{"id":177,"date":"2026-10-20T15:22:39","date_gmt":"2026-10-20T15:22:39","guid":{"rendered":"https:\/\/trapiantocapelli.com\/?p=177"},"modified":"2026-10-20T15:33:15","modified_gmt":"2026-10-20T15:33:15","slug":"graft-survival-biological-determinants","status":"publish","type":"post","link":"https:\/\/trapiantocapelli.com\/en\/reconstructive-surgery\/graft-survival-biological-determinants\/","title":{"rendered":"Follicular graft survival: biological determinants from harvesting to revascularisation"},"content":{"rendered":"<article class=\"tc-article\" lang=\"en\">\n<p class=\"tc-kicker\">Section 7 \u00b7 Graft Biology, Storage and Implantation<\/p>\n<h1>Follicular graft survival: biological determinants from harvesting to revascularisation<\/h1>\n<dl class=\"tc-meta\">\n<dt>Editorial direction<\/dt>\n<dd><a href=\"https:\/\/trapiantocapelli.com\/en\/team\/\">Dir. Mario Luigi Pallaoro<\/a>, Clinica Pallaoro, Padua<\/dd>\n<dt>Scientific review<\/dt>\n<dd><a href=\"https:\/\/www.pallaoro.it\/dott-gianandre-alvarez-pallaoro\" target=\"_blank\" rel=\"noopener\">Dr Gianandr\u00e8 Alvarez Pallaoro<\/a>, hair restoration surgeon, Clinica Pallaoro<\/dd>\n<dt>Audience<\/dt>\n<dd>Plastic surgeons, dermatologists, trichologists, researchers and residents<\/dd>\n<dt>Level of evidence<\/dt>\n<dd><span class=\"tc-evidence\">Level 3\u20134<\/span> in vitro studies, experimental models, small clinical studies and expert consensus; basic science for the mechanisms of injury<\/dd>\n<dt>Last updated<\/dt>\n<dd>October 2026<\/dd>\n<\/dl>\n<figure class=\"tc-figure\"><figcaption><strong>Figure 7.1<\/strong> \u2014 An isolated follicular unit in storage solution. The cuff of dermis and perifollicular fat protects the bulge and the dermal papilla, the two compartments on which regrowth depends, during the ischaemic period between harvesting and revascularisation in the recipient site.<\/figcaption><\/figure>\n<section class=\"tc-abstract\">\n<h2><span class=\"tc-num\">1.<\/span>Clinical abstract and executive summary<\/h2>\n<p>The number of hairs a patient sees growing after a transplant is not the same as the number of grafts harvested. Between harvesting and regrowth, each follicular unit goes through a sequence of unfavourable conditions: excision and handling, a period of ischaemia outside the body, insertion into the recipient site and several days of nutrition by diffusion alone before a circulation is re-established. At each of these stages a proportion of follicles may be lost or damaged<sup class=\"tc-cite\"><a href=\"#ref-1\">1<\/a><\/sup>.<\/p>\n<p>This pillar article describes the biological determinants of graft survival and the evidence available for each: structural integrity, out-of-body time, desiccation, temperature and storage solution, mechanical trauma, implantation density and the condition of the recipient site. The evidence is largely experimental or derived from small studies, often with differing methods. The individual topics are covered in depth in the other articles of section 7.<\/p>\n<ul class=\"tc-keypoints\">\n<li>Desiccation is the fastest-acting injury: viability falls after 20 minutes in air and markedly after 30 minutes<sup class=\"tc-cite\"><a href=\"#ref-2\">2<\/a><\/sup>.<\/li>\n<li>Out-of-body time has a progressive effect: losses remain limited in the first hours and rise sharply beyond 6\u20138 hours<sup class=\"tc-cite\"><a href=\"#ref-1\">1<\/a>,<a href=\"#ref-2\">2<\/a><\/sup>.<\/li>\n<li>Cooling to 4 \u00b0C appears useful mainly for prolonged storage; within 5\u20136 hours the difference from room temperature is small<sup class=\"tc-cite\"><a href=\"#ref-2\">2<\/a>,<a href=\"#ref-3\">3<\/a><\/sup>.<\/li>\n<li>Even minor follicle injuries reduce survival; follicle fracture is the most damaging<sup class=\"tc-cite\"><a href=\"#ref-5\">5<\/a><\/sup>.