Showing papers in "Journal of Materials Science: Materials in Medicine in 1995"

Glutaraldehyde as a crosslinking agent for collagen-based biomaterials

Abstract: The formation of Schiff bases during crosslinking of dermal sheep collagen (DSC) with glutaraldehyde (GA), their stability and their reactivity towards GA was studied. All available free amine groups had reacted with GA to form a Schiff base within 5 min after the start of the reaction under the conditions studied (0.5% (w/w) GA). Before crosslinks are formed the hydrolysable Schiff bases initially present were stabilized by further reaction with GA molecules. An increase in shrinkage temperature (Ts) from 56°C for non-crosslinked DSC (N-DSC) to 78°C for GA crosslinked DSC (G-DSC) was achieved after crosslinking for 1 h. From the relationship between the free amine group content and the Ts during crosslinking it was concluded that higher GA concentrations and longer reaction times will result in the introduction of pendant-GA-related molecules rather than crosslinks. After 24 h crosslinking an average uptake of 3 GA molecules per reacted amine group was found. No increase in the tensile strength of the materials was observed after crosslinking, which may be a result of formation of crosslinks within the fibres rather than in between fibres. Aligning of the fibres by applying a pre-strain to the samples and subsequent crosslinking yielded materials with an increased tensile strength.

Properties and mechanisms of fast-setting calcium phosphate cements

Abstract: The setting time of a calcium phosphate cement consisting of tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous (DCPA) was reduced from 30 to 5 min by use of a cement liquid that contained a phosphate concentration of 0.25 mol/l or higher. The diametral tensile strength and conversion of the cement ingredients to hydroxyapatite (OHAp) during the first 3 h were also significantly increased by the phosphate. However, the phosphate produced no significant effects on the properties of the 24-h cement samples. Results from additional experiments in a slurry system verified that the high phosphate concentration in the solution accelerated the formation of OHAp in the TTCP + DCPA system, and this reaction could explain the fast-setting properties of the cements.

The influence of high sintering temperatures on the mechanical properties of hydroxylapatite

Abstract: The kinetics of the thermal decomposition of stoichiometric hydroxylapatite (HA) has been studied up to 1500°C for the purpose of determining the maximum admissible combinations of temperature and time for sintering HA. The influence of the sintering temperature on shrinkage, density and grain growth is then investigated in the temperature range from 1000 to 1450°C. Nearly theoretical density was achieved above 1300°C. A maximum fracture toughness is obtained for the samples sintered at 1300°C whereas hardness increases up to a sintering temperature of 1400°C. These results are discussed in terms of the roles of porosity and grain size.

Structural characterization of plasma-sprayed hydroxylapatite coatings

Abstract: Plasma-sprayed hydroxylapatite coatings, widely used on metallic surgical implants to improve their adhesion to bone, are formed by rapid quenching of molten, or partly molten, particles which impact the substrate at high velocity. the performance of these coatings in the body depends upon their structure, which is not well understood. Coatings prepared under a range of spraying conditions have been studied by X-ray diffraction (XRD). differential thermal analysis (DTA), thermogravimetric analysis (TGA) and solid-state nuclear magnetic resonance spectroscopy (NMR). The results suggest that particles partly melt and lose combined water at lower plasma torch input powers forming a glass, by quenching of the liquid phase, and an OH-depleted hydroxylapatite residual crystalline phase. At higher power inputs an increasing amount of P2O5 is also lost and the coatings contain CaO and Ca4P2O9. Heat treatment of coatings in air at 600°C results in crystallization of the glass phase and reaction with water vapour to form hydroxylapatite. The results show that XRD is relatively insensitive to some of the structural details of hydroxylapatite coatings which may be significant to their performance. NMR provides more structural information and is a significant tool for coating characterization.

