Porous titanium granules in critical size defects of rabbit tibia with or without membranes

Recently, porous titanium granules （PTGs） have been indicated for the preservation of the dimensions of post-extraction sockets, as a filler in sinus lift procedures and for the treatment of peri-implant and periodontal defects, based on the osteoconductivity and dimensional stability of the titanium granules. However, there is a lack of information regarding the use of this material in larger defects and in conjunction with membranes. The objective of this study is to test the behavior of PTGs used to fill critical size defects in rabbit tibiae, with and without membranes. Critical defects were created in both tibiae of rabbits, divided randomly into three groups： Group A （defect filled with PTG）, Group B （defect filled with PTG＋collagen membrane） and a control group （empty defect）. After six weeks, histomorphometric analysis was performed. The results showed more defect closures at the cortical area （87.37%±2.2%） and more bone formation at the marrow area （57.6%± 1.3%） in Group B, in comparison with the other groups （P〈0.05）; the use of membranes improved the material stability expressed as more percentages of the original material when membranes were used （P〈0.05）. Finally, inflammatory reactions were observed when the granules were not protected by membranes. In spite of the limitations of this animal study, it may be concluded that PTG particles are osteoconductive and allow bone growth. The PTG particles must be covered by a membrane, especially when grafting larger defects, in order to control particle migration, promote clot stabilization and separate the PTG graft from undesired soft tissue cells.

Vascular restoration through local delivery of angiogenic factors stimulates bone regeneration in critical size defects

Critical size bone defects represent a significant challenge worldwide,often leading to persistent pain and physical disability that profoundly impact patients’quality of life and mental well-being.To address the intricate and complex repair processes involved in these defects,we performed single-cell RNA sequencing and revealed notable shifts in cellular populations within regenerative tissue.Specifically,we observed a decrease in progenitor lineage cells and endothelial cells,coupled with an increase in fibrotic lineage cells and pro-inflammatory cells within regenerative tissue.Furthermore,our analysis of differentially expressed genes and associated signaling pathway at the single-cell level highlighted impaired angiogenesis as a central pathway in critical size bone defects,notably influenced by reduction of Spp1 and Cxcl12 expression.This deficiency was particularly pronounced in progenitor lineage cells and myeloid lineage cells,underscoring its significance in the regeneration process.In response to these findings,we developed an innovative approach to enhance bone regeneration in critical size bone defects.Our fabrication process involves the integration of electrospun PCL fibers with electrosprayed PLGA microspheres carrying Spp1 and Cxcl12.This design allows for the gradual release of Spp1 and Cxcl12 in vitro and in vivo.To evaluate the efficacy of our approach,we locally applied PCL scaffolds loaded with Spp1 and Cxcl12 in a murine model of critical size bone defects.Our results demonstrated restored angiogenesis,accelerated bone regeneration,alleviated pain responses and improved mobility in treated mice.

Real-time-guided bone regeneration around standardized critical size calvarial defects using bone marrow-derived mesenchymal stem cells and collagen membrane with and without using tricalcium phosphate: an in vivo microcomputed tomographic and histologic e

The aim of the present real time in vivo micro-computed tomography （pCT） and histologic experiment was to assess the efficacy of guided bone regeneration （GBR） around standardized calvarial critical size defects （CSD） using bone marrow-derived mesenchymal stem cells （BMSCs）, and collagen membrane （CM） with and without tricalcium phosphate （TCP） graft material. In the calvaria of nine female Sprague-Dawley rats, full-thickness CSD （diameter 4.6 mm） were created under general anesthesia. Treatment-wise, rats were divided into three groups. In group 1, CSD was covered with a resorbable CM; in group 2, BMSCs were filled in CSD and covered with CM; and in group 3, TCP soaked in BMSCs was placed in CSD and covered with CM. All defects were closed using resorbable sutures. Bone volume and bone mineral density of newly formed bone （NFB） and remaining TCP particles and rate of new bone formation was determined at baseline, 2, 4, 6, and 10 weeks using in vivo pCT. At the lOth week, the rats were killed and calvarial segments were assessed histologically. The results showed that the hardness of NFB was similar to that of the native bone in groups I and 2 as compared to the NFB in group 3. Likewise, values for the modulus of elasticity were also significantly higher in group 3 compared to groups 1 and 2. This suggests that TCP when used in combination with BMSCs and without CM was unable to form bone of significant strength that could possibly provide mechanical ＂lock＂ between the natural bone and NFB. The use of BMSCs as adjuncts to conventional GBR initiated new bone formation as early as 2 weeks of treatment compared to when GBR is attempted without adiunct BMSC therapy.