<\/li>\n<\/ul>\n<\/section>\n<h2><span class=\"tc-num\">2.<\/span>Microscopic and ultrastructural anatomy of the graft<\/h2>\n<h3>What a graft contains<\/h3>\n<p>A follicular graft is a fragment of skin containing one or more follicular units with their surrounding dermis, perifollicular fat, sebaceous glands and arrector pili muscle. From the standpoint of regrowth, two compartments are essential: the bulge, in the upper third of the follicle, which houses the epithelial stem cells, and the bulb with the dermal papilla, which provides the inductive signals and produces the shaft during anagen. The rest of the graft serves a protective and supportive function.<\/p>\n<h3>The perifollicular cuff<\/h3>\n<p>The tissue surrounding the follicle acts as a buffer: it slows water loss, cushions the pressure of forceps and preserves part of the dermal sheath cells. In the same patient, Seager compared grafts made of single hairs trimmed close to the shaft with intact follicular units retaining dermis, fat and sebaceous glands: the intact units showed far higher survival<sup class=\"tc-cite\"><a href=\"#ref-6\">6<\/a><\/sup>. The study is small, but it helped steer practice towards grafts that are not excessively skeletonised.<\/p>\n<h3>Compartments of differing vulnerability<\/h3>\n<p>The bulb is the most metabolically active part of the anagen follicle: the matrix divides rapidly and has a high oxygen requirement. The bulge is more quiescent, but it is the reservoir from which each new cycle starts. Kim and Choi showed that follicular segments without the bulb can regrow<sup class=\"tc-cite\"><a href=\"#ref-7\">7<\/a><\/sup>: the regenerative capacity of the bulge and sheath explains why some damaged grafts survive, although often with a thinner shaft.<\/p>\n<h2><span class=\"tc-num\">3.<\/span>Molecular dynamics and signalling pathways of injury<\/h2>\n<h3>Ischaemia<\/h3>\n<p>Once separated from the circulation, the graft continues to consume energy. Without oxygen, ATP production collapses, membrane ion pumps stop, and the cell accumulates sodium and water and swells. Cooling slows metabolism and therefore ATP consumption: this is the principle of hypothermic organ preservation, from which hair restoration surgery has borrowed the concept. Intracellular-type solutions, with an ionic composition closer to that of the cytoplasm, have been proposed to limit cell swelling during cold storage<sup class=\"tc-cite\"><a href=\"#ref-1\">1<\/a><\/sup>.<\/p>\n<h3>Reperfusion and oxidative stress<\/h3>\n<p>The return of oxygen to ischaemic tissue generates reactive oxygen species that damage membrane lipids, proteins and DNA. In the follicular graft the phenomenon is more gradual than in an organ: for about three days the graft is nourished by diffusion from the plasma of the recipient site before new vascular connections form<sup class=\"tc-cite\"><a href=\"#ref-1\">1<\/a><\/sup>. Preliminary data have documented markers of lipid peroxidation in grafts and fewer signs of apoptosis in media containing antioxidants; the clinical role of ischaemia\u2013reperfusion injury nevertheless remains suggestive rather than proven<sup class=\"tc-cite\"><a href=\"#ref-1\">1<\/a><\/sup>.<\/p>\n<h3>Energy support<\/h3>\n<p>Raposio and colleagues stored anagen follicles for 5 hours either in saline or in a medium enriched with ATP\u2013magnesium chloride and deferoxamine, an iron chelator with antioxidant activity. After 10 days of culture, survival was 98% in the enriched medium and 87% in saline<sup class=\"tc-cite\"><a href=\"#ref-4\">4<\/a><\/sup>. The finding is in vitro and has not been replicated in controlled clinical studies, but it confirms that the energy balance of the graft is a plausible target.