Biomaterials (v.27, #26)
Editorial board (CO2).
The effect of natural extracellular matrix deposited on synthetic polymers on cultured primary hepatocytes by Takashi Hoshiba; Chong Su Cho; Akiko Murakawa; Yoshio Okahata; Toshihiro Akaike (4519-4528).
It is well known that natural extracellular matrix (ECM) molecules are deposited on the surface of biomaterials during culture of cells and affect cellular behaviors. However, it has not been fully understood what kinds of ECM molecules are deposited on the surface of biomaterials although the cellular behaviors were affected by deposited ECM. In this study, to investigate the effect of deposited natural ECM on behaviors of hepatocytes cultured on biomaterials such as poly (N-p-vinylbenzyl-4-O-β-d-galactopyranosyl-d-gluconamide) (PVLA) as a hepatocyte-specific matrix and poly (l-lysine) (PLL) as a non-specific one during the culture of hepatocytes in vitro, we investigated expression pattern of ECM genes and adsorption of ECM molecules onto PVLA- and PLL-coated surfaces. It was found that the expression levels of type I collagen and fibronectin genes in the hepatocytes cultured on PVLA-coated surface were different from them in the hepatocytes cultured on PLL-coated one. Also, the results showed that laminin was dominantly deposited on PVLA-coated surface whereas fibronectin was dominantly deposited on PLL-coated one. Hepatocytes maintained liver-specific functions on PVLA- and laminin-coated surfaces. It is thought that deposited laminin during the culture of hepatocytes affects the liver-specific functions of hepatocytes cultured on PVLA-coated surface.
Keywords: Hepatocyte; Extracellular matrix; Laminin; Fibronectin; Adsorption;
Monitoring cell adhesion on tantalum and oxidised polystyrene using a quartz crystal microbalance with dissipation by Megan Susan Lord; Charlotte Modin; Morten Foss; Mogens Duch; Anne Simmons; Finn S. Pedersen; Bruce K. Milthorpe; Flemming Besenbacher (4529-4537).
The quartz crystal microbalance with dissipation (QCM-D) (Q-Sense AB, Sweden) has been established as a useful tool for evaluating interactions between various biological and non-biological systems, and there has been increasing interest in using the QCM-D technique for cell monitoring applications. This study investigated the potential of the QCM-D to characterise the initial adhesion and spreading of cells in contact with protein precoated biocompatible surfaces. The QCM-D technique is attractive for monitoring cell adhesion and spreading as it allows in situ real-time measurements. The adhesion of NIH3T3 (EGFP) fibroblasts to tantalum (Ta) and oxidised polystyrene (PSox) surfaces precoated with serum proteins was examined using the QCM-D for a period of either 2 or 4 h. Time-lapse photography was performed at 30 min intervals to visually examine cell adhesion and spreading in order to relate cell morphology to the QCM-D response.Following adsorption of albumin, fibronectin or newborn calf serum onto the surfaces, QCM-D measurements showed that cells adhered and spread on the fibronectin and serum coated surfaces, while few cells adhered to the albumin coated surfaces. Cells adhered to albumin coated surfaces had a rounded morphology. The responses to fibronectin and serum precoated surfaces were quite different for each of the underlying substrates indicating that the process of cell adhesion and spreading elicits different responses depending on both the protein coating composition and the influence of the underlying substrate. The different response may be due to extracellular matrix remodelling as well as cytoskeletal changes. Frequency (f) and dissipation (D) changes associated with cell adhesion were less than would be expected from the Sauerbrey relation due to the viscoelastic properties of the cells.
Keywords: Quartz crystal microbalance; Cell adhesion; Fibroblast; Protein adsorption; Polystyrene; Tantalum;
Evaluation of mammalian cell adhesion on surface-modified porous silicon by Suet Peng Low; Keryn A. Williams; Leigh T. Canham; Nicolas H. Voelcker (4538-4546).
