寰枢椎后路柔性固定的生物力学研究

目的分析细棒、PEEK棒固定对寰枢关节稳定性的影响。方法采用6具新鲜成人枕骨(occipital bone,Oc)~颈椎C4节段进行测试,模拟以下手术及固定状态:①完整状态;②损伤状态:枢椎齿状突II型骨折;③坚强固定:寰枢椎均采用普通椎弓根螺钉固定,直径3.5 mm钛棒连接;④PEEK棒:直径3.5 mm的PEEK棒连接;⑤细棒:直径2.0 mm钛棒连接。采用重复测量实验设计,在完整、损伤和不同的固定状态下,通过脊柱试验机对标本分别施加1.5 N·m的前屈/后伸、左/右侧弯和左/右轴向旋转的纯力偶矩。采用Optotrak三维运动测量系统连续采集标本运动,分析寰枢椎之间角度运动范围和中性区。结果采用直径3.5 mm的钛棒,2.0 mm的细棒以及3.5 mm的PEEK棒固定后,在前屈、后伸、侧弯和旋转方向上均显著减小了固定节段的运动范围(P<0.05)。直径3.5 mm和2.0 mm的棒固定后的运动范围,在各个方向上无显著性差异。PEEK棒固定的运动范围仅在侧弯方向上大于坚强固定(P=0.005),其他方向无显著性差异。3种固定方式在屈伸、侧弯和旋转方向上均显著减小了固定节段的中性区(P<0.05)。各种固定方式之间相比较,无显著性差异(P>0.05)。结论在寰枢关节采用直径2.0 mm的细棒固定,与坚强固定的稳定性相当。采用直径3.5 mm的PEEK棒固定,在前屈、后伸、旋转方向上与坚强固定的稳定性相当,在侧弯方向上弱于坚强固定。     

镍钛形状记忆合金锯齿臂环抱器内径与开口距离对其抱持力影响的实验研究

目的观察镍钛形状记忆合金环抱器固定骨折时,环抱器臂拉开距离对环抱器回复力的影响;了解镍钛形状记忆合金环抱器固定骨折时,环抱器内径与需固定骨直径之比对其抱持力的影响。方法(1)用1-Cr-13钢制成直径5mm,长度为27、28、29、30、31、32和33mm一系列的小钢棒,在小钢棒上磨出一个平面,该平面长度等同于小钢棒长度、宽为3mm,再将应变片贴于平面上,密封,制成一系列不同长度的压力传感器。(2)利用不同长度的压力传感器模拟不同直径的骨,将环抱器臂初始开口处到不同距离的臂中间置入同一压力传感器,在环抱器升温回复过程中紧夹压力传感器,利用YJ-35电阻应变仪采样测得压力传感器发生的应变值,重复上述过程。环抱器臂之间置入不同长度的压力传感器,测得不同压力传感器发生的应变值。(3)利用SAS6.12统计软件分析以上所得数据。结果(1)环抱器臂升温后给予压力传感器的抱持力随着初始开口的增大逐渐减小。(2)当内径为27mm的环抱器初始开口与臂之间置入长度为32mm的压力传感器时,环抱器臂升温回复后给予压力传感器的抱持力最大。结论(1)环抱器的臂拉开至能够安放已复位的骨折处即可,应避免将环抱器臂拉开距离过大。(2)环抱器内径=0.87×骨直径可用作临床选取合适大小镍钛形状记忆合金环抱器的公式。     

