Freeze-dried Gelatin Research Articles

Chemical composition, functional properties, physico-chemical properties, and techno-functional characteristics of Satureja protein hydrolysate stabilized in a gelatin matrix.

The current evaluation was conducted to investigate the chemical composition and functional properties of protein hydrolysates from different Satureja species. The major amino acids (mg/100 g protein) in the protein from different Satureja species were arginine (6.06-14.37), asparagine (1.39-17.06), glutamine (2.42-11.60), glutamic acid (6.34-9.32), beta-aminoisobutyric acid (3.31-10.29), alanine (4.64-9.59), aspartic acid (5.73-9.54), proline (4.25-8.14), leucine (3.63-5.69), serine (2.64-4.83), lysine (1.89-4.56), glycine (0.96-5.27), valine (2.76-4.83), and phenylalanine (2.86-3.75). Protein hydrolysates from Satureja species exhibited comparable antioxidant activity (IC50 = 0.270-0.328 mg/mL), anti-linoleic acid oxidation (IC50 = 0.231-0.301 mg/mL), anti-lecithin oxidation (IC50 = 0.198-0.258 mg/mL), anti-starch oxidation (IC50 = 0.201-0.277 mg/mL), anti-amylase activity (IC50 = 0.314-0.337 mg/mL), and anti-lipase activity (IC50 = 0.309-0.369 mg/mL). The physico-chemical properties of gelatin dispersion were electrical conductivity (1197 microsiemens/cm), osmolarity (190 milliosmol/kg), surface tension (45 mN/m), particle size (179 nm), zeta potential (-48 mV), and viscosity (4.92 mPa.s). Techno-functional characteristics of freeze-dried gelatin particles were as follows: water content (7.68%), water solubility (84.57%), water swelling (151.33%), hygroscopicity (38.20%), hydrophobicity (6.50 μg/g), emulsification activity (68.54%), emulsification stability (57.86%), foam expansion activity (56.08%), foam stability (41.84%), oil-holding capacity (1.96 g/g), and water-holding capacity (4.45 g/g). Protein hydrolysate causes minor changes in the physico-chemical and techno-functional properties of gelatin. The current investigation introduces Satureja protein hydrolysate as a possible functional and techno-functional ingredient for bioactive food products for treating diabetes and oxidative stress and as a natural preservative for the food industry.

Techno-functional characterization of gelatin extracted from the smooth-hound shark skins: Impact of pretreatments and drying methods

Gelatin derived from marine by-products could be an interesting alternative to classic mammalian gelatin. The pretreatment and extraction conditions could influence the size of the resulting peptide chains and therefore their techno-functional properties. Thus, it is important to optimize the production process to get a gelatin for the appropriate applications. Skin pretreatment was done by microwaves or oven-drying and the extracted gelatin was dried by spray- or freeze-drying. Freeze-dried gelatin extracted from untreated skin (FGUS) had the highest gelatin yield (10.40%). Gelatin proximate composition showed that proteins were the major component (87.12–89.95%), while lipids showed the lowest contents (0.65–2.26%). Glycine showed the highest level (299–316/1000 residues) in the extracted gelatins. Proline and hydroxyproline residues of gelatins from untreated skin were significantly higher than those from pretreated skin-gelatin. FTIR spectra were characterized by peaks of the amide A (3430-3284 cm−1), B (3000-2931 cm−1), I (1636–1672 cm−1), II (1539–1586 cm−1) and III (1000–1107 cm−1). Spray-drying decreased the gelling properties of gelatins, since it reduced gelling and melting temperatures compared to freeze-drying. Skin pretreatment significantly reduced the gel strength of gelatin by about 50–100 g depending on the gelatin drying method. The FGUS showed better surface properties compared to other gelatins. The highest emulsion activity index (39.42 ± 1.02 m2/g) and foaming expansion (172.33 ± 2.35%) were measured at 3% FGUS. Therefore, the promising properties of freeze-dried gelatin derived from untreated skin, gave it the opportunity to be successfully used as a techno-functional ingredient in many formulations.

