背景:采用3D打印技术制备的多孔钛合金支架可以诱导骨整合,在术后早期修复骨缺损。然而,骨小梁的组织形态特征和化学成分在手术后的长期内仍缺乏深入的研究。
方法:将14只新西兰大白兔分为两组(手术组7只,对照组7只)。手术组每只兔的右股骨髁植入3D打印的多孔钛合金支架。在植入过程中,通过干涉组装在骨组织和支架之间的表面产生预载荷。对照组家兔无饲料。手术后第12周处死所有家兔以提取股骨髁。所有右侧股骨髁进行显微CT扫描,检测骨密度(BMD)和骨小梁组织形态参数,包括骨体积分数(BV/TV),骨表面/体积比(BS/BV),骨表面密度(BS/TV),结构模型指数(SMI),小梁厚度(Tb.Th),骨小梁数(Tb.N),小梁分离(Tb。Sp),孔隙度(PO),连接密度(康涅狄格州。Dn),和各向异性程度(DA)。采用扫描电镜观察成骨周围支架。进行傅里叶变换红外光谱(FTIR)扫描以分析支架周围小梁的化学成分。对手术组和对照组的所有骨小梁形态参数和骨密度进行统计学分析。
结果:骨整合12周后,支架的孔隙被向内生长的骨组织填充。然而,手术组支架周围BMD平均为800±20mg/cm3,比对照组降低18.37%。BV/TV有显著下降,TB。N,BS/TV,Tb有显著增加。手术组与对照组之间的Sp和PO(p<0.05)。Tb没有显著差异。Th,SMI,康恩Dn,BS/BV,和DA。虽然骨组织向内生长非常有效,通过SEM图像,在支架的部分梁上仍然发现了一些破碎的结缔组织而不是骨组织。FTIR显示手术组无明显的羟基磷灰石峰信号。对照组胶原主要以交联结构存在,而手术组无交联结构。
结论:Preload在术后早期可以促进与化学表面修饰方法相同的良好骨整合能力,术后中长期骨整合效果优于化学表面修饰法。然而,周围支架小梁的组织形态学特征仍处于退化和低胶原成熟度的压力屏蔽作用下。这项研究建议,应进行额外的体育锻炼以刺激骨骼重塑过程,以恢复到健康水平。
BACKGROUND: Porous titanium alloy scaffold fabricated by 3D printing technology could induce osseointegration well to repair bone defect during early postoperative period. However, trabecular histomorphological features and chemical compositions of ingrowth bone in the long term after surgery still lacked in-depth research.
METHODS: Fourteen New Zealand rabbits were divided into two groups (7 rabbits in surgery group and 7 rabbits in control group). A 3D-printed porous titanium alloy scaffold was implanted into right femoral condyle of each rabbit in the surgery group. Preload was produced at the surface between bone tissue and scaffold through interference assembly during implantation process. Rabbits in the control group were feed free. All rabbits were sacrificed to extract femoral condyles at week 12 after surgery. All right femoral condyles were performed micro-CT scanning to test bone mineral density (BMD) and trabecular histomorphological parameters, including bone volume fraction (BV/TV), bone surface/volume ratio (BS/BV), bone surface density (BS/TV), structure model index (SMI), trabecular thickness (Tb.Th), trabecular number (Tb.N), trabecular separation (Tb.Sp), porosity (PO), connectivity density (Conn.Dn), and degree of anisotropy (DA). Scanning electron microscope was used to observe osteogenesis peri-scaffold. Fourier transform infrared spectroscopy (FTIR) scanning was performed to analyze chemical compositions of peri-scaffold trabeculae. All trabecular morphological parameters and BMDs were statistically analyzed between surgery group and control group.
RESULTS: The pores of scaffold were filled with ingrowth bone tissues after 12 weeks osseointegration. However, the mean BMD peri-scaffold in surgery group was 800 ± 20 mg/cm3, which was 18.37% lower than that in the control group. There was a significant decrease in BV/TV, Tb.N, and BS/TV, and there was a significant increase in Tb.Sp and PO between the surgery group and control group (p < 0.05). There were no significant differences in Tb.Th, SMI, Conn.Dn, BS/BV, and DA. Although ingrowth of bone tissue was very effective, some fragmented connective tissues were still found instead of bone tissues on the partial beams of scaffolds through SEM images. It was found from FTIR that there was no significant hydroxyapatite peak signal in surgery group. Collagen in the control group mainly existed as cross-link structure, while non-cross-link structure in the surgery group.
CONCLUSIONS: Preload could promote the same good osseointegration ability as chemical surface modification method in the early term after surgery, and better osseointegration effect than chemical surface modification method in the mid-long term after surgery. However, histomorphological features of peri-scaffold trabeculae were still in deterioration and low collagen maturity caused by stress shielding. It was suggested from this study that extra physical training should be taken to stimulate the bone remodeling process for recovering to a healthy level.