Biomaterials (v.26, #31)

Calendar (I).

Synthesis and characterization of porous β -tricalcium phosphate blocks by M. Bohner; G.H. van Lenthe; S. Grünenfelder; W. Hirsiger; R. Evison; R. Müller (6099-6105).
Porous β -tricalcium phosphate ( β -TCP) blocks with four different macropore sizes (pore larger than 50 μm) were synthesized using “calcium phosphate emulsions”, and characterized by optical, geometrical, gravimetric, and radiological methods. The reproducibility of the synthesis method was excellent. Moreover, the macropore size could be easily controlled without modifying the microporosity (pore smaller than 50 μm) or the total porosity (microporosity+macroporosity). Based on the initial composition of the blocks and their final apparent density, the microporosity, macroporosity, and the total block porosity were calculated to be close to 21%, 54%, and 75%, respectively. These values were confirmed by microcomputed tomography (μCT). The mean macropore diameters were close to 150, 260, 510 and 1220 μm, as measured optically. Consistenly lower values (25% lower) were obtained by μCT, but the linear correlation between μCT and optical method was high ( r 2 > 0.97 ). The macropore size distribution calculated from μCT scans appears to be narrow and normally distributed. The very good correlation between the results of the various methods and the possibility to determine the pore size distribution suggest that μCT is an ideal tool to non-destructively characterize macroporous calcium phosphate bone substitutes.
Keywords: Pore; Size; Micro-computed tomography; Calcium phosphate; Bone;

Slow crack growth behaviour of hydroxyapatite ceramics by Chahid Benaqqa; Jerome Chevalier; Malika Saädaoui; Gilbert Fantozzi (6106-6112).
Among materials for medical applications, hydroxyapatite is one of the best candidates in orthopedics, since it exhibits a composition similar to the mineral part of bone. Double torsion technique was here performed to investigate slow crack growth behaviour of dense hydroxyapatite materials. Crack rate, V, versus stress intensity factor, K I, laws were obtained for different environments and processing conditions. Stress assisted corrosion by water molecules in oxide ceramics is generally responsible for slow crack growth. The different propagation stages obtained here could be analyzed in relation to this process. The presence of a threshold defining a safety range of use was also observed. Hydroxyapatite ceramics appear to be very sensitive to slow crack growth, crack propagation occurring even at very low K I. This can be explained by the fact that they contain hydroxyl groups (HAP: Ca10(PO4)6(OH)2), favouring water adsorption on the crack surface and thus a strong decrease of surface energy in the presence of water. This study demonstrates that processing conditions must be carefully controlled, specially sintering temperature, which plays a key role on V–K I laws. Sintering at 50 °C above or below the optimal temperature, for example, may shift the V–K I law towards very low stress intensity factors. The influence of ageing is finally discussed.
Keywords: Ageing; Crack growth; Fracture toughness; Hydroxyapatite; Mechanical properties;

The self-setting properties and in vitro bioactivity of tricalcium silicate by Wenyuan Zhao; Junying Wang; Wanyin Zhai; Zheng Wang; Jiang Chang (6113-6121).
In this study, tricalcium silicate (Ca3SiO5), as a new promising injectable bioactive material, was employed to investigate its physical and chemical properties for an injectable bioactive cement filler. The workable Ca3SiO5 pastes with a liquid to powder (L/P) ratio of 0.8–1.2 ml g−1could be injected for 15–60 min (nozzle diameter 2.0 mm). The setting process yielded cellular structures with compressive strength of 6.4–20.2 MPa after 2–28 days. The in vitro bioactivity of Ca3SiO5 paste was investigated by soaking in simulated body fluid (SBF) for various periods. The result showed that the Ca3SiO5 paste could induce hydroxyapatite (HA) formation and dissolve slowly in SBF. The result of indirect cytotoxicity evaluation indicated that Ca3SiO5 paste had a stimulatory effect on cell growth in a certain concentration range. The exothermic process showed that Ca3SiO5 had lower heat evolution rate during the hydration as compared to calcium phosphate cement (CPC). Our results indicated that Ca3SiO5 paste was bioactive and dissolvable, and it is a progressive candidate for further investigation as injectable tissue repairing substitute.
Keywords: Tricalcium silicate; Injectability; Self-setting; Bioactivity; Cell proliferation;

