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PubMed2001

Effect of the eluent pH and acidic modifiers in high-performance liquid chromatography retention of basic analytes.

The retention of ionogenic bases in liquid chromatography is strongly dependent upon the pH of the mobile phase. Chromatographic behavior of a series of substituted aniline and pyridine basic compounds has been studied on C18 bonded silica using acetonitrile-water (10:90) as the eluent with different pHs and at various concentrations of the acidic modifier counter anions. The effect of different acidic modifiers on solute retention over a pH range from 1.3 to 8.6 was studied. Ionized basic compounds showed increased retention with a decrease of the mobile phase pH. This increase in retention was attributed to the interaction with counter anions of the acidic modifiers. The increase in retention is dependent on the nature of the counter anion and its concentration in the mobile phase. It was shown that altering the concentration of counter anion of the acidic modifier allows the optimization of the selectivity between basic compounds as well as for neutral and acidic compounds.

Buffers↗
PubMed1985

Purification and peptide mapping of calmodulin and its chemically modified derivatives by reversed-phase high-performance liquid chromatography.

Methods were developed for the isolation and peptide mapping of calmodulin and its chemically modified derivatives by reversed-phase high-performance liquid chromatography (HPLC). Calmodulin and its guanidinated, iodinated, and performic acid-oxidized derivatives can be isolated on alkylphenyl columns by using gradients of acetonitrile in 10 mM potassium phosphate, pH 6.0, 2 mM EGTA. Peptide mapping by HPLC, following complete digestion of the proteins with clostripain, allows identification of the modified amino acids residues. Clostripain peptides are eluted in the order 87-90, 75-86, 91-106, 107-126, 127-148, 107-148, 1-37, and 38-74. Performic acid oxidation of methionines decreases the retention times of the modified peptides, whereas iodination of tyrosines or guanidination of lysines increases retention times of modified peptides. These HPLC methods are applicable to the identification of specific modifications of calmodulin, allowing the assessment of the role of individual amino acid residues in determining the unique physical, chemical, and spectroscopic properties of this ubiquitous intracellular calcium-binding protein.

Amino Acids↗
PubMed1987

Resolution of enantiomeric amides on a cellulose tribenzoate chiral stationary phase. Mobile phase modifier effects on retention and stereo-selectivity.

The effect of the steric structure and concentration of the mobile phase modifier on the retention (kappa') and stereoselectivity (alpha) of a series of enantiomeric amides has been investigated. The amides were chromatographed on a commercially available cellulose tribenzoate chiral stationary phase (CSP) using mobile phases composed of hexane and two homologous series of alcohols: methanol, ethanol, 1-propanol and 2-propanol, 2-butanol, 2-pentanol, 2-hexanol. The results of the study indicate that the alcoholic mobile phase modifiers compete with the solutes for achiral and chiral binding sites and that the steric bulk around the hydroxyl moiety of the modifier plays a role in this competition. Increased steric bulk tends to result in increased kappa' and alpha. However, the results also suggest that the effect of the alcoholic mobile phase modifiers on stereoselectivity may also be due to binding to achiral sites near or at the chiral cavities of the CSP which alters the steric environment of these cavities.

Alcohols↗
PubMed2003

Modified field amplification sample injection for micellar electrokinetic chromatography of neutral compounds with amino-substituted cyclodextrin as carrier and 1-adamantanecarboxylate as displacer.

A modified field amplification sample injection method was proposed and evaluated by using positively mono charged cyclodextrin (CD) as carrier and 1-adamantanecarboxylate as displacer for on-capillary preconcentration of neutral compounds and improvement of the concentration limit of detection in micellar electrokinetic chromatography. In modified sample injection mode a displacer plug was introduced before sample injection to reduce the length of the concentrated sample zone and increase the peak height by slowing down the forward movement of the neutral sample associated with beta-CD-NH2 and the backward movement of the neutral sample partitioned in the micelles of sodium dodecyl sulfate. Stability of the inclusion complexes formed between the carrier and the solute was found to be an important factor affecting stacking efficiency in both the conventional field amplification sample injection mode and the modified one. However, further enhancement of the stacking efficiency in the modified mode rested on the relative stability of the displacer-carrier complex to that of the solute-carrier complex. Practical limits to the stacking efficiencies in both modes were discussed as well.

Adamantane↗
PubMedDate not supplied

Differential analysis of behavior and diazepam-induced alterations in C57BL/6N and BALB/c mice using the modified hole board test.