Porous silicon is a promising biomaterial that is non-toxic and biodegradable. Surface modification can offer control over the degradation rate and can also impart properties that promote cell adhesion. In this study, we modified the surface of porous silicon surface by ozone oxidation, silanisation or coating with collagen or serum. For each surface, topography was characterised using atomic force microscopy, wettability by water contact angle measurements, degradation in aqueous buffer by interferometric reflectance spectroscopy and surface chemistry by Fourier-transform infrared spectroscopy. The adhesion of rat pheochromocytoma (PC12) and human lens epithelial cells to these surfaces was investigated. Cells were incubated on the surfaces for 4 and 24 h, and adhesion characteristics were determined by using a fluorescent vital stain and cell counts. Collagen coated and amino silanised porous silicon promoted cell attachment for both cell lines whereas cells attached poorly to ozone oxidised and polyethylene glycol silanised surfaces. We showed that the two cell lines had different adhesion characteristics on the various surfaces at different time points. The use of the vitality assays Alamar Blue (redox based assay) and neutral red (active cellular uptake assay) with porous silicon was also investigated. We reveal incompatibilities between certain resazurin (Alamar Blue), lysosomal incorporation assays (neutral red) and porous silicon.
Keywords: Porous silicon; Surface modification; Cell adhesion; Biodegradable materials; Vitality assays;
Strong binding of bioactive BMP-2 to nanocrystalline diamond by physisorption by Doris Steinmüller-Nethl; Frank R. Kloss; Muhammed Najam-Ul-Haq; Matthias Rainer; Karin Larsson; Christian Linsmeier; Gottfried Köhler; Christine Fehrer; Günter Lepperdinger; Xianjie Liu; Norbert Memmel; Erminald Bertel; Christian W. Huck; Robert Gassner; Günther Bonn (4547-4556).
Nano-crystalline diamond (NCD)-coated surfaces were efficiently functionalized with bone morphogenetic protein-2 (BMP-2) by means of physisorption. Due to their randomly oriented texture, NCD-coated surfaces appear to bind complex molecules firmly. Applying various highly sensitive analytical methods, the interaction was found extremely stable. The strength of the experimentally measured adherence between BMP-2 and NCD was further corroborated by theoretical calculations. Oxygen treatment rendered NCD hydrophilic by the appearance of surface oxygen containing groups. This particular NCD surface exhibited even higher binding energies towards BMP-2 than the hydrophobic surface, and this surface was also favoured by cultured cells. Most importantly in this context, bound BMP-2 was found fully active. When cultured on BMP-2-treated NCD, osteosarcoma cells strongly up-regulated alkaline phosphatase, a specific marker for osteogenic differentiation. Hence, this simple method will allow generating highly versatile surfaces with complex biomimetic coatings, essentials for novel medical devices and implants as well as for innovative scaffolds in tissue engineering.
Keywords: Physisorption; BMP-2; Bone tissue engineering; Nanocrystalline; Diamond;
In vitro biodegradation of three brushite calcium phosphate cements by a macrophage cell-line by Zhidao Xia; Liam Michael Grover; Yizhong Huang; Iannis E. Adamopoulos; Uwe Gbureck; James T. Triffitt; Richard M. Shelton; Jake E. Barralet (4557-4565).
Depending upon local conditions, brushite (CaHPO4·2H2O) cements may be largely resorbed or (following hydrolysis to hydroxyapatite) remain stable in vivo. To determine which factors influence cement resorption, previous studies have investigated the solution-driven degradation of brushite cements in vitro in the absence of any cells. However, the mechanism of cell-mediated biodegradation of the brushite cement is still unknown. The aim of the current study was to observe the cell-mediated biodegradation of brushite cement formulations in vitro. The cements were aged in the presence of a murine cell line (RAW264.7), which had the potential to form osteoclasts in the presence of the receptor for nuclear factor kappa B ligand (RANKL) in vitro, independently of macrophage colony stimulating factor (M-CSF). The cytotoxicity of the cements on RAW264.7 cells and the calcium and phosphate released from materials to the culture media were analysed. Scanning electron microscopy (SEM) and focused ion beam (FIB) microscopy were used to characterise the ultrastructure of the cells. The results showed that the RAW264.7 cell line formed multinucleated TRAP positive osteoclast-like cells, capable of ruffled border formation and lacunar resorption on the brushite calcium phosphate cement in vitro. In the osteoclast-like cell cultures, ultrastuctural analysis by SEM revealed phenotypic characteristics of osteoclasts including formation of a sealing zone and ruffled border. Penetration of the surface of the cement, was demonstrated using FIB, and this showed the potential demineralising effect of the cells on the cements. This study has set up a useful model to investigate the cell-mediated cement degradation in vitro.
