Animal bone-derived calcium hydroxyapatite (HA) particles were produced and characterized. Adult ... more Animal bone-derived calcium hydroxyapatite (HA) particles were produced and characterized. Adult bovine femoral bone was boiled, washed, cleaned and heated in air at 700 • C for 2 h. The resulting macroporous solid was ground, crushed and sieved into particles <50 m.
Isothermal microcalorimetry is becoming widely used for monitoring biological activities in vitro... more Isothermal microcalorimetry is becoming widely used for monitoring biological activities in vitro. Microcalorimeters are now able to measure heat production rates of less than a microwatt. As a result, metabolism and growth of relatively small numbers of cultured bacteria, protozoans, human cells and even small animals can be monitored continuously and extremely accurately at any chosen temperature. Dynamic effects on these organisms of changes in the culture environment-or of additions to it-are easily assessed over periods from hours to days. In addition microcalorimetry is a non-destructive method that does not require much sample preparation. It is also completely passive and thus allows subsequent evaluations of any kind on the undisturbed sample. In this review, we present a basic description of current microcalorimetry instruments and an overview of their use for various biomedical applications. These include detecting infections, evaluating effects of pharmaceutical or antimicrobial agents on cells, monitoring growth of cells harvested for tissue eingineering, and assessing medical and surgical device material physico-chemical stability and cellular biocompatibility.
In our attempts to detect early signs of osteoarthritis (OA) in the human hip and knee joint, we ... more In our attempts to detect early signs of osteoarthritis (OA) in the human hip and knee joint, we inspected the morphological and biomechanical status of articular cartilage biopsies representing different grades of OA according to the bOuterbridge scaleQ. Most significantly, the early changes (grades 0 to 2) which are often not yet symptomatic, were only detectable at the nanometer scale, but not at the micrometer or millimeter scale. These observations have been validated with articular cartilage of aging and OA mice. Motivated by these ...
The pathological changes in osteoarthritis—a degenerative joint disease prevalent among older peo... more The pathological changes in osteoarthritis—a degenerative joint disease prevalent among older people—start at the molecular scale and spread to the higher levels of the architecture of articular cartilage to cause progressive and irreversible structural and functional damage. At present, there are no treatments to cure or attenuate the degradation of cartilage. Early detection and the ability to monitor the progression of osteoarthritis are therefore important for developing effective therapies. Here, we show that indentation-type atomic force microscopy can monitor age-related morphological and biomechanical changes in the hips of normal and osteoarthritic mice. Early damage in the cartilage of osteoarthritic patients undergoing hip or knee replacements could similarly be detected using this method. Changes due to aging and osteoarthritis are clearly depicted at the nanometre scale well before morphological changes can be observed using current diagnostic methods. Indentation-type atomic force microscopy may potentially be developed into a minimally invasive arthroscopic tool to diagnose the early onset of osteoarthritis in situ.
As documented previously, articular cartilage exhibits a scale-dependent dynamic stiffness when p... more As documented previously, articular cartilage exhibits a scale-dependent dynamic stiffness when probed by indentation-type atomic force microscopy (IT-AFM). In this study, a micrometer-size spherical tip revealed an unimodal stiffness distribution (which we refer to as microstiffness), whereas probing articular cartilage with a nanometer-size pyramidal tip resulted in a bimodal nanostiffness distribution. We concluded that indentation of the cartilage's soft proteoglycan (PG) gel gave rise to the lower nanostiffness peak, whereas deformation of its collagen fibrils yielded the higher nanostiffness peak. To test our hypothesis, we produced a gel-microfiber composite consisting of a chondroitin sulfate-containing agarose gel and a fibrillar poly(ethylene glycol)-terephthalate/poly(butylene)-terephthalate block copolymer. In striking analogy to articular cartilage, the microstiffness distribution of the synthetic composite was unimodal, whereas its nanostiffness exhibited a bimodal distribution. Also, similar to the case with cartilage, addition of the negatively charged chondroitin sulfate rendered the gel-microfiber composite's water content responsive to salt. When the ionic strength of the surrounding buffer solution increased from 0.15 to 2 M NaCl, the cartilage's microstiffness increased by 21%, whereas that of the synthetic biomaterial went up by 31%. When the nanostiffness was measured after the ionic strength was raised by the same amount, the cartilage's lower peak increased by 28%, whereas that of the synthetic biomaterial went up by 34%. Of interest, the higher peak values remained unchanged for both materials. Taken together, these results demonstrate that the nanoscale lower peak is a measure of the soft PG gel, and the nanoscale higher peak measures collagen fibril stiffness. In contrast, the micrometer-scale measurements fail to resolve separate stiffness values for the PG and collagen fibril moieties. Therefore, we propose to use nanostiffness as a new biomarker to analyze structure-function relationships in normal, diseased, and engineered cartilage.
