Scaffold geometry and computational fluid dynamics simulation supporting osteogenic differentiation in dynamic culture.

Geometry of porous scaffolds is critical to the success of cell adhesion, proliferation, and differentiation in bone tissue engineering. In this study, the effect of scaffold geometry on osteogenic differentiation of MC3T3-E1 pre-osteoblasts in a perfusion bioreactor was investigated. Three geometries of oligolactide-HA scaffolds, named Woodpile, LC-1000, and LC-1400, were fabricated with uniform pore size distribution and interconnectivity using stereolithography (SL) technique, and tested to evaluate for the most suitable scaffold geometry. Compressive tests revealed sufficiently high strength of all scaffolds to support new bone formation. The LC-1400 scaffold showed the highest cell proliferation in accordance with the highest level of osteoblast-specific gene expression after 21 days of dynamic culture in a perfusion bioreactor; however, it deposited less amount of calcium than the LC-1000 scaffold. Computational fluid dynamics (CFD) simulation was employed to predict and explain the effect of flow behavior on cell response under dynamic culture. The findings concluded that appropriate flow shear stress enhanced cell differentiation and mineralization in the scaffold, with the LC-1000 scaffold performing best due to its optimal balance between permeability and flow-induced shear stress.

Assessment of Mechanical/Chemical Properties and Cytotoxicity of Resin-Modified Glass Ionomer Cements Containing Sr/F-Bioactive Glass Nanoparticles and Methacrylate Functionalized Polyacids.

This study prepared low-toxicity, elemental-releasing resin-modified glass ionomer cements (RMGICs). The effect of 2-hydroxyethyl methacrylate (HEMA, 0 or 5 wt%) and Sr/F-bioactive glass nanoparticles (Sr/F-BGNPs, 5 or 10 wt%) on chemical/mechanical properties and cytotoxicity were examined. Commercial RMGIC (Vitrebond, VB) and calcium silicate cement (Theracal LC, TC) were used as comparisons. Adding HEMA and increasing Sr/F-BGNPs concentration decreased monomer conversion and enhanced elemental release but without significant effect on cytotoxicity. Rising Sr/F-BGNPs reduced the strength of the materials. The degree of monomer conversion of VB (96%) was much higher than that of the experimental RMGICs (21-51%) and TC (28%). The highest biaxial flexural strength of experimental materials (31 MPa) was significantly lower than VB (46 MPa) (p < 0.01) but higher than TC (24 MPa). The RMGICs with 5 wt% HEMA showed higher cumulative fluoride release (137 ppm) than VB (88 ppm) (p < 0.01). Unlike VB, all experimental RMGICs showed Ca, P, and Sr release. Cell viability in the presence of extracts from experimental RMGICs (89-98%) and TC (93%) was significantly higher than for VB (4%). Experimental RMGICs showed desirable physical/mechanical properties with lower toxicity than the commercial material.

3D-printed medial arch supports of varying hardness versus a prefabricated arch support on plantar pressure: A 1-month randomized crossover study in healthy volunteers.

BACKGROUND: Foot orthoses are commonly used as a noninvasive treatment to relieve foot pain. The custom full-length insoles with various materials and designs have been studied for their effectiveness in reducing plantar pressure. However, few studies have been conducted with respect to custom medial arch support on the relationships between material hardness and measured plantar pressure and level of comfort. OBJECTIVES: To evaluate the effects of the hardness of custom medial arch supports on plantar pressure and comfort perception. STUDY DESIGN: Randomized crossover study. METHODS: Two custom silicone medial arch supports of varying hardness (A and B) were fabricated using 3D printing technology and tested in 12 healthy volunteers against a commercially prefabricated arch support (C). The volunteers wore three medial arch supports in a random order, one month for each arch support with 3-4 days of washout period before wearing the next one. The plantar pressure was measured and analyzed according to each foot zone: forefoot, midfoot, and hindfoot, comparing before intervention, immediately after intervention, and 1 month after intervention. The comfort perception was assessed by collecting volunteer feedback with a questionnaire after using each medial arch support. RESULTS: After 1-month intervention, both 3D-printed and prefabricated medial arch supports demonstrated significantly higher average pressure in the midfoot ( P < 0.001), whereas significantly lower average pressure in the forefoot ( P < 0.001) and hindfoot ( P = 0.014, 0.026, and 0.018 for A, B, and C, respectively), compared with those before intervention. There were no significant differences in plantar pressure distribution between the 3D-printed and prefabricated medial arch supports. However, the 3D-printed medial arch supports resulted in better comfort than the prefabricated arch support. CONCLUSIONS: The material hardness had no apparent effect on plantar pressure distribution. The three medial arch supports showed reducing plantar heel pressure. Further research is needed to investigate the potential effect of 3D-printed silicone medial arch supports on reducing foot pain in patients.