Efficient fabrication, characterization, and in vitro digestion of aerogel-templated oleogels from a facile method: Electrospun short fibers

In this work, an innovative and convenient approach was induced to construct aerogel-templated oleogels (ATO), which were simply made of camellia oil and gelatin. The freeze-dried gelatin aerogel templates were developed from uniformly dispersed electrospun short fibers (GF), which were further immersed in camellia oil within 5 min to form ATO facilely. Compared with traditional gelatin hydrogel-based (GH) aerogels, GF aerogel templates presented different micromorphology, thermal stabilities, and significant changes on infrared spectrum and secondary structure, where GF exhibited stronger internal interactions than GH. In compression tests, GH aerogels possessed strong resistance to stress while GF aerogels exhibited surprising resilient abilities. In addition, the oil adsorption capacity (OAC) and oil holding capacity (OHC) of GF aerogel templates considerably reached 125.31 g/g and 79.40%, respectively. Oleogels with different preparing methods and gelatin content presented outstanding rheological properties and in vitro digestibility. This work suggested that gelatin ATO could be fabricated from not only hydrogels but also electrospun short fibers, which owned a more desired physical structure and oil-related properties. Meanwhile, the properties of GF and GH systems could be significantly affected by the concentration of the biopolymer. • Aerogel templates were prepared from electrospun short fibers. • Oleogels were obtained by efficient oil adsorption within 5 min. • The fiber-based aerogels exhibited outstanding resilient abilities. • The oleogels showed considerable oil capacities and in vitro digestibilities.

Effect of gelatin drying methods on its amphiphilicity

Gelatin is a natural amphiphilic biopolymer that is widely used in food products, pharmaceuticals, and cosmetics. We studied the effect of spray and freeze drying on the solubility and amphiphilicity of gelatin samples.
 The control sample was a commercially produced edible gelatin. The experimental samples were spray- and freeze-dried gelatins obtained by enzymatic-acid hydrolysis of cattle bone. Amino acid sequences were determined by matrix-activated laser desorption/ionization. Solubility was assessed visually. Bloom strength of the gelatin gels was measured by a texture analyzer. The ProtScale online service was used to predict the amphiphilic topology of gelatin proteins. Molecular weight distribution of proteins was carried out by electrophoresis in polyacrylamide gel in the presence of sodium dodecyl sulfate.
 Spray drying reduced protein degradation and retained more α-chains, while freeze drying increased gelatin’s hydrophobicity and decreased its solubility. The predicted topology of protein hydrophobicity based on the amino acid sequences was in line with our results on solubility. The freeze-dried gelatin had a 18% larger amount of low-molecular weight peptides, compared to the control and the spray-dried samples. This was probably caused by the cleavage of peptides during the drying process. Thus, freeze drying can lead to maximum degradation of gelatin components, which may be associated with a longer heat treatment, compared to spray drying.
 Thus, spray drying is more suitable for gelatin, since this method improves the stability of its outer and inner structure, ensuring high hydrophilic properties.

Novel 3D Hybrid Nanofiber Scaffolds for Bone Regeneration.

Development of hybrid scaffolds and their formation methods occupies an important place in tissue engineering. In this paper, a novel method of 3D hybrid scaffold formation is presented as well as an explanation of the differences in scaffold properties, which were a consequence of different crosslinking mechanisms. Scaffolds were formed from 3D freeze-dried gelatin and electrospun poly(lactide-co-glicolide) (PLGA) fibers in a ratio of 1:1 w/w. In order to enhance osteoblast proliferation, the fibers were coated with hydroxyapatite nanoparticles (HAp) using sonochemical processing. All scaffolds were crosslinked using an EDC/NHS solution. The scaffolds’ morphology was imaged using scanning electron microscopy (SEM). The chemical composition of the scaffolds was analyzed using several methods. Water absorption and mass loss investigations proved a higher crosslinking degree of the hybrid scaffolds than a pure gelatin scaffold, caused by additional interactions between gelatin, PLGA, and HAp. Additionally, mechanical properties of the 3D hybrid scaffolds were higher than traditional hydrogels. In vitro studies revealed that fibroblasts and osteoblasts proliferated and migrated well on the 3D hybrid scaffolds, and also penetrated their structure during the seven days of the experiment.