A variety of test procedures are used in preclinical research on behavioral pharmacology and to dissociate behavioral differences or pharmacologically induced behavioral alterations several independent tests are usually performed. In the present study we introduce a modified hole board procedure for mice which allows us to investigate a variety of behavioral parameters such as anxiety, risk assessment, exploration, locomotion, food-intake inhibition, novelty seeking, and arousal by using only one test. The modified hole board was established by investigating the behavior of two inbred mouse strains, C57BL/6 and BALB. Significant differences in terms of locomotor activity, general exploration, and other parameters were found. Moreover, strain-specific exploration strategies could be detected in the modified hole board. Further, the test was validated by investigating the effects of diazepam as standard anxiolytic on the behavior in both mouse strains. Acute administration of diazepam (1 and 3 mg/kg) induced strong sedative effects in a dose-dependent manner in C57BL/6 mice. In BALB mice, the lower dosage of diazepam showed an activating and anxiolytic action while the 3 mg dosage revealed a slight sedative but still anxiolytic effect in these animals. Taken together, the results demonstrate that the modified hole board enables to differentially investigate behavioral phenotypes and also pharmacologically-induced behavioral alterations in mice. Therefore, this new strategy allows to reduce the number of experimental animals and the time needed, thus, representing an effective screening-tool for behavioral investigations.

Animals↗
PubMed2000

Pulmonary function after modified venovenous ultrafiltration in infants: a prospective, randomized trial.

OBJECTIVE: We sought to examine the effects of modified venovenous ultrafiltration after cardiopulmonary bypass on pulmonary compliance in infants. METHODS: We prospectively enrolled 38 infants undergoing their first operation for congenital heart disease. Infants were randomized to receive 20 minutes of modified ultrafiltration after bypass or control. Static and dynamic compliance was measured after induction of anesthesia, before and immediately after filtration in the operating theater, 1 hour after return to the pediatric intensive care unit, and 24 hours after the operation. Length of time on the ventilator, inotropic requirements, and length of stay in the intensive care unit were recorded. RESULTS: Modified ultrafiltration produced a significant immediate improvement in dynamic (pre-ultrafiltration 2.5 +/- 1.9 mL/cm H(2)O to post-ultrafiltration 2.9 +/- 2.7 mL/cm H(2)O, P =.03) and static (pre-ultrafiltration 2.1 +/- 0.9 mL/cm H(2)O to post-ultrafiltration 2.9 +/- 2.1 mL/cm H(2)O, P =.04) compliance. However, there was no significant difference in the change in dynamic (P =.3) or static (P =.7) compliance in the ultrafiltration and control groups when compared before the operation, after the operation, and at 24 hours. There was no significant difference in the time to extubation between patients and control subjects (140 +/- 91 hours vs 90 +/- 58 hours) or the length of intensive care unit stay (10.0 +/- 9.1 days vs 7.4 +/- 5.7 days). CONCLUSIONS: Modified ultrafiltration produces an improvement in pulmonary compliance after bypass in infants. However, these improvements are not sustained past the immediate post-ultrafiltration period and do not lead to a decreased length of intubation or intensive care unit stay.

Cardiopulmonary Bypass↗
PubMed1998

Dilutional and modified ultrafiltration reduces pulmonary hypertension after operations for congenital heart disease: a prospective randomized study.

OBJECTIVE: A prospective randomized study was performed to test whether removal of endothelin-1, by ultrafiltration techniques, will reduce pulmonary hypertension after operations for congenital heart disease. METHODS: Twenty-four patients with pulmonary hypertension (systolic pulmonary/systemic arterial pressure ratio > 60%) undergoing cardiac operations were randomized into a control group (n = 12) having conventional ultrafiltration and an experimental group (n = 12) undergoing dilutional ultrafiltration during and modified ultrafiltration after cardiopulmonary bypass. Plasma endothelin-1, nitric oxide metabolites, and cyclic guanosine monophosphate were assayed before bypass, 10 minutes into bypass, after bypass, and 0, 3, 6, and 12 hours after the operation in both groups, as well as in the ultrafiltrates and after modified ultrafiltration in the experimental group. Both groups received alpha-blockers (chlorpromazine and/or prazosin) postoperatively using the same guidelines. RESULTS: The ultrafiltrates contained significant amounts of endothelin-1 (1.81 +/- 0.86 pg/ml, dilutional, and 6.44 +/- 1.82 pg/ml, modified ultrafiltrate). Endothelin-1 and the pulmonary/systemic pressure ratio were significantly lower in experimental compared with control patients. Nitric oxide metabolites and cyclic guanosine monophosphate increased similarly in both groups for 12 hours after the operation (p = not significant). Three of 12 control patients (25%) but no experimental patients had pulmonary hypertensive crises (p = 0.07). The experimental patients required significantly less ventilatory support (67 +/- 47 hours vs 178 +/- 139 hours for control patients, p = 0.048). CONCLUSIONS: Dilutional and modified ultrafiltration reduce endothelin-1 and the pulmonary/systemic pressure ratio postoperatively and may become an important adjunct for preventing pulmonary hypertension after operations for congenital heart disease in high-risk patients.