<\/p>\n<h2><span class=\"tc-num\">4.<\/span>Pathophysiology and clinical correlations<\/h2>\n<h3>Desiccation<\/h3>\n<p>Water loss is the fastest and least reversible injury. In the study by Hwang and colleagues, follicles left on dry gauze at room temperature maintained an elongation rate of 94% up to 10 minutes, falling to 83% at 20 minutes and 68% at 30 minutes<sup class=\"tc-cite\"><a href=\"#ref-2\">2<\/a><\/sup>. In the operating room the greatest risk arises during waiting moments: grafts left on the work surface, on the operator&#8217;s finger or on the skin before insertion.<\/p>\n<h3>Out-of-body time<\/h3>\n<p>Limmer&#8217;s historical data on grafts stored in chilled saline, reported in the review by Parsley and Perez-Meza, show survival of 95% at 2 hours, around 90% between 4 and 8 hours, 79% at 24 hours and 54% at 48 hours<sup class=\"tc-cite\"><a href=\"#ref-1\">1<\/a><\/sup>. Hwang and colleagues observed a similar pattern: stable values up to 6 hours and a marked decline at 24 and 48 hours<sup class=\"tc-cite\"><a href=\"#ref-2\">2<\/a><\/sup>. In practice, a well-organised procedure keeps each graft&#8217;s time within the range where losses are limited.<\/p>\n<h3>Temperature<\/h3>\n<p>The benefit of cold depends on duration. Raposio and Santi found no difference between follicles stored for 5 hours at 1 \u00b0C and at 26 \u00b0C (survival 88% and 87%)<sup class=\"tc-cite\"><a href=\"#ref-3\">3<\/a><\/sup>. At 24 hours, by contrast, storage at 4 \u00b0C maintained 76% survival against 40% at room temperature<sup class=\"tc-cite\"><a href=\"#ref-2\">2<\/a><\/sup>. Cold therefore seems more relevant when the procedure is prolonged or when some of the grafts wait a long time before implantation.<\/p>\n<div class=\"tc-table-wrap\">\n<table class=\"tc-table\">\n<caption>Table 7.1 \u2014 Main determinants of graft survival: selected experimental data<\/caption>\n<thead>\n<tr>\n<th>Factor<\/th>\n<th>Condition<\/th>\n<th>Result<\/th>\n<th>Source<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Desiccation<\/td>\n<td>Dry gauze, room temperature<\/td>\n<td>Elongation 94% at 10 min, 83% at 20 min, 68% at 30 min<\/td>\n<td>Hwang 2002<sup class=\"tc-cite\"><a href=\"#ref-2\">2<\/a><\/sup><\/td>\n<\/tr>\n<tr>\n<td>Time and temperature<\/td>\n<td>Saline, 24 h<\/td>\n<td>76% at 4 \u00b0C versus 40% at room temperature<\/td>\n<td>Hwang 2002<sup class=\"tc-cite\"><a href=\"#ref-2\">2<\/a><\/sup><\/td>\n<\/tr>\n<tr>\n<td>Temperature<\/td>\n<td>5 h at 1 \u00b0C versus 26 \u00b0C<\/td>\n<td>88% versus 87%, no significant difference<\/td>\n<td>Raposio 1999<sup class=\"tc-cite\"><a href=\"#ref-3\">3<\/a><\/sup><\/td>\n<\/tr>\n<tr>\n<td>Storage medium<\/td>\n<td>5 h, ATP\u2013MgCl and deferoxamine versus saline<\/td>\n<td>98% versus 87% in culture<\/td>\n<td>Raposio 1998<sup class=\"tc-cite\"><a href=\"#ref-4\">4<\/a><\/sup><\/td>\n<\/tr>\n<tr>\n<td>FUE trauma<\/td>\n<td>Intact, pared, bulb-injured and fractured grafts<\/td>\n<td>71%, 51%, 44%, 13% in a murine model<\/td>\n<td>Kwack 2021<sup class=\"tc-cite\"><a href=\"#ref-5\">5<\/a><\/sup><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<h3>Mechanical trauma<\/h3>\n<p>The graft can be damaged by the punch, by forceps and by forced insertion into the recipient site. Kwack and colleagues classified the minor injuries produced by FUE and assessed their effect by implanting human grafts into mice: survival was 71% for intact grafts, 51% for those with partial loss of surface tissue (paring), 44% for those with bulb injury and 13% for fractured follicles<sup class=\"tc-cite\"><a href=\"#ref-5\">5<\/a><\/sup>. The absolute values depend on the animal model, but the hierarchy of damage is clear. Crushing of the bulge is considered more harmful than crushing of the bulb<sup class=\"tc-cite\"><a href=\"#ref-1\">1<\/a><\/sup>.