Effect of phosphate glass reinforcement on the mechanical and biological properties of freeze-dried gelatin composite scaffolds for bone tissue engineering applications

Development of three-dimensional scaffolds is an important step in tissue engineering to repair, rebuild and regenerate damaged tissues. In this study, three dimensional porous gelatin (G) and phosphate glass (PG, 1 and 2 wt%) reinforced gelatin composite (GPG1 and GPG2) scaffolds were developed by freeze drying technique and their suitability as tissue engineering scaffolds was evaluated. FESEM images revealed the formation of an interconnected porous network with porosity above 70% and pore size around 100−500 μm. The developed scaffolds showed swelling, biodegradation and apatite formation on the surface of the scaffolds. Four fold enhancement in compressive modulus was observed with the introduction of PG content in the gelatin matrix which increased further with increase in PG content. Cytotoxicity and cell attachment of the scaffolds were evaluated with MG-63 cells, which revealed non-toxic nature of the scaffold leading to attachment of cells. Cell proliferation of MG-63 on the scaffolds was examined by DNA quantification assay, which showed increased proliferation with PG content and further increase with increase in PG content. In order to evaluate the drug delivery performance of the PG reinforced gelatin composite, ciprofloxacin loaded gelatin and composite (GPG1 and GPG2) samples were prepared and release study was carried out. Prolonged and sustained release behaviour was observed for the PG reinforced gelatin scaffolds which were due to the strong interaction between the PG-ciprofloxacin-gelatin and Fickian diffusion mechanism was observed for GPG2 scaffold. The present study showed that the PG reinforced gelatin scaffold is a potential candidate for bone tissue engineering applications and also serve as drug delivery system.

Influence of spray-drying, freeze-drying and vacuum-drying on physicochemical and functional properties of gelatin from Labeo rohita swim bladder

Influence of different drying method on yield, physicochemical and functional properties of gelatin from rohu (Labeo rohita) swim bladder were investigated. Freeze-drying presented the highest gelatin yield (54.51 g/100 g, dry weight basis), followed by vacuum-drying (48.95 g/100 g) and spray-drying (41.76 g/100 g), respectively (P < 0.05). All gelatin samples showed glycine as the major amino acid followed by proline, glutamic acid, alanine, arginine and hydroxyproline, respectively. Freeze-dried gelatin (FDG) and spray-dried gelatin (SDG) showed α (α1 and α2), β-chains and γ-chain as the predominant components, whereas an absence of β- and γ-chains found in vacuum-dried gelatin (VDG). FTIR spectra revealed that the loss of the triple-helix was found in all gelatins which indicated the conversion of collagen to soluble gelatin. FDG and SDG had the highest surface hydrophobicity, protein solubility, emulsifying, foaming and gelation property than VDG (P < 0.05). Moreover, SDG showed slightly higher surface hydrophobicity, protein solubility, emulsifying and foaming properties as compared to FDG (P < 0.05). However, no significant difference was found in gelation properties of FDG and SDG (P > 0.05). Therefore, freeze-drying or spray-drying could be an appropriate drying method for preparation of gelatin from rohu swim bladder with better functionalities.

Improvement of mechanical properties and in vitro bioactivity of freeze-dried gelatin/chitosan scaffolds by functionalized carbon nanotubes

ABSTRACTFunctionalized multiwall carbon nanotubes (f-MWCNTs) were used to reinforce the freeze-dried gelatin (G)/chitosan (Ch) scaffolds for bone graft substitution. Two types of G/Ch scaffolds at a ratio of 2:1 and 3:1 by weight incorporated with 0.025, 0.05, or 0.1 and 0.2 or 0.4 wt% f-MWCNT, respectively, were prepared by freeze drying, and their structure, morphology, and physicochemical and compressive mechanical properties were evaluated. The scaffolds exhibited porous structure with pore size of 80–300 and 120–140 µm for the reinforced scaffolds of G/Ch 2:1 and 3:1, respectively, and porosity 90–93% which slightly decreased with an increase in f-MWCNTs content for both types. Incorporation of f-MWCNTs led to 11- and 9.6-fold increase in modulus, with respect to their pure biopolymer blend scaffolds at a level of 0.05 wt% for G/Ch 2:1 and 0.2 wt% for G/Ch 3:1, respectively. The higher content of f-MWCNTs resulted in loss of mechanical properties due to agglomeration. The highest value of compressive strength and modulus was obtained for G/Ch 2:1 with 0.05 wt% f-MWCNT as 411 kPa and 18.7 MPa, respectively. Improvement of in vitro bioactivity as a result of f-MWCNTs incorporation was proved by formation of a bone-like apatite layer on the surface of scaffolds upon immersion in simulated body fluid. The findings indicate that the f-MWCNT-reinforced gelatin/chitosan scaffolds may be a suitable candidate for bone tissue engineering.