Crosslinking of dermal sheep collagen using hexamethylene diisocyanate

Abstract: The use of hexamethylene diisocyanate (HMDIC) as a crosslinking agent for dermal sheep collagen (DSC) was studied. Because HMDIC is only slightly water soluble, a surfactant was used to obtain a clear and micellar crosslinking solution and to promote the penetration of HMDIC in the DSC matrix. Using optimized conditions treatment of non-crosslinked DSC (N-DSC) with HMDIC (H-DSC) increased the shrinkage temperature (Ts) of N-DSC from 56°C to 74°C for H-DSC. A linear relation between the decrease in free amine group content and the increase in Ts was observed. Crosslinking with HMDIC did not influence the tensile strength of the N-DSC samples but increased the elongation at break from 141% to 163% and decreased the high-strain modulus from 26 MPa to 16 MPa for the H-DSC samples, respectively.

Mechanical properties of hydroxyapatite formed at physiological temperature

Abstract: The mechanical properties of monoliths of calcium-deficient and carbonated hydroxyapatite formed by dissolution-precipitation reactions at 38°C have been determined. Particulate solid reactants were mixed at liquid-to-solid weight ratios of 0.11 and 0.2 and pressed into various configurations on which mechanical tests were carried out. Testing was performed on wet had formed. Calcium-deficient hydroxyapatite produced at a liquid-to-solids ratio of 0.11 exhibited a tensile strength as high as 18 MPa, an average compressive strength of 174 MPa and a Young's modulus of 6 GPa. These values were lower when a larger proportion of water (liquid-to-solid 0.2) was used in sample preparation. However, the compressive strengths of calcium-deficient hydroxyapatite prepared at 38°C are comparable to the compressive strengths of sintered hydroxyapatite containing an equivalent total porosity. Carbonated hydroxyapatite showed mechanical properties inferior to those exhibited by calcium-deficient material. These differences appear to be related to the microstructural variations between these compositions.

Pre-treatment of titanium implants with fluoride improves their retention in bone

Abstract: Fluoride pre-treatment of titanium improved the bone response to this material in the present study. Fluoride pre-treated titanium implants had a four times increased retention in rabbits ulna after four and eight weeks healing periods as measured by a push out technique. Scanning electron microscopic evaluation of the implants revealed that the F-treated implants were partly covered with bone after the push out procedure indicating that an internal fracture had occurred in the bone rather than between the bone and the implant. This was not observed in the titanium control group. It is suggested that the presence of a fluoride coat on the surface of titanium implants stimulates the bone response leading to a connection between titanium and phosphate from tissue fluids. Free fluoride ions will catalyse this reaction and induce the formation of fluoridated hydroxyapatite and fluorapatite in the surrounding bone.

Calcium phosphate coatings prepared by electrocrystallization from aqueous electrolytes

Abstract: The concept of biological fixation of artificial joint prosthesis by using bioactive calcium phosphate coatings has generated considerable interest in recent decades. This paper reports an electrochemical route for fabricating hydroxyapatite (HA), carbonated-HA and fluoridated-HA coatings on porous and non-porous substrates at relatively low temperatures, using aqueous electrolytes. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and infrared spectroscopy (IR) were used to characterize the morphology, structure and chemical composition of the coatings. The results suggest that the electrochemical route for the fabrication of bioactive calcium phosphate coatings may offer significant advantages over the currently used methods.

An animal study of c.p. titanium screws with different surface topographies

Abstract: Sixty screw-shaped commercially pure (c.p.) titanium implants were inserted in the tibial and the femoral metaphyses of adult rabbits. The implants were divided into four groups with different surface roughnesses. The surface roughness was characterized before and after implant insertion. One group was left as-machined, this group had an initial R a value of 0.4 μm. Two groups were blasted with 25 μm sized particles of TiO2 and Al2O3, respectively; corresponding R a values for these groups were 0.9 μm and 0.8 μm. One group was blasted with 250 μm sized particles of Al2O3. The R a value for this last group was 2.1 μm. After a healing time of 12 weeks the torque necessary for implant removal and histomorphometric evaluations was evaluated. After removal of the implants the R a values for the four above mentioned groups were 0.9, 1.3, 1.1 and 1.9 μm, respectively. We found a better bone response for implants blasted with 25 μm sized particles compared to an as-machined (turned) surface, but no differences between the implants blasted with 25 μm particles and the implants blasted with 250 μm sized particles.