Monomer Conversion, Dimensional Stability, Biaxial Flexural Strength, Ion Release, and Cytotoxicity of Resin-Modified Glass Ionomer Cements Containing Methacrylate-Functionalized Polyacids and Spherical Pre-Reacted Glass Fillers.

The aim of this study was to prepare RMGICs for pulp protection that contain polyacids functionalized with methacrylate groups (CMs) to enable light-activated polymerization without the need for toxic 2-hydroxyethyl methacrylate (HEMA) monomers. The effects of using CM liquids with 0 or 5 wt% HEMA on the physical/mechanical properties and cytotoxicity of the experimental RMGICs were assessed. Spherical pre-reacted glass fillers (SPG) were used as the powder phase. The experimental RMGICs were prepared by mixing SPG with CM liquid (0 wt% HEMA, F1) or CMH liquid (5 wt% HEMA, F2). Commercial materials (Vitrebond, VB; TheraCal LC, TC) were used for the comparisons. The degree of monomer conversion and fluoride release of both F1 and F2 were significantly lower than those of VB. F1 showed comparable biaxial flexural strength with VB but higher strength than TC. The dimensional stability (mass/volume changes) of the experimental materials was comparable with that of the commercial materials. F1 and F2 exhibited higher Sr/Ca ion release and relative cell viability than VB. The use of CMH liquid reduced the strength but enhanced the fluoride release of the experimental RMGICs. In conclusion, the experimental RMGICs showed comparable strength but lower cytotoxicity compared to the commercial RMGICs. These novel materials could be used as alternative materials for pulp protection.

Rheological Properties, Surface Microhardness, and Dentin Shear Bond Strength of Resin-Modified Glass Ionomer Cements Containing Methacrylate-Functionalized Polyacids and Spherical Pre-Reacted Glass Fillers.

The aim of this study was to prepare experimental resin-modified glass ionomer cements (RMGICs) containing low levels of hydroxyethyl methacrylate (HEMA) for pulp protection. Liquid and powder phases of the experimental RMGICs were polyacid functionalized with methacrylate groups and spherical pre-reacted glass fillers (SPG). Two types of liquid phase containing 0 wt. % HEMA (CM liquid) or 5 wt. % HEMA (CMH liquid) were formulated. The experimental RMGICs were prepared by mixing SPG fillers with CM liquid (F1) or CMH liquid (F2). Rheological properties were examined using a strain-controlled rheometer (n = 5). The Vickers microhardness (n = 5) and dentin shear bond strength (SBS) (n = 10) of the materials were tested. Commercial pulp protection materials (Vitrebond and TheraCal LC) were used as comparisons. The viscosity and surface microhardness of F1 (22 m Pa·s, 18 VHN) and F2 (18 m Pa·s, 16 VHN) were significantly higher than those of Vitrebond (6 mPa·s, 6 VHN) and TheraCal (0.1 mPa·s, 7 VHN). The SBS of F1 (10.7 MPa) and F2 (11.9 MPa) was comparable to that of Vitrebond (15.4 MPa) but higher than that of TheraCal LC (5.6 MPa). The addition of 5 wt. % HEMA showed no significant effect on viscosity, surface microhardness, or SBS of the experimental RMGICs. The experimental materials showed higher viscosity and microhardness but similar SBS when compared with the commercial RMGIC.

