Biomaterials (v.26, #27)

Calendar (I).

Electrospinning of chitosan dissolved in concentrated acetic acid solution by Xinying Geng; Oh-Hyeong Kwon; Jinho Jang (5427-5432).
Chitosan nanofibers were electrospun from aqueous chitosan solution using concentrated acetic acid solution as a solvent. A uniform nanofibrous mat of average fiber diameter of 130 nm was obtained from the following optimum condition: 7% chitosan solution in aqueous 90% acetic acid solution was successfully electrospun in the electric field of 4 kV/cm. The aqueous acetic acid concentration higher than 30% was prerequisite for chitosan nanofiber formation, because more concentrated acetic acid in water progressively decreased surface tension of the chitosan solution and concomitantly increased charge density of jet without significant effect on solution viscosity. However, acetic acid solution more than 90% did not dissolve enough chitosan to make spinnable viscous concentration. Only chitosan of a molecular weight of 106,000 g/mol produced bead-free chitosan nanofibers, while low- or high-molecular-weight chitosans of 30,000 and 398,000 g/mol did not. Average fiber diameters and size distribution decreased with increasing electric field and more bead defects appeared at 5 kV/cm or more.
Keywords: Chitosan; Nanofiber; Electrospinning; Acetic acid; Surface tension; Charge density;

Synergistic platelet integrin signaling and factor XII activation in poly-N-acetyl glucosamine fiber-mediated hemostasis by Thomas H. Fischer; Hemant S. Thatte; Timothy C. Nichols; Diane E. Bender-Neal; Dwight A. Bellinger; John N. Vournakis (5433-5443).
The polymer poly-N-acetylglucosamine (pGlcNAc) containing fiber material is becoming increasingly important as a topical agent for hemostasis at wound sites. The pGlcNAc polymeric fiber provides hemostasis through redundant mechanisms that include platelet activation for fibrin network formation. The research presented here better defines the mechanism for the effect of pGlcNAc containing fibers on platelet-mediated processes. Adsorption experiments demonstrated that pGlcNAc fibers tightly bind most major plasma proteins and a specific sub-set of platelet surface proteins, including the integrin β 3 subunit (CD61) and the von Willebrand receptor GP1b (CD42b). The result of this interaction is a platelet-dependent acceleration of fibrin gel formation. Accelerated fibrin polymerization is sensitive to factor XII inhibition by corn trypsin inhibitor and integrin inactivation with integrilin. Confocal microscopy studies show that when platelet integrins contact plasma protein-saturated pGlcNAc fibers, an increase in intracellular free calcium for platelet activation occurs to drive surface expression of phosphatidyl serine (PS). Thus, a catalytic surface for thrombin generation and accelerated fibrin clot formation results from the interaction of platelets with pGlcNAc. These findings, when considered with the observation that pGlcNAc fibers also induce red blood cell agglutination and vasoconstriction, provides an explanation for the ability of the pGlcNAc material to provide hemostasis in a wide variety of clinical applications.
Keywords: Poly-N-acetylglucosamine; Hemostasis; Platelet; Integrin; Factor XII;

In vivo bone regeneration with injectable calcium phosphate biomaterial: A three-dimensional micro-computed tomographic, biomechanical and SEM study by Olivier Gauthier; Ralph Müller; Dietrich von Stechow; Bernard Lamy; Pierre Weiss; Jean-Michel Bouler; Eric Aguado; Guy Daculsi (5444-5453).
This in vivo study investigated the efficiency of an injectable calcium phosphate bone substitute (IBS) for bone regenerative procedures through non-destructive three-dimensional (3D) micro-tomographic (μCT) imaging, biomechanical testing with a non-destructive micro-indentation technique and 2D scanning electron microscopy (SEM) analysis. The injectable biomaterial was obtained by mixing a biphasic calcium phosphate (BCP) ceramic mineral phase and a cellulosic polymer. The BCP particles were 200–500 μm or 80–200 μm in diameter. The injectable material was implanted for 6 weeks into critical-sized bone defects at the distal end of rabbit femurs.Extensive new bone apposition was noted with both 2D and 3D techniques. Micro-CT showed that newly formed bone was in perfect continuity with the trabecular host bone structure and demonstrated the high interconnectivity of the restored bone network. For both IBS formulations, SEM and μCT gave very close measurements. The only detected significant difference concerned the amount of newly formed bone obtained with IBS 80-200 that appeared significantly higher with μCT analysis than with SEM (p=0.00007). Student t-tests did not show any significant difference in the amount of newly formed bone and remaining ceramic obtained from μCT analysis or SEM. Regression analysis showed satisfactory correlation between both the amount of newly formed bone and remaining ceramic obtained from μCT or SEM. For IBS 200-500, the newly formed bone rate inside the defect was 28.0±5.2% with SEM and yield strength of the samples was 18.8±5.4 MPa. For IBS 80-200, the newly formed bone rate inside the defect was 31.7±5.1% with SEM and yield strength of the samples was 26.8±4.5 MPa. Yield strength appeared well correlated with the amount of newly formed bone, specially observed with μCT.This study showed the ability of non-destructive techniques to investigate biological and mechanical aspects of bone replacement with injectable biomaterials.
Keywords: Calcium phosphate; Composite; Biomaterial; Bone cement; In vivo test; Bone regeneration; Micro-computed tomography (μCT); Compressive strength;