Synthesis and processing of hydroxyapatite ceramic tapes with controlled porosity

Abstract: Hydroxyapatite (Ca10(PO4)6(OH)2) ceramic sheets with a wide range of porosities (up to 62%) have been prepared. The process is based on the reaction between dicalcium phosphate (CaHPO4) and calcium carbonate (CaCO3). When mixed with the appropriate Ca/P ratio, this proves to be a reliable new method for obtaining hydroxyapatite. Moreover, CaCO3 serves as a gas-forming agent (due to the evolution of carbon dioxide and water during the reaction), which leads to the development of highly porous microstructures. Alternatively, CaHPO4 and CaCO3 can be reacted by calcining at 1000°C to produce pure hydroxyapatite powders. When processed in a similar way, a dense ceramic results. By mixing 50 vol% of CaCO3 and CaHPO4 with precalcined powders, hydroxyapatite with an intermediate porosity was obtained. Moreover, it should be possible to achieve porosity control by mixing different amounts of uncalcined and precalcined powders. All of these powders are colloidally processed using tape casting to produce thin sheets 150–200 μm thick. This technique can be used to make laminates, with or without porosity gradients, up to several millimetres thick.

Characterization of two biodegradable polymers of potential application within the biomaterials field

Abstract: An extensive characterization of two biodegradable polymers that may constitute an alternative, if one is aiming at orthopaedic applications, to the currently used poly(glicolic acid), poly(lactic acid) or polyhydroxybutyrate was carried out. A cellulose acetate and three different grades of a novel starch based polymer were studied. The characterization included: tensile and instrumented impact tests, rheological measurements, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transformed infra-red spectroscopy (FTIR), differential scanning calorimetry (DSC), and long-term degradation trials in Hank's solution. The results show that both polymers, specially the starch based one, present a great potential for biomedical applications, on which adequate mechanical properties associated to a controlled degradation rate are required.

The influences of plasma spraying parameters on the characteristics of hydroxyapatite coatings: a quantitative study

Abstract: All laboratory-made plasma-sprayed hydroxylapatite coatings (HACs) were found to undergo, to different degrees, changes in phase composition, crystallinity, morphology and roughness dependent on plasma spraying parameters (PSPs) The PSPs, which were systematically varied, included the plasma atmosphere, the spraying current and the stand-off distance Through the determinations of the concentration of impurity phase (CIP) and the index of crystallinity (IOC), the extent of phase purity and the degree of crystallinity of HACs were quantitatively assessed, respectively Coatings consisting of at least 50% (IOC>50%) of the original crystalline structure and almostly 95% (CIP<5%) apatite with barely detectable extra phases were obtained The microstructure of HACs exhibited great deviations both in morphology from molten to partial molten state and in roughness from coating of high irregularity (R a=1448μm) to a smoother (R a=446 μm) one, dominantly influenced by the spraying atmosphere As the terms of CIP and IOC are defined and established, the biological responses related to phase purity and crystallinity of HACs can be further evaluated in vitro and in vivo

Calcium phosphate cement: in vitro and in vivo studies of the α-tricalcium phosphate-dicalcium phosphate dibasic-tetracalcium phosphate monoxide system

