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PubMedDate not supplied

Engineering bone: challenges and obstacles.

Repair of large bone defects is still a challenge for the orthopaedic, reconstructive and maxillo-facial surgeon. Availability of pluripotent stem cells from either autologous or allogenic sources and the potential of inducing the osteogenic phenotype is motivating exploration and development of custom-tailored materials known as "bioengineered bone constructs". In such cases, the clinical scenario involves either expansion of stem cells in monolayer and loading them into a porous scaffold prior to surgery or direct cell expansion within the scaffold, and implanting this novel construct back into the donor patient. In this review, we delineate, from an engineering perspective, the progress that has been made to date and the challenges remaining in successfully translating this promising (but not yet definitively established) approach from bench to the bed site.

Animals↗
PubMed1990

Multiple parameter assessment of vulvar irritant contact dermatitis.

Transepidermal water loss (TEWL), capacitance, pH, blood flow and color reflectance were evaluated for quantifying the irritant response of vulvar and forearm skin to 3% sodium lauryl sulfate in 9 healthy premenopausal women. TEWL, capacitance, pH, blood flow, and all parameters of color reflectance changed significantly in forearm irritant dermatitis. In vulvar irritant dermatitis, however, significant changes were observed only for blood flow and the color reflectance parameters a* and b*. Using the combination of TEWL, capacitance and blood flow, forearm irritant dermatitis was detected with a sensitivity of 84% and a specificity of 100%. In this study, the best combination of parameters to detect vulvar irritant dermatitis was pH, blood flow, a* and b*, which had a sensitivity of 78% and a specificity of 75%. It is concluded that available bioengineering techniques are less suitable to quantify irritant dermatitis in the vulva than in the forearm.

Adult↗
PubMed1991

Basal transepidermal water loss, skin thickness, skin blood flow and skin colour in relation to sodium-lauryl-sulphate-induced irritation in normal skin.

The influence of basal transepidermal water loss (TEWL), skin thickness, blood flow and skin colour on susceptibility to sodium-lauryl-sulphate(SLS)-induced irritant contact dermatitis was studied in 70 healthy volunteers. SLS 0.5% was applied as a patch test. For assessment of basal values and skin response to SLS, bioengineering methods were used: TEWL was measured by an evaporimeter, skin thickness by ultrasound A-scan, blood flow by laser Doppler flowmetry, and skin colour by a colorimeter, using the L*a*b* system of the Commission Internationale de l'Eclairage (CIE). By use of multiple regression analysis, it was demonstrated that basal TEWL was substantially related to skin susceptibility to SLS, high basal TEWL predicting an increased susceptibility to SLS. Also increased light reflection from the skin, indicating a 'fair' skin, was found to be associated with increased susceptibility to SLS.

Adult↗
PubMed1994

Faecal enzymes: in vivo human skin irritation.

Digestive enzymes in faeces have been reported to possess skin irritation potential. The present study was designed to investigate the in vivo irritant potentials of faecal concentrations of proteolytic and lipolytic digestive enzymes in bile salt mixtures. In a 21-day cumulative irritation assay, clinical evaluation and noninvasive bioengineering techniques were used. 5 days occlusive exposure to phosphate buffer (pH = 8) caused no visual skin damage but reflectance spectroscopy demonstrated significant vasodilation (p < 0.01) and increases in transepidermal water loss (TEWL) and skin pH were also observed (p < 0.01). These increases were still present at days 12 and 19. Occlusive exposure to physiologic concentrations of faecal enzymes resulted in significant visual and objective scores at day 5, 12, and 19, with increased readings as a function of exposure time (p < 0.01). The enzyme mixture containing lipase caused delayed onset of skin erythema and epidermal barrier disruption compared to elastase and chymotrypsin containing solutions. Prolonged occlusive exposure to digestive enzymes in faecal concentrations caused severe skin erythema and epidermal barrier disruption in a human model, suggesting a possible etiologic role of digestive enzymes in perianal, circumstomal or diaper dermatitis.

Adult↗
PubMed1994

The irritant effect of different metalworking fluids.

