Estimation of distal arm joint angles from EMG and shoulder orientation for transhumeral prostheses

In this paper, we quantify the extent to which shoulder orientation, upper-arm electromyography (EMG), and forearm EMG are predictors of distal arm joint angles during reaching in eight subjects without disability as well as three subjects with a unilateral transhumeral amputation and targeted reinnervation. Prior studies have shown that shoulder orientation and upper-arm EMG, taken separately, are predictors of both elbow flexion/extension and forearm pronation/supination. We show that, for eight subjects without disability, shoulder orientation and upper-arm EMG together are a significantly better predictor of both elbow flexion/extension during unilateral ($R^2=0.72$) and mirrored bilateral ($R^2=0.72$) reaches and of forearm pronation/supination during unilateral ($R^2=0.77$) and mirrored bilateral ($R^2=0.70$) reaches. We also show that adding forearm EMG further improves the prediction of forearm pronation/supination during unilateral ($R^2=0.82$) and mirrored bilateral ($R^2=0.75$) reaches. In principle, these results provide the basis for choosing inputs for control of transhumeral prostheses, both by subjects with targeted motor reinnervation (when forearm EMG is available) and by subjects without target motor reinnervation (when forearm EMG is not available). In particular, we confirm that shoulder orientation and upper-arm EMG together best predict elbow flexion/extension ($R^2=0.72$) for three subjects with unilateral transhumeral amputations and targeted motor reinnervation. However, shoulder orientation alone best predicts forearm pronation/supination ($R^2=0.88$) for these subjects, a contradictory result that merits further study.     

Protein crystal’s shape and polymorphism prediction within the limits resulting from the exploration of the Miyazawa–Jernigan matrix

A computer study of the prediction of the protein crystal’s shape and polymorphism of crystal’s structures within the limits resulting from the exploration of the Miyazawa–Jernigan matrix is presented. In this study, a coarse-graining procedure was applied to prepare a two-dimensional growth unit, where instead of full atom representation of the protein a two-type (hydrophobic–hydrophilic, HP) aminoacidal representation was used. The interaction energies between hydrophobic ($E_{\text{HH}}$) aminoacids were chosen from the well-known HP-type models ($E_{\text{HH}}\in [-4\text{,}-3\text{,}-2.3\text{,}-1]$), whereas interaction energies between hydrophobic and hydrophilic aminoacids ($E_{\text{HP}}$) as well as interaction energies between hydrophilic aminoacids ($E_{\text{PP}}$) were chosen from the range: $<-1\text{,}1>$, but not all values from this range fulfiled limitations resulting from the exploration of the Miyazawa–Jernigan matrix. Exploring every positively vetted combinations of energy interactions a polymorphism of the unit cell was observed what led to the fact that different final crystal’s shapes were obtained.     

Structural Analysis of a Trimer of β2-Microgloblin Fragment by Molecular Dynamics Simulations

A peptide ${\beta }_2$-${\text{m}}_{21?31}$, which is a fragment from residue 21 to residue 31 of ${\beta }_2$-microgloblin, is experimentally known to self-assemble and form amyloid fibrils. In order to understand the mechanism of amyloid fibril formations, we applied the replica-exchange molecular dynamics method to the system consisting of three fragments of ${\beta }_2$-${\text{m}}_{21?31}$. From the analyses on the temperature dependence, we found that there is a clear phase transition temperature in which the peptides aggregate with each other. Moreover, we found by the free energy analyses that there are two major stable states: One of them is like amyloid fibrils and the other is amorphous aggregates.     

New chemistry based on reduction of homobinuclear bis(μ-phosphido) metal complexes