The pathological changes in osteoarthritis-a degenerative joint disease prevalent among older peo... more The pathological changes in osteoarthritis-a degenerative joint disease prevalent among older people-start at the molecular scale and spread to the higher levels of the architecture of articular cartilage to cause progressive and irreversible structural and functional damage. At present, there are no treatments to cure or attenuate the degradation of cartilage. Early detection and the ability to monitor the progression of osteoarthritis are therefore important for developing effective therapies. Here, we show that indentation-type atomic force microscopy can monitor age-related morphological and biomechanical changes in the hips of normal and osteoarthritic mice. Early damage in the cartilage of osteoarthritic patients undergoing hip or knee replacements could similarly be detected using this method. Changes due to aging and osteoarthritis are clearly depicted at the nanometre scale well before morphological changes can be observed using current diagnostic methods. Indentation-type atomic force microscopy may potentially be developed into a minimally invasive arthroscopic tool to diagnose the early onset of osteoarthritis in situ.
Since articular cartilage has a limited potential for spontaneous healing, various techniques are... more Since articular cartilage has a limited potential for spontaneous healing, various techniques are employed to repair cartilage lesions. Acrylate-based double-network (DN) hydrogels containing ∼90 % water have shown promising properties as repair materials for skeletal system soft tissues. Although their mechanical properties approach those of native cartilage, the critical factor-stiffness-of DNgels does not equal the stiffness of articular cartilage. This study investigated whether revised PAMPS/PAAm compositions with lower water content result in stiffness parameters closer to cartilage. DN-gels containing 61, 86 and 90 % water were evaluated using two non-destructive, mm-scale indentation test modes: fast-impact (FI) and slow-sinusoidal (SS) deformation. Deformation resistance (dynamic modulus) and energy handling (loss angle) were determined. The dynamic modulus increased with decreasing water content in both testing modes. In the 61 % water DN-gel, the modulus resembled that of cartilage (FI-mode: DN-gel = 12, cartilage = 17; SS-mode: DN-gel = 4, cartilage = 1.7 MPa). Loss angle increased with decreasing water content in fast-impact, but not in slow-sinusoidal deformation. However, loss angle was still much lower than cartilage (FI: DN-gel = 5, cartilage = 11; SS: DN-gel = 10, cartilage = 32 • ), indicating somewhat less ability to dissipate energy. Overall, results show that it is possible to adapt DN-gel composition to produce dynamic stiffness properties close to normal articular cartilage.
Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) and MIC determination w... more Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) and MIC determination was evaluated. It was possible to differentiate between MRSA and MSSA within 4 h, whereas the standard method required 24 h. The MICs of cefoxitin were successfully determined for MRSA and MSSA by using IMC. by guest http://jcm.asm.org/ Downloaded from FIG. 2. MIC determination of cefoxitin for S. aureus ATCC 25923 (MSSA) in the range of 0.0 mg liter Ϫ1 to 8 mg liter Ϫ1 . (A) Heat flow curve; (B) Heat curve. Blank, Mueller-Hinton plus 2% NaCl alone. Curves are averages for three experiments.