Keywords: Brushite; Calcium phosphate cements; Biodegradation; Macrophage; Osteoclast; Focused ion beam microscopy (FIB);
Injectable calcium phosphate scaffold and bone marrow graft for bone reconstruction in irradiated areas: An experimental study in rats by Emmanuelle Lerouxel; Pierre Weiss; Bernard Giumelli; Anne Moreau; Paul Pilet; Jérôme Guicheux; Pierre Corre; Jean-Michel Bouler; Guy Daculsi; Olivier Malard (4566-4572).
The purpose of this study was to assess the possibilities for bone reconstruction of an injectable calcium phosphate scaffold (ICPS) associated with a bone marrow (BM) graft after irradiation in a rat model. External irradiation was delivered to 12 out of 27 inbred rats. Three weeks later, four osseous defects were created per animal and were kept empty or filled with either ICPS alone, BM graft alone or with a mixture of BM and ICPS. Three weeks after implantation, bone specimens were studied under light microscopy and by scanning electron microscopy. Filling irradiated defects with ICPS alone was not accompanied by the formation of new bone. The BM graft associated with ICPS significantly increased ceramic degradation ( p < 0.01 ) and bone ingrowth ( p < 0.01 ) in the irradiated areas. The results are evidence for the meaning of the BM in driving the bone repair in irradiated animals.
Keywords: Calcium phosphate; Injectable calcium phosphate scaffold; Bone marrow graft; Radiotherapy; Bone repair; Animal model;
Cartilage regeneration using mesenchymal stem cells and a PLGA–gelatin/chondroitin/hyaluronate hybrid scaffold by Hongbin Fan; Yunyu Hu; Chunli Zhang; Xusheng Li; Rong Lv; Ling Qin; Rui Zhu (4573-4580).
The study was to produce a novel hybrid poly-(lactic-co-glycolic acid) (PLGA)–gelatin/chondroitin/hyaluronate (PLGA–GCH) scaffold and evaluate its potentials in cartilage repair. The porous PLGA–GCH scaffold was developed to mimic the natural extra cellular matrix of cartilage. The differentiated mesenchymal stem cells (MSCs) seeded on PLGA–GCH or PLGA scaffold were incubated in vitro and showed that, compared to PLGA scaffold, the PLGA–GCH scaffold significantly augmented the proliferation of MSCs and GAG synthesis. Then autologous differentiated MSCs/PLGA–GCH was implanted to repair full-thickness cartilage defect in rabbit, while MSCs/PLGA for the contra lateral cartilage defect ( n = 30 ). Fifteen additional rabbits without treatment for defects were used as control. Histology observation showed the MSCs/PLGA–GCH repair group had better chondrocyte morphology, integration, continuous subchondral bone, and much thicker newly formed cartilage compared with MSCs/PLGA repair group 12 and 24 weeks postoperatively. There was a significant difference in histological grading score between these two groups, which both showed much better repair than control. The present study implied that the hybrid PLGA–GCH scaffold might serve as a new way to keep the differentiation of MSCs for enhancing cartilage repair.
Keywords: MSC (mesenchymal stem cell); Scaffold; Cartilage; Tissue engineering;
The effect of hyaluronic acid and phospholipid based lubricants on friction within a human cartilage damage model by Richard W. Forsey; John Fisher; Jonathan Thompson; Martin H. Stone; Carol Bell; Eileen Ingham (4581-4590).