滑槽钉生长棒内固定系统单边固定对幼猪脊柱发育的影响

目的观察滑槽钉生长棒内固定系统单边固定对幼猪脊柱发育的影响。方法将15只3月龄幼猪采用完全随机化法随机分为3组：A组（5只）为空白对照组,自幼猪后路单侧切开,仅显露单侧椎板;B组（5只）为对照组,同法显露单侧椎板后常规椎弓根钉系统固定;C组（5只）为实验组,同法显露后单侧置入滑槽钉生长棒内固定系统固定。术后3个月应用X线测量T6-10、T10-14椎体的平均高度,T6-10椎间隙的平均高度,以及C组的钛棒上下两端滑动的平均距离。术后3个月时处死实验动物,选取固定节段的椎间盘观察生长板软骨细胞的形态学变化。结果术后3个月,C组T6-10、T10-14椎体的平均高度分别为（26．81±1．70）mm、（27．43±2．92）mm,T6-10椎间隙的平均高度为（2．13±0．17）mm,与A组的（27．13±3．31）mm、（27．91±3．03）mm、（2．20±0．14）mm比较,差异均无统计学意义（P值均〉0．05）,而与B组的（22．30±2．52）mm、（22．62±2．11）mm、（0．82±0．41）mm比较增加明显,差异均有统计学意义（P值均〈0．05）,C组钛棒上下两端滑动平均距离42．7mm。C组生长板软骨细胞层高度（165．6±1．7）μm与A组（167．2±6．8）μm比较差异无统计学意义（P〉0．05）;而与B组（140．4±7．2）μm比较增加明显,差异有统计学意义（P〈0．05）。结论滑槽钉生长棒内固定系统单边固定对幼猪脊柱生长发育无明显影响。     

牙科正畸钢丝矫治力的三维力学研究

本文采用三维力学传感器对正畸钢丝的矫治力进行了初步研究。结果表明 :本实验系统可以对简单变形钢丝的回复力进行三维 6轴 (即正交力系X、Y、Z各轴的力 ,以及绕各轴的转矩Mx、My、Mz)力学测量。实验结果显示 :钢丝在弯曲变形的状态下产生的主要回复力有 :弯矩Mx(不锈钢丝弯曲约 6 0°时达到最大值 )、垂直于固定端轴线的力Fy和固定点摩擦力Fz;钢丝在绕轴线纯扭转变形的状态下产生的主要回复力有 :转矩Mz和两固定点间的推力Fz。 (在两固定点间距离为 5 0mm的条件下 ,不锈钢丝平均每扭转 1°产生的转矩约为 0 .0 2 7N·cm ,推力约为 0 .0 19N)     

钛表面微弧氧化涂层的细胞生物活性

背景：微弧氧化技术可改善钛或钛合金的表面特征。 目的：研究纯钛表面微弧氧化涂层的表面性能及其对MC3T3-E1细胞早期黏附、增殖及成骨能力的影响。 方法：将46个直径10 mm、厚度2 mm圆盘状纯钛试件分为实验组和对照组。实验组置于含0.02 mol/Lβ-甘油磷酸二钠盐及0.2 mol/L乙酸钙的电解液中进行微弧氧化处理,对照组对试件进行机械抛光。扫描电子显微镜观察试件表面形貌,X射线能谱分析检测涂层表面钙磷比,X射线衍射分析检测涂层晶相构成。将MC3T3-E1细胞接种在两组试件表面,1,2,4 h电镜下观察细胞形态,在2,4,7 d通过CCK-8方法检测细胞增殖,并于7,14 d检测碱性磷酸酶活性。 结果与结论：经微弧氧化处理后,钛表面形成粗糙多孔的钙磷涂层,微弧氧化涂层主要元素为Ca、P、O及Ti,微弧氧化膜层主要由氧化钛、钛酸钙、磷酸钙及偏磷酸钙构成。电镜观察显示1 h 微弧氧化涂层表面细胞已伸出伪足,4 h呈现较典型的细胞形态。细胞在微弧氧化处理钛表面4,7 d的细胞增殖和7,14 d的碱性磷酸酶活性高于对照组。表明微弧氧化技术生成的粗糙多孔钙磷涂层能显著促进MC3T3-E1细胞的早期黏附、增殖及成骨活性。     