Abstract: In this paper, calcium phosphate cement consisting of α-tricalcium phosphate (α-TCP), dicalcium phosphate dibasic (DCPD) and tetracalcium phosphate monoxide (TeCP) was investigated in vitro and in vivo. Measurements of compressive strength against soaking time in simulated body fluid (SBF) showed a rapid increase of the hardness for the first 7 days. The gained strength was retained up to 1 year and the maximal mean value was 94.7 (±14.4) MPa. X-ray diffraction (XRD) and scanning electron microscopy (SEM) presented precipitates of hydroxyapatite (HA) after mixing, also after soaking in SBF and after implantation in rat subcutaneous tissues. However, the conversion to HA happened in different ways between in vitro and in vivo exposures. Histologic examinations showed that the cement causes the same reactions at the interface with surrounding soft tissues as HA. The authors consider the cement to be a promising material as a bone substitute, bone cement or dental material, however, further studies in a paste form and in bone tissue environments are necessary.

Flexural and fatigue properties of a bone cement based upon polyethylmethacrylate and hydroxyapatite

Abstract: Polymethylmethacrylate (PMMA) bone cement is commonly used in surgery to fix joint replacements into the bone. Although the operations are generally successful, loosening of the prosthesis does occur with fracture of the bone cement treated as the source of failure in some instances. Polyethylmethacrylate (PEMA) bone cement offers a promising alternative to PMMA due to its high ductility, low toxicity and low exotherm. In addition, hydroxyapatite (HA) particles can be added, while retaining the ductile properties of the material. In this study, the flexural and fatigue properties of this experimental cement, with and without HA reinforcement, have been examined. It was found that up to 40wt.% HA could be added with increases in both flexural strength and modulus. Specimens were subjected to tensiontension cyclic loading at a number of stress levels until catastrophic failure occurred. In comparison with a commercial PMMA cement, tested at relatively high stresses, the PEMA cement failed at lower cycles to failure. However, the data converged at the lower stresses employed which are closer to the physiological loading situation. With the addition of HA, although the cycles to failure were decreased, the deformation experienced by the PEMA-HA cement whilst being cycled was reduced.

Apatite-mullite glass-ceramics

Abstract: Two series of fluoro-alumino-silicate glasses, one with varying phosphate content (P2O5) and one with fixed phosphate content and varying fluorite (CaF2) content have been investigated as potential bioglass-ceramics. Compositions with intermediate phosphate contents that contained fluorite crystallized to fluoroapatite and mullite. Compositions with high fluorite contents exhibited a low liquidus temperature, were readily castable and crystallized by a bulk nucleation mechanism. The fluoroapatite phase with appropriate heat treatment formed as thin needle-like crystals with a high aspect ratio.

Bond degradation at the plasma-sprayed HA coating/Ti-6AI-4V alloy interface: an in vitro study

Abstract: The successful use of the plasma-sprayed HA-coated Ti-6AI-4V system requires strong adhesion between the ceramic coating and the underlying metal substrate. The aim of this study was to evaluate the bond strength at the HA coating (HAC)/Ti-6AI-4V interface, for specimens that had and had not been subjected to immersion in a pH-buffered, serum-added simulated body fluid (SBF). Moreover, coating characteristics affecting the mechanical stability after having been immersed in SBF were clarified. The results showed that bonding degradation of approximately 25–33% of the original strength was measured after immersion in SBF, and that this predominantly depended on the characteristics of the HAC and the period of immersion. Since the surface morphologies of HACs have dissolved in the SBF, it is suggested that the interlamellar structure of the HAC was weakened and, therefore, the bond strength degraded. As both the crystallinity and impurity phases of the HAC increased with immersion time, it can be concluded that the dissolution of the HAC resulting from the initial microstructure has overtaken that of the coating crystallinity and phase purity. A denser microstructure is required to ensure a satisfactory HAC/Ti-6AI-4V interface.