AC electrospray biomaterials synthesis by Leslie Y. Yeo; Zachary Gagnon; Hsueh-Chia Chang (6122-6128).
A rapid, viable and safe fabrication method for biomaterials synthesis is reported using high-frequency AC electrospraying. We demonstrate its potential for polymeric nanoparticle fabrication, drug encapsulation in mono-dispersed micron-sized biodegradable polymer shells and the synthesis of 1 μm biodegradable fibers with adjustable pore sizes as bioscaffolds for tissue/orthopaedic engineering and wound care therapy. The absence of charge in the ejected drops and fibers facilitates pulmonary drug delivery, polymer encapsulation and minimizes protein/DNA denaturing or compound ionization.
Keywords: Electrospraying; Microencapsulation; Bioscaffold; Nanoparticles; Biodegradable polymer;

Improvement of surface bioactivity on titanium by water and hydrogen plasma immersion ion implantation by Youtao Xie; Xuanyong Liu; Anping Huang; Chuanxian Ding; Paul K. Chu (6129-6135).
We have investigated the surface bioactivity of titanium after water and hydrogen plasma immersion ion implantation. Plasma immersion ion implantation (PIII) excels in the surface treatment of components possessing a complicated shape such as medical implants. In addition, water and hydrogen PIII has been extensively studied as a method to fabricate silicon-on-insulator (SOI) substrates in the semiconductor industry and so it is relatively straightforward to transfer the technology to the biomedical field. In our investigation, water and hydrogen were plasma-implanted into titanium sequentially. Our objective is that water PIII introduces near-surface damages that trap hydrogen implanted in the subsequent step to improve the surface bioactivity while the desirable bulk properties of the materials are not compromised. Ti–OH functional groups can be detected on the (H2O+H2)-implanted titanium surface by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. After incubation in simulated body fluids (SBF) for cytocompatibililty evaluation in vitro, bone-like hydroxyapatite was found to precipitate on the (H2O+H2) implanted samples while no apatite was found on titanium samples plasma implanted with water or hydrogen alone. Human osteoblast cells were cultured on the (H2O+H2)-implanted titanium surface and they exhibited good adhesion and growth. Our results suggest a practical means to improve the surface bioactivity and cytocompatibility of medical implants made of titanium.
Keywords: Titanium; Plasma immersion ion implantation; Bioactivity; Cytocompatibility; Water; Hydrogen;

Recent studies have revealed that visible-light (VL)-irradiated camphorquinone (CQ), in the presence of a tertiary amine (e.g., N,N-dimethyl-p-toluidine, DMT), generates initiating radicals that may indiscriminately react with molecular oxygen forming reactive oxygen species (ROS). In this study, the ability of the antioxidants N-acetyl-l-cysteine (NAC) and ascorbic acid (AA) to reduce intracellular oxidative stress induced by VL-irradiated CQ/DMT or VL-irradiated hydrogen peroxide (H2O2) was assessed in an immortalized Murine cementoblast cell line (OCCM.30) and an immortalized Murine fibroblast cell line, 3T3-Swiss albino (3T3). Intracellular oxidative stress was measured with the membrane permeable dye, 2′,7′-dichlorodihydrofluorescein diacetate (H2DCF-DA). VL-irradiated CQ/DMT and VL-irradiated H2O2 each produced significantly ( p < 0.001 ) elevated intracellular oxidative levels in both cell types compared to intracellular ROS levels in VL-irradiated untreated cells. OCCM.30 cementoblasts were found to be almost twice as sensitive to VL-irradiated CQ/DMT and VL-irradiated H2O2 treatment compared to 3T3 fibroblasts. Furthermore, 10 mm NAC and 10 mm AA each eliminated oxidative stress induced by VL-irradiated CQ/DMT and VL-irradiated H2O2 in both cell types. Our results suggest that NAC and AA may effectively reduce or eliminate oxidative stress in cells exposed to VL-irradiated CQ/DMT following polymerization.
Keywords: Camphorquinone; Ascorbic acid; N-acetyl-l-cysteine; Reactive oxygen species; Oxidative stress; Antioxidants;

