Recording stretching response of single polymer chains adsorbed on solid substrates

Elastic traits of the extensible discrete wormlike chain model

Polymer models play the special role of elucidating the elementary features describing the physics of long molecules and become essential to interpret the measurements of their magnitudes. In this work the end-to-end distance of an extensible discrete wormlike chain polymer as a function of the applied force has been calculated both numerically and analytically, the latter as an effective approximation. The numerical evaluation uses the transfer matrix formalism to obtain an exact calculation of the partition function, while the analytic derivations generalize the simple phenomenological formulas largely used up to now. The obtained formulas are simple enough to be implemented in the fit analysis of experimental data of semiflexible extensible polymers, with the result that the elastic parameters obtained are compatible with previous measurements, and more, their accuracy strongly improves in a large range of chain extensibility.

Freely jointed chain models with extensible links

Analytical relations for the mechanical response of single polymer chains are valuable for modeling purposes, on both the molecular and the continuum scale. These relations can be obtained using statistical thermodynamics and an idealized single-chain model, such as the freely jointed chain model. To include bond stretching, the rigid links in the freely jointed chain model can be made extensible, but this almost always renders the model analytically intractable. Here, an asymptotically correct statistical thermodynamic theory is used to develop analytic approximations for the single-chain mechanical response of this model. The accuracy of these approximations is demonstrated using several link potential energy functions. This approach can be applied to other single-chain models, and to molecular stretching in general.

Traditional Chinese medicine (TCM) massage for the treatment of congenital muscular torticollis (CMT) in infants and children: A systematic review and meta-analysis

BACKGROUND AND PURPOSE

Congenital muscular torticollis (CMT) is a musculoskeletal condition occurring in infants and children. This systematic review is conducted to summarize the current evidence on the effects and safety of TCM massage therapy for the treatment of CMT in infants and children.

METHODS

We searched for randomized controlled trials (RCTs) and quasi-RCTs on TCM massage for CMT in PubMed, Embase, CENTRAL, CINAHL, AMED, PsycINFO, Ovid MEDLINE, TCMLARS, ICTRP, CSTJ, CNKI, Wanfang Data, CBM, Taiwan Electronic Periodical Services, and the Index to Taiwan Periodical Literature System. Two reviewers conducted the data collection and analysis separately. Cochrane's collaboration tool was used to assess the risk of bias, and GRADEpro was used to assess the overall quality of the evidence. RevMan 5.3 software was used for data analysis with a random-effect model.

RESULTS

A systematic review of six RCTs and one quasi-RCT was conducted with a meta-analysis of two of the RCTs. Pooled analysis showed that TCM massage has similar effects to those of stretching therapy on CMT symptoms in terms of effective rate (risk ratio: 1.00, 95% CI: 0.94-1.06; I² = 0%; P = 0.99).

CONCLUSION

Evidence suggests that TCM massage therapy is beneficial for treating CMT in infants and children. Further clinical trials with high-quality methodologies need to be conducted.

Pulling angle-dependent force microscopy

In this paper, we describe a method allowing one to perform three-dimensional displacement control in force spectroscopy by atomic force microscopy (AFM). Traditionally, AFM force curves are measured in the normal direction of the contacted surface. The method described can be employed to address not only the magnitude of the measured force but also its direction. We demonstrate the technique using a case study of angle-dependent desorption of a single poly(2-hydroxyethyl methacrylate) (PHEMA) chain from a planar silica surface in an aqueous solution. The chains were end-grafted from the AFM tip in high dilution, enabling single macromolecule pull experiments. Our experiments give evidence of angular dependence of the desorption force of single polymer chains and illustrate the added value of introducing force direction control in AFM.