Biomedical subjects

J Feijen

Publications and source records attributed to J Feijen.

At least 37 records · Page 2Linked to original sources

PubMed2003

Development and properties of polycaprolactone/hydroxyapatite composite biomaterials.

Polycaprolactone/hydroxyapatite (PCL/HA) composites were prepared by two different procedures. The first one consists of a conventional blending of the polymer and the reinforcement material in an extruder. The second method consists of grafting of PCL on the surface of HA particles. This was achieved by a ring opening polymerization of caprolactone in the presence of HA, where its OH groups act as initiators. By this method, it was possible to obtain, in one step, a composite of PCL and surface modified HA. In both methods different percentages of filler were used to obtain several composites. These composites were characterized with respect to their mechanical properties, in the dry and wet state, by means of tensile tests on compression molded samples. The polymer/filler interface was analyzed by scanning electron microscopy. Water uptake and weight loss degradation experiments were also performed. An increase in the modulus for higher amounts of filler was, as expected, observed in the composites obtained by both processes. Furthermore, the mechanical properties of the materials in the wet state are considerably lower than those in the dry state. However, this difference is more significant for the composites obtained by conventional blending than for composites obtained by the grafting procedure, indicating that the later procedure can be an adequate route to reduce water susceptibility of PCL/HA composites.

Journal Article↗

PubMed2003

Preparation of degradable porous structures based on 1,3-trimethylene carbonate and D,L-lactide (co)polymers for heart tissue engineering.

Biodegradable porous scaffolds for heart tissue engineering were prepared from amorphous elastomeric (co)polymers of 1,3-trimethylene carbonate (TMC) and D,L-lactide (DLLA). Leaching of salt from compression-molded polymer-salt composites allowed the preparation of highly porous structures in a reproducible fashion. By adjusting the salt particle size and the polymer-to-particle weight ratio in the polymer-salt composite preparation the pore size and porosity of the scaffolds could be precisely controlled. The thermal properties of the polymers used for scaffold preparation had a strong effect on the morphology, mechanical properties and dimensional stability of the scaffolds under physiological conditions. Interconnected highly porous structures (porosity, 94%; average pore size, 100 microm) based on a TMC-DLLA copolymer (19:81, mol%) had suitable mechanical properties and displayed adequate cell-material interactions to serve as scaffolds for cardiac cells. This copolymer is noncytotoxic and allows the adhesion and proliferation of cardiomyocytes. During incubation in phosphate-buffered saline at 37 degrees C, these scaffolds were dimensionally stable and the number average molecular weight (Mn) of the polymer decreased gradually from 2.0 x 10(5) to 0.3 x 10(5) in a period up to 4 months. The first signs of mass loss (5%) were detected after 4 months of incubation. The degradation behavior of the porous structures was similar to that of nonporous films with similar composition and can be described by autocatalyzed bulk hydrolysis.

Biocompatible Materials↗

PubMed2003

Endothelialization of small-diameter vascular prostheses.

In the field of arterial vascular reconstructions there is an increasing need for functional small-diameter artificial grafts (inner diameter < 6mm). When autologous replacement vessels are not available, for example because of the bad condition of the vascular system in the patient, the surgeon has no other alternative than to implant a synthetic polymer-based vessel. After implantation the initial major problem concerning these vessels is the almost immediate occlusion, due to blood coagulation and platelet deposition, under the relatively low flow conditions. As the search for the perfect bio-inert polymer has not revealed a material with suitable properties for this application, improved performance of small-diameter artificial blood vessels is now being sought in the biological field. The poor blood-compatibility of an artificial vascular graft is not simply because of its coagulation-stimulating or platelet-activating properties, but more due to its inability to actively participate in the prevention of blood coagulation and platelet deposition. As these functions are naturally performed by endothelial cells, the utilization of these cells seems inevitable for the construction of a functional small-diameter artificial blood vessels. This review describes the current status of the use of endothelial cells to improve the performance of artificial vascular prostheses.

Biocompatible Materials↗

PubMed2002

Tailoring the properties of asymmetric cellulose acetate membranes by gas plasma etching.