Studies are reported on the chemical reduction of the homobinuclear bis(μ-phosphido) metal complexes ${(CO)}_3\stackrel{︹}{Fe{(\mu -P{R}_2)}_{2}F}e{(CO)}_3$ (R = Ph or Me), ${(NO)}_2-\stackrel{︹}{Fe{(\mu -PP{h}_2)}_{2}F}e{(NO)}_2$ and ${(CO)}_4\stackrel{︹}{M{(\mu -PP{h}_2)}_{2}M}{(CO)}_4$ (M = Mo or W). Two reduction pathways have been observed which result in different two-electron transformations: (1) with Na or LiAlH₄, electron transfer to yield the corresponding symmetric dianions of the type L_nM(μ-PR₂)₂ML_n^2? without metalmetal bond and (2) with M′BR′₃H(M′ = Li, Na, or K; R′ = Et or sec-Bu), hydride transfer to give monoanionic complexes of the type $L_n\stackrel{︹}{M(\mu -P{R}_2)(\mu -L)M}{L}_{n?1}{(P{R}_{2}H)}^{?}$ or $L_n\stackrel{︹}{M(\mu -P{R}_2)M}{L}_n{(P{R}_{2}H)}^{?}$ (M = Fe, Mo, or W; L = CO or NO; R = Ph or Me). The monoanionic complexes can be deprotonated with n-BuLi at ?78 °C to the corresponding unsymmetric dianions $L_n\stackrel{︹}{M(\mu -P{R}_2)(\mu -L)M}{L}_{n?1}{(P{R}_2)}^{2?}$ (M = Fe; L = CO or NO; R = Ph) or symmetric dianions L_nM(μ-PR₂)₂ML_n^2? (M = Mo or W; L = CO; R = Ph). The unsymmetric dianions isomerize on slight warming to the symmetric dianions, which undergo protonation by CF₃COOH to yield the aforementioned monoanions. Reactions of several members of these three classes of binuclear anions with CF₃COOH, alkylating reagents, 1,1-diiodohydrocarbons and metal diiodo complexes have resulted in the synthesis of new binuclear and trinuclear compounds. Examples include ${(CO)}_3(H)\stackrel{︹}{Fe(\mu -PP{h}_2)Fe}{(CO)}_3(PP{H}_{2}H)$, ${(CO)}_3\stackrel{︹}{Fe(\mu -PP{h}_2)(\mu -C(R)O)Fe}{(CO)}_2(PP{h}_{2}R)$ (R = Me, Et, n-Pr, or i-Pr), ${(CO)}_4\stackrel{︹}{M{(\mu -PP{h}_2)}_{2}M}{(CO)}_3(C(R)Ome)$ (M = Mo or W; R = Me or Ph), ${(CO)}_2({\eta }^3?C_3{H}_5)\stackrel{︹}{Fe(\mu ?PP{h}_2)?F}e{(CO)}_3(PP{h}_2{C}_3{H}_5)$, ${(CO)}_4\stackrel{︹}{M{(\mu ?PP{h}_2)}_{2}M}{(CO)}_3(C(R)Ome)$, ${(NO)}_2\stackrel{︹}{Fe(\mu ?C{H}_2)(\mu ?P{h}_{2}PPP{h}_2)Fe}{(NO)}_2$, and Fe₂Co(η⁵-C₅H₅)(CO)(NO)₄(μ-PPh₂)₂. Synthetic and mechanistic studies on these reactions are presented.     

Modelling the mechanical response of elastin for arterial tissue

We compare two constitutive models proposed to model the elastinous constituents of an artery. Holzapfel and Weizsäcker [1998. Biomechanical behavior of the arterial wall and its numerical characterization. Comput. Biol. Med. 28, 377–392] attribute a neo-Hookean response, i.e. $\Psi =c(I_1-3))$, to the elastin whilst Zulliger et al. [2004a. A strain energy function for arteries accounting for wall composition and structure. J. Biomech. 37, 989–1000] propose $\Psi =c(I_1-3{)}^{3/2}$. We analyse these constitutive models for two specific cases: (i) uniaxial extension of an elastinous sheet; (ii) inflation of a cylindrical elastinous membrane. For case (i) we illustrate the functional relationships between: (a) the Cauchy stress (CS) and the Green–Lagrange (GL) strain; (b) the tangent modulus (gradient of the CS–GL strain curve) and linearised strain. The predicted mechanical responses are compared with recent uniaxial extension tests on elastin [Gundiah, N., Ratcliffe, M.B., Pruitt, L.A., 2007. Determination of strain energy function for arterial elastin: experiments using histology and mechanical tests. J. Biomech. 40, 586–594; Lillie, M.A., Gosline, J.M., 2007a. Limits to the durability of arterial elastic tissue. Biomaterials 28, 2021–2031; 2007b. Mechanical properties of elastin along the thoracic aorta in the pig. J. Biomech. 40, 2214–2221]. The neo-Hookean model accurately predicts the mechanical response of a single elastin fibre. However, it is unable to accurately capture the mechanical response of arterial elastin, e.g. the initial toe region of arterial elastin (if it exists) or the gradual increase in modulus of arterial elastin that occurs as it is stretched. The alternative constitutive model ($n=\frac{3}{2}$) yields a nonlinear mechanical response that departs from recent uniaxial test data mentioned above, for the same stretch range. For case (ii) we illustrate the pressure–circumferential stretch relationships and the gradients of the pressure–circumferential stretch curves: significant qualitative differences are observed. For the neo-Hookean model, the gradient decreases rapidly to zero, however, for $n=\frac{3}{2}$, the gradient decreases more gradually to a constant value. We conclude that whilst the neo-Hookean model has limitations, it appears to capture more accurately the mechanical response of elastin.