Plasma-treated nanostructured TiO2 surface supporting biomimetic growth of apatite by Xuanyong Liu; Xiaobing Zhao; Ricky K.Y. Fu; Joan P.Y. Ho; Chuanxian Ding; Paul K. Chu (6143-6150).
Although some types of TiO2 powders and gel-derived films can exhibit bioactivity, plasma-sprayed TiO2 coatings are always bioinert, thereby hampering wider applications in bone implants. We have successfully produced a bioactive nanostructured TiO2 surface with grain size smaller than 50 nm using nanoparticle plasma spraying followed by hydrogen plasma immersion ion implantation (PIII). The hydrogen PIII nano-TiO2 coating can induce bone-like apatite formation on its surface after immersion in a simulated body fluid. In contrast, apatite cannot form on either the as-sprayed TiO2 surfaces (both <50 nm grain size and >50 nm grain size) or hydrogen-implanted TiO2 with grain size larger than 50 nm. Hence, both a hydrogenated surface that gives rise to negatively charged functional groups on the surface and small grain size (<50 nm) that enhances surface adsorption are crucial to the growth of apatite. Introduction of surface bioactivity to plasma-sprayed TiO2 coatings, which are generally recognized to have excellent biocompatibility and corrosion resistance as well as high bonding to titanium alloys, makes them more superior than many current biomedical coatings.
Keywords: Nanostructured TiO2; Bioactivity; Plasma spraying; Apatite; Hydrogen; Plasma immersion ion implantation;

Bioactivation of inert alumina ceramics by hydroxylation by Horst Fischer; Christopher Niedhart; Nadine Kaltenborn; Andreas Prange; Rudolf Marx; Fritz Uwe Niethard; Rainer Telle (6151-6157).
Alumina ceramics (Al2O3) are frequently used for medical implants and prostheses because of the excellent biocompatibility, and the high mechanical reliability of the material. Inauspiciously alumina is not suitable for implant components with bone contact, because the material is bioinert and thereby no bony ongrowth, and subsequently loosening of the implant occurs. Here, we present a new method to bioactivate the surface of the material. Specimens made of high purity alumina were treated in sodium hydroxide. Cell culture tests with osteoblast-like cells as well as spectroscopical and mechanical tests were performed. Aluminium hydroxide groups were detected on the surface of the treated specimens. Enhanced cell adhesion, proliferation and secretion of osteocalcin were determined after hydroxylation. The bioactivating treatment had no deteriorating effect on the short- and long-term strength behaviour. Our results indicate that the described surface technique could be used to develop a new class of osseointegrative high-strength ceramic implants.
Keywords: Alumina; Suface treatment; Cell activation; Mechanical properties; Spectroscopy;

A histological evaluation for guided bone regeneration induced by a collagenous membrane by Yuya Taguchi; Norio Amizuka; Masayoshi Nakadate; Hideo Ohnishi; Noritaka Fujii; Kimimitsu Oda; Shuichi Nomura; Takeyasu Maeda (6158-6166).
This study was designed to evaluate the histological changes during ossification and cellular events including osteogenic differentiation responding to collagenous bioresorbable membranes utilized for GBR. Standardized artificial bony defects were prepared at rat maxillae, and covered with a collagenous bioresorbable membrane. These animals were sacrificed at 1, 2, 3 and 4 weeks after the GBR-operation. The paraffin sections were subject to tartrate resistant acid phosphatase (TRAP) enzyme histochemistry and immunohistochemistry for alkaline phosphatase (ALP), osteopontin (OP) and osteocalcin (OC). In the first week of the experimental group, woven bone with ALP-positive osteoblasts occupied the lower half of the cavity. The collagenous membrane included numerous ALP-negative cells and OP-immunoreactive extracellular matrices. At 2 weeks, the ALP-, OP- and OC-immunoreactivity came to be recognizable in the region of collagenous membrane. Since ALP-negative soft tissue separated the collagenous membrane and the new bone originating from the cavity bottom, the collagenous membrane appeared to induce osteogenesis in situ. At 3 weeks, numerous collagen fibers of the membrane were embedded in the adjacent bone matrix. At 4 weeks, the membrane-associated and the cavity-derived bones had completely integrated, showing the same height of the periosteal ridge as the surrounding alveolar bones. The collagen fibers of a GBR-membrane appear to participate in osteogenic differentiation.
Keywords: Guided bone regeneration (GBR); Resorbable membrane; Osteoblast; Bone defect; Bone formation;