Cellulose triacetate (CTA) ultrafilters and cellulose acetate blend (CAB) desalination membranes were treated with a radiofrequency gas plasma (tetrafluoromethane (CF(4)) or carbon dioxide (CO(2)), 47-49 W, 0.04-0.08 mbar). Treatment times were varied between 15 s and 120 min. The plasma-treated top layer of the membranes was characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and contact angle measurements to obtain information about surface structure, chemistry, and wettability, respectively. The membrane properties (e.g., permeability, selectivity, fouling) were studied by waterflux measurements, molecular weight cutoff measurements, and fouling experiments with bovine serum albumin. CO(2) plasma treatment resulted in gradual etching of the membrane's dense top layer. Permeation and selectivity changed significantly for treatment times of 0-15 min for CTA and 5-60 min for CAB membranes. Moreover, CTA membranes were hydrophilized during CO(2) plasma treatment whereas CF(4) plasma treatment led to hydrophobic surfaces due to strong fluorination of the top layer. This study shows that gas plasma etching can tailor the properties of asymmetric cellulose acetate membranes by simultaneously modifying the chemistry and structure of the top layer. The low fouling properties of CTA membranes were thereby largely maintained.

Animals↗

PubMed2002

Control of vitamin B12 release from poly(ethylene glycol)/poly(butylene terephthalate) multiblock copolymers.

The release of vitamin B12 (1355 Da) from matrices based on multiblock copolymers was studied. The copolymers were composed of hydrophilic poly(ethylene glycol)-terephthalate (PEGT) blocks and hydrophobic poly(butylene terephthalate) (PBT) blocks. Vitamin B12 loaded films were prepared by using a water-in-oil emulsion method. The copolymer properties, like permeability, could be varied by increasing the PEG-segment length from 300 up to 4,000 g/mol and by changing the wt% of PEGT. From permeation and release experiments. the diffusion coefficient of vitamin B12 through PEGT/PBT films of different compositions was determined. The diffusion coefficient of Vitamin B12 was strongly dependent on the composition of the copolymers. Although an increased wt% of PEGT (at a constant PEG-segment length) resulted in a higher diffusion coefficient, a major effect was observed at increasing PEG-segment length. By varying the copolymer composition, a complete release of vitamin B12 in 1 day up to a constant release for over 12 weeks was obtained. The release rate could be effectively tailored by blending copolymers with different PEG-segment lengths. The swelling and the crystallinity of the matrix could explain the effect of the matrix composition on the release behavior.

Biocompatible Materials↗

PubMed2002

Phase separation and physical properties of PEO-containing poly(ether ester amide)s.

Poly(ether ester amide) (PEEA) copolymers based on poly(ethylene glycol) (PEG), 1,4-butanediol, and dimethyl-7,12-diaza-6,13-dione-1,18-octadecanedioate (a diester-diamide monomer) were synthesized by a two-step polycondensation reaction. The obtained segmented copolymers are hydrophilic, with a water uptake of 24-340%. PEEA copolymers showed microphase separation, as observed by differential scanning calorimetry (DSC). The long spacing determined by small-angle X-ray scattering shows an increase in the hydrophilic domain size with increasing PEO content. By varying the copolymer composition, the E-modulus of PEEA could be varied between 61 and 427 MPa, with tensile strengths ranging from 12 to 39 MPa. The elongation at break can reach values up to 850%. The mechanical properties decrease with the uptake of water. However, PEEAs with a relatively low content of PEO still retain good tensile properties and are, in principle, suitable for biomedical applications.

Biocompatible Materials↗

PubMed2001

Expression of leukocyte adhesion molecules by endothelial cells seeded on various polymer surfaces.

Although endothelial cell seeding in small-diameter vascular prostheses significantly improves graft survival, the detachment of adherent endothelial cells after the restoration of circulation remains one of the major obstacles. Because in vivo experiments indicate that leukocyte infiltration is involved in endothelial cell loss, we hypothesize that seeded endothelial cells become activated and express leukocyte adhesion molecules and cytokines because of an interaction with the underlying polymer surface. The aim of this study was to investigate the expression of the leukocyte adhesion molecules ICAM-1, VCAM-1, PECAM-1, and E-selectin by cultured human umbilical vein endothelial cells (HUVECs) and human adipose microvascular endothelial cells (HAMVECs). The cells were seeded on tissue culture poly(styrene) and the vascular graft materials Dacron and Teflon. The results of this study indicate that the expression of leukocyte adhesion molecules by cultured endothelial cells is mainly affected by the endothelial cell origin, that is, umbilical vein or adipose tissue. Expressions of both ICAM-1 and E-selectin by HUVECs and HAMVECs are characterized by the presence of two cell populations with distinct levels of expression. With respect to endothelial cell seeding in vascular prostheses, the increased expression of E-selectin by microvascular endothelial cells deserves further attention.