Lymphocyte transformation tests (LTT) are time-consuming radioactive assays used in the clinic fo... more Lymphocyte transformation tests (LTT) are time-consuming radioactive assays used in the clinic for the determination of allergic drug reactions and extensively in basic immunological research. In the present study we propose an alternative method in the monitoring of T-cell responses by isothermal microcalorimetric (IMC) measurements of overall cellular heat production as a function of time. For mitogen-induced lymphocyte proliferation, we analyzed a concentration dependent effect of phytohemaglutinin (PHA) and both tests showed a good correlation. This was also the case for specific antigenic stimulation with Varidase ® or tetanus toxoid. On the other hand, antigeninduced lymphocyte proliferation analyzed by pre and post influenza vaccine (Inflexal ® V) samples, showed no such correlation. Our study suggests that IMC measurements, despite the advantages of simplicity, on-line recording of metabolic activity and no use of radioactivity, may be limited to monitoring mitogen-induced lymphocyte proliferation.
The purpose of this work was to produce and characterize SiO 2 -CaO-P 2 O 5 bioactive glass nanop... more The purpose of this work was to produce and characterize SiO 2 -CaO-P 2 O 5 bioactive glass nanoparticles with negative zeta potential for possible use in biomedical applications. 63S bioactive glass was obtained using the sol-gel method. X-ray fluorescence (XRF) spectroscopy and dispersive X-ray analysis (EDX) confirmed the preparation of the 63S bioactive glass with 62.17% SiO 2 , 28.47% CaO and 9.25% P 2 O 5 (in molar percentage). The in vitro apatite forming ability of prepared bioactive glass was evaluated by Fourier transform infrared spectroscopy (FTIR) after immersion in simulated body fluid (SBF). The result showed that high crystalline hydroxyapatite can form on glass particles. By the gas adsorption (BET method), particle specific surface area and theoretical particle size were 223.6 AE 0.5 m 2 /g and $24 nm, respectively. Laser dynamic light scattering (DLS) indicated particles were mostly agglomerated and had an average diameter between 100 and 500 nm. Finally, using laser Doppler electrophoresis (LDE) the zeta potential of bioactive glass nanoparticles suspended in physiological saline was determined. The zeta potential was negative for acidic, neutral and basic pH values and was À16.18 AE 1.8 mV at pH 7.4. In summary, the sol-gel derived nanoparticles revealed in vitro bioactivity in SBF and had a negative zeta potential in physiological saline solution. This negative surface charge is due to the amount and kind of the ions in glass structure and according to the literature, promotes cell attachment and facilitates osteogenesis. The nanometric particle size, bioactivity and negative zeta potential make this material a possible candidate for bone tissue engineering. #
Background: Antimicrobial susceptibility testing of microorganisms is performed by either disc di... more Background: Antimicrobial susceptibility testing of microorganisms is performed by either disc diffusion or broth dilution tests. In clinical use, the tests are often still performed manually although automated systems exist. Most systems, however, are based on turbidometric methods which have well-known drawbacks.
In focal repair of joint cartilage and meniscus, initial stiffness and strength of repairs are ge... more In focal repair of joint cartilage and meniscus, initial stiffness and strength of repairs are generally much less than surrounding tissue. This increases early failure potential. Secure primary fixation of the repair material is also a problem. Acrylamide polymer double-network (DN) hydrogels are candidate-improved repair materials. DN gels have exceptional strength and toughness compared to ordinary gels. This stems from the double-network structure in which there is a high molar ratio of the second network to the first network, with the first network highly crosslinked and the second loosely crosslinked. Previous studies of acrylic PAMPS/PDMAAm and PAMPS/PAAm DN gels demonstrated physicochemical stability and tissue compatibility as well as the ability to foster cartilage formation. Mechanical properties related to surgical use were tested in 2 types of DN gels. Remarkably, these >90%-water DN gels exhibited dynamic impact stiffness (E*) values (~1.1 and ~1.5 MPa) approaching ...