Gentamicin Released from Porous Scaffolds Fabricated by Stereolithography.

Porous oligolactide-hydroxyapatite composite scaffolds were obtained by stereolithographic fabrication. Gentamicin was then coated on the scaffolds afterwards, to achieve antimicrobial delivery ability to treat bone infection. The scaffolds examined by stereomicroscope, SEM, and µCT-scan showed a well-ordered pore structure with uniform pore distribution and pore interconnectivity. The physical and mechanical properties of the scaffolds were investigated. It was shown that not only porosity but also scaffold structure played a critical role in governing the strength of scaffolds. A good scaffold design could create proper orientation of pores in a way to strengthen the scaffold structure. The drug delivery profile of the porous scaffolds was also analyzed using microbiological assay. The release rates of gentamicin from the scaffolds showed prolonged drug release at the levels higher than the minimum inhibitory concentrations for S. aureus and E. coli over a 2-week period. It indicated a potential of the scaffolds to serve as local antibiotic delivery to prevent bacterial infection.

Influence of the cross-linking agent on mechanical properties of PMMA powder with compromised particle morphology.

OBJECTIVE: To investigate the effect of a cross-linking agent on the mechanical properties of self-cured orthodontic acrylic resin using PMMA powder (CPM-PMMA) with a compromised microstructure. MATERIALS AND METHODS: The mechanical properties of three sample groups were investigated in this study: CPM-PMMA, orthocryl and orthoplast. CPM-PMMA powder was prepared by suspension polymerization. It was mixed with a commercially available liquid (orthocryl) to yield a test specimen and to compare its flexural properties and Vicker hardness with the two commercial products. Molecular weight and particle size distribution of all groups were examined. Particle morphology was observed using scanning electron microscopy (SEM) and optical microscopy (OM). RESULTS: The average molecular weight of the CPM-PMMA powder was similar to that of the industrial products. Its particle size distribution was narrow and limited to large sizes (91.1-149µm). SEM and OM presented the compromise particle morphology. However, the flexural properties and Vicker hardness of CPM-PMMA powder mixed with orthocryl liquid showed no significant difference compared with orthocryl sample group. In addition, the CPM-PMMA had higher flexural properties than the orthoplast samples. CONCLUSIONS: Although the CPM-PMMA powder presented a compromised particle morphology and narrow particle size distribution, when mixed with orthocryl liquid, the cured resin produced acceptable mechanical properties due to the large amount of cross-linking agent. This result could indicate that the mechanical properties of self-cured acrylic resins are mainly dependent on the amount of cross-linking agent in the liquid component.

Mechanical and biological properties of photocurable oligolactide-HA composites investigated under accelerated degradation.

The major concern related to biodegradable bone substitute materials is the loss of mechanical strength which can be undesirable when occurring too quickly before new bone formation. In this study, the multifunctional lactide oligomers having 2, 3, and 4 arms end capped with methacrylate groups were synthesized with the aim of improving the degradation properties. Their composites with hydroxyapatite (HA) were photopolymerized and subjected to accelerated degradation at 60 °C. The results showed that increasing number of arms significantly improved thermal and mechanical properties as well as biocompatibility of the composites. All composites although varying in number of arms had similar levels of bone-specific gene expression and calcification indicating their equal bioactivity in supporting bone formation. The high HA content in the composites was proposed to be responsible for enhanced osteoblast response, and this tended to suppress the effects of polymeric structure.

Biocompatibility of hydroxyapatite scaffolds processed by lithography-based additive manufacturing.