Spectroscopic characterization of passivated titanium in a physiologic solution

Abstract: Titanium (Ti) has been used for many biomedical applications. Surface characteristics of titanium devices are critical to their success. In this study, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to analyse Ti surfaces prior to immersion in alpha-modification of Eagle's medium (α-MEM). The ionic constituents deposited onto Ti surfaces after in vitro exposure to α-MEM were investigated using XPS and Fourier transform infrared spectroscopy (FTIR). Surface studies revealed an amorphous oxide layer on the Ti surface, with a chemistry similar to TiO2. However, after exposure to the physiologic solution for 12 days, dynamic changes in surface chemistry were observed. Ions such as phosphorus (P) and calcium (Ca) were increasingly deposited as amorphous fine crystalline calcium-phosphate (Ca−P) compounds, having a Ca/P ratio of 1.2 and a chemistry similar to brushite.

Effect of various additives and temperature on some properties of an apatitic calcium phosphate cement

Abstract: The effect of additives and temperature on setting time, swelling time and compressive strength of a previously developed apatitic calcium phosphate cement was investigated Setting was faster at body temperature than at room temperature Early contact with aqueous solutions resembling blood and other body fluids had no effect Deliberate additions of soluble carbonates, pyrophosphate or magnesium salts to the cement powder retarded or even inhibited setting However, additions of calcium pyrophosphate, β-tertiary calcium phosphate or sintered hydroxyapatite to the cement powder in amounts up to 10% had no effect on the cement properties Several organic substances were used as additives They all retarded the setting and decreased the strength of the cement considerably

Evaluation of tricalciumphosphate/ hydroxyapatite cement for tooth replacement: an experimental animal study

Abstract: A calciumphosphate cement, consisting mainly of tricalciumphosphate (85% α-TCP and 15% β-TCP), was inserted in 16 surgical defects created in the tibia of goats. X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) showed that after 3 months of implantation the α-TCP was transformed to hydroxyapatite (HA). Histological evaluation revealed that the presence of cement stimulated the ingrowth of bone compared with unfilled cavities. Active resorption and remodelling of cement particles was observed. The cement did not evoke an inflammatory reaction. At 6 months after implantation no further changes in the composition of the cement occurred. All remaining material was surrounded by mature bone.

Coating of hydroxyapatite on metal plates using thermal dissociation of calcium-EDTA chelate in phosphate solutions under hydrothermal conditions

Abstract: Coating of hydroxyapatite on various metal plates was carried out by a homogeneous precipitation technique using hydrothermal reactions in Ca(edta)2-−NaH2PO4 at 140–200°C and pH 3.4–10.0. Hydroxyapatite films were formed on the surface of the iron plates in solutions at an initial pH above 4.7, whereas aggregates consisting of needle-like hydroxyapatite crystal radiating from a point in the form of flower deposited as islands on the surface of aluminum, copper and titanium plates. The upper part of the film formed on the surface of the iron plates consisted of needle-like hydroxyapatite particles whereas the bottom of the film consisted of spherical hydroxyapatite particles. The length of the needle-like hydroxyapatite particles increased with decreasing concentration of Ca(edta)2-.

Liquid phase sintering of hydroxyapatite by phosphate and silicate glass additions: structure and properties of the composites

Abstract: Phosphate- and silicate-based glasses were added to hydroxyapatite in order to improve its mechanical properties and to fabricate composites with different degrees of bioactivity. A strong chemical bonding was obtained between hydroxyapatite and the phosphate-based glasses leading to samples approaching theoretical density, according to density measurements and scanning electron microscopy. Bioglass® additions led to the formation of a complex calcium phosphate silicate which hampered the reinforcement process. The fracture toughness of the hydroxyapatite-glass composites was shown to be within the 1.1–1.2 MPam1/2 range, which is double that determined for sintered hydroxyapatite. A 2 μm thick apatite layer was observed on the surface of the hydroxyapatite-glass composites after 48 h immersion in a simulated human blood plasma, whereas only a few apatite crystals were detected on sintered hydroxyapatite after 7 days immersion. From the results obtained we anticipate that the composites might show a higher rate of bone bonding, leading to enhanced bioactivity.