Closed ampoule isothermal microcalorimetry (IMC) is a simple, powerful, nondestructive, and conve... more Closed ampoule isothermal microcalorimetry (IMC) is a simple, powerful, nondestructive, and convenient technique that allows continuous, real-time detection and evaluation of cultured cell activity and responses. At a selected set temperature, IMC measures the heat flow between a sample and a heat sink and compares it to the heat-flow between a thermally inactive reference and the heat sink. Since heat flow rates are proportional to the rates of chemical reactions and changes of state, IMC provides a means for dynamically following these processes in any type of specimen -including ones containing cultured cells. The ability of IMC instruments to provide measurements in the microwatt (mJ/s) range allows one to detect and follow the activity (including replication) of low numbers of cells in culture (ca. 10 3 -10 5 , depending on cell type). Closed ampoule IMC is increasingly being used in medical and environmental sciences. While a closed ampoule imposes limitations, it conversely provides simplicity and excellent control. Also, it is still usually possible with closed ampoules to follow mammalian cell activity and replication for several days. This chapter provides an overview of IMC measurement principles and provides examples of the use of IMC for evaluating cultured human and other mammalian cell activity and responses.
The pathological changes in osteoarthritis-a degenerative joint disease prevalent among older peo... more The pathological changes in osteoarthritis-a degenerative joint disease prevalent among older people-start at the molecular scale and spread to the higher levels of the architecture of articular cartilage to cause progressive and irreversible structural and functional damage. At present, there are no treatments to cure or attenuate the degradation of cartilage. Early detection and the ability to monitor the progression of osteoarthritis are therefore important for developing effective therapies. Here, we show that indentation-type atomic force microscopy can monitor age-related morphological and biomechanical changes in the hips of normal and osteoarthritic mice. Early damage in the cartilage of osteoarthritic patients undergoing hip or knee replacements could similarly be detected using this method. Changes due to aging and osteoarthritis are clearly depicted at the nanometre scale well before morphological changes can be observed using current diagnostic methods. Indentation-type atomic force microscopy may potentially be developed into a minimally invasive arthroscopic tool to diagnose the early onset of osteoarthritis in situ.
Animal bone-derived calcium hydroxyapatite (HA) particles were produced and characterized. Adult ... more Animal bone-derived calcium hydroxyapatite (HA) particles were produced and characterized. Adult bovine femoral bone was boiled, washed, cleaned and heated in air at 700 • C for 2 h. The resulting macroporous solid was ground, crushed and sieved into particles <50 m.
Isothermal microcalorimetry is becoming widely used for monitoring biological activities in vitro... more Isothermal microcalorimetry is becoming widely used for monitoring biological activities in vitro. Microcalorimeters are now able to measure heat production rates of less than a microwatt. As a result, metabolism and growth of relatively small numbers of cultured bacteria, protozoans, human cells and even small animals can be monitored continuously and extremely accurately at any chosen temperature. Dynamic effects on these organisms of changes in the culture environment-or of additions to it-are easily assessed over periods from hours to days. In addition microcalorimetry is a non-destructive method that does not require much sample preparation. It is also completely passive and thus allows subsequent evaluations of any kind on the undisturbed sample. In this review, we present a basic description of current microcalorimetry instruments and an overview of their use for various biomedical applications. These include detecting infections, evaluating effects of pharmaceutical or antimicrobial agents on cells, monitoring growth of cells harvested for tissue eingineering, and assessing medical and surgical device material physico-chemical stability and cellular biocompatibility.
In our attempts to detect early signs of osteoarthritis (OA) in the human hip and knee joint, we ... more In our attempts to detect early signs of osteoarthritis (OA) in the human hip and knee joint, we inspected the morphological and biomechanical status of articular cartilage biopsies representing different grades of OA according to the bOuterbridge scaleQ. Most significantly, the early changes (grades 0 to 2) which are often not yet symptomatic, were only detectable at the nanometer scale, but not at the micrometer or millimeter scale. These observations have been validated with articular cartilage of aging and OA mice. Motivated by these ...