The fabrication of hydroxyapatite scaffolds for bone tissue engineering applications by using lithography-based additive manufacturing techniques has been introduced due to the abilities to control porous structures with suitable resolutions. In this research, the use of hydroxyapatite cellular structures, which are processed by lithography-based additive manufacturing machine, as a bone tissue engineering scaffold was investigated. The utilization of digital light processing system for additive manufacturing machine in laboratory scale was performed in order to fabricate the hydroxyapatite scaffold, of which biocompatibilities were eventually evaluated by direct contact and cell-culturing tests. In addition, the density and compressive strength of the scaffolds were also characterized. The results show that the hydroxyapatite scaffold at 77% of porosity with 91% of theoretical density and 0.36 MPa of the compressive strength are able to be processed. In comparison with a conventionally sintered hydroxyapatite, the scaffold did not present any cytotoxic signs while the viability of cells at 95.1% was reported. After 14 days of cell-culturing tests, the scaffold was able to be attached by pre-osteoblasts (MC3T3-E1) leading to cell proliferation and differentiation. The hydroxyapatite scaffold for bone tissue engineering was able to be processed by the lithography-based additive manufacturing machine while the biocompatibilities were also confirmed.

Preparation and degradation study of photocurable oligolactide-HA composite: a potential resin for stereolithography application.

The merging of stereolithography (SLA) technology to the medical field certainly benefits the manufacturing of parts, especially those patient-specific for the clinical use. This technique, however, has hardly been exploited medically due to a limited number of biodegradable resins for SLA processing. To extend application of SLA in the biomedical field, photocurable oligolactide resins were developed and examined for biodegradation and biocompatibility. The degradation was studied by monitoring the changes in weight loss, and thermal and mechanical properties of the photocured specimens in phosphate buffered saline (PBS) at 37°C. The results demonstrated that a resin composition played an important role in degradation, and the retarded degradation rate was observed for the highly crosslinked resin containing hydroxyapatite (HA). The less cytotoxic sample was also obtained from the resin with higher content of HA. These findings suggest the possible use of the developed photocurable oligolactide resins in SLA manufacturing of biodegradable implants, where their degradation behaviors can be designed by varying the resin composition.

Enhancement effect of pre-reacted glass on strength of glass-ionomer cement.

In this paper, we report on the enhanced strength of glass ionomer cement (GIC) by using the process of pre acid-base reaction and spray drying in glass preparation. The pre acid-base reaction was induced by prior mixing of the glass powder with poly(alkenoic acid). The weight ratios of glass powder to poly(alkenoic acid) were varied to investigate the extent of the pre acid-base reaction of the glass. The effect of the spray drying process which produced spherical glass particles on cement strength was also studied and discussed. The results show that adding 2%-wt of poly(alkenoic acid) liquid in the pre-reacted step improved cement strength. GICs prepared using a mixture of pre-reacted glass with both spherical and irregular powders at 60:40 by weight exhibited the highest compressive strength at 138.64±7.73 MPa. It was concluded that glass ionomer cements containing pre-reacted glass with mixed glass morphology using both spherical and irregular forms are promising as restorative dental materials with improved mechanical properties and handling characteristics.

Efficacy of chitin-PAA-GTMAC gel in promoting wound healing: animal study.

Acrylic grafted chitin (chitin-PAA) was modified with glycidyltrimethylammonium chloride (GTMAC) with the aim of promoting wound healing. The chitin-PAA-GTMAC gels with different GTMAC contents were compared with the original chitin-PAA gel and Intrasite gel for their efficacy in deep wound healing of Wistar rats. Four full-thickness wounds were made on the dorsal skin of rats and then each was treated with 4 materials; chitin-PAA, chitin-PAA-GTMAC(1:4), chitin-PAA-GTMAC(1:10) and Intrasite gel. During 18 days of treatment, the wounds were visually observed and calculated for wound size using image analysis program. Skin wound tissues of sacrificed rats were processed for routine histological observation and immunohistochemistry of proliferating cell nuclear antigen (PCNA). The wounds covered with the chitin derivatives either with or without GTMAC showed a significant reduction in wound size in day 9 in comparison with day 12 for those covered with Intrasite gel. The faster rate and the better pattern of epidermal development observed in histological study as well as the higher dermal cell proliferation (PCNA expression) also demonstrated the better efficiency in wound healing of the chitin derivatives than Intrasite. The earliest epidermal development of the wounds treated with chitin-PAA-GTMAC (1:4) among the tested materials suggested the most promising of this material for the treatment of full-thickness open wound.

Synthesis of GTMAC modified chitin-PAA gel and evaluation of its biological properties.