<\/p>\n<h2><span class=\"tc-num\">5.<\/span>Surgical protocols and impact on FUE microsurgery<\/h2>\n<p>In FUE, harvesting and implantation are often simultaneous or close together, and out-of-body time can be shorter than with FUT. FUE grafts, however, have their own characteristics: less protective tissue, greater variability in shape and a higher proportion of partial injuries. The measures with the greatest practical impact are:<\/p>\n<ol class=\"tc-steps\">\n<li><strong>Reduce harvesting injuries.<\/strong> Punch alignment, appropriate depth and minimal traction limit transection, fractures and paring, which are the injuries with the most marked effect on survival<sup class=\"tc-cite\"><a href=\"#ref-5\">5<\/a><\/sup>.<\/li>\n<li><strong>Keep the graft hydrated at all times.<\/strong> Each graft passes directly from the skin to the storage solution and from the solution to the recipient site, without remaining in air.<\/li>\n<li><strong>Organise the timing.<\/strong> Harvesting and implanting in successive blocks reduces the maximum waiting time of individual grafts.<\/li>\n<li><strong>Store cold in long sessions.<\/strong> A solution kept at low temperature offers a safety margin when waiting exceeds a few hours<sup class=\"tc-cite\"><a href=\"#ref-2\">2<\/a><\/sup>.<\/li>\n<li><strong>Handle the perifollicular tissue, not the follicle.<\/strong> Forceps grasp the tissue cuff or the fat below the bulb, never the bulge.<\/li>\n<li><strong>Size the recipient site to the graft.<\/strong> A site that is too small forces insertion; one that is too large favours expulsion (popping) and growth of grafts in an incorrect position.<\/li>\n<\/ol>\n<h3>Implantation density<\/h3>\n<p>Very closely spaced sites reduce the perfusion available to each graft. Mayer&#8217;s data, reported by Parsley and Perez-Meza, indicate survival of 97% at 10 grafts\/cm\u00b2 and 92% at 20 grafts\/cm\u00b2, with lower values at 30\u201340 grafts\/cm\u00b2; other authors have reported good results even at higher densities<sup class=\"tc-cite\"><a href=\"#ref-1\">1<\/a><\/sup>. The safe density therefore depends on the vascularity of the recipient site, the quality of the grafts and the team&#8217;s experience rather than on an absolute value.<\/p>\n<h2><span class=\"tc-num\">6.<\/span>Regenerative medicine and adjuvant treatments<\/h2>\n<p>Several strategies aim to protect the graft during the ischaemic phase or to promote engraftment. Uebel and colleagues treated grafts with platelet-rich plasma before implantation in 23 patients, observing at one year a density of 18.7 follicular units\/cm\u00b2 versus 16.4 in the control area, an increase of 15.1%<sup class=\"tc-cite\"><a href=\"#ref-8\">8<\/a><\/sup>. Other small studies have shown no appreciable difference<sup class=\"tc-cite\"><a href=\"#ref-1\">1<\/a><\/sup>.<\/p>\n<p>Intracellular-type hypothermic solutions, energy additives such as ATP, antioxidants and inhibitors of nitric oxide synthesis have shown favourable effects in experimental models or small case series<sup class=\"tc-cite\"><a href=\"#ref-1\">1<\/a>,<a href=\"#ref-4\">4<\/a><\/sup>. None of these interventions yet has evidence strong enough to be recommended routinely. No adjuvant compensates for grafts that are desiccated, crushed or fractured.<\/p>\n<h2><span class=\"tc-num\">7.<\/span>Risk management and anatomical limits<\/h2>\n<ul>\n<li><strong>Inadvertent desiccation.<\/strong> This is the easiest risk to prevent: it must be controlled at every stage, especially during hand-overs between team members.<\/li>\n<li><strong>Grafts left waiting.<\/strong> In long sessions the time of the first grafts harvested must be monitored; the last grafts implanted should not be those that have stayed longest in solution.