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Biomedical subjects

E J Harper

Publications and source records attributed to E J Harper.

32 records · Page 2Linked to original sources
PubMed1999

In vitro evaluation of a new polymethylmethacrylate cement reinforced with hydroxyapatite.

The nature of the orthopedic implant surface affects the interaction between cells and subsequent bone formation. The bone/cement interface in cement-held prostheses is considered to be the main cause of fracture leading to implant revision. It is thought that the introduction of a bioactive phase, such as hydroxyapatite (HA), to cement may permit a stronger implant by encouraging direct bone apposition rather than encapsulation of the implant by fibrous tissue. Thus, a poly(methylmethacrylate) (PMMA) cement incorporating 17.5% HA by weight has been investigated. In this study, in order to analyze the interaction at the cellular level, the in vitro biological response of the HA/PMMA to a similar PMMA without HA incorporation has been studied. Primary human osteoblast-like cells (HOB) were used as they are a model of the cell type the cements might encounter in vivo. Cell proliferation and growth were assessed by measurement of total cellular DNA and tritiated thymidine ([3H]-TdR) incorporation. Alkaline phosphatase (ALP) production was measured as an indicator of HOB phenotype upon the cements. The results showed that HA/PMMA was a better substrate for HOB cells, resulting in increased proliferation and ALP activity. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that HOB cells cultured on the HA-filled PMMA preferentially anchored to HA particles exposed at the cement surface, with a close intimacy observed between HA and HOB cells.

Journal Article↗
PubMed1998

Isothermal and non-isothermal polymerization of a new bone cement.

A new bone cement based on poly(ethylmethacrylate) (PEMA), hydroxyapatite powder (HA) and n-butylmethacrylate monomer (n-BMA) has been studied using isothermal and non-isothermal polymerization. Methacrylate monomers are highly reactive and release a considerable amount of heat during polymerization. A quantitative understanding of the methacrylate polymerization is necessary because the thermal history of the polymerization has considerable influence on the final properties of a bone cement. In the first part, polymerization kinetics are analysed by means of differential scanning calorimetry (DSC). DSC data are used to evaluate a phenomenological model describing the cure kinetics of this new bone cement. In the second part, a kinetic model coupled with the energy balance is used to obtain temperature and degree of conversion profiles in the bone-cement-prosthesis system, under non-isothermal conditions, as function of initial temperature and thickness of the cement. Material properties, boundary and initial conditions and the kinetic behaviour are the input data for the numerically solved heat-transfer model. The temperature at the bone/cement interface, can be considered as a weak point, often responsible for total joint replacement failure. For this particular bone cement exhibiting a low exotherm and low glass transition temperature, the interfacial temperature is lower than the threshold level for thermal tissue damage (50 degrees C). The conversion occurs almost completely, avoiding problems with unreacted monomers that can be released by the cement, giving rise to tissue damage.

Journal Article↗
PubMed1998

Comparison between the polymerization behavior of a new bone cement and a commercial one: modeling and in vitro analysis.

The polymerization behavior of a new bone cement based on poly(ethylmethacrylate), hydroxyapatite powder and n-butylmethacrylate monomer and a commercial cement have been studied. Polymerization kinetics were analyzed by means of differential scanning calorimetry (DSC). DSC data have been used to evaluate a phenomenological model describing the cure kinetics of this new bone cement. The kinetic model coupled with the energy balance was then used to obtain temperature and degree of conversion profiles in the bone-cement-prosthesis system, under non-isothermal conditions, as function of initial temperature and thickness of the cement. Material properties, boundary and initial conditions and the kinetic behavior were the input data for the numerically solved heat-transfer model. The modeling results have been compared with in vitro results.

Journal Article↗
PubMed1998

Changing perspectives on aging and energy requirements: aging and energy intakes in humans, dogs and cats.

A series of cross-sectional and longitudinal studies conducted in humans has shown that aging is associated with a gradual decline in the maintenance energy requirement. Generally, this is equivalent to a total decrement of 20% of young adult maintenance energy requirements and is a result of a decrease in both physical activity and basal metabolic rate. Relatively few such studies have been conducted in dogs, but the results have been consistent. It appears that maintenance energy requirements decline by approximately 20%, and it is assumed that the causal factors are the same as those for humans. The situation appears to be somewhat different in cats, with evidence to date indicating that maintenance energy requirements remain constant throughout adult life. Why cats should be different from other species is not clear, but it is hypothesized that relative inactivity is typical of most cats' behavior, such that there is no obvious age-related change. In terms of feeding regimens for senior cats and dogs, it is appropriate to decrease energy provision for senior dogs by approximately 20%, whereas the energy provision for senior cats should not be decreased.