The pathological changes in osteoarthritis—a degenerative joint disease prevalent among older peo... more The pathological changes in osteoarthritis—a degenerative joint disease prevalent among older people—start at the molecular scale and spread to the higher levels of the architecture of articular cartilage to cause progressive and irreversible structural and functional damage. At present, there are no treatments to cure or attenuate the degradation of cartilage. Early detection and the ability to monitor the progression of osteoarthritis are therefore important for developing effective therapies. Here, we show that indentation-type atomic force microscopy can monitor age-related morphological and biomechanical changes in the hips of normal and osteoarthritic mice. Early damage in the cartilage of osteoarthritic patients undergoing hip or knee replacements could similarly be detected using this method. Changes due to aging and osteoarthritis are clearly depicted at the nanometre scale well before morphological changes can be observed using current diagnostic methods. Indentation-type atomic force microscopy may potentially be developed into a minimally invasive arthroscopic tool to diagnose the early onset of osteoarthritis in situ.
As documented previously, articular cartilage exhibits a scale-dependent dynamic stiffness when p... more As documented previously, articular cartilage exhibits a scale-dependent dynamic stiffness when probed by indentation-type atomic force microscopy (IT-AFM). In this study, a micrometer-size spherical tip revealed an unimodal stiffness distribution (which we refer to as microstiffness), whereas probing articular cartilage with a nanometer-size pyramidal tip resulted in a bimodal nanostiffness distribution. We concluded that indentation of the cartilage's soft proteoglycan (PG) gel gave rise to the lower nanostiffness peak, whereas deformation of its collagen fibrils yielded the higher nanostiffness peak. To test our hypothesis, we produced a gel-microfiber composite consisting of a chondroitin sulfate-containing agarose gel and a fibrillar poly(ethylene glycol)-terephthalate/poly(butylene)-terephthalate block copolymer. In striking analogy to articular cartilage, the microstiffness distribution of the synthetic composite was unimodal, whereas its nanostiffness exhibited a bimodal distribution. Also, similar to the case with cartilage, addition of the negatively charged chondroitin sulfate rendered the gel-microfiber composite's water content responsive to salt. When the ionic strength of the surrounding buffer solution increased from 0.15 to 2 M NaCl, the cartilage's microstiffness increased by 21%, whereas that of the synthetic biomaterial went up by 31%. When the nanostiffness was measured after the ionic strength was raised by the same amount, the cartilage's lower peak increased by 28%, whereas that of the synthetic biomaterial went up by 34%. Of interest, the higher peak values remained unchanged for both materials. Taken together, these results demonstrate that the nanoscale lower peak is a measure of the soft PG gel, and the nanoscale higher peak measures collagen fibril stiffness. In contrast, the micrometer-scale measurements fail to resolve separate stiffness values for the PG and collagen fibril moieties. Therefore, we propose to use nanostiffness as a new biomarker to analyze structure-function relationships in normal, diseased, and engineered cartilage.
The pathological changes in osteoarthritis-a degenerative joint disease prevalent among older peo... more The pathological changes in osteoarthritis-a degenerative joint disease prevalent among older people-start at the molecular scale and spread to the higher levels of the architecture of articular cartilage to cause progressive and irreversible structural and functional damage. At present, there are no treatments to cure or attenuate the degradation of cartilage. Early detection and the ability to monitor the progression of osteoarthritis are therefore important for developing effective therapies. Here, we show that indentation-type atomic force microscopy can monitor age-related morphological and biomechanical changes in the hips of normal and osteoarthritic mice. Early damage in the cartilage of osteoarthritic patients undergoing hip or knee replacements could similarly be detected using this method. Changes due to aging and osteoarthritis are clearly depicted at the nanometre scale well before morphological changes can be observed using current diagnostic methods. Indentation-type atomic force microscopy may potentially be developed into a minimally invasive arthroscopic tool to diagnose the early onset of osteoarthritis in situ.