<\/li>\n<li><strong>Excessive skeletonisation.<\/strong> Grafts stripped of all perifollicular tissue are more exposed to desiccation and trauma<sup class=\"tc-cite\"><a href=\"#ref-6\">6<\/a><\/sup>.<\/li>\n<li><strong>Compromised recipient site.<\/strong> Scarred skin, previous surgery, smoking and poor vascularity reduce tolerance to high density.<\/li>\n<li><strong>Outcome measurement.<\/strong> Survival should be assessed at 12 months, with counts in marked areas; remote photographic assessments cannot distinguish failure to grow from growth of thinner hairs.<\/li>\n<\/ul>\n<section class=\"tc-tips\">\n<h2><span class=\"tc-num\">8.<\/span>Clinical tips &amp; tricks from the medical team<\/h2>\n<ul>\n<li><strong>The graft never touches air.<\/strong> From the skin to the solution and from the solution to the recipient site: every second of exposure counts.<\/li>\n<li><strong>Work in blocks.<\/strong> Harvesting and implanting in successive sequences keeps each graft&#8217;s out-of-body time short.<\/li>\n<li><strong>Check grafts under the microscope.<\/strong> Sampling grafts for integrity, length and fractures allows the harvesting technique to be corrected during the procedure.<\/li>\n<li><strong>Forceps on tissue, not on the follicle.<\/strong> Grasping the perifollicular fat protects the bulge and the bulb.<\/li>\n<li><strong>Insert without force.<\/strong> If the graft does not go in easily, the site must be adapted: forcing insertion means crushing the follicle.<\/li>\n<\/ul>\n<p class=\"tc-signature\">\u2014 Methodological approach of the Clinica Pallaoro team, Padua<\/p>\n<\/section>\n<h2><span class=\"tc-num\">9.<\/span>Critical discussion and conclusions<\/h2>\n<p>Graft survival results from many factors that add up: each on its own may cause a modest loss, but together they can significantly reduce the final result. The available evidence has important limitations. Many data derive from in vitro cultures, which measure shaft elongation rather than regrowth in the scalp; others from animal models, whose absolute values do not transfer directly to humans; and others from clinical studies with few patients, often presented at congresses or in non-indexed publications. Definitions of survival and assessment times vary between studies.<\/p>\n<p>Despite these limitations, some principles are consistent across all studies: avoid desiccation, reduce mechanical trauma, limit out-of-body time and store cold when waiting is prolonged. Research prospects include more effective storage solutions, strategies to support graft metabolism and controlled clinical studies with standardised counting methods. Until then, the most important variable remains the rigour with which the team applies these principles at every stage of the procedure.<\/p>\n<h2><span class=\"tc-num\">10.<\/span>Annotated scientific bibliography<\/h2>\n<ol class=\"tc-refs\">\n<li id=\"ref-1\">Parsley WM, Perez-Meza D. Review of factors affecting the growth and survival of follicular grafts. <em>J Cutan Aesthet Surg.<\/em> 2010;3(2):69-75. <a href=\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC2956960\/\" target=\"_blank\" rel=\"noopener\">PMC<\/a><span class=\"tc-annot\">Review of factors influencing graft survival: time, temperature, solutions, trauma, ischaemia\u2013reperfusion, density and adjuvants.<\/span><\/li>\n<li id=\"ref-2\">Hwang SJ, Lee JJ, Oh BM, et al. The effects of dehydration, preservation temperature and time on the hair grafts. <em>Ann Dermatol.<\/em> 2002;14(3):149-152. <a href=\"https:\/\/doi.org\/10.5021\/ad.2002.14.3.149\" target=\"_blank\" rel=\"noopener\">DOI<\/a><span class=\"tc-annot\">Effects of desiccation, storage duration and temperature on follicle viability.