Cell Adhesion↗

PubMed2001

In vivo biocompatibility of carbodiimide-crosslinked collagen matrices: Effects of crosslink density, heparin immobilization, and bFGF loading.

Collagen matrices, crosslinked using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (E) and N-hydroxysuccinimide (N), were previously developed as a substrate for endothelial cell seeding of small-diameter vascular grafts. In the present study, the biocompatibility of various EN-crosslinked collagen matrices was evaluated following subcutaneous implantation in rats for periods up to 10 weeks. The effects of the crosslink density, referred to as the number of free primary amino groups per 1,000 amino acid residues (EN10, EN14, EN18, or EN22), the amount of heparin immobilized to EN14, and the effect of preloading heparinized EN14 with basic fibroblast growth factor (bFGF) on the induced tissue reaction were studied. EN-crosslinked collagen was biocompatible at both early and late time intervals, and matrices with high crosslink densities (i.e., EN14, EN10) especially demonstrated a significantly decreased antigenic response when compared to noncrosslinked collagen. Furthermore, increased crosslinking resulted in a decreased degradation rate. Immobilization of heparin onto EN14 resulted in a similar to EN14 (thus without heparin) or somewhat reduced tissue reaction, but fibrin formation and vascularization were increased with increasing quantities of immobilized heparin. Matrices preloaded with bFGF also demonstrated good biocompatibility, especially in combination with higher amounts of immobilized heparin. The latter matrices [EN14 with high heparin and bFGF, thus EN14-H (0.4)F and EN14-H(1.0)F] demonstrated significantly increased vascularization for periods up to 3 weeks. Neither heparin immobilization nor bFGF preloading induced an increased antigenic response. It is concluded that the results of this study justify further evaluation of bFGF preloaded, heparin immobilized EN14 collagen, as a matrix for endothelial cell seeding in experimental animals.

Animals↗

PubMed2001

Tissue reactions to epoxy-crosslinked porcine heart valves post-treated with detergents or a dicarboxylic acid.

Calcification limits the long-term durability of xenograft glutaraldehyde (GA)-crosslinked heart valves. Previously, a study in rats showed that epoxy-crosslinked heart valves reduced lymphocyte reactions to the same extent as the GA-crosslinked control and induced a similar foreign-body response and calcification reaction. The present study was aimed at reducing the occurrence of calcification of epoxy-crosslinked tissue. Two modifications were carried out and their influence on cellular reactions and the extent of calcification after 8 weeks' implantation in weanling rats was evaluated. First, epoxy-crosslinked valves were post-treated with two detergents to remove cellular elements, phospholipids and small soluble proteins, known to act as nucleation sites for calcification. The second approach was to study the effect of the impaired balance between negatively and positively charged amino acids by an additional crosslinking step with a dicarboxylic acid. The detergent treatment resulted in a washed-out appearance of especially the cusp tissue. With the dicarboxylic acid, both the cusps and the walls had a limited washed-out appearance. The wall also demonstrated some detachment of the subendothelium. After implantation, both detergent and dicarboxylic acid post-treatment histologically resulted in reduced calcification at the edges of cusps and walls. However, total amounts of calcification, measured by atomic emission spectroscopy, were not significantly reduced. Data concerning the presence of lymphocytes varied slightly, but were in the same range as the GA-crosslinked control, i.e., clearly reduced compared with a noncrosslinked control. It is concluded that both the double detergent and the dicarboxylic acid post-treatment of epoxy-crosslinked heart valve tissue do not represent a sound alternative in the fabrication of heart valve bioprostheses.

Animals↗

PubMed2001

Immobilization of heparin to EDC/NHS-crosslinked collagen. Characterization and in vitro evaluation.