The dressing prepared from GTMAC modified chitin-PAA was introduced with the aim of facilitating wound healing, particularly those effectively absorbing exudates, maintaining a moist wound environment and controlling bacterial proliferation. Chitin was chemically modified with acrylic acid to encourage a moist wound healing environment. The highly water-absorbable resulting product (chitin-PAA) was further reacted with glycidyltrimethylammonium chloride (GTMAC) to impart antibacterial activities. The final product, chitin-PAA-GTMAC was characterized by the techniques of Fourier Transform Infrared (FTIR), solid state (15) N NMR, and elemental analysis. Their cytotoxicity and antibacterial activities against S. epidermidis and E. coli were evaluated which found increasing effects in those properties with increasing degree substitution of GTMAC. All materials also showed good blood-clotting ability. The collagen gel contraction assay was used to analyze the behavior of fibroblasts after contact with the gels. The extent of the gel contraction as well as the examination of the secreted interleukin-8 (IL-8) and transforming growth factor-ß1 (TGF-ß1) were investigated. The results showed that chitin-PAA modified with GTMAC could stimulate the production of IL-8, but TGF-ß1. Fibroblasts presented normal spreading and formation of cellular processes in the collagen gels with all of the modifications. Furthermore, all modified gels except for the highest GTMAC content gel [chitin-PAA-GTMAC (1:20)] were found a greater extent in gel contraction than the unmodified chitin-PAA. It suggested the promoting effect of GTMAC on cell proliferation if the GTMAC content in the gel was not too high, that is, the mole ratio of glucosamine to GTMAC of the gel should not greater than 1:10.

Comparative study between chitin/polyacrylic acid (PAA) dressing, lipido-colloid absorbent dressing and alginate wound dressing: a pilot study in the treatment of partial-thickness wound.

BACKGROUND: Polyacrylic acid grafted chitin (Chitin-PAA) contains a hydrogel characteristic that makes it more suitable for wound dressing application. In animal models, Chitin-PAA dressing exhibited properties as a promising dressing. Epithelization promotion, rapid reduction of wound size, reduction of inflammatory cell response, and less toxicity had been noted. OBJECTIVE: Carryout a pilot clinical comparative study of Chitin-PAA dressing, lipido-colloid absorbent dressing, and alginate wound dressing in the treatment of partial-thickness wound. MATERIAL AND METHOD: Between June 2006 and March 2007, 36 partial-thickness wounds were randomized into three groups and three different types of dressing were used. Each wound was treated until it was completely healed, and a visual analogue scale was used for the pain evaluation. RESULT: The present study shows the visual analogue pain score in the Chitin-PAA group seems to be a bit higher than the Urgocell group but not statistically different. The completely healed day is not significantly different. Three patients in the lipido-colloid absorbent dressing groups had wound infection but eventually healed after treatment. CONCLUSION: There was no statistical difference in terms of visual analogue pain score and healing time between the lipido-colloid absorbent dressing, alginate dressing, and chitin-PAA dressing.

Preparation of acrylic grafted chitin for wound dressing application.

Chitin grafted with poly(acrylic acid) (chitin-PAA) was prepared with the aim of obtaining a hydrogel characteristic for wound dressing application. The chitin-PAA films were synthesized at various acrylic acid feed contents to investigate its effect on water sorption ability. Acrylic acid (AA) was first linked to chitin, acting as the active grafting sites on the chain that was further polymerized to form a network structure. The evidences of grafting were found from FTIR and solid state 13C NMR spectra. The TGA results exhibited the high degradation temperature of the grafted product suggesting the formation of a network structure. The degree of swelling (DS) of chitin-PAA films was found in the range of 30-60 times of their original weights depending upon the monomer feed content. The chitin-PAA film with 1:4 weight ratio of chitin:AA, possessed optimal physical properties. The cytocompatibility of the film was investigated with a cell line of L929 mouse fibroblasts. The morphology and behavior of the cells on the chitin-PAA film were determined after different time periods of culture up to 14 days. The L929 cells proliferated and attached well onto the film. These results suggested that the 1:4 chitin-PAA has a potential to be used as a wound dressing.