Recently, cell-based approaches utilizing adipogenic progenitor cells for fat tissue engineering have been developed and reported to have success in promoting in vivo adipogenesis and the repair of defect sites. For autologous applications, human bone marrow-derived mesenchymal stem cells (MSCs) have been suggested as a potential cell source for adipose tissue engineering applications due to their ability to be isolated and ex vivo expanded from adult bone marrow aspirates and their versatility for pluripotent differentiation into various mesenchymal lineages including adipogenic. Due to the relatively low frequency of MSCs present within bone marrow, extensive ex vivo expansion of these cells is necessary to obtain therapeutic cell populations for tissue engineering strategies. Currently, utilization of MSCs for adipose tissue engineering is limited due to the attenuation of their adipogenic differentiation potential following extensive ex vivo expansion on conventional tissue culture plastic (TCP) substrates. In the present study, the ability of a denatured collagen type I (DC) matrix to preserve MSC adipogenic potential during ex vivo expansion was examined. Adipocyte-related markers and functions were examined in vitro in response to adipogenic culture conditions for 21 days in comparison to early passage MSCs and late passage MSCs ex vivo expanded on TCP. The results demonstrated significant preservation of the ability of late passage MSCs ex vivo expanded on the DC matrix to express adipogenic markers (fatty acid-binding protein-4, lipoprotein lipase, acyl-CoA synthetase, adipsin, facilitative glucose transporter-4, and accumulation of lipids) similar to the early passage cells and in contrast to late passage MSCs expanded on TCP. The ability of the DC matrix to preserve adipocyte-related markers and functions of MSCs following extensive ex vivo expansion represents a novel culture technique to expand functional adipogenic progenitors for tissue engineering applications.
Keywords: Mesenchymal stem cell; Adipose tissue engineering; Collagen;

Electrospun chitosan-based nanofibers and their cellular compatibility by Narayan Bhattarai; Dennis Edmondson; Omid Veiseh; Frederick A. Matsen; Miqin Zhang (6176-6184).
Chitosan-based nanofibers with an average fiber diameter controllable from a few microns down to ∼40 nm and a narrow size distribution were fabricated by electrospinning solutions containing chitosan, polyethylene oxide (PEO), and Triton X-100™. Rheological study showed a strong dependence of spinnability and fiber morphology on solution viscosity and thus on chitosan-to-PEO ratio. The nanofibers can be deposited either as a nonwoven mat or as a highly aligned bundle of controllable size. Potential use of this nanofibrous matrix for tissue engineering was studied by examining its integrity in water and cellular compatibility. It was found that the matrix with a chitosan/PEO ratio of 90/10 retained excellent integrity of the fibrous structure in water. Experimental results from cell stain assay and SEM imaging showed that the nanofibrous structure promoted the attachment of human osteoblasts and chondrocytes and maintained characteristic cell morphology and viability throughout the period of study. This nanofibrous matrix is of particular interest in tissue engineering for controlled drug release and tissue remodeling.
Keywords: Chitosan; Nanofiber; Electrospinning; Biodegradable; Scaffold;