The irritant effect of different water-based cutting fluids (CFs) on the skin was investigated in healthy subjects (n = 10) using 2 non-invasive bioengineering methods. Transepidermal water loss (TEWL) was measured by an evaporimeter EP1 (Servo Med), skin blood flow (SBF) was recorded with a laser Doppler flowmeter (MBF 3D, Moor Instruments England). Additionally all test sites were evaluated by visual scoring before measurement. 3 cutting fluids A, B and C from different manufacturers were tested at use concentrations of 4% or 5%. Single 24-h patch tests and repeated patch tests were performed on the volar side of the right forearm. Measurements were carried out before and after exposure to assess basal values and the skin response to CF. Tests with CFs A and C resulted in significant increase in TEWL after 24 h and after cumulative treatment, compared with controls (p < 0.01). The TEWL values for CF B did not differ from the water probe. An increase in SBF was found only for CFs A and C after cumulative patch testing (p < 0.01). In spite of their similar alkalinity, the 3 CFs showed different irritant skin reactions, due to their chemical components. This was verified particularly by measurement of TEWL.

Adult↗
PubMed1996

Ultrasound description and quantification of irritant reactions induced by dithranol at different concentrations. A comparison with visual assessment and colorimetric measurements.

Dithranol (D) is used as a therapeutic topical agent to treat psoriasis, although it produces inflammation and staining of skin and clothing. D-induced irritation has been evaluated by visual scoring and by bioengineering techniques, evidencing modifications of the inflammatory parameters, but no alterations of the skin barrier. The aim of our study was to evaluate the irritant reactions induced by D using ultrasound, and to compare the B-scanning data with visual assessments and colorimetric measurements. 13 healthy women underwent 2, 3-h patch tests with, respectively, 0.02% and 0.1% D in white petrolatum and 1 24-h patch test with 2% sodium lauryl sulfate (SLS). For assessing skin reactions, clinical judgement, colorimetry and echography were employed. Echographic images were evaluated by skin thickness measurements and segmentation procedures, using an 0-30 interval, marking the hyporeflecting areas in the dermis, and a 201-255 interval, assessing the hyperreflecting components of the image (both epidermal and dermal). In all subjects, D produced uniform reactions, the intensity varying according to concentration. Both echographic parameters of inflammation (skin thickness and 0-30 areas) showed an increase at all times of assessment. The 201-255D/0-30 pixel ratio, describing the distribution of dermal edema, indicated that strong inflammatory reactions, such as those caused by the application of 0.1% D, are accompanied by edema in the lower portion of the dermis. Finally, in contrast to SLS reactions, where a 24-h reduction in epidermal reflectivity was observable, D reactions appeared with an accentuation of the 201-255 epidermal band at 24-96-h examinations.

Administration, Topical↗
PubMed1997

Acute irritant contact dermatitis: recovery time in man.

Our understanding of the details of the recovery time of acute irritant contact dermatitis (ICD) is limited. We examined skin reactivity to a model surfactant, sodium lauryl sulfate (SLS), on previous acute ICD and normal sites over time with visual grading and noninvasive instruments. Acute ICD was induced on the upper arms of 18 volunteers (aged 30 to 51 years) by occluded application of 1% SLS for 24 h. Previous ICD and normal sites were provoked by occluded application of 2% or 7.5% SLS 30 min daily 4 consecutive days. Skin reactivity was assessed daily by visual erythema scoring (VES), transepidermal water loss (TEWL), skin color reflectance (SCR) and electrical capacitance (EC). Skin function of previous ICD sites assessed by VES, TEWL, SCR, and EC did not normalize until 2 weeks later; all parameters of previous ICD returned to normal after 3 weeks. While skin reactivity to 2% and 7.5% SLS showed no differences between previous ICD and normal sites at 4 weeks, differences of irritant reactivity especially 7.5% SLS between previous ICD and normal sites were significant at 3 weeks post-provocation. Our results demonstrate that irritation evaluated with irritant provocation was long-lasting, even though skin functional parameters assessed by various bioengineering instruments returned to normal. Complete recovery of skin function including irritability after acute ICD induced by 1% SLS was achieved approximately 4 weeks later. The date were generated with a model surfactant; it remains to be determined whether similar responses will be noted with chemicals of different physiochemical properties.

Acute Disease↗
PubMed1999

In vitro testing of tensides employing monolayer cultures: a comparison with results of patch tests on human volunteers.

