We study the coefficient of performance (COP) and its bounds of the Canot-like refrigerator working between two heat reservoirs at constant temperatures T h and T c , under two optimization criteria χ and Ω. In view of the fact that an "adiabatic" process takes finite time and is nonisentropic, the nonadiabatic dissipation and the finite time required for the "adiabatic" processes are taken into account. For given optimization criteria, we find that the lower and upper bounds of the COP are the same as the corresponding ones obtained from the previous idealized models where any adiabatic process undergoes instantaneously with constant entropy. When the dissipations of two "isothermal" and two "adiabatic" processes are symmetric, respectively, our theoretical predictions match the observed COP's of real refrigerators more closely than the ones derived in the previous models, providing a strong argument in favor of our approach.

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Background and ObjectivesDeproteinization is an indispensable process for the elimination of antigenicity in xenograft bones. However, the hydrogen peroxide (H2O2) deproteinized xenograft, which is commonly used to repair bone defect, exhibits limited osteoinduction activity. The present study was designed to develop a new method for deproteinization and compare the osteogenic capacities of new pepsin deproteinized xenograft bones with those of conventional H2O2 deproteinized ones.MethodsBones were deproteinized in H2O2 or pepsin for 8 hours. The morphologies were compared by HE staining. The content of protein and collagen I were measured by the Kjeldahl method and HPLC-MS, respectively. The physical properties were evaluated by SEM and mechanical tests. For in vivo study, X-ray, micro-CT and HE staining were employed to monitor the healing processes of radius defects in rabbit models transplanted with different graft materials.ResultsCompared with H2O2 deproteinized bones, no distinct morphological and physical changes were observed. However, pepsin deproteinized bones showed a lower protein content, and a higher collagen content were preserved. In vivo studies showed that pepsin deproteinized bones exhibited better osteogenic performance than H2O2 deproteinized bones, moreover, the quantity and quality of the newly formed bones were improved as indicated by micro-CT analysis. From the results of histological examination, the newly formed bones in the pepsin group were mature bones.ConclusionsPepsin deproteinized xenograft bones show advantages over conventional H2O2 deproteinized bones with respect to osteogenic capacity; this new method may hold potential clinical value in the development of new biomaterials for bone grafting.

Treatment of bone and joint tuberculosis remains a challenge. The development of tissue‐engineered drug‐loaded biomaterials has increased the therapeutic options. However, for the treatment of osteoarticular tuberculosis with severe local infection risks and high weight‐bearing requirements, it is still necessary to design materials consistent with bone biomechanics, cytocompatibility, and osteogenesis and to provide more effective antimicrobial functions. The antitubercular drugs isoniazid and rifampicin are loaded with gellan gum, and a 3D‐printed porous tantalum surface is treated with polydopamine to increase adhesion. The osteogenic induction and differentiation are tested using alkaline phosphatase, alizarin red staining, sirius red staining, and polymerase chain reaction testing. Bone regeneration in vivo is measured by X‐ray, micro‐computerized tomography, hard tissue sections, and fluorescence staining. The drug is released slowly in vitro and in vivo, increasing the duration of antibacterial action. The composite bio‐scaffolds inhibit Staphylococcus aureus growth, have good biocompatibility, and does not inhibit the induction of osteogenic differentiation of rat bone marrow mesenchymal stem cells. The composite bio‐scaffold can simultaneously achieve localized long‐term controlled drug release and bone regeneration and is a promising route for bone and joint tuberculosis treatment.

Tantalum has unique advantages as a biomaterial for repairing bone defects due to its outstanding bioactivity, excellent corrosion resistance, and mechanical properties. Ideal implants for bone repair should be of good biocompatibility and bioactivity, as well as ability to simulate the microstructure and mechanical environment of human bone tissues. Additive manufacturing can facilitate freedom of design for the macrostructure/ microstructure of bone implants with controlled mechanical properties; thus, this method has great potential. Additively manufactured tantalum implants provide a novel alternative for bone repair and are gaining increasing attention. This systematic review aims to comprehensively summarize the subsistent evidence from physicochemical, cellular, animal, and clinical studies on additively manufactured tantalum implants in repairing bone defects, for the first time. This work may provide researchers an essential grasp on the advances of additively manufactured tantalum implants.

A chitosan-based microsphere delivery system has been fabricated for controlled release of alendronate (AL). The present study aimed to incorporate the chitosan/hydroxyapatite microspheres-loaded with AL (CH/nHA-AL) into poly(L-lactic acid)/nanohydroxyapatite (PLLA/nHA) matrix to prepare a novel microspheres-scaffold hybrid system (CM-ALs) for drug delivery and bone tissue engineering application. The characteristics of CM-ALs scaffolds containing 10% and 20% CH/nHA-AL were evaluated in vitro, including surface morphology and porosity, mechanical properties, drug release, degradation, and osteogenic differentiation. The in vivo bone repair for large segmental radius defects (1.5 cm) in a rabbit model was evaluated by radiography and histology. In vitro study showed more sustained drug release of CM-AL-containing scaffolds than these of CM/nHA-AL and PLLA/nHA/AL scaffolds, and the mechanical and degradation properties of CM-ALs (10%) scaffolds were comparable to that of PLLA/nHA control. The osteogenic differentiation of adipose-derived stem cells (ASCs) was significantly enhanced as indicated by increased alkaline phosphates (ALP) activity and calcium deposition. In vivo study further showed better performance of CM-ALs (10%) scaffolds with complete repair of large-sized bone defects within 8 weeks. A microspheres-scaffold-based release system containing AL-encapsulated chitosan microspheres was successfully fabricated in this study. Our results suggested the promising application of CM-ALs (10%) scaffolds for drug delivery and bone tissue engineering.

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