Hydroxyapatite (HA) is widely used in bone tissue engineering for its bioactivity and biocompatibility, and a growing number of researchers are exploring ways to improve the physical properties and biological functions of hydroxyapatite. Up to now, HA has been used as inorganic building blocks for tissue engineering or as nanofillers to blend with polymers, furthermore, various methods such as ion doping or surface modification have been also reported to prepare functionalized HA. In this review, we try to give a brief and comprehensive introduction about HA-based materials, including ion-doped HA, HA/polymer composites and surface modified HA and their applications in bone tissue engineering. In addition, the prospective of HA is also discussed. This review may be helpful for researchers to get a general understanding about the development of hydroxyapatite based materials.

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BACKGROUND: The design of implants comprised of biodegradable electrospun nanofibers for the purpose of bridging injuries in damaged spinal cord is discussed. Electrospun nanofibers structurally mimic the extracellular matrix on which neurons and other cell types grow in vivo. This property has created great interest for their use in tissue engineering applications. However, their employment as biomimetic surfaces for such in vivo applications is still in its infancy.RESULTS: A nonwoven fabric comprised of electrospun polyamide nanofibers supported modest axonal regeneration in injured adult rat spinal cord. Covalent modification of the nanofibers with a bioactive peptide derived from the neuroregulatory extracellular matrix molecule tenascin‐C enhanced the ability of the nanofibers to facilitate axonal regrowth. However, the random orientation of the nanofibrillar fabric folds was an impediment to the forward movement of axons.CONCLUSIONS: Polyamide nanofibers covalently modified with neuroactive molecules provide a promising material for grafts to promote spinal cord regeneration. However, for the proper guidance of regrowing axons, attention must be paid to the engineering of ordered nanofibrillar structures. Copyright © 2007 Society of Chemical Industry

heat engines and transforming the asgenerated mechanical energy into electricity. [2][3][4][5] Compared with traditional unsustainable method, thermoelectric materials, which can transform the temperature gradient from waste heat or solar thermal energy into electricity through the Seebeck effect, have triggered great interest in the development of wearable cooling/heating devices and low-temperature energy generators. [6][7][8][9][10][11][12][13][14][15][16][17] Inorganic thermoelectric materials exhibit superior thermoelectric figure of merit than the organic ones, but their low abundance, high-cost, heaviness, and brittleness usually prevents their applications for flexible and/or nontoxic devices. [18][19][20][21][22][23][24] In contrast, organic thermoelectric materials present intrinsically low thermal conductivity and high mechanical flexibility, making them versatile in green energy harvesting and thermoelectric refrigeration (Figure 1). [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] The energy conversion efficiency of the thermoelectric materials can be estimated by the dimensionless figure of merit ZT = S 2 σT/κ, where S is the thermopower or Seebeck coefficient, σ is electrical conductivity of materials, T is the absolute temperature, and κ represents the thermal conductivity. [43][44][45][46][47][48][49][50][51] Superficially, increasing S and σ, and decreasing κ can infinitely raise the value of ZT. However, the strong interdependence among these three parameters is extremely challenging. [52][53][54][55][56] Over the past years, scientists have managed to increase the ZT values of organic thermoelectric materials via molecular design, phonon, and electron transport decoupling, and production of hybrid composites incorporating high thermoelectric particles. [57][58][59][60][61][62][63][64][65][66][67][68][69] In this review, the thermoelectric performances of the organic single-component materials, hybrid composites, and novel ionogels developed over the last several years are discussed separately in terms of the respective parameter tuning and pathway optimization. The current state of the art of organic thermoelectric materials is primarily highlighted based on their structure-property relationship. In particular, the marvelous progress that has allowed organic thermoelectric materials to compete with traditional inorganic compounds is described. Finally, organic thermoelectric generators containing different legs with variousoutput powers and their multiple applications are briefly summarized.The enormous demand for waste heat utilization and burgeoning ecofriendly wearable materials has triggered huge interest in the development of thermoelectric materials that can harvest low-cost energy resources by converting waste heat to electricity efficiently. In particular, due to their high flexibility, nontoxicity, cost-effectivity, and promising applicability in various fields, organic thermoelectric materials are drawing more attention compared with their toxic, expensive, he...

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Thermoelectrics that enable direct heat–electricity conversion possess unique advantages for green and renewable energy revolution and have received rapidly growing attention in the past decade. Among various thermoelectric materials, metal–organic frameworks (MOFs) with intrinsic high porosity and tunable physical/chemical properties are emerging as a promising class of materials that have been demonstrated to exhibit many unique merits for thermoelectric applications. Their structural topologies and thermoelectric properties can be facilely regulated by precisely selecting and arranging metal centers and organic ligands. Besides, a large variety of guest molecules can be incorporated within their pores, giving rise to novel avenues of raising energy‐conversion efficiency. This review focuses on the recent advances in designing conductive MOFs and MOF‐based composites for thermoelectric applications. It first introduces the fundamental thermoelectric parameters and the underlying regulation mechanisms specifically effective for MOFs, then summarizes the related studies conducted in recent years, where the structural design strategies of tuning thermoelectric properties are demonstrated and discussed. In the final part, conclusions and perspectives with the envision of an outlook for this promising area are presented.

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