Biocompatibility analysis of poly(glycerol sebacate) as a nerve guide material by Cathryn A. Sundback; Jeffery Y. Shyu; Yadong Wang; William C. Faquin; Robert S. Langer; Joseph P. Vacanti; Tessa A. Hadlock (5454-5464).
No satisfactory method currently exists for bridging neural defects. Autografts lead to inadequate functional recovery, and most available artificial neural conduits possess unfavorable swelling and pro-inflammatory characteristics. This study examined the biocompatibility of a novel biodegradable elastomer, poly(glycerol sebacate) (PGS), for neural reconstruction applications, as the material possesses favorable mechanical property and degradation characteristics. The effect of PGS on Schwann cell metabolic activity, attachment, proliferation, and apoptosis were examined in vitro in comparison with poly(lactide-co-glycolide) (PLGA), a biomaterial widely utilized for tissue engineering applications. The in vivo tissue response to PGS was compared with PLGA implanted juxtaposed to the sciatic nerve; the physical changes in the implant material were measured during the degradation process. PGS had no deleterious effect on Schwann cell metabolic activity, attachment, or proliferation, and did not induce apoptosis; the in vitro effects of PGS were similar to or superior to that of PLGA. In vivo, PGS demonstrated a favorable tissue response profile compared with PLGA, with significantly less inflammation and fibrosis and without detectable swelling during degradation. PGS is an excellent candidate material for neural reconstruction applications given its lack of in vitro Schwann cell toxicity and minimal in vivo tissue response.
Keywords: Biocompatibility; Schwann cells; Nerve guide; Fibrosis; Degradation;

Bioactivity of titanium following sodium plasma immersion ion implantation and deposition by M.F. Maitz; R.W.Y. Poon; X.Y. Liu; M.-T. Pham; Paul K. Chu (5465-5473).
Bio-activation of titanium surface by Na plasma immersion ion implantation and deposition (PIII&D) is illustrated by precipitation of calcium phosphate and cell culture. The bioactivity of the plasma-implanted titanium is compared to that of the untreated, Na beam-line implanted and NaOH-treated titanium samples. Our data show that the samples can be classified into two groups: non-bioactive (untreated titanium and beam-line Na implanted titanium) and bioactive (Na-PIII&D and NaOH-treated titanium). None of the four types of surfaces exhibited major cell toxicity as determined by lactate dehydrogenase (LDH) release. However, the LDH release was higher on the more bioactive PIII and NaOH-treated surfaces. From a morphological point of view, cell adherence on the NaOH-treated titanium is the best. On the other hand, the cell activity and protein production were higher on the non-bioactive surfaces. The high alkaline phosphatase activity per cell suggests that the active surfaces support an osteogenic differentiation of the bone marrow cells at the expense of lower proliferation. The use of Na-PIII&D provides an environmentally cleaner technology to improve the bioactivity of Ti compared to conventional wet chemical processes. The technique is also particularly useful for the uniform and conformal treatment of medical implants that typically possess an irregular shape and are difficult to treat by conventional ion beam techniques.
Keywords: Titanium; Bioactivity; Sodium; Plasma immersion ion implantation;