The lubricating abilities of different formulations of high molecular weight hyaluronic acid (HA), dipalmitoyl phosphatidylcholine (DPCC) and mixtures of both HA and DPCC were assessed in an in vitro model. Levels of start-up friction were determined using an osteoarthritis (OA) damaged human cartilage model set within a specially designed friction rig. To examine the long term benefits of HA, the extent of penetration of HA into cartilage tissue was investigated using fluorescently labelled HA and confocal microscopy. It was found that in this model, all formulations of HA and the majority of DPCC lubricants reduced friction (HA 5 and 10 mg ml−1, DPPC 200 mg ml−1 reductions of 51.9%, 46.7% and 46.5% respectively), compared to a Ringers solution control. Lubrication was found not to be concentration dependant for HA formulations, but concentration was key for DPCC lubrication (100 mg ml−1 reduced friction by only 15.9%). By combining HA and DPCC (HA/DPPC; 5 mg ml−1/100 mg ml−1 and 10 mg ml−1/200 mg ml−1), a further improvement was noted (69.5% and 61.9%, respectively) as the mean levels of friction were reduced by up to a further 17% than the most effective individual formulation (HA 5 mg ml−1). Penetration of HA into bovine cartilage by up to 300 μm from the surface was observed over a 48 h period. It was observed that HA specifically targeted the chondrocytes as it was primarily found within the lacunae surrounding the cells.
Keywords: Hyaluronic acid/hyaluronan; Phospholipid; Friction; Cartilage; Arthritis;
Reduced contraction of skin equivalent engineered using cell sheets cultured in 3D matrices by Kee Woei Ng; Dietmar Werner Hutmacher (4591-4598).
In order to alleviate their extensive contraction, human fibroblast sheets were cultured in combination with three-dimensional matrices (knitted poly(lactic-co-glycolic acid) (PLGA) mesh and collagen–hyaluronic acid (CHA) sponge) to form contiguous dermal constructs for tissue engineering a bilayered skin equivalent. The resulting constructs were viable, and supported the development of bilayered skin equivalents which did not contract over the 4-week culture period. When implanted into full-thickness wounds in nude rats, cultured skin equivalents based on PLGA meshes registered a take rate of 100% and showed an extent of wound contraction that was statistically similar to autografts, while wounds grafted with PLGA meshes without cell sheets contracted more than autografts. On the other hand, skin equivalents based on CHA sponges were all sloughed off within 2 weeks of transplantation. In all cell sheet-incorporated specimens, cells from the constructs infiltrated and produced extracellular matrix within the neo-dermis, shown by positive human leukocyte antigen and collagen I expression. This technique offers an alternative approach for scaffold-based tissue engineering to produce mechanically stable grafts with matured neo-tissue.
Keywords: Extracellular matrix; Cell sheets; Skin equivalent; Poly(lactic-co-glycolic acid);
The support of adenosine release from adenosine kinase deficient ES cells by silk substrates by Lorenz Uebersax; Denise E. Fedele; Claudia Schumacher; David L. Kaplan; Hans P. Merkle; Detlev Boison; Lorenz Meinel (4599-4607).
Adenosine kinase deficient (Adk−/−) embryonic stem cells (ESCs) encapsulated in synthetic polymers have previously been shown to provide therapeutic adenosine release and transient seizure suppression in epileptic rats. Here we explored the utility of biopolymer-substrates to promote long-term adenosine release from Adk−/− ESCs. Three different substrates were studied: (1) type I collagen (Col-1), (2) silk-fibroin (SF), and (3) poly(l-ornithine) (PO) coated tissue culture plastic. Adk−/− or wild type (wt) ESC-derived glial precursor cells were seeded on the substrates and cultured either in proliferation medium containing growth factors or in differentiation medium devoid of growth factors. In proliferation medium cell proliferation was higher and metabolic activity lower on Col-1 and PO substrates as compared to SF. Cells from both genotypes readily differentiated into astrocytes after growth factor removal on all substrates. Adk−/− cells cultured on biopolymers released significantly more adenosine than their wt counterparts at all developmental stages. Adenosine release was similar on SF and PO substrates and the amounts released from Adk−/− cells (>20 ng/ml) were considered to be of therapeutic relevance. Taken together, these results suggest that silk matrices are particularly suitable biomaterials for ESC encapsulation and for the design of adenosine releasing bioincubators for the treatment of epilepsy.