Evaluation of the irritant potential of new products or ingredients prior to human testing is generally performed in vivo on animals. However, according to the 6th amendment and following updates of the European Community directive on cosmetic products (93/35/EEC), animal testing will be banned when suitable substitutes will be available. To know whether in vitro tests for assessment of skin irritancy provide results approaching human conditions, comparisons have to be made between data deriving from in vitro tests and skin response in humans. The aim of our study was to assess the validity of the monolayer culture system of normal human keratinocytes as a model for the evaluation of the irritant effects of detergents, by comparing in vitro cell culture data to in vivo acute skin irritancy effects of cocamidopropyl betaine (CAPB), an amphoteric compound, Tween 20 (TW20) (polysorbate 20) and Tween 80 (TW80) (polysorbate 80), representing nonionic compounds, applied to the skin of 24 healthy volunteers at a concentration similar to that employed in commercial products. As parameters for cytotoxicity, cell proliferation, cell membrane integrity and cell metabolism were assessed by cell counts, thymidine incorporation, MTT conversion, and Neutral Red uptake. In order to increase the sensitivity of the in vivo evaluation, bioengineering methods for assessment of the effects of test products on the skin were employed. Whereas all 4 in vitro methods ranked the tensides according to their toxicity in the following order: CAPB>SLS>TW20>TW80, both in vivo methods agreed in identifying SLS as the most irritating substance. Moreover, as compared with the irritation potential on human skin, all 4 in vitro tests overestimated the toxicity of CAPB. This suggests that the keratinocyte monolayer cell culture technique cannot directly replace in vivo methods, and that data obtained by this method should be interpreted cautiously.

Adolescent↗
PubMed1999

In vivo nickel allergic contact dermatitis: human model for topical therapeutics.

Techniques to determine efficacy of topical agents on allergic contact dermatitis (ACD) may benefit from refinement. The aim of this study was to develop an in vivo human model system for the bioengineering and visual quantification of the effect of topical agents on nickel ACD, and to correlate ACD parameters. 14 nickel patch-test-positive subjects were included in a placebo-controlled, double-blind study after a pre-screening procedure with a standard diagnostic patch test with nickel sulfate in 54 healthy human volunteers. 5% nickel sulfate in petrolatum in a Finn Chamber was applied on forearm skin for 48 h to create a standardized dermatitis. Thereafter, the dermatitis was treated with a model topical agent and a placebo control while recording endpoint parameters daily for 10 days. Resolution was quantified with 4 parameters: visual scoring (VS), transepidermal water loss (TEWL) (Tewameter), skin blood flow volume (BFV) (laser Doppler flowmeter), and skin color (a* value) (Colorimeter). The model agent reduced cutaneous allergic reactions, especially on day 8 to 10, in comparison with the placebo control. A highly significant linear relationship exists among all parameters, except between a* and BFV. This model may provide robust biometrics for determining the efficacy of topical therapeutics on experimentally induced ACD.

Administration, Cutaneous↗
PubMed2006

Transepidermal water loss reflects permeability barrier status: validation in human and rodent in vivo and ex vivo models.

Permeability barrier function is measured with instruments that assess transepidermal water loss (TEWL), either with closed- or open-loop systems. Yet, the validity of TEWL as a measure of barrier status has been questioned recently. Hence, we tested the validity of this measure by comparing TEWL across a wide range of perturbations, with a variety of methods, and in a variety of models. TEWL rates with two closed-chamber systems (VapoMeter and H4300) and one closed-loop system (MEECO) under different experimental in vivo conditions were compared with data from four open-loop instruments, i.e. TM 210, TM 300, DermaLab and EP 1. The instruments were compared in vivo both in humans and hairless mice skin subjected to different degrees of acute barrier disruption. The values obtained with bioengineering systems were correlated with absolute water loss rates, determined gravimetrically. Measurements with both closed and open systems correlated not only with each other, but each method detected different degrees of barrier dysfunction. Although all instruments differentiated among gradations in TEWL in the mid-range of barrier disruption in vivo, differences in very low and very high levels of disruption were less accurately measured with the H4300 and DermaLab systems. Nevertheless, a high Pearson correlation coefficient (r) was calculated for data from all instruments vs. gravimetrically assessed TEWL. Together, these results verify the utility of TEWL as a measure of permeability barrier status. Moreover, all tested instruments are reliable tools for the assessment of variations in permeability barrier function.

Adult↗
PubMed2004

Assessment of pigmented skin lesions in terms of blood perfusion estimates.