In the present study, heparin immobilization to a non-cytotoxic crosslinked collagen substrate for endothelial cell seeding was investigated. Crosslinking of collagen using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) resulted in a material containing 14 free primary amino groups per 1000 amino acid residues (E/N14C). At a fixed molar ratio NHS:EDC of 0.6, the amount of heparin covalently immobilized to E/N14C increased with increasing molar ratios of EDC to heparin carboxylic acid groups (Hep-COOH), to a maximum of approximately 5-5.5 wt% at a ratio of 2. Upon incubation in cell culture medium of endothelial cells, 4 to 7% of the immobilized heparin was released during 11 days. Immobilization of increasing amounts of heparin to E/N14C progressively reduced activation of contact activation proteases. Optimal anticoagulant activity, as measured by thrombin inhibition, was obtained after heparin immobilization using a ratio of EDC to Hep-COOH of 0.2-0.4 (14-20 mg heparin immobilized per gram of collagen). Platelets deposited to (heparinized) E/N14C showed only minor spreading and aggregation, although heparin immobilization slightly increased the number of adherent platelets. The results of this study suggest that heparin immobilization to EDC/NHS-crosslinked collagen may improve the in vivo blood compatibility of this material.

Biocompatible Materials↗

PubMed2001

Relation between cell density and the secretion of von Willebrand factor and prostacyclin by human umbilical vein endothelial cells.

In this study, the relation between the density of human umbilical vein endothelial cells (HUVECs) cultured on TCPS and (crosslinked) collagen, and the secretion of von Willebrand factor (vWF) and prostacyclin (PGI2) was determined. Collagen was crosslinked using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) in combination with N-hydroxy-succinimide (NHS), resulting in a matrix containing 14 free primary amino groups per 1000 amino acid residues after crosslinking (E/N14C). HUVECs were seeded on E/N14C, non-crosslinked collagen (N-Coll) and fibronectin-coated TCPS at densities ranging from 2500 to 50,000 cells/cm2. After 1 day of culture, both basal and A23187-stimulated secretion of vWF (expressed per 1,000,000 cells) was considerably increased at low cell densities (i.e. below 5000 cells/cm2) on all substrates. Secretion of PGI2 gradually increased with decreasing cell densities below 10,000 cells/cm2. After 10 days of proliferation, cell numbers on all substrates exceeded 50,000 cells/cm2, irrespective of the seeding density. Concomitantly, the initial higher secretion of PGI2 and vWF at the lowest seeding densities was decreased after longer times of culture, to values comparable to those obtained for higher seeding densities.

Biocompatible Materials↗

PubMed2001

Binding and release of basic fibroblast growth factor from heparinized collagen matrices.

Endothelial cell seeding is a promising method to improve the performance of small-diameter vascular grafts. Growth of endothelial cells seeded on the luminal surface of synthetic vascular grafts, coated with a matrix suitable for cell seeding (e.g. collagen), can be accelerated by local, sustained release of basic fibroblast growth factor (bFGF). In this study two potential matrices for in vivo endothelial cell seeding were studied with respect to bFGF binding and release: collagen crosslinked using N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS), as well as heparinized EDC/NHS-crosslinked collagen. bFGF binding was determined after incubation of circular samples (10 mm diameter) with 0.25 ml bFGF solution for 90 min. Immobilization of increasing amounts of heparin, also using EDC and NHS, to crosslinked collagen containing 14 free primary amino groups per 1000 amino acid residues (E/N14C) resulted in binding of increasing amounts of bFGF. A plateau in bFGF binding was observed for heparinized E/N14C containing approximately 2.0-3.0 wt% of immobilized heparin which was obtained using a molar ratio of EDC to heparin-carboxylic acid groups of 0.4 during heparin immobilization (E/N14C-H(0.4)). At concentrations up to 840 ng bFGF/ml, 10% of the added bFGF bound to E/N14C, while binding of bFGF to E/N14C-H(0.4) amounted to 22%. Both E/N14C and E/N14C-H(0.4) pre-loaded with bFGF showed sustained bFGF release. A burst release of 30% in endothelial cell culture medium (CM) was observed for E/N14C during the first 6 h, compared to 2% release from E/N14C-H(0.4). After 28 days, the bFGF release from E/N14C and E/N14C-H(0.4) in CM amounted to 100 and 65%, respectively. Combined results of binding and release of bFGF indicate that compared to E/N14C, E/N14C-H(0.4) is the substrate of choice for bFGF pre-loading and subsequent endothelial cell seeding.