Effect of drying method on functional properties and antioxidant activities of chicken skin gelatin hydrolysate

The aim of this study is to investigate the functional and antioxidant properties of chicken skin gelatin hydrolysate (CSGH) as affected by the drying method used in the preparation of gelatin (freeze-dried and vacuum dried). CSGH obtained from freeze-dried gelatin showed better functional properties such as emulsifying activity index (EAI), water holding and oil binding capacity at different pH compared to CSGH produced from vacuum dried gelatin. Meanwhile, the CSGH of the vacuum dried gelatin exhibited a better emulsifying stability index (ESI), foaming capacity and stability. CSGH from freeze-dried gelatin showed better antioxidant, DPPH radical scavenging and metal chelating activity.

Crosslinking strategies for porous gelatin scaffolds

The present work reports on the application and the evaluation of a multitude of crosslinking approaches including high-energy irradiation, redox-initiating systems and conventional carbodiimide-coupling chemistry for frozen and/or freeze-dried porous gelatin scaffolds. The latter is particularly relevant for a plethora of biomedical applications such as tissue engineering supports, wound dressings, adhesive and absorbent pads for surgery, etc. Moreover, the results obtained for gelatin can be considered a proof-of-concept to be extrapolated to other polymer systems containing double bonds and/or amines and carboxylic acids to also realize scaffold crosslinking in dry or frozen state. The results showed that high-energy irradiation at −5 °C enabled sufficient segmental mobility to induce chemical crosslinking after performing a cryogenic treatment of methacrylamide-modified gelatin scaffolds. Alternatively, although several redox-initiating systems were unable to chemically crosslink functionalized gelatin, the combination of ammonium persulphate and TEMED resulted in the formation of scaffolds with a reasonable gel fraction. Interestingly, carbodiimide-coupling was found suitable to crosslink freeze-dried gelatin matrices.

Effect of Pretreatments and Drying Methods on the Properties and Fishy Odor/Flavor of Gelatin from Seabass (Lates calcarifer) skin

ABSTRACTEffects of different pretreatments of seabass skin and various drying methods on properties and fishy odor/flavor of resulting gelatin were evaluated. All gelatins contained α- and β-chains as the predominant components. Generally, a higher gel strength was found in the freeze-dried gelatin, compared with spray-dried counterpart (p < 0.05). Gel strength of gelatin decreased as the inlet temperature for spray drying increased (p < 0.05). All gelatin samples had creamy whitish color but became more yellow as the inlet temperature for spray drying increased. All gelatin gels were sponge- or coral-like in structure. Gelatin from skin pretreated with citric acid had lower fishy odor/flavor than that from skin pretreated using acetic acid. The lower fishy odor/flavor with coincidentally lower abundance of volatile compounds, including aldehydes, ketones, and alcohols, etc., was found in gelatin obtained by spray drying, in comparison with its freeze-dried counterpart. The lower fishy odor/flavor in spray-dried gelatin was in accordance with the lower thiobarbituric acid reactive substances and peroxide values. Thus, spray drying in conjunction with an appropriated pretreatment could be an effective method for production of gelatin with negligible undesirable fishy odor and flavor.

Mineralization and Characterization of Composite Lyophilized Gelatin Sponges Intended for Early Bone Regeneration.

The application of freeze-dried gelatin sponges as alternative bone grafting substitutes has many advantages, including the ability to swell, high porosity, tailorable degradation, and versatility to incorporate multiple components such as growth factors and nanofillers. The purpose of this study was to mineralize (M) and further characterize 1-Ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC) cross-linked gelatin sponges enhanced with preparations rich in growth factors, hydroxyapatite, and chitin whiskers (PHCE). Sponges were characterized for their swelling and in vitro mineralization potential, surface characteristics, protein release, mechanical properties, and MG-63 cell attachment and infiltration. All sponges swelled up to 50% of their original volume upon hydration. Scanning electron microscopy showed sparse mineral deposition for gelatin-M scaffolds while PHCE-M scaffolds exhibited more uniform mineral nucleation. Over 21 days, PHCE-M scaffolds cumulatively released significantly more (30%) of its initial protein content than all other scaffolds. PHCE-M scaffolds reported lower modulus values (1.3-1.6 MPa) when compared to gelatin control scaffolds (1.6-3.2 MPa). Increased cell attachment and infiltration was noticed on PHCE and PHCE-M scaffolds. The results of the study demonstrate the enhanced performance of PHCE and PHCE-M scaffolds to serve as bone healing scaffolds. Their potential to release incorporated factors, comparable composition/mechanical properties to tissues developed in the early stages of bone healing, and enhanced initial cellular response make them suitable for further studies evaluating more complex cellular interactions.