Cardiopulmonary Bypass↗
PubMed2002

Leukotriene modifiers.

Leukotrienes (LTs) are 5-lipoxygenase products formed from arachidonic acid metabolism. There is compelling evidence that LTs play an important role in the pathogenesis of asthma. LTs affect vascular permeability, mucus production, and smooth muscle constriction, and may contribute to airway remodeling. In mild-to-moderate asthma, LT modifiers improve measures of airflow limitation and quality of life and reduce the frequency of asthma exacerbations and the need for short-acting bronchodilator therapy. In moderate-to-severe asthma, an LT modifier in combination with an inhaled corticosteroid results in improvements in lung function and asthma control over that achieved with an inhaled corticosteroid alone. LT modifiers are effective in the treatment of exercise-induced bronchoconstriction and aspirin-induced asthma. There are few adverse effects of LT modifiers.

Asthma↗
PubMed2003

Association between promyelocyte protein and small ubiquitin-like modifier protein and the progression of cervical neoplasia.

OBJECTIVE: To examine the association between the size and number of promyelocyte protein-containing nuclear bodies, their colocalization with the small ubiquitin-like modifier protein, and existing histopathologic staging of cervical neoplasia progressing toward squamous cell carcinoma. METHODS: Fluorescence-based immunodetection of the promyelocyte protein and the small ubiquitin-like modifier protein was performed on paraffin-embedded and histopathologically graded human uterine cervical tissues. Quantitative measurements of the size and number of the promyelocyte protein-containing nuclear bodies were made and statistically analyzed. RESULTS: We found that promyelocyte protein-containing nuclear bodies exhibit changes in both size and number throughout the continuum of cervical intraepithelial neoplasia (CIN) and cervical squamous cell carcinoma. An increase in number and size of the bodies occurs with progression from normal to CIN I/CIN II. In CIN III, two new subcategories of nuclear body are present with distinctly different promyelocyte protein patterns, with the type B CIN III losing the small ubiquitin-like modifier protein partnership. In squamous cell carcinoma, we see the loss of this colocalization in both well and poorly differentiated tumors, with a distinctly different promyelocyte protein pattern. Well-differentiated tumors have bigger nuclear bodies that are more numerous than those of the poorly differentiated tumors. CONCLUSION: These data support the use of promyelocyte and small ubiquitin-like modifier proteins as a cytodiagnostic marker that parallels cervical cancer progression.

Adult↗
PubMed1998

Structure of a snake venom phospholipase A2 modified by p-bromo-phenacyl-bromide.

The crystal structure of acidic phospholipase A2 (APLA2) from Agkistrodon halys pallas covalently modified by p-bromo-phenacyl-bromide (pBPB) was determined to a resolution of 2.0 A by an isomorphous difference Fourier method with the native APLA2 structure as an initial model and refined to a crystallographic R factor of 15.3%. The modified APLA2 structure is remarkably similar to that of the native one. Least-squares superposition of C alpha atoms of native and modified APLA2 results in a root-mean-square coordinate deviation of 0.243 A. The p-bromo-phenacyl group near the active site occupies a position similar to that in pBPB modified bovine pancreatic PLA2. The inhibitor covalently bound to the NDI atom of His48 fits well in the hydrophobic channel, forming extensive hydrophobic interactions with the surrounding residues, especially with the side chains of Phe5 and Cys45 and the main chain of Gly30. However, the inhibitor does not change the conformation of these residues except that Trp31 at the entrance of the hydrophobic channel moves slightly toward the inhibitor. Compared with native APLA2, the Ca2+-binding loop shows a little conformational change and a cation, probably Na+, occupies in the position of Ca2+. The binding of pBPB to APLA2 induce no other significant conformational changes in the enzyme molecule elsewhere.