The effect of RGD peptide-conjugated magnetite cationic liposomes on cell growth and cell sheet harvesting by Akira Ito; Kousuke Ino; Takeshi Kobayashi; Hiroyuki Honda (6185-6193).
Tissue engineering requires novel technologies for establishing 3D constructs, and the layered method of culturing cell sheets (cell sheet engineering) is one potentially useful approach. In the present study, we investigated whether coating the culture surface with RGD (Arg–Gly–Asp) peptide-conjugated magnetite cationic liposomes (RGD-MCLs) was able to facilitate cell growth, cell sheet construction and cell sheet harvest using magnetic force without enzymatic treatment. To promote cell attachment, an RGD-motif-containing peptide was coupled to the phospholipid of our original magnetite cationic liposomes (MCLs). The RGD-MCLs were added to a commercially available 24-well ultra-low-attachment plate the surface of which comprised a covalently bound hydrogel layer that was hydrophilic and neutrally charged. A magnet was placed on the underside of the well in order to attract the RGD-MCLs to the surface of the well, and then NIH/3T3 cells were seeded into the well. Cells adhered to the bottom of the culture surface, which was coated with RGD-MCLs, and the cells spread and proliferated to confluency. After incubation, the magnet was removed and the cells were detached from the bottom of the plates, forming a contiguous cell sheet. Because the sheets contained magnetite nanoparticles, they could be harvested using a magnet inserted into the well. These results suggest that this novel methodology using RGD-MCLs and magnetic force, which we have termed ‘magnetic force-based tissue engineering (Mag-TE)’, is a promising approach for tissue engineering.
Keywords: Magnetite nanoparticles; Liposomes; RGD peptide; Tissue engineering; Cell culture;

The effect of matrix composition of 3D constructs on embryonic stem cell differentiation by Sabrina Battista; Daniela Guarnieri; Cristina Borselli; Stefania Zeppetelli; Assunta Borzacchiello; Laura Mayol; Diego Gerbasio; Douglas R. Keene; Luigi Ambrosio; Paolo A. Netti (6194-6207).
The use of embryonic stem (ES) cells as unlimited cell source in tissue engineering has ignited the hope of regenerating any kind of tissue in vitro. However, the role of the material in control and guidance of their development and commitment into complex and viable three-dimensional (3D) tissues is still poorly understood. In this work, we investigate the role of material composition and structure on promoting ES cells growth and differentiation, by culturing mouse ES cell-derived embryoid bodies (EBs) in various semi-interpenetrating polymer networks (SIPNs), made of collagen, fibronectin (FN) and laminin (LM). We show that both composition and strength of the supportive matrix play an important role in EBs development. High collagen concentrations inhibit EBs cavitation and hence the following EBs differentiation, by inhibiting apoptosis. The presence of FN in 3D collagen constructs strongly stimulates endothelial cell differentiation and vascularization. Conversely, LM increases the ability of ES cells to differentiate into beating cardiomyocytes. Our data suggest that matrix composition has an important role in EBs development and that it is possible to influence stem cell differentiation toward preferential pattern, by modulating the physical and biochemical properties of the scaffold.
Keywords: Stem cell; Collagen; Fibronectin; Laminin;

Titanium fiber mesh scaffolds have been shown to be a suitable material for culture of primary marrow stromal cells in an effort to create tissue engineered constructs for bone tissue replacement. In native bone tissue, these cells are known to attach to extracellular matrix molecules via integrin receptors for specific peptide sequences, and these attachments can be a source of cell signaling, affecting cell behaviors such as differentiation. In this study, we examined the ability of primary rat marrow stromal cells at two different stages of osteoblastic differentiation to further differentiate into osteoblasts both in vitro and in vivo when seeded on titanium fiber mesh scaffolds either with or without RGD peptide tethered to the surface. In vitro, the tethered RGD peptide resulted in reduced initial cell proliferation. In vivo, there was no effect of tethered RGD peptide on ectopic bone formation in a rat subcutaneous implant model. Scaffold/cell constructs exposed to dexamethasone for 4 days prior to implantation (+dex constructs) resulted in significant bone formation whereas no bone formation was observed in −dex constructs. These results show that the osteoblastic differentiation of marrow stromal cells was not dependent on surface tethered RGD peptide, and that the initial differentiation stage of implanted cells plays an important role in bone formation in titanium fiber mesh bone tissue engineering constructs.
Keywords: Marrow stromal cell; Osteoblast; RGD; Titanium; Bone tissue engineering;