The effects of temperature on the behaviour of an apatitic calcium phosphate cement

Abstract: An apatitic calcium phosphate cement is obtained by mixing α-tricalcium phosphate (α-TCP) and precipitated hydroxyapatite into a cement powder, and by then mixing this powder with an aqueous solution of Na2HPO4 as an accelerator. Setting times were reduced by about 30% by increasing the temperature from 22 to 37°C. Compressive strength reached higher intermediate and final values at 37 °C. Degrees of transformation of the α-TCP in the resulting calcium-deficient hydroxyapatite (CDHA) were much higher at 37 °C after 24 h of storage in Ringer's solution according to X-ray diffraction. Differential scanning calorimetry indicated that the rate of reaction increased by a factor of about 5 when the temperature was increased from 25 to 37 °C. Scanning electron microscopy showed that the microstructure was more homogeneous and that a more tight entanglement of the precipitated CDHA crystals occurred after storage at 37 °C than at room temperature.

Growth of calcium phosphate on surface-modified cotton

Abstract: A study of the growth of amorphous calcium phosphate on surface-modified cotton fibres by a combination of scanning electron microscopy/electron diffraction X-ray analysis, micro-FTIR and X-ray photoelectron spectroscopy is reported. Cotton fibres phosphorylated by the urea/phosphorous acid method and then soaked in saturated Ca(OH)2 for approximately one week were found to stimulate the growth of a calcium phosphate coating on their surfaces after soaking in 1.5×SBF for as little as 1 day. Ca(OH)2 soaking of the fibres is found to produce highly crystalline clusters lodged in the fibres which were confirmed by micro-FTIR to be calcium phosphite monohydrate (CaHPO3·H2O). In contrast, phosphorylated fibres not subjected to the Ca(OH)2 treatment did not exhibit calcium phosphate growth upon immersion in 1.5×SBF solution. Soaking of the Ca(OH)2-treated fibres with time in the 1.5×SBF solution produced progressively thicker layers of calcium phosphate on the fibres as confirmed by scanning electron microscopy and X-ray photoelectron spectroscopy. In general, calcium phosphate coatings formed over 1 1–5 day period soaking in 1.5×SBF solution appeared to consist of agglomerations of a large number of small spherical particles, while coatings formed after 17 days of soaking were distinctly chunky, thick and non-uniform in appearance. Micro-FTIR indicated that CaHPO3·H2O clusters were still present in cotton samples even after 4 days of soaking, while after 17 days, only the infrared spectrum typical of calcium phosphate was observed. EDX-measured Ca:P ratios of the coatings, although variable, suggested amorphous calcium phosphate. The mechanism of formation of the coating is believed to involve dissolution of the CaHPO3.H2O clusters upon introduction of the Ca(OH)2-treated phosphorylated cotton into the 1.5×SBF solution which elevates the Ca2+ ion concentration in the vicinity of the fibres so stimulating calcium phosphate formation. It is postulated that phosphite groups chemically bound to the cotton fibre surface or a calcium phosphite coating on the fibres act as nucleation sites for calcium phosphate growth in 1.5×SBF solution.

XRD and XPS characterization of superplastic TiO2 coatings prepared on Ti6Al4V surgical alloy by an electrochemical method

Abstract: X-ray diffraction (XRD) and X-Ray photoelectron spectroscopy (XPS), in conjunction with argon ion etching, were used to characterize the microstructure and the chemical composition of alkoxy-derived TiO2 coatings prepared on Ti6Al4V surgical alloy by an electrochemical method. The as-deposited oxide coatings prepared at room temperature (up to 40 μm thick) were amorphous, but transformed into nanocrystalline anatase at 550°C. Using a micro-indentation technique, it was found that nanocrystalline anatase coatings were ductile, permitting significant plastic deformation at room temperature. The XPS data also revealed the presence of significant proportion of physisorbed (OH) and chemisorbed H2O (i.e. Ti−OH) on the oxide surface, indicating that these coatings, similar to sol-gel-prepared titania, may serve as reactive substrates for heterogeneous nucleation of apatite under physiological conditions.