Porosity of 3D biomaterial scaffolds and osteogenesis by Vassilis Karageorgiou; David Kaplan (5474-5491).
Porosity and pore size of biomaterial scaffolds play a critical role in bone formation in vitro and in vivo. This review explores the state of knowledge regarding the relationship between porosity and pore size of biomaterials used for bone regeneration. The effect of these morphological features on osteogenesis in vitro and in vivo, as well as relationships to mechanical properties of the scaffolds, are addressed. In vitro, lower porosity stimulates osteogenesis by suppressing cell proliferation and forcing cell aggregation. In contrast, in vivo, higher porosity and pore size result in greater bone ingrowth, a conclusion that is supported by the absence of reports that show enhanced osteogenic outcomes for scaffolds with low void volumes. However, this trend results in diminished mechanical properties, thereby setting an upper functional limit for pore size and porosity. Thus, a balance must be reached depending on the repair, rate of remodeling and rate of degradation of the scaffold material. Based on early studies, the minimum requirement for pore size is considered to be ∼100 μm due to cell size, migration requirements and transport. However, pore sizes >300 μm are recommended, due to enhanced new bone formation and the formation of capillaries. Because of vasculariziation, pore size has been shown to affect the progression of osteogenesis. Small pores favored hypoxic conditions and induced osteochondral formation before osteogenesis, while large pores, that are well-vascularized, lead to direct osteogenesis (without preceding cartilage formation). Gradients in pore sizes are recommended for future studies focused on the formation of multiple tissues and tissue interfaces. New fabrication techniques, such as solid-free form fabrication, can potentially be used to generate scaffolds with morphological and mechanical properties more selectively designed to meet the specificity of bone-repair needs.
Keywords: Porosity; Scaffolds; Bone; Osteogenesis; Tissue engineering; Polymeric biomaterials;

We present a series of experiments investigating the in vitro biological activity of zinc-containing organoapatite (ZnOA)-coated titanium meshes. ZnOA is a hydroxyapatite-based material that contains poly(l-lysine) and zinc ions and can be coated onto titanium by treating the metal surface with poly(amino acids) that allow for electrostatic bonding of the mineral to the titanium surface. Preosteoblastic mouse calyaria cells were cultured on ZnOA-coated titanium meshes in a three-dimensional (3D) bioreactor, which provides an in vitro culture environment that better simulates what cells experience in vivo, compared to traditional 2D cultures. Results of these studies show a time-dependent cascade of events leading to an earlier onset of alkaline phosphatase (ALP) expression and biomineralization of ZnOA-coated samples as compared to controls. After the observation of peak ALP levels in ZnOA-coated titanium samples, mineralized bone nodules were observed by scanning electron microscopy. Tetracycline staining confirmed that the observed mineral nodules were newly synthesized biomineral, and not due to the inorganic coating. ZnOA-coated titanium substrates represent a new class of materials for human repair that provide, mechanical stability, as well as chemical and biochemical signals to promote new bone growth.
Keywords: Biomineralization; Bioreactor; Bone repair; Bone tissue engineering;

Characterization of chitosan–polycaprolactone blends for tissue engineering applications by Aparna Sarasam; Sundararajan V. Madihally (5500-5508).
The objective of this work was to study the effect of blending chitosan with poly( ε -caprolactone) (PCL) on their biomechanical properties. After testing the effect of molecular weight (MW), temperature, and humidity on the tensile properties in dry, wet at 25 °C and wet at 37 °C conditions, chitosan with a MW>310 kD was selected for use in the blend. Homogeneous blends of 25%, 50% and 75% PCL compositions were formed by dissolving chitosan and 80 kD PCL in a common solvent of ∼77% aqueous acetic acid. Taking advantage of the low melting point of PCL, blend membranes were processed at 25, 37, 55 °C water bath or 55 °C oven into films. Also, membranes were solvent annealed using chloroform vapors. Tensile properties were analyzed in wet conditions at 25 °C. Support for cell viability and distribution of cytoskeletal actin were analyzed by in vitro cell culture of mouse embryonic fibroblasts (MEFs). Differential scanning calorimetry studies indicated the miscibility of the two components when approximated using Nishi–Wang equation. Drying the films at 55 °C in an oven formed membranes without separation of two phases. However, the analyzed tensile properties showed no significant alterations relative to chitosan. On the contrary, significant improvements were observed after solvent annealing. Interestingly, increased viability and redistribution of actin fibers was observed on blends formed with 50% PCL and 75% PCL relative to individual polymers. In summary, 50:50 blends when processed at 55 °C in an oven showed significant improvement in mechanical properties as well as support for cellular activity relative to chitosan.
Keywords: Chitosan; Polycaprolactone; Miscibility; Tensile properties; Blends; Cellular activity; Nishi–Wang equation;