Acetophenones↗
PubMed2002

Oxidation of diethylene glycol with ozone and modified Fenton processes.

This paper describes a study of oxidation of diethylene glycol (DEG) by ozone and modified Fenton process (hydrogen peroxide and ferric salt mixture) in aqueous solution. Both oxidation processes were able to oxidize relatively high concentrations of DEG effectively. DEG reacted primarily through hydroxyl radical produced by decomposition of ozone, and about 3 mol of ozone were consumed per mole of DEG removed during the process. For modified Fenton oxidation, stepwise addition of hydrogen peroxide (H2O2) and ferric salt (Fe(III)) resulted in much higher removal of DEG than one-time pulse addition of the chemicals. The extent of DEG removal increased with increasing concentrations of both H2O2 and Fe(III). Oxidant consumption per mole of DEG oxidized was one order of magnitude higher for hydrogen peroxide than those observed for ozone. Overall, ozonation produced higher concentrations of aldehydes, and modified Fenton treatment produced higher concentrations of carboxylic acids for the same levels of DEG oxidation. The major products of ozonation were glycolaldehyde, glyoxal, formaldehyde, acetaldehyde, and acetic, formic, pyruvic, oxalic and glyoxalic acids. The major products of modified Fenton oxidation were formaldehyde, and formic and acetic acids.

Environmental Pollution↗
PubMed2000

Stimulating effect of biologically modified low density lipoproteins on ADP-induced aggregation of washed platelets persists in absence of specific binding.

Oxidized low density lipoproteins are closely associated with atherosclerosis and also might be directly involved in thrombosis because they have been shown to mediate a stimulating effect on human platelets. In this work, we used biologically modified low density lipoproteins (i.e., low density lipoproteins sufficiently oxidized to show specificity for the macrophage scavenger receptor system) to examine if specific binding of the oxidized apolipoprotein moiety to the platelet surface is a prerequisite for the platelet-stimulating effects reported by other authors. We find that biologically modified low density lipoproteins show specific binding to human platelets (K(d)=5.83+/-0.4 microg/mL, 3850+/-620 sites/platelet) and strongly augment both ADP- and thrombin-induced aggregation of washed platelets. Maleylated albumin, an antagonist of oxidized low density lipoproteins binding to all currently classified scavenger receptors, is able to reduce platelet oxidized low density lipoproteins binding to background levels. Nevertheless, maleylated albumin is not able to exert any kind of normalizing effect on the augmented ADP-induced aggregation response observed in the presence of biologically modified low density lipoproteins. From these data, we conclude that specific binding of oxidatively modified apolipoprotein B to the platelet surface is not essential to the process of platelet stimulation. Therefore, we conclude that these stimulating effects may be mediated by unidentified compounds formed in the lipid phase of the lipoproteins.

Adenosine Diphosphate↗
PubMed2002

Human urothelial cells grown on collagen adsorbed to surface-modified polymers.

OBJECTIVES: Tissue engineering methods can be applied to regenerate diseased, or congenitally missing, urinary tract tissues. Urinary tract tissue cell cultures must be established in vitro and adequate matrices, acting as cell carriers, must be developed. Although degradable and nondegradable polymer matrices offer adequate mechanical stability, they are not optimal for cell adherence and growth. To overcome this problem, extracellular matrix proteins, permitting cell adhesion and regulation of cell proliferation and differentiation, can be adsorbed to the surface-modified polymer. METHODS: In this study, nondegradable polymer films, poly(ethylene terephthalate), were used as an experimental model. Films were modified by graft polymerization of acrylic acid to subsequently allow collagen type I and III immobilization. The following adhesion, proliferation of human urothelial cells, and induction of their stratification were analyzed. RESULTS: Collagen adsorption on 0.2 microg/cm2 poly(acrylic acid)-grafted polymer films rendered the matrix apt for human urothelial cell adhesion and proliferation. Furthermore, stratification of urothelial cells was demonstrated on these surface-modified matrices. CONCLUSIONS: These results have shown that surface-modified polymer matrices can be used to act as cell carriers for cultured human urothelial cells. Such a cell-matrix construct could be applied in reparative surgery of the urinary tract.

Animals↗
PubMed2000

Modified Pereyra bladder neck suspension in patients with intrinsic sphincter deficiency and bladder neck hypermobility: patient satisfaction with a mean follow-up of 4 years.