枕颈区后路柔性动态固定的生物力学研究

目的 探讨柔性和动态固定方式对枕颈区稳定性的影响。 方法 采用6具新鲜成人枕颈区Oc~C4节段进行测试,模拟以下状态：（1）完整状态;（2）损伤状态：齿状突II型骨折加寰枕关节囊损伤;（3）坚强固定：C1、C2用普通椎弓根螺钉固定,C3侧块螺钉,直径3.5 mm钛棒连接;(4)柔性固定：直径2.0 mm钛棒连接;(5)C1用2枚转动钉固定;(6)C1、C2用4枚转动钉固定;（7）C1、C2、C3用6枚转动钉固定。通过脊柱试验机对标本施加1.5 Nm的纯力偶矩,三维运动测量系统分析枕颈区Oc~C3角度运动范围和中性区。 结果 直径2.0 mm的棒固定后的运动范围,在各个方向上均大于坚强固定,有显著性差异（P<0.05）。与坚强固定比较,在 C1、C2采用2~4枚转动钉固定,在各方向上运动范围相当（P>0.05）。 C1、C2、C3使用6枚转动钉固定仅在旋转方向上明显增加了Oc~C3运动范围,差别有统计学意义（P=0.031）。不同固定方式在屈伸、侧弯和旋转方向上均显著减小了固定节段的中性区（P<0.05）。 结论 枕颈区Oc~C3节段,采用直径2.0 mm的细棒固定,各方向的稳定性均弱于坚强固定。在C1、C2采用2~4枚转动钉固定,与坚强固定的稳定性相当。在C1、C2、C3采用6枚转动钉固定,仅在旋转方向上弱于坚强固定。     

不同表面处理方法对纯钛表面形貌及成分的影响

分别用HNO3、热H2SO4/H2O2、热H2SO4/HC l处理纯钛片30 m in。采用扫描电子显微镜、X射线光电子能谱对试样的表面形貌及成分进行分析。扫描电镜结果显示,HNO3组表面形貌光滑,平整;而H2SO4/HC l、H2SO4/H2O2处理方法可获得粗糙的表面,其中H2SO4/HC l处理后的表面孔隙更大。X射线光电子能谱分析表明:三组钛片表面的主要成分均为钛、氧和碳,H2SO4/H2O2组的碳含量最低,而H2SO4/HC l组碳含量最高。HNO3组和H2SO4/H2O2组表面除了T iO2还存在T i2O3、T iO、金属T i等多种物质,而H2SO4/HC l组表面只存在T iO2。     

射频消融肾交感神经的体外实验研究

目的射频消融肾交感神经治疗顽固性高血压在临床上取得一定的疗效,它是通过插入肾动脉的射频导管释放能量,选择性毁坏外膜上的肾交感神经纤维,降低其活性以达到降压的目的,但是射频能量在消融交感神经的穿透能力受消融条件影响。本实验采用体外肝脏中的血管模仿肾动脉,探究不同消融条件下温度场的变化情况。方法实验中使用含有血管的体外牛肝21个(分解块),采用水流模拟血管中的血液流动,进行射频消融。采集血管壁外周距离消融点上方8~10 mm处组织中的温度以及下游水流中心区的温度,研究该条件下射频消融对组织和血管下游的影响。同时通过改变消融时间以及水流速度,研究不同情况下的消融结果。结果 (1)当消融点与水流中心测温点的距离增加,水流中心消融前后温度ΔT值就会降低。在距离7 cm的情况下,水流温度只上升了1.11℃,说明射频能量对血流下游温度的影响是有限的。(2)随着消融时间由8 min逐渐增加到10 min,水流温度ΔT值与消融点上方组织温度ΔT值均增加。(3)水流速度由0.28 m/s增加到0.365 m/s,则水流温度的ΔT值与消融点上方组织温度ΔT值均下降。(4)射频消融所造成的温度变化,消融点上方组织平均升高3.97℃,水流中心点平均升高2.17℃。结论在10 min内对血管内壁进行消融,消融点外周上方组织和下游水流的温度上升,最大不超过6℃,对血液流动影响有限,基本验证了血管内射频消融术治疗的可行性。     

腰椎椎体间镍钛记忆合金支架的生物力学分析

目的 测试镍钛记忆合金支架的力学性能及用于腰椎间融合术的体外生物力学性能。方法 通过力学测试机测试支架的力学性能,并在新鲜腰椎标本上模拟腰椎间融合术,对比分析镍钛记忆合金支架及其配套的骨粒-可吸收骨水泥混凝物浇注植骨方法、传统盒状融合器用于腰椎间融合术的生物力学性能。结果 镍钛记忆合金支架最大抗压强度为(12 964±962) N,记忆特性有效范围内最大形变为(4.68±0.03) mm,形状恢复率为99.86%。相比于正常腰椎模型,单独使用镍钛记忆合金支架植入模拟腰椎间融合术后手术节段稳定性在前屈、后伸、侧屈、旋转方向上均有增加,与采用传统盒状融合器相当(P>0.05)。而在复合使用配套设计的自体骨粒-可吸收骨水泥混凝物植骨后,手术节段活动度进一步降低(P<0.05),节段稳定性与附加椎弓根螺钉内固定组相当(P>0.05)。镍钛记忆合金支架植入后的抗拔出强度弱于传统盒状融合器(P<0.05),在配合使用自体骨粒-可吸收骨水泥混凝物植骨时的抗拔出强度显著强于传统盒状融合器(P<0.05)。结论 本研究的镍钛记忆合金支架同时配套设计了相匹配的骨粒-骨水泥混凝...     