Since articular cartilage has a limited potential for spontaneous healing, various techniques are... more Since articular cartilage has a limited potential for spontaneous healing, various techniques are employed to repair cartilage lesions. Acrylate-based double-network (DN) hydrogels containing ∼90 % water have shown promising properties as repair materials for skeletal system soft tissues. Although their mechanical properties approach those of native cartilage, the critical factor-stiffness-of DNgels does not equal the stiffness of articular cartilage. This study investigated whether revised PAMPS/PAAm compositions with lower water content result in stiffness parameters closer to cartilage. DN-gels containing 61, 86 and 90 % water were evaluated using two non-destructive, mm-scale indentation test modes: fast-impact (FI) and slow-sinusoidal (SS) deformation. Deformation resistance (dynamic modulus) and energy handling (loss angle) were determined. The dynamic modulus increased with decreasing water content in both testing modes. In the 61 % water DN-gel, the modulus resembled that of cartilage (FI-mode: DN-gel = 12, cartilage = 17; SS-mode: DN-gel = 4, cartilage = 1.7 MPa). Loss angle increased with decreasing water content in fast-impact, but not in slow-sinusoidal deformation. However, loss angle was still much lower than cartilage (FI: DN-gel = 5, cartilage = 11; SS: DN-gel = 10, cartilage = 32 • ), indicating somewhat less ability to dissipate energy. Overall, results show that it is possible to adapt DN-gel composition to produce dynamic stiffness properties close to normal articular cartilage.
Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) and MIC determination w... more Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) and MIC determination was evaluated. It was possible to differentiate between MRSA and MSSA within 4 h, whereas the standard method required 24 h. The MICs of cefoxitin were successfully determined for MRSA and MSSA by using IMC. by guest http://jcm.asm.org/ Downloaded from FIG. 2. MIC determination of cefoxitin for S. aureus ATCC 25923 (MSSA) in the range of 0.0 mg liter Ϫ1 to 8 mg liter Ϫ1 . (A) Heat flow curve; (B) Heat curve. Blank, Mueller-Hinton plus 2% NaCl alone. Curves are averages for three experiments.
Lymphocyte transformation tests (LTT) are time-consuming radioactive assays used in the clinic fo... more Lymphocyte transformation tests (LTT) are time-consuming radioactive assays used in the clinic for the determination of allergic drug reactions and extensively in basic immunological research. In the present study we propose an alternative method in the monitoring of T-cell responses by isothermal microcalorimetric (IMC) measurements of overall cellular heat production as a function of time. For mitogen-induced lymphocyte proliferation, we analyzed a concentration dependent effect of phytohemaglutinin (PHA) and both tests showed a good correlation. This was also the case for specific antigenic stimulation with Varidase ® or tetanus toxoid. On the other hand, antigeninduced lymphocyte proliferation analyzed by pre and post influenza vaccine (Inflexal ® V) samples, showed no such correlation. Our study suggests that IMC measurements, despite the advantages of simplicity, on-line recording of metabolic activity and no use of radioactivity, may be limited to monitoring mitogen-induced lymphocyte proliferation.
The purpose of this work was to produce and characterize SiO 2 -CaO-P 2 O 5 bioactive glass nanop... more The purpose of this work was to produce and characterize SiO 2 -CaO-P 2 O 5 bioactive glass nanoparticles with negative zeta potential for possible use in biomedical applications. 63S bioactive glass was obtained using the sol-gel method. X-ray fluorescence (XRF) spectroscopy and dispersive X-ray analysis (EDX) confirmed the preparation of the 63S bioactive glass with 62.17% SiO 2 , 28.47% CaO and 9.25% P 2 O 5 (in molar percentage). The in vitro apatite forming ability of prepared bioactive glass was evaluated by Fourier transform infrared spectroscopy (FTIR) after immersion in simulated body fluid (SBF). The result showed that high crystalline hydroxyapatite can form on glass particles. By the gas adsorption (BET method), particle specific surface area and theoretical particle size were 223.6 AE 0.5 m 2 /g and $24 nm, respectively. Laser dynamic light scattering (DLS) indicated particles were mostly agglomerated and had an average diameter between 100 and 500 nm. Finally, using laser Doppler electrophoresis (LDE) the zeta potential of bioactive glass nanoparticles suspended in physiological saline was determined. The zeta potential was negative for acidic, neutral and basic pH values and was À16.18 AE 1.8 mV at pH 7.4. In summary, the sol-gel derived nanoparticles revealed in vitro bioactivity in SBF and had a negative zeta potential in physiological saline solution. This negative surface charge is due to the amount and kind of the ions in glass structure and according to the literature, promotes cell attachment and facilitates osteogenesis. The nanometric particle size, bioactivity and negative zeta potential make this material a possible candidate for bone tissue engineering. #
Background: Antimicrobial susceptibility testing of microorganisms is performed by either disc di... more Background: Antimicrobial susceptibility testing of microorganisms is performed by either disc diffusion or broth dilution tests. In clinical use, the tests are often still performed manually although automated systems exist. Most systems, however, are based on turbidometric methods which have well-known drawbacks.
