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Regeneration of severely damaged enamel (e.g. deep demineralized lesions) is currently not possible, because the structural units of enamel crystal construction are removed after its maturation. The aim of this in vitro study was to evaluate the effect of surface impregnation by leucine-rich amelogenin peptide (LRAP) on the remineralization of eroded enamel using micro-focus x-ray computed tomography (µCT). Fifteen bovine enamel blocks were embedded in resin and three zones (sound, demineralization, and remineralization) were defined on each specimen. Lesions were prepared by immersing the samples in demineralization solution for 7 d. The samples were soaked in distilled water or 60 or 120 µg mL(-1) solution of LRAP in water for 30 min. After the surface treatment, specimens were incubated in artificial saliva for either 5 or 10 d at 37 °C. The amount of mineral gain (dΔZ%) and the relative changes in the lesion depth (dLD%), obtained from µCT, were used to evaluate the effect of LRAP on the remineralization of lesions. The effects of LRAP on cross-sectional integrated hardness ΔINH were studied after 10 d using nanoindentation. ANOVA test was used to determine the effect of time and/or LRAP concentration on dΔZ%, dLD% and ΔINH mean values. Tukey's analysis was used for multiple comparison testing (α = 0.05). Analysis of µCT data showed significant effect of time and LRAP concentration on the dΔZ% (p = 0.013, p = 0.003) and the dLD% (p  <  0.001, p = 0.002) mean values. The nanoindentation hardness was significantly improved by 120 µg mL(-1) LRAP (p = 0.02). Also, the peptide treatment affected the mineral distribution throughout the lesion by inhibiting of superficial deposition. This study showed that the treatment of eroded lesions in enamel by LRAP can improve and regulate the pattern of remineralization in vitro.

Objective: The objective of this research is to characterize the mechanical interactions of (1) soft, compliant and (2) non-compliant implants with the surrounding brain tissue in a rodent brain. Understanding such interactions will enable the engineering of novel materials that will improve stability and reliability of brain implants., Approach: Acute force measurements were made using a load cell in n = 3 live rats, each with 4 craniotomies. Using an indentation method, brain tissue was tested for changes in force using established protocols. A total of 4 non-compliant, bare silicon microshanks, 3 non-compliant polyvinyl acetate (PVAc)-coated silicon microshanks, and 6 compliant, nanocomposite microshanks were tested. Stress values were calculated by dividing the force by surface area and strain was estimated using a linear stress-strain relationship. Micromotion effects from breathing and vascular pulsatility on tissue stress were estimated from a 5 s interval of steady-state measurements. Viscoelastic properties were estimated using a second-order Prony series expansion of stress-displacement curves for each shank., Main Results: The distribution of strain values imposed on brain tissue for both compliant nanocomposite microshanks and PVAc-coated, non-compliant silicon microshanks were significantly lower compared to non-compliant bare silicon shanks. Interestingly, step-indentation experiments also showed that compliant, nanocomposite materials significantly decreased stress relaxation rates in the brain tissue at the interface (p < 0.05) compared to non-compliant silicon and PVAc-coated silicon materials. Furthermore, both PVAc-coated non-compliant silicon and compliant nanocomposite shanks showed significantly reduced (by 4-5 fold) stresses due to tissue micromotion at the interface., Significance: The results of this study showed that soft, adaptive materials reduce strains and strain rates and micromotion induced stresses in the surrounding brain tissue. Understanding the material behavior at the site of tissue contact will help to improve neural implant design.

Cell behavior is guided by the complex interplay of matrix mechanical properties as well as soluble and immobilized biochemical signals. The development of synthetic scaffolds that incorporate key functionalities of the native extracellular matrix (ECM) for support of cell proliferation and tissue regeneration requires that stiffness and immobilized concentrations of ECM signals within these biomaterials be tuned and optimized prior to in vitro and in vivo studies. A detailed experimental sensitivity analysis was conducted to identify the key polymerization conditions that result in significant changes in both elastic modulus and immobilized YRGDS within visible light photopolymerized poly(ethylene glycol) diacrylate hydrogels. Among the polymerization conditions investigated, single as well as simultaneous variations in N-vinylpyrrolidinone and precursor concentrations of acryl-PEG3400-YRGDS resulted in a broad range of the hydrogel elastic modulus (81-1178 kPa) and YRGDS surface concentration (0.04-1.72 pmol cm(-2)). Increasing the YRGDS surface concentration enhanced fibroblast cell adhesion and proliferation for a given stiffness, while increases in the hydrogel elastic modulus caused decreases in cell adhesion and increases in proliferation. The identification of key polymerization conditions is critical for the tuning and optimization of biomaterial properties and the controlled study of cell-substrate interactions.