Three-dimensional culture and differentiation of human osteogenic cells in an injectable hydroxypropylmethylcellulose hydrogel by Christophe Trojani; Pierre Weiss; Jean-François Michiels; Claire Vinatier; Jérôme Guicheux; Guy Daculsi; Patrick Gaudray; Georges F Carle; Nathalie Rochet (5509-5517).
The present work evaluates a newly developed silated hydroxypropylmethylcellulose (Si-HPMC)-based hydrogel as a scaffold for 3D culture of osteogenic cells. The pH variation at room temperature catalyzes the reticulation and self-hardening of the viscous polymer solution into a gelatine state. We designed reticulation time, final consistency and pH in order to obtain an easy handling matrice, suitable for in vitro culture and in vivo injection. Three human osteogenic cell lines and normal human osteogenic (HOST) cells were cultured in 3D inside this Si-HPMC hydrogel. We show here that osteosarcoma cells proliferate as clonogenic spheroids and that HOST colonies survive for at least 3 weeks. Mineralization assay and gene expression analysis of osteoblastic markers and cytokines, indicate that all the cells cultured in 3D into this hydrogel, exhibited a more mature differentiation status than cells cultured in monolayer on plastic. This study demonstrates that this Si-HPMC hydrogel is well suited to support osteoblastic survival, proliferation and differentiation when used as a new scaffold for 3D culture and represents also a potential basis for an innovative bone repair material.
Keywords: 3D Scaffold; Si-HPMC hydrogel; Osteoblast; Human; Gene expression;

Analytically derived material properties of multilaminated extracellular matrix devices using the ball-burst test by Donald O. Freytes; Ann E. Rundell; Jonathan Vande Geest; David A. Vorp; Thomas J. Webster; Stephen F. Badylak (5518-5531).
Xenogeneic extracellular matrices (ECMs) have been shown to be effective as naturally occurring scaffolds for soft-tissue repair. As acellular tissue substitutes at the time of surgical implantation, ECMs are subjected to the mechanical forces and micro-environmental conditions representative of the anatomical location in which they are placed. Ideally such natural scaffolds would possess mechanical properties that allow for normal tissue function in and around the implant site. The ball-burst test was used to simulate biaxial forces and to determine the strength of the ECM scaffold under a relevant physiological loading condition. The ball-burst test, in itself, does not quantify intrinsic mechanical properties and therefore a methodology was developed to determine the maximum stress resultant tangent modulus (MSRTM) or the maximum stress tangent modulus (MSTM), stress to failure ( σ f ) , failure stress resultant ( N f ) , ball-burst pressure ( P ) , and maximum elongation ( λ max ) from the raw ball-burst data obtained at a constant-rate of transverse. The analytical methodology was compared to finite element simulations and showed good correlation with the analytical solution presented. The proposed approximations were used to compute biaxial failure properties for a variety of multilaminate ECM devices with varying number of layers, disinfection and sterilization, and organ origin.
Keywords: Bladder; ECM; Multilaminate devices; Mechanical properties; Mechanical test; Ball-burst test; Scaffold;

Damage accumulation, fatigue and creep behaviour of vacuum mixed bone cement by Jonathan R.T. Jeffers; Martin Browne; Mark Taylor (5532-5541).
The behaviour of bone cement under fatigue loading is of interest to assess the long-term in vivo performance. In this study, uniaxial tensile fatigue tests were performed on CMW-1 bone cement. Acoustic emission sensors and an extensometer were attached to monitor damage accumulation and creep deformation respectively. The S-N data exhibited the scatter synonymous with bone cement fatigue, with large pores generally responsible for premature failure; at 20 MPa specimens failed between 2×103 and 2×104 load cycles, while at 7 MPa specimens failed from 3×105 load cycles but others were still intact after 3×106 load cycles. Acoustic emission data revealed a non-linear accumulation of damage with respect to time, with increasing non-linearity at higher stress levels. The damage accumulation process was not continuous, but occurred in bursts separated by periods of inactivity. Damage in the specimen was located by acoustic emissions, and allowed the failure site to be predicted. Acoustic emission data were also used to predict when failure was not imminent. When this was the case at 3 million load cycles, the tests were terminated. Creep strain was plotted against the number of load cycles and a linear relationship was found when a double logarithmic scale was employed. This is the first time a brand of cement has been characterised in such detail, i.e. fatigue life, creep and damage accumulation. Results are presented in a manner that allows direct comparison with published data for other cements. The data can also be used to characterise CMW-1 in computational simulations of the damage accumulation process. Further evidence is provided for the condition-monitoring capabilities of the acoustic emission technique in orthopaedic applications.
Keywords: Bone cement; Fatigue; Creep; Damage accumulation; Acoustic emission;