In focal repair of joint cartilage and meniscus, initial stiffness and strength of repairs are ge... more In focal repair of joint cartilage and meniscus, initial stiffness and strength of repairs are generally much less than surrounding tissue. This increases early failure potential. Secure primary fixation of the repair material is also a problem. Acrylamide polymer double-network (DN) hydrogels are candidate-improved repair materials. DN gels have exceptional strength and toughness compared to ordinary gels. This stems from the double-network structure in which there is a high molar ratio of the second network to the first network, with the first network highly crosslinked and the second loosely crosslinked. Previous studies of acrylic PAMPS/PDMAAm and PAMPS/PAAm DN gels demonstrated physicochemical stability and tissue compatibility as well as the ability to foster cartilage formation. Mechanical properties related to surgical use were tested in 2 types of DN gels. Remarkably, these >90%-water DN gels exhibited dynamic impact stiffness (E*) values (~1.1 and ~1.5 MPa) approaching ...
Closed ampoule isothermal microcalorimetry (IMC) is a simple, powerful, nondestructive, and conve... more Closed ampoule isothermal microcalorimetry (IMC) is a simple, powerful, nondestructive, and convenient technique that allows continuous, real-time detection and evaluation of cultured cell activity and responses. At a selected set temperature, IMC measures the heat flow between a sample and a heat sink and compares it to the heat-flow between a thermally inactive reference and the heat sink. Since heat flow rates are proportional to the rates of chemical reactions and changes of state, IMC provides a means for dynamically following these processes in any type of specimen -including ones containing cultured cells. The ability of IMC instruments to provide measurements in the microwatt (mJ/s) range allows one to detect and follow the activity (including replication) of low numbers of cells in culture (ca. 10 3 -10 5 , depending on cell type). Closed ampoule IMC is increasingly being used in medical and environmental sciences. While a closed ampoule imposes limitations, it conversely provides simplicity and excellent control. Also, it is still usually possible with closed ampoules to follow mammalian cell activity and replication for several days. This chapter provides an overview of IMC measurement principles and provides examples of the use of IMC for evaluating cultured human and other mammalian cell activity and responses.
The pathological changes in osteoarthritis-a degenerative joint disease prevalent among older peo... more The pathological changes in osteoarthritis-a degenerative joint disease prevalent among older people-start at the molecular scale and spread to the higher levels of the architecture of articular cartilage to cause progressive and irreversible structural and functional damage. At present, there are no treatments to cure or attenuate the degradation of cartilage. Early detection and the ability to monitor the progression of osteoarthritis are therefore important for developing effective therapies. Here, we show that indentation-type atomic force microscopy can monitor age-related morphological and biomechanical changes in the hips of normal and osteoarthritic mice. Early damage in the cartilage of osteoarthritic patients undergoing hip or knee replacements could similarly be detected using this method. Changes due to aging and osteoarthritis are clearly depicted at the nanometre scale well before morphological changes can be observed using current diagnostic methods. Indentation-type atomic force microscopy may potentially be developed into a minimally invasive arthroscopic tool to diagnose the early onset of osteoarthritis in situ.
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Papers by A.U. Daniels