In vivo behaviour of three calcium phosphate cements and a magnesium phosphate cement

Abstract: Three types of calcium phosphate cements and one magnesium phosphate cement were implanted subcutaneously in rats under exclusion of direct cellular contact. Retrieval times were either 1, 2, 4 or 8 weeks. Before and after retrieval the compressive strength, the diametral tensile strength, the quantitative chemical composition, the qualitative phase composition, the FTIR spectrum and the microstructure were determined. The three calcium phosphate cements maintained their strength during implantation. The phase DCPD was completely transformed into a Na- and CO3-containing apatite, the phases DCP and CDHA only partially. It could not be ruled out that OCP is also transformed into a bone-mineral-like apatite to a certain extent. That this latter process occurs much faster during the turn-over of living bone, is probably due to the very small crystal size of the OCP particles in bone.

Apatite coated on organic polymers by biomimetic process: improvement in adhesion to substrate by HCl treatment

Abstract: A dense, uniform and highly biologically active bone-like apatite layer can be formed in arbitrary thickness on any kind and shape of solid substance by the following biomimetic method at normal temperature and pressure: first, a substrate is set in contact with particles of CaO-SiO2-based glass soaked in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. Second, the substrate is soaked in another solution with ion concentrations 1.5 times those of SBF (1.5 SBF). In the present study, organic polymer substrates were treated with 1 m HCl solution, then subjected to the above mentioned biomimetic process. The induction periods for the apatite nucleation on polyethyleneterephthalate, polymethylmethacrylate, polyamide 6 and polyethersulfone substrates were reduced from 24 to 12 h with the HCl treatment. The adhesive strength of the formed apatite layer to the polyethyleneterephthalate, polymethylmethacrylate and polyamide 6 substrates were increased from 3.5 to 7.0 MPa from 1.1 to 2.8 MPa and from 0.6 to 3.1 MPa, respectively, with the HCl treatment. It is supposed that highly polar carboxyl group formed by the HCl hydrolysis reaction of ester group in polyethyleneterephthalate and polymethylmethacrylate or amide group in polyamide 6 increased the affinity of the substrates with a silicate ion to decrease the induction period, and also increased the affinity of the substrate with the apatite to increase the adhesive strength. The apatite-organic polymer composites thus obtained are expected to be useful as bone-repairing materials as well as soft-tissue-repairing materials.

Grooved substrata facilitate in vitro healing of completely divided flexor tendons

Abstract: Multiple grooved substrata with groove depth 5 μm were found to facilitate the healing of completely divided rat flexor tendons in vitro. Sections of tendons cultured on plain substrata showed only partial healing with incompletely sealed epitenon layers and immature thin collagen fibres. Tendons cultured on patterned substrata healed with complete restoration of the epitenon layer and reconstitution of the internal structure of collagen fibres. Epitenon fibroblasts isolated from the surface of rat flexor tendons were shown to be more sensitive to topographical features than fibroblasts of the same size BHK fibroblasts. They remained more elongated and better aligned to the groove direction than BHK cells. Multiple grooved substrata facilitated epitenon cell movement. Cells were found to move with higher speed on patterned substrata than on plain substrata. In summary, we conclude that the use of multiple grooved substrata promotes tendon healing in vitro and may find application in clinical practice in tendon repair.

In vitro evaluation of biocompatibility of different wound dressing materials

Abstract: The in vitro biocompatibility of newly developed wound dressings consisting of different chitosan salts (chitosan lactate, glutamate and chloride) and a chitosan derivative (methylpyroolidinone chitosan) was compared with three commercially available wound dressings made of collagen, calciumalginate, and gelatin, by evaluation in a fibroblast cell culture system. Three experimental models which reflect relevant stages of wound healing were used, and the significant influence of the experimental setting on the results was demonstrated. Collagen and methylpyrrolidinone chitosan were the most compatible materials under the investigated test conditions. Chitosan chloride and glutamate were the least compatible substances. The results indicated that wound dressings made of chitosan lactate and methylpyrrolidinone chitosan as well as the three commercially available dressings are well tolerated.

