal. It appears that this novel non-HEMA-containing RMGIC system based on amino acid derivatives will be a better dental restorative because it demonstrated improved mechanical strengths and may eliminate potential cytotoxicity in current RMGICs caused by leached HEMA. The optimal MBA-modified GIC were 20% higher in CS, 70% higher in DTS and 93% higher in FS, compared to Fuji II LC.

Acrylates↗

PubMed2004

Rationale for the application of immediate load in implant dentistry: Part I.

Immediate loading in implant dentistry is increasing in popularity as a clinical procedure. A scientific rationale of immediate occlusal loading of the implant support system should emphasize methods to decrease surgical trauma during implant placement and to decrease bone loading trauma during the early loading period. The surgical trauma may be reduced by decreasing heat generation and pressure necrosis. The early loading trauma may be decreased by decreasing the bone strain adjacent to the implant interface. Greater microstrain conditions in bone increase the remodeling rate of bone. The higher the remodeling rate, the weaker the bone and the more risk of occlusal overload. Occlusal overload may lead to implant failure. Since strain is directly related to stress, methods to decrease stress are beneficial. In the present report, the stress-reducing influences include increasing the number of implants.

Dental Implantation, Endosseous↗

PubMed2004

Rationale for the application of immediate load in implant dentistry: part II.

Immediate loading of an implant interface has been used for completely and partially edentulous patients. A biomechanical rationale to decrease the initial risk of overload is reasonable, because implant failure and overload has been well established. This article addresses methods to decrease stress to the transitional restoration. Forces may be influenced by patient factors, implant position, cantilever forces, occlusal load direction, occlusal contact intensity, and diet. The surface area of load distribution may be increased by implant size, implant design, and surface condition of the implant body. A blend of these factors affects the amount of stress to the developing implant interface and hence may affect the risk of immediate occlusal loading for implant prostheses.

Alveolar Process↗

PubMed2003

Polyethylene damage on the nonarticular surface of modular total knee prostheses.

Modular tibial implants submitted for retrieval analysis were examined for evidence of cold flow, wear, or polyethylene failure. All retrieved components showed areas of cold flow and wear. Significant damage, defined as pitting, gouging, or delamination was observed in 77% of the retrieved implants. Cold flow deformation commonly was observed at the junction of the polyethylene and locking mechanisms or junction of the polyethylene and the edge of the tibial tray. Control implants did not show such areas of damage. Clinical factors such as age, activity status, length of implantation, limb alignment before revision, and thickness of the tibial insert did not correlate with backside wear. No association was found between polyethylene thickness, time of implantation, limb or prosthesis alignment, or activity status or weight of the patient.

Adult↗