Biocompatible Materials↗

PubMed2001

Partially carboxymethylated feather keratins. 2. Thermal and mechanical properties of films.

Free cysteine thiol groups of keratin extracted from chicken feathers were partially carboxymethylated with iodoacetic acid (25-76% cysteine modification). Stable dispersions were used for the preparation of films by solution casting. Glycerol was used as a plasticizer (0.05-0.47 g/g of keratin), and films were stored at a constant relative humidity (20, 30, 50, 70, or 90%). The degree of crystallinity in the films was higher when more cysteine residues were carboxymethylated. The films displayed an optimum in mechanical properties at approximately 50% cysteine carboxymethylation. The tensile strength at this optimum was 25 MPa, the E modulus, 350 MPa, and the elongation at break, 50%. Probably, this optimum was the result of both a decreasing amount of disulfide bonds and an increasing degree of crystallinity for higher degrees of cysteine modification. The influences of a higher amount of glycerol and of different storage conditions on the mechanical properties of films from keratin with a defined degree of cysteine modification were also investigated.

Animals↗

PubMed2001

Improved platelet compatiblity of water vapour glow discharge treated non-woven poly(ethylene terephthalate) leukocyte-reduction filters for different types of platelet concentrates.

Non-woven poly[ethylene terephthalate] (NW-PET) filter fabric, usually used for leucocyte removal of red cells, was modified by water vapour glow discharge (WVGD) treatment to improve platelet compatibility. Modified filter material was evaluated with different kinds of platelet concentrates (PCs). In addition, modified filter materials were gamma-sterilized and tested after different time intervals at different storage conditions. Modification of the filter material resulted in an improved platelet recovery after filtration of PC from 57 to about 80%. No significant difference in platelet recovery was observed when filtering either freshly prepared (79 +/- 3.5%, mean +/- SD), overnight-stored single BC-PC (78 +/- 3.3%), overnight-stored single PRP-PC (75 +/- 8.8%) or overnight-stored pooled BC-PC (79 +/- 8.9%). However, freshly prepared pooled BC-PC gave a significantly higher platelet recovery (84 +/- 3.5%). Leukocyte depletion did not differ significantly between the different types of PC. gamma-Sterilization and subsequent storage of the modified filter material for 5, 14 and 26 weeks at 20 degrees C or 37 degrees C had no significant influence on the filtration results of overnight-stored pooled BC-PC. The results of the present study show that WVGD-treated NW-PET is platelet compatible and can be used for leucocyte removal from preferably BC-PC. It can be gamma-sterilized and stored for at least 6 months prior to filtration without affecting the platelet recovery and leucocyte removal.

Biocompatible Materials↗

PubMed2001

Antimicrobial effects of positively charged surfaces on adhering Gram-positive and Gram-negative bacteria.

The infection of biomaterials is determined by an interplay of adhesion and surface growth of the infecting organisms. In this study, the antimicrobial effects on adhering bacteria of a positively charged poly(methacrylate) surface (xi potential +12 mV) were compared with those of negatively charged poly(methyl methacrylate) (-12 mV) and a highly negatively charged poly(methacrylate) (-18 mV) surface. Initial adhesion of Staphylococcus aureus ATCC 12600, Staphylococcus epidermidis HBH(2) 102, Escherichia coli O2K2 and Pseudomonas aeruginosa AK1 to these surfaces was measured in a parallel plate flow chamber in phosphate-buffered saline. Adhering bacteria were allowed to multiply by perfusing the flow chamber with growth medium. All bacteria adhered most rapidly to the positively charged surface, but there was no subsequent surface growth of the Gram-negative strains. On the negatively charged surfaces, despite a slower initial adhesion, surface growth of the adhering bacteria was exponential for both Gram-positive and Gram-negative strains. These results suggest that positively charged biomaterial surfaces exert an antimicrobial effect on adhering Gram-negative bacteria, but not on Gram-positive ones.

Bacterial Adhesion↗

PubMed2001

Copolymers of trimethylene carbonate and epsilon-caprolactone for porous nerve guides: synthesis and properties.