BACKGROUND/AIMS: Cutaneous malignant melanoma is a disease of increasing clinical and economical importance. The prognosis is good with early diagnosis. The chief differential diagnosis is benign melanocytic naevus, a common lesion in Caucasians. Attempts have been made to use bioengineering techniques to aid in the initial diagnosis. The present study proposes a method of extracting possibly discriminative blood perfusion properties in pigmented skin lesions by combining information on the lesions' blood perfusion with optical or visual information of their spatial extent. METHODS: A total of 46 blood perfusion measurements were performed on 22 pigmented skin lesions, the ultimate diagnosis of which was three histologically proven malignant melanomas, four histologically proven benign naevi and fifteen naevi assessed by two specialist dermatologists as being benign. Laser Doppler perfusion imaging gave two different types of two-dimensional data sets (64x64 pixels), one representing the total backscattered light intensity at each measurement point (TLI image) and the second corresponding to perfusion values. The boundaries of each examined lesion were derived from the TLI image employing greyscale thresholding, thus resulting in an estimated region of interest (ROI) approximating the optical extent of the lesion. The ROI was superimposed on the perfusion image and extraction of perfusion features was then performed. RESULTS: The processing of the TLI images was successful in delineating the lesions' boundaries. The first hypothesis that the mean perfusion quotients in MM and benign naevi are equal could not be rejected at the chosen 5% level of significance. The second hypothesis that the mean percent-age of elevated perfusion values (image pixels) within the ROI shows no difference between MM and benign naevi could be rejected at a 5% level of significance. CONCLUSIONS: This study has presented a method of extracting blood perfusion parameters of pigmented skin lesions by combining blood perfusion information with information on the lesion's optical extent. The proposed method of presenting data could prove to be a useful discriminative adjunct in the assessment of pigmented skin lesions.

Adult↗
PubMed2005

Non-invasive preoperative assessment of basal cell carcinoma of nodular and superficial types.

BACKGROUND/AIMS: Although various biophysical properties can be used to distinguish basal cell carcinoma (BCC) tissue from normal skin, none permits typing of the tumour. In this study, we assessed nodular (NBCC) and superficial (SBCC) types of BCC using three different non-invasive instruments and placed special emphasis on their clinical value as diagnostic tools. METHODS: We included 35 patients with 35 tumours (15 NBCC and 20 SBCC), which had been diagnosed clinically. All lesions were evaluated preoperatively with an instrument measuring electrical impedance (IMP). Methods for determining transepidermal water loss (TEWL) and laser Doppler (LD) were also used. Measurements were also made in healthy skin on the contralateral side as reference. The diagnosis was confirmed by histological examination. RESULTS: We found clear differences between the lesions and their reference values, using all three bioengineering techniques for NBCC and SBCC. The biophysical parameters of all types vary with anatomical location. Since most of the NBCC were located on the face and most SBCC on the trunk, their baseline impedance characteristics (i.e., impedance indices magnitude index (MIX) and imaginary part index (IMIX)) differed significantly. We therefore compared delta (a difference between the reference and tumour) MIX and IMIX of NBCC and SBCC instead of the absolute figures. We found no significant differences in TEWL, blood flow and IMP between the two types of BCC and attribute this to biological variation and electromagnetic noise. CONCLUSIONS: As with LD and TEWL, definite differences in IMP were detected between healthy skin and BCC lesions. However, at this stage of development of the bioimpedance technique, we were unable to distinguish between the two types of BCC. An improved IMP device with semi- invasive probes or a more sophisticated type of data analysis may increase the diagnostic usefulness of the IMP method.

Adult↗
PubMed2006

In vivo engineering of metabolically active hepatic tissues in a neovascularized subcutaneous cavity.

Recent success in clinical hepatocyte transplantation therapy has encouraged further investigation into bioengineering hepatic tissues in vivo. Engineering tissues in the subcutaneous space is an attractive method; however, hepatocyte survival has been transient due to insufficient vascular network formation. To establish a vascularized cavity, we created a polyethylene terephthalate mesh device coated with poly(vinylalcohol) that allowed for the gradual release of basic fibroblast growth factor (bFGF), a potent angiogenic factor. The efficacy of the bFGF-releasing device in inducing vascular network formation in the subcutaneous space was observed in mouse and rat studies. Isolated mouse hepatocytes transplanted into newly vascularized subcutaneous cavities allowed for persistent survival up to 120 days. In the absence of a vascularized compartment, the survival of the transplanted hepatocytes was markedly diminished. Functional maintenance of the engineered hepatic tissues was confirmed by high expression of liver-specific mRNAs and proteins. These engineered hepatic tissues have the ability to take up inoculated compounds and express strong induction of drug-metabolizing enzymes, demonstrating functional relevance as a metabolic tissue. In conclusion, we have created a novel technology to engineer functionally active hepatic tissues in the subcutaneous space, which will likely facilitate hepatocyte-based therapies.

Animals↗
PubMedDate not supplied

Role of biodental engineering factors (BEF) in the etiology of root caries.

