Therapeutic strategy for hair regeneration: hair cycle activation, niche environment modulation, wound-induced follicle neogenesis, and stem cell engineering.

INTRODUCTION: There are major new advancements in the fields of stem cell biology, developmental biology, regenerative hair cycling, and tissue engineering. The time is ripe to integrate, translate, and apply these findings to tissue engineering and regenerative medicine. Readers will learn about new progress in cellular and molecular aspects of hair follicle development, regeneration, and potential therapeutic opportunities these advances may offer. AREAS COVERED: Here, we use hair follicle formation to illustrate this progress and to identify targets for potential strategies in therapeutics. Hair regeneration is discussed in four different categories: i) Intra-follicle regeneration (or renewal) is the basic production of hair fibers from hair stem cells and dermal papillae in existing follicles. ii) Chimeric follicles via epithelial-mesenchymal recombination to identify stem cells and signaling centers. iii) Extra-follicular factors including local dermal and systemic factors can modulate the regenerative behavior of hair follicles, and may be relatively easy therapeutic targets. iv) Follicular neogenesis means the de novo formation of new follicles. In addition, scientists are working to engineer hair follicles, which require hair-forming competent epidermal cells and hair-inducing dermal cells. EXPERT OPINION: Ideally self-organizing processes similar to those occurring during embryonic development should be elicited with some help from biomaterials.

Failure analysis of broken pedicle screws on spinal instrumentation.

Revised spinal surgery is needed when there is a broken pedicle screw in the patient. This study investigated the pedicle screw breakage by conducting retrieval analyses of broken pedicle screws from 16 patients clinically and by performing stress analyses in the posterolateral fusion computationally using finite element (FE) models. Fracture surface of screws was studied by scanning electron microscope (SEM). The FE model of the posterolateral fusion with the screw showed that screws on the caudal side had larger axial stress than those on the cephalic side, supporting the clinical findings that 75% of the patients had the screw breakage on the caudal side. SEM fractography showed that all broken screws exhibited beach marks or striations on the fractured surface, indicating fatigue failure. Screws of patients with spinal fracture showed fatigue striations and final ductile fracture around the edge. Among the 16 patients who had broken pedicle screws 69% of them achieved bone union in the bone graft, showing that bone union in the bone graft did not warrant the prevention of screw breakage.

Collagen-hydroxyapatite/tricalcium phosphate microspheres as a delivery system for recombinant human transforming growth factor-beta 1.

The purpose of this study is to evaluate the carrier capability of collagen-hydroxyapatite/tricalcium phosphate (Col-HA/TCP) microspheres to the rhTGF-beta 1 (recombinant human transforming growth factor-beta 1). After anesthesia, a bone defect (7.0 mm in diameter and 10.0 mm in depth) was created at the distal femoral condyles of New Zealand white rabbits. These defects were then completely filled with the implant materials. After 5, 7, 9, 11, 13, and 15 weeks, the animals were sacrificed and histological evaluations were performed. The results showed that when the defects were treated with Col-HA/TCP microspheres without rhTGF-beta 1, there was only spotty new bone formation during the 15 week experimental period and most of the defect was filled with fibrous tissue and inflammatory cells, whereas active bone formation with mature marrow tissue formation was evident in the defect treated with Col-HA/TCP microspheres containing rhTGF-beta 1. Collagen-hydroxyapatite/tricalcium phosphate microspheres were expected to be replaced by the regenerated bone structure as the bone reconstruction and bone-remodeling process occurred. It was apparent that bone regeneration was influenced by the addition of rhTGF-beta 1. Collagen-hydroxyapatite/tricalcium phosphate microspheres were a good carrier for rhTGF-beta 1.

Collagen-hydroxyapatite microspheres as carriers for bone morphogenic protein-4.

The purpose of the current study is to evaluate the carrier capability of collagen-hydroxyapatite microspheres to the bone morphogenic proteins (BMP). After anesthesia, a bone defect (6.0 mm in diameter and 10.0 mm in depth) was created at the distal femoral condyles of New Zealand white rabbits. These 10.0 mm3 defects were then completely filled with the implant materials. After 2, 4, 6, and 8 weeks, the animals were sacrificed and histological evaluations were performed. The results showed that when the defects were left untreated, there was no evidence of bone formation during the eight-week experimental period. In the group treated with collagen-hydroxyapatite microspheres without BMP-4, the defect was filled with fibrous tissue and inflammatory cells, while active bone formation with mature marrow tissue formation was evident in the defect treated with collagen-hydroxyapatite microspheres containing BMP-4. Collagen-hydroxyapatite microspheres were expected to be replaced by the regenerated bone structure as the bone reconstruction and bone remodelling process occurred. It was apparent that bone regeneration was influenced by the addition of BMP-4. Collagen-hydroxyapatite microspheres were good carriers for bone morphogenic proteins.