<\/span><\/li>\n<li id=\"ref-3\">Raposio E, Santi P. Effects of cooling micrografts in hair transplantation surgery. <em>Dermatol Surg.<\/em> 1999;25(9):705-707. <a href=\"https:\/\/pubmed.ncbi.nlm.nih.gov\/10491061\/\" target=\"_blank\" rel=\"noopener\">PubMed<\/a><span class=\"tc-annot\">No difference in survival between storage at 1 \u00b0C and at room temperature for 5 hours.<\/span><\/li>\n<li id=\"ref-4\">Raposio E, Cella A, Panarese P, et al. Power boosting the grafts in hair transplantation surgery: evaluation of a new storage medium. <em>Dermatol Surg.<\/em> 1998;24(12):1342-1345. <a href=\"https:\/\/pubmed.ncbi.nlm.nih.gov\/9865201\/\" target=\"_blank\" rel=\"noopener\">PubMed<\/a><span class=\"tc-annot\">Medium enriched with ATP\u2013MgCl and deferoxamine: higher survival in culture than saline.<\/span><\/li>\n<li id=\"ref-5\">Kwack MH, Kim MK, You SH, et al. Comparative graft survival study of follicular unit excision grafts with or without minor injury. <em>Dermatol Surg.<\/em> 2021;47(5):e191-e194. <a href=\"https:\/\/doi.org\/10.1097\/DSS.0000000000002878\" target=\"_blank\" rel=\"noopener\">DOI<\/a><span class=\"tc-annot\">Survival of FUE grafts by type of minor injury, in a murine model.<\/span><\/li>\n<li id=\"ref-6\">Seager DJ. Micrograft size and subsequent survival. <em>Dermatol Surg.<\/em> 1997;23(9):757-761. <a href=\"https:\/\/pubmed.ncbi.nlm.nih.gov\/9311369\/\" target=\"_blank\" rel=\"noopener\">PubMed<\/a><span class=\"tc-annot\">Intact follicular units with perifollicular tissue versus trimmed single hairs: a clear difference in survival.<\/span><\/li>\n<li id=\"ref-7\">Kim JC, Choi YC. Regrowth of grafted human scalp hair after removal of the bulb. <em>Dermatol Surg.<\/em> 1995;21(4):312-313. <a href=\"https:\/\/research.knu.ac.kr\/en\/publications\/regrowth-of-grafted-human-scalp-hair-after-removal-of-the-bulb\/\" target=\"_blank\" rel=\"noopener\">Kyungpook National University<\/a><span class=\"tc-annot\">Regenerative capacity of the upper follicular segments in the absence of the bulb.<\/span><\/li>\n<li id=\"ref-8\">Uebel CO, da Silva JB, Cantarelli D, Martins P. The role of platelet plasma growth factors in male pattern baldness surgery. <em>Plast Reconstr Surg.<\/em> 2006;118(6):1458-1466. <a href=\"https:\/\/pubmed.ncbi.nlm.nih.gov\/17051119\/\" target=\"_blank\" rel=\"noopener\">PubMed<\/a><span class=\"tc-annot\">Treatment of grafts with platelet-rich plasma and follicular density at one year.<\/span><\/li>\n<\/ol>\n<p class=\"tc-disclaimer\">Content intended for healthcare professionals for continuing scientific education. It does not replace individual clinical assessment. \u00a9 Clinica Pallaoro \u2014 trapiantocapelli.com<\/p>\n<\/article>\n","protected":false},"excerpt":{"rendered":"<p>Section 7 \u00b7 Graft Biology, Storage and Implantation Follicular graft  [&#8230;]<\/p>\n","protected":false},"author":1,"featured_media":178,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[42],"tags":[],"class_list":["post-177","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-reconstructive-surgery"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.7 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Graft Survival: Biological Determinants - trapiantocapelli.com<\/title>\n<meta name=\"description\" content=\"Follicular graft survival: integrity of the bulge and dermal papilla, out-of-body time, desiccation, temperature, storage solutions, mechanical trauma and the recipient site.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/trapiantocapelli.com\/en\/reconstructive-surgery\/graft-survival-biological-determinants\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Graft Survival: Biological Determinants - 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