OBJECTIVES: To determine the long-term success rate for the modified Pereyra bladder neck suspension and to identify preoperative characteristics that create differences in surgical outcome. We attempted retrospectively to separate those patients with what we now recognize was significant intrinsic sphincter deficiency (ISD) before routine use of Valsalva leak point pressures (VLPPs) was available. METHODS: The charts and videourodynamic reports of 208 patients who underwent a modified Pereyra bladder neck suspension from June 1988 to June 1996 were reviewed, and survey questionnaires were mailed to all patients. All videourodynamic study reports and charts were reviewed to identify those with what we now recognize was significant ISD and compare them with a group that we believed had more pure descent problems. RESULTS: A total of 135 patients or 65% of the population responded. The mean time after surgery was 4.14 years. At the follow-up survey, 14% reported no leakage at all, 42% reported very little or mild leakage, 38% reported moderate leakage, and 6% reported severe leakage. Fifty-three percent of patients continued to wear pads. Seventy-nine percent reported improvement in their leakage compared with the preoperative state, and 69% were satisfied with the results. When patients with preoperative ISD were compared with patients with pure bladder neck hypermobility, the ISD group had more leakage and less improvement after surgery than patients with bladder neck hypermobility. CONCLUSIONS: With an average follow-up of greater than 4 years, most women continued to leak with symptoms of stress urinary incontinence. Even though 79% reported improvement over their preoperative condition and 69% were satisfied, the results were disappointing. Patients with significant ISD had a worse outcome (2.6% dry) than patients with pure bladder neck hypermobility (20% dry). Given the above data, significant ISD is a contraindication for a modified Pereyra transvaginal needle suspension, and these data cast further doubt on the ability of the modified Pereyra needle suspension to consistently cure even anatomic incontinence.

Female↗
PubMed2001

Fluoride release of polyacid-modified composite resins with and without bonding agents.

OBJECTIVES: The aim of this study was to investigate the influence of the proprietary bonding agents Hytac OSB (OSB) (Espe), Prime&Bond 2.1 (PB) (Dentsply DeTrey) and Syntac Single Component (SSC) (Vivadent) on the fluoride release of the corresponding polyacid-modified composite resins Hytac (HTC), Dyract AP (DAP) and Compoglass F (CGF), respectively. METHODS: Ten cylindrical specimens (6mm diameter and 3mm thick) of each polyacid-modified composite were prepared according to the manufacturers' instructions: five with bonding agent applied and five without bonding agent as a control. The specimens were immersed individually in 10ml ultra-pure water at 37 degrees C immediately after light-curing of the polyacid-modified composite resins. Over 140 days, the water was regularly renewed and the fluoride concentration eluted during each period was determined with a combined fluoride ion selective electrode. RESULTS: The fluoride release decreases according to the sequence: CGF>DAP>HTC. The bonding agent significantly reduces the fluoride released by DAP and CGF, respectively, by a factor 2-3 and +/-1.4. For HTC, the bonding agent reduces the fluoride released initially by a factor of +/-2, but the difference between the fluoride release with and without bonding agent becomes insignificant after approximately 3 weeks. SIGNIFICANCE: It can be concluded that the use of bonding agent can significantly reduce fluoride release of polyacid-modified composite resins in the long-term, and especially in the short-term. The decrease in fluoride release might reduce the material's potential to prevent recurrent caries.

Algorithms↗
PubMed1996

Long-term mechanical characteristics of resin-modified glass ionomer restorative materials.

OBJECTIVES: The purpose of this study was to compare the effects of long-term water storage on the mechanical characteristics of four resin-modified glass ionomer restorative materials with those of a conventional glass ionomer cement and a resin composite material. METHODS: Cylindrical specimens were prepared and stored in water for 1 h, 24 h, 1 wk, 1 mon, 3 mon and 6 mon prior to determination of diametral tensile strength (DTS) and depth of surface indentation both under 1 N load and after removal of the load. RESULTS: Diametral tensile strength was lowest for the conventional glass ionomer cement and highest for the composite; the resin-modified glass ionomer cements were intermediate between the reference materials. Water storage reduced DTS between 24 h and 1 wk or 1 mon but then remained unaffected until the final measurements after 6 mon. The materials showed a trend toward a slight increase in the depth of indentation both under load and after removal of the load with increasing storage time. These mechanical properties indicate the position of four resin-modified glass ionomer cements on a continuum with conventional glass ionomer cement and resin composite as the end points. SIGNIFICANCE: The mechanical properties of resin-modified glass ionomers show that this group of materials is weaker than resin composite but stronger than conventional glass ionomer cement. Water storage for 6 mon has little adverse effect on the mechanical properties.