制作颊侧多曲簧的牙用不锈钢丝的性能分析

目的 通过测试并比较480℃加热退火处理的四种不同品牌,直径为φ0.8 mm牙用不锈钢丝的电镜断口形貌和拉伸断裂机制,为临床选用适宜的牙用不锈钢丝制备颊侧多曲簧提供一定的参考。方法 选用弯制颊侧多曲簧的直径为φ0.8 mm的上齿牌、上海康桥牌、锋棱牌、上海荣祥牌的牙用不锈钢丝,应用万能拉伸仪测量比较四种材料480℃加热退火后的拉伸试验、金相组织微观测试及EDX能谱分析。结果 四种不同品牌的牙用不锈钢丝在480℃加热退火处理下,直径为φ0.8 mm锋棱牌牙用不锈钢丝拉伸能力最好,电镜观察见韧窝大小不一,深浅有别,Ni含量最高,更适合临床弯制颊侧多曲簧。结论 直径为φ0.8 mm锋棱牌牙用不锈钢丝较其他品牌牙用不锈钢丝,更适合弯制颊侧多曲簧,可考虑临床应用。     

Defining the heating characteristics of ferromagnetic implants using calorimetry

The induction heating of small, cylindrical ferromagnetic implants for localized tumors is currently under investigation. These thermal rods are implanted within a lesion in 1 cm(2) arrays and subsequently exposed to an externally applied alternating magnetic field. Implants absorb energy from the field and transfer it as heat to the surrounding tissue. To achieve a uniform temperature rise throughout the tissue volume and to account for any field-rod misalignment, 400 mW of power per implant is used as the design specification. The temperature to necrose cells must be greater than 46 degrees C. A calorimeter was constructed to confirm that the rod power output specification is satisfied at temperatures adequate for inducing cell death. The rods were designed to undergo a ferromagnetic to paramagnetic transition at temperatures of 55 degrees C, 60 degrees C, 65 degrees C, and 70 degrees C; this transition produces rods that are temperature self-regulating. Calorimetric results demonstrated that 55 degrees C, 60 degrees C, 65 degrees C, and 70 degrees C rods provided 400 mW at 47-51 degrees C, 51-53.5 degrees C, 57 degrees C, and 62.5-63.5 degrees C, respectively. Thermal rods provide sufficient power output at the temperatures necessary to cause thermal ablation of tumors. The higher-temperature rods give a greater margin to ensure that necrotizing temperatures can be achieved throughout the rod array even with minor misalignment.     

Experimental verification of conditions for near infrared spectroscopy (NIRS).

OBJECTIVES: in vitro assessment of the reproducibility and the optimal separation and position of the optodes in continuous wave (CW-) NIRS measurement of local inhomogeneities in absorption and/or scattering. METHODS: a CW- NIRS system (OXYMON) was used with laser diodes at wavelengths of 767 nm, 845 nm, 905 nm, 945 nm and 975 nm. For practical considerations (dimensions of neonatal head) the measurements were performed on a cylindrical tissue-equivalent phantom (70 mm diameter of base material with mua = 0.01 mm(-1) (800 nm) and mu's = 1.00 mm(-1) (800 nm)), containing rods with 10 x absorption, or 10 x scattering, and 5 x both Monte Carlo simulations were carried out of a cylinder with transport scattering coefficient mu's = 0.525 mm(-1) and absorption coefficient mua = 0.075 mm(-1) and two optode positions. RESULTS: reproducibility of repeated measurements (n = 10) was +/- 0.005 OD. Maximum OD in case of absorbing rod, and of absorbing + scattering rod was measured with optodes separated by 90 degrees and rod position angle symmetrically (45 degrees ) in between. Minimum OD for these rods was obtained with optodes at 150 degrees angle and rod position at 240 degrees (i.e. relative to transmitting optode position at 0 degrees ). A second maximum OD was obtained at an optode angle 180 degrees and rod position at 180 degrees. Maximum OD (i.e. attenuation) for the scattering rod was at optode separation angle of 90 degrees and rod at 0 degrees. Minimum OD for this case was obtained with optode angle of 180 degrees and rod positions around 80 degrees and 280 degrees. Maximum OD changes by absorbing rod were in the order of +0.12 OD and -0.04 OD, respectively. Simulations at an optode separation angle of 90 degrees showed a spatial sensitivity path enclosing the rod position at maximum absorption found experimentally. CONCLUSIONS: when considering the phantom as a realistic geometrical model for the neonatal head, it can be concluded that the optode position at 90 degrees angle would be optimal for detecting an inhomogeneity at 15 mm depth, i.e. the location of the periventricular white matter. Since the rods are relatively strongly different from the base material the question remains to be answered whether local ischemia, which might lead to irreversible brain damage, can be detected by CW-NIRS     