Esophageal epithelial cell interaction with synthetic and natural scaffolds for tissue engineering by Benjamin L. Beckstead; Sheng Pan; Amit D. Bhrany; Andrés M. Bratt-Leal; Buddy D. Ratner; Cecilia M. Giachelli (6217-6228).
As an initial step towards a tissue-engineered esophagus, rat esophageal epithelial cells (REEC) were isolated and characterized for epithelial identity, adhesion protein preference, and in vitro interaction with natural and synthetic scaffolds. The scaffolds consisted of AlloDerm (LifeCell Corporation, Branchburg, NJ), poly(l-lactic acid) (PLLA), poly(lactic-co-glycolic) acid (75:25) (PLGA75), poly(lactic-co-glycolic) acid (50:50) (PLGA50), and polycaprolactone/poly(l-lactic acid) (50:50) (PCL/PLLA). Various factors—including calcium concentration, scaffold composition, and pore size—were evaluated for their influence on epithelial growth and differentiation. By day 18, keratinocytes seeded on AlloDerm cultured under high Ca++ (1.5 mm) conditions showed a proliferating basal cell layer, epithelial stratification (5–6 layers) and a thick keratin layer. The synthetic scaffolds (PLGA, PLLA, PCL/PLLA) also showed complete surface coverage, regions of proliferating basal cells, and evidence of stratification (2–3 layers) and keratinization. The highly porous nature of the synthetic scaffolds, however, limited the formation of a continuous epithelial layer and resulted in a lack of overall spatially-defined differentiation. In conclusion, rat esophageal epithelial cells were successfully isolated and characterized, with cells seeded on AlloDerm showing superior epithelial organization and stratification compared to synthetic scaffolds. Modification of the synthetic scaffold's surface properties and pore size may be necessary to mimic epithelial behavior on natural scaffolds.
Keywords: Epithelial cell; Keratinocyte; Polycaprolactone; Poly(glycolic acid); Poly(lactic acid); Scaffold;

Biological fabrication of nacreous coating on titanium dental implant by Xiao-Xiang Wang; Lei Xie; Rizhi Wang (6229-6232).
Titanium screws with 3.5 mm diameter and 8 mm length, as well as titanium flat sheets with size 4 mm×8 mm×0.3 mm, were implanted into the epithelial mantle pearl sacs of a fresh water bivalve (Hyriopsis cumingii Lea) by replacing the pearls. After 45 days of cultivation, the implant surfaces were deposited with a nacre coating with iridescent luster. The coating could conform to some extent the thread topography of the screw implant and was about 200–600 μm in thickness. The coating was composed of a laminated nacreous layer and a transitional non-laminated layer that consisted mainly of vaterite and calcite polymorphs of calcium carbonate. The transitional layer was around 2–10 μm thick in the convex and flat region of the implant surface and could form close contact with titanium surface; while the transitional layer was much thicker in the steep concave regions and could not form close contact with the titanium surface. The reasons for inhomogeneity in thickness and the variation in interface character were discussed and the improvement to the design of the dental implant with respect to this coating method was suggested in the paper. The results suggest that it is possible to fabricate a biologically active and degradable, and mechanically tough and strong nacre coating on titanium dental implant by this novel coating technology.
Keywords: Nacre; Biomineralization; Nacreous coating; Dental implant;