Adult↗
PubMed1998

Changing perspectives on aging and energy requirements: aging, body weight and body composition in humans, dogs and cats.

The drivers of the age-related decline in maintenance energy requirement in humans are primarily reduced physical activity and a decrease in basal metabolic rate, which is largely driven by changes in body composition. Most studies indicate that there is a significant loss of lean body mass and a concomitant increase in fat mass with advancing age. The causal factors appear to be changes in physical activity and a reduction in the activity of growth hormone. Sustained physical activity and/or administration of growth hormone have been shown to offset age-related changes in lean:fat ratios in humans and in rats. Very little information is available on dogs, but current data suggest that aging is accompanied by a decrease in lean:fat ratios. The rate and extent of change is similar to that observed in aging humans and it is assumed that the same causal factors are responsible. On this basis, it is likely that basal metabolic rate declines in older dogs. New evidence suggests that the situation is very different in cats, with no apparent change in lean:fat ratios with advancing age. This is probably related to constant activity levels throughout life and suggests that basal metabolic rate probably does not decrease as cats age. On the basis of this evidence, there is no reason to reduce energy provision to the majority of older cats.

Adult↗
PubMed1998

Changing perspectives on aging and energy requirements: aging and digestive function in humans, dogs and cats.

When considering the question of energy balance, it is important to take into account energy provision and the ability of aging animals to digest macronutrients and thus obtain their maintenance energy requirement. A large number of studies have been conducted in humans in an effort to establish whether aging of the gastrointestinal tract has a significant effect on availability of dietary energy. The results of these studies have been conflicting, with indications that some aspects of gut functionality do decline with age, but little evidence overall to suggest that aging humans are at risk of energy deficit due to compromised digestive efficiency. A number of digestibility studies carried out with dogs confirm that there is no evidence of an age-related decline in digestive efficiency. This knowledge makes the determination of energy provision to senior dogs relatively straightforward to calculate. Many senior cats appear to exhibit quite a marked reduction in their ability to digest macronutrients, particularly fat, efficiently. Because this reduces the overall capacity to obtain energy from the diet, it is recommended that old cats should not routinely be offered reduced energy diets. For senior cats, the feeding regimen in later life should be to offer highly digestible diets that provide as much energy as adult maintenance rations.

Aged↗
PubMed1998

Bioactive bone cements.

Poly(methylmethacrylate) (PMMA) bone cement, used to fix implants into the bone, produces good surgical results if used correctly. However, prostheses do eventually become loose and the breakdown of the cement mantle is a factor in this failure. Limitations of PMMA cement, which lead to problems with the fixation of the implant, include its mechanical characteristics and its influence upon surrounding bone, associated with the polymerization reaction. A bioactive bone cement is particularly designed to produce a better interface between the cement and bone. However, an improvement in mechanical properties, especially fatigue, creep and fracture toughness, are an added necessary requirement to increase the lifetime of a cemented implant. The development of a bioactive cement has been conducted mainly in two ways; firstly, to improve existing PMMA cement by the addition of various bioactive agents and secondly, to design an alternative matrix for the bioactive material to be combined with. The most promising investigations which have been conducted, along with their relative benefits and drawbacks, are discussed.

Biocompatible Materials↗
PubMed1998

Use of the breath hydrogen test to assess the effect of age on orocecal transit time and carbohydrate assimilation in cats.

OBJECTIVE: To evaluate the effect of age on orocecal transit time (OCTT) in cats, using the breath hydrogen test, and to assess potential differences in nutrient absorption. ANIMALS: 27 healthy cats. PROCEDURE: Cats were allocated to the following 3 groups on the basis of age: group A (9 kittens, 5 to 7 months old), group B (9 young adults, 3 to 5 years old), and group C (9 older cats, 12 to 15 years old). Cats were fed a standard canned diet for 2 weeks prior to measurement of OCTT. Exhaled hydrogen concentration (parts per minute [ppm x min]) was monitored for 8 hours after feeding 60 g of the canned diet. RESULTS: Mean OCTT in group-A cats was 203 minutes (range, 90 to 345 minutes), which was significantly different from that in group-B (317 minutes; range, 180 to 435 minutes) and group-C (309 minutes; range, 225 to 375 minutes) cats. Median area under the breath hydrogen excretion time curve (ppm x min) for the 8-hour monitoring period, first 45 minutes, and 105 minutes after OCTT for the 3 groups was not significantly different among groups. CONCLUSIONS: Kittens had significantly faster OCTT than did adult cats.