In vitro and in vivo studies on bioabsorbable ultra-high-strength poly(L-lactide) rods.

Ultra-high-strength poly(L-lactide) (PLLA) rods were fabricated using a drawing technique. Rods with a diameter of 3.2 mm and a draw ratio of 2.5:1 showed initial bending strength and modulus values of 240 MPa and 13 GPa, respectively. The purpose of this study was to investigate the in vitro and in vivo degradation of PLLA rods with a draw ratio of 2.5:1. The greater the rod diameter, the longer the bending strength was maintained in phosphate buffered saline at 37 degrees C. The bending strength retention of rods (diam. 3.2 mm) implanted in the subcutis of rabbits was almost equal to that of rods in the in vitro study, while those rods implanted in the medullary cavity of rabbit femora showed a slightly lower bending strength retention. Molecular weight was reduced to the greatest extent in the medullary cavity, followed by in the subcutis and in vitro. The weight of PLLA rods in the medullary cavity was reduced by 22% at 52 weeks and by 70% at 78 weeks after implantation. Histologically, no inflammatory or foreign body reaction was observed in the medullary cavity for 52 weeks. The drawn PLLA rods maintained a bending strength exceeding that of human cortical bone in the medullary canal for a period of 8 weeks, suggesting that the drawn PLLA rods may be useful in the repair of fractured human bones.     

The electrochemical behavior of Ti-6Al-7Nb alloy with and without plasma-sprayed hydroxyapatite coating in Hank's solution

The electrochemical behavior of Ti-6Al-7Nb alloy with and without plasma-sprayed hydroxyapatite (HA) coating was investigated in Hank's balanced salt solution at 37 degrees C. This behavior was evaluated by analyzing both corrosion potential variation with time curves and potentiodynamic polarization curves. The polarization curves were determined both in aerated and deaerated solutions. It was found that the corrosion potential of uncoated sample is always more noble than that of coated one. In aerated solutions the polarization curve of a coating-free alloy presents a typical passive/transpassive behavior, which is absent in the HA-coated alloy and in deaerated solution for both coated and uncoated conditions. In the latter polarization curves, the current density continuously increases with the increase of the potential. The corrosion rate determined from polarization curves is higher for HA-coated alloys, but it still can be considered negligible (less than 1 microA/cm(2)).     

Dimensional behavior of curing bone cement masses.

The curing of bone cements is accompanied by release of polymerization heat and, hence, by a temperature rise of the curing cement mass. This temperature rise causes expansion of enclosed air bubbles and evaporation of the volatile monomer. An overall expansion of 3 to 5 vol % has been mentioned in the literature. It has often been stated that this expansion favours the fixation of metal endoprostheses in the marrow cavity of bone. To check for the influence of this expansion on linear dimensions of the cured cement mass we filled stainless steel cylinders with a precision bore of 22,000 +/- 0,005 mm and a length of 120 mm with bone cement. After curing of the cement in a environment of 37 degrees C the resulting cement rod was released from the cylinder and the diameter of the rod was measured at 37 degrees C. The influence of the "foaming effect" on the transverse dimensions of the rods was studied by curing the cement at 37 degrees C and 2 atm air pressure in a high-pressure-vessel. This method of curing eliminates porosity in the cement almost completely, so that curing shrinkage is to be expected rather than expansion of the cement mass. The results indicate that a volumetric expansion of the cement during curing of cylindrical rods in laboratory experiments, can be accompanied by a linear diametrical shrinkage of the cement mass. The explanation of this phenomenon is to be sought in the fact that the volumetric expansion takes place at a time when the cement is still plastic; by the formation of gas bubbles, the cement is forced in longitudinal direction into the cylinder and when the temperature of the mass has passed through a maximum, the cooling of the cement mass results in a thermal shrinkage of approximately 0.4% linearly. Extrapolating this laboratory result to clinical situation one might doubt whether the overall expansion of bone cements during curing will result in a permanent positive pressure on the walls of marrow cavity and whether it will contribute to a better fixation of endoprostheses than in the case of a, still hypothetical, nonporous cement.     