Analysis of Variance↗
PubMed2002

Adsorption and dissolution behavior of human plasma fibronectin on thermally and chemically modified titanium dioxide particles.

Titanium is known for its biocompatibility and is widely used in dental and orthopedic reconstructive surgery. There are reports that osteointegration of these implants is not optimal. The objective of this study was to modify titanium dioxide particles and examine the resultant effects on protein adsorption to these altered surfaces using a model cell binding protein, human plasma fibronectin (HPF). HPF is an important matrix glycoprotein that plays a major role in cell and protein attachment, Titanium dioxide surfaces were modified by heating the titanium dioxide powder at 800 degrees C for 1 h or treating with an oxidizing agent: peroxide in ammonium hydroxide followed by peroxide in hydrochloric acid. Oxidized and control samples were further treated with 9:1 butanol:water for 30 min. Brunauer-Emmett-Teller showed no change in particle surface area as a result of thermal or chemical treatment. Hydrophobicity increased with butanol treatment of titanium dioxide. Diffuse reflectance Fourier transform infrared spectroscopy showed the presence of -CH2 and -CH3 vibrations in the region of 2850-3000 cm(-1) for both the heated, butanol and peroxide/butanol-treated samples. The absence of increased C-O and O-C=O features as determined by electron spectroscopy for chemical analysis indicates that butanol adsorption is not occurring via an esterification mechanism. The interaction between butanol and pre-heated or peroxide-treated titanium dioxide may be one of association (weak electrostatic and/or Van der Waals forces) rather than direct ionic bonding. Maximum HPF adsorption on modified or unmodified titanium dioxide occurred within 30 min, with greater protein adsorption occurring on butanol-treated samples. Desorption was minimal with all modifications. Zeta potential measurements showed that HPF adsorption caused an increase in the negative zeta potential with the greatest change noted for the butanol-treated samples. These findings suggest that wettability and surface charge both play an important role in protein adsorption to titanium dioxide. Thus, by modifying the physico-chemical properties of titanium dioxide surfaces, it may be possible to alter protein adsorption and hence optimize cell attachment.

1-Butanol↗
PubMed2002

Release of gentamicin sulphate from a modified commercial bone cement. Effect of (2-hydroxyethyl methacrylate) comonomer and poly(N-vinyl-2-pyrrolidone) additive on release mechanism and kinetics.

The influence of the (2-hydroxyethyl methacrylate) (HEMA) monomer addition as a comonomer to the cement liquid component and of a polymer, poly(N-vinyl-2-pyrrolidone) (PVP) to the solid component of a standard CMW-1 bone cement on gentamicin sulphate (GS) on its drug release properties have been studied. The addition of HEMA modifies the habit of the delivery curves. The incorporation of PVP into the cement matrix, apparently, did not very much modify the shape of the HEMA modified cement release curves, but led to a remarkable increase of the maximum amount of GS released. This effect was proportional to the PVP concentration incorporated. From the matrix composition and SEM data, a model based on the morphology of the matrix has been proposed. The cumulative amount of GS released by each slab Mt is most adequately fitted and represented by the equation Mt = c + at 1/2 + b[1 - exp(-nt)], which corroborates that the release occurs according to the model proposed. by means of three discrete mechanisms, namely: (i) a short-term initial elution due to the imperfections in the poly(methyl methacrylate) covering of the most external GS beads, burst effect by the buffer solution; (ii) followed by a fracture by stress cracking in an active media of the coated GS beads located on the external surface of the matrix where water molecules enter to dissolve GS molecules releasing them into the buffer solution by a diffusion-controlled process; and (iii) a third process in which the buffer solution penetrates into the internal voids and cracks creating a series of channels in a labyrinthic structure, which may facilitate the access of water molecules to the plastic-coated GS beads within the bulk matrix. This third process is enhanced by the incorporation of PVP beads as dissolved molecules within the matrix. This water-soluble additive is leachable, generating a highly porous structure in the cement. This HEMA and PVP modified cement may be used as a drug delivery system to modulate the GS release rate.

Anti-Bacterial Agents↗