Keywords: Silk; Embryonic stem cells; Adenosine kinase; Adenosine; Epilepsy; Bioreactor;
Dendrimer crosslinked collagen as a corneal tissue engineering scaffold: Mechanical properties and corneal epithelial cell interactions by X. Duan; H. Sheardown (4608-4617).
Generation 2 polypropyleneimine octaamine dendrimers were used to generate highly crosslinked collagen with mechanical properties that would make it appropriate for use as a corneal tissue-engineering scaffold. Crosslinking of a highly concentrated collagen solution (2–4%) was effected using the water-soluble carbodiimide 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide hydrochloride (EDC). The multifunctional dendrimers were introduced as novel multifunctional crosslinkers after the activation of the carboxylic acid groups of glutamic and aspartic acid residues in collagen. Glutaraldehyde, a common collagen crosslinker, was used as comparison, as was EDC, itself an alternative crosslinker, which forms “zero-length or self-crosslinking”. The mechanical properties resultant gels were determined. Young's modulus of the dendrimer crosslinked gels was significantly higher than that observed with the other crosslinkers, increasing to 5 MPa compared with 0.1 MPa for the EDC crosslinked gels. Transmission electron microscopy (TEM) analysis of the gels demonstrated the presence of fibrils in the thermally gelled collagen controls; no fibrils were observed in the dendrimer crosslinked gels. As a result, the optical transparency of the dendrimer crosslinked collagen was significantly better than that of the collagen thermal gels. The EDC and glutaraldehyde crosslinked gels were generally less transparent than those crosslinked with the dendrimers. Glucose permeation results demonstrated that the dendrimer crosslinked collagen had higher glucose permeability than natural human cornea. Dendrimer crosslinked collagen gels supported human corneal epithelial cell growth and adhesion, with no cell toxicity. In comparison, some potentially cytotoxic effects were observed with glutaraldehyde crosslinked collagen. Overall, the dendrimer crosslinked collagen gels showed promising properties that suggest that these might be suitable scaffolds for corneal tissue engineering and potentially other tissue engineering applications.
Keywords: Collagen; Crosslinking; Dendrimer; EDC; Artificial cornea; Scaffold;
Polyhedral oligomeric silsequioxane–polyurethane nanocomposite microvessels for an artificial capillary bed by Ruben Y. Kannan; Henryk J. Salacinski; Mohan J. Edirisinghe; George Hamilton; Alexander M. Seifalian (4618-4626).
Fabricating artificial vascularised tissue would involve tissue-engineering techniques, but current technology limits this as cultured cells depend on growth media in vitro and on diffusion in vivo. Therefore, there is a need to construct a synthetic microvascular network, which would sustain these cultured cells in a similar manner to normal tissue. This is again hampered by the poor patency rates of current microvascular grafts. Based on our previous work on polyhedral oligomeric silsesquioxane-polyurethane nanocomposites, which have shown the unique ability to repel coagulant proteins whilst still allowing endothelialisation, we have now developed a new generation of microvascular prosthesis using this polymer. Using these dip-coated nanocomposite microvessels, we have shown that it is possible to mimic the hydraulic conductivity and pressure-responsive radial compliance characteristics of biological microvessels. This would allow nutrient exchange across its walls as well as minimise compliance mismatch throughout the physiological pressure range thus reducing intimal hyperplasia in the long term. This microvessel would have the following implications: (1) as a microvascular substitute to vein grafts and (2) in the future as a component of a microvascular network.