Here we document the complete process of bioresorption and bone replacement of rods made of forged composites of unsintered hydroxyapatite particles/poly l-lactide (F-u-HA/PLLA) implanted in the femoral medullary cavities of rabbits. Bioresorption, osteoconductive bioactivity and bone replacement were compared in three implantation sites. In the first site, the end of the rod was located near the endosteum in the proximal medullary cavity. In the second, the rod was located at the centre of the bone marrow space without contacting the endosteum. In the third, the rod was in direct contact with cancellous bone within the distal femoral condyle. Micro-computerised tomography, scanning electron microscopy and photomicrographs of stained sections were used to document the complete process of bioresorption and bone replacement. At the first implantation site, the rod was completely resorbed and unbound u-HA particles were detected in and around the endosteum 5–6 years after implantation. At the second site, the rod showed significant shrinkage 4–5 years after implantation due to the release of almost all the PLLA, although a contracted cylindrical structure containing a few u-HA persisted even after ∼6 years. At the third site, u-HA particles were almost completely replaced with bone after 5–6 years. Conversely, PLLA-only rods showed little bone conduction, and small amounts of degraded PLLA debris and intervening some tissue persisted even after long periods. Namely, the u-HA/PLLA composites were replaced with bone in the distal femoral condyle, where they were in direct contact with the bone and new bone formation was anatomically necessary. By contrast, composite rods were resorbed without replacement in the proximal medullary cavity, in which new bone growth was not required. We therefore conclude that the F-u-HA30/40 composites containing 30 wt%/40 wt% u-HA particles are clinically effective for use in high-strength bioactive, bioresorbable bone-fixation devices with the capacity for total bone replacement.
Keywords: Bioactivity; Biodegradation; Bioresorption; Bone regeneration; Calcium phosphates; Hydroxyapatite/PLLA composites;

The inhibition of neutrophil antibacterial activity by ultra-high molecular weight polyethylene particles by Louis Bernard; Pierre Vaudaux; Corinne Merle; Richard Stern; Elzbieta Huggler; Daniel Lew; Pierre Hoffmeyer (5552-5557).
Following infection, bacterial killing by polymorphonuclear leukocytes (neutrophils) is the main host defense against bacteria. Our hypothesis is that particles of ultra-high molecular weight polyethylene (UHMWP) may impair local neutrophil function and consequently reduce neutrophil bacterial killing. To determine how the in vitro phagocytic–bactericidal activity of neutrophils was affected by exposure to wear particles, tests were run comparing the effects of different particle composition, and different concentrations and sizes of UHMWP particles. There was a significant correlation between the number of particles and the decrease in neutrophil bactericidal activity ( p < 0.01 ), and the greatest effect was obtained with a concentration of 107  UHMWP/ml. There was a significant decrease in neutrophil bactericidal activity by incubation with particles of 0.1–5 μm ( p < 0.01 ), but not with larger size. The results suggest that neutrophil functional defects triggered by the presence of UHMWP particles may potentially contribute to the susceptibility of loose implants to bacterial infections.
Keywords: Neutrophil; Antibacterial activity; Polyethylene particles;

DNA strands robed with ionic liquid moiety by Naomi Nishimura; Yasuhiro Nomura; Nobuhumi Nakamura; Hiroyuki Ohno (5558-5563).
An ionic liquid domain was successfully prepared outside double-stranded DNA by fixing 1-alkyl-3-methyl-imidazolium (C n MI) cations on the phosphate groups of DNA. First, four species of ionic liquid were made using phosphoric acid di-n-butyl ester and C n MI (n=2,4,8, and 12) as a low molecular weight model. They were obtained as liquid salts, and their ionic conductivity ranged up to 10−5  S cm−1 at 50 °C. Based on this model study, counter cations of the phosphate groups of DNA were exchanged for four kinds of imidazolium cations. The resulting ionic liquid-robed DNA (IL-robed DNA) was soluble in ordinary organic solvents such as methanol or ethanol. Ionic conductivity was low, because the ion density was insufficient to form a continuous ionic liquid domain around the DNA strands. When 11 mol% 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4), which is a typical ionic liquid, was mixed with the IL-robed DNA, an ionic conductivity of 5.4×10−5  S cm−1 at 30 °C was observed because a continuous ionic liquid domain was successfully formed.
Keywords: DNA; Ionic liquid; Ion conduction; Biofilm;