Aging↗
PubMed1997

Influence of sterilization upon a range of properties of experimental bone cements.

Bone cement, used to fix prostheses into the bone, must be sterilized prior to implantation. Two sterilization techniques, gamma and beta radiation, were investigated, examining the influence upon molecular weight, static and dynamic mechanical characteristics and rheological properties. A number of experimental cements were studied prepared from methylmethacrylate (MMA) co-polymers, either single powders or powder blends, mixed with MMA monomer. It was found that with both gamma and beta radiation, there was a decrease in molecular weight of all powders, including a MMA/styrene co-polymer, in relation to the radiation dose. This fall in molecular weight resulted in a drop in tensile strength, Young's modulus and strain to failure of all cements tested. However, the deterioration in mechanical strength was highlighted by the dynamic testing. Fatigue lives of cements after testing in tension-tension, at 2 Hz under load control and irradiated with 25 kGy gamma radiation, displayed significant decreases. This result indicated the utmost importance of conducting such tests upon experimental bone cements prior to in vivo use. The rheological time profiles of curing cements were also found to be influenced by 25 kGy gamma radiation, with a reduction of complex viscosity after sterilization.

Journal Article↗
PubMed1996

In situ analysis of the degree of polymerization of bone cement by using FT-Raman spectroscopy.

A method has been developed which enables an in situ analysis of the degree of polymerization of bone cement. The concentration of monomeric double bond is monitored continuously during the entire curing process and hence the method can be used for quantitative studies of polymerization kinetics. In this study, Fourier Transform Raman (FTR) spectroscopy was utilized to investigate the degree of polymerization of a novel bone cement in situ, and the results are compared with the thermal profile obtained for polymerization.

Biocompatible Materials↗
PubMedDate not supplied

Age-related changes in apparent digestibility in growing kittens.

The ability of the growing kitten to digest protein, fat, carbohydrate, dry-matter and energy were assessed. Kittens were divided into two groups; one group was fed a wet diet, the other a dry diet. Both groups were allowed ad libitum access to food. Apparent digestibility of the two diets, and kitten bodyweights were measured over a 24-week period. There were no significant differences in mean bodyweight between the two groups. Digestible energy intake of the kittens decreased with increased age; regression analysis of the data generated two fitted models which appeared to accurately predict the digestible energy intake between 39 and 41 weeks of age. There was a significant (P < 0.05) effect of diet on the apparent digestibility of protein, organic-matter and dry-matter. Age had a significant (P < 0.05) effect on the apparent digestibility of all the parameters measured. Newman-Keuls multiple range tests showed that apparent digestibility of carbohydrate, organic-matter and total energy significantly (P < 0.05) increased in kittens older than 19 weeks. This suggests that the digestive capacity of the younger cat may be affected by the physiological development of the gut, and dietary induced enzyme modulation.

Aging↗
PubMedDate not supplied

The effect of ageing on nutrient digestibility by cats fed beef tallow-, sunflower oil- or olive oil-enriched diets.

Nutrient digestibility and absorption decline with age in several mammalian species. The aim of this study was to compare apparent fat digestibility of different dietary fats in young and senior cats. Three diets enriched with either beef tallow (high in saturated fatty acids), olive oil (high in monounsaturated fatty acids) or sunflower oil (high in polyunsaturated fatty acids) were fed to 6 young (3.0+/-0.9y) and 6 senior (11.6+/-1.4y) cats at 300kJ metabolisable energy/kgBW0.75/d in a 3*3 Latin square design. Food and faecal samples collected over two consecutive 7d periods were analysed for fat, protein, moisture, ash, gross energy and fatty acid content. Apparent digestibilities of fat and energy were significantly lower (P=0.03) in senior cats compared to young cats (fat: 0.922 compared to 0.944; energy: 0.848 compared to 0.885, for senior and young cats, respectively) in all three diets. Senior cats exhibited a lower apparent digestibility for all fatty acid groups compared to the younger cats (saturated: 0.932 compared to 0.952; monounsaturated: 0.964 compared to 0.982; polyunsaturated: 0.980 compared to 0.987, for senior and young cats, respectively). Saturated fatty acids had the lowest apparent digestibility in both young and senior cats, and shorter chain fatty acids were digested more easily than the longer chain fatty acids. These results suggest that the age-related reduction in apparent fat digestibility was a general phenomenon affecting all fatty acids, and was not due to one particular fatty acid group.

Aging↗