Keywords: Nanocomposite; Biomaterials; Bypass graft; Microvascular; Tissue engineering;
The effects of combined gentamicin–hydroxyapatite coating for cementless joint prostheses on the reduction of infection rates in a rabbit infection prophylaxis model by Volker Alt; Achim Bitschnau; Jana Österling; Andreas Sewing; Christof Meyer; Ralf Kraus; Stefan A. Meissner; Sabine Wenisch; Eugen Domann; Reinhard Schnettler (4627-4634).
Infections remain a critical issue in total joint arthroplasty. Addition of antibiotics to bone cement was shown to significantly improve antimicrobial prophylaxis in cemented joint arthroplasty. In cementless joint arthroplasty a comparable prophylaxis by local antibiotics has not been possible yet. The aim of the current study was to investigate the antimicrobial effect of two different gentamicin–hydroxyapatite (HA) coatings for cementless prostheses in a rabbit infection model. Staphylococcus aureus with a dose of 107 CFUs was inoculated into the intramedullary canal of the tibia of 30 rabbits followed by the implantation of standard steel HA K-wires ( n = 10 ), steel K-wires coated with a gentamicin–HA combination ( n = 10 ), and steel K-wires coated with a gentamicin–RGD–HA combination ( n = 10 ), respectively. The animals were sacrificed after 28 days and clinical, histological and microbiological assessment on the bone and on the removed K-wire itself by agar plating and DNA-pulsed field gel electrophoresis were carried out to detect infection. There was a statistically significant reduction of infection rates by both gentamicin-coating types (0 infections in both groups) compared to standard HA coating (7 infections in 8 animals; 2 animals were lost due to acute diarrhea) ( p < 0.001 ). An excellent correlation between agar plating testing results of the K-wires and of the bone samples was found. Detailed histology showed cortical lysis, abscess and sequester formation in the infected animals. Both gentamicin-coating types showed significant improvement of infection prophylaxis compared to standard HA coating and, therefore, this coating technology could help to improve infection prophylaxis in cementless total joint arthroplasty. In further studies biocompatibility of the coatings has to be assessed.
Keywords: Arthroplasty; Infection; Antibacterial; Surface treatment;
Nanoparticulate drug carriers based on hybrid poly(d,l-lactide-co-glycolide)-dendron structures by Luca Costantino; Francesca Gandolfi; Leila Bossy-Nobs; Giovanni Tosi; Robert Gurny; Francesco Rivasi; Maria Angela Vandelli; Flavio Forni (4635-4645).
We describe a general method for incorporating target moieties in a well-defined arrangement into the surface of biocompatible polyester poly(d,l-lactic-co-glycolic acid) (PLGA) materials using dendrons. In this way it is possible to obtain nanoparticles (NPs) with a high degree of surface coverage. This new strategy was successfully applied to the preparation of peptide- and β-d-glucose-covered NPs. The first application is based on the discovery of NPs made of conjugates between PLGA and short peptidic sequences able to cross the blood–brain barrier (BBB) after systemic administration. In this paper, we used a branched structure (dendron) in order to prepare a derivative of PLGA able to form, by simple nanoprecipitation, NPs with a higher degree of surface coverage than previously reported by us, characteristic that could influence the uptake by the liver and spleen. The NPs thus obtained retain the ability to cross the BBB and possess a core-shell structure, as evidenced from zeta-potential, X-ray photoelectron (ESCA) spectroscopy and elemental analyses. These results are comparable with the NPs obtained by the derivatization of preformed NPs. The same strategy, namely the use of a branched spacer (a dendron or a G1 dendrimer) inserted between one end of the PLGA chain and a derivatizing molecule, was also successfully applied to obtain β-d-glucose-covered NPs; in this case, the surface analysis of the NPs was performed by using high resolution magic angle spinning (HRMAS) NMR spectroscopy and zeta-potential measurements.
Keywords: Nanoparticles; Peptides; Lin's amine; PLGA; Dendrimers;
Alginate–whey protein granular microspheres as oral delivery vehicles for bioactive compounds by Lingyun Chen; Muriel Subirade (4646-4654).