Different principles for production of “autologous fibrin sealant” have been established, and commercial devices employing these methods are nowadays available and used in clinical routine. Users might anticipate for these autologous fibrin sealants features comparable to commercial homologous fibrin sealants, used in surgical routine for many years. However, only little is known about biochemical properties, formation, cross-linking and stability of fibrin sealant clots produced for autologous use with the aid of commercially available devices.We have investigated protein composition, formation and stability of clots obtained from autologuous fibrin sealants produced with commercially available devices (CryoSeal® and Vivostat®) and compared these parameters to those of the industrially produced homologous fibrin sealant Tissucol/Tisseel®.The CryoSeal® product is a mixture of many plasma proteins; the Vivostat® product and Tissucol/Tisseel® appear as comparatively pure plasma derivatives. The products differ in their protein composition and concentrations, including their concentration in fibrin. Significant fibrin α and γ -chain cross-linking by FXIIIa occurs only in Tissucol/Tisseel® clots. In test tubes CryoSeal® and Vivostat® (tranexamic acid-free formulation) fibrin clots liquefy within 1–2 days, but Vivostat® (tranexamic acid containing formulation) clots were stable for 4 days and showed partial liquefaction after 5 days. Tissucol/Tisseel® clots, containing the protease inhibitor aprotinin, appeared unchanged over the observation period of 5 days. In an in vitro model mimicking in vivo conditions (diffusion of protease inhibitors and proteolytic digestion) clot liquefaction occurs at day 1 for all autologous fibrin sealants clots, with an observable delay for the tranexamic acid containing Vivostat®, and day 5 for Tissucol/Tisseel® clots.Characterization of the CryoSeal® and Vivostat® fibrin sealants and Tissucol/Tisseel® and their performance show a clear difference in biochemical properties.
Keywords: Wound closure; Fibrin sealant; Fibrinogen; Fibrin cross-linking;

Characterization and biocompatibility of organogels based on l-alanine for parenteral drug delivery implants by Aude Motulsky; Michel Lafleur; Anne-Claude Couffin-Hoarau; Didier Hoarau; Frank Boury; Jean-Pierre Benoit; Jean-Christophe Leroux (6242-6253).
The development of simple and efficient drug delivery systems for the sustained release of peptides/proteins and low molecular weight hydrophilic molecules is an ongoing challenge. The purpose of this work was to prepare and characterize novel biodegradable in situ-forming implants obtained via the self-assembly of l-alanine derivatives in pharmaceutical oils. Six different amphiphilic organogelators based on l-alanine were synthesized. These derivatives could successfully gel various vegetable and synthetic oils approved for parenteral administration. Gelation was thermoreversible, and phase transition temperatures depended on gelator structure, concentration and solvent. Hydrogen bonds and van der Waals interactions were shown to be the main forces implicated in network formation. Selected formulations were then injected subcutaneously in rats for preliminary assessment of biocompatibility. Histopathological analysis of the surrounding tissues revealed mild, chronic inflammation and an overall good biocompatibility profile of the implants over the 8 wk evaluation period. This study demonstrates that in situ-forming organogels represent a potentially promising platform for sustained drug delivery.
Keywords: In situ-forming implant; Biocompatibility; Controlled drug release; Organogel;

Multiscale structure of sheet nacre by Marthe Rousseau; Evelyne Lopez; Philippe Stempflé; Marcel Brendlé; Loïc Franke; Alain Guette; Roger Naslain; Xavier Bourrat (6254-6262).
This work was conducted on Pinctada maxima nacre (mother of pearl) in order to understand its multiscale ordering and the role of the organic matrix in its structure. Intermittent-contact atomic force microscopy with phase detection imaging reveals a nanostructure within the tablet. A continuous organic framework divides each tablet into nanograins. Their shape is supposed to be flat with a mean extension of 45 nm. TEM performed in the darkfield mode evidences that at least part of the intracrystalline matrix is crystallized and responds like a ‘single crystal’. The tablet is a ‘hybrid composite’. The organic matrix is continuous. The mineral phase is thus finely divided still behaving as a single crystal. It is proposed that each tablet results from the coherent aggregation of nanograins keeping strictly the same crystallographic orientation thanks to a hetero-epitaxy mechanism. Finally, high-resolution TEM performed on bridges from one tablet to the next, in the overlying row, did not permit to evidence a mineral lattice but crystallized organic bridges. The same organic bridges were evidenced by SEM in the interlaminar sequence.
Keywords: Nacre; Aragonite; Nanocomposite; Biomineralization; AFM; TEM;