(Ti, O)/Ti and (Ti, O, N)/Ti composite coatings fabricated via PIIID for the medical application of NiTi shape memory alloy

In this investigation, the plasma immersion ion implantation and deposition (PIIID) technique was used to fabricate (Ti, O)/Ti or (Ti, O, N)/Ti coatings on a NiTi shape memory alloy (SMA, 50.8 at.% Ni) to improve its corrosion, wear resistance, and bioactivity. After coating fabrication, the structure and properties of composite coatings were studied, and the coated and uncoated NiTi SMA samples were compared with each other. Scanning electron microscopic (SEM) examination of coating surfaces and cross-sections showed that (Ti, O)/Ti and (Ti, O, N)/Ti composite coatings were dense and uniform, having thickness values of 1.16 ± 0.08 μm and 0.95 ± 0.06 μm, respectively. X-ray diffraction (XRD) results revealed that there were no diffraction peaks corresponding to TiO(2) or TiN for (Ti, O)/Ti and (Ti, O, N)/Ti composite coatings, suggesting that after the PIIID treatment, TiO(2) and TiN were amorphous or nanosized in the coatings. Energy dispersive X-ray (EDX) analysis indicated that the interface between the coating and NiTi SMA substrate was gradual rather than sharp. In addition, EDX elemental mapping of coating cross-sections showed that Ni was depleted from the surface. Differential scanning calorimetry (DSC) curves revealed that the shape memory ability of NiTi SMA was not degraded by the PIIID treatment. The width of wear tracks on (Ti, O, N)/Ti coated NiTi SMA samples was reduced 6.5-fold, in comparison with that on uncoated samples. The corrosion potential (E(corr) ) was improved from -466.20 ± 37.82 mV for uncoated samples to 125.50 ± 21.49 mV and -185.40 ± 37.05 mV for (Ti, O)/Ti coated and (Ti, O, N)/Ti coated samples, respectively. Both types of coatings facilitated bone-like apatite formation on the surface of NiTi SMA in simulated body fluid (SBF), indicating their in vitro bioactivity.     

Biodegradable polyhydroxyalkanoate implants for osteomyelitis therapy: in vitro antibiotic release

Various random copolyesters of 3-hydroxybutyrate and 3-hydroxyvalerate (PHBV) and 3-hydroxybutyrate and 4-hydroxybutyrate P(3HB-4HB) were used in the construction of biodegradable, implantable rods for the local delivery of antibiotics (Sulperazone and Duocid) in chronic osteomyelitis therapy. Drug loading, type of active agent, and additional coating of the implant surface all have significant contributions to the in vitro release profile. The rate and duration of Sulperazone release from P(3HB-4HB) rods were controlled by the polymer/drug ratio (drug loading). The rate of drug dissolution was substantially higher than that of polymer degradation. Therefore, the release phenomenon was more dependent on drug dissolution rather than on polymer degradation or diffusion. Coating rods with the same type of polymer substantially reduced the initial burst effect observed with the uncoated rods, and significantly decreased the release rate so that the release kinetics became almost zero order. Antibiotic release from coated rods was sustained for over a period of 2 weeks at a constant rate, whereas uncoated rods released their contents in less than a week. Impregnation of Duocid into the hydrophobic polymer matrix yielded a rod with a smoother surface topography. The release from these rods was significantly higher than for rods loaded with Sulperazone and a zero order release could not be obtained with these samples.     

Laboratory analysis of superelastic NiTi compression springs.