Stabilization of Microcapsules Using a Freeze-Dried Gelatin Matrix: Aqueous Redispersibility and the Ingredient Activity

Microcapsules are of great interest to the food and pharmaceutical industries as vehicles to deliver active ingredients to the gastrointestinal tract. Drying plays an important role in stabilizing microcapsules to prolong their lifetime; however, drying often produces undesirable changes in the microcapsules, such as irreversible aggregation of the microcapsules and activity loss of the encapsulated ingredient. In this work, poly(epsilon-caprolactone) microcapsules containing a model bioactive compound (tocopherol) were prepared and stabilized in a freeze-dried gelatin matrix. This dried product was rehydrated and the aqueous redispersibility of the microcapsules and the tocopherol activity were investigated. The experimental results suggested that a kinetic balance between dehydration (caused by freezing) and gel network formation is a critical factor that affects the redispersibility and ingredient activity of the products. It was further suggested that a hydrogel-based product could be strategically freeze dried to maximize product quality by tuning its freezing process; that is, by employing a controllable dehydration process.

PLGA Microspheres Incorporated Gelatin Scaffold: Microspheres Modulate Scaffold Properties

Freeze drying is one of the popular methods of fabrication for poly(lactide-co-glycolide) (PLGA) microspheres incorporated polymer scaffolds. However, the consequence of microspheres incorporation on physical and biological properties of scaffold has not been studied yet. In this study, attempt has been made to characterize the effect of PLGA microsphere incorporation on the physical properties of freeze-dried gelatin scaffold and its influence on cytocompatibility. Scaffolds loaded with varying amount of PLGA microspheres (10%, 1%, 0.1% w/w) were subjected to microarchitecture analysis, swelling, porosity, mechanical properties, biodegradation, cell adhesion, and cell proliferation studies. Results revealed that an increase in percentage loading of microspheres reduced the pore size and uniformity of the pore structure. Moreover, loading of PLGA microspheres up to 1% w/w significantly increased porosity, swelling, and mechanical properties of the scaffold but variations were not proportional for 10% w/w loading. Results also showed that PLGA microspheres have no significant effect on cell adhesion but influenced the growth kinetics.

The Effects of Cryoprotectants on the Survival Rate of Saccharomyces cerevisiae in a Freeze-Dried Gelatin Matrix

This study was carried out to determine the effects of cryoprotectants on yeast survival rate. Here, yeast was mixed with the following cryoprotectants: saccharose, hydroxyethylstarch, trehalose, lactose, caboxymethyl cellulose, and ?-carrageenan, and then frozen at -40°C, -30°C, and -18°C, respectively. The freeze-dried gelatin matrices were cut horizontally into 5 mm thick slices from the bottom and their pore sizes were measured. The freezing temperature (-40°C, -30°C, and -18°C) affected the freezing rate, and the partial freezing rate in the matrix was dependent on the distance. The higher the sample distance was from the bottom, the lower the partial freezing rate. We also found that the cryoprotectant concentration affected the freezing rate. Furthermore, the cryoprotectant and freezing rate affected the different survival rates of the yeast. The highest survival rate occurred with saccharose and trehalose, and was obtained by freezing at -40°C, which depended significantly on the concentration of trehalose. The ice dendrite sizes that formed during freezing at -40°C, -30°C, and -18°C showed a direct relationship with the freezing rate and cryoprotectant concentration. In the samples, the maximum primary ice dendrite size was 215.9 ?m at 1%, and the minimum primary ice dendrite size was 145.6 ?m at 5%, from the experiments at -18°C.

Bile salts secretion in cirrhosis.

The bile salts secretion was studied in ten normal subjects and sixteen patients with alcoholic cirrhosis, in a basal period and during 60 minutes after Secretin injection. Total bile salts were measured by a modification of the enzymatic method of Iwata and Yamasaki and the individual bile salts were separated by silica gel thin-layer chromatography. During the 60 minutes after Secretin the mean concentration was 2.88 +/- 2.58 muM/ml in normals and 1.96 +/- 1.25 muM/ml in cirrhotics. The difference is not significant. During the first 20 minutes however the concentration was higher than 3 muM/ml in 8 out of 10 normals and lower than 2 muM/ml in 10 out 16 cirrhotics. The ratios of tri-to dihydroxy bile salts was similar in both groups. The ratios between bile salts conjugated with glycine and with taurine was higher in normals, and the ratio between free to conjugated bile salts was higher in cirrhotics. The lower concentration of total bile salts immediatly after Secretin, the higher proportion of taurin conjugates and of free bile salts could be important factors in the difficulties of fact digestion and absorption frequently found in patients with alcoholic cirrhosis.