Copolymers of trimethylene carbonate and epsilon-caprolactone were synthesized and characterized with the aim of assessing their potential in the development of a flexible and slowly degrading artificial nerve guide for the bridging of large nerve defects. The effect of the monomer ratio on the physical properties of the polymers and its influence on the processability of the materials was investigated. Under the applied polymerization conditions (130 degrees C, 3 days using stannous octoate as a catalyst) high molecular weight polymers (Mn above 93 000) were obtained. All copolymers had glass transition temperatures below room temperature. At trimethylene carbonate contents higher than 25 mol% no crystallinity was detected. A decrease in crystallinity resulted in the loss of strength and decrease in toughness, as well as in an increased polymer wettability. Amorphous poly(trimethylene carbonate), however, showed excellent ultimate mechanical properties due to strain-induced crystallization (Tm = 36 degrees C). Low crystallinity copolymers could be processed into dimensionally stable porous structures by means of immersion precipitation and by combination of this technique with the use of porosifying agents. Porous membranes of poly(trimethylene carbonate) could be prepared when blended with small amounts of high molecular weight poly(ethylene oxide). Poly(trimethylene carbonate) and poly(trimethylene carbonate-co-epsilon-caprolactone) copolymers with high epsilon-caprolactone content possess good physical properties and are processable into porous structures. These materials are most suitable for the preparation of porous artificial nerve guides.

Biocompatible Materials↗

PubMed2000

The kinetics of 1,4-butanediol diglycidyl ether crosslinking of dermal sheep collagen.

Dermal sheep collagen was crosslinked with 1,4-butanediol diglycidyl ether (BDDGE) or modified with glycidyl isopropyl ether (PGE). The reduction in amine groups as a function of time was followed to study the overall reaction kinetics of collagen with either BDDGE or PGE. Linearization of the experimental data resulted in a reaction order of 2 with respect to the amine groups in the PGE masking reaction, whereas a reaction order of 2.5 was obtained in the BDDGE crosslinking reaction. The reaction orders were independent of the pH in the range of 8.5-10.5 and the reagent concentration (1-4 wt %). The reaction order with respect to epoxide groups was equal to 1 for both reagents. As expected, the reaction rate was favored by a higher reagent concentration and a higher solution pH. Because the BDDGE crosslinking reaction occurs via two distinct reaction steps, the content of pendant epoxide groups in the collagen matrix was determined by treating the collagen with either O-phosphoryl ethanolamine or lysine methyl ester. The increase in either phosphor or primary amine groups was related to the content of pendant groups. Crosslinking at pH 9.0 resulted in a low reaction rate but in a high crosslink efficacy, especially after prolonged reaction times. A maximum concentration of pendant epoxide groups was detected after 50 h. Reaction at pH 10.0 was faster, but a lower crosslinking efficacy was obtained. At pH 10.0, the ratio between pendant epoxide groups and crosslinks was almost equal to 1 during the course of the crosslinking reaction.

Animals↗

PubMed2000

Thrombocidins, microbicidal proteins from human blood platelets, are C-terminal deletion products of CXC chemokines.

Antibacterial proteins are components of the innate immune system found in many organisms and produced by a variety of cell types. Human blood platelets contain a number of antibacterial proteins in their alpha-granules that are released upon thrombin activation. The present study was designed to purify these proteins obtained from human platelets and to characterize them chemically and biologically. Two antibacterial proteins were purified from platelet granules in a two-step protocol using cation exchange chromatography and continuous acid urea polyacrylamide gel electrophoresis and were designated thrombocidin (TC)-1 and TC-2. Characterization of these proteins using mass spectrometry and N-terminal sequencing revealed that TC-1 and TC-2 are variants of the CXC chemokines neutrophil-activating peptide-2 and connective tissue-activating peptide-III, respectively. TC-1 and TC-2 differ from these chemokines by a C-terminal truncation of 2 amino acids. Both TCs, but not neutrophil-activating peptide-2 and connective tissue-activating peptide-III, were bactericidal for Bacillus subtilis, Escherichia coli, Staphylococcus aureus, and Lactococcus lactis and fungicidal for Cryptococcus neoformans. Killing of B. subtilis by either TC appeared to be very rapid. Because TCs were unable to dissipate the membrane potential of L. lactis, the mechanism of TC-mediated killing most probably does not involve pore formation.

Amino Acid Sequence↗