The force/compression characteristics of 32 commercially available nickel titanium (NiTi) compression springs from seven distributors were investigated in vitro in order to support the orthodontist in deciding to select an appropriate spring for a given treatment. The geometrical properties of the coil springs, i.e., inner spring diameter, winding diameter and winding configuration, differed significantly, as well as the alloy composition and the thermo-mechanical treatment of the springs. All springs were mounted on a guiding rod made of an orthodontic steel wire (dimension: 0.016" x 0.022"), were compressed to a maximum extent and then relieved. Force/compression characteristics were measured at ambient temperatures of 27 degrees C, 37 degrees C and 47 degrees C. Three specimens were taken from each individual compression spring of a certain manufacturer and batch to check for constant material behaviour. A possible influence of sterilization on the mechanical properties of the compression springs was studied by autoclaving one spring of each manufacturer five times (6 minutes at 134 degrees C) and subsequently performing a force/deflection measurement. The NiTi compression springs were classified into three groups and covered a broad range of orthodontic forces between 0.5 N and 3.5 N. The width of the superelastic plateaus of the different NiTi coil springs reached from 0% to 66% of relative compression. An increase in the application temperature from 27 degrees C to 47 degrees C caused a rise in the height and a shortening of the width of the superelastic plateau. The resultant change in plateau force was as high as 0.4 N to 0.9 N, depending on the spring type investigated, the width of the plateaus was shortened by 4.0% to 15% of relative compression. All compression springs investigated displayed constant material behaviour within a certain batch. However, differences from one batch to another had a high level of significance. Forces on the plateau varied from one batch to the other by about +/-18%. An influence of sterilization on the force/compression behaviour could not be proved. Consequently, springs made of superelastic NiTi alloys cover a broad field of application with predefined and nearly constant force levels.     

Partially biodegradable polyacrylic-polyester composites for internal bone fracture fixation

New partially resorbable composite formulations based on components used in surgery were synthesized in rod form (length 15-20 mm, diameter 4 mm). The biostable components were poly(methyl methacrylate) in hydrophobic implants and poly(2-hydroxy ethyl methacrylate) in hydrophilic ones. The biodegradable components were commercially available suture yarn made from poly (alpha-hydroxy esters): polyglycolide, a polyester derived from glycolic acid; and a copolyester of glycolic and lactic acids, polyglactin 910. Biodegradation in phosphate-buffered solution at pH 7.0 and 37 +/- 0.5 degrees C was analysed gravimetrically. There was no measurable loss of mass after treatment for 20-25 d. Composite microstructure was examined by phase-contrast, cross-polarized light microscopy.     

In vivo bone response to 3D periodic hydroxyapatite scaffolds assembled by direct ink writing

The in vivo bone response of 3D periodic hydroxyapatite (HA) scaffolds is investigated. Two groups of HA scaffolds (11 mm diameter x 3.5 mm thick) are fabricated by direct-write assembly of a concentrated HA ink. The scaffolds consist of cylindrical rods periodically arranged into four quadrants with varying separation distances between rods. In the first group, HA rods (250 microm in diameter) are patterned to create pore channels, whose areal dimensions are 250 x 250 microm(2) in quadrant 1, 250 x 500 microm(2) in quadrants 2 and 4, and 500 x 500 microm(2) in quadrant 3. In the second group, HA rods (400 microm in diameter) are patterned to create pore channels, whose areal dimensions of 500 x 500 microm(2) in quadrant 1, 500 x 750 microm(2) in quadrants 2 and 4, and 750 x 750 microm(2) in quadrant 3. Each group of scaffolds is partially densified by sintering at 1200 degrees C prior to being implanted bilaterally in trephine defects of skeletally mature New Zealand White rabbits. Their tissue response is evaluated at 8 and 16 weeks using micro-computed tomography, histology, and scanning electron microscopy. New trabecular bone is conducted rapidly and efficiently across substantial distances within these patterned 3D HA scaffolds. Our observations suggest that HA rods are first coated with a layer of new bone followed by subsequent scaffold infilling via outward and inward radial growth of the coated regions. Direct-write assembly of 3D periodic scaffolds composed of micro-porous HA rods arrayed to produce macro-pores that are size-matched to trabecular bone may represent an optimal strategy for bone repair and replacement structures.