Thermal Unfolding of Gelatin in Solids as Affected by the Glass Transition

ABSTRACT: The thermal unfolding or denaturation of solid-state proteins during processing can affect their functionality. This project explored the relation between the glass transition temperature (Tg) and thermal unfolding temperature (Tm) using gelatin as a model system. Freeze-dried gelatin was prepared containing various polyol types at several concentrations. Using differential scanning calorimetry, Tm andTg were determined. Moisture and polyols (that is, glycerol, xylitol, sorbitol, sucrose, and trehalose) promoted a lowering of both Tg andTm, the extent of which depended upon the plasticizer type and concentration. For all the data, Tm > Tg, and a plot of Tm against Tg indicated a linear relationship (R2= 0.95). These results suggest that formulations must be in the rubbery state to have the necessary mobility for hydrogen bond disruption that leads to protein unfolding. Glass transition data should be considered when developing processing parameters for proteinaceous systems.

A gelatin coated collagen-polyglycolic acid composite membrane as a dural substitute.

We designed a new biodegradable composite membrane for use as a dural substitute. This membrane is composed of polyglycolic acid (PGA) mesh, collagen sponge, and gelatin sponge. Collagen layers are attached on both sides of the PGA mesh. One side of the membrane is coated with freeze-dried gelatin to prevent tissue adhesion. We examined the mechanical properties of the membrane and evaluated its efficacy in vivo by implanting it into dogs. When the mechanical properties of the membrane were measured under wet conditions, tensile strength and resistance against cutting by a suture were approximately 20 N/cm and 13 N, respectively, which are adequate for a surgical material. In the in vivo experiment, our dural substitute was implanted into six adult beagle dogs to repair a 25 x 15 mm defect in the dura mater. Two dogs each were killed at 2 and 4 months after implantation and two were observed over 6 months. At 4 months after implantation, the implanted dural substitute was almost absorbed and a fibrous membrane resembling native host dura had regenerated at the site. No foreign body reaction or significant adhesion to the cerebral cortex was observed. These results indicate the clinical potential of our novel dural substitute.

Effect of Porous Structure on the Degradation of Freeze-Dried Gelatin Hydrogels

Porous biodegradable hydrogels were prepared by glutaraldehyde crosslinking of acidic gelatin with an isoelectric point of 5.0, followed by freeze-drying. The inner structures of the freeze-dried hydrogels were strongly dependent on the preliminary freezing temperatures prior to freeze-drying. As the freezing temperature was raised, the pore size of the freeze-dried hydrogels increased while their wall thickness decreased. The hydrogels frozen at -20°C swell more rapidly in water than those at 408 and -196°C. In vivo and in vitro degradations of freeze-dried hydrogels with different inner structures were evaluated subcutis in mice and in a collagenase aqueous solution, respectively. The hydrogels prepared at -20°C were more rapidly degraded both in vitro and in vivo, compared to those at -80° and -196°C. The hydrogels freeze-dried at -196°C had the smallest pore size, thickest gelatin walls, and required a longer time for complete degradation. Basic fibroblast growth factor (bFGF) was impregnated into the gelatin hydrogels and the in vitro bFGF release was evaluated. No influence by the inner structure on the release profile of bFGF was observed. Since bFGF is ionically completed with acidic gelatin, it is possible that it was released from these gelatin hydrogels in a similar fashion, irrespective of the hydrogel inner structure.

Distribution of ions in Neurospora crassa determined by quantitative electron microprobe analysis.

It was investigated whether the low membrane potential at the tip of hyphae ofNeurospora crassa could be described as a diffusion potential. The distribution of Na, K and P inNeurospora was measured by electron microprobe analysis of freeze-dried hyphae. Quantitative determinations were made with freeze-dried gelatin standards and with crystalline standards. The local concentrations of Na and K were in accordance with the theory that at the tip of the hyphe, these ions are distributed passively across the plasma membrane.