Alginate (AL)–whey protein isolate (WPI) microspheres of varied WPI/AL ratio, particle diameter and concentration of polymer bead forming solution (C AL+WPI) were prepared in order to develop a biocompatible vehicle for oral administration of bioactive compounds. Microscopy revealed a special matrix/granular structure for microspheres with a WPI/AL ratio of 8:2, 100 μm diameter and C AL+WPI of 5% (AL–WPI A2), featuring WPI granules 3–10 μm in diameter homogeneously distributed within an AL spherical matrix. The compound release properties of these microspheres were investigated in simulated gastric and intestinal fluids (SGF and SIF). They demonstrated the desirable property of retarding riboflavin release in SGF and underwent alginate matrix erosion together with liberation of WPI granules in SIF, followed by complete release of the riboflavin. Riboflavin release in SGF and in SIF without pancreatin followed the Higuchi diffusion model while release in SIF in the presence of pancreatin was attributed to WPI granule degradation.
Keywords: Microspheres; Alginate; Whey protein; Bioactive compounds; Oral administration;
In situ observation of biomolecules patterned on a PEG-modified Si surface by scanning probe lithography by Inhee Choi; Sung Koo Kang; Jeongjin Lee; Younghun Kim; Jongheop Yi (4655-4660).
A Si(1 0 0) wafer was modified with methoxy-poly(ethylene glycol) (M-PEG silane) via a self-assembly technique and nano-/micro-sized patterns were then fabricated by scanning probe lithography. The protrusive silicon dioxide pattern was more reactive compared to the non-patterned area, i.e. the PEG deposited area. To demonstrate the feasibility of the submicron patterning of protein based on the anodic oxidation of the Si surface by atomic force microscopy (AFM), streptavidin labelled with Au-colloidal particle and non-labelled streptavidin were site-selectively immobilized on the patterned areas. The streptavidin-patterned surface produced by these procedures can be utilized for the detection of biotinylated materials, such as an antibody and an antigen. A patterned silicon surface is the basis of biosensing devices, in which the patterned areas serve as sensing elements that directly interact with bioanalytes, while the background of the substrate remains passive to the deposition of analytes, thus resulting in a high signal-to-noise ratio.
Keywords: Atomic force microscopy (AFM); Self-assembly; Scanning probe lithography (SPL); Surface modification; Patterning; Protein adsorption;
Biomimetic synthesis of calcium-deficient hydroxyapatite in a natural hydrogel by Stacy A. Hutchens; Roberto S. Benson; Barbara R. Evans; Hugh M. O’Neill; Claudia J. Rawn (4661-4670).
A novel composite material consisting of calcium-deficient hydroxyapatite (CdHAP) biomimetically deposited in a bacterial cellulose hydrogel was synthesized and characterized. Cellulose produced by Gluconacetobacter hansenii was purified and sequentially incubated in solutions of calcium chloride followed by sodium phosphate dibasic. A substantial amount of apatite (50–90% of total dry weight) was homogeneously incorporated throughout the hydrogel after this treatment. X-ray diffractometry (XRD) showed that CdHAP crystallites had formed in the cellulose. XRD further demonstrated that the CdHAP was comprised of 10–50 nm anisotropic crystallites elongated in the c-axis, similar to natural bone apatite. Fourier transform infrared (FTIR) spectroscopy demonstrated that hydroxyl IR bands of the cellulose shifted to lower wave numbers indicating that a coordinate bond had possibly formed between the CdHAP and the cellulose hydroxyl groups. FTIR also suggested that the CdHAP had formed from an octacalcium phosphate precursor similar to physiological bone. Scanning electron microscopy (SEM) images confirmed that uniform ∼1 μm spherical CdHAP particles comprised of nanosized crystallites with a lamellar morphology had formed in the cellulose. The synthesis of the composite mimics the natural biomineralization of bone indicating that bacterial cellulose can be used as a template for biomimetic apatite formation. This composite may have potential use as an orthopedic biomaterial.
Keywords: Bacterial cellulose; Hydrogel; Hydroxyapatite composite; Biomimetic material;