A preliminary study and hypothesis of the etiology of root caries is presented with appropriate data suggesting that biodental engineering factors (BEF) be introduced into the equation that is generally accepted in the formation of all caries. Principally, because of the rapid progression and location of root caries, BEF in addition to bacterial plaque and suitable substrate contribute to the development of these unique lesions. The dominant and most significant factors recognized by bioengineers are tooth flexure, stress concentration, stress corrosion, and piezo-electricity. All of these factors interplay during the dynamics of occlusal activity causing the loss of tooth substance. A new and revised model is being presented that provides a basis for the etiology of root caries.

Bite Force↗
PubMed2006

The potent inhibitory activity of histone H1.2 C-terminal fragments on furin.

Many physiologically important proproteins, pathogenic bacterial exotoxins and viral envelope glycoproteins are activated by the proprotein convertase furin, which makes furin inhibitor a hot target for basic research and drug design. Although synthetic and bioengineered inhibitors of furin have been well characterized, its endogenous inhibitor has not been directly purified from mammalian tissues to date. In this study, three inhibitors were purified from the porcine liver by using a combination of chromatographic techniques, and identified to be the C-terminal truncated fragments with different sizes of histone H1.2. The gene of porcine histone H1.2 was cloned and sequenced, further confirming the determined sequences. These three C-terminal fragments inhibited furin with Ki values around 2 x 10(-7) m while the full-length histone H1.2 inhibited it with a lesser activity, suggesting that the inhibitory activity relies on the C-terminal lysine-rich domain. Though the inhibition was temporary, these inhibitors were specific, and the reactive site of one C-terminal fragment was identified. A 36 amino acid peptide around the reactive site was synthesized, which could still inhibit furin with a Ki of 5.2 x 10(-7) m.

Amino Acid Sequence↗
PubMed2006

Advances in the management of leg ulcers--the potential role of growth factors.

Venous ulcers are a major health problem because of the increased costs of the treatment and the refractory nature of the ulcers. The treatment cost is estimated to be around 1 billion dollars per year in the United States (US), and the average cost for one patient over a lifetime exceeds dollars 400,000. There has been an increasing trend in the use of growth factors in their management. Genetic engineering has revolutionised the research of wound healing, as the majority of recombinant growth factors are now available for in vitro and in vivo studies. Online searches of Medline, Pub Medical and Embase were carried out using the terms venous ulcers, leg ulcers, growth factors and growth hormone. The literature regarding the potential role of growth factors in the management of leg ulcers is reviewed. The important clinical studies are critically analysed with a view to appreciate the emerging therapies and the further research possibilities in the management of venous leg ulcers. Clinical results with the use of growth factors in non-healing wounds are encouraging. However, small sample sizes and inconsistent end points in different clinical studies have been the main hurdle in reaching a definite conclusion. Further research is needed to provide the definite evidence. Future developments may include different delivery methods for the growth factors, use of different combinations of growth factors administered simultaneously or, sequentially, bioengineered skin grafts and chemical induction of angiogenesis with the use of gene transfer techniques.

Growth Substances↗
PubMed1987

Role of platelet membrane glycoproteins and von Willebrand factor in adhesion of platelets to subendothelium and collagen.

Development of in vitro perfusion systems and quantitative methods to evaluate various aspects of platelet-surface interactions have helped to elucidate some complex interactions in platelet adhesion and platelet-platelet cohesion. The importance of platelet GPs in these interactions was soon evident, and rapid progress in biochemistry and immunology has made it possible to study the roles of these GPs in more detail. From our studies, which made use of platelets with GP deficiencies, MAbs, purified vWF, proteolytic fragments of vWF, a synthetic peptide, and in vitro perfusion systems, it appeared that GPIb and GPIIb/IIIa function as receptors for vWF, which binds platelets to connective tissue at sites of vascular lesions (FIGURE 8). More detailed information about these interactions is expected in the near future when bioengineered products are available for testing in flow models and in other experimental approaches.

Antibodies, Monoclonal↗
PubMed1998

Protein disulfide isomerase assists protein folding as both an isomerase and a chaperone.

Protein disulfide isomerase (PDI) is the physiological catalyst of native disulfide bond formation of nascent peptides in the cells. As a foldase, PDI has both isomerase and chaperone activities. The chaperone activity is intrinsic and independent of its isomerase activity. Both chaperone and isomerase activities are required for PDI to assist folding of denatured and reduced disulfide-containing proteins. PDI may have great applications in protein production by bioengineering for its function as a foldase.

Disulfides↗