Determining the critical size of a rabbit rib segmental bone defect model

In order to establish and standardize the rabbit rib segmental bone defect model,it is of vital importance to determine rabbit rib critical size defect(CSD).According to the general time needed for spontaneous long-bone regeneration,three-month observation period was set to determine the CSD.The rabbit rib segmental bone defects with different sizes from 1 to 5cm with or without periosteum were performed in the eighth rib of 4-month-old male New Zealand rabbits and underwent Xray examinations at the 4th,8th and 12th weeks postoperatively.The gross and histological examinations at postoperative week 12 were evaluated,which showed that the critical sizes in the rabbit rib models with and without periosteum were 5 and 2 cm,respectively.This study provides prerequisite data for establishing rabbit rib CSD model and evaluating bonematerials using this model.

Oxygen generating scaffolds regenerate critical size bone defects

Recent innovations in bone tissue engineering have introduced biomaterials that generate oxygen to substitute vasculature.This strategy provides the immediate oxygen required for tissue viability and graft maturation.Here we demonstrate a novel oxygen-generating tissue scaffold with predictable oxygen release kinetics and modular material properties.These hydrogel scaffolds were reinforced with microparticles comprised of emulsified calcium peroxide(CaO_(2))within polycaprolactone(PCL).The alterations of the assembled materials produced constructs within 5±0.81 kPa to 34±0.9 kPa in mechanical strength.The mass swelling ratios varied between 11%and 25%.Our in vitro and in vivo results revealed consistent tissue viability,metabolic activity,and osteogenic differentiation over two weeks.The optimized in vitro cell culture system remained stable at pH 8-9.The in vivo rodent models demonstrated that these scaffolds support a 70 mm^(3) bone volume that was comparable to the native bone and yielded over 90%regeneration in critical size cranial defects.Furthermore,the in vivo bone remodeling and vascularization results were validated by tartrate-resistant acid phosphatase(TRAP)and vascular endothelial growth factor(VEGF)staining.The promising results of this work are translatable to a repertoire of regenerative medicine applications including advancement and expansion of bone substitutes and disease models.

Next-generation resorbable polymer scaffolds with surface-precipitated calcium phosphate coatings

Next-generation synthetic bone graft therapies will most likely be composed of resorbable polymers in combination with bioactive components.In this article,we continue our exploration of E1001(1k),a tyrosine-derived polycarbonate,as an orthopedic implant material.Specifically,we use E1001(1k),which is degradable,nontoxic,and osteoconductive,to fabricate porous bone regeneration scaffolds that were enhanced by two different types of calcium phosphate(CP)coatings:in one case,pure dicalcium phosphate dihydrate was precipitated on the scaffold surface and throughout its porous structure(E1001(1k)+CP).In the other case,bone matrix minerals(BMM)such as zinc,manganese and fluoride were co-precipitated within the dicalcium phosphate dihydrate coating(E1001(1k)+BMM).These scaffold compositions were compared against each other and against ChronOS(Synthes USA,West Chester,PA,USA),a clinically used bone graft substitute(BGS),which served as the positive control in our experimental design.This BGS is composed of poly(lactide co-e-caprolactone)and beta-tricalcium phosphate.We used the established rabbit calvaria critical-sized defect model to determine bone regeneration within the defect for each of the three scaffold compositions.New bone formation was determined after 2,4,6,8 and 12 weeks by micro-computerized tomography(mCT)and histology.The experimental tyrosine-derived polycarbonate,enhanced with dicalcium phosphate dihydrate,E1001(1k)+CP,supported significant bone formation within the defects and was superior to the same scaffold containing a mix of BMM,E1001(1k)+BMM.The comparison with the commercially available BGS was complicated by the large variability in bone formation observed for the laboratory preparations of E1001(1k)scaffolds.At all time points,there was a trend for E1001(1k)+CP to be superior to the commercial BGS.However,only at the 6-week time point did this trend reach statistical significance.Detailed analysis of the μCT data suggested an increase in bone formation from 2 through 12 weeks in implant sites treated with E1001(1k)+CP.At 2 and 4 weeks post-implantation,bone formation occurred at the interface where the E1001(1k)+CP scaffold was in contact with the bone borders of the implant site.Thereafter,during weeks 6,8 and 12 bone formation progressed throughout the E1001(1k)+CP test implants.This trend was not observed with E1001(1k)+BMM scaffolds or the clinically used BGS.Our results suggest that E1001(1k)+CP should be tested further for osteoregenerative applications.