The mechanical damage caused by the insertion of a foreign body into living tissue is inevitable, especially when a considerable stiffness mismatch is present, as in the case of micromachined neural implants and brain tissue. However, the response surface model based on a central composite experimental design described in this study showed that for particular configurations of the implant tip angle, width, thickness or insertion speed, some of these factors could be safely increased without causing an unwanted significant force or tissue dimpling increase. The model covers chisel tip angles between 10° and 50°, implant widths within the 200-400 µm range and thicknesses between 50 and 150 µm. The insertion speed has been varied from 10 up to 100 µm s(-1) to reach a final insertion depth of 6 mm. Coating the implant with parylene C proved to be beneficial in reducing the friction between the implant and the surrounding tissue. Successfully validated for a particular implant geometry, this model could be used as an insertion behavior prediction tool for the design optimization of future neural implants.

A new titanium alloy (Ti-12.5Zr-3Nb-2.5Sn) was developed to meet the needs of clinical requirements for medical titanium alloys and improve the properties of existing titanium alloys. The as-prepared alloy was solution treated at 500 °C for 3 h in vacuum followed by water quenching. Tensile, wear and hardness tests were carried out to examine the mechanical properties of the Ti-Zr-Nb-Sn alloy. Oral mucous membrane irritation test was performed to evaluate the surface biological properties of the Ti-Zr-Nb-Sn alloy. The results suggested that the surface hardness and wear-resistant properties of the Ti-12.5Zr-3Nb-2.5Sn alloy were superior to commercially pure Ti. The oral mucous irritation test showed that all samples had no mucous membrane irritation. It indicates that Ti-12.5Zr-3Nb-2.5Sn has large potential to be used as dental restoration material.

The aim of this study was to evaluate the mechanical behavior of endodontically treated teeth restored with fiber reinforced composite posts versus titanium posts, by both experimental testing and numerical simulation (finite element analysis (FEA)). Forty maxillary central incisors were endodontically treated to a size 45 file and then obturated using gutta-percha points and sealer with the lateral condensation technique. The teeth were divided into four groups of ten teeth each. All the posts were of similar dimensions. The first group was restored using carbon fiber reinforced posts (CB), the second and third groups were restored using glass fiber reinforced posts (DP and FW, respectively), and the fourth group (control group) was restored using conventional titanium posts (PP). Half of the specimens of every group were submitted to hydrothermal cycling (2000 cycles, at 5 °C and 55 °C, respectively). All specimens were loaded until failure at a 45° angle with respect to the longitudinal axis at a cross head speed of 0.5 mm min(-1). A two-dimensional finite element model was designed in order to simulate the experimentally obtained results. Mechanical testing revealed that teeth restored with titanium posts exhibited the highest fracture strength. Debonding of the core was the main failure mode observed in glass fiber posts, whereas vertical root fractures were observed in the titanium posts. FEA revealed that the maximum stresses were developed at the interface between the post, dentin and the composite core critical regions in all three cases. Hydrothermal cycling had no significant effect on the fracture behavior of fiber reinforced composite posts.

The cleaning of fresh bones to remove their soft tissues while maintaining their structural integrity is a basic and essential part of bone studies. The primary issue is how the cleaning process influences bone microstructures and mechanical properties. We cleaned fresh lamb femurs using enzymatic maceration in comparison with water maceration at room temperature. The microstructures of these compact bones were examined using scanning electron microscopy (SEM) and their porosities were quantified using image processing software. The bone microhardness was measured using a Vickers indentation tester for studying the mechanical properties. The results show that enzymatic maceration of compact bone resulted in a significant microhardness reduction in comparison with water maceration. However, enzymatic maceration did not cause any significant change of porosity in bone structures.

Epiretinal prostheses used to treat degenerative retina diseases apply stimulus via an electrode array fixed to the ganglion cell side of the retina. Mechanical pressure applied by these arrays to the retina, both during initial insertion and throughout chronic use, could cause sufficient retinal damage to reduce the device's effectiveness. In order to understand and minimize potential mechanical damage, we have used finite element analysis to model mechanical interactions between an electrode array and the retina in both acute and chronic loading configurations. Modeling indicates that an acute tacking force distributes stress primarily underneath the tack site and heel edge of the array, while more moderate chronic stresses are distributed more evenly underneath the array. Retinal damage in a canine model chronically implanted with a similar array occurred in correlating locations, and model predictions correlate well with benchtop eyewall compression tests. This model provides retinal prosthesis researchers with a tool to optimize the mechanical electrode array design, but the techniques used here represent a unique effort to combine a modifiable device and soft biological tissues in the same model and those techniques could be extended to other devices that come into mechanical contact with soft neural tissues.