A method for the molecular imprinting of hemoglobin on silica surfaces using silanes by Toru Shiomi; Masayoshi Matsui; Fujio Mizukami; Kengo Sakaguchi (5564-5571).
A new molecular imprinting technique using covalently immobilized hemoglobin (Hb) is described for creating Hb-specific recognition cavities on silica. Two kinds of organic silane (3-aminopropyltrimethoxysilane: APTMS, and trimethoxypropylsilane: TMPS) were polymerized on a surface of porous silica after the Hb template was covalently immobilized by forming imine bonds, and their influence was analyzed. The results showed that not only the silane amount but also the relative proportions play an important role in protein imprinting. Pore size distribution on Hb imprinted silica was determined by nitrogen adsorption/desorption after removing the template Hb. The Hb-imprinted silica using covalently immobilized Hb (MIPi) as a template proved superior to silica using free Hb (MIPf) regarding displacement of template Hb, and selective re-adsorption as compared with other non-template proteins. The results suggested the capacity for selective adsorption of MIPi to be not only based on the isoelectric point (pI) and protein molecular weight, but also the characteristics of protein recognition cavities imprinted on base silica.
Keywords: Molecular imprinting; Silica; Silane; Siloxane; Protein adsorption; Hemoglobin; Immobilized; Template;

Cell microarrays on photochemically modified polytetrafluoroethylene by Regina Mikulikova; Sieglinde Moritz; Thomas Gumpenberger; Michael Olbrich; Christoph Romanin; Lucie Bacakova; Vaclav Svorcik; Johannes Heitz (5572-5580).
We studied the adhesion, proliferation, and viability of human umbilical vein endothelial cells (HUVEC) and human embryonic kidney cells (HEK) on modified spots at polytetrafluoroethylene (PTFE) surfaces. The viability of the cells was assessed using an aqueous non-radioactive cell proliferation assay. Round spots with a diameter of 100 μm were modified by exposure to the ultraviolet (UV) light of a Xe 2 * -excimer lamp at a wavelength of 172 nm in an ammonia atmosphere employing a contact mask. The spots were arranged in a quadratic pattern with 300 μm center-to-center spot distances. With optimized degree of modification, the cells adhered to the modified spots with a high degree of selectivity (70–90%). The adhered cells on the spots proliferated. This resulted in a significant increase in the number of adhering HUVECS or HEK cells after seeding and in the formation of confluent cell clusters after 3–4 days. With higher start seeding density, these clusters were not only confined to the modified spots but extended several micrometer to the neighborhood. The high potential of the cell microarrays for gene analysis in living cells was demonstrated with HEK cells transfected by yellow fluorescent protein (YFP).
Keywords: Polytetrafluoroethylene; Surface modification; Endothelial cells; Cell adhesion; Cell proliferation; Cell viability; Gene transfer;

Diffusion in three-dimensionally ordered scaffolds with inverted colloidal crystal geometry by Sachin Shanbhag; Jung Woo Lee; Nicholas Kotov (5581-5585).
Inverted colloidal crystal geometry has been recently utilized in the design of highly organized 3D cell scaffolds. The regularity of the resulting scaffolds enables computational modeling of scaffold properties. In this work we probe the resistance offered by these scaffolds to nutrient transport, by using Brownian dynamics and Monte Carlo simulations to model the effective nutrient diffusivity. Brownian dynamics simulations indicate that the effective diffusivity for small nutrients in the scaffold, D eff = 0.3 D 0 , where D 0 is the free solution diffusivity. Further, results of Monte Carlo simulations for dilute solutions of larger particles show that the D eff decreases linearly with the size of the particles.
Keywords: Three-dimensional cell scaffolds; Inverted colloidal crystals; Diffusion modeling; Brownian dynamics; Cell culture optimization;