HMDC crosslinking of bovine pericardial tissue: a potential role of the solvent environment in the design of bioprosthetic materials

Abstract: The need for alternative crosslinking techniques in the processing of bioprosthetic materials is widely recognized. While glutaraldehyde remains the most commonly used crosslinking agent in biomaterial applications there is increasing concern as to its biocompatibility-principally due to its association with enhanced calcification, cytotoxicity, and undesirable changes in the mechanical properties of bioprosthetic materials. Hexamethylene diisocyanate (HMDC), like glutaraldehyde, is a bifunctional molecule which covalently bonds with amino groups of lysine residues to form covalent crosslinks. Evidence within the literature indicates HMDC-treated materials are less cytotoxic than glutaraldehyde-treated materials; however, there is limited characterization of the material properties of HMDC-treated tissue. This study uses a multi-disciplined approach to characterize the mechanical, thermal, and biochemical properties of HMDC-treated bovine pericardial tissue. Further, to facilitate stabilization of the HMDC reagent, non-aqueous solvent environments were investigated. HMDC treatment produced changes in mechanical properties, denaturation temperature, and enzymatic resistance consistent with crosslinking similar to that seen in glutaraldehyde treated tissue. The significantly lower extensibility and stiffness observed under low stresses may be attributed to the effect of the 2-propanol solvent environment during crosslinking. While the overall acceptability of HMDC as a crosslinking agent for biomaterial applications remains unclear, it appears to be an interesting alternative to glutaraldehyde with many similar features.

Further studies of calcium phosphate growth on phosphorylated cotton fibres

Abstract: Further studies using scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX), micro-Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and solid state magic angle spinning nuclear magnetic resonance (MAS NMR) techniques of calcium phosphate growth on Ca(OH)2-treated urea/H3PO3- and urea/H3PO4-modified cotton fibres are reported. In the case of the Ca(OH)2-treated urea/H3PO3-modified fibres which have been reported in an earlier paper, further experiments subjecting the urea/H3PO3-modified cotton to alternative soaking treatment procedures to Ca(OH)2 as well as different calcium phosphate growth media such as the alkaline phosphatase-catalysed hydrolysis of disodium p-nitrophenylphosphate to free phosphate have reaffirmed the importance of the Ca(OH)2 treatment step for the stimulus and growth of calcium phosphate growth on the fibres. Studies on cotton phosphorylated by a slightly different method using urea/H3PO4 instead of urea/H3PO3 show that a phosphorylated cotton with similar properties to the urea/H3PO3-modified fibres can be produced. Soaking of these fibres in saturated Ca(OH)2 solution leads to cotton coated with thin layers of calcium phosphate formed by partial hydrolysis of the PO4 functionalities in the phosphorylated cotton which are believed to act as nucleation layers for further calcium phosphate deposition when the fibres are subsequently soaked in 1.5×SBF solution. SEM/EDX studies of the calcium phosphate coatings formed on the Ca(OH)2-treated urea-H3PO4 fibres as a function of soaking time in 1.5 × SBF show that coatings deposit and become noticeably thick after approximately 9 days. XPS studies indicated the presence of carbonate species in the calcium phosphate coating deposited. In common with the calcium phosphate coated Ca(OH)2-treated urea/H3PO3-modified fibres studied earlier, the average EDX-measured Ca: P ratios of the coatings formed on the Ca(OH)2-treated urea/H3PO4 fibres are ∼ 1.60 and give very similar micro-FTIR spectra with evidence of carbonate which suggests that amorphous calcium deficient apatite has deposited.